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Electroweak and top mass studies for the LHC Craig Buttar Sheffield University Cosners House meeting.

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Presentation on theme: "Electroweak and top mass studies for the LHC Craig Buttar Sheffield University Cosners House meeting."— Presentation transcript:

1 Electroweak and top mass studies for the LHC Craig Buttar Sheffield University Cosners House meeting

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

3 LHC numbers Processσ (nb)Ns -1 Events/year ( L = 10 fb -1 ) W e ν 15 ~ 10 8 Z e + e 1.5 ~ 10 7 tt 0.8 ~ 10 7 Inclusive jets p T > 200 GeV 100 ~ 10 9 Statistics vs systematics throw out 90% of events and still have enough for precision measurements ! Typical SM processes 1 low luminosity year=10fb -1

4 ATLAS: Design and Performance Magnetic Field 2T solenoid plus air core toroid Inner Detector /p T ~ 0.05% p T (GeV) (+) 0.1% Tracking in range | | < 2.5 EM Calorimetry /E ~ 10% / E(GeV) (+) 1% Fine granularity up to | | < 2.5 Hadronic Calorimetry /E ~ 50% / E(GeV) (+) 3% Muon Spectrometer /p T ~ 2-7 % Covers < 2.7 Precision physics in | |<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 Cuts: Isolated charged lepton p T > 25 GeV | | < 2.4 Missing transverse energy E T Miss > 25 GeV No jets with p T > 30 GeV Recoil < 20GeV Sources of Uncertainty: Statistical uncertainty pp W + X = 30 nb (l= e, ) W l l 3 x 10 8 events < 2MeV for 10 fb-1 Systematic Error Detector performance Physics Relies on good modelling of detector and physics in Monte Carlo For EW fits:

7 W-mass Source M W (MeV) Statistics 2 Lepton E-p scale15 Lepton E/p resolution5 Recoil model5 Lepton identification5 pTWpTW 5 Parton distribution functions 10 W width7 Radiative decays10 Background5 Total 25 1 year, 1 lepton species: 25 MeV Combining lepton channels: 20 MeV Combining experiments: 15 MeV cf Tevatron ~25-30MeV combined ~2fb -1 P t W < 20 GeV CDF mass shift ~10MeV due to HO QED and QCD Use Z ll control sample

8 Top Mass Together with M W 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 tt leptonic decays (t bW) Single lepton W l, W jj 29.6 % 2.5 x 10 6 events Di-lepton W l, W l 4.9 % 400,000 events -

9 Top mass semi-leptonic decay Source m t Statistics0.1GeV b fragmentation0.1GeV ISR0.1GeV FSR1.0GeV Background0.1GeV Light q jet energy calibration0.2GeV b quark jet energy calibration0.7GeV Total~1.3GeV ATLAS estimates of systematicsUse Z/g-j, W(tt) jj, Z-b control samples 60k events/10fb -1

10 Reducing effect of FSR Source m t Statistics0.1GeV b fragmentation0.1GeV ISR0.1GeV FSR0.5GeV Background0.1GeV Light q jet energy calibration0.2GeV b quark jet energy calibration0.7GeV Total~0.9GeV Use kinematic fit

11 High-p t top M t ISR0.7 FSR0.1 B-fragmentation0.3 UE estimate1.3 Mass scale calibration GeV 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/ CMS A.Kharchilava Phys. Lett. B476 (2000) 73 Reconstruct M(J/ l) Relies on simulation to determine Mt M(J/ +l)

13 Top summary M t GeV Dominant error Semileptonic (kinematic fit) FSR+b-energy scale Semileptonic high pt1.8Mass-scale+UE Di-leptons1.7b-quark fragmentation Multijet3.0FSR J/ 1.4Statistics 500fb -1 +b-quark fragmentation Range of top-quark mas measurements with different systematic errors M t ~2GeV seems feasible M t ~3GeV with 2fb -1 at Run-II

14 EW single top quark production W q q b t W q q t b b g g W t b b b q q t W W-gluon fusion Wt process W* process σ Wg ~ 250 pb σ Wt ~ 60 pb σ W* ~ 10 pb Probe the t-W-b vertex Background: tt, Wbb, Wjj -- Directly measurement (only) of the CKM matrix element V tb at ATLAS (assumes CKM unitarity ) ( lower theoretical uncertainties! ) for each process: σ |V tb | 2 ProcessS/B V tb / V tb – statistical V tb / V tb – theory W-gluon %7.5% Wt %9.5% W* %3.8% L = 30 fb -1 Systematic errors : b-jet tagging, luminosity ( L ~ 5 – 10%), theoretical (dominate V tb measurements!). New physics : heavy vector boson W Source of high polarized tops!

15 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: g 1 Z, Z, Z and,, *In the SM, g 1 Z = = Z =1 and = Z = 0 usually quote the deviations from the SM: g 1 Z, Z, Z and, (=0 in SM) *At LHC, greater sensitivity due to higher luminosity and higher centre-of-mass energy Gauge Couplings: Phenomenology

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 WW in W production q q q q q q W W W W

17 Consider ppW with Wl, l = e, Maximum likelihood method applied to the p T spectrum of offers good sensitivity to possible anomalous couplings and TGCs Example 1: WW Selection: P T > 100GeV P Tl > 25 GeV P T miss > 25 GeV R l > 1 Expect ~3000 events in 30fb -1 (as plotted) sensitivity is in high p T tail (where backgrounds are small)

18 W result Predicted 95% CL for TevatronPredicted CL for LHC 30fb -1

19 Can also measure ATGC contribution to WWZ through ppWZ Maximum likelihood method applied to p T spectrum of the Z offers good sensitivity to couplings g 1 Z, Z and Z TGCs Example 2: WWZ Selection: 3 leptons with p T > 25GeV (One pair should be of same flavour, opposite sign and satisfy |m ll -m Z | < 10 GeV) P T miss > 25GeV Expect ~1200 events in 30fb -1

20 ATLAS: Precision Reach and Couplings Triple 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. LEP2Tevatron LHC κγκγ λγλγ g1zg1z Z Z -.007

21 Underlying event Underlying event associated with hard-scatters important for energy corrections, central jet veto High P T scatter Beam remnants ISR

22 Core x2 default Default P t -min=1.9 Increasing core size Default Transverse vs jet p T Tuning Pythia to CDF run-I analysis

23 Minimum biasUnderlying event MSUB(94)=1 (D=0) MSUB(95)=1 (D=1) MSUB(95)=1 (D=1) MSTP(51)=7 (D=7) MSTP(81) = 1 (D=1) MSTP(82) = 4 (D=1) PARP(82) =1.8 (D=1.9) PARP(84) = 0.5 (D=0.2) PARP(90)=0.16 (D=0.16) PARP(90)=0.16 (D=0.16) π 0, K 0 s and Λ 0 stable (D=decays on!) MC distributions corrected. Non-diff. + d.diff. CTEQ 5L Double Gaussian Exclude 8% of chd. tracks Primary vertex D = PYTHIAs default Required to compare to data PYTHIA Tuning (AM Tune) Multiple interactions PT0 Core size PT0 energy dependence

24 LHC predictions Tevatron CDF 1.8 TeV PYTHIA tuned dN/dη (η=0) N ch jet- p t =20GeV 1.8TeV (pp) TeV (pp)7.0 increase~x1.8~x3 ~80% ~200% LHC prediction Tevatron PYTHIA tuned CDF 1.8 TeV LHC

25 Central-jet veto: Cut non-tag jets in |η|<3.2 P T >20GeV ModelCJV efficiencySignificance Default pythia82%8.1 Default DG71%7.5 AM tuning76%7.6 Paper86%8.2 Pythia ATLFAST 602 e- channel only M H =160GeV Tagging jet H W W Z/W Effect of underlying event on central jet veto in vector boson fusion

26 Summary and conclusions Top and W-Mass MW Tevatron~30MeV LHC~20GeV Mt Tevaton~3GeV LHC~2GeV Large statistics at LHC allow for better control of systematics through control samples Tevatron 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 Couplings Neutral Triple Gauge Couplings Not Present in the Standard Model Possible anomalous Z /ZZ contribution to ppZ Couplings specified by 4 parameters: f i V with i=4,5 and V=Z, Possible anomalous ZZ /ZZZ contribution to ppZZ: Couplings specified by 8 parameters: h i V with i=1…4 and V=Z, Example: Fit to the p T spectrum of the =>Again, the sensitivity is in the tail of the distribution

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