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, July 2005

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)2 The CMS detector : design sketch 76k pieces 16k pieces

21st of July 2005Jorgen 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 : ð Tracker : serious speed-up of production, overall good quality of modules ð ECAL : ⅔ of barrel crystals delivered, first SuperClusters for endcap made ð HCAL : assembled, start with electronics integration, calibration ongoing ð Magnet : completed and succesfully tested for leaks ð 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)

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)4 The CMS detector : becoming a reality barrel tracker silicon detectors magnet muon RPC’s

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)5 Example of an Event IGUANA low luminosity SUSY event p T > 1.0 GeV |  | < 2.4

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)6 Example of an Event IGUANA high luminosity SUSY event p T > 1.0 GeV |  | < 2.4

21st of July 2005Jorgen 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 ð does not include many features present in dedicated generators ð fast simulation : the PYTHIA objects are smeared to mimic the detector ð the particle interactions are not simulated with GEANT  Results in this presentation: studies based on fast simulation (‘ FAMOS ’) ð large efforts have been made to optimize the reconstruction code ð large Data-Challenge efforts have been made to provide dedicated GEANT-4 simulation (created ~100M simulated events, ~1Mb/event) ð 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

21st of July 2005Jorgen 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. ~10 9 events/10fb -1 W (200 per second) ~10 8 events/10fb -1 Z (50 per second) ~10 7 events/10fb -1 tt (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.

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)9 Top Quark Physics : top quark mass 10 tt pairs per Tevatron  1 tt pair per LHC qq →tt : 85% gg→tt : 87% width of peak ~10 GeV  m t (stat) ~ 300 MeV (10fb -1 ) fastsim 10fb -1 Most important parameter is the top quark mass (m t ), to be estimated with an accuracy of around  m t ~ 1 GeV/c 2. Golden channel : semi-leptonic tt →bWbW→blvbqq Selection via lepton, miss.E T, 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.

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)10 Top Quark Physics : top quark mass  From t  l + J/  + X decays : → 100 fb -1 gives after selection ~ 1,000 signal events (S/B > 100) ü the large mass of the J/  induces a strong correlation with the top mass ü easier to identify (extremely clean sample) M BR(overall in tt) ~ 5.3 x ü no jet related systematics !! hep-ph/ New method : hep-ex/ correlate the b transverse decay length with m t CMS fast simulation slope

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)11 Top Quark Physics : top versus anti-top  Spin correlations ð the top quark does not loss its spin information before it is decaying into W and b with A =0.431 (gg) and A = (qQ) ð two observables  + (  - ): angle between t(T) direction in the tT c.m. frame and the l + ( l - ) direction of flight in the t(T) rest frame ð fit to double differential distribution ð result (30fb -1 ) : A (stat) = and A (syst) =  Measuring the difference between m t and m T ð almost all systematics cancel when measuring the difference between both ð after several years the precision could be around 50 MeV/c 2 ð what we could learn from that ? CPT violation… ? ð differences between t and T can learn us something about the PDF’s (rapidity distributions)

21st of July 2005Jorgen 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 |V tb | to percent level (s-channel preferred, t-channel dominated by PDF scale uncertainties of ~10%)

21st of July 2005Jorgen 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  defined as : angle between lepton (in W rest frame) and W (in top rest frame) Standard Model prediction : f 0 = m t 2 / (2 m W 2 + m t 2 ) ~ 0.7 and f R ~ 0 (m b ~0) LH: (1±cos  ) 2 Long: sin 2  PYTHIA 5.7, 1 year CMS only W→ev and W→  v Expected uncertainty  stat f 0 =  syst f 0 = estimation of systematic uncertainties conservative most of the time limited by the statistical precision of the effect

21st of July 2005Jorgen 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 . W W   pp→W  cross-section enhanced when anomalous couplings are present p t -spectrum of photon sensitive to anomalous couplings (  =1.5 TeV) p t (  ) (GeV) =0.3,  =0 =0,  =0 =0,  =0.95 (  =2TeV) for 100 fb -1 (  =2TeV )  |  | < 0.1  | | < large improvement for compared to Tevatron BAUR MC generator For ZZ  and Z  couplings both the p T (  ) and the M T (ll  ) spectrum are sensitive to h i V (V=Z,  ) anomalous couplings

21st of July 2005Jorgen 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 A FB and hence sin 2  eff lept : LHC reaches much higher masses Z/  q q e-,-e-,- e+,+e+,+ inverse of e + e - → qq at LEP Precision will exceed the magnitude of the EW corrections up to M ll =2 TeV Rel. exp. uncertainty on  ll (in %) 5% 10% 0% Weak-mixing angle sin 2  eff lept can be determined to  sin 2  eff lept ~ using forward lepton tagging main systematic uncertainty is the knowledge of the PDF’s can also use sin 2  eff lept to constrain the PDF’s

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)16 Parton Probability Functions y = pseudorapidity DGLAP evolution How to find the partons in the colliding protons ? → need for precise PDF(x,Q 2 ) Extrapolate from HERA, but also use the huge LHC data itself Ratio of W + /W - cross-section is related to u(x)/d(x) 0.1 fb -1 differentiate between several models

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)17 Parton Probability Functions The PDF’s for the heavy quarks can also be measured Isolated  with high p T + jet including  Isolated e/  with high p T + jet including  Estimate 5-10% accuracy on PDF‘s limited by fragmentation functions 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.

21st of July 2005Jorgen 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-p T objects)  CP violation  measurements of B s oscillations  rare decays  life-time  B c mesons  etc... Example : ( alternative to lepton-tag method ) CKM angle  via B d 0 →J/  K s 0 in B** ± →B d 0( * )  ± The flavour of B 0 is tagged with  ± Expected precision is  (sin2  )=0.022 (10fb -1 ) (to be repeated with higher trigger thresholds) related to angle  after selection ICHEP’04 : sin(2  ) = ± all B-physics studies require a profound knowledge of the detector performance

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)19 The SM-like scalar Higgs boson can be observed in several physics channels ( depending on its mass m H which is a free parameter of the model, LEP m H > ) Standard Model Brout-Englert-Higgs boson production cross-sectiondecay branching ratios balance between production rate, decay rate and reconstruction efficiency

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)20 Standard Model Brout-Englert-Higgs boson H → ZZ* → 4l H →  qqH → qq  H → WW* →lvlv ttH → ttbb qqH → qq  m H =130,150,170 m H =130 m H =115 m H =140 m H =115 m H =135 signal signal signal 100fb -1 60fb -1 30fb -1

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)21 Combined discovery potential as a function of m H Standard Model Brout-Englert-Higgs boson zoom in low mass region WW  ZZ 5  at 2 fb -1 at 10 fb -1 at 30 fb -1 At 10 fb -1 full 5  coverage from LEP to 800 GeV LEP limit 5  at 10 fb -1 at 30 fb -1 at 60 fb -1  WW/ZZ

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)22 Integrated luminosity needed for 5  discovery as a function of m H Standard Model Brout-Englert-Higgs boson zoom in low mass region 30 fb -1

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)23 Comparing the direct and indirect values of m H Ultimate test of the Standard Model To give m t and m W equal weight :  m W =  m t Goal of LHC experiments :  m t < 1 GeV  m W < 15 MeV   m H /m H < 25 % After a discovery one can use EW measurements to differentiate between SM or MSSM Higgs bosons

21st of July 2005Jorgen D'Hondt (Vrije Universiteit Brussel, CMS Collaboration)24 Outlook for CMS activities  First fast-simulation studies (presented) ð significant improvement in Standard Model measurements ð Higgs boson mass range completely covered after 10fb -1  Current progress within the CMS Collaboration ð created large amounts of dedicated/realistic simulation ð large effort in optimizing our reconstruction methods ð gradually design more advanced analyses techniques ð start studies on detector calibration/alignment (check influence)  Outlook for the near future ð write-up of all the above into a Physics-Technical Design Report ð this will summarize the physics potential of the experiment in great detail ð foreseen by December 2005 (Volume-I) and by April 2006 (Volume-II) P thanks to all CMS collaborators who contributed to these Standard Model studies