Expectations from LHC for Top Physics

1

Expectations from LHC for Top Physics

Top Mass

Couplings and decays

Top spin polarization

Single top production

Marina Cobal - HCP2004

P 2 Motivations for Top Physics studies

Top quark mass is a fundamental parameter of the EW theory By far has the largest mass of all known fundamental particles In SM: top- and W-mass constrain Higgs mass

Sensitivity through radiative corrections Scrutinize SM by precise determination top mass

Top quark exists and will be produced abundantly ! window for new physics Many heavy particles decay in tt Handle on new physics by detailed properties of top

And in addition…

Experiment: Top quark useful to calibrate the detector (LHC) Beyond Top: Top quarks will be a major source of background for

almost every search for physics beyond the SM (LHC)


P 3

TOTEM

ALICE : heavy ions,p-ions

ATLAS and CMS :pp, general purpose

LHCb : pp, B-physics

27 km ring 1232 dipoles B=8.3 T

LHC and experiments

pp (mainly) at s = 14 TeV Startup in April 2007

Initial/low lumi L1033 cm-2 s-1

2 minimum bias/x-ing “Tevatron-like” environment

10 fb-1 /year Design/high lumi L=1034 cm-2 s-1

after ~ 3 years ~ 20 minimum bias/x-ing

fast ( 50 ns) radhard detect 100 fb-1 /year


P 4

LC machine

Maybe some years after the LHC startup

ECM of operation 200-500 GeV, possible upgrade to 1 TeV

80% Polarization of e- beam

Luminosity: 300 fb-1/year


P 5

Top production at LHC

Cross section determined to NLO precision Total NLO(tt) = 834 ± 100 pb Largest uncertainty from scale variation

Compare to other production processes:

Top production cross section approximately 100x Tevatron

Opposite @ FNAL

32121 10~ ; ˆ xxxsxs

~90% gg~10% qqProcess N/s N/year

Total collected before start of LHC

W e 15 108 104 LEP / 107 FNAL

Z ee 1.5 107 107 LEP

tt 1 107 104 Tevatron

bb 106 1012-13 109 Belle/BaBar ?

H (130) 0.02 105 ?

LHC is a top factory!

Low lumi


P 6

The ttbar cross section is ~103 smaller than at LHC, but higher L ~0,85 pb at max, around 390 GeV, and falls down with energy as 1/s

..and at LC?

~200000 tt/year at TESLA parameters


P 7

Top decay In the SM the top decays to W+b

All decay channels investigated Using ‘fast parameterized’ detector

response Checks with detailed simulations

1. Di-leptons (e/) BR≈4.9% 0.4x106 ev/y No top reconstructed Clean sample

2. Single Lepton (e/) BR=29.6% 2.5x106 ev/y One top reconstructed Clean sample

3. Fully Hadronic BR≈45% 3.5x106 ev/y Two tops reconstructed Huge QCD background Large combinatorial bckgnd


P 8

Top mass: Where we are


P 9

Tevatron only (di-lepton events or lepton+jet ) from W decaysStatus of inputs (preliminary):mmtt=(178.0 =(178.0 2.7 2.7 (stat) (stat) 3.3 3.3 (syst)(syst)) GeV/c) GeV/c22

(latest Tevatron updated combination – RunI data)(latest Tevatron updated combination – RunI data) mmtt=(175 =(175 17 17 (stat) (stat) 8 8 (syst)(syst)) GeV/c) GeV/c22

(CDF di-leptons – RunII data)(CDF di-leptons – RunII data)

mmtt=(178=(178+13+13-9-9 (stat) (stat) 7 7 (syst)(syst)) GeV/c) GeV/c22

(CDF lepton+jets – RunII data)(CDF lepton+jets – RunII data)

Matter of statistics (also for the main systematics) and optimized use of the Matter of statistics (also for the main systematics) and optimized use of the available information. Each experiment expects 500 b-tagged tt l+jets events/fb available information. Each experiment expects 500 b-tagged tt l+jets events/fb Mtop ~ 2-3 GeV/cMtop ~ 2-3 GeV/c22 for the Tevatron combined (2-4/fb) for the Tevatron combined (2-4/fb)

mmt t 2.5 GeV ; 2.5 GeV ; mmW W 30 MeV 30 MeV mmHH/m/mH H 35% 35%

Near future of Mtop

In 2009 (if upgrade is respected) from Tevatron: Mtop = 1.5 GeV !!


P 10

What is the Top Mass?

Problem for the top: what is the mass of a colored object? The top pole mass is not IR safe (affected by large long-distance

contributions), cannot be determined to better than O(QCD)

Measurement of mt: At Tevatron/LHC: kinematic reconstruction, fit to invariant mass dist.

at the LHC: accuracy 1-2 GeV (limited by FSR)

At the LC, mainly from threshold behavior Measurement comparison data – Monte Carlo: involves transition from actually

measured quantity to suitably defined (short-distance) top mass ‘Threshold mass’ at the LC: accuracy 20 MeV [M. Martinez, R. Miquel ’03] Transition to MS mass: m 100 MeV [A. Hoang et al. ’00]


P 11

LHC: MTop from lepton+jet

Br(ttbbjjl)=30%for electron + muon

Golden channel Clean trigger from isolated lepton

The reconstruction starts with the W mass: different ways to pair the right jets

to form the W jet energies calibrated using mW

Important to tag the b-jets: enormously reduces background

(physics and combinatorial) clean up the reconstruction

Lepton side

Hadron side

Typical selection efficiency: ~5-10%:

•Isolated lepton PT>20 GeV

•ETmiss>20 GeV

•4 jets with ET>40 GeV

•>1 b-jet (b40%, uds10-3,

c10-2)

Background: <2%

W/Z+jets, WW/ZZ/WZ


P 12 LHC: Lepton + jet, reconstruct top

Hadronic side W from jet pair with closest invariant mass

to MW

Require |MW-Mjj|<20 GeV

Assign a b-jet to the W to reconstruct Mtop

Kinematic fit Using remaining l+b-jet, the leptonic part is

reconstructed |mlb -<mjjb>| < 35 GeV Kinematic fit to the tt hypothesis,

using MW constraintsj1

j2

b-jet

t

Selection efficiency 5-10%


P 13

LHC: MTop systematics

Method works: Linear with input Mtop

Largely independent on Top PT

Biggest uncertainties: Jet energy calibration FSR: ‘out of cone’ give

large variations in mass B-fragmentation

Verified with detailed detector simulation and realistic calibration

Source of uncertainty

Hadronic

Mtop

(GeV)

Fitted Mtop (GeV)

Light jet scale

0.9 0.2

b-jet scale 0.7 0.7

b-quark fragm

0.1 0.1

ISR 0.1 0.1

FSR 1.9 0.5

Comb bkg 0.4 0.1

Total 2.3 0.9

Challenge:

determine the mass of the top around 1 GeV accuracy in one year of LHC


P 14 LHC: Alternative mass determination

Select high PT back-to-back top events: Hemisphere separation

(bckgnd reduction, much less combinatorial) Higher probability for jet overlapping

Use the events where both W’s decay leptonically (Br~5%) Much cleaner environment Less information available from two ’s

Use events where both W’s decay hadronically (Br~45%) Difficult ‘jet’ environment Select PT>200 GeV

Mtop

Various methods all have different systematics


P 15

Use exclusive b-decays with high mass products (J/) Higher correlation with Mtop Clean reconstruction (background free) BR(ttqqb+J/) 5 10-5 ~ 30% 103 ev./100 fb-1

(need high lumi)

Top mass from J/

Different systematics (almost no sensitivity to FSR)

Uncertainty on the b-quark fragmentation function becomes the dominant error

M(J/+l) Pttop

MlJ/

M(J/+l)


P 16

Mtop at LC

Scan of the threshold for e+e-ttbar Very precise measurements (< 20 MeV)

To perform this analysis with small systematic errors need to study:

beam spread

beamstrahlung

initial state radiation

Simultaneous measurements of 3 physical observables: tt

Pt of top

Forward-Backward asimmetry of top AtFB

Multiparameter fit up to 4 parameters Mt (1S)

s(MZ)

t

gtH

Theoretical uncertainties to relate the 1S to the MS mass is ~ 100 MeV

)(GeVs(

pb)


P 17

Georg Weiglin, LCWS04 Paris


P 18

LHC: Search for resonances

Many theoretical models include the existence of resonances decaying to top-topbar SM Higgs (but BR smaller with respect to the WW and ZZ decays) MSSM Higgs (H/A, if mH,mA>2mt, BR(H/A→tt)≈1 for tanβ≈1) Technicolor Models, strong ElectroWeak Symmetry Breaking, Topcolor, “colorons”

production, […]

Study of a resonance Χ once known σΧ, ΓΧ and BR(Χ→tt) at LHC Reconstruction efficiency for semileptonic channel:

20% mtt=400 GeV 15% mtt=2 TeV

1.6 TeV resonance

Mtt

xBR required for a discovery

mtt [GeV/c2]

σxB

R [

fb]

30 fb-1

300 fb-1

1 TeV

830 fb


P 19

Couplings and decays

Does the top quark behaves as expected in the SM? Yukawa coupling to Higgs from ttbarH events Electric charge Top spin polarization CP violation

At the LHC Yukawa coupling can be measured to < 20% from t-tbar H production

@ the LC, the precision of the measurement of the top Yukawa coupling will be better than ~ 10 % if mH ≤ 190 GeV/c2

For a light Higgs (mH ~120 GeV/c2): Precision ~ 5-6 %


P 20

LHC: Couplings and decays

According to the SM: Br(t Wb) 99.9%, Br(t Ws) 0.1%, Br(t Wd) 0.01%

(difficult to measure)

Can probe t W[non-b] by measuring ratio of double b-tag to single b-tag Statistics more than sufficient to be sensitive to SM expectation for

Br(t W + s/d) need excellent understanding of b-tagging efficiency/purity


P 21

The Wtb vertex can be probed and measured using either top pair production or single top production Total tt rate depends weakly from Wtb vertex structure C and P asymmetries, top polarization, spin correlations can provide

interesting info The single top production rate is instead directly proportional to the square

of the Wtb coupling

LHC could rivale the reach of a high L (500 fb-1) 500 GeV LC

Search for anomalous Wtb couplings

)(2

)(2

22WWWW

RWWWW

L ihfM

FandihfM

F


P 22

In the SM the FCNC decays are highly suppressed (Br<10-13-10-10) Any observation would be sign of new physics FCNC can be detected through top decay or single top production

Sensitivity according to CMS studies (of top decays) :

t Zq (CDF Br<0.137, ALEPH Br<17%, OPAL Br<13.7%) Reconstruct t Zq (l+l-)j Sensitivity to Br(t Zq) = 1,6 X 10-4 (100 fb-1)

t q (CDF Br<0.032) Sensitivity to Br(t q) = 2,5 X 10-5 (100 fb-1)

t gq Difficult identification because of the huge QCD bakground One looks for “like-sign” top production (ie. tt) Sensitivity to Br(t gq) = 1,6 X 10-3 (100 fb-1)

LHC: FCNC Rare decays


P 23

In general, the LHC will improve by a factor of at least 10 the Tevatron sensitivity to top-quark FCNC couplings

LC has smaller statistics but also smaller background For anomalous interactions with a gluon the LHC has an evident

advantage

FCNC


P 24

Studied at LHC:

Interesting: BR depends strongly on Mtop

Since Mtop~MW+Mb+MZ

With present error mt 5 GeV, BR varies over a factor 3

B-jet too soft to be efficiently identified “semi-inclusive” study for a WZ near

threshold, with Z l+l- and W ->jj Requiring 3 leptons reduces

the Z+jets background

Sensitivity to Br(t WbZ) 10-3 for 1 year at low lumi. Even at high L can’t reach SM predictions ( 10-7 - 10-6)

G. Mahlon hep-ph/9810485

M(top) (GeV)

(t

WbZ

)/(t

Wb)

LHC: tWbZ rare decay


P 25 LHC: Top Charge determination

Can we establish Qtop=2/3? Currently cannot exclude exotic possibility Qtop=-4/3

Assign the ‘wrong’ W to the b-quark in top decays tW-b with Qtop=-4/3 instead of tW+b with Qtop=2/3 ?

Technique: Hard radiation from top quarks

Radiative top production, pptt cross section proportional to Q2top

Radiative top decay, tWb

On-mass approach for decaying top: two processes treated independently

Matrix elements havebeen calculated and fed intoPythia MC

Radiative top production

Radiative top decay


P 26 LHC: Top Charge determination

Yield of radiative photons allows to distinguish top charge

Q=2/3 Q=-4/3

pptt 101 ± 10 295 ± 17

pptt ; tWb 6.2 ± 2.5 2.4 ± 1.5

Total background 38 ± 6

Determine charge of b-jet andcombine with lepton Use di-lepton sample Investigate ‘wrong’ combination

b-jet charge and lepton charge

Effective separation b and b-bar possible in first year LHC

Study systematics in progress

i

κ

i

i

κ

ii

bjet

pj

pjqq

pT()

events

10 fb-1

One year low lumi


P 27

LHC: Top spin correlations

In SM with Mtop175 GeV, (t) 1.4 GeV » QCD

Top decays before hadronization, and so can study the decay of ‘bare quark’ Substantial ttbar spin correlations predicted in pair production

Can study polarization effects through helicity analysis of daughters Study with di-lepton events Correlation between

helicity angles + and -

for e+/+ and e-/-

e+/+

top+

With helicity correlationNo helicity correlation

<CosΘ+ · CosΘ-> <CosΘ+ · CosΘ->

leptons)for 1 :qualityanalyser (spin

base)helicity in n correlatiospin of (degree 34.0

4

coscos1

coscos

1 2

C

C

dd

d


P 28

Top spin correlations

Able to observe spin correlations in parameter C 30 fb-1 of data:

± 0,035 statistical error ± 0,028 systematic error

10 statistical significance for a non-zero value with 10 fb-1

30 fb-1<CosΘ+ · CosΘ->

For the LC case one can find a top spin quantization axis in which there will be very strong spin correlations . Detailed studies, both at the ttbar threshold and in the continuum region remain to be done.


P 29

LHC: Single top production

Direct determination of the tWb vertex (=Vtb)

Discriminants:- Jet multiplicity (higher for Wt)

- More than one b-jet (increase W* signal over W- gluon fusion)- 2-jets mass distribution (mjj ~ mW for the Wt signal only)

Three production mechanisms at LHC:

Main Background [xBR(W→ℓ), ℓ=e,μ]: tt σ=833 pb [ 246 pb] Wbb σ=300 pb [ 66.7 pb] Wjj σ=18·103 pb [4·103 pb]

Wg fusion: 245±27 pbS.Willenbrock et al., Phys.Rev.D56, 5919

Wt: 62.2 pbA.Belyaev, E.Boos, Phys.Rev.D63, 034012

-3. 7

+16.6 W* 10.2±0.7 pbM.Smith et al., Phys.Rev.D54, 6696

Wg [54.2 pb]

Wt [17.8 pb]

W* [2.2 pb]

1) Determination of Vtb

2) Independent mass measurement

3) Opportunity to measure top spin pol.

4) May probe FCNC


P 30

Signal unambiguous, after 30 fb-1:

Complementary methods to extract Vtb

With 30 fb-1 of data, Vtb can be determined to %-level or better(experimentally)

LHC: Single top results

Detector performance critical to observe signal

Fake lepton rate b and fake rate id Reconstruction and vetoing of

low energy jets Identification of forward jets

Each of the processes have different systematic errors for Vtb and are sensitive to different new physics

heavy W’ increase in the s-channel W*

FCNC gu t increase in the W-gluon fusion channel

ProcessVtb

(stat)Vtb

(theory)

Wg fusion 0.4% 6%

Wt 1.4% 6%

W* 2.7% 5%

Process Signal Bckgnd S/B

Wg fusion 27k 8.5k 3.1

Wt 6.8k 30k 0.22

W* 1.1k 2.4k 0.46


P 31

Single top at LC e+ e- e+bt, ebt

Cross section calculated to LO at e+e-, and e collision modes, including various beam polarizations

Recently calculated NLO corrections in the e case, well under control

Production in e collisions is of special interest Rate is smaller than the top pair rate in e+e- only by a factor of 1/8 at

500-800 GeV energies. It becomes the dominant LC process for top production at a multi-TeV LC

Direct Vtb measurement:

Same precision as LHC in the e+e- option. Can arrive to 1% for a polarized e collider.

Improved accuracy in |Vtb| could be input for LHC Measure b-quark distribution function in proton

(or be used as consistency check for new interactions)


P 32

Few final thoughts…

LHC pp collision at 14 TeV

Kinematics:

can use PT conservationComposite nature of protons

Underlying events, not fixedStrongly interacting particle

Large QCD background Under construction

s

e+-e- collisions at 0.5-1 TeV

Kinematics:

can use momentum conservationBetter defined initial stateBackground smaller than LHCNot sure yet IF, WHEN, WHERE it will be built


P 33

Interplay between LHC and LC

Not much interaction between the LHC and LC communities up to short time ago

In 2002 a LHC/LC study group was formed first in Europe and then soon it took a worldwide character

Working Group contains 116 members from among Theorists, CMS, ATLAS, Members of all the LC study Groups + Tevatron contact persons.

Document in preparation: www.ippp.dur.ac.uk/~georg/lhclc

Electroweak and QCD precision physics

E. Boos, A deRoeck, S. Heinemeyer, W.J. Stirling.


P 34

CMS yoke

LHC is a reality now:

Huge construction activities going on!!

ATLAS cavern


P 35 What is left before the LHC starts?

Cover topics still open: cross section, couplings, exotic, resonances,

Define a strategy for validation of the MC input models (e.g: UE modeling and subtraction, jet fragmentation properties, jet energy profiles, b-fragmentation functions..)see M. Mangano talk at IFAE 2004

Explore the effects of changing detector parameters in evaluating the top mass.

Perform commissioning studies with top events Contribute to simulation validation …


P 36 LHC: Commissioning the detectors

Determination MTop in initial phase Use ‘Golden plated’ lepton+jet

Selection: Isolated lepton with PT>20 GeV Exactly 4 jets (R=0.4) with

PT>40 GeV Reconstruction:

Select 3 jets with maximal resulting PT

Signal can be improved by kinematic constrained fit

Assuming MW1=MW2

and MT1=MT2

PeriodStat Mtop (GeV)

Stat /

1 year 0.1 0.2%

1 month 0.2 0.4%

1 week 0.4 2.5%No background

included

Calibrating detector in comissioning phase

Assume pessimistic scenario:

-) No b-tagging

-) No jet calibration

-) But: Good lepton identification


P 37LHC: Commissioning the detectors

Signal plus background at initial phase of LHC

Most important background for top: W+4 jets Leptonic decay of W, with 4 extra ‘light’ jets

Alpgen, Monte Carlo has ‘hard’ matrix element for 4 extra jets(not available in Pythia/Herwig)

ALPGEN:

W+4 extra light jets

Jet: PT>10, ||<2.5, R>0.4

No lepton cuts

Effective : ~2400 pb

With extreme simple selection and reconstruction the top-peak should be visible at LHC

L = 150 pb-1

(2/3 days low lumi)

measure top mass (to 5-7 GeV) give feedback on detector performance


P 38

Conclusions

Precise determination of Mtop is crucial for EW physics: Precision tests, constraints on Higgs sector, sensitivity to new physics Challenge to get Mtop ~ 1 GeV with LHC, and ~ 100 MeV with LC

Confirmation that top-quark is SM particle and search for deviation from SM Measure Vtb, charge, CP, spin, decays Many precision measurements from LC

Use top quark for the LHC detectors commissioning

Interplay between LC and LHC could be as useful as it was for LEP+SLC+Tevatron

39

BACKUP SLIDES


P 40

1cos22

2

WZ

W

m

m

No observable directly related to mNo observable directly related to mHH. However the dependence can . However the dependence can appear through radiative correctionsappear through radiative corrections. tree level quantities changedtree level quantities changed

mH

, , r r = f [ln(m= f [ln(mHH/m/mWW), m), mtt22]]

By making precision measurements (already interesting per se):By making precision measurements (already interesting per se):• • one can get information on the missing parameter mone can get information on the missing parameter mHH• • one can test the validity of the Standard Modelone can test the validity of the Standard Model

SMmfermions (9)

mbosons (2)

VCKM (4)

GF (1)

s(1)

)1(sin2 2

2 rG

mFW

W

The uncertainties on mThe uncertainties on mtt, m, mWW are the dominating ones in the electroweak fit are the dominating ones in the electroweak fit

predictions

(down to 0.1% level)

lepteffcbl

bclFBcblhWZWZ AARm 2

,,,,,00

,,0

,, sin,,,,,,

tWW mm ,,

had

W2sin

WW CsQ 2sin)(

LEP+SLD:LEP+SLD:

UA2+Tevatron:UA2+Tevatron:

NuTeV:NuTeV:

APV:APV:

eeeeqq l.e.:qq l.e.:

What we know..


P 41

.

Graphically summarizedby Jae Yu

LC Timeline


P 42

BASELINE MACHINEo ECM of operation 200-500 GeV

o Luminosity and reliability for 500 fb-1 in 4 yearso Energy scan capability with <10% downtimeo Beam energy precision and stability below about 0.1%o Electron polarization of > 80%o Two IRs with detectorso ECM down to 90Gev for calibration

UPGRADESo ECM about 1 TeV

o Allow for ~1 ab-1 in about 3-4 years

http://www.fnal.gov/directorate/ icfa/LC_parameters.pdf

LC Machines


P 43

Rare SM top decays

Direct measurement of Vts, Vtd via decays tsW, tdW

Decay tbWZ is near threshold

(mt~MW+ MZ+mb)

BRcut(t bWZ) 610-7

(cut on m(ee) is 0.8 MW)

Decay tcWW suppressed by GIM

factor BR(t cWW) ~ 110-13

If Higgs boson is light: tbWH FCNC decays: tcg, tc, tcZ (BR: 510-11 , 510-13 , 1.310-13 ) Semi-exclusive t-decays tbM

(final state 1 hadron recoiling against a jet:

BR(t b) 410-8, BR(t bDs) 210-7)

2 2b Wm M


P 44

Various approaches studied Previously: ttbarHq Wb(b-bbar)j(lb)

for m(H) = 115 GeV Sensitivity to Br(t Hq) = 4.5 X 10-3

(100 fb-1)

New results for: t tbarHq WbWW*q Wb(l lj) (lb)

≥ 3 isolated lepton with pT(lep) > 30 GeV pTmiss > 45 GeV ≥ 2 jets with pT(j) > 30 GeV, incl. ≥ 1 jet con b-tag Kinematical cuts making use of angular correlations

Sensitive to Br(t Hq) = 2.4 X 10-3

for m(H) = 160 GeV (100 fb-1)

Signal

ttH

tt

Signal

ttH

tt

topHq


P 45

Non-SM Decays of Top 4thfermion family

Constraints on Vtqrelaxed:

Supersymmetry (MSSM) Observed bosons and fermions would have superpartners 2-body decays into squarks and gauginos (t H+ b )

Big impact on 1 loop FCNC two Higgs doublets

H LEP limit 77.4 GeV (LEP WG 2000) Decay t H+ b can compete with t W+ b 5 states (h0,H0,A0,H+,H-) survive after giving W & Z masses H couples to heaviest fermions detection through breakdown of e / m / t

universality in tt production

at ( ( )) ~ 3bBR t W b W c 10 m 100GeV

, , 01 1 1 1 1t t g t b t t


P 46

Alternative methods

Continuous jet algorithm Reduce dependence on MC Reduce jet scale uncertainty

Repeat analysis for many cone sizes R

Sum all determined top mass:robust estimator top-mass

Determining Mtop from (tt)? huge statistics, totally different systematics

But: Theory uncertainty on the pdfs kills the idea 10% th. uncertainty mt 4 GeV Constraining the pdf would be very precious… (up to a few % might not be a dream !!!)

Luminosity uncertainty then plays the game (5%?)

Luminosity uncertainty then plays the game (5%?)


P 47

Top mass from di-leptons

Use the events where both W’s decay leptonically (Br~5%) Much cleaner environment Less information available due to two neutrino’s

Sophisticated procedure for fitting the whole event, i.e. all kinematical info taken into account (cf D0/CDF) Compute mean probability as function of top mass hypothesis

Maximal probability corresponds to top massSource of uncertainty

Di-lepton Mtop (GeV)

statistics 0.3

b-jet scale 0.6

b-quark fragm 0.7

ISR 0.4

FSR 0.6

pdf 1.2

Total 1.7

80000 events

(tt) = 20 %

S/B = 10

Mea

n pr

oba

bilit

y

mass

Selection:

2 isolated opposite sign leptons

Pt>35 and Pt>25 GeV

2 b-tagged jets

ETmiss>40 GeV


P 48

Top mass from hadronic decay

Use events where both W’s decay hadronically (Br~45%) Difficult ‘jet’ environment

(QCD, Pt>100) ~ 1.73 mb (signal) ~ 370 pb

Perform kinematic fit on whole event b-jet to W assignment for combination

that minimize top mass difference Increase S/B:

Require pT(tops)>200 GeV

Source of uncertainty

Hadronic Mtop

(GeV)

Statistics 0.2

Light jet scale 0.8

b-jet scale 0.7

b-quark fragm 0.3

ISR 0.4

FSR 2.8

Total 3.0

3300 events selected:

(tt) = 0.63 %

(QCD)= 2·10-5 %

S/B = 18

Selection

6 jets (R=0.4), Pt>40 GeV

2 b-tagged jets

Note: Event shape variables like HT, A, S, C, etc not effective at LHC (contrast to Tevatron)


P 49

High Pt sample

The high pT selected sample deserves independent analysis: Hemisphere separation (bckgnd reduction, much less combinatorial) Higher probability for jet overlapping

Use all clusters in a large cone R=[0.8-1.2] around the reconstructed top- direction Less prone to QCD, FSR,

calibration UE can be subtracted

j1

j2

b-jet

t

Statistics seems OK and syst. under control

R

Mtop Mtop


P 50

Uncertainty On b-jet scale: Hadronic 1% Mt = 0.7 GeV5% Mt = 3.5 GeV10% Mt = 7.0 GeV

Uncertainty on light jet scale: Hadronic 1% Mt < 0.7 GeV10% Mt = 3 GeV

Jet scale calibration

Calibration demands: Ultimately jet energy scale calibrated within 1%

Uncertainty on b-jet scale dominates Mtop: light jet scale constrained by mW

At startup jet-energy scale known to lesser precision

Scale b-jet energyScale light-jet energy

MTop MTop

±10%


P 51

Uncertainty On b-jet scale: Hadronic 1% Mt = 0.7 GeV5% Mt = 3.5 GeV10% Mt = 7.0 GeV

Uncertainty on light jet scale: Hadronic 1% Mt < 0.7 GeV10% Mt = 3 GeV

LHC: Jet scale calibration

Calibration demands: Ultimately jet energy scale calibrated within 1%

Uncertainty on b-jet scale dominates Mtop: light jet scale constrained by mW

At startup jet-energy scale known to lesser precision

Scale b-jet energyScale light-jet energy

MTop MTop

±10%

Documents

Expectations from LHC for Top Physics