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Potential for Standard Model physics with CMS at the LHC
Where are we with hard- and software ? From the Tevatron/LEP to the LHC Top quark, EW, QCD, B physics, ... How to search for the Standard Model Higgs ?
Jorgen D’Hondt (Vrije Universiteit Brussel)on behalf of the CMS Collaboration
HEP-EPS Conference, Lisbon, 21-27 July 2005
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 2
The CMS detector : design sketch
76k pieces
16k pieces
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 3
The CMS detector : construction progress
Large activities are ongoing to makeprevious sketch into reality
Main underground cavern is ready
Several sub-detector systems are completed or being completed :
Tracker : serious speed-up of production, overall good quality of modules ECAL : ⅔ of barrel crystals delivered, first SuperClusters for endcap made HCAL : assembled, start with electronics integration, calibration ongoing Magnet : completed and succesfully tested for leaks Muons : CSC’s completed, RPC’s being constructed and gradually integrated, 80% of DT’s are completed
Trigger boards are being produced
“ CMS* will be closed and ready for beam on 30 June 2007 ” (T.Virdee, HCP’05 talk)
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 4
The CMS detector : becoming a reality
barrel trackersilicon detectors
magnet
muon RPC’s
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 5
Example of an Event
IGUANAlow luminosity
SUSY eventpT > 1.0 GeV|| < 2.4
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 6
Example of an Event
IGUANAhigh luminosity
SUSY eventpT > 1.0 GeV|| < 2.4
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 7
Current status of Simulationand Reconstruction
Still a few years before real data… hence all based on Monte Carlo simulationfirst data expected in 2007
Main generator used : PYTHIA 6.2 does not include many features present in dedicated generators fast simulation : the PYTHIA objects are smeared to mimic the detector the particle interactions are not simulated with GEANT
Results in this presentation: studies based on fast simulation (‘FAMOS’) large efforts have been made to optimize the reconstruction code large Data-Challenge efforts have been made to provide dedicated
GEANT-4 simulation (created ~100M simulated events, ~1Mb/event) in the process of writing a Physics - Technical Design Report with this
accurate simulation and reconstruction tools (expected early 2006) Current results to be digested as an illustration of what can be learned from
CMS data upon arrival
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 8
From Tevatron/LEP to LHC
Obtaining orders in magnitude in both the integrated luminosity and the energy, we will collect a huge amount of Standard Model benchmarks channels.
~109 events/10fb-1 W (200 per second)~108 events/10fb-1 Z (50 per second)~107 events/10fb-1 tt (1 per second)
These can be used as control/calibration samples for searches beyond the Standard Model, but can also be used to scrutinize even further the Standard Model.
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 9
Top Quark Physics : top quark mass
10 tt pairs per day @ Tevatron 1 tt pair per second @ LHCqq →tt : 85% gg→tt : 87%
width of peak~10 GeV
mt(stat) ~ 300 MeV (10fb-1)
fastsim10fb-1
Most important parameter is the top quark mass (mt), to be estimated with an accuracy of around mt ~ 1 GeV/c2.
Golden channel : semi-leptonic tt →bWbW→blvbqq
Selection via lepton, miss.ET, 4 jets, 2 b-tags (S/B~>20)Top mass from hadronic side t→qqbMain systematics are the jet energy scale
Improve with kinematic fit and more advancedstatistical inference techniques are ongoing.
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 10
Top Quark Physics : top quark mass
From t l + J/ + X decays :
→ 100 fb-1 gives after selection ~ 1,000 signal events (S/B > 100) the large mass of the J/ induces a strong correlation with the top mass easier to identify (extremely clean sample) BR(overall in tt) ~ 5.3 x 10-5
no jet related systematics !!
hep-ph/9912320
60
New method : hep-ex/0501043correlate the b transverse decay length with m t
CMS fast simulation
slope
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 11
Top Quark Physics : top versus anti-top
Spin correlations the top quark does not loss its spin information before it is decaying into W and b
with A =0.431 (gg) and A = - 0.469 (qQ)
two observables +(-): angle between t(T) direction in the tT c.m. frame and the l+(l-) direction of flight in the t(T) rest frame fit to double differential distribution
result (30fb-1) : A (stat) = 0.035 and A (syst) = 0.028
Measuring the difference between mt and mT
almost all systematics cancel when measuring the difference between both after several years the precision could be around 50 MeV/c2
what we could learn from that ? CPT violation… ? differences between t and T can learn us something about the PDF’s (rapidity
distributions)
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 12
Top Quark Physics : single-top-channelNever observed !!
Each channel sensitive to different signals
• heavy W’ → s-channel• FCNC → t-channel• H± → Wt-channel
Also directly related to |Vtb| to percent level(s-channel preferred, t-channel dominated by PDF scale uncertainties of ~10%)
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 13
W polarization in top decays
The large top quark mass allows the W boson to be longitudinaly polarized
defined as : angle between lepton (in W rest frame) and W (in top rest frame)Standard Model prediction : f0 = mt
2 / (2 mW2 + mt
2) ~ 0.7 and fR ~ 0 (mb~0)
LH: (1±cos)2
Long: sin2PYTHIA 5.7, 1 year CMSonly W→ev and W→v
Expected uncertainty
stat f0 = 0.023 syst f0 = 0.022
estimation of systematic uncertainties conservativemost of the time limited by the statistical precision of the effect
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 14
Gauge Boson Couplings
Direct measurements of vector boson couplings are possible via the cross-section measurements of the processes in which they appear. They test the non-Abelian nature of the Standard Model gauge theory.
Anomalous couplings or new physics can be included in the effective Lagrangian at a fundamental scale .
W
W
pp→Wcross-section
enhanced when anomalous couplings
are present
pt-spectrum of photon sensitive to anomalous couplings (=1.5 TeV)
pt() (GeV)
=0.3, =0
=0, =0
=0, =0.95
Limits @95%CL (=2TeV)
for 100 fb-1 (=2TeV) || < 0.1 || < 0.0009
large improvement for compared to Tevatron
BAUR MC generator
For ZZ and Z couplings both the pT() and the MT(ll) spectrum are sensitive to hi
V (V=Z,) anomalous couplings
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 15
Drell-Yan Production of Lepton Pairs
The Drell-Yan process pp→l +l - is a measure for AFB and hence sin2efflept :
LHC reaches much higher masses
Z/
q
q
e-,-
e+,+
inverse of e+e- → qq at LEP
Precision will exceed the magnitude of the EW corrections up to Mll=2 TeV
Rel. exp. uncertainty on ll (in %)
5%
10%
0%
Weak-mixing anglesin2eff
lept can bedetermined to
sin2efflept ~ 0.00014
using forward lepton tagging
main systematic uncertainty is the
knowledge of the PDF’s
can also use sin2efflept to
constrain the PDF’s
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 16
Parton Probability Functions
y = pseudorapidity
DGLAP ev
olutio
n
How to find the partons in the colliding protons ?
→ need for precise PDF(x,Q2)
Extrapolate from HERA, but also use the huge LHC data itself
Ratio of W+/W- cross-section is related to u(x)/d(x)
0.1 fb-1 differentiate between several models
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 17
Parton Probability Functions
The PDF’s for the heavy quarks can also be measured
Isolated with high pT
+ jet including
Isolated e/ with high pT
+ jet including
Estimate 5-10% accuracy on PDF‘slimited by fragmentation functions
The PDF’s can be determined relative to each other, and therefore depend on the accuracy of the theoretical calculations.
In a similar way the gluon luminosity function can be obtained with a 1% accuracy.
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 18
B-physics
The CMS detector allows a rich B-physics program due to its precise tracking and vertexing(but no Particle ID detectors, usually triggers on high-pT objects)
CP violation measurements of Bs oscillations rare decays life-time Bc mesons etc...
Example : (alternative to lepton-tag method) CKM angle via Bd
0→J/ Ks0 in B**±→Bd
0(*) ±
The flavour of B0 is tagged with ±
Expected precision is (sin2)=0.022 (10fb-1) (to be repeated with higher trigger thresholds)
related to angle
after selection
ICHEP’04 : sin(2) = 0.725 ± 0.037
all B-physics studies require a profound knowledge of the detector performance
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 19
The SM-like scalar Higgs boson can be observed in several physics channels (depending on its mass mH which is a free
parameter of the model, LEP mH > 114.4 GeV @95%CL)
Standard Model Brout-Englert-Higgs boson
production cross-section decay branching ratios
balance between production rate, decay rate and reconstruction efficiency
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 20
Standard Model Brout-Englert-Higgs boson
H → ZZ* → 4l H → qqH → qq
H → WW* →lvlv ttH → ttbb qqH → qq
mH=130,150,170 mH=130 mH=115
mH=140 mH=115 mH=135
signal
signal signal
signalsignal
signalsignal
signal
100fb-1 100fb-1 60fb-1
30fb-1 30fb-1 30fb-1
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 21
Combined discovery potential as a function of mH
Standard Model Brout-Englert-Higgs boson
zoom in low mass region
WW ZZ
5 at 2 fb-1
at 10 fb-1
at 30 fb-1
At 10 fb-1 full 5 coverage from LEP to 800 GeVLEP limit
5 at 10 fb-1
at 30 fb-1
at 60 fb-1
WW/ZZ
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 22
Integrated luminosity needed for 5 discovery as a function of mH
Standard Model Brout-Englert-Higgs boson
zoom in low mass region
30 fb-1
30 fb-1
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 23
Comparing the direct and indirect values of mH
Ultimate test of the Standard Model
To give mt and mW equal weight :mW = 0.7 10-2 mt
Goal of LHC experiments :mt < 1 GeVmW < 15 MeV
mH/mH < 25 %
After a discovery one can use EW measurements to differentiate
between SM or MSSM Higgs bosons
21st of July 2005 Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration) 24
Outlook for CMS activities
First fast-simulation studies (presented)
significant improvement in Standard Model measurements Higgs boson mass range completely covered after 10fb-1
Current progress within the CMS Collaboration
created large amounts of dedicated/realistic simulation large effort in optimizing our reconstruction methods gradually design more advanced analyses techniques start studies on detector calibration/alignment (check influence)
Outlook for the near future
write-up of all the above into a Physics-Technical Design Report this will summarize the physics potential of the experiment in great detail foreseen by December 2005 (Volume-I) and by April 2006 (Volume-II)
thanks to all CMS collaborators who contributed to these Standard Model studies