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Dijet Cross Section and Longitudinal Double SpinAsymmetry Measurements in Polarized Proton-proton Collisions at radics = 200 GeV at STARTo cite this article Tai Sakuma et al 2011 J Phys Conf Ser 295 012068

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Dijet Cross Section

and Longitudinal Double Spin Asymmetry

Measurements in Polarized Proton-proton Collisions

atradics =200 GeV at STAR

Tai Sakuma1 and Matthew Walker2 for the STAR collaboration1Texas AampM University Department of Physics and Astronomy4242 TAMU College Station TX 778432Massachusetts Institute of Technology Laboratory for Nuclear Science Cambridge MA 02139

E-mail sakumabnlgov

Abstract These proceedings show the preliminary results of the dijet cross sections andthe dijet longitudinal double spin asymmetries ALL in polarized proton-proton collisions atradics = 200 GeV at the mid-rapidity |η| le 08 The integrated luminosity of 539 pbminus1 collected

during RHIC Run-6 was used in the measurements The preliminary results are presented asfunctions of the dijet invariant mass Mjj The dijet cross sections are in agreement with next-to-leading-order pQCD predictions The ALL is compared with theoretical predictions based onvarious parameterizations of polarized parton distributions of the proton Projected precisionof data analyzed to date from Run-9 are shown

1 IntroductionThe jet production rate in polarized proton-proton collisions is sensitive to the polarized gluondistribution ∆g(xQ2) of the proton The polarized gluon distribution is of particular interestin the proton spin physics because the first moment of this distribution is the fraction of theproton spin carried by the gluon spin ∆G

The ∆G is one of the four terms in the decomposition of the proton spin in the infinitemomentum frame

1

2=

1

2Σ + ∆G+ Lq + Lg

where Σ Lq and Lg are the contributions from quark spin quark orbital motion and gluonorbital motion The quark spin contribution Σ has been measured using polarized deep inelasticscattering (pDIS) data combined with neutron and hyperon β decay data [1]

One of the primary objects of the spin physics program at RHIC (RHIC-Spin) is to determine∆G by using polarized proton-proton collisions An advantage of using proton-proton collisionsis that gluons participate in high-pT events at the leading order However it is challenging todetermine the kinematics of parton-level interactions which are desirable quantities to determinein an experimental study of the structure of the proton

19th International Spin Physics Symposium (SPIN2010) IOP PublishingJournal of Physics Conference Series 295 (2011) 012068 doi1010881742-65962951012068

Published under licence by IOP Publishing Ltd 1

In order to determine the kinematics of leading-order parton-level interactions in proton-proton collisions the momenta of both outgoing partons are needed

x1 =pTradics

(e+y3 + e+y4) x2 =pTradics

(eminusy3 + eminusy4)

where the subscripts 1 2 indicate the incoming partons of the hard interactions 3 4 indicatethe outgoing partons The momenta of outgoing partons can be estimated by observing twofinal state objects in events such as dijets and photon-jets Furthermore the invariant mass andaverage pseudorapidity of the two objects are sensitive to the kinematics according to

Mjj =radicx1x2s

η3 + η42

=1

2lnx1x2

These proceedings show the preliminary results of the longitudinal double spin asymmetriesALL of the dijet production as a function of the dijet invariant mass Mjj

ALL =σuarruarr minus σuarrdarr

σuarruarr + σuarrdarr

The arrows (uarrdarr) indicate the orientations of the helicities of the colliding protons ALL is sensitiveto the polarized parton distributions In fact in the framework of QCD factorization ALL canbe written as follows

ALL =

sumij

intdx1

intdx2∆fi(x1 Q

2)∆fj(x2 Q2)aLLσ(cos θlowast)

sumij

intdx1

intdx2fi(x1 Q

2)fj(x2 Q2)σ(cos θlowast)

where ∆fi is the polarized distribution of the parton i fi is the unpolarized one σ is the parton-level cross section aLL is the parton-level longitudinally double spin asymmetries and i and jrun over quark flavors and gluons

The proceedings also show the preliminary results of the dijet cross sections as a functionof the dijet invariant mass Mjj The cross sections are measured to support the theoreticalframework which relates polarized parton distributions and measured ALL by showing theunpolarized equivalent of the same framework can quantitatively relate the unpolarized partondistributions and measured cross sections

2 STAR DetectorSTAR the Solenoidal Tracker At RHIC was built to measure wide varieties of nuclearinteractions in high energy heavy ion collisions and polarized proton collisions [2] Figure 1shows the cross sectional view of the STAR detector The detector subsystems particularlyrelevant to the measurements presented in these proceedings are the Time Projection Chamber(TPC) the Barrel Electromagnetic Calorimeter (BEMC) and the Beam-Beam Counters (BBC)

The Time Projection Chamber (TPC) [3] is the primary tracking system of the STARdetector It has a cylindrical shape operated within a solenoidal magnetic field of 05 T andprovides the momentum measurements over a range from 100 MeV to 30 GeV Its acceptanceis |η| lt 18 with full azimuth

The Barrel Electromagnetic Calorimeter (BEMC) is the primary calorimeter at mid-rapidity[4] It is a cylindrical annulus which surrounds the TPC The BEMC covers |η| lt 1 with fullazimuth and has a depth of about twenty radiation lengths (20X0) at η = 0 The BEMC has4800 towers in total and each tower covers ∆η times∆ϕ = 005times 005


2

=-1 =0 =1

TPC

BEMC

BBC

=2

+zYellowBlue

WestEast

+y

IP

BBC

Magnet

EEMC

Figure 1 The STAR detector

The Beam-Beam Counters (BBC) [5] are scintillator annuli of hexagonal tiles Theiracceptance is approximately 33 lt |η| lt 50 The BBCs are used to trigger minimum bias(MINB) events The MINB condition is a coincidence between the east BBC and the west BBCThe cross section of the MINB events is σMB = 261plusmn 20 mb [6] The MC simulation estimatesthat 87 plusmn 8 of non-singly diffractive collisions result in a MINB trigger [5]

3 Event SelectionThe BJP1 (Barrel Jet Patch 1) trigger was primarily used in the measurements Thistrigger requires a minimum transverse energy ET deposit in a patch of calorimeter towers(∆η times ∆ϕ = 1 times 1) as well as the MINB condition The ET threshold required for offlineanalysis was 108 GeV which was above the trigger turn-on to ensure high trigger efficiency

The BBC coincidence has some allowed time difference This difference is measured as 4-bitvalues called timebin which roughly corresponds to the vertex position of the events To selectevents close to the interaction point (IP) events are required to be in a specific timebin Thevertex distribution of the events in this timebin has approximately a Gaussian distribution withthe mean -19 cm and the standard deviation 30 cm About 26 of the MINB events were inthis timebin In addition events are required to have a reconstructed vertex

4 Jet and Dijet DefinitionJets can be defined at three different levels the parton level the hadron level and the detectorlevel In an experiment jets are reconstructed at the detector level whereas perturbative QCDcalculations predict jet productions at the parton level MC simulated events are used to evaluatethe effects of the transitions between different jet levels as jets can be reconstructed at all threelevels in MC simulation

Jets are defined as collections of four-momenta selected by the mid-point cone jet-findingalgorithm [7] with the cone radius 07 and splitmerge fraction 05 Four-momenta of jetsare the four-vector sum of the four-momenta that define the jets Four-momenta that composedetector-level jets are constructed from charged tracks in the TPC and energy deposits in BEMCtowers Tracks are assumed to have the mass of a charged pion (13975 MeV) and towers areassumed to be massless In order to avoid measuring the same charged particles twice both in


3

the TPC and in the BEMC if a track points to a BEMC tower the energy that a MIP wouldleave in the tower is subtracted from the tower energy

In order to reject the beam-gas background the neutral energy ratio RT the fraction ofjet transverse energy ET reconstructed from energy deposits in the BEMC are required tobe smaller than particular values that depend on jet pT RT lt 10 (5 lt pT le 1731 GeV)RT lt 099 (1731 lt pT le 213 GeV) RT lt 097 (213 lt pT le 2619 GeV) and RT lt090 (2619 GeV lt pT)

Dijets are defined as the two leading-pT jets of events Dijets are required to contain at leastone trigger jet a jet which caused the BJP1 trigger If only one jet is a trigger jet the jet iscalled the same side jet If both jets are trigger jets the jet that triggered with higher ET is thesame side jet The other jet is called the away side jet Dijets are required to have balanced pT073 le pawayT psame

T le 11 because pT-balanced dijets are more likely to carry momentum closerto that of parton level than do unbalanced jets

Asymmetric pT cuts (max(pT) gt 100 GeV and min(pT) gt 70 GeV) are used because a NLOpQCD calculation has little prediction power of dijets cross sections and ALL with symmetricpT cuts The minus08 lt η lt 08 cuts are applied for the detector acceptance The |η3 minus η4| lt 10cut is necessary for both jets to be in the acceptance at the same time The ∆ϕ gt 20 cut isapplied to select back-to-back dijet events

5 MC Simulation

Mjj [GeV]

Dije

t Yie

ld

1

10

102

103

104

30 50 70 90 110

Run-6DataMC

STAR Preliminary

Mjj [GeV]

(Dat

a - M

C)

MC

-1

0

1

40 60 80 100

STAR Preliminary

Dije

t Yie

ld

1

10

102103

24 lt M lt 36 GeV 36 lt M lt 536 GeV 536 lt M lt 845 GeV

1

10

102103

845 lt M lt 1685 GeV

DataMC

η

(Dat

a - M

C)

MC

-1

0

1

-05 00 05 -05 00 05 -05 00 05 -05 00 05

-1

0

1

STAR Preliminary

Dije

t Yie

ld

1

10

102103


1

10

102103


DataMC

|Δη|

(Dat

a - M

C)

MC

-1

0

1

05 10 15 05 10 15 05 10 15 05 10 15

-1

0

1

STAR Preliminary

Figure 2 The data-MC comparison of the dijet kinematic distributions ( left) The invariant massMjj distributions (top right) The average pseudo-rapidity η distributions (bottom right) The pseudo-rapidity difference ∆η distributions The MC yields are scaled so that the yield becomes the same as thedata

The events are generated by the Pythia 6410 event generator [8] with the CTEQ5L parton


4

distributions [9] using parton pT between 3 and 65 GeV The detector responses to the eventsare simulated with a GEANT3 [10] based STAR detector simulation program

In the MC simulation jets are reconstructed at all three jet levels using the same jet finderas in the data The detector-level jets are defined in the same way as in the data The hadron-level jets are collections of final state particles in the event generator while the parton-level jetsare composed of outgoing partons of the hard interactions and the radiation from the outgoingpartons

The MC events well reproduce the data Fig 2 shows the data-MC comparison of the dijetkinematic distributions the invariant mass Mjj the average pseudo-rapidity η = (η3 + η4)2and the pseudo-rapidity difference ∆η = η3 minus η4 distributions

6 Cross Section MeasurementThe dijet cross sections are estimated for each Mjj bin with the formula

d3σ

dMjjdη3dη4=

1intLdtmiddot 1

∆Mjj∆η3∆η4middot 1

Cmiddot J

J is the dijet yields at the detector level C is the correction factors which correct the dijet yieldsto the hadron level The correction factors C are estimated from the MC events as bin-by-binratios of the dijet yields at the detector level and at the hadron level ∆Mjj∆η3∆η4 normalizesthe cross sections to per unit space volume

intLdt = 539plusmn041 pbminus1 is the integrated luminosity

measured using the BBCsThe major systematic uncertainty is due to the uncertainty on the jet energy scale (JES)

Because the Mjj dependence is steeply decreasing the uncertainty of the cross section is verysensitive to systematic uncertainty on the JES

The track portion of the jet energy has 56 of systematic uncertainty To evaluate theeffect of this uncertainty on the cross sections the cross section was reevaluated with the 56 variation of the track portion of the jet energy

Energy deposits in the BEMC towers have 48 of systematic uncertainty The effect of thisuncertainty was evaluated by varying the BEMC tower energies After the energies were variedthe offline trigger thresholds were reapplied and the jet finding algorithm was rerun

Systematic uncertainty due to the correction for the pile-up and the timebin selection areestimated to be small compared to the JES uncertainty The cross section has 76 of correlatedsystematic uncertainty due to the uncertainty of the integrated luminosity

The dijet cross sections are calculated by next-to-leading order perturbative QCD with theCTEQ6M [11] parton distributions Jets are defined by a cone jetfinding algorithm with coneradius 07 Both the renormalization scale and the factorization scale are micro = Mjj The scaleuncertainty is calculated by varying the scale from 05Mjj to 2Mjj

The effects of the hadronization and the underlying events were evaluated by using the MCevents The correction factors CHAD were obtained for each Mjj bin as the ratios of the crosssection at the hadron level and at the parton level The systematic uncertainty on CHAD wascalculated by varying the cone radius from 06 to 08

Figure 3 shows the preliminary results of the dijet cross section measurements The measureddijet cross sections are well described by the theory This indicates that measured ALL aswell can be interpreted in the same theory and suggests ways to constrain the polarized gluondistributions from dijet ALL


5

Mjj [GeV]

d3σdMdη

3dη4

[pb

GeV

]

1

10

102

103

104

105

30 40 50 60 70 80 90

Systematic Uncertainty

TheoryNLO pQCD + CTEQ6M

Had and UE Corrections

STAR Run-6

Dijet Cross Sectionpp 200 GeVCone Radius = 07max(pT) gt 10 GeV min(pT) gt 7 GeV-08 lt η lt 08 |Δη| lt 10|Δϕ| gt 20

⌠⌡Ldt = 539pbminus1

d3σ

dMdη3dη4

STAR Preliminary

Mjj [GeV]

(Dat

a - T

heor

y)

Theo

ry-10

-05

00

05

10

30 40 50 60 70 80 90

Systematic UncertaintyTheoretical Uncertainty

STAR Run-6

Theory CTEQ6M NLO pQCD Had UE Corrections

Data-theory Comparisonof Dijet Cross Sectionpp 200 GeVCone Radius = 07max(pT) gt 10 GeV min(pT) gt 7 GeV-08 lt η lt 08 |Δη| lt 10 |Δϕ| gt 20

⌠⌡Ldt = 539 pbminus1STAR Preliminary

Figure 3 (left) The dijet cross sections compared to theoretical predictions The systematic uncertaintydoes not include 768 of uncertainly due to the uncertainly on the integrated luminosity (right) Theratios (data - theory)theory The theory includes the NLO pQCD predictions and the corrections forthe effects of hadronization and underlying events The ratios are taken bin by bin

7 Longitudinal Double Spin Asymmetry ALL MeasurementThe dijet longitudinally double spin asymmetries ALL were measured as the ratios of the spinsorted dijet yields with the corrections for the relative luminosity and polarizations

ALL =

sumPYPB(Nuarruarr +Ndarrdarr)minusR(Nuarrdarr +Ndarruarr)sumP 2YP

2B(Nuarruarr +Ndarrdarr) +R(Nuarrdarr +Ndarruarr)

The arrows (uarrdarr) indicate the orientations of the helicities of the proton beams The relativeluminosity R = (Luarruarr+Ldarrdarr)(Luarrdarr+Ldarruarr) was measured using the BBCs The relative luminosityvaried between approximately 09 and 11 The polarizations (PYPB) was measured by the pCCNI polarimeter and the polarized H jet polarimeter [12] The average polarization for theYellow beam and the Blue beam of RHIC were PY = 59 and PB = 56 respectively Thefigure-of-merit = P 2

YP2BL for this measurement is 059 pb-1

Four false asymmetries which should vanish are measured for a systematic check of the dataTwo single spin asymmetries and two wrong-sign spin asymmetries were consistent with zerowithin the statistical uncertainties

The largest systematic uncertainty is the trigger bias which is the uncertainty in the changesof ALL from the parton level to the detector level This was evaluated using the MC events withseveral polarized parton distributions which are compatible with the current experimental dataDSSV GRSV std and the GRSV series with ∆G from -045 to 03 [13] [14] In this evaluationin order to calculate ALL with the unpolarized event generator Pythia the MC events wereweighted by the products of the spin asymmetries of the parton distributions and parton-levelcross sections (∆f1(x1i Q

2i )∆f2(x2i Q

2i )f1(x1i Q

2i )f2(x2i Q

2i )) middot aLL(cos θlowasti )


6

Figure 4 shows the preliminary results of dijet ALL measurements It can be seen thatthe results are consistent with the next-to-leading perturbative QCD prediction of the DSSVpolarized parton distributions The results are also consistent with GRSV zero scenario andlarger values of ∆g in GRSV are disfavored

Mjj [GeV]

ALL

-002

000

002

004

006

008

30 40 50 60 70 80

Dijet ALLpp 200 GeVCone Radius = 07max(pT) gt 10 GeVmin(pT) gt 7 GeV-08 lt η lt 08 |Δη| lt 10|Δϕ| gt 20

Data Run-6

Sys Uncertainty

GRSV STDDSSV

GRSV Δg = 0GRSV Δg = minusg ⌠⌡Ldt = 539pbminus1

STARPreliminary

Figure 4 The double longitudinal spin asymmetry ALL for the dijet production as a function of dijetmass Mjj The vertical bars on the data points indicate the size of the statistical errors The horizontalbars on the data points indicate the bin widths The data points are plotted at the mean values of Mjj

of the events in the bins Predictions of next-to-leading perturbative QCD with various models of thepolarized gluon distributions are shown

8 Projected SensitivityData collected during 2009 at RHIC represents a considerable increase in sensitivity to ALL fordijet production Approximately 22 pb-1 were recorded with an average polarization of 59 inboth beams Data corresponding to a figure-of-merit of 096 pb-1 have been processed usingthe TPC and BEMC to measure dijets at mid-rapidity With the additional statistics the datacan be divided into different pseudorapidity acceptances which provides sensitivity to the ratioof x1x2 The invariant mass distribution for different pseudorapidity acceptances is thereforesensitive to different x1 x2 phase space and allows extraction of constraints on the shape of∆g(x)

The two interesting divisions are when the two jets have the same sign pseudorapidity andwhen they have opposite signs The statistical precision of the data analyzed to date can beseen in Fig 5 which is improved over comparable figure-of-merits from previous years dueto improvements in trigger efficiency An expected increase in the figure-of-merit by a factorof between 15 and 20 will provide further improvement of the sensitivity Various studies tounderstand systematic uncertainties are underway

9 SummaryThese proceedings showed the preliminary results of the dijet cross sections and dijet ALL inpolarized proton-proton collisions at

radics = 200 GeV from Run-6 These results agree well

with pQCD calculations and provide constraints on the gluon polarization ∆g(x) in the proton


7

Wed Sep 22 151855 2010 ]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006

east barrel - east barrel and west barrel - west barrel

MCGRSV stdGRSV m03GRSV zeroGS-C(pdf set NLO)

2009 STAR Data

]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

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005

006

east barrel - west barrel

Scale uncertaintyGRSV stdDSSV

Figure 5 The statistical precision of 2009 STAR dijet data analyzed to date The data has been dividedinto two pseudorapidity regions which provide different sensitivities to the Bjorken-x phase space Thedata in the left (right) panel are from when the two jets have the same (opposite) sign pseudorapidity

Projected precision from Run-9 data in multiple acceptances shows that STAR will be able toadd new constraints to the shape of ∆g(x)

AcknowledgmentsWe thank Daniel de Florian for providing tools for theoretical calculations We thank the RHICOperations Group and RCF at BNL and the NERSC Center at LBNL for their support Thiswork was supported in part by the Offices of NP and HEP within the US DOE Office of Sciencethe US NSF the BMBF of Germany CNRSIN2P3 RA RPL and EMN of France EPSRCof the United Kingdom FAPESP of Brazil the Russian Ministry of Education and Science theMinistry of Education and the NNSFC of China IRP and GA of the Czech Republic FOM ofthe Netherlands DAE DST and CSIR of the Government of India Swiss NSF the Polish StateCommittee for Scientific Research SRDA of Slovakia and the Korea Sci amp Eng FoundationFinally we gratefully acknowledge a sponsored research grant for the 2006 run period fromRenaissance Technologies Corporation

References[1] Ashman J et al 1988 Physics Letters B 206 364 ndash 370[2] Ackermann K H et al (STAR) 2003 Nucl Instrum Meth A499 624ndash632[3] Anderson M et al 2003 Nucl Instrum Meth A499 659ndash678 (Preprint nucl-ex0301015)[4] Beddo M et al (STAR) 2003 Nucl Instrum Meth A499 725ndash739[5] Adams J et al (STAR) 2003 Phys Rev Lett 91 172302 (Preprint nucl-ex0305015)[6] Drees A and Xu Z Presented at IEEE Particle Accelerator Conference (PAC2001) Chicago Illinois 18-22

Jun 2001[7] Blazey G C et al 2000 (Preprint hep-ex0005012)[8] Sjostrand T Mrenna S and Skands P 2006 JHEP 05 026 (Preprint hep-ph0603175)[9] Lai H L et al (CTEQ) 2000 Eur Phys J C12 375ndash392 (Preprint hep-ph9903282)

[10] Brun R et al 1987 Technical Report CERN-DDEE84-1[11] Pumplin J et al 2002 JHEP 07 012 (Preprint hep-ph0201195)[12] Okada H et al 2008 Polarized Ion Sources 980 370[13] Gluck M Reya E and Stratmann M 2001 Physical Review D[14] de Florian D Sassot R Stratmann M and Vogelsang W 2008 Phys Rev Lett 101 072001


8

Dijet Cross Section

and Longitudinal Double Spin Asymmetry

Measurements in Polarized Proton-proton Collisions

atradics =200 GeV at STAR

Tai Sakuma1 and Matthew Walker2 for the STAR collaboration1Texas AampM University Department of Physics and Astronomy4242 TAMU College Station TX 778432Massachusetts Institute of Technology Laboratory for Nuclear Science Cambridge MA 02139

E-mail sakumabnlgov

Abstract These proceedings show the preliminary results of the dijet cross sections andthe dijet longitudinal double spin asymmetries ALL in polarized proton-proton collisions atradics = 200 GeV at the mid-rapidity |η| le 08 The integrated luminosity of 539 pbminus1 collected

during RHIC Run-6 was used in the measurements The preliminary results are presented asfunctions of the dijet invariant mass Mjj The dijet cross sections are in agreement with next-to-leading-order pQCD predictions The ALL is compared with theoretical predictions based onvarious parameterizations of polarized parton distributions of the proton Projected precisionof data analyzed to date from Run-9 are shown

1 IntroductionThe jet production rate in polarized proton-proton collisions is sensitive to the polarized gluondistribution ∆g(xQ2) of the proton The polarized gluon distribution is of particular interestin the proton spin physics because the first moment of this distribution is the fraction of theproton spin carried by the gluon spin ∆G

The ∆G is one of the four terms in the decomposition of the proton spin in the infinitemomentum frame

1

2=

1

2Σ + ∆G+ Lq + Lg

where Σ Lq and Lg are the contributions from quark spin quark orbital motion and gluonorbital motion The quark spin contribution Σ has been measured using polarized deep inelasticscattering (pDIS) data combined with neutron and hyperon β decay data [1]

One of the primary objects of the spin physics program at RHIC (RHIC-Spin) is to determine∆G by using polarized proton-proton collisions An advantage of using proton-proton collisionsis that gluons participate in high-pT events at the leading order However it is challenging todetermine the kinematics of parton-level interactions which are desirable quantities to determinein an experimental study of the structure of the proton


Published under licence by IOP Publishing Ltd 1


x1 =pTradics




Mjj =radicx1x2s

η3 + η42

=1

2lnx1x2





ALL =

sumij

intdx1

intdx2∆fi(x1 Q


sumij

intdx1

intdx2fi(x1 Q








2

=-1 =0 =1

TPC

BEMC

BBC

=2

+zYellowBlue

WestEast

+y

IP

BBC

Magnet

EEMC








3






5 MC Simulation

Mjj [GeV]

Dije

t Yie

ld

1

10

102

103

104

30 50 70 90 110

Run-6DataMC

STAR Preliminary

Mjj [GeV]

(Dat

a - M

C)

MC

-1

0

1

40 60 80 100

STAR Preliminary

Dije

t Yie

ld

1

10

102103


1

10

102103


DataMC

η

(Dat

a - M

C)

MC

-1

0

1

-05 00 05 -05 00 05 -05 00 05 -05 00 05

-1

0

1

STAR Preliminary

Dije

t Yie

ld

1

10

102103


1

10

102103


DataMC

|Δη|

(Dat

a - M

C)

MC

-1

0

1

05 10 15 05 10 15 05 10 15 05 10 15

-1

0

1

STAR Preliminary




4





d3σ

dMjjdη3dη4=

1intLdtmiddot 1


Cmiddot J












5

Mjj [GeV]

d3σdMdη

3dη4

[pb

GeV

]

1

10

102

103

104

105

30 40 50 60 70 80 90




STAR Run-6



d3σ

dMdη3dη4

STAR Preliminary

Mjj [GeV]

(Dat

a - T

heor

y)

Theo

ry-10

-05

00

05

10

30 40 50 60 70 80 90


STAR Run-6






ALL =







2i )∆f2(x2i Q

2i )f1(x1i Q

2i )f2(x2i Q



6


Mjj [GeV]

ALL

-002

000

002

004

006

008

30 40 50 60 70 80


Data Run-6

Sys Uncertainty

GRSV STDDSSV


STARPreliminary









7

Wed Sep 22 151855 2010 ]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006



2009 STAR Data

]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006










8


x1 =pTradics




Mjj =radicx1x2s

η3 + η42

=1

2lnx1x2





ALL =

sumij

intdx1

intdx2∆fi(x1 Q


sumij

intdx1

intdx2fi(x1 Q








2

=-1 =0 =1

TPC

BEMC

BBC

=2

+zYellowBlue

WestEast

+y

IP

BBC

Magnet

EEMC








3






5 MC Simulation

Mjj [GeV]

Dije

t Yie

ld

1

10

102

103

104

30 50 70 90 110

Run-6DataMC

STAR Preliminary

Mjj [GeV]

(Dat

a - M

C)

MC

-1

0

1

40 60 80 100

STAR Preliminary

Dije

t Yie

ld

1

10

102103


1

10

102103


DataMC

η

(Dat

a - M

C)

MC

-1

0

1

-05 00 05 -05 00 05 -05 00 05 -05 00 05

-1

0

1

STAR Preliminary

Dije

t Yie

ld

1

10

102103


1

10

102103


DataMC

|Δη|

(Dat

a - M

C)

MC

-1

0

1

05 10 15 05 10 15 05 10 15 05 10 15

-1

0

1

STAR Preliminary




4





d3σ

dMjjdη3dη4=

1intLdtmiddot 1


Cmiddot J












5

Mjj [GeV]

d3σdMdη

3dη4

[pb

GeV

]

1

10

102

103

104

105

30 40 50 60 70 80 90




STAR Run-6



d3σ

dMdη3dη4

STAR Preliminary

Mjj [GeV]

(Dat

a - T

heor

y)

Theo

ry-10

-05

00

05

10

30 40 50 60 70 80 90


STAR Run-6






ALL =







2i )∆f2(x2i Q

2i )f1(x1i Q

2i )f2(x2i Q



6


Mjj [GeV]

ALL

-002

000

002

004

006

008

30 40 50 60 70 80


Data Run-6

Sys Uncertainty

GRSV STDDSSV


STARPreliminary









7

Wed Sep 22 151855 2010 ]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006



2009 STAR Data

]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006










8

=-1 =0 =1

TPC

BEMC

BBC

=2

+zYellowBlue

WestEast

+y

IP

BBC

Magnet

EEMC








3






5 MC Simulation

Mjj [GeV]

Dije

t Yie

ld

1

10

102

103

104

30 50 70 90 110

Run-6DataMC

STAR Preliminary

Mjj [GeV]

(Dat

a - M

C)

MC

-1

0

1

40 60 80 100

STAR Preliminary

Dije

t Yie

ld

1

10

102103


1

10

102103


DataMC

η

(Dat

a - M

C)

MC

-1

0

1

-05 00 05 -05 00 05 -05 00 05 -05 00 05

-1

0

1

STAR Preliminary

Dije

t Yie

ld

1

10

102103


1

10

102103


DataMC

|Δη|

(Dat

a - M

C)

MC

-1

0

1

05 10 15 05 10 15 05 10 15 05 10 15

-1

0

1

STAR Preliminary




4





d3σ

dMjjdη3dη4=

1intLdtmiddot 1


Cmiddot J












5

Mjj [GeV]

d3σdMdη

3dη4

[pb

GeV

]

1

10

102

103

104

105

30 40 50 60 70 80 90




STAR Run-6



d3σ

dMdη3dη4

STAR Preliminary

Mjj [GeV]

(Dat

a - T

heor

y)

Theo

ry-10

-05

00

05

10

30 40 50 60 70 80 90


STAR Run-6






ALL =







2i )∆f2(x2i Q

2i )f1(x1i Q

2i )f2(x2i Q



6


Mjj [GeV]

ALL

-002

000

002

004

006

008

30 40 50 60 70 80


Data Run-6

Sys Uncertainty

GRSV STDDSSV


STARPreliminary









7

Wed Sep 22 151855 2010 ]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006



2009 STAR Data

]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006










8






5 MC Simulation

Mjj [GeV]

Dije

t Yie

ld

1

10

102

103

104

30 50 70 90 110

Run-6DataMC

STAR Preliminary

Mjj [GeV]

(Dat

a - M

C)

MC

-1

0

1

40 60 80 100

STAR Preliminary

Dije

t Yie

ld

1

10

102103


1

10

102103


DataMC

η

(Dat

a - M

C)

MC

-1

0

1

-05 00 05 -05 00 05 -05 00 05 -05 00 05

-1

0

1

STAR Preliminary

Dije

t Yie

ld

1

10

102103


1

10

102103


DataMC

|Δη|

(Dat

a - M

C)

MC

-1

0

1

05 10 15 05 10 15 05 10 15 05 10 15

-1

0

1

STAR Preliminary




4





d3σ

dMjjdη3dη4=

1intLdtmiddot 1


Cmiddot J












5

Mjj [GeV]

d3σdMdη

3dη4

[pb

GeV

]

1

10

102

103

104

105

30 40 50 60 70 80 90




STAR Run-6



d3σ

dMdη3dη4

STAR Preliminary

Mjj [GeV]

(Dat

a - T

heor

y)

Theo

ry-10

-05

00

05

10

30 40 50 60 70 80 90


STAR Run-6






ALL =







2i )∆f2(x2i Q

2i )f1(x1i Q

2i )f2(x2i Q



6


Mjj [GeV]

ALL

-002

000

002

004

006

008

30 40 50 60 70 80


Data Run-6

Sys Uncertainty

GRSV STDDSSV


STARPreliminary









7

Wed Sep 22 151855 2010 ]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006



2009 STAR Data

]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006










8





d3σ

dMjjdη3dη4=

1intLdtmiddot 1


Cmiddot J












5

Mjj [GeV]

d3σdMdη

3dη4

[pb

GeV

]

1

10

102

103

104

105

30 40 50 60 70 80 90




STAR Run-6



d3σ

dMdη3dη4

STAR Preliminary

Mjj [GeV]

(Dat

a - T

heor

y)

Theo

ry-10

-05

00

05

10

30 40 50 60 70 80 90


STAR Run-6






ALL =







2i )∆f2(x2i Q

2i )f1(x1i Q

2i )f2(x2i Q



6


Mjj [GeV]

ALL

-002

000

002

004

006

008

30 40 50 60 70 80


Data Run-6

Sys Uncertainty

GRSV STDDSSV


STARPreliminary









7

Wed Sep 22 151855 2010 ]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006



2009 STAR Data

]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006










8

Mjj [GeV]

d3σdMdη

3dη4

[pb

GeV

]

1

10

102

103

104

105

30 40 50 60 70 80 90




STAR Run-6



d3σ

dMdη3dη4

STAR Preliminary

Mjj [GeV]

(Dat

a - T

heor

y)

Theo

ry-10

-05

00

05

10

30 40 50 60 70 80 90


STAR Run-6






ALL =







2i )∆f2(x2i Q

2i )f1(x1i Q

2i )f2(x2i Q



6


Mjj [GeV]

ALL

-002

000

002

004

006

008

30 40 50 60 70 80


Data Run-6

Sys Uncertainty

GRSV STDDSSV


STARPreliminary









7

Wed Sep 22 151855 2010 ]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006



2009 STAR Data

]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006










8


Mjj [GeV]

ALL

-002

000

002

004

006

008

30 40 50 60 70 80


Data Run-6

Sys Uncertainty

GRSV STDDSSV


STARPreliminary









7

Wed Sep 22 151855 2010 ]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006



2009 STAR Data

]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006










8

Wed Sep 22 151855 2010 ]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006



2009 STAR Data

]2M [GeVc

20 30 40 50 60 70 80

LLA

-002

-001

0

001

002

003

004

005

006










8

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