W/Z inclusive measurements in ATLAS

Transcription

1 /Z inclusive measurements in J-B. Blanchard On behalf of the Atlas collaboration Standard LHC 1-1/4/1

2 Introduction /Z physics at the LHC LHC: a /Z factory... heoretically well understood bosons, produced at high rates Unique signature in the lepton decay... in a QCD environment Cross sections factorise at scale µ on PDF: σ pp = dx a dx b f a(x a, µ) f b (x b, µ) ˆσ ab (ŝ) (a,b) Explore phase space uncovered so far: Motivations Q = M /Z and x 1/ = e ±y M /Z s est pqcd predictions up to NNLO est phenomenological models: ME+PS, soft gluon resummations... Provide precision measurements: lepton universality, polarisation, m... Q / GeV Atlas and CMS (7 ev) Atlas and CMS rapidity plateau D Central+Fwd. Jets CDF/D Central Jets H1 ZEUS NMC BCDMS E665 SLAC /Z@LHC x 1/4/1 Standard LHC 1 - J-B. Blanchard / 18

3 /Z cross-section : In τ lepton Outline Introduction /Z cross-section In τ lepton In light flavour leptons Differential measurement in e/µ Analysis of these cross-sections Polarisation measurements Conclusion 1/4/1 Standard LHC 1 - J-B. Blanchard 3 / 18

4 /Z cross-section : In τ lepton τ ν and Z τ τ cross sections τ ν using data ( 35 pb 1 ) Z τ τ using fb 1 in three channels: µ + hadrons + 3ν (τ µτ h ) e + hadrons + 3ν (τ eτ h ) e + µ + 4ν (τ eτ µ) = % systematic uncertainties m vis (µ, τ ) [GeV] h Validation of τ reconstruction performances critical for searches Events/.5 GeV Preliminary Ldt = 1.55 fb, s = 7 ev 6 Data 11 γ*/z τ τ 5 Multijet µ ν τ ν 4 γ*/z µ µ t t Diboson 3 Measurement in agreement with other leptonic decay channels τ ν τ Z τ µ τ h 1.55fb Z τ e τ h 1.34fb Preliminary e ν e µ ν µ Data ( = 7 ev) s Stat uncertainty Sys Stat Sys Stat Lumi Prediction (NNLO) heory uncertainty Z τ e τ µ 1.55fb Z ee/µµ combined 33 36pb Z ττ combined fb Stat Syst Stat Syst Stat Lumi heory (NNLO) σ(z ττ, 66<m <116 [GeV]) [nb] inv σ( l ν l ) [nb] References Phys. Lett. B76 (76-94), -CONF-1-6 1/4/1 Standard LHC 1 - J-B. Blanchard 4 / 18

5 /Z cross-section : In light flavour leptons Lepton universality ± ± lν and Z l + l for l = e, µ Inclusive measurements done with data ( 35 pb 1 ) = experimental accuracy of few %. Ratio of e and µ cross sections in common fiducial region = R =1.6±.4, to compare with world average 1.17±.19 = R Z =1.18±.31, when world average is.9991±.4 (LEP) Precise measurements guarantee lepton flavours combination µν) ± BR( 1.1 L dt = pb eν) / σ ± BR( R = σ % CL ellipse area Data ( s = 7 ev) PDG world average R PDG world average R Z Standard Model R Z = σ Z BR(Z e e ) / σ Z BR(Z µ arxiv: sub. PRD 1/4/1 Standard LHC 1 - J-B. Blanchard 5 / µ ) Reference

6 /Z cross-section : In light flavour leptons Flavour combined cross sections Combination of lepton flavour Cross sections provided with correlations between channels (Z l + l, + l + ν, l ν ) Ratios of fiducial cross sections avoid phase space extrapolation (larger theoretical uncertainty), and cancel luminosity terms Broad agreement with NNLO predictions, different PDF dependences σ fid / σ fid + sensitive to up-down PDF differences σ fid / σ fid ± Z rather PDF insensitive (provided sea is flavour symmetric) L dt = pb Data ( s = 7 ev) total uncertainty exp. uncertainty ABKM9 JR9 HERAPDF1.5 MS8 L dt = pb Data ( s = 7 ev) total uncertainty exp. uncertainty ABKM9 JR9 HERAPDF1.5 MS σ fid / σ fid fid + σ fid / σ ± Z/γ* Reference arxiv: sub. PRD 1/4/1 Standard LHC 1 - J-B. Blanchard 6 / 18

7 /Z cross-section : Differential measurement in e/µ /Z transverse momentum Low p High p est multiple models of QCD predictions soft/collinear partons. Logarithmic resummations up to NNLL in resbos PS (pythia, herwig) iterative splitting and radiation of parton ME+PS (mc@nlo, powheg), with ME O(α s) hard partons. fewz, dynnlo available to O(α s ) ME+PS (sherpa, alpgen). High order ME but tree-level production hard parton (Data,Prediction) / RESBOS Combined Data Stat. Uncert. DYNNLO O(α s ) DYNNLO O(α s ) MCFM O(α s ) MCFM O(α s ) RESBOS Ldt 31 pb = 7 ev p [GeV] s (Data,Prediction) / RESBOS Combined Data Stat. Uncert. ALPGEN+HERIG MC@NLO POHEG+PYHIA PYHIA RESBOS SHERPA Ldt 31 pb = 7 ev p [GeV] s Overall p range Agreement within % of resbos alpgen pythia sherpa References Phys. Rev. D85 (15), Phys. Lett. B75 ( ) 1/4/1 Standard LHC 1 - J-B. Blanchard 7 / 18

8 /Z cross-section : Differential measurement in e/µ /Z rapidity Boson rapidity linked to parton momentum fraction x 1/ = e ±y M /Z s In the boson case, lepton pseudo-rapidity η l is used. Comparison to NNLO models shows broad agreement shows PDF sensitivity (even tension with few sets) [pb] l dσ/d η heory/data L dt = pb Data ( MS8 HERAPDF1.5 ABKM9 JR9 s = 7 ev) + + l νl Uncorr. uncertainty otal uncertainty η l [pb] l dσ/d η heory/data L dt = pb Data ( MS8 HERAPDF1.5 ABKM9 JR9 s = 7 ev) l νl Uncorr. uncertainty otal uncertainty η l [pb] Z dσ/d y heory/data L dt = pb Data ( MS8 HERAPDF1.5 ABKM9 s = 7 ev) + Z l l Uncorr. uncertainty otal uncertainty JR y Z Reference arxiv: sub. PRD 1/4/1 Standard LHC 1 - J-B. Blanchard 8 / 18

9 Analysis of these cross-sections : charge asymmetry Outline Introduction /Z cross-section Analysis of these cross-sections charge asymmetry Strange quark density Polarisation measurements Conclusion 1/4/1 Standard LHC 1 - J-B. Blanchard 9 / 18

10 Analysis of these cross-sections : charge asymmetry charge asymmetry Definiton A l.35.3 Data ( s = 7 ev) MS8 HERAPDF1.5 ABKM9 JR9 Stat. uncertainty otal uncertainty A(η l ) = dσ +(η l) dσ (η l ) dσ +(η l ) + dσ (η l ) Sensitive to valence quark (u d + /dū ) Lepton charge asymmetry Usable to constrain u v / d v at low x s=7 ev pl > GeV (extrapolated data, lν) 35 pb CMS ( µν) 36 pb LHCb ( µν) 36 pb MS8 prediction (MC@NLO, 9% C.L.) CEQ66 prediction (MC@NLO, 9% C.L.) +CMS+LHCb Preliminary Combined results L dt = pb HERA1. prediction (MC@NLO, 9% C.L.) References η -CONF-11-19, arxiv: sub. PRD 1/4/1 Standard LHC 1 - J-B. Blanchard / 18 More constrained in central region (CMS+) Extended up to η 3.7 (LHCb) η l

11 Analysis of these cross-sections : Strange quark density Strange density: state of the art ) = 1.9 GeV x(s+s)(x, Q s+s distribution at Q = 1.9 GeV NLO PDF (68% C.L.) MS8 C NNPDF.1 ABKM9 HERAPDF1. G. att Little is known about strange density Flavour SU(3) suggests equal proportion in sea (u, d and s) r s = 1 (s(x) + s(x)) d(x) s suppression assumed in many PDFs because of s mass (r s.5) -3 - (NueV, CCFR) -1 x Motivations Higher relevance than at evatron central + c s 3%(pp) / %(p p) Better accuracy needed for precision measurement as m (c and b already measured by HERA with 5% and % accuracy) Might be constrained by Z rapidity and +charm 1/4/1 Standard LHC 1 - J-B. Blanchard 11 / 18

12 Analysis of these cross-sections : Strange quark density Measurement principle Perform NNLO fits on HERA ep DIS data (sensitive to linear combination of q + q) cover 4 x.6 for 1 Q 4 GeV +, and Z data (sensitive to bilinear combination of q + q) cover.1 x.1 for Q = M /Z GeV Results extrapolated to low Q with pqcd (chosen scale Q = 1.9 GeV ) fits procedure χ /NDF Fixed s/ d Free s/ d All data 546.1/ /565 data 45./3 33.9/3 Free s/ d fit determines value of r s +. r s = 1. ±. exp ±.7 mod.15par +.6 [pb] Z dσ/d y free/fixed s α s ±.8 th y Z Reference Z l l L dt = pb Data ( s= 7 ev) (uncorr. sys. stat. uncertainty) epz fixed s epz free s arxiv: sub. PRL 1/4/1 Standard LHC 1 - J-B. Blanchard 1 / 18

13 Analysis of these cross-sections : Strange quark density Results and interpretations xs Results in two kinematical zones (Q,x)=(1.9,.3) and (M /Z,.13) Uncertainties are smaller at Q = M /Z gluon splitting into q q flavour independant = Same tension with predictions s.45 Q = 1.9 GeV.4 epz fixed s.35 epz free s.3 Effect of s increasing ū, d decrease by % total sea is enhanced by 8% Q = 1.9 GeV, x=.3 ABKM9 NNPDF.1 MS8 C (NLO) total uncertainty experimental uncertainty epz free s r s Q = M epz free s, x=.13 Z ABKM9 NNPDF.1 MS8 C (NLO) total uncertainty experimental uncertainty r s L dt = pb Data ( s= 7 ev) total uncertainty exp. uncertainty ABKM9 JR9 HERAPDF1.5 MS8 epz free s.5 better agreement found in 3 ratio σ fid /σ fid ± Z fid σ fid ± / σ Z/γ* x Reference arxiv: sub. PRL 1/4/1 Standard LHC 1 - J-B. Blanchard 13 / 18

14 Polarisation measurements Outline Introduction /Z cross-section Analysis of these cross-sections Polarisation measurements boson polarisation τ polarisation from τν Conclusion 1/4/1 Standard LHC 1 - J-B. Blanchard 14 / 18

15 Polarisation measurements : boson polarisation boson polarisation Motivations in three states: f L, f and f R : LO: predominantly left-handed NLO: all states possibles. Compare to LO and NLO predictions Good understanding needed for precision measurement Entries/ Data ( s=7 ev) + e + ν p > 5 GeV Fit result Left L dt = 37 pb Longitudinal Right Principle No p ν z use reduction of cosθ cos θ D = ( p l p )/( p l p ) 35 < p < 5 and p > 5 GeV emplate fits give access to f and f L f R Entries/ Data ( s=7 ev) L dt = 37 pb Fit result Left ν e Longitudinal Right p > 5 GeV cos(θ D ) cos(θ D ) Reference arxiv: sub. EPJC /4/1 Standard LHC 1 - J-B. Blanchard 15 / 18

16 Polarisation measurements : boson polarisation boson polarisation l l Measurement and results f Measurement done with Monte-Carlo generators: mc@nlo, powheg get uncertainty for unfolding procedure High sensitivity to energy scale (lepton, /E ) Scale uncertainty on f L f R drastically reduced when averaged over charge Agreement with predictions within uncertainties (f L f R 5%) ν p > 5 GeV, η l >.4, p > GeV, 5 < m < 1 GeV, 35 < p < 5 GeV Data s = 7 ev 1 σ uncertainty MC@NLO POHEG Unphysical area f R f L f ν p > 5 GeV, η l >.4, p > GeV, 5 < m < 1 GeV, p > 5 GeV Data [%] f [%] f s + 4 l ν Simulation MC@NLO 35 POHEG 3 35<p <5 GeV Blackhat = 7 ev 1 σ uncertainty MC@NLO POHEG Unphysical area y 4 l ν Simulation MC@NLO 35 POHEG 3 35<p <5 GeV Blackhat f R f L y Future [%] f [%] f + 4 l ν Simulation MC@NLO 35 POHEG 3 5<p <7 GeV Blackhat y 4 l ν Simulation MC@NLO 35 POHEG 3 5<p <7 GeV Blackhat y ould like to have access to the 9 polarisation matrix elements in MC Reference arxiv: sub. EPJC 1/4/1 Standard LHC 1 - J-B. Blanchard 16 / 18

17 Polarisation measurements : τ polarisation from τν τ polarisation from τ ν decay τ polarisation P τ =(σ R σ L )/(σ R + σ L ) can be measured at LHC τ h ν Z ττ H ττ H τν Expected P τ First τ polarisation measurement at LHC Use charged asymmetry variable in one prong decay Υ = (E π E π )/ p π + p π Produce left- and right-handed templates Fit 4 pb 1 with these templates +.5 P τ = 1.6 ±.4 stat.7syst Results in agreement with SM predictions Entries/ Preliminary s = 7 ev L dt = 4 pb Data Fit Left handed Right handed ϒ Entries/.1 Entries/ τ L Preliminary = 7 ev Data τ L ν Multijets E τ R s L dt = 4 pb Preliminary = 7 ev Data τ R ν Multijets E s L dt = 4 pb Reference -CONF-1-9 1/4/1 Standard LHC 1 - J-B. Blanchard 17 / 18 ϒ ϒ

18 Conclusion Conclusion /Z cross section Inclusive measurement done with every lepton channel Differential measurement as function of p, η or y very accurate measurement in e/µ (R comparable to world average) Can already be used to constrain PDFs models charge asymmetry for u/d strange quark density (underestimated in most PDF sets) Particles properties τ polarisation from τν decay boson polarisation o be pursued Exploit much larger dataset available to explore more differential distributions Increase the menu of measurements 1/4/1 Standard LHC 1 - J-B. Blanchard 18 / 18

19 Back-up

20 Back-up Effect of r s on PDFs u v d v g xu v Q = 1.9 GeV epz fixed s epz free s xd v Q = 1.9 GeV epz fixed s epz free s xg xu Q = 1.9 GeV epz fixed s epz free s x x xd Q = 1.9 GeV epz fixed s epz free s x x Q = 1.9 GeV epz fixed s epz free s ū d (ū+ d+ s) xσ = x(u+d+s) Q = 1.9 GeV epz fixed s epz free s x x 1/4/1 Standard LHC 1 - J-B. Blanchard / 18