Физика t-кварка.

(задачи)

The top group CSC Notes

TopGroupNoteT1Leptons? (Pralavorio) TopGroupNoteT2LightJets? (Schwindling) TopGroupNoteT3BJets (Hawkings) TopGroupNoteT5Trigger (Wengler) TopGroupNoteT6CrossSection (Bentvelsen, Cobal) TopGroupNoteT7TopProperties? (Onofre, Tokar) TopGroupNoteT8SingleTop (A. Lucotte, S. Rolli, A.

Shibata) TopGroupNoteT9TopMass (Pallin, Etienvre)

T1Leptons lepton performance in all top samples (MCatNLO? +HERWIG

and AcerMC +Pythia): reconstruction efficiency, purity and isolation as well as momemtum and angular resolutions. The interplay between the lepton selection and the trigger will also be discussed. Emphasis will be put on what can be expected at the LHC start-up, namely measurements with standalone detectors (Tracker, EM calorimeter, Muon spectrometer). Degradations induced by the "as-built" geometry will be adressed.

tt-decays as lepton source. σtt = 833 pb → 8M events/year (low L=1033cm-2s-1) tt→l+jets (l=e,µ) 30%

2.5M/year tt→l+l 5% tt→jets 44%l+jets : S/B≈80 → clear sample

T8SingleTop

σt=1/3σtt → 2M/year These measurements will constitute the first

direct measurement of Vtb at the few percent level of precision, and constitute a powerful probe for new physics, via the search for evidence of anomalous couplings to the top quark or the measurements of additional bosonic contributions to the single top production.

Vtb=0.999100+0.000034−0.000004 (PDG2006)

Single top channels

List of contributors

M. Barisonzi (NIKHEF) F. Chevallier, A. Lleres, A. Lucotte (LPSC/IN2P3) M. Cobal (INFN) C. Cojocaru, M. Khakzad (U. Carleton) A. Shibata (Queen Mary, U. of London) B.G. Pope, P. Ryan, R. Shwienhorst (Michigan State

U.) S. Rolli (Tufts) N. Triplett (Iowa State U.)

Synopsis (proposal)

Introduction ... [Simona,Arnaud]

I. Single-top Phenomenology [Arnaud,Reinhard] :

Single top cross-section SM backgrounds

Synopsis (proposal)II Single top pre-selection 1. L1 Triggering ..... [Bernard,Reinhard,Patrick, Alessandro, others ?]

1. Inclusive lepton triggers 2. Jet triggers 3. Trigger efficiency & redundance

2. Preselection ..... [All] 1. Lepton selection (in link with lepton perf. note)

1. Selection efficiency 2. Definition & reconstruction efficiency

2. Light jet selection [Mohsen,Claudiu, Akira, Marcello, others?] 1. Definition % recon efficiency : cone size studies (in link with jet perf. note) 2. Threshold optimization (non-top, top pair bckgds)

3. b-tagged jet selection ..... [Simona,Monica,Mohsen,Claudiu,Akira] 1. Definition % recon efficiency : cone size studies (in link with jet perf. note) 2. Threshold optimization (non-top, top pair bckgds) .

4. Missing ET 5. W-transverse mass and /or angular discriminating power [Reinhard, others?]

1. Definition 2. Performance

6. Leptonic top mass reconstruction ..... [Claudiu, Mohsen, Akira] 1. optimization of the neutrino solution 2. optimization in the M(lvb) reconstruction 3. Influence of jet cone algorithm & size

Synopsis (proposal)III Single top cross-section measurements 1. Wg channel analysis

standard cut-based selection [Claudiu, Mohsen,Akira, Marcello] NeuralNet? selection [Nathan] systematics : [All the above]

b-tagging Jet Energy scale Gluon radiation Modeling Forward jet reconstruction & b-tagging

2. Wt channel analysis ..... [Marina, Annick, others ?] Selection & performance systematics :

b-tagging Jet Energy scale Gluon radiation Modeling

3. W* channel analysis ..... [Arnaud, others?] selection & performance systematics :

b-tagging Jet Energy scale Gluon radiation Modeling

Synopsis (proposal)

IV. Interpretation : top width measurements ..... [Ketevi,others ?]

1. Selected samples 2. Performance and systematics

V. Single top evidence with the early data ..... [Bernard, Reinhard,Patrick,Akira,Alessandro]

1. Triggering [Bernard, Reinhard, Patrick] 2. Selection

1. Influence of b-tagging performance 2. Background studies [Akira, Reinhard]

3. Combined Wg and other single top channels ? [Bernard, Reinhard, Patrick,Alessandro, ?]

T9TopMass

Motivations:

observables in the Standard Model (SM) and the Minimal Supersymetric Standard Model (MSSM) depend on the value of the top mass

The most important top mass dependence

contribution to the Electroweak observables arises via the one-loop radiative correction term

ΔR ~ mt2/mZ

2 , ~log mH/mZ

)1(sin2 2

2 RG

mWF

W

Mt

PDG : Mt  = 172.5 ± 2.7 GeV (using data from Tevatron

Run-I and Run-II )

Theoretical uncertainties (hep-ex/0403021) : renormalisation scale < 10 MeV αS < 75 MeV

fragmentation effects ~O(ΛQCD) ~250 MeV

LHC (10 fb-1, 1 year at L=1033cm-2s-1) : statistical error ≈ 100 MeV systematic ≈ 1 GeV

Cross section

Process σ(pb) ε(%)

tt signal 250 3.5

bb → lν + jets 2.2 × 106 3 × 10−8

W + jets → lν + jets 7.8 × 103 2 × 10−4

Z + jets → l+l− + jets 1.2 × 103 6 × 10−5

WW → lν + jets 17.1 7 × 10−3

WZ → lν + jets 3.4 1 × 10−2

ZZ → l+l− + jets 9.2 3 × 10−3

Event selection and background rejection One isolated lepton with pT > 20 GeV, ET

miss > 20 GeV

at least 4 jets reconstructed with a cone size of R = 0.4 with pT > 40 GeV and |η| < 2.5

at least one is tagged as b-jets

→ S/B ≈ 78

Top mass measurement

lepton plus jets channel1. using the hadronic top decay

2. using a kinematic fit

3. using a continuous jet algorithm (ATL-PHYS-2001-006, V. Kostioukhine IHEP,Protvino)

4. using large pT events (large cone R=0.8-1.8)

dilepton channel six jets channel leptonic final states with J/Ψ

top mass in the l+jets channel with 2 b-tagged jets

Summary of the systematics errors

Source of error Lepton+jets Lepton+jets Dilepton All jetsin GeV inclusive large clusters high

pT sample sample sample

Energy scaleLight jet energy scale0.2 - - 0.8b-jet energy scale 0.7 - 0.6 0.7Mass scale calibration - 0.9 - -UE estimate - 1.3 - -

PhysicsBackground 0.1 0.1 0.2 0.4b-quark fragmentation 0.1 0.3 0.7 0.3Initial state radiation 0.1 0.1 0.1 0.4Final state radiation 0.5 0.1 0.6 2.8PDF - - 1.2 -

Jets scale calibrations

mis-measurement of 1% of the Ej → ΔMt≈ 1.6 GeV.

mis-measurement of 1% of the cosθjj → ΔMt≈ 1.2 GeV.

fast MC : differences of the physics effects between light quark jets and b-jets → systematic error ≈ 130 MeV

full simulation?

Contributors

Clermont FD (E Cogneras,PO Defay,D Pallin) Saclay (AI Etienvre, A.Marzin, JP Meyer, J Schwindling)

Nikhef (S bentvelsen, I Van Vulpen, W Verkerke) Prague (R Leitner, V Simak, J chudoba) Lpnhe (F Derue, D Lacour, I Nikolic-Audit,M Ridel, S Trincaz-

Duvoid, P Cavalleri ) MPI Munich (N Ghobdane, R Nisius, T Goettfert, R Haertel) Athens ( N Giokaris, A Kalogeropoulos, C Vellidis,A

Manousakis,G Arabitze, V Giakoumopoulou) Victoria ( K Edmonds, M Lefebvre, R McPherson?, R Seuster) TUFTS (K Sliwa, S Rolli) Dortmund(Joerg Walbersloh,Ingo Reisinger,Daniel

Dobos,Reiner Klingenberg)