Electroweak measurements at the LHC

Transcription

1 Electroweak measurements at the LHC!!! Samira Hassani CEA- Saclay, IRFU/SPP 21 May 2013

2 2 Success of Run Excellent collider performance :! 23 fb -1 luminosity delivered in 2012! Excellent detector performance :! Operational efficiency ~96%! Robust and high reconstruction efficiency in presence of pile-up! Physics highlight of the run :! Discovery of a Higgs-like particle! We are beginning to probe its properties! Gigantic amount of work on searches for SUSY, extra dimensions,! Null so far! Insightful Standard Model measurements have been performed! Analysis of full 2012 sample still in early stages!

3 Standard Model physics 3 Important on their own and as foundation for Higgs and New Physics searches! Fundamental milestones in the rediscovery of the Standard Model at 7 TeV! Powerful tools to constrain quark,gluon distributions inside proton (PDF)! Zà ll is gold-plated process to calibrate the detector to the ultimate precision! (E and p scales and resolutions in EM calo, tracker, muon spectrometer; lepton identification,...)! Precision tests of the standard model are enabled by an excellent performance of the ATLAS and CMS detectors! One important ingredient enabling success of the Standard Model physics analyses at the LHC is the accurate determination of the luminosity which is measured to better than 4%! Standard Model predictions at the LHC require higher order QCD calculations and knowledge of the proton structure!

4 4 Overview Observables that are really Electroweak (EWK)! Forward-Backward Asymmetries! dσ/dm from Drell-Yan! Triple gauge couplings! Observables that use EWK bosons to probe the structure of the hard interactions! Inclusive cross-section of W and Z! Ratios of W/Z, W + /W -! Charge Asymmetries! V+jets (V=W,Z)!!

5 LHC data LHC performance impressive! But this was possible only by running with 50ns bunch spacing and more protons per bunch than nominal! Very high average number of interactions excellent for discovery reach, but not so good for precision EW physics! p p Z->µµ events with 25 reconstructed vertices (Atlas) More collisions per crossing than expected! Challenge for Jets (energy scale, resolution) and Missing Et! Simulated in MC! 5

6 ATLAS Detector Performance Stability of EM calorimeter response vs time (and pile-up) <0.1% Electron reco ε measured with Zà ee Muon reco ε measured with Zà µµ Precision tests of the standard model are enabled by an excellent performance of the detector! e, μ identification efficiency is understood to ~ 1% accuracy with high background suppression! Calorimeter calibration / spectrometer scale are known to better than 1% precision! Jet energy scale known to better 2.5% for central jets with 60< p T < 800 GeV! LHC luminosity is known to 2.8% accuracy! 6

7 Analysis methods proton - (anti)proton cross sections Production cross-sections differ by orders of magnitude between signal and potential background! σ tot Tevatron LHC Use leptonic decays of W and Z to separate signal from background! Require isolated high p T lepton! Require high missing energy when ν involved! Use «data-driven» background estimations (side bands, control regions, fake factors ) for all jet-induced backgrounds! MC simulations (used for lepton efficiency and resolution) validated on data by «tag and probe» methods! σ (nb) σ jet (E T jet > s/20) σ W σ Z σ jet (E jet T > 100 GeV) M H =125 GeV WJS2012 σ b σ WW σ σ { t ZZ σ ggh σ WH σ VBF s (TeV) With 20 fb 8 TeV,! ~ 400 millions Wà lν! ~ 8000 WWà lνl'ν! (l = e and µ)! events / sec for L = cm -2 s -1

8 Cross sections at the LHC Standard Model predictions at the LHC require higher order QCD calculations and knowledge of the proton structure! 8

9 9 W and Z production at LHC W and Z production at LHC proceeds at the hard scattering level and first order via collisions of a valence quark (u,d) and a sea anti-quark (Q 100 GeV):! u + d(s)! W + u + u! Z d + u(c)! W " d + d! Z Since parton fractions in this process are typically 10-3 < x < 10-1 : sea-sea qq contributions are also important! Leading order relation between rapidity y and x 1, x 2 :! W production in pp collisions is globally charge asymmetric:! x 1,2 = M ll s e±y ll pp has 2X more (udbar) than (dubar) collisions due to uud valence quark content of proton! sea quark-sea quark charge symmetric production dilutes W + /W ratio from 2 to ~1.4!

10 10 Cross section definitions Measurements are corrected to consistently defined truth level to allow proper theory comparisons! Measure fiducial cross section (with minimal phase space extrapolations) and total cross section! efficiency corrections! Acceptance! Cross sections are given for three lepton definitions:! bare leptons, after QED FSR! dressed leptons: bare leptons recombined with! QED FSR photons in cone ΔR < 0.1! born leptons, before QED FSR (usually used for e μ channel combination)!

11 W and Z cross sections 7 TeV cross sections measured with 1% precision (with 36 pb -1 )! From pqcd prediction, expect an increase of the cross section of % from 7 to 8 TeV! Good agreement with NNLO prediction! Discriminating power against different PDF sets! ATLAS points overlap with CMS in the plot@7tev! 11

12 12 Connection with the PDF ATLAS fiducial cross sections W,Z TeV data! CMS total cross sections W,Z TeV data! Data is becoming more discriminating.!

13 Ratio of W and Z cross- sections Ratios: W+/W and W/Z production cross sections are insensitive to luminosity and other sources of uncertainties (2% precision)! provide precision test of perturbative QCD and proton PDFs! For σ W /σ Z PDF errors are reduced, the ratio is sensitive to s /d densities ratio! Measured Theory NNLO ATLAS 7 TeV ± (stat) ± (syst) ± (acc) CMS 7 TeV ± 0.07 (stat) ± 0.08 (syst) ± 0.16 (th) ± 0.04 CMS 8 TeV ± 0.11 (stat) ± 0.23 (syst) ±

14 W- lepton charge asymmetry This measurement is very sensitive to PDFs as most uncertainties cancel in the ratio! It tells us about the valence quarks! This translates into a difference in predictions for the W-lepton asymmetry pseudo-rapidity spectrum! A W =! W +!! W!! W + +! W! A W " u! d u + d " u V! d V u V + d V + 2u sea ATLAS and CMS results complementary! to other LHC measurements! ATLAS, CMS: Medium, small-x region,! light quarks/antiquarks! LHCb: high rapidity data: small-x region! Discrimination beteween PDF at low η CMS clearly disfavour MSTW2008! (MSTW have addressed this in more! recent versions of their PDFs)! 14

15 15 High Drell- Yan cross section (1) Excellent test of perturbative QCD within SM, using latest NNLO PDFs and NLO EWK corrections! Drell-Yan differential cross section measured in 116 < m ee <1500 GeV (E T >25 GeV, η <2.5)! Dominant uncertainties :! Background estimate ( %)! Electron reconstruction and identification (2.8-3%)! Electron energy scale and resolution ( %)! Measurement limited by the statistics for m ee >400 GeV!

16 High Drell- Yan cross section(2) Good agreement between shape in data with PYTHIA, and SHERPA! Good agreement between shape in data and predictions of perturbative QCD at NNLO (FEWZ), within the uncertainty, with all the PDF sets considered.! Comparing results with and without photon-induced background (γγà e + e - ), it is observed that this contribution is of similar size to the sum of the PDF and α s uncertainties! 16

17 17 Differential and double- differential Drell- Yan cross section Low mass! High mass Excellent agreement on several orders of magnitude with the NNLO theoretical predictions! Double differential cross section normalized to the Z peak region and Y < 2.4! d 2 σ /dmdy measurements are compared to the predictions of NNLO FEWZ + Different PDF sets à Can be used to constrain PDFʼs!

18 18 Z/γ* transverse momentum (dσ/dφ η (ll)) Use φ η variable to probe modelling of p T of Z boson in MC (ResBos(NNLL) and FEWZ)! Has advantage that angular resolution is better than p T resolution! φ η is highly correlated with a T / Q T! tan(! acop / 2)sin" *! * " tan(! acop / 2)sin" * θ* scattering angle of the leptons! relative to the proton beam direction in the dilepton rest frame!

19 19 Z/γ* transverse momentum (dσ/dφ η (ll)) Use φ η variable to probe modelling of p T of Z boson in MC (ResBos(NNLL) and FEWZ)! Has advantage that angular resolution is better than p T resolution! φ η is highly correlated with a T / Q T! tan(! acop / 2)sin" *! * " tan(! acop / 2)sin" * θ* scattering angle of the leptons! relative to the proton beam direction in the dilepton rest frame! Data-RESBOS difference within 2% for φ*<0.1, increasing to 5% for higher φ*!

20 Z/γ* transverse momentum (dσ/dφ η (ll)) Calculations from A. Banfi et al. (resummed QCD predictions+fixed-order pqcd) is less good than ResBos! Measurement precision about one order of magnitude lower than the present theoretical uncertainties! FEWZ predictions undershoot the data by ~10% which confirm previous CDF observation (PRD 86,052010)! 20

21 21 Drell- Yan Forward- Backward asymmetry Asymmetry A FB in qqà γ*/zà ll! Parity violations in EW interactions! Vector-Axial couplings! d σ 3 d cos θ * 8 (1+ cos2 θ * ) + A FB cosθ * with A FB = σ F σ B σ F + σ B θ* is the angle of the negative lepton relative the quark momentum in the dilepton centre-of-mass frame! Quark direction unknown at pp collider :! Take longitudinal boost of the resulting lepton pair in the laboratory frame, and assume that this is in the same direction as the incoming quark.! This ambiguity produces a significant dilutionà reduction of the measured asymmetry A FB.!

22 Drell- Yan Forward- Backward asymmetry Central-Central electrons! Central-Forward electrons! Muons! ATLAS measurement in 3 channels : central-central electron, centralforward electron and muons! Forward region displays reduced effect from dilution! Unfolding the A FB spectra to correct for detector effects, radiative corrections and dilution! A FB spectra found to be consistent with the corresponding Standard Model predictions! 22

23 23 Drell- Yan Forward- Backward asymmetry Unfolded to born level combined measurements! Asymmetry measured as a function of mass (M ll ) and rapidity (Y ll )! Measurement in both dilepton channels and combination! Raw and unfolded to born level results agree with SM predictions!

24 Weak mixing angle measurement CMS :! sin 2 θ eff = ± (stat) ± (syst)!! ATLAS :! sin 2 θ eff = ± (stat) ± (syst)!! Asymmetries at the Z pole dominated by lepton couplings à sensitivity to sin 2 θ eff! CMS : multivariate likelihood method using decay angle cos θ, invariant mass and rapidity Y to disentangle forward-backward direction on statistical basis (using 1.1fb -1 of data)! ATLAS : use a χ 2 comparison of the raw A FB spectra to different templates, which were constructed using weights produced at generatorlevel with different values of sin 2 θ eff! As precise as best hadron collider results!!! 24

25 25 W/Z+jets production : Motivation Main background to Higgs and beyond Standard Model searches! Test of recent NLO pqcd predictions for large jet multiplicities (not accessible before)! Test of limitations of ME+PS generators and fixed order pqcd in regions where large logarithmic corrections and EW NLO corrections become important! Probe the strange and heavy flavour content in proton (various Flavor Number Schemes,FNS)! Experimental systematic is dominated by jet energy scale uncertainty!

26 26 Analysis Procedure Subtract background! Correct & unfold data! for efficiencies, resolution,! bin migration! Detector Level! (data)! Comparison! Correct for non perturbative! effects (Underlying Event,! fragmentation)! Particle Level! (fiducial region)! Parton Level! (Theory predictions)!!me

27 27 Analysis Procedure Uncertainties!! Statistics!! JES, JER,! Lepton reco +ID &Trigger!!!!! Non perturbative effects (UE, fragmentation)!! PDF, α s!! Detector Level! (data)! Particle Level! (fiducial region)! Parton Level! Theory predictions!!me

28 28 Examples of theory predictions Many predictions of NLO: W/Z + 1, 2, 3, 4, 5 jets! Predictions at Parton Level! BLACKHAT+SHERPA : NLO fixed order pqcd (up to 4p)! MCFM : NLO fixed order pqcd! Predictions at Particle level! PYTHIA, HERWIG: LO Matrix Element + Parton Shower! ALPGEN, SHERPA: LO Matrix Element + Parton Shower tree level multipartons up to 5p! SHERPA: Matrix Element NLO+ Parton Shower! MADGRAPH+PYTHIA: LO Matrix Element + Parton Shower tree level multipartons up to 5p! MC@NLO+HERWIG: NLO + Parton Shower! POWHEG+PYTHIA : NLO + Parton Shower!

29 Differential Z/γ* + jets cross section (1) inclusive jet multiplicity! transverse moment of Z! Jet multiplicity up to 7 jets: well described by ME+PS generators (up to 5 jets) and BlackHat+Sherpa, MC@NLO fails! ALPGEN predicts a high rate for high p T Z bosons! 29

30 Differential Z/γ* + jets cross section (2) Rapidity gap! H T : scalar p T sum of the leptons and the jets! Sherpa overestimates the cross section for large Δy jj, consistent with the too wide rapidity spectra! Important for VBF Higgs searches and other searches! Fixed order calculations (BlackHat +SHERPA) fail to describe H T! Large H T corresponds to large number of jets! A better description by ME+PS! 30

31 31 EWK production with 2 forward jets Vector boson centrally produced! Jets well separated in rapidity! Probe Triple gauge couplings! Background to Higgs VBF searches! Measured (fb) VBFNLO NLO (fb) CMS 7TeV 154 ± 24 (stat) ± 46 (syst) ± 27(theory) ± 3(lumi) 166 Kinematic region of the reported cross section : M ll >50 GeV, P T (jet)>25 GeV, η <4, m jj >120 GeV! Obtain the Signal contribution and Drell-Yan+jets from a fit to the BDT output! Signal and dominant background are simulated with Madgraph!

32 32 W production in association with b jets (1) W+b-jets important background to Higgs boson production in WH, Hà bb! Irreducible background in BSM searches and single-top measurements! Comparison with 4FNS scheme! Powheg (NLO) +PYTHIA! Alpgen+HERWIG (normalized to NNLO! using inclusive W)! MCFM (4FNS+5FNS), corrected for:! Hadronisation! Double-parton interactions (DPI) using! Alpgen+HERWIG (~25% correction! Intriguing published results:! CDF, ATLAS: σ above NLO! D0: agrees with the NLO! CMS: Z+b-jets (agrees)!

33 33 W production in association with b jets (2) Very challenging : 85% events are background from:! QCD multijets! tt process! single top! W+jet! b-tagging used to discriminate signal processes! Require p T l > 25 GeV, η l < 2.5, p T ν > 25 GeV, m T (W) > 60 GeV, up to 2 jets each with p T j > 25 GeV, y j < 2.1! 1+2 jet exclusive cross section: 7.1 ± 0.5 (stat.) ± 1.4 (syst.) pb! Measurement within 1.5 σ consistent with MCFM NLO prediction!

34 W production in association with b jets (3) One jet bin! without subtracting single top! In the one jet bin, the measurement is systematically higher than the MCFM prediction, but compatible within uncertainties! Data/MC ratio raises with p T (b-jet)! Best seen when no single-top subtraction is used! 34

35 35 W+c production σ(w + c-jets) sensitive to strange PDF!! ATLAS : charm is tagged by exclusive reconstruction of four D-hadron (D ±, D *± ) decay channels ( No jet requirement, Sensitive to lower charm p T )! CMS : c-jets tagged via vertex based algorithms consistent with a D ±, D 0, cà X lν! Counting measurement after OS SS Subtraction (sign charge of charm wrt W lepton)!

36 W+c production Cross sections consistent with theory within uncertainties. A symmetric strange sea, as implemented in NNPDF2.3coll seems disfavored! PDFs where the s-quark and d-quark sea contributions are comparable at x 0.01 are favored (NNPDF2.3coll)! Too early to draw conclusions. Need more data!! 36

37 37 Diboson production Fundamental test of Standard Model! Probe for new physics! Triple gauge couplings (TGC)! Resonances with diboson final states! Irreducible background for Higgs searches!

38 38 W W 7-8 TeV Signal : dileptons (e and µ) and missing energy! Main backgrounds (25 30%,):! Z ll + fake missing Et à Z-veto in ee and µµ channels! W+jets (jet faking a lepton)à Control region with one nominal lepton and one loose lepton! tw and tt à Jet multiplicity distribution in ttbar control region (using b-tagged jets)!

39 39 W W production@ 7-8 TeV Measured (pb)! ATLAS! 7 TeV! 51.9 ± 2.0 (stat) ± 3.9 (syst) ± 2.0 (lumi)! MCFM NLO (pb)! CMS! 7 TeV! 52.4 ± 2.0 (stat) ± 4.5 (syst) ± 1.2 (lumi)! 47.0 ± 2.0! CMS! 8 TeV! 69.9 ± 2.8 (stat) ± 5.6 (syst) ± 3.1 (lumi)! Higgs contribution of the order of 3 (4)% at 7 (8) TeV (not considered)! Measured cross sections slightly above theoretical predictions. Significance are small (1.4σ,1σ,1.7σ), but starting to draw attention.! Are the NLO predictions sufficiently precise?! Could be a subtle sign of New Physics?! Measurement precisions are systematics-limited. Leading source of systematics is the jet veto (5%)! Experimental : jet-energy scale and resolution affects the jet p T threshold! Theoretical : number of jets in WW+jets! We need to see the results from the full 8TeV data.!

40 40 Electroweak corrections to WW production Small corrections to the total cross section (predictions from MCFM do not include EWK corrections)! BUT : Sizable negative EW corrections (-30%) at high energies, comparable to QCD corrections! Significant contributions of photon-induced channels at large scattering angles! See talk by Tobias Kasprzik (ICHEP 12)! Important to understand the interplay of the cancellations between EW and QCD, since we have experimental data up to high masses! s = 14 TeV!

41 W Z production@ 8TeV [pb] ATLAS Preliminary total σ WZ NLO QCD (MCFM, CT10) WZ (pp)(66<m <116 GeV) 10 ll WZ (pp)(66<m <116 GeV) ll 1 LHC Data 2012 ( s=8 TeV) ATLAS WZ lνll (66<m <116 GeV) L=13 fb ll LHC Data 2011 ( s=7 TeV) ATLAS WZ lνll (66<m <116 GeV) L=4.6 fb ll Tevatron ( s=1.96 TeV) -1 D0 WZ lνll (60<m <120 GeV) L=8.6 fb ll -1 CDF WZ lνll L=7.1 fb -1-1 Signal = tri-lepton (including one Z) and missing energy! s [TeV] Main backgrounds : Z+jets, ttbar (jet faking a lepton), other dibosons! Measured (pb) ATLAS 7 TeV 19.0 ± 1.4 (stat) ± 0.8 (syst) ± 0.4 (lumi) MCFM NLO (pb) ATLAS 8TeV 20.3 ± 0.7(stat) ±1.1(syst) ±0.6(lumi) 20.3 ± 0.8 CMS 7 TeV 17.0 ± 2.4 (stat) ± 1.1 (syst) ± 1.0 (lumi) 17.5 ±

42 42 ZZ 7-8 TeV ZZà 4l! ZZà 2l2τ ZZà 4l! ZZà llνν

43 43 Z Z production@ 8TeV Measured (pb) MCFM NLO (pb) ATLAS 7 TeV 7.2 ± 1.4 (stat) ± 0.8 (syst) ± 0.4 (lumi) 6.5 ± 0.3 CMS 7 TeV 6.2 ± 2.4 (stat) ± 1.1 (syst) ± 1.0 (lumi) 6.3 ± 0.4 ATLAS 8 TeV 7.1 ± 0.4 (stat) ± 0.3 (syst) ± 0.2 (lumi) 7.2 ± 0.3 CMS 8 TeV 8.4 ± 1.0 (stat) ± 0.7 (syst) ± 0.4 (lumi) 7.7 ± 0.4

44 44 Wγ/Zγ 7 TeV Zγà ννγ Zγà ννγ Analyses of lνγ, llγ and ννγ final states! γ with high E T Large ΔR(l,γ) (suppress FSR)! Isolated lepton with high E T Missing energy if ννγ ΔR(E miss T,γ) separation! Wγà lνγ

45 Wγ/Zγ 7 TeV Wγà lνγ Zγà llγ Inclusive Wγ cross sections above theory (MCFM NLO)! No multiple quark / gluon emission in MCFM! Fair agreement for Zγ! 45

46 46 Diboson with semi- leptonic 7TeV ATLAS and CMS have measured (WW+WZ)à lνjj! Backgrounds: W/Z+jets! Major systematics: Background estimation, jet scale/resolution! Measured (pb) MCFM NLO (pb) CMS 7 TeV 68.9 ± 8.7 (stat) ± 9.7 (syst) ± 1.5 (lumi) 65.6 ± 2.2 ATLAS 7 TeV 72 ± 9 (stat) ± 15 (syst) ± 13 (MC stat) 63.4 ± 2.6

47 W, Z and diboson cross sections [pb] σ total pb pb fb fb fb fb fb ATLAS Preliminary LHC pp fb Theory fb s = 7 TeV -1 Data (L = fb ) LHC pp s = 8 TeV Theory -1 Data (L = fb ) fb fb W Z tt t WW WZ Wt ZZ fb [pb] σ tot Production Cross Section, Nov j 2j W 3j 4j 1j 2j jet E T > 30 GeV jet η < , 19 pb JHEP10(2011)132 Z 3j JHEP01(2012)010 CMS-PAS-SMP (W/Z 8 TeV) 4j Wγ Zγ γ E T > 15 GeV ΔR(γ,l) > fb CMS EWK WW+WZ fb WW fb fb WZ fb CMS-PAS-EWK (WZ) CMS-PAS-SMP (WW7), 007(ZZ7), 013(WW8), 014(ZZ8), 015(WV) CMS 7 TeV CMS measurement (stat syst) 8 TeV CMS measurement (stat syst) 7 TeV Theory prediction 8 TeV Theory prediction ZZ fb fb Major advances in ability to predict SM rates! Largest improvement from theory! New NLO and NNLO calculations and NLO with showering! Confidence in QCD calculations of production rates! Reduction of systematic uncertainties on background! Can be used in extraction of couplings (eg for Higgs)! 47

48 48 Anomalous Triple Gauge Coupling Effect of atgcs are modelled using an effective Lagrangian which depends on few parameters! Increase of cross section at high invariant mass and high transverse momentum! Neutral TGC are not allowed in the SM. In SM all parameters are 0, except g V 1 and κv which are 1! Analysis on full 2011 dataset! Coupling! parameters! channel! Charged! Neutral! WWγ λ γ, Δκ γ WW, Wγ! WWZ! λ Ζ, Δκ Ζ, Δg Z 1 WW, WZ! ZZγ! h Z 3, hz 4 Zγ! Zγγ! h γ 3, hγ 4 Zγ! ZZZ! f Z 4, fz 5 ZZ! ZγZ! f γ 4, fγ 5 ZZ!

49 Anomalous triple gauge coupling : WWZ and WWγ Maximum likelihood fit performed for events in bin p T lepton! Statistics still limited : so only one or two parameters left free during atgc fits. The other ones are fixed to their SM value (=0)! No sign of deviation from SM predictions! 49

50 50 Charged Anomalous Triple Gauge Coupling Results Limits on WWγ atgc couplings! Limits on WWZ atgc couplings! CMS Results! 95% C.L.! Δκ γ λ Δg Z! 1 Wγà lνγ [-0.38, 0.29]! [-0.05, 0.037]! -! W + W - à lνlν! [-0.21, 0.22]! [-0.048, 0.048]! [-0.095, 0.095]! W + W - +WZà lνjj! [-0.111, 0.142]! [-0.038, 0.030]! -! No sign of deviation from SM predictions!

51 51 Neutral Anomalous Triple Gauge Coupling Results Limits on neutral atgc ZZγ and ZZZ couplings! Limits on neutral atgc Zγγ and ZZγ couplings! Limits surpassing Tevatron and LEP! Fully compatible with Standard Model! Most stringent limits from CMS ννγ analysis! Last bin: p T (γ) > 400 GeV! ATLAS use p T (γ) > 100 GeV!

52 WW excess and TGC? Shouldnʼt the WW excess show up as anomalous TGCs?! The TGC sensitivity is concentrated in the highest bins of the leading lepton p T! Excesses are mostly at low p T where anomalous TGC donʼt contribute! If the excess is real, it is not a kind of physics described with atgcs à not a heavy new particle in the s-channel loop diagrams! 52

53 53 Summary of atgc All channels studied. No deviations from SM expectations! But sensitivity still low :! Channel with highest statistics Wγ give Δκ γ < 0.4 and λ γ < 0.05! while the «interesting» range is rather Δκ γ ~ 0.01 and λ γ ~ 0.001! Expected improvements soon with the full 2012 stat to be analysed (23 fb-1) and combination of channels measuring the same couplings! Need to run at 13 TeV (higher sensitivity with increasing s) and 100 fb-1 (2 to 3 years) to probe the «interesting» region!

54 54 Conclusion LHC program well underway:! Precise test of the Standard Model at TeV scale! Significant contribution to PDFs! Stable ground for New Physics searches! Agreement with theory across orders of magnitude is impressive! Cross section measurements have been performed in WW, WZ, Wγ, Zγ and ZZ channels! Triple Gauge Coupling have been measured in all the channels and no deviations from SM were observed! Still most of the LHC data at 8 TeV to be analysed more results with improved precision expected soon!

55 Anomalous Quartic Couplings 55

56 Anomalous Quartic Couplings 56

57 57 W Mass Measurements at Tevatron and LHC Factor of 2-5 bigger samples of W and Z bosons available at Tevatron! Huge samples at LHC! For most of the sources of systematic uncertainties, Tevatron have demonstrated that we can find ways to constrain them with data and scale systematic uncertainties with data statistics! Exception is the PDF uncertainty, where Tevatron have not made a dedicated effort to constrain the PDFs within the analysis: current PDF uncertainty is 10 MeV at the Tevatron, total MW uncertainty is 15 MeV! We need to address specific PDF degrees of freedom to answer the question:! Can we achieve total uncertainty on MW< 10 MeV at the Tevatron? 5 MeV at the LHC?!

58 58 W Mass Measurements at Tevatron and LHC Newer PDF sets, e.g. CT10W include more recent data, such as Tevatron. W charge asymmetry data, to be improved with LHC data! Dominant sources of W mass uncertainty are the d_valence and d-u degrees of freedom at the Tevatron! What are the important degrees of freedom for PDFs at the LHC?! Tevatron and LHC measurements that can further constrain PDFs:! Z boson rapidity distribution! W lν lepton rapidity distribution! W boson charge asymmetry! W+charm production constraining strange quark distribution!!

59 59 Triple and Quartic Gauge Couplings Triple gauge couplings measured at the few % level! New physics sensitivity possible at the 0.1% level?! LHC has opened new era of quartic gauge coupling measurements!! Measurements of longitudinal vector boson scattering is of particular interest to confirm unitarization! the search for new resonances in vector boson scattering in multi TeV range to probe the Higgs sector is well-motivated! even if SM Higgs implies that no new resonances are needed for unitarization!

60 60 When electroweak corrections matter? At the ~TeV scale, they significantly modify production cross sections through Sudakov logs of order! This typically exceeds ~10% of LO when mu is of order 1 TeV! We are now encountering data where the precision at the TeV scale is of order 10%! Experimentalists are aware of the situation, 2 ways to cope with:! Either use data-driven/ empirical methods for shape & yields! Or live with larger theoretical syst. uncertainty for now!

61 61 A classic example: when EWK corr. are too strong For inclusive jet production at 14 TeV, negative virtual contribution! dominates over real emission at ~1 TeV and cross section! decreases from LO result by ~20% at 2TeV, >30% at 4TeV!

62 62

63 Z/γ* transverse momentum (dσ/dφ η (ll)) 63

64 64 Differential Z/γ* + jets cross section JES dominant component to total uncertainty!

65 W+b inclusive results 65

66 Unfolding 66

67 Unfolding - Methodology 67

68 Systematics uncertainties on diboson 68

69 69 Monte Carlo Generators FEWZ and DYNNLO: include fixed order O(αs2) calculations - diverge for vanishing ptz! RESBOS: soft gluon resummation (low ptz) matched to fixed order pqcd at O(αs) corrected to O(αs2) with K-factors (high ptz)! Parton shower programs provide an all-order approximation of parton radiation in the soft and collinear region (low ptz)! Pythia and Herwig: apply weights to the first/hardest branching to merge O(αs0) and O(αs) predictions in order to describe the high ptz region! Alpgen and Sherpa: tree level matrix elements for W/Z+partons matched to parton showers (avoiding double counting)! Each of these models can be used with different tunings and PDF sets!

70 Drell- Yan Forward- Backward asymmetry 70

71 Weak Mixing Angle This method has reduced dependence on the MC generator as it does not require any correcyon for acceptance and diluyon. 71

72 W ±, Z(γ) rapidity dependence flavour decomposition 72

73 Z/γ* transverse momentum (dσ/dφ η (ll)) SHERPA describes the data within 2%, better than RESBOS, for φ η >0.1 (RESBOS still better for φ η <0.1)! POWHEG+Pythia8 describes the data within 5% over the full range! does not properly describe the data for φ η >0.1! 73

74 Azimuthal correlations in Z+Jets events Jet multiplicities and azimuthal correlations ΔΦ(Z, Leading Jet)! Selection : >=1 jet, 2 high p T leptons, Z-mass requirement! Distributions unfolded back to particle level! MADGRAPH, SHERPA describe data well! Also true for other observables : ΔΦ(jet, jet), ΔΦ(Z, jet2), transverse event trust in two p T (Z) regions > 0, 150 GeV! 74

75 W+c production Predictions: (ATLAS) & MCFM (CMS) + NLO and NNLO PDF sets! differing in the s-quark content! NLO theory predictions (MCFM + different PDF sets) describe reasonably the shape of the η distribution.! The shapes of the p D T distributions for the different PDF sets are similar, but the predicted cross sections differ by as much as 25%.! 75

76 76 Electron/muon universality R W = σ ( pp W e ν ) σ ( pp W μ ν ) = Br(W e ν ) Br(W μ ν ) = 1.006± 0.004( stat)± 0.006( unc)± 0.022( cor) = 1.006± R Z = σ ( pp Z ee) σ ( pp Z μ μ) = Br( Z ee) Br ( Z μ μ) = 1.018± 0.014( stat )± 0.016( unc)± 0.028( cor) = 1.018± Ratio of cross section measurements in e and μ channel provides lepton universality check! R W is already comparable to the present world average of ± 0.019! R Z is fully dominated by LEP result ± !