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W and Z boson measurements in Pb + Pb collisions at =2.76 TeV with the ATLAS detector. Jiří Dolejší Charles University Prague for the ATLAS collaboration QM 20 12 , Washington DC. Z boson production Run 2010: Z  mm decays using 6.7 μ b -1

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slide1

W and Z boson measurements

in Pb+Pbcollisionsat =2.76 TeV

with the ATLAS detector

JiříDolejší

Charles University Prague

for theATLAS collaborationQM 2012, Washington DC

slide2

Z boson production

  • Run 2010:Z mmdecaysusing6.7 μb-1
  • (Phys.Lett. B697 (2011) 294-312)
  • Run 2011:Zmmand Z eeusing 0.15 nb-1
  • W boson production
  • measured via single muons (W mn) from 5 mb-1of 2010 run.
  • W & Zbosons are expected to beproduced in initial NN collisions and theirdecayproducts to traverse thedense and hot medium unaffected …
  • YieldsscalingwiththenumberofbinaryNNcollisonscan and shouldbetested
  • W&Z canbeused as a tagforjets
  • Productioncanprovideinformation on nuclear PDF‘s
slide3

Z boson production

Z eecandidate.

FCalSum ET = 0.42 TeV(40-50 % Centrality),

mee= 90.8 GeV,

pTof Z = 1.6 GeV,

yZ= -0.2.

slide4

Overviewof ATLAS subdetectors

InnerDetector:

Tracking in 2 T fieldin therange||< 2.5

Pixels

SCT

TRT

Calorimeters:

EM LAr||< 3.2

Tilecal||< 1.7

LArhadronic EC 1.5 < ||< 3.2

LArFCal 3.1 < ||< 4.9

LAr

Tilecal

slide5

Overviewof ATLAS subdetectors

Muon system

Precisiontracking

(MDT, CSC)for

||< 2.7

Trigger (RPC, TGC) within

||< 2.4

SCT

TRT

slide6

Z boson production – eventselection

  • Trigger: Minimum Bias:ET > 50 GeV OR both ZDC & ID track
  • e-candidates: L1 EMcaloclustersET > 14 GeV
  • m-candidates: L1 mtriggerwithpT > 4 GeV, HLT (MS OR MS + ID), additionalpT> 10 GeVmuonscan
slide7

Z boson production – eventselection

  • Collision centrality is characterised by classes according to the FCal (modelisbased onGlauber MC)
  • Centrality parameterslike
  • <Npart>, <Ncoll> calculatedfrom Glauber MC
slide8

Zproduction – e, mselection and efficiencies

  • e: ||< 2.5, ET > 20 GeV, ID track matchingLAr cluster, matchingcriteriamodifiedwrtpp, underlyingeventsubtracted
  • m: „highquality“… MS & ID, combined. Whenbothm‘sh.q. pT > 10 GeVrequiredforboth,
  • Whenonlyoneh.q. pT > 20 GeVrequiredforboth.

… very weak centrality dependence

slide11

Z boson production – correcteddistributions

Yields for each centrality bin are comparedto model

… Pythia NNLO with proper TAA

  • Spectra in all centrality bins are consistentwiththe model employingthebinaryscaling
slide12

Z boson production – correcteddistributions

Model …

… Pythia NNLO with proper TAA

  • Rapidityspectrumisconsistentwiththe model employingthebinaryscaling
slide13

Z boson production – binaryscaling

ZyieldsfromZ eeand Z mm are consistentwitheachother and are consistentwithbinaryscaling.

slide14

Z boson production – zeroflow?

  • v2= −0.015 ± 0.018(stat) ± 0.014(sys)
slide15

W boson production in mnchannel

  • … single muonmeasurements in Minimum Biasevents

UncorrectedinclusivemuonpTspectrum.

Fit (solid line) withtwocomponents:

signalW mn(shadedarea) simulatedwith PYTHIA in NN,

and a backgroundparametrisation (dashed line) fromcc m + X and bb m + X in ppsimulations.

slide16

W boson production – binaryscaling

Yields for each centrality bin are normalized to the themost central bin.

RPC

(peripheral to central ratio)

consistentwith unity

slide17

W boson production – W+/W- and W/Z

Measured ratio RW+/W- = 0.97 + 0.18 - 0.19,

to becomparedwithRW+/W- = 1.65 ± 0.03 forpp and RW+/W- = 0.62 ± 0.03 fornncalculatedwith NNLO QCD usingMSTW2008 PDF‘s*.

MeasuredRW/Z= 10.5 + 2.3 - 2.4,

to becomparedwithabovementioned NNLO QCD* givingRW/Z = 11.3 ± 0.6 forppand RW/Z = 10.8 ± 0.6 fornn.

*A.D.Martin et al. Eur. J. Phys. C 14 (2000) 133

slide18

Summary

  • ATLAS measured a totalof 772 Z eeand 1223 Z mmcandidateswithin |yZ| < 2.5 and 66 < mll < 102 GeVin the 2011 PbPb data.
  • ATLAS measured a totalof 399 +36-38 W bosons in the 2010 PbPb data.
  • ThetotalZ and W yieldsintegratedoverrapidity are consistentwithbinaryscaling.
  • Zellipticflowconsistentwithzero.
  • ATLAS measured ratia RW+/W-and RW/Z.
slide19

Sourcesoffurtherinformation

ATLAS Public Results

https://twiki.cern.ch/twiki/bin/view/Atlas/AtlasResults

Especially notes

ATLAS-CONF-2012-052 and ATLAS-CONF-2011-078

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