1

Gas Tracking R&D

EIC User Meeting: Jan 6-9, 2016

Constraining the Sea Quark Distributions Through W± Cross Section Ratio

Measurements at STAR

DIS 2017 University of Birmingham

April 3-7 2017

SalvatoreFazio(BNL) onbehalfofMatthewPosik (TempleUniversity)

STARCollaboration

2

Motivation

o PartonDistributionFunctions(PDFs)probetheinternalstructureoftheproton.

o Thex-dependence ofthesePDFsallowyoutodistinguishbetweentheintrinsicpropertiesoftheprotonandQCDradiation.

o Severalglobalanalyses(CT14,MMHT14,BS15,etc.)haveextractedPDFsusingvariousdataandfunctionalfit assumptions.

DIS 2017 : April 4-7, 2017

non-lineardynamicRegime

110-310-4 10-2 10-1

Few-body/ valence quark

Regime

x(proton)

Many-body Regime

QCD radiationdominated

Regime

10-5

arXiv:1412.3989

3

Motivation

o E-866 suggestsatrendwherethedbar/ubar ratioappearstobedecreasingatlarge-x.

o Unpolarizeddbar/ubar distributioncanbeprobedviaDrell-Yanproduction.

B.Kernsetal.(SeaQuest Collaboration),APSAprilMeeting2016.

o Thepreliminary SeaQuest trendappearsleveloutathigherx.Howeverpreliminarydatahavelargeerrorbarsatlarge-x.Stillawaitingfullstatisticalsample.

o Moredirect andindirect dataareneededathigh-x tohelpconstrain theseaquarkdistributions.

DIS 2017 : April 4-7, 2017

o NewmeasurementsfromdifferentexperimentscanprovidedataatdifferentQ2 andfromdifferentscatteringprocesses.

§ Thiswillallowfordifferentsystematiceffects andalsoserveasacrosscheckofourunderstandingofthephysics.

4

W Boson Production Through p+p Collisions

DIS 2017 : April 4-7, 2017

�W+

�W�=

✓N+

O �N+B

N�O �N�

B

◆✓✏�

✏+

◆ o +/- ispositron/electronfromWleptonicdecayo NO isnumberofobservedWeventso NB isnumberofbackgroundeventso ε isthemeasuredWefficiency

o Wbosonsaresensitive toquark/anti-quarkdistributions.TheycanbeaccessedviatheWleptonicdecaychannelsinproton+protoncollisions

u+ d ! W+ ! e+ + ⌫

d+ u ! W� ! e� + ⌫

Ø

Ø

o ThechargedWcross-sectionratio

Ø isproportionaltothedbar/ubar ratio

Ø canbeusedtoconstrain theseaquarkdistributions

�W+

�W�⇡ u(x1)d(x2) + d(x1)u(x2)

u(x1)d(x2) + d(x1)u(x2)

5

Relativistic Heavy Ion Collider

o OverthepastseveralyearsluminosityatRHIChassteadilyincreased

o RHIC istheworld’sfirstpolarizedhadroncollider

DIS 2017 : April 4-7, 2017

6

Solenoidal Tracker At RHIC𝛈 =-1 𝛈 =0

𝛈 =1

𝛈 =2

o Calorimetrysystemwith2𝜋 coverageØ Barrelelectromagneticcalorimeter

(BEMC),-1<𝜂 <1Ø Endcapelectromagneticcalorimeter

(EEMC),1.1<𝜂 <2

o Timeprojectionchamber(TPC),|𝜂|<1.3

Year ~Luminosity(pb-1)2011 25(sampled)2012 75(sampled)2013 250(sampled)2017 400(delivered)

Combined 750

o The2017 (transversep+p √s=510GeV)runisexpectedtodeliver~400pb-1 moredata

Productionrunsat√s=500/510GeV

DIS 2017 : April 4-7, 2017

7

STAR Kinematics

RHICBOS-CT10pT >25GeV/c

e+/- pseudo-rapidity

x1x2<x>

o ApproximatekinematicrangeatSTARmid-rapidity (TPC+BEMC)

Ø 0.1<x<0.3for-1<𝜂 <1

o Forcollisionenergiesof√s=500GeVand𝜂 =0,(x1 ≈x2)Ø x=MW/√s=0.16

DIS 2017 : April 4-7, 2017

8

STAR Kinematics

o ApproximatekinematicrangeatSTARmid-rapidity (TPC+BEMC)

Ø 0.1<x<0.3for-1<𝜂 <1

o Forcollisionenergiesof√s=500GeVand𝜂 =0,(x1 ≈x2)Ø x=MW/√s=0.16

o InSTARtheEEMC couldbeusedtoobtainamoreforwardeta-bin(1.1<𝜂 <2)whichwouldextendthexreachofSTARØ 0.06<x<0.4for-2<𝜂 <2

o AnalysisofthisforwardEEMCeta-biniscurrentlyunderway

RHICBOS-CT10pT >25GeV/c

e+/- pseudo-rapidity

x1x2<x>

DIS 2017 : April 4-7, 2017

9

Selecting W Candidates

o Mid-rapiditySTARWselectioncriteria

Ø Isolationratio1/Isolationratio2

Ø pT-balancecut

Ø MatchpT >10GeV/ctracktoBEMCcluster

W+

W-

TPCtrackextrapolatedtoBEMCtowergrid

Ø Leadstogoodchargediscrimination

DIS 2017 : April 4-7, 2017

10

Reconstruction W bosons

DIS 2017 : April 4-7, 2017

TheSTARdetector@RHIC

Ingredientsfortheanalysis• Isolatedelectron• neutrino(notmeasureddirectly)• Hadronic recoil

q SelecteventswiththeW-signature(STEP1)Ø IsolatedhighPT electron

qNeutrinotransversemomentumisreconstructedfrommissingPT(Step2)

qNeutrino’slongitudinalmomentumisreconstructedfromthedecaykinematics(Step3)

€

! P Tν ≈ −

! P T

i

i∈clusterstracks

∑

€

MW2 = Ee + Eν( )2 − ! p e +

! p ν( )2

WbosonmomentumreconstructiontechniquewelltestedatFermiLab andLHC

[CDF:PRD70,032004(2004);ATLAS:JHEP1012(2010)060]

BarrelEMCAL(|η|<1)TPC (|η|<1.4)

FirstdevelopedatSTARforrun11transversesingle-spinasymmetrymeasurementofWbosonsPhys.Rev.Lett.116(2016)

(GeV)T E10 20 30 40 50 60 700

50

100

150

200

250

300

350

400Data Run-12

Total Sum

MCν e →W

Data-Driven QCD

Second EEMC

MCν τ →W

ee MC→Z

Background Contributions+Run-12: W

(GeV)T E10 20 30 40 50 60 700

2040

6080

100

120140

160

180200

220240

Data Run-12Total Sum

MCν e →WData-Driven QCDSecond EEMC

MCν τ →W ee MC→Z

Background Contributions-Run-12: W

11

Mid-Rapidity W+/- Backgrounds

o Data-drivenQCDbackgroundssatisfye+/- isolationcuts

o SecondEEMCbackgroundsresultfrombackward(“Jet”)atnon-existingcalorimetercoveragefor-2<<-1.1𝜂

o SecondEEMCbackgroundsareestimatedfromEEMClocatedat1.1<<2𝜂

o Electro-weakbackground fromZdecayisdonewithPYTHIA/MCsimulations.

o SmallbackgroundcontributionfromZdecay.

W+

Run12

W-

Run12

DIS 2017 : April 4-7, 2017

12

W+/- Efficiencies (Runs 11 and 12)

Eta-Bin1 2 3 4 5 6 7 8

Effic

ienc

y

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Run-12

W+ Efficiency

W- Efficiency

Eta-Bin1 2 3 4 5 6 7 8

Effic

ienc

y

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Run-11

W+ Efficiency

W- Efficiency

Run11 Run12

o 2012 running hadlowerW+/- efficienciesduetohigherluminosityrunning.

o Thisleadstomorepile-upintheTPC,whichresultedinlessefficient trackreconstruction.

o MinimalchargedependenceleadstosmallcontributiontothechargedWcross-sectionratio

DIS 2017 : April 4-7, 2017

13

Charged W Cross Section Ratios

Run11+12preliminaryresult (~100pb-1)

o ChargeWcross-sectionratiovs.lepton pseudo-rapidity precisionisdominatedbystatistics.

o Run13shouldaddanother~250pb-1 ofdata

o WhileRun17isprojectedtodeliver~400pb-1

Run11+12Preliminary

𝝶e

W+ /W

-

DIS 2017 : April 4-7, 2017

14

Charged W Cross Section Ratios

Run11+12preliminaryresult (~100pb-1)

o TheWbosonrapiditycannowalsobereconstructedatSTARviaitsrecoil.(Neededforrun11transversesingle-spinasymmetrymeasurement,Phys.Rev.Lett.116(2016))

o WorkisongoingtoimprovethesystematicuncertaintyassociatedwiththereconstructedWbosonrapidity.

W+ /W

-

DIS 2017 : April 4-7, 2017

yW

15

STAR Run 13 Statistical Impact

o Run13willsignificantlyimprovethestatisticalprecisionoftheSTARmeasuredW+/W- crosssectionratio.

o FurtherimprovementisexpectedfromRun17p+p 510GeVrun,whichisexpectedtodeliver~400pb-1.

DIS 2017 : April 4-7, 2017

16

Run 13 Analysis Update

Ø W+andW- efficienciesforrun13showsimilarbehaviorasthosemeasuredinrun12

1) Run13 recentlyswitchedovertoanewtrackingalgorithmwhichresultedin

Ø Highertrackreconstructionefficiencyatlargeluminosity

2) TheBEMCwascalibratedusingrun13p+p 510GeVdataandisnowappliedtotheongoingrun13analysis(usedinSTAR2013WAL Prelim.ResultsshownatINPCandSPIN2016).

DIS 2017 : April 4-7, 2017

o TheseanalysisupdateswereincludedintheSTAR2013mid-rapidityWAL preliminaryresultfirstshownatINPCandSPIN2016.

o PreliminaryWAL resultsintheforwardregionwillbeshownatthisconferenceduringthetalkonWed.17:00intheWG6session!

o Overthepastyearorso,therun13datasethashadsomeupdates/calibrationsimplemented.

17

W+/- Efficiencies (Run 13)

Eta-Bin-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

Effic

ienc

y

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Run-13 Period 2

W+ Efficiency

W- Efficiency

Eta-Bin-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

Effic

ienc

y

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Run-13 Period 1

W+ Efficiency

W- Efficiency

Run13(Day76-126)

Run13(Day129-161)

o W+andW- efficienciesforrun13showsimilarbehaviorasthosemeasuredinrun12Ø Averageefficiency~50%Ø SmalltonegligibledifferencebetweenW+andW- efficiency

o Efficiencydip seendays129-161isduetoinsertionofanewsubdetector (HFT).

DIS 2017 : April 4-7, 2017

𝜂 𝜂

18

Summaryo STARmeasuredcross-sectionratiousingWproduction

Ø AcomplimentarymeasurementtoSeaQuest andE-866Ø Shouldhelpfurtherconstrain theseaquarkPDFs

o Preliminaryresultsofmeasuredcross-sectionratiosusingRun11and12datasetshavebeenreleasedasafunctionofleptonpseudo-rapidityandWbosonrapidity

o Run13analysisnowtakesadvantageofrecentlyimplemented

o Run13dataset(~250pb-1 )tobeincludedintothecross-sectionratiomeasurementsoon

Ø BarrelelectromagneticcalorimetercalibrationØ Trackingalgorithm

o Long510GeVrunin2017attransversespinpolarizationisexpectedtodeliver400pb-1 whichshouldfurtherimprove thechargedWcross-sectionratioprecision.

o Moreforward eta-bin(1.1– 2.0)lookingtobeaddedtothecrosssectionratioviatheelectromagneticendcap

DIS 2017 : April 4-7, 2017