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Nuclear Physics A NuclearPhysicsA00(2016)1–4 www.elsevier.com/locate/procedia Transverse Energy Measurements from the Beam Energy Scan in PHENIX 6 1 J.T. Mitchell (for the PHENIX Collaboration)1 0 2 BrookhavenNationalLaboratory,Building510C,P.O.Box5000,Upton,NY11973-5000 n a J 5 ] Abstract x e TransverseenergydistributionsatmidrapidityhavebeenmeasuredbythePHENIXexperimentattheBNLRelativistic - HeavyIonCollider(RHIC)forAu+Au,U+U,Cu+Au,Cu+Cu,3He+Au,d+Au,andp+pcollisionsoverawideenergy l c rangefrom √s =7.7GeVto √s =200GeVasafunctionofcentrality.ForcentralAu+Aucollisions,itisobserved u thatthemidrapNidNityBjorkenenergNyNdensitydemonstratesapowerlawbehaviorfrom √s =7.7GeVto √s =2.76 n NN NN TeV.Atagivencollisionenergy, thedatapresentedasafunctionof N areindependent ofthesizeofthecollision [ part system. ForAu+Au,Cu+Au,andCu+Cucollisions,thecentrality-dependentdataarebetterdescribedbyscalingwith 1 thenumberofconstituentquarkparticipantsthanscalingwiththenumberofnucleonparticipants. v Keywords: 4 0 9 1. Introduction 0 0 ThePHENIXexperimentattheBNLRelativistic HeavyIonCollider(RHIC)hascompiledacompre- . 1 hensive dataset from the years 2000 to 2015 that includes collisions of Au+Au, U+U, Cu+Au, Cu+Cu, 0 3He+Au,d+Au,and p+pcollisionsatavarietyofcollisionenergies.Thisdatasetcanbeexploitedtostudy 6 the dynamics of the colliding system with measurements of transverse energy production at midrapidity, 1 : dET/dη, as a function of collision energy and centrality. This study is complementary and extends pre- v viousstudies of dynamicsbased on chargedparticle multiplicity productionby the PHOBOS experiment i X [1]. AlthoughPHENIXhasalsomeasuredchargedparticlemultiplicity[2,3],onlytransverseenergymea- r surementswill bepresentedin thisarticle. Moredetailsonthe PHENIXtransverseenergymeasurements a presentedherecanbefoundelsewhere[2,4,3]. 2. EnergyDependenceofTransverseEnergyProduction Figure1(left)showstransverseenergyproduction,(dE /dη)/(0.5N ),forcentralAu+AuandPb+Pb T part collisionsatmidrapidityasafunctionof √sNN. Above √sNN = 7.7GeV, thevalueof(dET/dη)/(0.5Npart) 1ForthefullPHENIXCollaborationauthorlistandacknowledgements,seeAppendix“Collaboration”ofthisvolume. 2 /NuclearPhysicsA00(2016)1–4 is observed to be well described by a power law, (dET/dη)/(0.5Npart) ∝ √sNNb, where the exponent is b=0.428 0.021.TheseresultscanalsobeexpressedintermsoftheBjorkenenergydensity[5] ± 1 dE ε = T (1) BJ A τ dη ⊥ where A isthetransverseoverlapareaofthenucleideterminedfromtheGlaubermodelandτisthefor- mationti⊥me,typicallyestimatedtobe1fm/c. Figure1(right)showstheBjorkenenergydensitymultiplied bytheformationtimeforcentralAu+AuandPb+Pbcollisionsabove √s =7.7GeV.Thesedataarewell NN describedbyεBJτ∝ √sNNb,whereb=0.422±0.035. 10 PHENIX 0-5% Au+Au V] 10 CMS 0-5% Pb+Pb 5 N) [Gepart1 PCHMESN 0IX-5 0%-5 P%b +APub+Au 2eV/(fm c)] 0. G η/(/dET10-1 SNTAA4R9 00--75%% APbu++APbu τε [ BJ d E802 0-5% Au+Au FOPI 0-1% Au+Au 10-2 1 1 10 102 103 10 102 103 s [GeV] s [GeV] NN NN Fig.1. (Left)(dET/dη)/(0.5Npart)asafunctionof √sNN forcentralAu+AuandPb+Pbcollisions. InadditiontothePHENIXdata, dataareshownfromFOPI[6],E802[7],NA49[8],STAR[9],andCMS[10].ThelineisapowerlawfittothePHENIXdata.(Right) εBJmultipliedbyτasafunctionof √sNN forcentralAu+AuandPb+Pbcollisions. InadditiontothePHENIXdata,dataareshown fromCMS[10].Thelineisapowerlawfittoallofthedatapoints. 3. SystemSizeDependenceofTransverseEnergyProduction ThePHENIXdatasetincludesAu+Au,Cu+Au,andCu+Cucollisionsat √s =200GeValongwith NN Au+AuandCu+Cucollisionsat √s =62.4GeV.Thisfacilitatesastudyofthesystemsizedependenceof NN transverseenergyproduction. Figure2showstheBjorkenenergydensitymultipliedbytheformationtime asa functionof N forthese systems. Atagivencollisionenergy,ε forsystemsofdifferingsizes are part BJ consistentwitheachother. ThisdemonstratesthatεBJ isindependentofthesystemsizeat √sNN =200and 62.4GeV. 4. CentralityDependenceofTransverseEnergyProduction Thecentralitydependenceof(dE /dη)/(0.5N )istypicallyexpressedintermsofthenumberofnu- T part cleonparticipants,Npart,asshowninFigure3(left)forAu+Aucollisionsfrom √sNN =7.7to200GeV.Note thatthe midrapiditydata increase with increasing N and are notconsistentwith scaling by the number part ofnucleonparticipantsinAu+Aucollisionsfrom √s =200GeVallthewaydownto √s =7.7GeV. NN NN The data can also be examined as a function of centrality expressed as the number of constituent quark participants,N [11]. ThishasbeenestimatedusingaGlaubermodelcalculationthathasbeenmodifiedto qp replacenucleonswiththeirconstituentquarks[3]. TheresultsareshowninFigure3(right),whichshows (dET/dη)/(0.5Nqp)asafunctionofNqp forAu+Aucollisionsfrom √sNN =200GeVdownto7.7GeV.For allenergies,thedataarebetterdescribedbyscalingwithN thanscalingwithN . Thisisconsistentwith qp part /NuclearPhysicsA00(2016)1–4 3 6 200 GeV Cu+Au 200 GeV Cu+Cu 62.4 GeV Cu+Cu 200 GeV Au+Au c)] 62.4 GeV Au+Au 2 m 4 V/(f e G τ [ BJ 2 ε PHENIX 0 100 200 300 400 N part Fig.2. εBJasafunctionof √sNN forAu+Au,Cu+Au,andCu+Cucollisionsat √sNN =200and62.4GeV.Theerrorbarsrepresent thestatisticalandsystematicerrors. previousstudiesofchargedparticlemultiplicitydistributionsmeasuredbyPHOBOSdownto √s =19.6 NN GeV[12].Figure4shows(dET/dη)/(0.5Nqp)asafunctionofNqpforCu+AuandCu+Cucollisionsat √sNN =200and62.4GeV.ThedataarealsobetterdescribedbyscalingwithN forthesmallersystems. qp eV] 5 200 GeV Au+Au eV] 200 GeV Au+Au G 130 GeV Au+Au G 130 GeV Au+Au η [)) / (0.5 N/d(dE[y=0]Tpart43 63211729794.7... 465GG G eeGGGeVVeeeV VVVAA A uuAAAu++uuu+AA+++AuuAAAuuuu η [)) / (0.5 N/d(dE1qp[y=0]T.521 63211729794.7... 465GG G eeGGGeVVeeeV VVVAA A uuAAAu++uuu+AA+++AuuAAAuuuu 2 0.5 1 PHENIX PHENIX 0 0 100 200 300 Np4ar0t0 0 500 100N0qp Fig. 3. (Left) (dET/dη)/(0.5Npart) as a function of Npart for Au+Au collisions from √sNN = 200 GeV to 7.7 GeV. (Right) (dET/dη)/(0.5Nqp)asafunctionofNqp forAu+Aucollisionsfrom √sNN =200GeVto7.7GeV.Forbothplots,thelinesbound- ingthepointsrepresentthetriggerefficiencyuncertaintywithinwhichthepointscanbetilted. Theerrorbarsrepresenttheremaining statisticalandsystematicerrors. 5. Summary ThePHENIXexperimenthascompletedasystematicsurveyoftransverseenergyproductioninavariety ofcollisionsystemsfor √s =7.7GeVto √s =200GeV.TheBjorkenenergydensityforcentralAu+Au NN NN collisionsatmidrapidityiswelldescribedbya powerlaw from √s = 7.7GeV upto √s = 2.76TeV. NN NN At √sNN = 200 and 62.4 GeV, (dET/dη)/(0.5Npart) presented as a function of Npart is independentof the size of the system. For √s = 7.7 to 200 GeV, it is observedthattransverse energyproductionis better NN 4 /NuclearPhysicsA00(2016)1–4 V] 2 e G [)N1qp[y=0].5 5 0. η) / ( d /ET d 1 ( 200 GeV Cu+Au 200 GeV Cu+Cu 0.5 62.4 GeV Cu+Cu PHENIX 0 0 200 400 600 N qp Fig.4. (dET/dη)/(0.5Nqp)asafunctionofNqpforCu+AuandCu+Cucollisionsfor √sNN =200GeVand √sNN =62.4GeV.The linesboundingthepointsrepresentthetriggerefficiencyuncertaintywithinwhichthepointscanbetilted.Theerrorbarsrepresentthe remainingstatisticalandsystematicerrors. described by scaling with respect to the number of constituent quark participants than by the number of nucleonparticipants. References [1] B. Alver, et al., Phobos results on charged particle multiplicity and pseudorapidity distributions in Au+Au, Cu+Cu, d+Au, and p+p collisions at ultra-relativistic energies, Phys.Rev. C83 (2011) 024913. arXiv:1011.1940, doi:10.1103/PhysRevC.83.024913. [2] S. 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