Gauge-boson Physics at the LHC

1. Gauge-boson Physicsat the LHC Hadron Collider Physics 2004 Michigan State U. Matt Dobbs Lawrence Berkeley Laboratory, USA

2. Outline • LHC Physics Environment • ATLAS and CMS Detectors • Precision Gauge Boson Physics • W-mass • AFB and sin2θW • Di-bosons • Triple Gauge-boson Couplings • Tri-bosons • Challenges ahead: • Monte Carlo Tools • Experimental measurements – PDFs, energy scales, etc.

3. 14 TeV proton-proton collisions • broad-band q & g collider, • scales →few TeV • Low L→ 2x1033/cm2/s • precision physics • High L →1034 /cm2/s (~23 interactions/crossing) 300 fb-1 in ≤ 10 years Large Hadron Collider

4. The ATLAS Detector Inner Detector Tracking in range |h| < 2.5 Silicon Pixels, Strips & TRT EM Calorimetry Fine granularity up to |h| < 2.5 Pb/LAr Accordian Hadronic Calorimetry Barrel: Fe/Scintillating tiles Endcaps: Cu & W / LArFine Muon Spectrometer: s/pT ~ 7 % at 1 TeV Covers |h| < 2.7 Magnet 2T solenoid plus air core toroid

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: s/pT ~5% at 1 TeV(combined) Drift tubes, cathode strip chambers and resistive plate chambers One Magnet: 4T Solenoid

6. W-Mass

7. Mass(W) • electroweak fit such that MW is not the dominant error in EW fit. constrains MHiggs & consistency check (LEP2: 42 MeV, Tev RunI: 59 MeV)

8. Measuring Mass(W) • Measured with MTRAN of Leptonic Channels • MTRAN very sensitive to detector effects vs. • PTl± very sensitive to higher order corrections PT(W)=0 Finite PT(W) + detector effects Baur, hep-ph/0304266

9. Measuring Mass(W) • Combining channels and CMS data, expect ΔMW ≈ 15 MeV • expect improvements from using MTRAN(W)/MTRAN(Z)

10. W-mass: Challenges • 0.03% knowledge of lepton energy scale • calibrate with 6 million Zl+l- events • tracker material to 1% • overall alignment to 1 μm • B-field knowledge to 0.1% • muon E-loss to ¼% • (CDF/D0 achieved 1% despite small Z samples) • Well constrained PDFs • active program for measuring PDFs at LHC from Day 1 • new LHC-HERA workshop • mitigate some theory errors by using W/Z ratio methods • but MC model of ppZll is further behind in some cases (no multi-photon corrections) • Zll ≠ Wlν • Theory modeling of radiative decays and recoil ATLAS: C. Marques, Lisbon

11. The State of the Art Today • confused? a word from our sponsors…

14. Weinberg Angle: sin2θW

15. Measuring sin2θW with AFB Z°/γ e- θFB AntiProton Beam Proton Beam AntiProton Beam Proton Beam e+ • At the Tevatron, defining AFB is easy. • But for symmetric proton-proton beams (LHC), there is no asymmetry WRT the beams. known to NLO in EW, QCD (effects can be as large as 30%)

16. Measuring sin2θW with AFB Z°/γ Z°/γ Valence q Sea q Proton Beam Proton Beam Sea q Valence q Proton Beam Proton Beam • Instead, we “sign” the forward direction by the l+l- boost. • Measure asymmetry in charged lepton direction WRT CMS boost direction • Asymmetry increases at high Y(l+l-)

17. Measuring sin2θW with AFB • Statistical precision using 100 fb-1 • Performance issue: • increasing forward lepton tagging acceptance greatly improves measurement • Systematic PDF uncertainty is most challenging. ATLAS-PHYS-2000-018 CMS IN 2000/35 for comparison, Δ sin2θeff=0.00053 combining 4 LEP expts and e,μ,τ channels [CERN-EP/2001-098]

18. Triple Gauge-bosonCouplings

19. Probing theTriple Gauge-boson Couplings big advantage for LHC • non-abelian SU(2)L×U(1) Y gauge group (foundation of SM!)  WWγ WWZcouplings • most-general C & P conserving WWZ,WWγ vertices are specified by just 5 parameters:  model independent parameterization • Probe tool: sensitive to low energy remnants of new physics operating at a higher scale • complement to direct searches

20. 95% C.L. for Wγ • binned max. likelihood fit to PT(V) distribution • sensitivity comes from a few events in the high PT(V) tail ATLAS

21. TGC Limits vs. Integrated Luminosity confidence limit systematic contribution ATLAS • typically order of magnitude better than LEP/TeVa [O(.10-.20),95% C.L.] • Statistics will dominate LHC measurements (except for Δ g1) • sensitivity derived from a few events in the high PT(V) tail • Dominant systematics are theoretical: • neglected higher orders and pdf’s

22. Limits vs. Form Factor Scale ATLAS • new form factor strategy is introduced • rather than imposing an arbitrary form factor in the model, • the limits are reported as a function of a mass scale cutoff unitarity limit expt limit unitarity limit expt limit

23. Neutral TGC’s Z,γ Z/γ Z • no tree level neutral couplings in SM • typically 3-5 orders of magnitude improvement in limits at LHC over LEP. Zγ

24. The State of the Art Today

25. Tri-boson Production • sensitive to quartic gauge-boson couplings (QGC’s) van der Bij, Ghinculov hep-ph/9909409 “gold-plated” channels would require full LHC data set

26. Tri-boson Production • pp Wγγ • σ x BR(Wl,ν) • √s > MW production threshold • σ = 1.96 fb (μ±,e± after efficiency, detector effects) • WWγγ couplings Eboli, Gonzalez-Garcia, Lietti, Phys Lett D63, 2001 ATL-PHYS 2003-051 W2GRAD (Baur, Stelzer)

27. Conclusions • CMS & ATLAS are under construction. • LHC physics potential includes competitive precision electroweak measurements: sin2θW, mass(W) • Order of magnitude and better improvement in anomalous TGC limits  precision arena for diboson production • Challenges include: • Detector performance: lepton energy scale, forward tagging • More precise measurement of PDFs • no good prediction of LHC precision exists. • Theory: next-generation codes need QCD + QED