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Potential for Standard Model physics at the LHC

Potential for Standard Model physics at the LHC. Where are we with hard- and software ? From the Tevatron/LEP to the LHC Top quark, EW, QCD, B physics, ... How to search for the Standard Model Higgs ?. Jorgen D’Hondt (Vrije Universiteit Brussel) on behalf of the LHC Collaborations

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Potential for Standard Model physics at the LHC

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  1. Potential for Standard Model physics at the LHC Where are we with hard- and software ? From the Tevatron/LEP to the LHC Top quark, EW, QCD, B physics, ... How to search for the Standard Model Higgs ? Jorgen D’Hondt (Vrije Universiteit Brussel) on behalf of the LHC Collaborations WHEPP-9, Bhubaneswar, 3-14 January 2006

  2. Thanks for the wonderful activities !!

  3. The Large Hadron Collider 7x1012 eV Beam Energy Proton collisions 1034 cm-2 s-1 Luminosity 2835 Bunches/Beam 1011 Protons/Bunch New Particle Production Parton Collisions 109 Hz (Higgs, SUSY, ....) 10-5 Hz 27 km length 100m underground What is the origine of mass ? Jorgen D'Hondt (Vrije Universiteit Brussel)

  4. The CMS detector : design sketch 76k pieces 16k pieces Jorgen D'Hondt (Vrije Universiteit Brussel)

  5. The CMS detector : construction progress • Large activities are ongoing to make • previous sketch into reality • Main underground cavern is ready • Several sub-detector systems are completed or being completed : • Tracker : serious speed-up of production, overall good quality of modules • ECAL : ⅔ of barrel crystals delivered, first SuperClusters for endcap made • HCAL : assembled, start with electronics integration, calibration ongoing • Magnet : completed and succesfully tested for leaks • Muons : CSC’s completed, RPC’s being constructed and gradually integrated, 80% of DT’s are completed • Trigger boards are being produced “ CMS* will be closed and ready for beam on 30 June 2007 ” (T.Virdee, HCP’05 talk) Jorgen D'Hondt (Vrije Universiteit Brussel)

  6. The CMS detector : becoming a reality barrel tracker silicon detectors muon RPC’s magnet Jorgen D'Hondt (Vrije Universiteit Brussel)

  7. Example of an Event SUSY event pT > 1.0 GeV |h| < 2.4 IGUANA low luminosity Jorgen D'Hondt (Vrije Universiteit Brussel)

  8. Example of an Event SUSY event pT > 1.0 GeV |h| < 2.4 IGUANA high luminosity Jorgen D'Hondt (Vrije Universiteit Brussel)

  9. The ATLAS detector : design sketch Overall dimensions: length = 42 m, diameter = 22 m, weight = 7000 tons • Combined pixel, Si strip and straw tube tracker, inside 2T central solenoidal field • LAr accordion EM calorimeter • LAr (EC) and Steel-Scintillator (Barrel) HCAL • Drift tubes and CSCs in toroidal muon spectrometer, with RPCs and TGCs for triggering For |η|< 2.5 (precision region): GOALS • Lepton E,p scale:0.02% precision • Jet energy scale:1% precision • b-tagging:b60%, ruds100, rc10 Jorgen D'Hondt (Vrije Universiteit Brussel)

  10. The ATLAS detector : construction progress Ongoing assembly of SCT barrel Assembled Barrel TRT LAr EMBarrel Calorimeter Jorgen D'Hondt (Vrije Universiteit Brussel)

  11. The ATLAS detector : becoming a reality Recent picture in the cavern (5th of Jan ’06) Jorgen D'Hondt (Vrije Universiteit Brussel)

  12. Current status of Simulation and Reconstruction Still a few years before real data… hence all based on Monte Carlo simulation first beams expected in 2007 • Main generator used : PYTHIA 6.2 • does not include many features present in dedicated generators • fast simulation : the PYTHIA objects are smeared to mimic the detector • the particle interactions are not simulated with GEANT • Results in this presentation: studies based on fast simulation • large efforts have been made to optimize the reconstruction code • large Data-Challenge efforts have been made to provide dedicated GEANT-4 simulation (created ~100M simulated events, ~1Mb/event) • CMS is writing a Physics - Technical Design Report with this accurate simulation and reconstruction tools (expected early 2006) • Current results to be digested as an illustration of what can be learned from CMS and ATLAS data upon arrival Jorgen D'Hondt (Vrije Universiteit Brussel)

  13. From Tevatron/LEP to LHC • Obtaining orders in magnitude in both the integrated luminosity and the energy, we will collect a huge amount of Standard Model benchmarks channels. • ~109 events/10fb-1W (200 per second) • ~108 events/10fb-1Z (50 per second) • ~107 events/10fb-1tt (1 per second) • These can be used as control/calibration samples for searches beyond the Standard Model, but can also be used to scrutinize even further the Standard Model. Jorgen D'Hondt (Vrije Universiteit Brussel)

  14. Top Quark Production ~87 % • Many physics parameters to be measured with these events (hence reconstruct the complete event !) • Also it is the main background for searches beyond the Standard Model at the LHC • NLO cross-section for tT production sNLO = 833 pb  ~8M events for 10fb-1 (10 fb-1 = 1 year of LHC running at low luminosity, hence by summer 2009) BR(t→Wb) ~ 1 Jorgen D'Hondt (Vrije Universiteit Brussel)

  15. Top Quark Selection Main background processes for pp→tT→WbWb : • Fully hadronic channel : 3.7Mevnt/10fb-1 • QCD multijet (2→2 parton processes) • 6-jets pT>40GeV, b-tags≥2 : S/B~1/19, e~2.7% • Lepton + jets channel (lepton = e/m) : 2.5Mevnt/10fb-1 • bb→lv+jets, W+jets→lv+jets, Z+jets→ll+jets, WW→lv+jets, WZ→lv+jets, ZZ→ll+jets • before selection we have S/B ~ 10-5 • pTlepton>20GeV, ETmiss>20GeV, pTjet>40GeV, b-tags≥2 : S/B ~ 78, e~3.5% • pTlepton>20GeV, ETmiss>20GeV, pTjet>40GeV, b-tags≥1 : S/B ~ 28, e~14% • Di-lepton channel : 0.4Mevnt/10fb-1 • Drell-Yan processes, Z+jets→ll+jets, WW+jets, bb • pTl+>35GeV, pTl->25GeV, ETmiss>40GeV, pTjets>25GeV : S/B~10, e~20% ATLAS numbers Jorgen D'Hondt (Vrije Universiteit Brussel)

  16. Top Quark Production Cross-Section • Sensitive to top mass : Ds/s ~ 5 Dmt/mt  5% on s gives 2 GeV on mt  10 % sNLO K = sLO systematics dominated by the uncertainty on the luminosity ATLAS preliminary Cross-section sensitive to renormalisation and factorisation scale, and to the choice of PDF (Parton Density Function) Jorgen D'Hondt (Vrije Universiteit Brussel)

  17. Top Quark Physics : top quark mass 10 tt pairs per day @ Tevatron  1 tt pair per second @ LHC qq →tt : 85% gg→tt : 87% Most important parameter is the top quark mass (mt), to be estimated with an accuracy of around Dmt ~ 1 GeV/c2. Golden channel : semi-leptonic tt →bWbW→blvbqq Selection via lepton, miss.ET, 4 jets, 2 b-tags (S/B~>20) Top mass from hadronic side t→qqb Main systematics are the jet energy scale Improve with kinematic fit and more advanced statistical inference techniques are ongoing. fastsim 10fb-1 Jorgen D'Hondt (Vrije Universiteit Brussel)

  18. Top Quark Physics : top quark mass width of peak ~10 GeV width of peak 10.6 GeV ATLAS CMS dmt(stat) ~ 300 MeV (10fb-1) dmt(stat) ~ 100 MeV (10fb-1) ATLAS ATLAS kinematic fit Jorgen D'Hondt (Vrije Universiteit Brussel)

  19. Top Quark Physics : kinematic fit Using kinematic fit techniques (applying Least-Square methods with Lagrange multipliers) mass constraints can be enforced to the reconstructed event topology. → in the t→Wb decay constrain the W boson mass to its precisely measured value ~70% purity To obtain the same precision without the fit, one needs 5 times more data (the bias wrt 175GeV is reduced) Jorgen D'Hondt (Vrije Universiteit Brussel)

  20. Top Quark Physics : top quark mass • Single lepton plus jets :High pT sample with pT(jjb)> 200 GeV(Jet-Analysis) • back-to-back top pair production (lab-frame) : hence different hemi-spheres • less combinatorial background or other background • smaller systematics from energy calibration and gluon radiation • statistical uncertainty Dmt ~ 250 MeV/c2 • jet overlapping probability increases → affects jet calibration • Single lepton plus jets :High pT sample with pT(jjb)> 200 GeV(Cluster-Analysis) • collect all energy in a cone around the top direction • less sensitive to jet calibration and the jet topology of the event • large dependence on cone size • should subtract underlying event energy • mW estimate in tT→lepton+jets (data based) Yellow Report LHC ATLAS-COM-PHYS-99-050 generated bias via mW estimate Jorgen D'Hondt (Vrije Universiteit Brussel)

  21. Top Quark Physics : top quark mass • From t  l + J/y + X decays : • 100 fb-1 gives after selection ~ 1,000 signal events (S/B > 100) • the large mass of the J/y induces a strong correlation with the top mass • easier to identify (extremely clean sample) • BR(overall in tt) ~ 5.3 x 10-5 • no jet related systematics !! CMS fast simulation hep-ph/9912320 slope 60 New method : hep-ex/0501043 correlate the b transverse decay length with mt Jorgen D'Hondt (Vrije Universiteit Brussel)

  22. Top Quark Physics : top quark mass • Continuous jet algorithms : • use the same event selection as for the nominal analysis • use the cone-based jet clustering algorithm, but scan the hole DR range • for each event several mt are determined depending on DR • let the event itself choose its jet broadness… less sensitive to radiation • statistical unc. (10fb-1) ~ 100 MeV/c2 • systematics : b-jet energy scale ATLAS paper hep-ex/0403021 Jorgen D'Hondt (Vrije Universiteit Brussel)

  23. Top Quark Physics : top quark mass • Di-lepton channel : 0.4Mevtn/10fb-1 (Jet-Analysis with mlb, Jet-Energies, Tri-lepton events and Full-reconstruction) • 10 fb-1 gives after selection ~ 80,000 signal events (S/B ~ 10) • mt2 = MW2 + 2 <mlb2> / (1- <cosqlb>) (high pT b-tagged jets → 15,000 events) • statistical uncertainty ~ 900 MeV/c2 • b-quark fragmentation could give large systematics • energy distribution of two leading jets • match with correct MC distribution • statistical uncertainty ~ 400 MeV/c2 • jet energy calibration ~ 1.5 GeV/c2 • tlvb followed by blvc • invariant mass distribution of the two leptons from the same top decay • only about 7250 events • statistical uncertainty ~ 1000 MeV/c2 • systematics from b-quark and ISR and FSR up to 1.5 GeV/c2 i. ii. iii. Jorgen D'Hondt (Vrije Universiteit Brussel)

  24. Top Quark Physics : top quark mass • full event reconstruction by assuming a fixed value for the top mass a c2 can be determined as a function of this value mt → c2(mt) • based on solving a set of equations (kinematic constraints) • solution is found in 98% of the selected events • dmt(stat) ~ 300 MeV (10fb-1) • small systematics due to radiation (switching on/off ISR/FSR) iv. ATLAS mean weight mt 20% Jorgen D'Hondt (Vrije Universiteit Brussel)

  25. Top Quark Physics : top quark mass CMS notes [1] ATLAS paper hep-ex/0403021 [2] LHC Yellow Report on Standard Model Physics [3] Stat.Unc. MeV Syst.Unc. MeV • Single-lepton channel (Full-Analysis) [1,2]100 ~1000 • High pT single-lepton sample (Jet-Analysis) [3] 250 ~1000 (?) • High pT single-lepton sample (Cluster-Analysis) [3] 150 ~1500 • Single-lepton channel (Continuous jet algorithm) [2] 100 ~1000 • Di-lepton channel (Jet-Analysis with mlb) [3] 900 ~1300 • Di-lepton channel (Energy-Analysis) [3] 400 ~2000 • Di-lepton channel (Tri-lepton events) [3] 1000 ~1500 • Di-lepton channel (Full-reconstruction) [2] 300 ~1300 • From t  l + J/y + X decays (4 years high lumi) [1,2,3] 1000 <1000 • High pT fully-hadronic channel [2] 180 >3500 • combining all those results could lead to a more precise measurement (correlations to be estimated !!) • systematic effects do not necessary overlap between analyses • Expectation : top mass determination better than 1 GeV after understanding the detector Jorgen D'Hondt (Vrije Universiteit Brussel)

  26. Top Quark Physics : top versus anti-top • Spin correlations • the top quark does not loss its spin information before it is decaying into W and b with A =0.431 (gg) and A = - 0.469 (qQ) • two observables q+(q-): angle between t(T) direction in the tT c.m. frame and the l+(l-) direction of flight in the t(T) rest frame • fit to double differential distribution • result (30fb-1) : A (stat) = 0.035 and A (syst) = 0.028 • Measuring thedifference between mt and mT • almost all systematics cancel when measuring the difference between both • after several years the precision could be around 50 MeV/c2 • what we could learn from that ? CPT violation… ? • differences between t and T can learn us something about the PDF’s (rapidity distributions) Jorgen D'Hondt (Vrije Universiteit Brussel)

  27. Top Quark Physics : discovery topics • A lot more when we differentiate the selected events in phase-space !! • search for resonances in the dstT/dMtT spectrum • SM : BR(H → tT) to small to be visible above continuum tT production (GH too large) • MSSM : if MH,A > 2mt then BR(H/A → tT)  100 % for tanb  1 • Technicolor models : in some models heavy particles decaying to tT • selection of lepton plus jets channel • precise kinematic reconstruction : dmtt/mtt ~ 6.6% Yellow Report LHC For a random resonance : (choose jet combination which match best the tT event kinematics) Resonance of 1600 GeV 5s discovery potential of resonance sxBR needed for discovery wrong combinations discovery no discovery mtT(GeV) Jorgen D'Hondt (Vrije Universiteit Brussel)

  28. Top Quark Physics : discovery topics • Inclusive cross-section stT : infuenced by SUSY • test the consistency of the SUSY model after discovery • Invariant tT-mass distribution : significant distortions of the shape expected • when including MSSM EW corrections (one-loop) • for heavy Higgs A0 between tT threshold ~350 GeV and ~500 GeV inference between A and H could destroy the signal SM corrections much smaller Yellow Report LHC Jorgen D'Hondt (Vrije Universiteit Brussel)

  29. Top Quark Physics : single-top-channel Never observed !! • Each channel sensitive to different signals • heavy W’ → s-channel • FCNC → t-channel • H± → Wt-channel • Also directly related to |Vtb| to percent level • (s-channel preferred, t-channel dominated by PDF scale uncertainties of ~10%) Jorgen D'Hondt (Vrije Universiteit Brussel)

  30. W polarization in top decays The large top quark mass allows the W boson to be longitudinaly polarized q defined as : angle between lepton (in W rest frame) and W (in top rest frame) Standard Model prediction : f0 = mt2 / (2 mW2 + mt2) ~ 0.7 and fR ~ 0 (mb~0) LH: (1±cosq)2 Long: sin2q PYTHIA 5.7, 1 year CMS only W→ev and W→mv Expected uncertainty Dstat f0 = 0.023 Dsyst f0 = 0.022 estimation of systematic uncertainties conservative most of the time limited by the statistical precision of the effect Jorgen D'Hondt (Vrije Universiteit Brussel)

  31. Gauge Boson Couplings Direct measurements of vector boson couplings are possible via the cross-section measurements of the processes in which they appear. They test the non-Abelian nature of the Standard Model gauge theory. Anomalous couplings or new physics can be included in the effective Lagrangian at a fundamental scale L. pt-spectrum of photon sensitive to anomalous couplings (L=1.5 TeV) g W Limits @95%CL (L=2TeV) l=0.3, k=0 l=0, k=0.95 Dk,l W BAUR MC generator pp→Wg l=0, k=0 cross-section enhanced when anomalous couplings are present pt(g) (GeV) for 100 fb-1 (L=2TeV) |Dk| < 0.1 |l| < 0.0009 large improvement for l compared to Tevatron For ZZg and Zgg couplings both the pT(g) and the MT(llg) spectrum are sensitive to hiV (V=Z,g) anomalous couplings Jorgen D'Hondt (Vrije Universiteit Brussel)

  32. Drell-Yan Production of Lepton Pairs The Drell-Yan process pp→l +l - is a measure for AFBand hence sin2qefflept : e-,m- q Weak-mixing angle sin2qefflept can be determined to Dsin2qefflept ~ 0.00014 using forward lepton tagging Precision will exceed the magnitude of the EW corrections up to Mll=2 TeV Z/g e+,m+ q inverse of e+e- → qq at LEP Rel. exp. uncertainty on sll (in %) LHC reaches much higher masses main systematic uncertainty is the knowledge of the PDF’s 10% 5% 0% can also use sin2qefflept to constrain the PDF’s Jorgen D'Hondt (Vrije Universiteit Brussel)

  33. Parton Probability Functions How to find the partons in the colliding protons ? →need for precisePDF(x,Q2) Extrapolate from HERA, but also use the huge LHC data itself Ratio of W+/W- cross-section is related to u(x)/d(x) y = pseudorapidity differentiate between several models 0.1 fb-1 DGLAP evolution Jorgen D'Hondt (Vrije Universiteit Brussel)

  34. Parton Probability Functions The PDF’s for the heavy quarks can also be measured Isolated g with high pT + jet including m Estimate 5-10% accuracy on PDF‘s limited by fragmentation functions Isolated e/m with high pT + jet including m The PDF’s can be determined relative to each other, and therefore depend on the accuracy of the theoretical calculations. In a similar way the gluon luminosity function can be obtained with a 1% accuracy. Jorgen D'Hondt (Vrije Universiteit Brussel)

  35. B-physics • The CMS/ATLAS detectors allow a rich B-physics program due to precise tracking and vertexing • (but no Particle ID detectors, usually triggers on high-pT objects) • CP violation • measurements of Bs oscillations • rare decays • life-time • Bc mesons • etc... all B-physics studies require a profound knowledge of the detector performance Example : (alternative to lepton-tag method) CKM angle b via Bd0→J/j Ks0 in B**±→Bd0(*)p± The flavour of B0 is tagged with p± Expected precision is D(sin2b)=0.022 (10fb-1) (to be repeated with higher trigger thresholds) after selection related to angle b ICHEP’04 : sin(2b) = 0.725 ± 0.037 Jorgen D'Hondt (Vrije Universiteit Brussel)

  36. Mass of the W boson • free parameter (normalization schemes) • test of SM : direct versus indirect measurement (mZ) radiative one-loop corrections from tree level (Dr=0) indirect constraint on Higgs mass • only logarithmic • quadratic terms at two loops • For equal contribution as top quark mass • in mH uncertainty : DMt< 2 GeV DMW < 15 MeV Challenging !! Jorgen D'Hondt (Vrije Universiteit Brussel)

  37. Mass of the W boson Events:pp→W+X with W→lv the lepton being a muon or electron Cross-section: 30nb (300 million events per year of 10fb-1) • Measurement method: MC thruth Estimated with W recoil • Isolated lepton PT>25 GeV • ETmiss>25 GeV • No jet with ET<30 GeV • W recoil < 20 GeV Full sim.  60M evts/10 fb-1 Efficiency:~20% (50 times more compared to the Tevatron Run-2) MTW (GeV) Sensitivity to MW through falling edge Compare data with Z0 tuned MC samples where input MW varies in 1 MeV steps Minimize c2(data-MC): 2 MeV statistical precision Jorgen D'Hondt (Vrije Universiteit Brussel)

  38. Mass of the W boson • Systematics errors on MW(MeV) from experiment and theory * Z reduce syst. on MWEx.: Correlation between Z and W cross-section 16.0 1 point=1 PDF set 15.9 sW (nb) 15.8 15.7 15.6 15.5 15.4 15.3 15.2 1.50 1.51 1.52 1.53 1.54 1.55 1.56 1.57 1.58 sZ (nb)  deduce W kinematics from Z Jorgen D'Hondt (Vrije Universiteit Brussel)

  39. Ultimate test of the Standard Model Comparing the direct and indirect values of mH To give mt and mW equal weight : DmW = 0.7 10-2Dmt Goal of LHC experiments : Dmt < 1 GeV DmW < 15 MeV  DmH/mH < 25 % After a discovery one can use EW measurements to differentiate between SM or MSSM Higgs bosons Jorgen D'Hondt (Vrije Universiteit Brussel)

  40. Standard Model Brout-Englert-Higgs boson Combined discovery potential as a function of mH zoom in low mass region 5s at 2 fb-1 WW/ZZ at 10 fb-1 5s at 10 fb-1 gg at 30 fb-1 at 30 fb-1 at 60 fb-1 gg WW ZZ At 10 fb-1 full 5s coverage from LEP to 800 GeV LEP limit Jorgen D'Hondt (Vrije Universiteit Brussel)

  41. Standard Model Brout-Englert-Higgs boson Integrated luminosity needed for 5s discovery as a function of mH zoom in low mass region 30 fb-1 30 fb-1 Jorgen D'Hondt (Vrije Universiteit Brussel)

  42. Outlook • First fast-simulation studies (presented) • significant improvement in Standard Model measurements • Higgs boson mass range completely covered after 10fb-1 • Current progress • created large amounts of dedicated/realistic simulation (GEANT based and NLO for most channels) • large effort in optimizing reconstruction methods (aim for common definitions of for example jets) • gradually design more advanced analyses techniques • start studies on detector calibration/alignment • Outlook for the near future • write-up into a Physics-Technical Design Report (CMS) (summarize the physics potential of the experiment) (foreseen by February ‘06 (Vol-I) and June ‘06 (Vol-II)) • new papers with updated studies from P-TDR (ATLAS) Jorgen D'Hondt (Vrije Universiteit Brussel)

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