1. Electroweak Physics at the LHC Precision Measurements and New Physics PY898: Special Topics in LHC Physics By Keith Otis 4/13/2009

2. Outline Electroweak Parameters Electroweak Parameters W-Mass W-Mass Top-Mass Top-Mass Electroweak Mixing Angle Electroweak Mixing Angle Drell-Yan Drell-Yan Forward-Backward Asymmerty in Z Decays (A FB ) Forward-Backward Asymmerty in Z Decays (A FB ) Triple Gauge Boson Couplings Triple Gauge Boson Couplings Charged TGCs Charged TGCs Neutral TGCs Neutral TGCs Anomalous Quartic Couplings Anomalous Quartic Couplings Heavy Leptons Heavy Leptons

3. Electroweak Parameters The main parameters of EW theory are measured to very high precision. The main parameters of EW theory are measured to very high precision. The mass of the W (M W ) is known with an uncertainty of 0.03% The mass of the W (M W ) is known with an uncertainty of 0.03% M W = 80.428 ± 0.039 GeV UA2/CDF/D0, 80.376 ± 0.033 GeV LEP 2 M W = 80.428 ± 0.039 GeV UA2/CDF/D0, 80.376 ± 0.033 GeV LEP 2 SM predicts 80.375 ± 0.015 GeV SM predicts 80.375 ± 0.015 GeV The uncertainty in the mass of the Top (m t ) is 0.7% The uncertainty in the mass of the Top (m t ) is 0.7% m t = 170.9 ± 1.8 GeV m t = 170.9 ± 1.8 GeV SM predicts 171.1 ± 1.9 GeV SM predicts 171.1 ± 1.9 GeV The uncertainty on the electroweak-mixing angle (θ w ) is 0.07% The uncertainty on the electroweak-mixing angle (θ w ) is 0.07% cos(θ w )= M w /M z cos(θ w )= M w /M z The LHC will be able to improve on these in a relatively short period of time. The LHC will be able to improve on these in a relatively short period of time.

4. Tevatron: 2 TeV Tevatron: 2 TeV LHC: 10-14TeV LHC: 10-14TeV LHC @ 10 33 Luminosity LHC @ 10 33 Luminosity 150 Hz W 150 Hz W 50 Hz z 50 Hz z 1 Hz tT 1 Hz tT 10 pb -1 of Luminocity 10 pb -1 of Luminocity 150k W→eν 150k W→eν 15k Z→ee 15k Z→ee 10k tT 10k tT

5. W-Mass W→ l v signature W→ l v signature Isolated charged lepton pT > 25 GeV |  | < 2.4 Missing transverse energy ETMiss > 25 GeV No jets with pT > 30 GeV Recoil < 20GeV For an integrated luminosity of 1 fb −1, 4 million events with W→ l v (ℓ = e or μ) decays are expected. For an integrated luminosity of 1 fb −1, 4 million events with W→ l v (ℓ = e or μ) decays are expected. ) ( direct indirect Summer 2005 result 68% CL

6. W mass extraction The W mass is extracted from the measured p l T distribution or from the Jacobian peak observed in the transverse mass of the lepton-neutrino system, M W T. The W mass is extracted from the measured p l T distribution or from the Jacobian peak observed in the transverse mass of the lepton-neutrino system, M W T. The W mass is obtained by comparing the measured distributions with template distributions generated from data (Z events) or MC. The W mass is obtained by comparing the measured distributions with template distributions generated from data (Z events) or MC.

7. MC Template method Source  M W (MeV) M T e (W) P T (e) Statistics  2 2 2 2  2 2 2 2 Background55 Lepton E-p scale 4(15) Lepton E/p resolution (5)(5) Recoil model 5 Lepton identification 88 Total Instrumental <20<20 pTWpTWpTWpTW5 Parton distribution functions 3(  10) W width 1(7) Radiative decays 1010 Based on 10fb -1 of data corresponding to ~10M W  l Fit M T (W) or p T (e) to Z 0 tuned MC Z-Samples play a crucial role in reducing systematics and theoretical uncertainties Requires further study ATLAS W-mass: ATLAS

8. Scaled observables Use Z events as templates Use Z events as templates Scaled observable using weighting fn Scaled observable using weighting fn Morphing using kinematic transformation Morphing using kinematic transformation Limited by Z-statistics Limited by Z-statistics Detector and theoretical effects cancel at least partially Detector and theoretical effects cancel at least partially Pt(l) better than MT as it is not sensitive to E T systematics Pt(l) better than MT as it is not sensitive to E T systematics But needs P T (W) to be understood But needs P T (W) to be understood CMS Scaled p T (l ) W  e W  e “Morphed” m T W   Statistical1515 Instrumental<20<30 PDF<10<10 WWWW<15<10 P T (W) 30-- Systematic uncertainties (MeV) on W-mass for 10fb -1 P T (W) needs to reducedE T -systematics W-mass: CMS

10. New Physics? For equal contribution to M H uncertainty: M W is a fundamental SM parameter linked to the top, Higgs masses and sin  W.  M t < 2 GeV   M W < 15 MeV Mar 06 LEP2+Tevatron  M W =30MeV Tevatron run2 (2fb -1 )  30MeV combined Can get  M H /M H ~30% Important cross-check with direct measurements

11. W-mass summary A number of methods have been studied A number of methods have been studied Direct measurement of M T p T (l) Direct measurement of M T p T (l) Z-events used to tune W MC Z-events used to tune W MC scaled observable pt(l), ‘morphing’ scaled observable pt(l), ‘morphing’ Z-events used as a template Z-events used as a template Systematics greatly improved using Z-samples Systematics greatly improved using Z-samples All methods are giving  M w in range of 20MeV per channel per variable, so combined <15MeV per experiment seems to be achievable for 10fb -1 All methods are giving  M w in range of 20MeV per channel per variable, so combined <15MeV per experiment seems to be achievable for 10fb -1 Need to understand correlations Need to understand correlations Main issues at E T for M T and P T (W) for p t (l) Main issues at E T for M T and P T (W) for p t (l)  M W ~10MeV looks possible  M W ~10MeV looks possible Requires  M t <1GeV for EW fits Requires  M t <1GeV for EW fits

12. Top Mass Top quark pairs, mainly produced via gluon fusion, yields a production cross- section of 833 pb, at next to leading order, 100 times higher than at Tevatron. The "golden" channel is the semi-leptonic channel: tT→Wb+WB→ (lv)b+(jj)B

13. Top Mass Golden Channel event selection: Golden Channel event selection: Isolated high p T lepton, E miss T and at least 4 jets, two of which are b- tagged. Isolated high p T lepton, E miss T and at least 4 jets, two of which are b- tagged. This gives a signal efficiency of ~5% with a signal to background ratio of the order 10. This gives a signal efficiency of ~5% with a signal to background ratio of the order 10. Primary backgrounds Primary backgrounds The main backgrounds are single top events, mainly reduced by the4 jet cut, fully hadronic t T events, reduced by the lepton requirements, W+jet and Z+jet events The main backgrounds are single top events, mainly reduced by the4 jet cut, fully hadronic t T events, reduced by the lepton requirements, W+jet and Z+jet events

14. Finding the Top Mass Reconstruction of the hadronic side of the decay is done by minimization procedure. Reconstruction of the hadronic side of the decay is done by minimization procedure. This minimization constrains the light jet pair mass to M w, via corrections to the light jet energies. This minimization constrains the light jet pair mass to M w, via corrections to the light jet energies. After trying all possible jet combinations the one minimizing the χ 2 is kept. After trying all possible jet combinations the one minimizing the χ 2 is kept. The b-jet closest to the hadronic W is associated to the chosen pair. The b-jet closest to the hadronic W is associated to the chosen pair. The three jet invariant mass is then fitted with a Gaussian plus a polynomial The three jet invariant mass is then fitted with a Gaussian plus a polynomial The Result: M t = 175.0±0.2(stat.)±1.0(syst.) GeV, for an input mass of 175 GeV and 1 fb −1. The Result: M t = 175.0±0.2(stat.)±1.0(syst.) GeV, for an input mass of 175 GeV and 1 fb −1.

15. Drell-Yan As discussed in previous weeks this is where a heavier neutral gauge boson (Z’) would show up As discussed in previous weeks this is where a heavier neutral gauge boson (Z’) would show up A FB of the leptons from Zs A FB of the leptons from Zs

16. Drell Yan Important benchmark process: Measure cross-section parton-parton luminosity functions constrain PDFs measure sin2  W Deviations from SM

17. Need to define direction At the Tevatron -- well defined At LHC no asymmetry wrt beam Assume that there is a Q-qbar collision  quark direction from y(ll)  Requires measurement at high y(ll) Determination of sin 2 θ eff lept (M Z 2 ) A FB = b { a - sin 2 θ eff lept ( M Z 2 ) } Measure A fb with leptons in Z 0 DY events Qq qq Can fit with M t to constrain M H a, b calculated to NLO QED and QCD.

18. Determination of sin 2 θ eff lept (M Z 2 ) y cuts – e + e - (|y(Z)| > 1) ATLAS ∆A FB (Stat) ATLAS ∆sin 2 θ eff lept (Stat) |y( l 1,2 )| < 2.5 3.0 x 10 -4 4.0 x 10 -4 |y( l 1 )| < 2.5 + |y( l 2 )| < 4.9 2.3 x 10 -4 1.4 x 10 -4 Can be further improved by combining Z decay channels [%]  Systematics: PDF, lepton acc. (~0.1%), radiative correction calculations Current error on world average 1.6x10 -4 sin 2 θ eff =0.23153±0.00016

19. Associated Production of Gauge Bosons

20. Triple gauge boson couplings SM gauge group SU(2) L xU(1) Y  WW  and WWZ couplings (charged TGCs) Couplings described by 5 independent parameters All are zero in SM Any deviations is a signal of new physics

21. Anomalous couplings in WW  Most sensitive measurement is looking for high p T Zs or  s 30fb -1 ~3000 evts ATLAS CMS

24. Charged TGC predictions 95% CL 30fb -1 (inc syst) -0.0035<  <+0.0035 -0.0073< Z <+0.0073 -0.075<   <+0.076 -0.11<  Z <+0.12 -0..86<  g 1 Z <+0.011 Results expected to be ~x10 better than LEP/Tevatron Results are statistics limited (except for g 1 Z )

25. All are zero in SM Neutral TGCs No tree level neutral couplings in SM Leads to 3-5 order of magnitude improvement compared to LEP 95% CL 100fb -1 (inc syst) -6.5x10 -4 <h 30 Z <+6.4x10 -4 -1.8x10 -6 < h 40 Z < +1.7x10 -6 CMS

26. Quartic Couplings

27. Anomalous Quartic couplings Look for W , low production threshold at M w S/B~1 ATLAS 30fb -1 e -  ~14 events  (~x4 for l +/-  )

28. Heavy Leptons “Evidence grows for charged heavy lepton at 1.8-2.0 GeV”- Physics Today (1977) “Evidence grows for charged heavy lepton at 1.8-2.0 GeV”- Physics Today (1977) Current limits: m L(±) >100.8GeV Current limits: m L(±) >100.8GeV Neutral Heavy Lepton Mass Limits Neutral Heavy Lepton Mass Limits Mass m> 45.0 GeV, 95% CL (Dirac) Mass m> 45.0 GeV, 95% CL (Dirac) Mass m> 39.5 GeV, 95% CL (Majorana) Mass m> 39.5 GeV, 95% CL (Majorana)

29. Heavy Leptons Relic abundance of the leptons must not “over-close” the universe. Relic abundance of the leptons must not “over-close” the universe. Can’t provide more than the critical energy density (10 -5 GeV cm - 3 ) Can’t provide more than the critical energy density (10 -5 GeV cm - 3 ) A stable, charged lepton must have a low enough relic abundance for it not to have been detected in searches for heavy isotopes in ordinary matter A stable, charged lepton must have a low enough relic abundance for it not to have been detected in searches for heavy isotopes in ordinary matter The mass and lifetime of the new leptons musts not be such that they would have been detected in a previous collider experiment. The mass and lifetime of the new leptons musts not be such that they would have been detected in a previous collider experiment. There are no theoretical constraints found for lifetimes less that ~10 6 s even for masses up to the TeV scale. There are no theoretical constraints found for lifetimes less that ~10 6 s even for masses up to the TeV scale. Only limits are the experimental ones Only limits are the experimental ones

30. Heavy Leptons Where do we look for heavy Leptons? Where do we look for heavy Leptons? Drell-Yan Drell-Yan Other mechanisms Other mechanisms pp→γγ→L + L - pp→γγ→L + L - pp→Zγ→L + L - pp→Zγ→L + L - Mechanisms for introducing new leptons Mechanisms for introducing new leptons New fermionic degrees of freedom New fermionic degrees of freedom Vector Singlet Model (VSM) Vector Singlet Model (VSM) Vector Doublet Model (VDM) Vector Doublet Model (VDM) Fermion-mirror-fermion Model (FMFM) Fermion-mirror-fermion Model (FMFM)

31. Heavy Leptons In these new models: In these new models: Exotic leptons mix with the standard leptons through the standard weak vector bosons and according to the Lagrangians Exotic leptons mix with the standard leptons through the standard weak vector bosons and according to the Lagrangians

32. L ± Detection Time-of-Flight Time-of-Flight Heavy particles Heavy particles Detectable in both the central tracker and muon chambers Detectable in both the central tracker and muon chambers Use measured momentum and time delay to reconstruct the mass Use measured momentum and time delay to reconstruct the mass

33. L ± Detection Imperfections in the time and momentum resolutions will cause a spread in the mass peak Imperfections in the time and momentum resolutions will cause a spread in the mass peak Bunch crossing identification Bunch crossing identification Muons from D-Y and heavy quark decays Muons from D-Y and heavy quark decays For a background signal to look like a heavy lepton neutral current two opposite charge muons would have to be mis-identified at the same time. For a background signal to look like a heavy lepton neutral current two opposite charge muons would have to be mis-identified at the same time. Make p T cut at 50 GeV to eliminate heavy quark decays Make p T cut at 50 GeV to eliminate heavy quark decays

35. L ± Detection Detection at the LHC is entirely cross section limited. Detection at the LHC is entirely cross section limited.

36. L ± Detection Detection of up to 1TeV should be possible a the LHC Detection of up to 1TeV should be possible a the LHC

37. Leptons vs. Sleptons Study the angular distribution Study the angular distribution

38. Leptons vs. Sleptons

39. Heavy Lepton Summary Assuming standard model couplings and long lifetime: Assuming standard model couplings and long lifetime: We can detect heavy charged leptons in intermediate scale models up to 950 GeV with 100 fb -1 We can detect heavy charged leptons in intermediate scale models up to 950 GeV with 100 fb -1 Above 580 GeV it’s hard to distinguish them from scalar leptons Above 580 GeV it’s hard to distinguish them from scalar leptons

40. Summary The Electroweak sector, while one of the better understood sectors of the SM, still holds important information and even some exciting new physics at the LHC The Electroweak sector, while one of the better understood sectors of the SM, still holds important information and even some exciting new physics at the LHC

41. Backup slides

43.   2.5 Constraining gluon PDF with Ws Many W+Z measurements have pdf uncertainties at LHC Q 2 ~M Z 2 corresponds to sea-sea collisions  depends on gluon from g  qq Need to improve understanding of gluon

44. ZEUS to MRST01 central value difference ~5% ZEUS to CTEQ6.1 central value difference ~3.5% (From LHAPDF eigenvectors) W Rapidity Distributions for different PDFs CTEQ6.1M MRST02 GOAL: syst. exp. error ~3-5% ~ ±5.2% @y=0 ~ ±8.7% @y=0 ~ ±3.6% @ y=0 ZEUS-S

45. At Detector level reflects generator level distributions ~8% PDF uncertainty at y=0 remains CTEQ61 MRST01 ZEUS-S CTEQ61 MRST01 ZEUS-S e - rapidity e + rapidity Generator Level ATLAS Detector Level with sel. cuts Error boxes are the Full PDF Uncertainties Electron distributions

46. First measurements of W and Z W and Z cross-sections For ~1fb-1 data, systematics dominate (CMS) tracker efficiency Main theoretical contribution P T (W/Z) LO-NLO ~2% ETET Initial luminosity uncertainty ~10%, reduced to 5% ATLAS  -reconstruction efficiency from 20pb -1 Z   Barrel and endcap To 0.5% in 0.2  bins

47. Minimum bias and Underlying Event Tevatron ● CDF 1.8 TeV PYTHIA6.214 - tuned dN/dη (η=0) N ch jet- p t =20GeV 1.8TeV (pp) 4.12.3 14TeV (pp) 7.07.0 increase~x1.8~x3 ~80% ~200% LHC prediction Tevatron PYTHIA6.214 - tuned ● CDF 1.8 TeV MB only UE includes radiation and small impact parameter bias LHC

48. First measurements at the LHC ? Charged particle density at  = 0 (Only need central inner tracker and a few thousand pp events) LHC? Min bias events are also crucial for intercalibration  CMS require 18M events to intercalibrate ECAL in  at 2% ATLAS studies of use of MB events to study L1 trigger rates

49. Measuring the minimum bias events at ATLAS dN ch /d  dN ch /dp T Black = Generated (Pythia6.2) Blue = TrkTrack: iPatRec Red = TrkTrack: xKalman Only a fraction of tracks reconstructed,: limited rapidity coverage limited rapidity coverage  Measure central plateau can only reconstruct track p T with good efficiency down to ~500MeV, but most particles in min-bias events have p T < 500MeV can only reconstruct track p T with good efficiency down to ~500MeV, but most particles in min-bias events have p T < 500MeV  Hard extrapolation. Reconstruct tracks with: 1) pT>500MeV 1) pT>500MeV 2) |d 0 | < 1mm 2) |d 0 | < 1mm 3) # B-layer hits >= 1 3) # B-layer hits >= 1 4) # precision hits >= 8 4) # precision hits >= 8 p T (MeV) 

50. UE uncertainties Transverse PYTHIA6.214 - tuned PHOJET1.12 x 3 LHC x1.5 Extrapolation of UE to LHC is unknown Depends on Multiple interactions Radiation PDFs CDF definition of UE

51. Ratio / Leading jet E T (GeV) Reconstructin g the underlying event N jets > 1, |η jet | < 2.5, E T jet >10 GeV, |η track | < 2.5, p T track > 1.0 GeV/c ATLAS DC2 Simulated data Analyse with first data (a la CDF) Need to ensure overlap between MB and jet trigger Require ~20M MB events to get p t jet ~30GeV