Even if the prediction of the Standard Model of particle physics are validated by the experiment at the currently probed energy, a deeper understanding and a better measurement of the Standard Model parameters at higher energy will allow to constrain the theory and search for deviation, highlighting in the same time signs of new physics. Here is a review of the SM related analysis foreseen by ATLAS and CMS detectors at LHC

COGNERAS, E

Even if the predictions of the Standard Model of particle physics are validated by the experiments at the energy currently probed, a deeper understanding and a better measurement of the Standard Model parameters at higher energy will allow to constrain the theory and search for deviations, highlighting in the same time signs of new physics. Here is a review of the Standard Model related analysis foreseen by ATLAS and CMS detectors in the context of the new generation proton-proton collider LHC. 

Eric Cogneras

CiteSeerX

Standard Model at LHC

Cogneras, E.

HAL Clermont Université

Standard model at LHCE. CognerasTo cite this version:E. Cogneras. Standard model at LHC. HEP-MAD 07, 3rd High-Energy Physics Conference inMadagascar, Sep 2007, Antananarivo, Madagascar. 7 p., 2007. <in2p3-00186449>HAL Id: in2p3-00186449http://hal.in2p3.fr/in2p3-00186449Submitted on 9 Nov 2007HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.Standard Model at LHC ∗Eric Cogneras †Laboratoire de Physique Corpusculaire, CNRS/IN2P3Universite´ Blaise Pascal, Clermont-Ferrand, FRANCEOctober 31, 2007AbstractEven if the predictions of the Standard Model of particle physics are validated by the experimentsat the energy currently probed, a deeper understanding and a better measurement of the StandardModel parameters at higher energy will allow to constrain the theory and search for deviations,highlighting in the same time signs of new physics. Here is a review of the Standard Model relatedanalysis foreseen by ATLAS and CMS detectors in the context of the new generation proton-protoncollider LHC.1 IntroductionThe Standard Model of particle physics (SM) has been successfully tested at the energy provided by theLEP and Tevatron colliders. However, many topics remain unclear, especially the electroweak symmetrybreaking mechanism. The aim of the LHC (Large Hadron Collider) is to cover physics at the energy ofthis symmetry breaking mechanism, where evidences of new physics are expected. As we learned fromthe Tevatron, hadron colliders are able to perform precision measurements, as soon as the systematicsuncertainties are understood and under control. Then, the LHC will allow to precisely measure SMparameters in view to :• have a better understanding of SM, performing precision electroweak measurements and Topphysics studies. Especially, a precise measurement of the W boson mass, the Top mass and theWeinberg angle can constrain the mass of the Higgs boson and then fix the limits of the SM;• search for direct and indirect deviation from SM in experimental spectra.To perform such a physics programme, the LHC proton-proton collider has been designed to reachan energy equal to√s = 14 TeV in the center of mass of the collision. A first luminosity phase at1033 cm−2s−1 providing 10 fb−1 per year is foreseen to perform the precision measurements. In a secondphase, devoted mainly to new particles searches, the luminosity will reach 1034 cm−2s−1 providing 100fb−1 of data per year.2 Experimental frameworkAmongst the four detectors on the main ring of the LHC, ATLAS [1] and CMS [2] are two generalpurpose physics detectors allowing to study many physics channels related to the precise measurement∗Talk given in the HEP-MAD 07 conference, 10-15th september 2007, Antananarivo, Madagascar.†On behalf the ATLAS and CMS collaborations.1of SM parameters thanks to there high granularity sub-detectors, covering the whole solid angle. Evenif the technologies used by these two detectors are different, they will reach equivalent precision onmeasurements.Thanks to the very high energy delivered by the proton-proton collider, the cross section of the mainphysical processes are one or two orders of magnitude larger than at the Tevatron. The LHC will be aW, Z and Top quark factory what will reduce the statistical error on measurements, which is the mainsource of uncertainty at the Tevatron. In addition, the large amount of collected data will also be used tounderstand the detector behaviour and control the systematics.Nevertheless, protons beams are not ideal since protons are composite particles, leading to parton-parton collisions carrying only a part of the initial beam energy.3 Precision electroweak measurement3.1 W mass measurementLHC expects to measure the W mass with a precision of 15 MeV/c2. To perform this study, the usefuldecay channel is W → lν , as at the Tevatron, but the main advantage of the LHC is its production rate :60 million of reconstructed W per year at low luminosity.The measurement of the W mass can be performed using several methods :• the W mass can be assessed from the measurement of the MTW /MTZ ratio : in such a way, thesystematics are small but the use of the Z boson reduces the statistics;• CMS uses the transverse momentum of the lepton whose spectrum shape is sensitive to the Wmass. This method, which relies on the well known Z boson spectrum shape, is weakly biasedby the pile-up and suffers from the theoretical knowledge of the transverse momentum spectrumshape of the W boson;• MTW can be used to assess the W mass at low luminosity. This method, which suffers from the pile-up, is traditionally used in ATLAS to cope with the unmeasured pνz . The transverse momentum ofthe neutrino is estimated using the measured plT and the recoil of the W.In both ATLAS and CMS methods discussed here, the W mass is extracted by a fit of the experimentalshape to Monte-Carlo samples simulated with different values of MW .Table 1 summarizes the different sources of uncertainties on the W mass measurement. The statisticalerror is negligible and the systematics come from physics and detector effects reported on the table. Atthe LHC, these systematics will be estimated using other physics channels. For example, the PDF aresensitive to W → eν rapidity distributions (electron and positron rapidity in figure 1). Despite the effectof the detector, the cross section in function of the rapidity will allow to distinguish between various PDFsets.With only one channel of the W decay, the LHC expects to reach a precision on the W mass mea-surement better than 25 MeV/c2 after one year at low luminosity. Combining the channels and bothexperiments, the LHC should reach an uncertainty of 15 MeV/c2. A precise measurement of W mass isone of the challenge of LHC, pushed by the last results from Tevatron which are already very precise(∼ 26 MeV/c2).3.2 Weinberg angleThe Weinberg angle will be measured using the Forward-Backward asymmetry (AFB) which occurs inthe angular distribution of the lepton from the Z boson decay due to the parity violation in neutral current.2source of CDF, RunII, Combined channel LHC [1]uncertainty 200 pb−1 [3] 60 M event, 10 pb−1Statistics 0 MeV/c2 < 2 MeV/c2Lepton scale 17 MeV/c2 15 MeV/c2Energy resolution 3 MeV/c2 5 MeV/c2Recoil model 12 MeV/c2 5 MeV/c2Lepton id. ——— 5 MeV/c2pTW 3 MeV/c2 5 MeV/c2PDF 11 MeV/c2 10 MeV/c2W width ——— 7 MeV/c2Radiative decays 11 MeV/c2 < 10 MeV/c2Background 0 MeV/c2 5 MeV/c2TOTAL 26 MeV/c2 25 MeV/c2Table 1: Source of uncertainties related to the W mass measurement in W → lν channel for LHC (onelepton species, at low luminosity, per experiment after one year) compared to last results from CDF(electron and muon combined channels).Figure 1: Differential cross section for various PDF sets in function of the e± rapidity.3Coupling Current value LHC sensibility(95% C.L., 30 fb−1, 1 experiment)∆gZ1 −0.016+0.022−0.019 0.005-0.011∆κγ −0.027+0.044−0.045 0.03-0.076∆κZ −0.076+0.061−0.064 0.06-0.12λγ −0.028+0.020−0.021 0.0023-0.0035λZ −0.088+0.063−0.061 0.0055-0.0073Table 2: Current value and uncertainty on 5 Triple Gauge Couplings parameters, and expected uncer-tainty at LHC for one experiment after three years of data taking at low luminosity.More specifically, at the Z pole, AFB comes from interferences between vector and axial components ofthe coupling, leading to :AFB = b(a− sin2θW )where a and b are calculated to NLO in QED and QCD.The Z boson is produced by qq¯ fusion. The q¯, coming from the sea, has in average a lower momen-tum. At LHC, the assumption is made that the quark direction is the same as the boost of the Z. Thisassumption is valid for large di-lepton rapidities, this is why Z → e+e− channel is used thanks to thelarger η coverage of the electromagnetic calorimeter.The sensitivity on AFB increasing with forward electrons, cuts are applied on the rapidity of eachlepton and di-leptons, leading to a statistical uncertainty on AFB of the order of 2.3×10−4. The statisticaluncertainty on the Weinberg angle is then 1.4×10−4 [4], of the order of the world average error. To reacha global uncertainty of the order of the current one, the systematics have to be small enough. So, errorsdue to the parton density function (PDF), the lepton acceptance and efficiency, and the effects of higherorder QCD have to be well estimated, and under control. This will be only reached after few years ofdata taking.3.3 Triple gauge boson couplingsLHC planned also to probe the non abelian structure of the SM from the measurement of Triple GaugeCouplings leading to WW, ZW, γW production in the final state. Thus, the measurement of the TripleGauge Couplings will be assessed from the diboson cross sections, the shape of high pT bosons spectrumor the production angle between the two final state bosons.In the SM framework, only the WWγ and WW Z interactions are allowed, leading to 14 possiblecouplings. Among them, only 5 independent, CP conserving, gauge invariant preserving are used. Atthe SM tree level, each of these parameters is equal to zero. Their behaviour in function of the energy inthe center of mass is however different : ∆gZ1 , ∆κγ and ∆κZ are growing with√s whereas λγ and λZ aregrowing with s what is a big advantage for the LHC.Table 2 reports the current values and LHC expected sensitivity for each parameter : the LHC expec-tation are similar to the current world average uncertainty [5].4 Top quark physicsDiscovered in 1995, the Top quark, whose high mass is still a mystery, completes the three familystructure of the SM. The large amount of Top events produced at LHC will allow to measure mostof the Top properties.4tt¯ Channel Luminosity (fb−1) ∆σtt¯/σtt¯semi-leptonic 10 9.7%(syst)±0.4%(stat)±3%(lumi)di-lepton 10 16%(syst)±1.3%(stat)±3%(lumi)full hadronic 1 20%(syst)±3%(stat)±5%(lumi)Table 3: Precision on the tt¯ cross section measurement expected by CMS.The Top quark can be produced by strong interaction leading to a t t¯ pair in the final state, with a crosssection of about 833±100 pb at the LHC [6], leading to 8 million of Top pairs per year at low luminosity.The Top quark can also be produced in a single way from weak interaction with a cross section of 330 pb.The signature of tt¯ events is dominated by the W decay leading to two quarks or a lepton/ν pair. So,the three possible final states are :• the fully hadronic channel where both W decay into quarks. Even if this channel is the dominantone, it suffers from a huge background mainly from QCD.• the di-lepton channel where both W decay into lepton/ν pair. This channel benefits from a verysmall background but the two neutrinos make difficult the complete reconstruction of the Topquarks.• the golden channel is the semi-leptonic one where, in the leptonic side, the lepton is used to triggerthe event, and where the hadronic Top is completely reconstructed on the other side. This channelbenefits from a large event yield and a small background.In the golden channel, the events are selected requiring at least 4 jets with pT > 40 GeV/c, one electron(or muon) with pT > 20(25) GeV/c according to the trigger menu and a missing transverse energy above20 GeV.4.1 Top quark mass measurementFor the Top quark mass measurement, ATLAS foresee to reconstruct t t¯ events with early data withoutapplying b-tag algorithms which will not be optimized at the LHC start. Top quarks are reconstructedusing the 3 jets whose the sum of the pT is the highest [7], with a reconstruction efficiency of about 5 %.When using the b-tagging, requiring the presence of 2 b-jets among the jets, 100 pb−1 of data lead toa significance of S/B = 100 and an efficiency of roughly 1 %. The precision on the Top mass is then ofthe order of 1.3 GeV/c2 [8]. An other method, using both leptonic and hadronic sides and a kinematicalfit can reach a precision of the order of 1 GeV/c2 [8] on the Top mass measurement.4.2 tt¯ cross-section measurementThe tt¯ events reconstruction will also be used to measure the production cross section. These studieshave been performed for each of the 3 channels of t t¯ decay. The semi-leptonic channel gives the bestprecision on the cross section measurement, with the best reconstruction efficiency. Other channels leadto a precision between 17 % and 21 % on this measurement [9], as shown on table 3.4.3 Top polarizationThe Top polarization will be measured through the polarization of the W boson coming from the t →W bvertex. So, the three polarizations F0, FL and FR will be measured using the angular distribution of the5Figure 2: Differential cross section in function of cosθ ∗l in the Standard Model framework.Standard Model Error(mt = 175 GeV/c2) ±stat ± systF0 0.703 ±0.004±0.015FL 0.297 ±0.003±0.024FR 0.000 ±0.003±0.012(mb = 0 GeV/c2)Table 4: Expected statistical and systematics uncertainties on Top polarization parameters at LHC (AT-LAS).leptons :1ΓdΓd cosθ ∗l=38 (1+ cosθ∗l )2FR +38 (1− cosθ∗l )2FL +34 sin2 θ ∗l F0θ ∗l being the angle between the lepton in the W rest frame and the W in the Top rest frame.Figure 2 shows the expected differential cross section in function of cosθ ∗l in the Standard Modelframework, leading to the measurement of F0, FL and FR reported in table 4, with the statistical andsystematics uncertainties foreseen by ATLAS experiment [10].4.4 Single Top cross-section measurementThe three single Top production processes will be measured at LHC. Table 5 gives the expected uncer-tainty on the cross section measurement for both ATLAS and CMS experiments, for each single Topchannel.5 ConclusionThe precise measurement of electroweak parameters, as well as the Top physics studies allowed by theLHC will lead us to a better understanding of the Nature, providing constraints on the SM. With fewyears of data taking at low luminosity, both ATLAS and CMS experiments can reach a precision on thesemeasurements of the order of the current world average precision, what will improve the sensitivity tonew physics phenomena.6Channel ∆σ/σ ATLAS ∆σ/σ CMS(30 fb−1) [11] (10 fb−1) [9]t-channel 12%(syst)±1%(stat)±5%(lumi) 8%(syst)±2.7%(stat)±5%(lumi)Wt-channel 14%(syst)±1.5%(stat)±5%(lumi) 23.9%(syst)±8.8%(stat)±9.9%(MC)s-channel 16%(syst)±12%(stat)±5%(lumi) 31%(syst)±18%(stat)±5%(lumi)Table 5: Precision on the single Top cross section measurement expected by ATLAS and CMS.6 AcknowledgmentsMany thanks to Stephan Narison and the local organizers for this enjoyable conference. I thank also theATLAS and CMS collaborations for giving me the opportunity to speak on there behalf in HEP-MAD 07.I’d like to acknowledge the speakers and auditors for the friendly atmosphere and the fruitful discussions.References[1] The ATLAS Collaboration, ATLAS Technical Proposal, 1994, CERN/LHCC/94-43.[2] The CMS Collaboration, CMS Technical Proposal, 1994, CERN/LHCC/94-38.[3] T. Aaltonen et al., First Measurement of the W Boson Mass in Run II of the Tevatron, 2007,hep-ex/0707.0085.[4] K. Sliwa, S. Riley, U. Baur, Effects of possible extensions to rapidity coverage of the ATLASdetector on the determination of sin2Θe f f (M2Z)., 2000, ATL-PHYS-2000-018.[5] Tom LeCompte, Precision Electroweak Measurements at the LHC, 2007 Aspen Winter Con-ference on Particle Physics Program, {http://conferences.fnal.gov/aspen07/monday/LeCompte_PrecisionEWK.ppt}.[6] Bonciani R. et al., Nucl. Phys. B529 (1998).[7] S. Bentvelsen, M. Cobal, Top studies for the ATLAS Detector Commissioning, 2005, ATL-PHYS-PUB-2005-024.[8] I. Borjanovic et al., Investigation of top mass measurements with the ATLAS detector at LHC,2005, [hep-ex/0403021].[9] The CMS Collaboration, CMS Physics TDR: Volume II (PTDR2), Physics Performance, 2006,CERN-LHCC-2006-021.[10] F. Hubaut, E. Monnier, P. Pralavorio, V. Simk, K. Smolek, ATLAS Collaboration, ATLAS sensi-tivity to top quark and W boson polarization in t t¯ events, 2005, SN-ATLAS-2005-052.[11] A. Lucotte, A. Llres, F. Chevallier, Prospects for single top cross-section measurements in ATLAS,2007, ATL-PHYS-PUB-2007-005.7

Standard model at LHC

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Standard Model at LHCEric COGNERAS, LPC Clermont-FerrandOn behalf of the ATLAS and CMS collaborationsHEP-MAD 07, Antananarivo, Madagascar2007, september 14Motivation• SM successfully tested at current energy• LHC ⇒ prospect physics at higher energy :u c td s bγW      – Able to search directly beyond SMBut also precise measurements of SMeνeµνµτντ gZ–      parameters• Goal for SM physics:    – Deeper understand the SM with :• Precision EW measurements (MW, sin2θW ,…)• Top physics (mass,cross section,… measurement) – Indirect estimate the Higgs massU i M i 2θ i t• s ng W, mTop, s n W prec se measuremen– Search for deviation from SM14/09/2007 Eric COGNERAS - Standard Model @ LHC 2Experimental FrameworkThe LHC– CERN (Geneva) – pp collision @ √s = 14 TeV (10 × Tevatron)– Luminosity :EW precisionmeasurement • Low luminosity phase L∼1033 cm-2s-1 (2008-2009?) [10 fb-1/year : 10× TV]• High luminosity phase L∼1034 cm-2s-1 (2010?-X) [100 fb-1/year : 100×TV]ExperimentsATLAS and CMS ⇒ general purpose physicsLHCb ⇒ b physicsALICE ⇒ heavy ion physics14/09/2007 Eric COGNERAS - Standard Model @ LHC 3Experimental Framework• Tracking (|η|<2.5, B=2T) :– Si pixels and stripsT i i R di i D ( /• Tracking (|η|<2.5, B=4T) :– Si pixel and strips– rans t on a at on etector e πseparation)• Calorimetry (|η|<5) :EM Pb/LAr with Accordeon shape   • Calorimetry (|η|<5) :– EM : PbWO4 crystals– HAD : brass/scintillator (central,end-cap), –  : – HAD : Fe/scintillator (central), Cu-W/Lar(forward)• MuonSpectrometer (|η|<2 7) :Fe/Quartz (forward)• MuonSpectrometer (|η|<2.5) :– return yoke of solenoid instrumented14/09/2007 Eric COGNERAS - Standard Model @ LHC 4.  – air-core toroids with muon chamberswith muon chambersp-p collisionsCross section and Event rateProcess σ (nb) Evt/y (Low L:10 fb-1)Minimum Bias 108 ∼ 1015Inclusive jets (pT>200 GeV)100 ∼ 109W→lν (l=e,µ) 30 ∼ 108Z→e+e- 1.5 ∼ 107tt 0.83 ∼ 106bb 5.105 ∼ 1012d f d l h1 or 2 or ers o  magnitu e arger t an TevatronLHC is a W, Z, top factory :• small statistical errors in precisionx2x      measurements• large samples for studies of systematic ff t ( lib ti d t t l )Hadron collider problem :114/09/2007 Eric COGNERAS - Standard Model @ LHC 5e ec s ca ra on an  sys . con ro s  PDF to be better knownSM physics @ LHC• W/ Z physics (precision EW measurement)– Parameters related to indirect MH measurement : • W mass and width   • sin²ΘW– Constraints on the PDF• W/Z inclusive cross section as well as W/Z+jets       • W rapidity– Measurement of gauge boson pair production• Triple Gauge Boson Coupling• Top physics– Parameters related to indirect MH measurement : • Top mass/cross section  – Deeper understanding of Top quark :• Top spin correlation, probe of the Wtb vertex, single Top cross section, Top charge• QCD (→ see Albert talk on tuesday)      • Higgs boson direct search• B physics• …14/09/2007 6Eric COGNERAS - Standard Model @ LHCPrecision EW MeasurementMW measurement• LHC expects :Event selection:• 1 isolated lepton (e,µ) q   δMW < 15 MeVpT> 25 GeV in |η|<2.4• missing ET > 25 GeVN j t ith 30 G Vq’• W channel : same as the Tevatron⇒ using W→lν decay• o e  w pT>  e  •Recoil |u|< 20 GeVBut LHC statistics is higher (60M recons. W→lν @ low Lumi [10× TV])• Several methods available: 9 R=MTW / MTZ spectrum ⇒ Small syst, sample /109 pTl spectrum ⇒ pile-up , theo. know. of PTW9 MTW ⇒ high stat, pile-up14/09/2007 7Eric COGNERAS - Standard Model @ LHCPrecision EW MeasurementMW measurement9 Use Transverse mass to 9 Use the knowledge on the Z boson to constrain the W massμφ νυ )cos1(2 , elppM llT =Δ−=cope with unmeasured pLν9 l t h i iti t, ,l Z l WZT TWMP PM=,TTW  ,9 pTν from pTl & recoilpT spec rum s ape s sens ve o MW9 pTν not necessaryW mass : fit exp. shape to MC sample with different Values of MW14/09/2007 8Eric COGNERAS - Standard Model @ LHCPrecision EW MeasurementMW measurement : systematics¾ LHC goals : W→lν : one lepton species low L per experiment after 1 year      , ,  ,   source CDF RunII, combined channel LHC200 pb-1 60Mevts, 10fb-1stat. error : negligibleStatistics 0 MeV <2 MeVLepton scale 17 MeV 15 MeVEnergy resolution 3 MeV 5 MeVsyst. error :•MC modelling of phys.•detector responses Recoil model 12 MeV 5 MeVLepton id. --------- 5 MeVPTW 3 MeV 5 MeVPTW spectrumPDFW id hZ→llLHC dataZ ll R TphysicsPDF 11 MeV 10 MeVW width --------- 7 MeVRadiative decays 11 MeV <10 MEV w tW rad. decaysBackground→ , , evatronTheo. calculationMCdetector   Background 0 MeV 5 MeVTOTAL 26 MeV <25 MeVlepton  E&p scaleLepton resolutionRecoilZ→ll, E/p for e±Z→ll, E/p for e±Z→ll14/09/2007 9Eric COGNERAS - Standard Model @ LHC¾ Combining channels and ATLAS/CMS exp., should reach    ΔMW ≈ 15 MeV   Precision EW MeasurementDetermination of sin²ΘWZ/ * l lParity violation in neutral current ⇒ Asymmetry in the angular distribution of leptons from Z decayUse AFB  in p-p→ γ → + -Test of the Standard Model(θ-dependence of cross-section) (universality)All eventsEvents with quark direction At the Z pole, AFB comes from the interference of vector and axial component of the coupling2( i )A b θ correctly estimatedWhere a, b calculated to NLO QED and QCDAssumption for p-p colliders : the quark direction is s nFB Wa= −the same as the boost of the ZCorrect for large di-lepton rapiditiesOnly EM calorimeters provide the required 14/09/2007 10Eric COGNERAS - Standard Model @ LHClarge η-coverage (Z→e+e-)Precision EW MeasurementDetermination of sin²ΘWEvent selection: Sensitivity increasesOnly Forward Electrons• pTe > 20 GeV •85.2 < Mee < 97.2 GeVwith forward electrons• ResultsAll Events     t + A i 2θL = 100 fb-1y cu s – e e-(|y(Z)| > 1)∆ FB(Stat)∆s n W(Stat)|y( l1,2 )| < 2.5 3.0 x 10-4 4.0 x 10-4|y( l1 )| < 2.5 +     |y( l2 )| < 4.92.3 x 10-4 1.4 x 10-4• Current error on world average 1 6x10-4     .• need small systematic error :• PDF uncertainty,• precise knowledge of lepton acceptance and efficiency14/09/2007 11Eric COGNERAS - Standard Model @ LHC      • effects of higher order QCDPrecision EW MeasurementTriple gauge boson coupling¾P b th b li t t f SMro e e non a e an s ruc ure o  • LO Feynman diagram :qV1, V2, V3 = Z, W, γ→ WW, ZW, Wγ• Diboson final states have predictable σproduction and manifest the gauge boson couplingl h d l d ll dq’• 14 possible WWγ and WWZ coupling• In SM, on y c arge coup ing WW γ an  WWZ are a owes-channel• Use 5 independent, CP conserving, EM gauge invariance preserving couplings : g1Z, κγ, κZ, λγ, λZ TGC manifest in :– At SM tree level, g1Z=κγ=κZ=1 and  λγ=λZ =0– λγ and λZ grow with s ⇒ big advantage for LHCΔκ = κ 1 Δg Z = g Z 1 Δκ = κ 1 grow with √s• Cross section enhancement• High pT(V=W, Z, γ)• Production angle– γ γ- , 1 1  - , Z Z -    14/09/2007 12Eric COGNERAS - Standard Model @ LHCPrecision EW MeasurementTriple gauge boson couplingExemple of WZ production   • Use only leptonic final state• Event selection:• Exactly 3 leptons with pT>25 GeV• At least one pair of leptons with same flavour and opposite charge and |mll-MZ|<10 GeV• …SMCoupling Present Value LHC Sensitivity(95% CL, 30 fb-1, 1 exp)Δg1Z 0.005-0.011Δκγ 0.03-0.076022.0019.0016.0+−−044.00450027.0+−Δg1Z = 0.05ΔκZ 0.06-0.12λγ 0.0023-0.0035.−020.0021.0028.0+−−061.0064.0076.0+−−14/09/2007 13Eric COGNERAS - Standard Model @ LHCλZ 0.0055-0.0073063.0 061.0088.0 +−−QCD-oriented MeasurementMeasurement of W/Z cross sectionsEstimation of the cross sectionZ→μμ∫=→+→ LdtXWZpp totalBackgroundCandidates )f-(1Nεμμσ )/(    Event selection:Z : 2 isolated µ, pTµ > 20 GeV, |η|<2, 84<Mµµ<99 GeV,... W : 1 isolated µ pTµ > 25 GeV |η|<2 40<MT(µ ETMiss)<200GeV• Results (L=1 fb-1 [~600k  Z→μμ, ~6M W→μν])σ(ZÆμμ + X) = 1160 ± 1.5 (stat) ± 27 (syst) ± 116 (lumi) pb  ,   , , , ,... CERN/LHCC 2006-021CMS TDR 8.2σ(WÆμν + X) = 14700 ± 6 (stat) ± 485 (syst) ± 1470 (lumi) pbAlready dominated by systematics W→μνSystematics come mainly from theory(acceptance+PDF uncertainty).At a later stage these processes can be used as l i it it (E l i it 5%)14/09/2007 14Eric COGNERAS - Standard Model @ LHCum nos y mon or rror on um nos y: ~QCD-oriented MeasurementConstraints on PDF using W rapidity distributions++WdAt LHC i t l t i t iνν−− →→→→eWudeue- rapidity e+ rapidityy•  , exper men a  uncer a n y s dominated by systematics (large event production)• The theoritical uncertainties areW→eν)/d  dominated by PDFs¾ Exp. uncertainty sufficiently small to distinguish between different PDF sets GeneratedGeneratedydσ(W   ; PDF error sensitive to W→eν rapidity distributionCTEQ61CTEQ61W→eν)/dy ¾ e± rapidity spectrum shape sensitive to gluon shape parameter (valence quark density)MRST02ZEUS02MRST02ZEUS02ydσ(WReconstructed Reconstructed; Probe low-x gluon PDF at Q²=MW2; PDF uncertainties only slightly degraded after detector simulation and 14/09/2007 15Eric COGNERAS - Standard Model @ LHCselection cutsTop Quark Physics• Direct discovery  in 1995 (Fermilab)• Completes the 3 family structure of the SMV hi h 175 G Vl+Production Top Mass W helicityAnomalous CouplingsTop SpinTop Width• ery g  mass ∼  eτhad = ΛQCD-1 >> τdecay⇒ No Top Hadron : Opportunity to t bW+νcross-sectionResonance productionProduction CP violation Top Chargemeasure parameters of a free quark• Production at LHC: tYkinematicsTop Spin PolarizationR / SM D s_• tt production+X|Vtb|Branching Ratiosare non  ecay• single top production(90%) (10%)σ ~ 833±100pb @ 14TeV (NLO)8M evts/y @ Low Lum   14/09/2007 16Eric COGNERAS - Standard Model @ LHCt-channel Wt-channel W* (s-channel)σ ~ 250 pb σ ~70pb σ ~ 10 pbtt Physics• Decay : Determined by decay of Ws• Fully hadronic channel (44 %)• Di-leptonic channel (5 %)Golden ChannelW (h d) • Semi-leptonic channel (30 % no τ)≥4 jets (ΔR=0.4) pT>40 GeV t (had) a• Selection :/pT>20 (25) GeV• Only e µ events⇒ Trigger2 b-jets• large event yield• small backbround14/09/2007 Eric COGNERAS - Standard Model @ LHC 17pT>20 GeV t (lep)tt PhysicsTop quark mass measurement (Invariant mass spectrum of reconstructed Had. Top : most straightforward technique)      Without b-tagging (early data) With b-taggingSelection efficiency : ε 5 3 %Event topology: 3 jets with highest ∑ pT100120S/B=O(100)Very small SM Bck Top signalber of tsL=O(100) pb-1(few days @ 1033 cm-2s-1)= .  (ATL-PHYS-PUB-2005-024) 406080W+jets backgroundNumbEventL=100 pb-1(1 day @ 1033 cm-2s-1)Signal (MC@NLO)Full simulationEvents0 50 100 150 200 250 300 350 400020Top mass (GeV)Selection efficiency :  W+n jets (Alpgen) + combinatorialIn this way, Δm(top) ~1.3 GeVWhen Kinematical Fit (using the leptonicε=1-2%14/09/2007 Eric COGNERAS - Standard Model @ LHC 18Mjjj (GeV)  side) is used, Δm(top) ~1 GeVtt Physicstt cross section CERN/LHCC 2006-021CMS TDR 8.2• Semi-leptonic channel (tt→bbqqμνl): L=10fb-1Δσtt/σtt= 9.7%(syst)±0.4%(stat)±3%(lum)εreco = 6.3%• Di-leptonic channel (tt→bb lνl lνl): L=10fb-1Δσtt/σtt= 11%(syst)±0.9%(stat)±3%(lum)εreco = 5% (S/B=5.5) With Tau leptons (tt→bb τντ lνl, τ →hadrons):Δσtt/σtt= 16%(syst)±1.3%(stat)±3%(lum)[ εreco=2%, S/B~1, ετ-tag=30% ]• Fully Hadronic channel:Δσtt/σtt= 20%(syst)±3%(stat)±5%(lum)L=1fb-114/09/2007 Eric COGNERAS - Standard Model @ LHC 19εreco=2%, S/B<1/9 (QCD) tt PhysicsTop polarizationTest the t→bW decay vertex      Measure W polarization (F0, FL, FR) through lepton angular distribution in W cm system:(Eur.Phys.J.C44S2 2005 13-33)SM Error (±stat ±syst)(Mt=175 GeV)L=10fb-1Γ/dcos(θl*)Semilep. +Dileptonic 0.2970.703± 0.003 ± 0.024FL± 0.004 ± 0.015F0(1/Γ)dΓ• Syst ( E m FSR )0.000(mb=0)± 0.003 ± 0.012FRcos(θ *)14/09/2007 Eric COGNERAS - Standard Model @ LHC 20 b-jet, top,• δF0/ F0 ~ 2% ;  δFR ~ 0.01lsingle Top PhysicsProduction cross sectionCommon feature:1 lepton, pT>25GeV/cHigh Missing ET≥2 jets (at least 1 b-jet)     (ATL-PHYS-PUB-2007-005)L=30fb-1 Separate Channels by (Nj,Nb) in final state:t-channel: Stat: 7000 events (S/B=3)(Nj=2,Nb=1) Δσ/σ= 12%(syst)±1%(stat)±5%(lum)Wt-channel: Stat: ε~1% (S/B=15%)(Nj=3,Nb=1) Δσ/σ= 14%(syst)±1.5%(stat)±5%(lum)s-channel: Stat: 1200 events for tb (S/B=10%)(Nj=2,Nb=2) Δσ/σ= 16%(syst)±12%(stat)±5%(lum)t-channel:     Δσ/σ= 8%(syst)±2.7%(stat)±5%(lum)Wt-channel: Δσ/σ= 23 9%(syst)±8 8%(stat)±9 9%(MC)L=10fb-1 (CERN/LHCC 2006-021, CMS TDR 8.2)14/09/2007 Eric COGNERAS - Standard Model @ LHC 21  . . .s-channel:     Δσ/σ= 31%(syst)±18%(stat)±5%(lum)Conclusion• Precision measurements are possible with hadron collider, as demonstrated by the Tevatron• LHC will prospect higher energy physics:Detector to be understood with early data;Hi h l i itg er um nos y;Better S/B ratio• LHC goals are ambitious–  δMW < 15 MeV–  δmtop < 1 GeVδ i 2θ ~ 10 4– s n W  -But reachable …as soon as the detectors performances and the systematics will beunderstood14/09/2007 22Eric COGNERAS - Standard Model @ LHCBack-up SlidesPrecision EW MeasurementMW measurement9 Simple and powerful in principle : consider pTll i b Z d W dspectrum corre at on etween  an   ecayCMS NOTE 2006/0619stat. error negligible (~2 MeV)9 BUT need to predict the spectrum precisely !14/09/2007 24Eric COGNERAS - Standard Model @ LHCtt PhysicsKinematical Fit (use leptonic side)– Minimization of a χ² function with constraints on W and Top masses           2 2 222   , , ,  meas fit meas fit meas fit meas fiti i i i i i i ii i ii jets i jets lepton i x y zE iE E P Pν νη ϕ νη η ϕ ϕχσ σ σ σ= = =⎛ ⎞⎛ ⎞ ⎛ ⎞ ⎛ ⎞⎛ ⎞− − − −⎜ ⎟= + + +⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎝ ⎠ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎝ ⎠∑ ∑ ∑; Reduces FSR systematics2 2hfitPDG PDGjjb Topjj W l WW W tM MM M M Mνσ σ σ⎛⎛ ⎞ −− ⎛ ⎞−+ + + ⎜⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜⎝ ⎠⎝ ⎠ ⎝2 2lfitjjb ToptM Mσ⎞ ⎛ ⎞−+⎟ ⎜ ⎟⎟ ⎜ ⎟⎠ ⎝ ⎠  ; Cleaner event sample (using a cut on χ²); measure mtop as a function of χ²)2 (GeV/cfittopM185190 2 =173.9-2.072fitMf tM170175180 χ⋅topuncertainty Δm(top) [GeV]Hadronic TopΔm(top) [GeV]Kinematical Fitli ht j t l (1%) 0 2 0 22χ0 0.5 1 1.5 2 2.5 3 3.5 4160165ATLAS Preliminaryg - e  nergy sca e . .b-jet nergy scale (1%) 0.7 0.7FSR 1 0.514/09/2007 Eric COGNERAS - Standard Model @ LHC 25TOTAL 1.3 0.9tt PhysicsTop spin correlationTesting the tt Production cross sectionAlthough t and t are produced unpolarized their spins are correlated    -σ(tLtL) + σ(tRtR) - σ(tLtR) - σ(tRtL)σ(tLtL) + σ(tRtR) + σ(tLtR) + σ(tRtL)A=A(LO)A(NLO)0.3190.326SM:φqOther angular distributions:1  dN        1( 1 – A α α cosφ=l+,νtlqt AD(LO)A (NLO)-0.2170 237SM: αX=spin analysing f XN dcosφ 2   D X X´  )14/09/2007 Eric COGNERAS - Standard Model @ LHC 26D - . power  o  tt PhysicsTop spin correlationA) Spin correlations and angular distributions: L=10fb-1(Eur.Phys.J.C44S2 2005 13-33)• Semileptonic + Dileptonic• Syst (Eb jet mtop FSR)0.42SMMtt<550 GeV±0.014 ±0.023AError (±stat ±syst)  - , ,• ~4% precision-0.29 ±0.008 ±0.010AD (CERN/LHCC 2006 021 CM TDR 8 2)B) Spin Asymmetries can also be used (X-check) - , S  .l νtθl,νqAN(cosφ > 0) - N(cosφ < 0) 1Ã,tθq(for L=10fb-1 precision A,AD below 10% )      N(cosφ > 0)  +  N(cosφ < 0)= - ADαXαx´2xx´14/09/2007 Eric COGNERAS - Standard Model @ LHC 27(hep-ex/0605190, subm. to Eur.Phys.J.C)tt PhysicsProbe the Wtb vertexB) Anomalous Couplings in the  t→bW  decay(PRD67 (2003) 014009, mb≠0)Angular Asymmetries: AFB, A+ and A-AFB [t=0]  A± [t=  (22/3-1)]±A-AFBA+SM(LO):14/09/2007 Eric COGNERAS - Standard Model @ LHC 28cos(θl*)tt PhysicsProbe the Wtb vertexB) Anomalous Couplings in the  t→bW  decaySM(LO)1 l: ρL=0.423ρR=0.0005 (mb≠0)σ Resu ts:14/09/2007 Eric COGNERAS - Standard Model @ LHC 29

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