samira!hassani! !! cea saclay,irfu/spp! 21!may!2013 · cea saclay,irfu/spp!! 21!may!2013....

ì Electroweak measurements at the LHC

!!!

Samira Hassani

CEA-‐Saclay, IRFU/SPP

21 May 2013

Success of 2010-‐2012 Run ì  Excellent collider performance :!

ì  23 fb-1 luminosity delivered in 2012!

ì  Excellent detector performance :!ì  Operational efficiency ~96%!ì  Robust and high reconstruction efficiency in presence of pile-up!

ì  Physics highlight of the run :!ì  Discovery of a Higgs-like particle!ì  We are beginning to probe its properties!

ì  Gigantic amount of work on searches for SUSY, extra dimensions, …!ì  Null so far!

ì  Insightful Standard Model measurements have been performed !ì  Analysis of full 2012 sample still in early stages!

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Standard Model physics ì  Important on their own and as foundation for Higgs and New Physics

searches !

ì  Fundamental milestones in the “rediscovery” of the Standard Model at 7 TeV !

ì  Powerful tools to constrain quark,gluon distributions inside proton (PDF)!

ì  Zàll 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, ...)!

ì  Precision tests of the standard model are enabled by an excellent performance of the ATLAS and CMS detectors!

ì  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% !

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

Overview

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ì  Observables that are really Electroweak (EWK)!ì  Forward-Backward Asymmetries!ì  dσ/dM from Drell-Yan!ì  Triple gauge couplings!

ì  Observables that use EWK bosons to probe the structure of the hard interactions!ì  Inclusive cross-section of W and Z!ì  Ratios of W/Z, W+/W-!ì  Charge Asymmetries!ì  V+jets (V=W,Z) !

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LHC data

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2011

2012 Z->µµ events with 25 reconstructed vertices (Atlas)

p p

ì  LHC performance impressive!

ì  But this was possible only by running with 50ns bunch spacing and more protons per bunch than nominal!

ì  Very high average number of interactions excellent for discovery reach, but not so good for precision EW physics!

ì  More collisions per crossing than expected!ì  Challenge for Jets (energy scale, resolution)

and Missing Et!ì  Simulated in MC!

ATLAS Detector Performance

ì  Precision tests of the standard model are enabled by an excellent performance of the detector!

ì  e, μ identification efficiency is understood to ~ 1% accuracy with high background suppression!

ì  Calorimeter calibration / spectrometer scale are known to better than 1% precision!

ì  Jet energy scale known to better 2.5% for central jets with 60< pT < 800 GeV!

ì  LHC luminosity is known to 2.8% accuracy!6

Electron reco ε measured with Zàee Stability of EM calorimeter response vs time (and pile-up)

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Analysis methods

ì  Production cross-sections differ by orders of magnitude between signal and potential background!

ì  Use leptonic decays of W and Z to separate signal from background!

ì  Require isolated high pT lepton!

ì  Require high missing energy when ν involved!

ì  Use « data-driven » background estimations (side bands, control regions, fake factors…) for all jet-induced backgrounds!

ì  MC simulations (used for lepton efficiency and resolution) validated on data by « tag and probe » methods! With 20 fb-1 @ 8 TeV, !

~ 400 millions Wàlν !~ 8000 WWàlνl'ν !(l = e and µ)!

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σσσσZZ

σσσσWW

σσσσWH

σσσσVBF

MH=125 GeV

WJS2012

σσσσjet

(ET

jet > 100 GeV)

σσσσjet

(ET

jet > √√√√s/20)

σσσσggH

LHCTevatron

eve

nts

/ s

ec f

or L

= 1

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3 c

m-2s

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σσσσb

σσσσtot

proton - (anti)proton cross sections

σσσσW

σσσσZ

σσσσt

σ

σ

σ

σ

(( ((nb

)) ))√√√√s (TeV)

{

Cross sections at the LHC

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

W and Z production at LHC ì  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):!

ì  Since parton fractions in this process are typically 10-3 < x < 10-1 : sea-sea qq contributions are also important!

ì  Leading order relation between rapidity y and x1, x2 :!

ì  W production in pp collisions is globally charge asymmetric:!ì  pp has 2X more (udbar) than (dubar)

collisions due to uud valence quark content of proton!

ì  sea quark-sea quark charge symmetric production dilutes W+/W− ratio from 2 to ~1.4!

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x1,2 =Mllse±yll

u+ d(s)!W +

d +u(c)!W "u+u! Z

d + d! Z

Cross section definitions ì  Measurements are corrected to consistently defined “truth level” to allow

proper theory comparisons!

ì  Measure fiducial cross section (with minimal phase space extrapolations) and total cross section !

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ì  Cross sections are given for three lepton definitions:!ì  “bare” leptons, after QED FSR!ì  “dressed” leptons: “bare” leptons recombined with ! QED FSR photons in cone ΔR < 0.1!ì  “born” leptons, before QED FSR

(usually used for e − μ channel combination)!

efficiency corrections! Acceptance!

W and Z cross sections

ì  7 TeV cross sections measured with 1% precision (with 36 pb-1)!

ì  From pQCD prediction, expect an increase of the cross section of 15 - 20 % from 7 to 8 TeV!

ì  Good agreement with NNLO prediction!ì  Discriminating power against different PDF sets!

ì  ATLAS points overlap with CMS in the plot@7TeV!11

Connection with the PDF

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ATLAS fiducial cross sections W,Z 2010 @7 TeV data!

CMS total cross sections W,Z 2011! @8 TeV data!

ì  Data is becoming more discriminating. !

Ratio of W and Z cross-‐sections

Measured Theory NNLO ATLAS 7 TeV 10.893 ± 0.079 (stat) ± 0.110 (syst) ± 0.116 (acc)

10.74 ± 0.04 CMS 7 TeV 10.54 ± 0.07 (stat) ± 0.08 (syst) ± 0.16 (th)

CMS 8 TeV 10.65 ± 0.11 (stat) ± 0.23 (syst) 11.04 ± 0.04

ì  Ratios: W+/W− and W/Z production cross sections are insensitive to luminosity and other sources of uncertainties (2% precision)!ì  provide precision test of perturbative QCD and proton PDFs !

ì  For σW/σZ PDF errors are reduced, the ratio is sensitive to s¯/d¯ densities ratio!

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W-‐lepton charge asymmetry

Discrimination beteween PDF at low η

CMS clearly disfavour MSTW2008!(MSTW have addressed this in more! recent versions of their PDFs)!

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ì  This measurement is very sensitive to PDFs as most uncertainties cancel in the ratio!

ì  It tells us about the valence quarks!

ì  This translates into a difference in predictions for the W-lepton asymmetry pseudo-rapidity spectrum!

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!

AW =!W +!!

W !

!W ++!

W !

AW "u! du+ d

"uV ! dV

uV + dV + 2usea

High Drell-‐Yan cross section (1)

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ì  Excellent test of perturbative QCD within SM, using latest NNLO PDFs and NLO EWK corrections!

ì  Drell-Yan differential cross section measured in 116 < mee 25 GeV, |η|400 GeV !

High Drell-‐Yan cross section(2)

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ì  Good agreement between shape in data with PYTHIA, MC@NLO and SHERPA !

ì  Good agreement between shape in data and predictions of perturbative QCD at NNLO (FEWZ), within the uncertainty, with all the PDF sets considered. !

ì  Comparing results with and without photon-induced background (γγàe+e-), it is observed that this contribution is of similar size to the sum of the PDF and αs uncertainties!

Differential and double-‐differential Drell-‐Yan cross section

ì  Excellent agreement on several orders of magnitude with the NNLO theoretical predictions!

ì  Double differential cross section normalized to the Z peak region and |Y| < 2.4!

ì  d2σ /dMdY measurements are compared to the predictions of NNLO FEWZ + Different PDF sets àCan be used to constrain PDFʼs !

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Low mass! High mass

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

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ì  Use φ*η variable to probe modelling of pT of Z boson in MC (ResBos(NNLL) and FEWZ)!

ì  Has advantage that angular resolution is better than pT resolution !

ì  φ*η is highly correlated with

θ* scattering angle of the leptons!relative to the proton beam direction in the dilepton rest frame!

aT /QT ! tan(!acop / 2)sin"*

!* " tan(!acop / 2)sin"*


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ì  Use φ*η variable to probe modelling of pT of Z boson in MC (ResBos(NNLL) and FEWZ)!

ì  Has advantage that angular resolution is better than pT resolution !

ì  φ*η is highly correlated with

ì  Data-RESBOS difference within 2% for φ*


ì  Calculations from A. Banfi et al. (resummed QCD predictions+fixed-order pQCD) is less good than ResBos !

ì  Measurement precision about one order of magnitude lower than the present theoretical uncertainties !

ì  FEWZ predictions undershoot the data by ~10% which confirm previous CDF observation (PRD 86,052010)!

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Drell-‐Yan Forward-‐Backward asymmetry ì  Asymmetry AFB in qqàγ*/Zàll !

ì  Parity violations in EW interactions!ì  Vector-Axial couplings!

ì  θ* is the angle of the negative lepton relative the quark momentum in the dilepton centre-of-mass frame!

ì  Quark direction unknown at pp collider :!ì  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.!

ì  This ambiguity produces a significant dilutionà reduction of the measured asymmetry AFB.!

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d σd cosθ*

∝ 38 (1+ cos2θ*) + AFB cosθ* with AFB =

σ F− σ Bσ F+ σ B

Drell-‐Yan Forward-‐Backward asymmetry

ì  ATLAS measurement in 3 channels : central-central electron, central-forward electron and muons!ì  Forward region displays reduced effect from dilution!

ì  Unfolding the AFB spectra to correct for detector effects, radiative corrections and dilution!

ì  AFB spectra found to be consistent with the corresponding Standard Model predictions!

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Central-Central electrons! Central-Forward electrons! Muons!

Drell-‐Yan Forward-‐Backward asymmetry ì  Unfolded to born level

combined measurements!

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ì  Asymmetry measured as a function of mass (Mll) and rapidity (Yll)!

ì  Measurement in both dilepton channels and combination!

ì  Raw and unfolded to born level results agree with SM predictions!

Weak mixing angle measurement

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ì  Asymmetries at the Z pole dominated by lepton couplings à sensitivity to sin2θeff !

ì  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) !

ì  ATLAS : use a χ2 comparison of the raw AFB spectra to different templates, which were constructed using weights produced at generator-level with different values of sin2θeff!

ì  As precise as best hadron collider results!!!

CMS : !sin2θeff = 0.2287 ± 0.0020 (stat) ± 0.0025 (syst)!!ATLAS : ! sin2θeff = 0.2297± 0.0004(stat) ± 0.0009(syst)!!

W/Z+jets production : Motivation ì  Main background to Higgs and beyond Standard Model searches!

ì  Test of recent NLO pQCD predictions for large jet multiplicities (not accessible before)!

ì  Test of limitations of ME+PS generators and fixed order pQCD in regions where large logarithmic corrections and EW NLO corrections become important!

ì  Probe the strange and heavy flavour content in proton (various Flavor Number Schemes,FNS)!

ì  Experimental systematic is dominated by jet energy scale uncertainty!

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Analysis Procedure

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Detector Level!(data)!

Particle Level!(fiducial region)!

Parton Level!(Theory predictions)!

Subtract background!Correct & unfold data!for efficiencies, resolution,!bin migration!

Correct for non perturbative!effects (Underlying Event,!fragmentation)!

Comparison!

!me

Analysis Procedure

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Detector Level!(data)!

Particle Level!(fiducial region)!

Parton Level!Theory predictions!

Uncertainties!!Statistics!!JES, JER,!Lepton reco +ID &Trigger!!!!!Non perturbative effects (UE, fragmentation)!!PDF, αs!!

!me

Examples of theory predictions ì  Many predictions of pQCD @ NLO: W/Z + 1, 2, 3, 4, 5 jets!

ì  Predictions at Parton Level!ì  BLACKHAT+SHERPA : NLO fixed order pQCD (up to 4p)!ì  MCFM : NLO fixed order pQCD!

ì  Predictions at Particle level!ì  PYTHIA, HERWIG: LO Matrix Element + Parton Shower!ì  ALPGEN, SHERPA: LO Matrix Element + Parton Shower tree level

multipartons up to 5p!ì  SHERPA: Matrix Element NLO+ Parton Shower!ì  MADGRAPH+PYTHIA: LO Matrix Element + Parton Shower tree level

multipartons up to 5p!ì  MC@NLO+HERWIG: NLO + Parton Shower!ì  POWHEG+PYTHIA : NLO + Parton Shower!

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Differential Z/γ* + jets cross section (1)

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ì  Jet multiplicity up to 7 jets: well described by ME+PS generators (up to 5 jets) and BlackHat+Sherpa, MC@NLO fails!

ì  ALPGEN predicts a high rate for high pT Z bosons!

inclusive jet multiplicity! transverse moment of Z!

Differential Z/γ* + jets cross section (2)

ì  Sherpa overestimates the cross section for large Δyjj , consistent with the too wide rapidity spectra!

ì  Important for VBF Higgs searches and other searches! 30

Rapidity gap! HT: scalar pT sum of the leptons and the jets!

ì  Fixed order calculations (BlackHat+SHERPA) fail to describe HT!

ì  Large HT corresponds to large number of jets!

ì  A better description by ME+PS!

EWK production with 2 forward jets

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ì  Vector boson centrally produced!

ì  Jets well separated in rapidity!

ì  Probe Triple gauge couplings!

ì  Background to Higgs VBF searches!

Measured (fb) VBFNLO NLO (fb) CMS 7TeV 154 ± 24 (stat) ± 46 (syst) ± 27(theory) ± 3(lumi) 166

ì  Kinematic region of the reported cross section : Mll >50 GeV, PT(jet)>25 GeV, |η|120 GeV !

ì  Obtain the Signal contribution and Drell-Yan+jets from a fit to the BDT output !

ì  Signal and dominant background are simulated with Madgraph!

W production in association with b jets (1)

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ì  W+b-jets important background to Higgs boson production in WH, Hàbb !

ì  Irreducible background in BSM searches and single-top measurements !

ì  Comparison with 4FNS scheme!ì  Powheg (NLO) +PYTHIA!ì  Alpgen+HERWIG (normalized to NNLO! using inclusive W)!

ì  MCFM (4FNS+5FNS), corrected for:!ì  Hadronisation!ì  Double-parton interactions (DPI) using ! Alpgen+HERWIG (~25% correction!

ì  Intriguing published results:!ì  CDF, ATLAS: 1.5 – 2.8 σ above NLO!ì  D0: agrees with the NLO!ì  CMS: Z+b-jets (agrees)!


ì  Require pTl > 25 GeV, |ηl| < 2.5, pTν > 25 GeV, mT (W) > 60 GeV, up to 2 jets each with pT j > 25 GeV, |yj| < 2.1 !

ì  1+2 jet exclusive cross section: 7.1 ± 0.5 (stat.) ± 1.4 (syst.) pb!

ì  Measurement within 1.5 σ consistent with MCFM NLO prediction !

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ì  Very challenging : 85% events are background from:!ì  QCD multijets!ì  tt process!ì  single top!ì  W+jet!

ì  b-tagging used to discriminate signal processes!


ì  In the one jet bin, the measurement is systematically higher than the MCFM prediction, but compatible within uncertainties!

ì  Data/MC ratio raises with pT(b-jet)!ì  Best seen when no single-top subtraction is used!

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One jet bin! without subtracting single top!

W+c production ì  σ(W + c-jets) sensitive to strange PDF!

!

ì  ATLAS : charm is tagged by exclusive reconstruction of four D-hadron (D±, D*±) decay channels ( No jet requirement, Sensitive to lower charm pT)!

ì  CMS : c-jets tagged via vertex based algorithms consistent with a D±, D0, càX lν!

ì  Counting measurement after OS – SS Subtraction (sign charge of charm wrt W lepton)!

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W+c production

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ì  Cross sections consistent with theory within uncertainties. A symmetric strange sea, as implemented in NNPDF2.3coll seems disfavored!

ì  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! !

Diboson production ì  Fundamental test of Standard Model!

ì  Probe for new physics!ì  Triple gauge couplings (TGC)!ì  Resonances with diboson final states!

ì  Irreducible background for Higgs searches!

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W W production @ 7-‐8 TeV

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ì  Signal : dileptons (e and µ) and missing energy!ì  Main backgrounds (25 – 30%,):!

ì  Z → ll + fake missing Et à Z-veto in ee and µµ channels!ì  W+jets (jet faking a lepton)à Control region with one nominal lepton and one

loose lepton!ì  tW and tt à Jet multiplicity distribution in ttbar control region (using b-tagged jets)!

W W production@ 7-‐8 TeV

Measured (pb)! MCFM NLO (pb)!ATLAS! 7 TeV! 51.9 ± 2.0 (stat) ± 3.9 (syst) ± 2.0 (lumi)!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)!

44.7 − 1.9+ 2.1

57.3 − 1.6+ 2.4

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ì  Higgs contribution of the order of 3 (4)% at 7 (8) TeV (not considered)!

ì  Measured cross sections slightly above theoretical predictions. Significance are small (1.4σ,1σ,1.7σ), but starting to draw attention.!ì  Are the NLO predictions sufficiently precise?!ì  Could be a subtle sign of New Physics?!

ì  Measurement precisions are systematics-limited. Leading source of systematics is the jet veto (5%)!ì  Experimental : jet-energy scale and resolution affects the jet pT threshold!ì  Theoretical : number of jets in WW+jets!

ì  We need to see the results from the full 8TeV data.!

Electroweak corrections to WW production ì  Small corrections to the total cross section (predictions from MCFM do

not include EWK corrections)!

ì  BUT : Sizable negative EW corrections (-30%) at high energies, comparable to QCD corrections!

ì  Significant contributions of photon-induced channels at large scattering angles!

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√s = 14 TeV!

See talk by Tobias Kasprzik (ICHEP 12)!

ì  Important to understand the interplay of the cancellations between EW and QCD, since we have experimental data up to high masses!

W Z production@ 8TeV

Measured (pb) MCFM NLO (pb)

ATLAS 7 TeV 19.0 ± 1.4 (stat) ± 0.8 (syst) ± 0.4 (lumi)

ATLAS CMS

8TeV 7 TeV

20.3 ± 0.7(stat) ±1.1(syst) ±0.6(lumi) 17.0 ± 2.4 (stat) ± 1.1 (syst) ± 1.0 (lumi)

20.3 ± 0.8 17.5 ± 0.6

17.6 − 1.0+ 1.1

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ì  Signal = tri-lepton (including one Z) and missing energy!

ì  Main backgrounds : Z+jets, ttbar (jet faking a lepton), other dibosons!

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ZZ production@ 7-‐8 TeV

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ZZà4l! ZZà2l2τ

ZZàllνν

ZZà4l!

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

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Wγ/Zγ production@ 7 TeV

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ì  Analyses of lνγ, llγ and ννγ final states!ì  γ with high ET ì  Large ΔR(l,γ) (suppress FSR)!ì  Isolated lepton with high ET ì  Missing energy if ννγ

ì  ΔR(ETmiss ,γ) separation!

Zγàννγ

Zγàννγ

Wγà lνγ

Wγ/Zγ production @ 7 TeV

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ì  Inclusive Wγ cross sections above theory (MCFM NLO)!

ì  No multiple quark / gluon emission in MCFM!

ì  Fair agreement for Zγ !

Wγà lνγ

Zγà llγ

Diboson with semi-‐leptonic decays@ 7TeV

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

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ì  ATLAS and CMS have measured (WW+WZ)àlνjj!

ì  Backgrounds: W/Z+jets !

ì  Major systematics: Background estimation, jet scale/resolution !

W, Z and diboson cross sections

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JHEP10(2011)132JHEP01(2012)010

CMS-PAS-SMP-12-011 (W/Z 8 TeV)

CMS EWK-11-009 CMS-PAS-EWK-11-010 (WZ)CMS-PAS-SMP-12-005 (WW7),

007(ZZ7), 013(WW8), 014(ZZ8), 015(WV)

syst) ⊕7 TeV CMS measurement (stat

syst) ⊕8 TeV CMS measurement (stat

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ATLAS PreliminaryATLAS PreliminaryATLAS Preliminary

ì  Major advances in ability to predict SM rates!

ì  Largest improvement from theory!

ì  New NLO and NNLO calculations and NLO with showering!

ì  Confidence in QCD calculations of production rates!ì  Reduction of systematic uncertainties on background!ì  Can be used in extraction of couplings (eg for Higgs)!

Anomalous Triple Gauge Coupling ì  Effect of aTGCs are modelled using an effective

Lagrangian which depends on few parameters!

ì  Increase of cross section at high invariant mass and high transverse momentum!

ì  Neutral TGC are not allowed in the SM. In SM all parameters are 0, except gV1 and κV which are 1!

ì  Analysis on full 2011 dataset!

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Charged!

Neutral!

Coupling! parameters! channel!WWγ

λγ, Δκγ

WW, Wγ!WWZ! λΖ, ΔκΖ, ΔgZ1

WW, WZ!ZZγ! hZ3, hZ4 Zγ!Zγγ! hγ3, hγ4 Zγ!ZZZ! fZ4, fZ5 ZZ!ZγZ! fγ4, fγ5 ZZ!

Anomalous triple gauge coupling : WWZ and WWγ

ì  Maximum likelihood fit performed for events in bin pTlepton!

ì  Statistics still limited : so only one or two parameters left free during aTGC fits. The other ones are fixed to their SM value (=0)!

ì  No sign of deviation from SM predictions!

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Charged Anomalous Triple Gauge Coupling Results

ì  No sign of deviation from SM predictions!

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Limits on WWγ aTGC couplings ! Limits on WWZ aTGC couplings !

95% C.L.! Δκγ

λ

Δg1Z!

Wγàlνγ

[-0.38, 0.29]! [-0.05, 0.037]! -!W+W-àlνlν! [-0.21, 0.22]! [-0.048, 0.048]! [-0.095, 0.095]!

W+W-+WZàlνjj! [-0.111, 0.142]! [-0.038, 0.030]! -!

CMS Results!

Neutral Anomalous Triple Gauge Coupling Results

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Limits on neutral aTGC ZZγ and ZZZ couplings! Limits on neutral aTGC Zγγ and ZZγ couplings !

ì  Limits surpassing Tevatron and LEP!

ì  Fully compatible with Standard Model!

ì  Most stringent limits from CMS ννγ analysis!ì  Last bin: pT(γ) > 400 GeV!ì  ATLAS use pT(γ) > 100 GeV!

WW excess and TGC? ì  Shouldnʼt the WW “excess” show up as anomalous TGCs? !

ì  The TGC sensitivity is concentrated in the highest bins of the leading lepton pT!

ì  Excesses are mostly at low pT where anomalous TGC donʼt contribute!

ì  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!

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Summary of aTGC

ì  All channels studied. No deviations from SM expectations!

ì  But sensitivity still low : !ì  Channel with highest statistics Wγ give Δκγ < 0.4 and λγ < 0.05 !ì  while the « interesting » range is rather Δκγ ~ 0.01 and λγ ~ 0.001!

ì  Expected improvements soon with the full 2012 stat to be analysed (23 fb-1) and combination of channels measuring the same couplings!

ì  Need to run at 13 TeV (higher sensitivity with increasing s) and 100 fb-1 (2 to 3 years) to probe the « interesting » region !

Conclusion

ì  LHC program well underway:!ì  Precise test of the Standard Model at TeV scale!ì  Significant contribution to PDFs!ì  Stable ground for New Physics searches!

ì  Agreement with theory across orders of magnitude is impressive!

ì  Cross section measurements have been performed in WW, WZ, Wγ, Zγ and ZZ channels!

ì  Triple Gauge Coupling have been measured in all the channels and no deviations from SM were observed!

ì  Still most of the LHC data at 8 TeV to be analysed … more results with improved precision expected soon!

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Anomalous Quartic Couplings

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Anomalous Quartic Couplings

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W Mass Measurements at Tevatron and LHC

ì  Factor of 2-5 bigger samples of W and Z bosons available at Tevatron!

ì  Huge samples at LHC!

ì  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!

ì  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!

ì  We need to address specific PDF degrees of freedom to answer the question:!ì  Can we achieve total uncertainty on MW< 10 MeV at the Tevatron?

5 MeV at the LHC ?!

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W Mass Measurements at Tevatron and LHC

ì  Newer PDF sets, e.g. CT10W include more recent data, such as

Tevatron. W charge asymmetry data, to be improved with LHC data!

ì  Dominant sources of W mass uncertainty are the d_valence and d-u degrees of freedom at the Tevatron!ì  What are the important degrees of freedom for PDFs at the LHC ?!

ì  Tevatron and LHC measurements that can further constrain PDFs:!ì  Z boson rapidity distribution!ì  W → lν lepton rapidity distribution!ì  W boson charge asymmetry!ì  W+charm production constraining strange quark distribution!

ì  !

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Triple and Quartic Gauge Couplings

ì  Triple gauge couplings measured at the “few %” level!ì  New physics sensitivity possible at the 0.1% level?!

ì  LHC has opened new era of quartic gauge coupling measurements!ì  Measurements of longitudinal vector boson scattering is of

particular interest to confirm unitarization!ì  the search for new resonances in vector boson scattering in

multi –TeV range to probe the Higgs sector is well-motivated!ì  even if SM Higgs implies that no new resonances are

needed for unitarization!!

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When electroweak corrections matter?

ì  At the ~TeV scale, they significantly modify production cross sections through Sudakov logs of order !

ì  This typically exceeds ~10% of LO when mu is of order 1 TeV!

ì  We are now encountering data where the precision at the TeV scale is of order 10%!

ì  Experimentalists are aware of the situation, 2 ways to cope with:!ì  Either use data-driven/ empirical methods for shape & yields!ì  Or live with larger theoretical syst. uncertainty for now!

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A classic example: when EWK corr. are too strong

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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!


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Differential Z/γ* + jets cross section

ì  JES dominant component to total uncertainty!

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W+b inclusive results

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Unfolding

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Unfolding -‐ Methodology

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Systematics uncertainties on diboson

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Monte Carlo Generators ì  FEWZ and DYNNLO: include fixed order O(αs2) calculations -

diverge for vanishing pTZ!

ì  RESBOS: soft gluon resummation (low pTZ) matched to fixed order pQCD at O(αs) corrected to O(αs2) with K-factors (high pTZ)!

ì  Parton shower programs provide an all-order approximation of parton radiation in the soft and collinear region (low pTZ)!

ì  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!

ì  Alpgen and Sherpa: tree level matrix elements for W/Z+partons matched to parton showers (avoiding double counting)!

ì  Each of these models can be used with different tunings and PDF sets!

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Drell-‐Yan Forward-‐Backward asymmetry

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Weak Mixing Angle

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This method has reduced dependence on the MC generator as it does not require any correcYon for acceptance and diluYon.

W±, Z(γ) rapidity dependence flavour decomposition

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ì  SHERPA describes the data within 2%, better than RESBOS, for φ*η>0.1 (RESBOS still better for φ*η0.1!

Azimuthal correlations in Z+Jets events

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ì  Jet multiplicities and azimuthal correlations ΔΦ(Z, Leading Jet)!ì  Selection : >=1 jet, 2 high pT leptons, Z-mass requirement!ì  Distributions unfolded back to particle level!

ì  MADGRAPH, SHERPA describe data well!ì  Also true for other observables : ΔΦ(jet, jet), ΔΦ(Z, jet2), transverse event

trust in two pT(Z) regions > 0, 150 GeV!

W+c production

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ì  NLO theory predictions (MCFM + different PDF sets) describe reasonably the shape of the η distribution.!

ì  The shapes of the pT D distributions for the different PDF sets are similar, but the predicted cross sections differ by as much as 25%.!

Predictions: aMC@NLO (ATLAS) & MCFM (CMS) + NLO and NNLO PDF sets!differing in the s-quark content!

Electron/muon universality

RW =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± 0.024

RZ =σ ( pp→Z→ee)σ ( pp→Z→μμ)

= Br (Z→ee )Br (Z→μμ)

= 1.018± 0.014( stat )± 0.016 (unc)± 0.028(cor ) = 1.018± 0.031

ì  Ratio of cross section measurements in e and μ channel provides lepton universality check!

ì  RW is already comparable to the present world average of 1.017 ± 0.019!

ì  RZ is fully dominated by LEP result 0.9991 ± 0.0024!

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samira!hassani! !! cea saclay,irfu/spp! 21!may!2013 · cea saclay,irfu/spp!! 21!may!2013....

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