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Potential for Standard Model physics with CMS at the LHC

Potential for Standard Model physics with CMS 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)

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Potential for Standard Model physics with CMS at the LHC

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  1. Potential for Standard Model physics with CMS 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 CMS Collaboration HEP-EPS Conference, Lisbon, 21-27 July 2005

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

  3. 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, CMS Collaboration)

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

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

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

  7. Current status of Simulation and Reconstruction Still a few years before real data… hence all based on Monte Carlo simulation first data 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 (‘FAMOS’) • 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) • in the process of 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 data upon arrival Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)

  8. 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, CMS Collaboration)

  9. 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. width of peak ~10 GeV 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 dmt(stat) ~ 300 MeV (10fb-1) Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)

  10. 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, CMS Collaboration)

  11. 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, CMS Collaboration)

  12. 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, CMS Collaboration)

  13. 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, CMS Collaboration)

  14. 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, CMS Collaboration)

  15. 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, CMS Collaboration)

  16. 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, CMS Collaboration)

  17. 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, CMS Collaboration)

  18. B-physics • The CMS detector allows a rich B-physics program due to its 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, CMS Collaboration)

  19. Standard Model Brout-Englert-Higgs boson The SM-like scalar Higgs boson can be observed in several physics channels (depending on its mass mH which is a free parameter of the model, LEP mH > 114.4 GeV @95%CL) production cross-section decay branching ratios balance between production rate, decay rate and reconstruction efficiency Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)

  20. Standard Model Brout-Englert-Higgs boson qqH → qqgg 60fb-1 H → gg 100fb-1 H → ZZ* → 4l 100fb-1 mH=130 mH=130,150,170 mH=115 signal signal signal qqH → qqtt ttH → ttbb 30fb-1 30fb-1 H → WW* →lvlv 30fb-1 mH=135 mH=115 mH=140 signal signal signal Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)

  21. 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, CMS Collaboration)

  22. 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, CMS Collaboration)

  23. 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, CMS Collaboration)

  24. Outlook for CMS activities • First fast-simulation studies (presented) • significant improvement in Standard Model measurements • Higgs boson mass range completely covered after 10fb-1 • Current progress within the CMS Collaboration • created large amounts of dedicated/realistic simulation • large effort in optimizing our reconstruction methods • gradually design more advanced analyses techniques • start studies on detector calibration/alignment (check influence) • Outlook for the near future • write-up of all the above into a Physics-Technical Design Report • this will summarize the physics potential of the experiment in great detail • foreseen by December 2005 (Volume-I) and by April 2006 (Volume-II) • thanks to all CMS collaborators who contributed to these Standard Model studies Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)

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