Les Rencontres de Physique de la Vallee d‘Aoste, La Thuile, March 2015
QCD and Vector Boson + jets measurements
with ATLAS
Kristof Schmieden, on behalf of the ATLAS collaboration
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
The Summary at the Beginning
2
pp
total
80 µb−1
JetsR=0.4
|y |<3.0
0.1 < pT < 2 TeV
DijetsR=0.4
|y |<3.0y∗<3.0
0.3 < mjj < 5 TeV
W
fiducial
35 pb−1
njet ≥ 0
njet ≥ 1
njet ≥ 2
njet ≥ 3
njet ≥ 4
njet ≥ 5
njet ≥ 6
njet ≥ 7
Z
fiducial
35 pb−1
njet ≥ 0
njet ≥ 1
njet ≥ 2
njet ≥ 3
njet ≥ 4
njet ≥ 5
njet ≥ 6
njet ≥ 7
t̄t
total
njet ≥ 0
njet ≥ 4
njet ≥ 5
njet ≥ 6
njet ≥ 7
njet ≥ 8
tt−chan
total
WW+WZtotal
WW
total
γγ
fiducial
4.9 fb−1
Wt
total
2.0 fb−1
WZ
total
13.0 fb−1
ZZ
total
t̄tγ
fiducial
1.0 fb−1
Wγ
fiducial
njet=0
Zγ
fiducial
njet=0
t̄tW
total
t̄tZ
total
95% CL
upper
limit
ZjjEWK
fiducial
H→γγ
fiducial
W±W±jj
EWK
fiducial
ts−chan
total
95% CL
upper
limit
0.7 fb−1
σ[p
b]
10−3
10−2
10−1
1
101
102
103
104
105
106
1011
LHC pp√s = 7 TeV
Theory
Data 4.5 − 4.7 fb−1
LHC pp√s = 8 TeV
Theory
Data 20.3 fb−1
Standard Model Production Cross Section Measurements Status: July 2014
ATLAS Preliminary Run 1√s = 7, 8 TeV
pp
total
80 µb−1
JetsR=0.4
|y |<3.0
0.1 < pT < 2 TeV
DijetsR=0.4
|y |<3.0y∗<3.0
0.3 < mjj < 5 TeV
W
fiducial
35 pb−1
njet ≥ 0
njet ≥ 1
njet ≥ 2
njet ≥ 3
njet ≥ 4
njet ≥ 5
njet ≥ 6
njet ≥ 7
Z
fiducial
35 pb−1
njet ≥ 0
njet ≥ 1
njet ≥ 2
njet ≥ 3
njet ≥ 4
njet ≥ 5
njet ≥ 6
njet ≥ 7
t̄t
total
njet ≥ 0
njet ≥ 4
njet ≥ 5
njet ≥ 6
njet ≥ 7
njet ≥ 8
tt−chan
total
WW+WZtotal
WW
total
γγ
fiducial
4.9 fb−1
Wt
total
2.0 fb−1
WZ
total
13.0 fb−1
ZZ
total
t̄tγ
fiducial
1.0 fb−1
Wγ
fiducial
njet=0
Zγ
fiducial
njet=0
t̄tW
total
t̄tZ
total
95% CL
upper
limit
ZjjEWK
fiducial
H→γγ
fiducial
W±W±jj
EWK
fiducial
ts−chan
total
95% CL
upper
limit
0.7 fb−1
σ[p
b]
10−3
10−2
10−1
1
101
102
103
104
105
106
1011
LHC pp√s = 7 TeV
Theory
Data 4.5 − 4.7 fb−1
LHC pp√s = 8 TeV
Theory
Data 20.3 fb−1
Standard Model Production Cross Section Measurements Status: July 2014
ATLAS Preliminary Run 1√s = 7, 8 TeV
di-Boson results: see K. Bachas and J. Gao talks on Thursday
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
Motivation: jets and V+jets
3
• Jet production in association with W/Z bosons is dominated by strong interactions:
• Number of jets:• Sensitive to pQCD effects → parton shower
• Jet transverse momentum• Sensitive to higher order ME, QCD & EWK!
• Angular separation and invariant mass of leading jets• Sensitive to higher order ME & pQCD effects
• Clean leptonic signature of V decay
QCD radiation
Z-boson Bremsstrahlung
Non resonant
• Jet inclusive measurement:• QCD dominated• sensitive pQCD effects PDFs, ...
jetsN
0≥ 1≥ 2≥ 3≥ 4≥
Rel
ativ
e U
ncer
tain
ty
00.05
0.10.150.2
0.250.3
0.350.4
0.450.5
)) + jets-e+ e→))/(Z(ν e→(W(Statistical UncertaintyTotal Systematic UncertaintyJetsElectronMETUnfoldingBackgrounds
ATLAS
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
Motivation: Ratio Measurements σ(W+jets) / σ(Z+jets)
4
• Probes kinematic differences of jet-system recoiling against W or Z
• Many uncertainties cancel!• Experimental:• Positively correlated uncertainties (Energy scales / backgrounds / Jet uncertainties)
• Prediction:• Scale & PDF uncertainties• Parton shower / hadronization
σ(W+jets) / σ(Z+jets)
jetsN
0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Rel
ativ
e U
ncer
tain
ty
00.05
0.10.150.2
0.250.3
0.350.4
0.450.5
) + jetsν e→W(Statistical UncertaintyTotal Systematic UncertaintyJetsElectronMETUnfoldingBackgrounds
ATLAS
σ(W+jets)
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• W + jets cross section (Accepted by EPJC; arXiv:1409.8639) (Sep. 2014)
• W + jets/Z + jets cross section ratio (Eur. Phys. J. C (2014) 74:3168)
• Z + b-jets cross section (JHEP10(2014)141) (Nov. 2014)
• Inclusive Jet cross section (arXiv:1410.8857) (Oct. 2014)
• Differential 3 Jet measurement (arXiv:1411.1855) (Nov. 2014)
• Z + jets cross section (JHEP 07 (2013) 032) (not discussed)
• W +b-jets cross section (JHEP 06 (2013) 084)
• W +c-jets cross section (JHEP 05 (2014) 068)
Recent ATLAS measurements
5
• All shown results are obtained using the data measured in 2011 (4.6fb-1 @ 7 TeV)
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Several Monte Carlo generators used to calculate predictions• Alpgen:
• Multiparton LO ME generator for SM processes • Special emphasis on multijet final states: explicitly takes helicity correlations of intermediate gauge bosons and final state particles into account• PS by external program
• Sherpa• Multiparton LO ME, provides complete hadronic final states, sophisticated ME/PS merging
• BlackHat + Sherpa for PS• Evaluates QCD one-loop matrix elements for up to 4 final state jets
• HEJ• All-order summation of perturbative terms• Any number of hard jets > 2, jet rates (up to 4 jets) fully matched to tree-level accuracy.
• MEPS@NLO• Merge resumed logs from PS with fixed order ME calculation• Jets evolve with PS, cross section accurate to Born level
• NLOJET• NLO pQCD (fixed order) calculations, including hadronisation and electroweak corrections
Theory Predictions - overview of tools
6
Results for W+jets and Ratio W/Z + jets measurements
arXiv:1409.8639 &
Eur. Phys. J. C (2014) 74
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• W→lν• Exactly 1 lepton• pT > 25GeV,|η| < 2.4 / 2.47 (µ/e)
• ETmiss > 25 GeV• mT > 40 GeV
• Jets:• pT > 30 GeV• |y| < 4.4• Removed if overlapping with lepton ΔR > 0.4
Event Selection
8
• Z→ll• Exactly 2 leptons with opposite charge• pT > 20GeV, |η| < 2.4 / 2.47 (µ/e)
• ΔR(l,l) > 0.2• 66 ≤ mll ≤ 116 GeV
• Jets:• pT > 30 GeV• |y| < 4.4• Removed if overlapping with lepton ΔR > 0.4
Z+jets cross section JHEP 07 (2013) 032
Event selection:
Lepton:
Electron channel:
pT > 20 GeV,
|h | < 2.47 (excluding
1.37 < |h | < 1.52)
Muon channel:
pT > 20 GeV,
|h | < 2.4
Z ! `` criteria:
Exactly 2 OS leptons
�R(`,`) > 0.2
66 m`` 116 GeV
Jet criteria:
pT > 30 GeV
|y | < 4.4 GeV
Jet overlap removal:
�R(`, jet) > 0.5
jetN 0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Even
ts /
bin
10
210
310
410
510
610
710 -1 L dt = 4.6 fb∫) + jets-µ+µ →*(γZ/
jets, R = 0.4,tanti-k| < 4.4jet > 30 GeV, |yjet
Tp
= 7 TeV)sData 2011 (* + jets (ALPGEN)γZ/* + jets (SHERPA)γZ/
TopElectroweakMulti-jets
ATLAS
jetN 0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
MC
/ D
ata
0.81
1.2 ALPGEN SHERPA
[GeV]µµ
Tp
0 100 200 300 400 500
>je
t<N
0.5
1
1.5
2
2.5
3
3.5-1 L dt = 4.6 fb∫
) + jets-µ+µ →*(γZ/ jets, R = 0.4,tanti-k
| < 4.4jet > 30 GeV, |yjetT
p
= 7 TeV)sData 2011 (Z+jets(ALPGEN)Z+jets(SHERPA)
ATLAS
[GeV]µµ
Tp
0 100 200 300 400 500
MC
/ D
ata
0.9
1
1.1 ALPGEN SHERPA
A. Ruiz (CERN) JVMO 2014 17 July 2014 11
jetsN0 1 2 3 4 5 6 7 8
Even
ts
10
210
310
410
510
610
710
810
910
1010 -1 = 7 TeV, 4.6 fbsData, (ALPGEN)ν e→W
ttOther
ee→ZMultijets
(SHERPA)ν e→W
Pred sysstat⊗Pred sys
ATLAS
jetsN0 1 2 3 4 5 6 7 8
Pred
/ D
ata
0.5
1
1.5
arXiv:1409.8639 & Eur. Phys. J. C (2014) 74
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• BlackHat and ALPGEN give good description of data for Njets < 5
Inclusive number of jets
9
jetsN0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
) [pb
]je
ts(W
+Nσ
-210
-110
1
10
210
310
410
510
610 ATLAS jets, R=0.4,tanti-k
| < 4.4j > 30 GeV, |yjT
p
) + jetsν l→W(Data,
-1 = 7 TeV, 4.6 fbs+SHERPAATHLACKB
HEJALPGENSHERPAMEPS@NLO jetsN
0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pred
. / D
ata
0.60.8
11.21.4 +SHERPAATHLACKB
ATLAS
jetsN0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pred
. / D
ata
0.60.8
11.21.4 HEJ
jetsN0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pred
. / D
ata
0.60.8
11.21.4 ALPGEN
jetsN0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pred
. / D
ata
0.60.8
11.21.4
SHERPA
MEPS@NLO
jetsN0≥ 1≥ 2≥ 3≥ 4≥
)je
tsZ+
Nσ
)/(je
tsW
+Nσ(
8
10
12
14
16
18ATLAS
jets, R=0.4,tanti-k| < 4.4j > 30 GeV, |yj
Tp
)) + jets-l+ l→))/(Z(ν l→(W(-1=7 TeV, 4.6 fbsData,
+SHERPAATHLACKBALPGEN+HERWIGSHERPA
jetsN0≥ 1≥ 2≥ 3≥ 4≥
NLO
/ Da
ta
0.80.9
11.11.2 +SHERPAATHLACKB
jetsN0≥ 1≥ 2≥ 3≥ 4≥
MC
/ Dat
a
0.80.9
11.11.2 ALPGEN
jetsN0≥ 1≥ 2≥ 3≥ 4≥
MC
/ Dat
a
0.80.9
11.11.2 SHERPA
W → lν
Ratio measurement
• Trend toward large Njets (Alpgen & Sherpa) • still compatible with data within the large errors
• In ratio measurement: deviation of Sherpa prediciton becomes significant
arXiv:1409.8639 & Eur. Phys. J. C (2014) 74
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Alpgen and Sherpa describe data well
• BH and LoopSim underestimate high pT cross section
Transverse Momentum of Leading Jet (≥ 1 jet)
10
W → lν
(leading jet) [GeV]jT
p100 200 300 400 500 600 700 800 900 1000
[1/G
eV]
j T/d
p1j≥
W+
σd
-510
-410
-310
-210
-110
1
10
210
310 ATLAS jets, R=0.4,tanti-k
| < 4.4j > 30 GeV, |yjT
pScaled Predictions
1 jet≥) + ν l→W(Data,
-1 = 7 TeV, 4.6 fbs+SHERPAATHLACKB
BH+S Excl. SumLoopSimALPGENSHERPAMEPS@NLO
(leading jet) [GeV]jT
p100 200 300 400 500 600 700 800 900 1000
Pred
. / D
ata
0.60.8
11.21.4 BH+S BH+S Excl. Sum
ATLAS
(leading jet) [GeV]jT
p100 200 300 400 500 600 700 800 900 1000
Pred
. / D
ata
0.60.8
11.21.4 LoopSim
(leading jet) [GeV]jT
p100 200 300 400 500 600 700 800 900 1000
Pred
. / D
ata
0.60.8
11.21.4 ALPGEN
(leading jet) [GeV]jT
p100 200 300 400 500 600 700 800 900 1000
Pred
. / D
ata
0.60.8
11.21.4
SHERPA
MEPS@NLO
(leading jet) [GeV]jT
p100 200 300 400 500 600 700
)j T/d
p1j≥
Z+σ
)/(d
j T/d
p1j≥
W+
σ)(d
1j≥(1
/R
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2ATLAS
jets, R=0.4,tanti-k| < 4.4j > 30 GeV, |yj
Tp
1 jet≥)) + -l+ l→))/(Z(ν l→(W(-1=7 TeV, 4.6 fbsData,
+SHERPAATHLACKBALPGEN+HERWIGSHERPA
(leading jet) [GeV]jT
p100 200 300 400 500 600 700
NLO
/ Da
ta
0.80.9
11.11.21.3 +SHERPAATHLACKB
(leading jet) [GeV]jT
p100 200 300 400 500 600 700
MC
/ Dat
a
0.80.9
11.11.21.3 ALPGEN
(leading jet) [GeV]jT
p100 200 300 400 500 600 700
MC
/ Dat
a
0.80.9
11.11.21.3 SHERPA
Ratio measurement
arXiv:1409.8639 & Eur. Phys. J. C (2014) 74
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Pronounced offset in HEJ prediction
• Ratio is modeled well, except for very low pT
Transverse Momentum of Leading Jet (≥2 jets)
11
W → lν
(leading jet) [GeV]jT
p100 200 300 400 500 600 700
[1/G
eV]
j T/d
p2j≥
W+
σd
-410
-310
-210
-110
1
10
210ATLAS
jets, R=0.4,tanti-k| < 4.4j > 30 GeV, |yj
TpScaled Predictions
2 jet≥) + ν l→W(Data,
-1 = 7 TeV, 4.6 fbs+SHERPAATHLACKB
HEJALPGENSHERPAMEPS@NLO (leading jet) [GeV]j
Tp
100 200 300 400 500 600 700
Pred
. / D
ata
0.60.8
11.21.4 +SHERPAATHLACKB
ATLAS
(leading jet) [GeV]jT
p100 200 300 400 500 600 700
Pred
. / D
ata
0.60.8
11.21.4 HEJ
(leading jet) [GeV]jT
p100 200 300 400 500 600 700
Pred
. / D
ata
0.60.8
11.21.4 ALPGEN
(leading jet) [GeV]jT
p100 200 300 400 500 600 700
Pred
. / D
ata
0.60.8
11.21.4
SHERPA
MEPS@NLO
(leading jet) [GeV]jT
p100 200 300 400 500
)j T/d
p2j≥
Z+σ
)/(d
j T/d
p2j≥
W+
σ)(d
2j≥(1
/R
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2ATLAS
jets, R=0.4,tanti-k| < 4.4j > 30 GeV, |yj
Tp
2 jet≥)) + -l+ l→))/(Z(ν l→(W(-1=7 TeV, 4.6 fbsData,
+SHERPAATHLACKBALPGEN+HERWIGSHERPA
(leading jet) [GeV]jT
p100 200 300 400 500
NLO
/ Da
ta
0.80.9
11.11.21.3 +SHERPAATHLACKB
(leading jet) [GeV]jT
p100 200 300 400 500
MC
/ Dat
a
0.80.9
11.11.21.3 ALPGEN
(leading jet) [GeV]jT
p100 200 300 400 500
MC
/ Dat
a
0.80.9
11.11.21.3 SHERPA
Ratio measurement
arXiv:1409.8639 & Eur. Phys. J. C (2014) 74
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
Angular separation of jets
12
W → lν
j1,j2 RΔ
1 2 3 4 5 6
j1
,j2 R
Δ/d
2j≥
W+
σd
1
10
210
310
ATLAS jets, R=0.4,tanti-k
| < 4.4j > 30 GeV, |yjT
pScaled Predictions
2 jet≥) + ν l→W(Data,
-1 = 7 TeV, 4.6 fbs+SHERPAATHLACKB
HEJALPGENSHERPAMEPS@NLO j1,j2 RΔ
1 2 3 4 5 6
Pred
. / D
ata
0.60.8
11.21.4 +SHERPAATHLACKB
ATLAS
j1,j2 RΔ
1 2 3 4 5 6
Pred
. / D
ata
0.60.8
11.21.4 HEJ
j1,j2 RΔ
1 2 3 4 5 6
Pred
. / D
ata
0.60.8
11.21.4 ALPGEN
j1,j2 RΔ1 2 3 4 5 6
Pred
. / D
ata
0.60.8
11.21.4
SHERPA
MEPS@NLO
j1,j2 RΔ
1 2 3 4 5
)j1
,j2 R
Δ/d
2j≥Z+σ
)/(d
j1,j2
RΔ
/d2j≥
W+
σ)(d
2j≥(1
/R
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2ATLAS
jets, R=0.4,tanti-k| < 4.4j > 30 GeV, |yj
Tp
2 jet≥)) + -l+ l→))/(Z(ν l→(W(-1=7 TeV, 4.6 fbsData,
+SHERPAATHLACKBALPGEN+HERWIGSHERPA
j1,j2 RΔ1 2 3 4 5
NLO
/ Da
ta
0.80.9
11.11.21.3 +SHERPAATHLACKB
j1,j2 RΔ1 2 3 4 5
MC
/ Dat
a
0.80.9
11.11.21.3 ALPGEN
j1,j2 RΔ1 2 3 4 5
MC
/ Dat
a
0.80.9
11.11.21.3 SHERPA
• sensitive to hard parton radiation at large angles • ME / PS matching
• MEPS@NLO: trend at large separation• ALPGEN: trend over full range
Ratio measurement
arXiv:1409.8639 & Eur. Phys. J. C (2014) 74
Z + b-jets
JHEP10(2014)141
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Important BG for associated Higgs production with H → bb and BSM models
• 2 schemes used in pQCD calculations: 4 and 5 flavors in initial state• (a) only existent in 5 flavor scheme• sensitive to b-quark PDF
Motivation
14
considers parton densities of gluons and of the first two quark generations in the proton.
The other is the five-flavour number scheme (5FNS), which allows a b-quark density in the
initial state and raises the prospect that measurements of heavy flavour production could
constrain the b-quark parton density function (PDF) of the proton. In a calculation to all
orders, the 4FNS and 5FNS methods must give identical results; however, at a given order
differences can occur between the two. A recent discussion on the status of theoretical
calculations and the advantages and disadvantages of the different flavour number schemes
can be found in Ref. [1].
Next-to-leading-order (NLO) matrix element calculations have been available for as-
sociated Z+b and Z+bb̄ production at parton-level for a number of years [2–4]. The
leading order (LO) Feynman diagrams shown in Figure 1 illustrate some of the contribut-
ing processes. Full particle-level predictions have existed at LO for some time, obtained
by matching parton shower generators to LO multi-leg matrix elements in the 4FNS [5,6],
5FNS [7], or both [8]. More recently, a full particle-level prediction for Z+ ≥ 2 b-jets at
NLO in the 4FNS with matched parton shower has become available [9, 10]. The same
framework can also be used to provide a full particle-level prediction for Z+ ≥ 1 b-jet at
NLO in the 5FNS. In this article data are compared with several theoretical predictions
following different approaches.
Differential measurements of Z+b-jets production have been made in proton-antiproton
collisions at√s=1.96 TeV by the CDF and D0 experiments [11, 12] as well as inclusively
in√s=7 TeV proton-proton collisions at the LHC by the ATLAS and CMS experiments
[13, 14]. The results presented in this paper significantly extend the scope of the previous
ATLAS measurement, which used around 36 pb−1of data recorded in 2010. The current
analysis takes advantage of the full sample of√s=7 TeV proton-proton collisions recorded
in 2011, corresponding to an integrated luminosity of 4.6 fb−1, and uses improved methods
for b-jet identification to cover a wider kinematic region. The larger data sample allows
differential production cross-section measurements of a Z boson with b-jets at the LHC.
These complement the recently reported results of associated production of a Z boson with
two b-hadrons at√s=7 TeV by CMS [15].
A total of 12 differential cross-sections are presented here, covering a variety of Z boson
and b-jet kinematics and angular variables sensitive to different aspects of the theoretical
b
b
Z
g
(a)
q
q
b
b
Z
(b)
q Z
b
bq
(c)
Figure 1. Leading order Feynman diagrams contributing to Z+b-jets production. Process 1(a) isonly present in a 5FNS calculation, while 1(b) and 1(c) are present in both the 4FNS and 5FNScalculations.
– 2 –
JHEP10(2014)141
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Sensitivity to PDF• In particular N flavors
• Shape of b-jet pT fairly well described
Z+b-jets: Results
15
(Zb) [pb]σ
0 1 2 3 4 5 6
(stat.)-1 = 7 TeV, 4.6 fbsData syst.)⊕ (stat.-1 = 7 TeV, 4.6 fbsData
NLO MSTW2008⊗MCFM CT10⊗MCFM NNPDF2.3⊗MCFM
MSTW2008⊗aMC@NLO 4FNS MSTW2008⊗aMC@NLO 5FNS
LO multileg CT10⊗SHERPA
CTEQ6L1⊗ALPGEN+HJ
ATLAS1 b-jet≥Z+
(a)
(Zbb) [pb]σ
0 0.1 0.2 0.3 0.4 0.5 0.6
(stat.)-1 = 7 TeV, 4.6 fbsData syst.)⊕ (stat.-1 = 7 TeV, 4.6 fbsData
NLO MSTW2008⊗MCFM CT10⊗MCFM NNPDF2.3⊗MCFM
MSTW2008⊗aMC@NLO 4FNS MSTW2008⊗aMC@NLO 5FNS
LO multileg CT10⊗SHERPA
CTEQ6L1⊗ALPGEN+HJ
ATLAS2 b-jet≥Z+
(b)
Figure 6. Cross-sections for (a) Z+ ≥ 1 b-jet, and (b) Z+ ≥ 2 b-jets. The measurement is shown asa vertical blue line with the inner blue shaded band showing the corresponding statistical uncertaintyand the outer green shaded band showing the sum in quadrature of statistical and systematicuncertainties. Comparison is made to NLO predictions from mcfm interfaced to different PDF setsand amc@nlo interfaced to the same PDF set in both the 4FNS and 5FNS. The statistical (innerbar) and total (outer bar) uncertainties are shown for these predictions, which are dominated by thetheoretical scale uncertainty calculated as described in the text. Comparisons are also made to LOmulti-legged predictions from Alpgen+Herwig+Jimmy and Sherpa; in this case the uncertaintybars are statistical only, and smaller than the marker.
– 22 –
2
[pb/
GeV
]b-
jets
/N ) Td(
b-je
t p(Zb)
σd
-410
-310
-210
-110
aData-1 = 7 TeV, 4.6 fbs
MCFMaMC@NLO 5FNSaMC@NLO 4FNSALPGEN+HJSHERPA
ATLAS 1 b-jet≥Z+
Data
NLO
0.60.8
11.21.4
[GeV]Tb-jet p30 40 50 210 210×2
Data
LO m
ultile
g
0.40.60.8
11.2
(a)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
[pb]
b-je
ts/N
d(b-
jet |
y|)
(Zb)
σd
0.5
1
1.5
2
2.5
3
3.5
4aData
-1 = 7 TeV, 4.6 fbsMCFMaMC@NLO 5FNSaMC@NLO 4FNSALPGEN+HJSHERPA
ATLAS 1 b-jet≥Z+
Data
NLO
0.60.8
11.21.4
b-jet |y|0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Data
LO m
ultile
g
0.40.60.8
11.2
(b)
Figure 7. The inclusive b-jet cross-section σ(Zb) × Nb-jet as a function of b-jet pT (a) and|y| (b). The top panels show measured differential cross-sections as filled circles with statistical(inner) and total (outer bar) uncertainties. Overlayed for comparison are the NLO predictionsfrom mcfm and amc@nlo both using the MSTW2008 PDF set. The shaded bands represents thetotal theoretical uncertainty for mcfm and the uncertainty bands on amc@nlo points representthe dominant theoretical scale uncertainty only. Also overlaid are LO multi-legged predictions forAlpgen+Herwig+Jimmy and Sherpa. The middle panels show the ratio of NLO predictions todata, and the lower panels show the ratio of LO predictions to data.
– 23 –
(Zb) [pb]σ
0 1 2 3 4 5 6
(stat.)-1 = 7 TeV, 4.6 fbsData syst.)⊕ (stat.-1 = 7 TeV, 4.6 fbsData
NLO MSTW2008⊗MCFM CT10⊗MCFM NNPDF2.3⊗MCFM
MSTW2008⊗aMC@NLO 4FNS MSTW2008⊗aMC@NLO 5FNS
LO multileg CT10⊗SHERPA
CTEQ6L1⊗ALPGEN+HJ
ATLAS1 b-jet≥Z+
(a)
(Zbb) [pb]σ
0 0.1 0.2 0.3 0.4 0.5 0.6
(stat.)-1 = 7 TeV, 4.6 fbsData syst.)⊕ (stat.-1 = 7 TeV, 4.6 fbsData
NLO MSTW2008⊗MCFM CT10⊗MCFM NNPDF2.3⊗MCFM
MSTW2008⊗aMC@NLO 4FNS MSTW2008⊗aMC@NLO 5FNS
LO multileg CT10⊗SHERPA
CTEQ6L1⊗ALPGEN+HJ
ATLAS2 b-jet≥Z+
(b)
Figure 6. Cross-sections for (a) Z+ ≥ 1 b-jet, and (b) Z+ ≥ 2 b-jets. The measurement is shown asa vertical blue line with the inner blue shaded band showing the corresponding statistical uncertaintyand the outer green shaded band showing the sum in quadrature of statistical and systematicuncertainties. Comparison is made to NLO predictions from mcfm interfaced to different PDF setsand amc@nlo interfaced to the same PDF set in both the 4FNS and 5FNS. The statistical (innerbar) and total (outer bar) uncertainties are shown for these predictions, which are dominated by thetheoretical scale uncertainty calculated as described in the text. Comparisons are also made to LOmulti-legged predictions from Alpgen+Herwig+Jimmy and Sherpa; in this case the uncertaintybars are statistical only, and smaller than the marker.
– 22 –
Good agreement in 5 FNS (≥ 1b)
Bad agreement in 5 FNS! (≥ 2b)
≥ 1b
≥ 2b
4FNS
5FNS
4FNS
5FNS
JHEP10(2014)141
Inclusive Jet Double Differential Measurement
arXiv:1410.8857
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Anti-kt reconstruction algorithm, radius R=0.4 (0.6)• Jets calibrated using insitu methods• pT > 100 GeV & |y| < 3
• Data from 2011 and 2010 are consistent
Inclusive Jet Double Differential Measurement
17
[GeV]Tp
210 310
[pb/
GeV
]y
d Tp/dσ2 d
-2010
-1710
-1410
-1110
-810
-510
-210
10
410
710
1010ATLAS
=7 TeVs, -1 dt=4.5 fbL ∫=0.4R jets, tanti-k
uncertaintiesSystematic
EW corr.×Non-pert. corr. ×NLOJET++ (CT10)
)0 10×| < 0.5 (y|)-3 10×| < 1.0 (y |≤0.5 )-6 10×| < 1.5 (y |≤1.0 )-9 10×| < 2.0 (y |≤1.5 )-12 10×| < 2.5 (y |≤2.0 )-15 10×| < 3.0 (y |≤2.5
Double differential cross sections:
0.6
0.8
1
1.2
1.4 | < 0.3y|
0.6
0.8
1
1.2
1.4 | < 0.8y |≤0.3
[GeV]Tp
210 3100.60.8
11.21.4 | < 1.2y |≤0.8
0.6
0.8
1
1.2
1.4 | < 2.1y |≤1.2
[GeV]Tp
210 3100.60.8
11.21.4 | < 2.8y |≤2.1
Rat
io
Rat
io ATLAS-1 dt = 36 pbL ∫2010 :
-1 dt = 4.5 fbL ∫2011 :
=7 TeVs
=0.4R jets, tanti-k
uncertainty2011 syst. and stat.
uncertainty2010 syst. and stat.
• Larger dataset: extension to higher pT values (2 TeV), reduces systematics
NLOJET prediction matched well with double differential
measured cross section
arXiv:1410.8857
Comparison of 2011 and 2010 data:
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Dominant systematic uncertainty:• Jet Energy Scale
• Data compared to NLOJET prediction with several different PDF sets (including corrections for non perturbative and electroweak effects):
• Only ABM11 PDF shows significant deviations from measured values
• Fairly good agreement for all other tested PDF sets
• Similar results for R=0.6
• Quantitative comparison including correlations of uncertainties• All information published
Impact on PDFs
18
0.6
0.8
1
1.2| < 0.5y|
0.6
0.8
1
1.2| < 1.0y |≤0.5
[GeV]Tp
210 310
0.81
1.21.4 | < 1.5y |≤1.0
0.5
1
1.5
2 | < 2.0y |≤1.5
0.5
1
1.5
2 | < 2.5y |≤2.0
[GeV]Tp
210 310
0.5
1
1.5
2 | < 3.0y |≤2.5
Theo
ry /
data
Theo
ry /
data ATLAS
= 7 TeVs
-1 dt = 4.5 fbL ∫
=0.4R jets, tanti-k
NLOJET++maxTp =
Rµ =
Fµ
EW corr.Non-pert and
Data
1.5HERAPDF
CT10
= 5fnABM11
0.6
0.8
1
1.2| < 0.5y|
0.6
0.8
1
1.2| < 1.0y |≤0.5
[GeV]Tp
210 310
0.81
1.21.4 | < 1.5y |≤1.0
0.5
1
1.5
2 | < 2.0y |≤1.5
0.5
1
1.5
2 | < 2.5y |≤2.0
[GeV]Tp
210 310
0.5
1
1.5
2 | < 3.0y |≤2.5
Theo
ry /
data
Theo
ry /
data ATLAS
= 7 TeVs
-1 dt = 4.5 fbL ∫
=0.4R jets, tanti-k
NLOJET++maxTp =
Rµ =
Fµ
EW corr.Non-pert and
Data
MSTW 2008
CT10
NNPDF 2.1
arXiv:1410.8857
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Comparison of Perugia 2011 and AUET2B tunes
• Perugia tune yields consistently larger cross section prediction than AUET2B
• Shape well reproduced by POWHEG
• Similar Results for R=0.6
ME+PS element generator vs. pQCD calculation
19
0.6
0.8
1
1.2| < 0.5y|
0.6
0.8
1
1.2| < 1.0y |≤0.5
[GeV]Tp
210 310
0.81
1.21.4 | < 1.5y |≤1.0
0.5
1
1.5
2 | < 2.0y |≤1.5
0.5
1
1.5
2 | < 2.5y |≤2.0
[GeV]Tp
210 310
0.5
1
1.5
2 | < 3.0y |≤2.5
Theo
ry /
data
Theo
ry /
data ATLAS
= 7 TeVs
-1 dt = 4.5 fbL ∫
=0.4R jets, tanti-k
POWHEG+PYTHIA
BornTp =
Rµ =
FµCT10,
Data
EW corr.×2011
Perugia
EW corr.×Non-pert. corr.
×(CT10) NLOJET++
EW corr.×AUET2B
arXiv:1410.8857
3 Jet Production
arXiv:1411.1855
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Double differential measurement in Rapidity and tri-jet mass
• Dominating systematic uncertainty: JES
• Good agreement with prediction over 7 orders of magnitude!
3 Jet Production
21
[GeV]jjjm400 1000 2000 3000
/d|Y
*| [p
b/G
eV]
jjj/d
mσ2 d
-610
-410
-210
1
210
410 ATLAS-1L dt = 4.5 fb∫
= 7 TeVs
R = 0.4tkanti-
non-pert. corr×CT 10⊗NLO QCD
)0 |Y*|<2 (x10 )12<|Y*|<4 (x10 )24<|Y*|<6 (x10 )36<|Y*|<8 (x10 )48<|Y*|<10 (x10
Event Selection:
• Anti-kt reconstruction algorithm, radius R=0.4 (0.6)
• Jets calibrated using insitu methods
• At least 3 jets with• pT > 50 GeV & |y| < 3• leading jet: pT > 150 GeV• sub-leasing jet: pT > 100 GeV
• |Y*| = |y1 - y2| + |y2 - y3| + |y1 - y3|
arXiv:1411.1855
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Similar picture to previous analysis
• ABM11 PDF yield systematically lower predictions, in particular in low rapidity region
• Good agreement for R=0.4
• Shifted prediction/data ratio for R=0.6 towards lower values
3 Jet Production - PDF impact
22
[GeV]jjjm210×4 310 310×2
Pred
ictio
n/Da
ta
0.60.8
11.21.4 |Y*|<2
[GeV]jjjm210×4 310 310×2
0.60.8
11.21.4 2<|Y*|<4
[GeV]jjjm210×4 310 310×20.40.60.8
11.21.41.6 6<|Y*|<8 [GeV]jjjm210×4 310 310×2
0.6
0.8
1
1.2
1.4 4<|Y*|<6
[GeV]jjjm210×4 310 310×20.40.60.8
11.21.41.6 8<|Y*|<10
ATLAS-1 L dt = 4.5 fb∫
= 7 TeVs R = 0.4tkanti-
DATA Uncert.TotalStatistical
non-pert. corr.× PDF⊗NLO QCD
NNPDF 2.3ABM 11HERA 1.5
[GeV]jjjm210×4 310 310×2
Pred
ictio
n/Da
ta
0.60.8
11.21.4 |Y*|<2
[GeV]jjjm210×4 310 310×2
0.60.8
11.21.4 2<|Y*|<4
[GeV]jjjm210×4 310 310×20.40.60.8
11.21.41.6 6<|Y*|<8 [GeV]jjjm210×4 310 310×2
0.6
0.8
1
1.2
1.4 4<|Y*|<6
[GeV]jjjm210×4 310 310×20.40.60.8
11.21.41.6 8<|Y*|<10
ATLAS-1 L dt = 4.5 fb∫
= 7 TeVs R = 0.6tkanti-
DATA Uncert.TotalStatistical
non-pert. corr.× PDF⊗NLO QCD
NNPDF 2.3ABM 11HERA 1.5
R=0.4
R=0.6
arXiv:1411.1855
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Inclusive Jet production and the association with Vector Bosons contain interesting physics!
• Many results from ATLAS• Few are shown:• W+jets: large sensitivity to higher order ME corrections, PS and merging technique. Still room for improvements!
• W/Z + jets ratios: smaller uncertainties, well modeled by generators
• Z+b-jets: sensitivity to PDFs and initial state description
• Inclusive Jets: good agreement with fixed-order NLOpQCD calculations + corrections (non perturbative & EWK) and ME + matched PS
• 3 Jet production: similar to inclusive Jets: ABM11 PDF shows deviations from measurement in low Y* region;
for R=0.6: ratio theory / data systematically lower compared to R=0.4
Conclusions
23
BACKUP
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Promt, isolated photon production cross section
• Shape well described by Pythia and Herwig
• Absolute cross section predicted lower than measuremed
• PDF uncertainties become important for high ET • Good agreement with NLO pQCD predictions
Promt Photon Production
25
[GeV]isoTE
-10 -5 0 5 10 15 20 25 30 35 40
Entri
es /
GeV
0
20
40
60
80
100
120
140
160
180
200310×
=7 TeVsData 2011 γtight
γnon-tight
|<1.37γη>100 GeV |γ
TE
ATLAS
-1 L dt = 4.6 fb∫
0 0.5 1 1.5 2 2.5
50
100
150
200
250
300
350
400
0 0.5 1 1.5 2 2.5 [p
b]γ η
/ d
σd
100
200
300
400
0 0.5 1 1.5 2 2.5 [p
b]γ η
/ d
σd
100
200
300
400>100 GeVγ
TE =7 TeVsData 2011 PYTHIA (MRST 2007 LO*)HERWIG (MRST 2007 LO*)
NLO (Jetphox) CT10Total uncertaintyScale uncertaintyNLO (Jetphox) MSTW2008nlo
-1 L dt = 4.6 fb∫
ATLAS
0 0.5 1 1.5 2 2.50.7
0.8
0.9
1
1.1
1.2
|γη|0 0.5 1 1.5 2 2.5
0.8
1
1.2Th
eory
/Dat
a100 200 300 400 500 600 700 800 900 1000
-510
-410
-310
-210
-110
1
10
1002003004005006007008009001000
[pb/
GeV
]γ T
/ d
Eσ
d
-510
-410
-310
-210
-110
1
10
1002003004005006007008009001000
[pb/
GeV
]γ T
/ d
Eσ
d
-510
-410
-310
-210
-110
1
10
|<1.37γη|
=7 TeVsData 2011 PYTHIA (MRST 2007 LO*)HERWIG (MRST 2007 LO*)
NLO (Jetphox) CT10Total uncertaintyScale uncertainty
NLO (Jetphox) MSTW2008nlo
-1 L dt = 4.6 fb∫
ATLAS
100 200 300 400 500 600 700 800 900 10000.50.60.70.80.9
11.11.21.31.4
[GeV]γTE
100 200 300 400 500 600 700 800 900 10000.60.8
11.21.4
Theo
ry/D
ata
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Ratio well described by all generators
• Good description by HEJ for single channel
Invariant di-jet mass
26
W → lν
[GeV]12m0 500 1000 1500 2000
[1/G
eV]
12/d
m2j≥
W+
σd
-510
-410
-310
-210
-110
1
10
ATLAS jets, R=0.4,tanti-k
| < 4.4j > 30 GeV, |yjT
pScaled Predictions
2 jet≥) + ν l→W(Data,
-1 = 7 TeV, 4.6 fbs+SHERPAATHLACKB
HEJALPGENSHERPAMEPS@NLO [GeV]12m
0 500 1000 1500 2000
Pred
. / D
ata
0.60.8
11.21.4 +SHERPAATHLACKB
ATLAS
[GeV]12m0 500 1000 1500 2000
Pred
. / D
ata
0.60.8
11.21.4 HEJ
[GeV]12m0 500 1000 1500 2000
Pred
. / D
ata
0.60.8
11.21.4 ALPGEN
[GeV]12m0 500 1000 1500 2000
Pred
. / D
ata
0.60.8
11.21.4
SHERPA
MEPS@NLO
[GeV]12m0 100 200 300 400 500 600 700 800 900 1000
)12
/dm
2j≥Z+σ
)/(d
12/d
m2j≥
W+
σ)(d
2j≥(1
/R
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2ATLAS
jets, R=0.4,tanti-k| < 4.4j > 30 GeV, |yj
Tp
2 jet≥)) + -l+ l→))/(Z(ν l→(W(-1=7 TeV, 4.6 fbsData,
+SHERPAATHLACKBALPGEN+HERWIGSHERPA
[GeV]12m0 100 200 300 400 500 600 700 800 900 1000
NLO
/ Da
ta
0.80.9
11.11.21.3 +SHERPAATHLACKB
[GeV]12m0 100 200 300 400 500 600 700 800 900 1000
MC
/ Dat
a
0.80.9
11.11.21.3 ALPGEN
[GeV]12m0 100 200 300 400 500 600 700 800 900 1000
MC
/ Dat
a
0.80.9
11.11.21.3 SHERPA
Ratio measurement
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015 27
[GeV]TH500 1000 1500 2000
[1/G
eV]
T/d
H1j≥
W+
σd
-610
-510
-410
-310
-210
-110
1
10
210
310
410ATLAS
jets, R=0.4,tanti-k| < 4.4j > 30 GeV, |yj
TpScaled Predictions
1 jet≥) + ν l→W(Data,
-1 = 7 TeV, 4.6 fbs+SHERPAATHLACKB
BH+S Excl. SumLoopSimALPGENSHERPAMEPS@NLO
[GeV]TH500 1000 1500 2000
Pred
. / D
ata
0.5
1
1.5 BH+S BH+S Excl. Sum
ATLAS
[GeV]TH500 1000 1500 2000
Pred
. / D
ata
0.5
1
1.5 LoopSim
[GeV]TH500 1000 1500 2000
Pred
. / D
ata
0.5
1
1.5 ALPGEN
[GeV]TH500 1000 1500 2000
Pred
. / D
ata
0.5
1
1.5
SHERPA
MEPS@NLO
Inclusive Jets - HT
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015 28
| (leading jet)j|y0 0.5 1 1.5 2 2.5 3 3.5 4
j/d
y1j≥
W+
σd
1
10
210
310
ATLAS jets, R=0.4,tanti-k
| < 4.4j > 30 GeV, |yjT
pScaled Predictions
1 jet≥) + ν l→W(Data,
-1 = 7 TeV, 4.6 fbs+SHERPAATHLACKB
ALPGENSHERPAMEPS@NLO
| (leading jet)j|y
0 0.5 1 1.5 2 2.5 3 3.5 4
Pred
. / D
ata
0.60.8
11.21.4 +SHERPAATHLACKB
ATLAS
| (leading jet)j|y
0 0.5 1 1.5 2 2.5 3 3.5 4
Pred
. / D
ata
0.60.8
11.21.4 ALPGEN
| (leading jet)j|y0 0.5 1 1.5 2 2.5 3 3.5 4
Pred
. / D
ata
0.60.8
11.21.4
SHERPA
MEPS@NLO
Inclusive Jets - Rapidity Leading Jet
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
Inclusive Jets Double Differential Measurement
29
0.6
0.8
1
1.2
1.4 | < 0.3y|
0.6
0.8
1
1.2
1.4 | < 0.8y |≤0.3
[GeV]Tp
210 3100.60.8
11.21.4 | < 1.2y |≤0.8
0.6
0.8
1
1.2
1.4 | < 2.1y |≤1.2
[GeV]Tp
210 3100.60.8
11.21.4 | < 2.8y |≤2.1
Rat
io
Rat
io ATLAS-1 dt = 36 pbL ∫2010 :
-1 dt = 4.5 fbL ∫2011 :
=7 TeVs
=0.6R jets, tanti-k
uncertainty2011 syst. and stat.
uncertainty2010 syst. and stat.
[GeV]Tp
210 310
[pb/
GeV
]y
d Tp/dσ2 d
-2010
-1710
-1410
-1110
-810
-510
-210
10
410
710
1010ATLAS
=7 TeVs, -1 dt=4.5 fbL ∫=0.6R jets, tanti-k
uncertaintiesSystematic
EW corr.×Non-pert. corr. ×NLOJET++ (CT10)
)0 10×| < 0.5 (y|)-3 10×| < 1.0 (y |≤0.5 )-6 10×| < 1.5 (y |≤1.0 )-9 10×| < 2.0 (y |≤1.5 )-12 10×| < 2.5 (y |≤2.0 )-15 10×| < 3.0 (y |≤2.5
• Anti-kt reconstruction algorithm, radius R=0.6 • Jets calibrated using local hadronic calibration weights (LCW)• pT > 100 GeV & |y| < 3
• Data from 2011 and 2010 are consistent
• NLOJET prediction matched well with double differential measurement
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
Impact of PDFs
30
0.6
0.8
1
1.2| < 0.5y|
0.6
0.8
1
1.2| < 1.0y |≤0.5
[GeV]Tp
210 310
0.81
1.21.4 | < 1.5y |≤1.0
0.5
1
1.5
2 | < 2.0y |≤1.5
0.5
1
1.5
2 | < 2.5y |≤2.0
[GeV]Tp
210 310
0.5
1
1.5
2 | < 3.0y |≤2.5
Theo
ry /
data
Theo
ry /
data ATLAS
= 7 TeVs
-1 dt = 4.5 fbL ∫
=0.6R jets, tanti-k
NLOJET++maxTp =
Rµ =
Fµ
EW corr.Non-pert and
Data
1.5HERAPDF
CT10
= 5fnABM11
0.6
0.8
1
1.2| < 0.5y|
0.6
0.8
1
1.2| < 1.0y |≤0.5
[GeV]Tp
210 310
0.81
1.21.4 | < 1.5y |≤1.0
0.5
1
1.5
2 | < 2.0y |≤1.5
0.5
1
1.5
2 | < 2.5y |≤2.0
[GeV]Tp
210 310
0.5
1
1.5
2 | < 3.0y |≤2.5
Theo
ry /
data
Theo
ry /
data ATLAS
= 7 TeVs
-1 dt = 4.5 fbL ∫
=0.6R jets, tanti-k
NLOJET++maxTp =
Rµ =
Fµ
EW corr.Non-pert and
Data
MSTW 2008
CT10
NNPDF 2.1
• Dominant systematic uncertainty:• Jet Energy Scale
• Data compared to NLOJET prediction with several different PDF sets (including corrections for non perturbative and electroweak effects):
• Only ABM11 PDF shows significant deviations from measured values
• Fairly good agreement for all other tested PDF sets
• Similar results for R=0.4
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
ME element generator vs. pQCD calculation
31
0.6
0.8
1
1.2| < 0.5y|
0.6
0.8
1
1.2| < 1.0y |≤0.5
[GeV]Tp
210 310
0.81
1.21.4 | < 1.5y |≤1.0
0.5
1
1.5
2 | < 2.0y |≤1.5
0.5
1
1.5
2 | < 2.5y |≤2.0
[GeV]Tp
210 310
0.5
1
1.5
2 | < 3.0y |≤2.5
Theo
ry /
data
Theo
ry /
data ATLAS
= 7 TeVs
-1 dt = 4.5 fbL ∫
=0.6R jets, tanti-k
POWHEG+PYTHIA
BornTp =
Rµ =
FµCT10,
Data
EW corr.×2011
Perugia
EW corr.×Non-pert. corr.
×(CT10) NLOJET++
EW corr.×AUET2B
• Comparison of Perugia 2011 and AUET2B tunes
Perugia tune yields consistently larger cross section prediction than AUET2B
• Shape well reproduced by POWHEG
• Similar Results for R=0.4
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
3 Jet Production - R=0.6
32
[GeV]jjjm400 1000 2000 3000
/d|Y
*| [p
b/G
eV]
jjj/d
mσ2 d
-610
-410
-210
1
210
410 ATLAS-1L dt = 4.5 fb∫
= 7 TeVs
R = 0.6tkanti-
non-pert. corr×CT 10⊗NLO QCD
)0 |Y*|<2 (x10 )12<|Y*|<4 (x10 )24<|Y*|<6 (x10 )36<|Y*|<8 (x10 )48<|Y*|<10 (x10
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
3 Jet Production - more PDFs
33
[GeV]jjjm210×4 310 310×2
Pred
ictio
n/Da
ta
0.60.8
11.21.4 |Y*|<2
[GeV]jjjm210×4 310 310×2
0.60.8
11.21.4 2<|Y*|<4
[GeV]jjjm210×4 310 310×20.40.60.8
11.21.41.6 6<|Y*|<8 [GeV]jjjm210×4 310 310×2
0.6
0.8
1
1.2
1.4 4<|Y*|<6
[GeV]jjjm210×4 310 310×20.40.60.8
11.21.41.6 8<|Y*|<10
ATLAS-1 L dt = 4.5 fb∫
= 7 TeVs R = 0.6tkanti-
DATA Uncert.TotalStatistical
non-pert. corr.× PDF⊗NLO QCD
CT 10MSTW 2008GJR 08
[GeV]jjjm210×4 310 310×2
Pred
ictio
n/Da
ta
0.60.8
11.21.4 |Y*|<2
[GeV]jjjm210×4 310 310×2
0.60.8
11.21.4 2<|Y*|<4
[GeV]jjjm210×4 310 310×20.40.60.8
11.21.41.6 6<|Y*|<8 [GeV]jjjm210×4 310 310×2
0.6
0.8
1
1.2
1.4 4<|Y*|<6
[GeV]jjjm210×4 310 310×20.40.60.8
11.21.41.6 8<|Y*|<10
ATLAS-1 L dt = 4.5 fb∫
= 7 TeVs R = 0.4tkanti-
DATA Uncert.TotalStatistical
non-pert. corr.× PDF⊗NLO QCD
CT 10MSTW 2008GJR 08
Electroweak production of V+jets
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Production via purely electroweak processes is rare• Mainly interested in:
Motivation - EWK production
35
• What we can learn from them?• Probe triple and quadratic gauge boson self-interactions• Can be used in a model independent approach to explore new physics, that modifies gauge boson self-interactions (anomalous couplings)
• Probe the nature of the EW symmetry breaking, testing the unitarization in VV scattering by HVV contribution (VBS)
• Understand irreducible background to Higgs and beyond-SM searches• Constrain MC modeling of QCD-initiated processes in VBF-like regions
Vector Boson fusion Vector Boson scattering
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
Zjj: VBF - strategy of measurement
36
Baseline
pTj1> 55 GeV pT
j2> 45GeV
High pT or high mass
pTj1> 85 GeV
pTj2> 75GeV
mjj > 1TeV
Search mjj > 250 GeV
pTll> 20 GeV
pTbal<0.15
Njets gap= 0
Control mjj > 250 GeV
pTbal,3<0.15
Njetgap>= 1
pTll> 20 GeV
Z
Z Z
• Measure inclusive (QCD+EW) Zjj cross section and differential distributions in 5 fiducial regions with varying sensitivity to the EW component:
• 3 regions with simple topologies:
• “baseline”
• “high pT” and “high mass” • probe impact of EW component
• 2 ad hoc selections:• “search region” and “control region”
• Extract electroweak component cross section from “search region”, constraining background modeling (QCD Zjj) from “control region”
• Set limits on anomalous triple gauge couplings
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Electroweak production becomes important!• Overestimated in Sherpa
• Sherpa predicts harder mass spectrum
• Powheg is in good agreement with data
Zjj: VBF - Results
37
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
[pb]
Zjj
σ
-110
1
10ATLAS
-1 L dt = 20.3 fb∫ = 8 TeVs
Data 2012Powheg (Zjj) + Sherpa (VZ)
baselineT
high p search control high mass
theo
ryσ
data
σ0.80.9
11.1
Figure 4. Fiducial cross-section measurements for inclusive Zjj production in the Z ! `+`�
decay channel, compared to the Powheg prediction for strong and electroweak Zjj production andthe small contribution from ZV production predicted by Sherpa. The (black) circles represent thedata and the associated error bar is the total uncertainty in the measurement. The (red) trianglesrepresent the theoretical prediction, the associated error bar (or hatched band in the lower plot) isthe total theoretical uncertainty on the prediction.
• 1
�
· d�
d|�y| : The normalised distribution of the di↵erence in rapidity between the two
leading jets, |�y|.
• 1
�
· d�
d|��(j,j)| : The normalised distribution of the di↵erence in azimuthal angle between
the two leading jets, ��(j, j).
The distributions sensitive to the di↵erence in t-channel colour flow between electroweak
and strong production of Zjj events include:
• 1
�
· d�
dN
gapjet
: The normalised distribution of the number of jets, Ngap
jet
, with pT
> 25 GeV
in the rapidity interval bounded by the two highest-pT
jets.
• 1
�
· d�
dp
balanceT
: The normalised distribution of the pT
-balancing distribution, pbalanceT
(see
eq. 6.2).
• The fraction of events that contain no additional jets with pT
> 25 GeV in the
rapidity interval bounded by the two highest-pT
jets (the jet veto e�ciency) as a
function of mjj
and |�y|.
• The average number of jets with pT
> 25 GeV in the rapidity interval bounded by
the two highest-pT
jets, hNgap
jet
i, as a function of mjj
and |�y|.
• The fraction of events with pbalanceT
< 0.15 (pbalanceT
cut e�ciency) as a function of
mjj
and |�y|.
– 14 –
0 500 1000 1500 2000 2500 3000
jjdmσd
σ1
-710
-610
-510
-410
-310
ATLAS-1 L dt = 20.3 fb∫
= 8 TeVsbaseline region
Data (2012)
Sherpa Zjj (QCD + EW)
Sherpa Zjj (QCD)
Powheg Zjj (QCD + EW)
Powheg Zjj (QCD)
0 500 1000 1500 2000 2500 3000
D
ata
Sher
pa
1
1.5
2
[GeV]jjm0 500 1000 1500 2000 2500 3000
D
ata
Pow
heg
1
1.5
(a)
500 1000 1500 2000 2500 3000
jjdmσd
σ1
-710
-610
-510
-410
-310
ATLAS-1 L dt = 20.3 fb∫
= 8 TeVssearch region
Data (2012)
Sherpa Zjj (QCD + EW)
Sherpa Zjj (QCD)
Powheg Zjj (QCD + EW)
Powheg Zjj (QCD)
500 1000 1500 2000 2500 3000
D
ata
Sher
pa
0.81
1.2
[GeV]jjm500 1000 1500 2000 2500 3000
D
ata
Pow
heg
0.81
1.2
(b)
Figure 6. Unfolded 1� · d�
dmjjdistribution in the (a) baseline and (b) search regions. The data
are shown as filled (black) circles. The vertical error bars show the size of the total uncertaintyon the measurement, with tick marks used to reflect the size of the statistical uncertainty only.Particle-level predictions from Sherpa and Powheg are shown for combined strong and electroweakZjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, aroundthe central prediction, which is shown as a solid line. The predictions from Sherpa and Powheg forstrong Zjj production (labelled QCD) are shown as dashed lines.
in electroweak Zjj production.
In the baseline region, the Powheg prediction is accurate to NLO in perturbative QCD
and better describes the data at the highest values of mjj
and |�y| than Sherpa, which is
accurate to LO. In particular, Sherpa predicts too large a fraction of events at large mjj
and |�y|, a feature also seen in previous measurements at the LHC and Tevatron [57, 58].
In the search region, the veto on additional jet activity means that both Sherpa and Powheg
are accurate only to LO. Despite this, both predictions give a satisfactory description of
the data if both strong and electroweak Zjj production are included. The contribution
from electroweak Zjj production is evident at high mjj
and high |�y| in the search region
for both event generators.
The unfolded 1
�
· d�
dN
gapjet
, 1
�
· d�
dp
balanceT
and 1
�
· d�
d|��(j,j)| distributions are shown in the
high-mass region in figure 8. Quark/gluon radiation from the electroweak Zjj process is
much less likely than in the strong Zjj process because there is no colour flow between the
two jets. The contribution from electroweak Zjj production is clear in the low-multiplicity
region of the 1
�
· d�
dN
gapjet
distribution for both Powheg and Sherpa, demonstrating the ef-
– 17 –
baseline regionsearch region used to get aTGC limits
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
Limit on anomalous triple gauge coupling
38
• Zjj sensitive to TGC• Sensitivity to new physics modifying gauge boson self-interaction
• Generic aTGC couplings parametrized by effective Lagrangian
• 3 contributing couplings• g1,Z, λZ, κZ
• Limits weaker but complementary than those from di-boson production• Di-boson: all 3 bosons have time-like momentum• Here 2 W have space-like momentum
Table 7. The 95% confidence intervals obtained on the aTGC parameters from counting thenumber of events with mjj > 1 TeV in the search region. Observed and expected intervals, labelled‘obs’ and ‘exp’ respectively, are presented for unitarisation scales of ⇤ = 6 TeV and ⇤ = 1. Theparameter �g1,Z refers to the deviation of g1,Z from the SM value.
aTGC ⇤ = 6 TeV (obs) ⇤ = 6 TeV (exp) ⇤ = 1 (obs) ⇤ = 1 (exp)
�g1,Z
[�0.65, 0.33] [�0.58, 0.27] [�0.50, 0.26] [�0.45, 0.22]
�Z
[�0.22, 0.19] [�0.19, 0.16] [�0.15, 0.13] [�0.14, 0.11]
the Lagrangian that contain a derivative of the W -boson field. Table 7 shows the 95%
confidence intervals obtained on the anomalous coupling parameters �Z
and g1,Z
. The
limits are not as stringent as those set in WZ production [72], which are approximately a
factor of three smaller in the �Z
coupling, for example.
9 Summary
Fiducial cross sections for electroweak Zjj production have been presented for proton-
proton collisions atps = 8 TeV, using a dataset corresponding to an integrated luminos-
ity of 20.3 fb�1 collected by the ATLAS experiment at the Large Hadron Collider. The
background-only model has been rejected above the 5� level and these measurements con-
stitute observation of the electroweak Zjj process. The measured cross sections are in good
agreement with the Standard Model expectation and limits have been set on anomalous
triple gauge couplings. In addition, cross sections and di↵erential distributions have been
measured for inclusive Zjj production in five fiducial regions. The cross-section measure-
ments are all in good agreement with the prediction from Powheg for Zjj production. The
di↵erential distributions are sensitive to the electroweak component of Zjj production, as
well as the modelling of strong Zjj production in the extreme phase-space regions probed.
The data are compared to theoretical predictions from the Sherpa and Powheg event gen-
erators. Neither prediction is able to fully reproduce the data for all distributions and
the data can be used to constrain the theoretical modelling in these extreme phase-space
regions.
Acknowledgements
We thank CERN for the very successful operation of the LHC, as well as the support
sta↵ from our institutions without whom ATLAS could not be operated e�ciently. We
also thank Stefan Hoeche and Frank Krauss for insight and cross-checks related to the
interference between electroweak and strong Zjj production as predicted by the Sherpa
event generator.
We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Aus-
tralia; BMWF and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP,
Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and
– 31 –
95% confidence intervals
W�
W+Z
q
q
q0
µ+, e+
µ�, e�
q0
(a) vector boson fusion
W±
Z
q
q
q0
q0
µ+, e+
µ�, e�
(b) Z-boson bremsstrahlung
Z
Z
q
q
q
µ+, e+
µ�, e�
q
(c) non-resonant `+`�jj
Figure 1. Representative leading-order Feynman diagrams for electroweak Zjj production at theLHC: (a) vector boson fusion (b) Z-boson bremsstrahlung and (c) non-resonant `+`�jj production.
the additional jets arising as a result of the strong interaction. Production of Zjj events via
the t-channel exchange of an electroweak gauge boson is a purely electroweak process and is
therefore much rarer. Electroweak Zjj production in the leptonic decay channel is defined
to include all contributions to `+`�jj production for which there is a t-channel exchange
of an electroweak gauge boson [1, 2]. These contributions include Z-boson production
via vector boson fusion (VBF), Z-boson bremsstrahlung and non-resonant production, as
shown in figure 1. The VBF process is of particular interest because of the similarity to
the VBF production of a Higgs boson and the sensitivity to anomalous WWZ triple gauge
couplings.2
This paper presents two measurements of Zjj production using 20.3 fb�1 of proton-
proton collision data collected by the ATLAS experiment [3] at a centre-of-mass energy ofps = 8 TeV:
1. Measurements of fiducial cross sections and di↵erential distributions of inclusive Zjj
production. These measurements are performed in five fiducial regions with di↵erent
sensitivity to the electroweak component. Inclusive Zjj production is dominated by
the strong production process, an example of which is shown in figure 2(a). The data
therefore provide important constraints on the theoretical modelling of QCD-initiated
processes that produce VBF-like topologies.3
2. Observation of electroweak Zjj production and measurements of the cross section in
two fiducial regions. Limits are also placed on anomalous WWZ couplings.
These measurements are performed using a combination of the Z ! e+e� and Z ! µ+µ�
decay channels.
Using electroweak Zjj production as a probe of colour-singlet exchange and as a val-
idation of the vector boson fusion process has been discussed extensively in the litera-
ture [1, 4, 5]. A previous measurement by the CMS Collaboration showed evidence for
2The VBF process cannot be isolated due to a large destructive interference with the electroweak Z-
boson bremsstrahlung process. The contribution to the electroweak cross section from non-resonant `+`�jj
production is less than 1% after applying the selection criteria used in this analysis.3Inclusive Zjj production contains a small (percent-level) contribution from diboson events (figure 2(b)).
– 2 –
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• Strategy of the measurement is about the same as for EW Zjj:
• Measure inclusive (QCD+EW) W±W±jj cross section in 2 fiducial regions • (“inclusive region” and “VBS region”): varying sensitivity to the EW component
• Extraction on the EW W±W±jj production from the “VBS region”
• Set limits on anomalous quadratic gauge couplings
Vector Boson scattering
39
q
q
q0
W+
W+
q0
q
q
q0
W+
W+
q0
q
q
q0
W+
W+
q0
q
q
q0
W+
W+
q0
Self-interaction Higgs contribution Non resonant
Electroweak process:Sensitive to anomalous quartic gauge couplings
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
• First evidence for VBS
• BG only hypothesis excluded at 4.5σ• Counted 34 events, ~16 BG events
• Measurement in agreement with SM prediction
Vector Boson Scattering
40
4
Inclusive Region VBS Regione
±e
±e
±µ
±µ
±µ
±e
±e
±e
±µ
±µ
±µ
±
Prompt 3.0 ± 0.7 6.1 ± 1.3 2.6 ± 0.6 2.2 ± 0.5 4.2 ± 1.0 1.9 ± 0.5Conversions 3.2 ± 0.7 2.4 ± 0.8 – 2.1 ± 0.5 1.9 ± 0.7 –Other non-prompt 0.61 ± 0.30 1.9 ± 0.8 0.41 ± 0.22 0.50 ± 0.26 1.5 ± 0.6 0.34 ± 0.19W
±W
±jj Strong 0.89 ± 0.15 2.5 ± 0.4 1.42 ± 0.23 0.25 ± 0.06 0.71 ± 0.14 0.38 ± 0.08
W
±W
±jj Electroweak 3.07 ± 0.30 9.0 ± 0.8 4.9 ± 0.5 2.55 ± 0.25 7.3 ± 0.6 4.0 ± 0.4
Total background 6.8 ± 1.2 10.3 ± 2.0 3.0 ± 0.6 5.0 ± 0.9 8.3 ± 1.6 2.6 ± 0.5Total predicted 10.7 ± 1.4 21.7 ± 2.6 9.3 ± 1.0 7.6 ± 1.0 15.6 ± 2.0 6.6 ± 0.8Data 12 26 12 6 18 10
TABLE II: Estimated background yields, observed number of data events, and predicted signal yields for the three channelsare shown with their systematic uncertainty. Contributions due to interference are included in the W
±W
±jj electroweak
prediction.
[GeV]jjm
Even
ts/5
0 G
eV
-110
1
10
210 Data 2012 Syst. Uncertainty
jj Electroweak±W± Wjj Strong±W± W
Prompt Conversions Other non-prompt
ATLAS = 8 TeVs, -120.3 fb
[GeV]jjm200 400 600 800 1000 1200 1400 1600 1800 2000Da
ta/B
ackg
roun
d
0
5
Data/BkgBkg Uncertainty(Sig+Bkg)/Bkg
FIG. 1: The mjj distribution for events passing the inclu-sive region selections except for the mjj selection indicatedby the dashed line. The black hatched band in the upper plotrepresents the systematic uncertainty on the total prediction.On the lower plot the shaded band represents the fractionaluncertainty of the total background while the solid line andhatched band represents the ratio of the total prediction tobackground only and its uncertainty. The W
±W
±jj predic-
tion is normalized to the SM expectation.
production, and the fiducial cross sections in the two re-gions (�fid) are measured by combining the three decaychannels in a likelihood function. Systematic uncertain-ties are taken into account with nuisance parameters.
The signal e�ciency in each fiducial region is definedas the number of expected signal events after selectionsdivided by the number of events passing the respectivefiducial region selections at particle level. The e�ciencyaccounts for the detector reconstruction, migration intoand out of the fiducial volume, identification, and triggere�ciency; it is 56%, 72%, 77% for the inclusive region and57%, 73%, 83% for the VBS region in the e±e±, e±µ±,
|jjyΔ|0 1 2 3 4 5 6 7 8 9
Even
ts
5
10
15
20
25
30 Data 2012 Syst. Uncertainty
jj Electroweak±W± Wjj Strong±W± W
Prompt Conversions Other non-prompt
ATLAS = 8 TeVs, -120.3 fb
> 500 GeVjjm
FIG. 2: The |�yjj | distribution for events passing all inclu-sive region selections. The |�yjj | selection is indicated by adashed line. The W
±W
±jj prediction is normalized to the
SM expectation.
µ±µ± channels respectively. The e�ciency also accountsfor the contribution of leptonic ⌧ decays, which are notincluded in the fiducial cross-section definition: 10% ofsignal candidates are expected to originate from leptonic⌧ decays. The uncertainty on the signal e�ciency is dom-inated by the jet reconstruction uncertainty of 6%.
The measured fiducial cross section for strong and elec-troweak W±W±jj production in the inclusive region is�fid = 2.1± 0.5(stat)± 0.3(syst) fb. The measured fidu-cial cross section for electroweak W±W±jj production,including interference with strong production in the VBSregion, is �fid = 1.3± 0.4(stat)± 0.2(syst) fb. The mea-sured cross sections are in agreement with the respectiveSM expectations of 1.52± 0.11 fb and 0.95± 0.06 fb.
Additional contributions to W±W±jj production canbe expressed in a model-independent way using higher-dimensional operators leading to anomalous quarticgauge boson couplings (aQGCs). The measured crosssection in the VBS fiducial region is used to set lim-its on aQGCs a↵ecting vertices with four interactingW bosons. The Whizard event-generator [39] is used
]-4 [TeV4Λ / S,0f-800 -600 -400 -200 0 200 400 600 800
]-4
[TeV
4Λ
/ S,
1f
-2000
-1000
0
1000
2000 ATLAS��20.3 fb-1, s = 8 TeV�pp → W± W± jj�K-matrix unitarization
68% CL95% CLexpected 95% CLStandard Model
confidence intervals
aQGC interpretation:
[fb]VBS.WW σ
-1 -0.5 0 0.5 1 1.5 2 2.50
0.2
0.4
0.6
0.8
1
±e±e
±µ±e
±µ±µ
Combination
4.0 [fb]± 1.0 ±0.4
0.25 [fb]± 0.6 ±1.3
0.15 [fb]± 0.8 ±1.7
0.2 [fb]± 0.4 ±1.3
ATLAS=8 TeVs,-120.3 fb
0.06 [fb]±=0.95 VBSWWσSM
NLO, POWHEG-BOX, CT10
Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015
Conclusion EWK production
41
Electroweak prod.: evidence of VBS, sensitive to anomalous coupling no deviation from SM predictions observed