Electroweak and top mass studies for the LHC

1. Electroweak and top mass studies for the LHC Craig Buttar Sheffield University Cosner’s House meeting

2. SM model physics at LHC • W-mass • Top mass • Single top production • TGCs • MB+UE

3. LHC numbers Typical SM processes 1 low luminosity year=10fb-1 Statistics vs systematics throw out 90% of events and still have enough for precision measurements !

4. ATLAS: Design and Performance Magnetic Field 2T solenoid plus air core toroid Inner Detector s/pT ~ 0.05% pT(GeV) (+) 0.1% Tracking in range |h| < 2.5 EM Calorimetry s/E ~ 10% / √E(GeV) (+) 1% Fine granularity up to |h| < 2.5 Hadronic Calorimetry s/E ~ 50% / √E(GeV) (+) 3% Muon Spectrometer s/pT ~ 2-7 % Covers |h| < 2.7 Precision physics in |h|<2.5

5. The CMS Detector Inner Detector: Silicon pixels and strips Preshower: Lead and silicon strips EM Calorimeter: Lead Tungstate Hadron Calorimeters: Barrel & Endcap: Cu/Scintillating sheets Forward: Steel and Quartz fibre Muon Spectrometer: Drift tubes, cathode strip chambers and resistive plate chambers Magnet: 4T Solenoid

6. W-mass For EW fits: Cuts: Isolated charged lepton pT > 25 GeV || < 2.4 Missing transverse energy ETMiss > 25 GeV No jets with pT > 30 GeV Recoil < 20GeV Sources of Uncertainty: • Statistical uncertainty pp  W + X  = 30 nb (l= e,) W  ll 3 x 108 events < 2MeV for 10 fb-1 • Systematic Error Detector performance Physics Relies on good modelling of detector and physics in Monte Carlo

7. W-mass 1 year, 1 lepton species:  25 MeV Combining lepton channels:  20 MeV Combining experiments:  15 MeV cf Tevatron ~25-30MeV combined ~2fb-1 CDF PtW < 20 GeV Use Z ll control sample mass shift ~10MeV due to HO QED and QCD

8. Together with MW helps to constrain the SM Higgs mass tt production: main background to new physics processes: production and decay of Higgs bosons and SUSY particles Top events used to calibrate the calorimeter jet scale Precision measurements in the top sector provide information of the fermion mass hierarchy At low luminosity: Semi-leptonic: best channel for top mass measurement (pure hadronic channel can also be used) Error dominated by systematic errors: Jet energy scale Final state gluon radiation Top Mass -

9. Top masssemi-leptonic decay 60k events/10fb-1 Use Z/g-j, W(tt)jj, Z-b control samples ATLAS estimates of systematics

10. Reducing effect of FSR Use kinematic fit

11. High-pt top Reconstruct top decay in large cone directly from calorimeter cells Sensitive to the underlying event Requires rescaling of the mass sample of ~4k events/10fb-1

12. Top mass via J/Y CMS A.Kharchilava Phys. Lett. B476 (2000) 73 Reconstruct M(J/Y+l) Relies on simulation to determine Mt M(J/Y+l)

13. Top summary Range of top-quark mas measurements with different systematic errors dMt ~2GeV seems feasible dMt~3GeV with 2fb-1 at Run-II

14. EW single top quark production q’ q t W q W b W b - q’ - q’ b g t t q W b - W* process t b Wt process g σW*~ 10 pb b σWt~ 60 pb ( lower theoretical uncertainties! ) W-gluon fusion for each process: σ∝|Vtb|2 σWg~ 250 pb • Probe the t-W-b vertex • Directly measurement (only) of • the CKM matrix element Vtb at ATLAS • (assumes CKM unitarity) Systematic errors: b-jet tagging, luminosity (∆L ~ 5 – 10%), theoretical (dominate Vtb measurements!). • New physics: heavy vector boson W’ - - L= 30 fb-1 • Source of high polarized tops! • Background: tt, Wbb, Wjj

15. Gauge Couplings: Phenomenology The self -couplings between the electroweak gauge bosons are specified by the SU(2)L× U(1)Y gauge symmetry of the Standard Model Measurements of the gauge couplings therefore: • Provide a test of this non-Abelian structure • the SM TGCs WWg and WWZ have been beautifully confirmed at LEP. But also, probe for possible new physics • Anomalous triple (or quartic) gauge couplings • The most general Lorentz invariant parametrisation of WWV with V=Z,g is governed by 14 couplings, 7 for each vertex. • EM gauge invariance, C, P and CP conservation: g1Z, kZ, lZ and kg, lg, * In the SM, g1Z = kg= kZ =1 and lg= lZ = 0 • usually quote the deviations from the SM: Dg1Z, DkZ, lZ and Dkg,lg (=0 in SM) * At LHC, greater sensitivity due to higher luminosity and higher centre-of-mass energy

16. TGCs: Measurement • Any ATGC contribution to some process gives a quadratic increase in the cross-section with the anomalous parameter • can set limits on ATGC parameters by comparing observed and expected event rates • Method is sensitive to overall normalisation hence systematic errors in, e.g. luminosity, and gives no information about where any AQGC contribution originates • Better to use a fit to the spectrum of some observable using a MC prediction Example 1: Measure possible anomalous contribution to WWg in Wg production q q g q g W W q g q q W W

17. TGCs Example 1: WWg • Consider pp→Wg with W→ln, l = e,m • Maximum likelihood method applied to the pT spectrum of g offers good sensitivity to possible anomalous couplings Dkg and lg Selection: PTg > 100GeV PTl > 25 GeV PTmiss > 25 GeV DRlg > 1 • Expect ~3000 events in 30fb-1 (as plotted) • sensitivity is in high pT tail (where backgrounds are small)

18. Wg result Predicted 95% CL for Tevatron Predicted CL for LHC 30fb-1

19. TGCs Example 2: WWZ • Can also measure ATGC contribution to WWZ through pp→WZ • Maximum likelihood method applied to pT spectrum of the Z offers good sensitivity to couplingsDg1Z,DkZ and lZ Selection: 3 leptons with pT > 25GeV (One pair should be of same flavour, opposite sign and satisfy |mll-mZ| < 10 GeV) PTmiss > 25GeV • Expect ~1200 events in 30fb-1

20. ATLAS: Precision Reach and CouplingsTriple Gauge Couplings: Precision • Table shows expected 95% CLs on individual couplings in 30fb-1 (three years of low luminosity running) • Both systematics and statistics limited since the sensitivity in the tails of the distributions. • ~Order of magnitude improvement over LEP limits.

21. High PT scatter Beam remnants ISR Underlying event • Underlying event associated with ‘hard’-scatters • important for energy corrections, central jet veto

22. Tuning Pythia to CDF run-I analysis Default Core x2 default Increasing core size Default Pt-min=1.9 Transverse <Nch> vs jet pT

23. PYTHIA Tuning (AM Tune) “D” = PYTHIA’s default Non-diff. + d.diff. CTEQ 5L Multiple interactions Required to compare to data Double Gaussian PT0 Core size PT0 energy dependence Primary vertex Exclude 8% of chd. tracks

24. LHC prediction Tevatron LHC predictions LHC Tevatron PYTHIA6.214 - tuned ● CDF 1.8 TeV ~80% ~200% ● CDF 1.8 TeV PYTHIA6.214 - tuned

25. Tagging jet W Z/W H Z/W W Tagging jet Effect of underlying event on central jet veto in vector boson fusion Pythia 6.214 ATLFAST 602 Central-jet veto: Cut non-tag jets in |η|<3.2 PT>20GeV e- channel only MH=160GeV

26. Summary and conclusions • Top and W-MassdMW Tevatron~30MeV LHC~20GeVdMt Tevaton~3GeV LHC~2GeVLarge statistics at LHC allow for better control of systematics through control samplesTevatron will be essential for developing MCs with higher order corrections for precision measurements • Single top should be observed • TGC limits should improve • Tuning of MCs to underlying event data from the Tevatron ensures development of robust analysis and reconstruction code

27. Top Mass Measurements Predicted error on the top mass measurement from the semi-leptonic channel of 1.3 GeV (Di-leptonic channel:  2 GeV)

28. Pt-min is ~1.9GeV default value

29. ATLAS: Precision Reach and CouplingsNeutral Triple Gauge Couplings Not Present in the Standard Model • Possible anomalous Zgg/ZZg contribution to pp→Zg Couplings specified by 8 parameters: hiV with i=1…4 and V=Z,g • Possible anomalous ZZg/ZZZ contribution to pp→ZZ: Couplings specified by 4 parameters: fiV with i=4,5 and V=Z,g Example: Fit to the pT spectrum of the g => Again, the sensitivity is in the tail of the distribution