Precision SM tests at the LHC using ATLAS and CMS

1. Precision SM tests at the LHC using ATLAS and CMS Peter R Hobson School of Engineering & Design Brunel University Talk given at RAL on 13 June 2005

2. Contents • ATLAS & CMS • Jets • Drell-Yan • B physics • Top physics • Electroweak (TGC) • Single photons

3. ATLAS

4. CMS

5. Day 1 of LHC p+p From F Gianotti, LHC Physics, La Thuile 2005

6. Year 1 at the LHC From F Gianotti, LHC Physics, La Thuile 2005

7. Year 1 at the LHC From F Gianotti, LHC Physics, La Thuile 2005

8. Effects on physics reach

9. Effects on physics reach b-tagging in ATLAS From G Polisello, Les Houches 2005

10. Jet Physics Atlas • Measure jet ET spectrum, rate varies over 11 orders of magnitude • Test QCD at the multi-TeV scale Inclusive jet rates for 300 fb-1: From J Mnich, Physics at the LHC, Vienna 2004

11. Test of pQCD in an energy regime never probed! The measurement of di-jets and their properties (ET and η1,2) can be used to constrain p.d.f.’s Inclusive jet cross section: αsmeasurement with 10% accuracy Multi-jet productionis important for several physics studies: Top-pair production with hadronic final states Higgs production in association with tt and bb Search for R-parity violating SUSY (8 – 12 jets). Systematic uncertaintiess (statistical will be small): luminosity (dominant uncertainty 5% -10% ) jet energy scale calorimeter response (linearity) jet trigger efficiency knowledge of p.d.f.’s value of strong coupling constant, αs uncertainties in parton shower modeling Jet signatures - - ET Jet [GeV] From VA Mitsou, QCD Conference Montpellier 2004

12. Drell-Yan Lepton-Pair Production q e, /Z pT > 6 GeV || < 2.5 e+, + q Inversion of e+e qq at LEP LHC 1 fb-1 Z pole • Total cross section • pdf • parton lumi • search for Z, extra dim. , ... • Much higher mass reach as • compared to Tevatron From J Mnich, Physics at the LHC, Vienna 2004

13. Drell-Yan Lepton-Pair Production • Forward-backward asymmetry • estimate quark direction • assuming xq > xq • Measurement of sin2W effective • 2004: LEP & SLD • sin2W = 0.23150  0.00016 • AFB around Z-pole • large cross section at the LHC • (Z  e+e)  1.5 nb • stat. error in 100 fb-1 • incl. forward electron tagging • (per channel & expt.) • sin2W  0.00014 • Systematics (probably larger) • PDF • Lepton acceptance • Radiative corrections Atlas [%] From J Mnich, Physics at the LHC, Vienna 2004

14. QCD effects enter DY production in initial state only  predictions less uncertain Reconstruction of leptons (e, μ) unambiguous identification ( opposed to jets ) Di-lepton production constrains proton structure atQ2≈ mℓℓ2 W and Z production: huge statistical samples ~105 events containing W (pTW > 400 GeV, L=30fb-1) ~104 events containing Z (pTZ > 400 GeV, L = 30fb-1) W± production: higher cross-section for W+ than for W- different yW-distributions: W+ forward; W- central constrain quark and anti-quarkdensities in the proton [ud(bar)W+; u(bar) d W-] W+jet production study colour coherence Z production provides accurate reconstruction of final state (no neutrino!) Pair production (WW, ZZ, WZ) study triple gauge boson constants NLO calculation pTmiss>20 GeV |ηℓ|<2.5 Drell-Yan processes • Represent background sources to many new phenomena searches From VA Mitsou, QCD Conference Montpellier 2004

15. B Physics at ATLAS & CMS From VM Ghete Physics at LHC Vienna, 2004

16. B Physics at ATLAS & CMS From VM Ghete Physics at LHC Vienna, 2004

17. B Physics at ATLAS & CMS From VM Ghete Physics at LHC Vienna, 2004

18. - ggbb - gggg, g bb c & b production - - • Dominant production mechanism for heavy quarks (b and t) is gg fusion • Cross-section calculation: • pQCD processes leading to QQ state • non-pQCD to transform into colour-singlets • tuning with Tevatron data • Measurements of heavy quark production will provide constraints on the gluon density • Jet-flavour identification (c-jet or b-jet): • high-pT muons (ε≈ 85%, σ=39 MeV) • b-tagging (vertexing detectors) • b-quark • lower-pT mesons are experimentally accessible compared to charm-quarks • 10-4<x<0.1 • b-b(bar) correlations: • Δφμμ≈π  mostly LO QCD • Δφμμ≈0 only NLO QCD ψ´ J/ψ gbgb From VA Mitsou, QCD Conference Montpellier 2004

19. Cross section determined to NLO precision Total NLO(tt) = 834 ± 100 pb Largest uncertainty from scale variation Compare to other production processes: Top production cross section approximately 100x Tevatron Opposite @ FNAL Top production ~90% gg~10% qq LHC is a top factory! From S Bentvelsen, QCD Conference Moriond 2004

20. Br(ttbbjjl)=30%for electron +muon Golden channel Clean trigger from isolated lepton The reconstruction starts with the W mass: different ways to pair the right jets to form the W jet energies calibrated using mW Important to tag the b-jets: enormously reduces background (physics and combinatorial) clean up the reconstruction Lepton side Hadron side Golden-plated MTop channel • Typical selection efficiency: ~5-10%: • Isolated lepton PT>20 GeV • ETmiss>20 GeV • 4 jets with ET>40 GeV • >1 b-jet (b40%, uds10-3, c10-2) Background:<2% W/Z+jets, WW/ZZ/WZ

21. Hadronic side W from jet pair with closest invariant mass to MW Require |MW-Mjj|<20 GeV Assign a b-jet to the W to reconstruct Mtop Kinematic fit Using remaining l+b-jet, the leptonic part is reconstructed |mlb -<mjjb>| < 35 GeV Kinematic fit to the tt hypothesis, using MW constraints j2 j1 b-jet t Lepton + jet: reconstruct top • Selection efficiency 5-10% W-mass From S Bentvelsen, QCD Conference Moriond 2004

22. Method works: Linear with input Mtop Largely independent on Top PT Biggest uncertainties: Jet energy calibration FSR: ‘out of cone’ give large variations in mass B-fragmentation Verified with detailed detector simulation and realistic calibration Top mass systematics Challenge: determine the mass of the top around 1 GeV accuracy in one year of LHC From S Bentvelsen, QCD Conference Moriond 2004

23. Use exclusive b-decays with high mass products (J/) Higher correlation with Mtop Clean reconstruction (background free) BR(ttqqb+J/)  5 10-5  ~ 30%  103 ev./100 fb-1 (need high lumi) Top mass from J/ MlJ/ Different systematics (almost no sensitivity to FSR) Uncertainty on the b-quark fragmentation function becomes the dominant error M(J/+l) M(J/+l) From S Bentvelsen, QCD Conference Moriond 2004 Mtop

24. Determination MTop in initial phase Use ‘Golden plated’ lepton+jet Selection: Isolated lepton with PT>20 GeV Exactly 4 jets (R=0.4) with PT>40 GeV Reconstruction: Select 3 jets with maximal resulting PT Signal can be improved by kinematic constrained fit Assuming MW1=MW2 and MT1=MT2 Top During Commissioning Calibrating detector in comissioning phase Assume pessimistic scenario: -) No b-tagging -) No jet calibration -) But: Good lepton identification No background included From S Bentvelsen, QCD Conference Moriond 2004

25. Signal plus background at initial phase of LHC Most important background for top: W+4 jets Leptonic decay of W, with 4 extra ‘light’ jets Alpgen, Monte Carlo has ‘hard’ matrix element for 4 extra jets(not available in Pythia/Herwig) Top During Commissioning ALPGEN: W+4 extra light jets Jet: PT>10, ||<2.5, R>0.4 No lepton cuts Effective : ~2400 pb L = 150 pb-1 (2/3 days low lumi) With extreme simple selection and reconstruction the top-peak should be visible at LHC measure top mass (to 5-7 GeV) give feedback on detector performance From S Bentvelsen, QCD Conference Moriond 2004

26.  R(|Vtb|)=   Direct |Vtb| extraction: single top / single W Moreover, in principle, many theoretical errors would disappear by normalising s-channel events over single W events: (with care in choosing coherent cuts for the two processes, to avoid the reintroduction of the same errors in a subtler way) From A Giammanco, Les Houches 2005

27. 3rd jet: b (mostly undetectable) T-channel 2nd jet: recoil 1st jet: b from t Single top: “how to” For MET and Ht, single top lies in the middle between non-top and ttbar bkgs.S-channel: S/B<0.2, main bkgs: ttbar->2l (1 lost), Wbb, t-channel. T-channel is much easier to select, due to higher cross section and unique topology. General strategy (both s/t-ch.): • 1 isolated lepton • 2 high Et jets • at least 1 tagged b-jet • missing Et • l+MET: MT compatible with W • Ht (scalar sum of all Et’s) • M(lb) in a window around Mt s/t-channel separation: • 2(b-t-b)/1 tagged b-jets • 0/1 jets in the forward calo • 2/1 central jets • angular distance between the reco top and the remaining jet CMS note 1999/048 From A Giammanco, Les Houches 2005

28. TGC From M Dobbs, Hadron Collider Physics 2004

29. TGC From M Dobbs, Hadron Collider Physics 2004

30. QGC From M Dobbs, Hadron Collider Physics 2004

31. TGC CMS studies • W (Kate Mackay, Peter Hobson, Karlsruhe Group) • CMSJET studies with BAUR generator (Phys Rev D41 1476 (1990)) • Full background study • CMS Notes: 2000/017, 2001/052, 2001/056, CMS Thesis 1999/019 • Z (Kate Mackay, Peter Hobson, Davy Machin, Karlsruhe Group) • CMSJET studies with BAUR Z generator • Full background study • CMS notes: 2000/017, 2002/028, CMS Thesis 2005 • WZ • No CMS specific study • W (Richard Croft) • CMSJET study with W2GRAD generator

32. Status of CMS W Analysis • Signal • BAUR NLO MC • Used in CMSJET studies • Backgrounds • W+jet – main background • Radiative W decay • Quark-Gluon fusion • Cuts: • isolated high pt photon, lepton and missing energy. • pT()> 100 GeV • pT(l)> 25 GeV • pT()> 50 GeV • MT(,l,) > 90 GeV • R(,l) > 0.7 • pT 2nd Jet < 25 GeV • || < 2.5 Peter Hobson, Kate Mackay

33. Status of CMS W Analysis Peter Hobson, Kate Mackay

34. Direct photon - • Two main contributions: • qg→q QCD Compton scattering (dominating) • qq→g annihilation process • Information on gluon density in the proton ( requires good knowledge of αs ) • Background: jetswith a leading π0 • Isolation cut: low hadronic activity in a cone around the photon • ATLAS: high granularity calorimeters ( |η| < 3.2 ) allow good γ/jet separation • Di-photon production: mγγand Δφγγ sensitive to soft gluon emission • Understanding irreducible background from fragmentation in gg fusion: crucial for Hγγ searches LO γγ production From VA Mitsou, QCD Conference Montpellier 2004