7.7 11.5 bulk spectra day-one physics and plans · bulk spectra day-one physics and plans frank...

BulkSpectraday-onephysicsandplans

FrankGeurtsRiceUniversity

7.7 11.5

19.6

27

39

ExploringtheQCDPhaseDiagramMotivation:• HadronicgasphaseatlowTandμB

• LatticeQCDcalculations⇾ expectacross-overathighenergies

ØStudyonsetofQGPathighTandμB• nuclearmodification(RCP)• NCQscalingofellipticflow

ØDoweobserveaphasetransitionaswelowerthebeamenergy?Whattypeofphasetransition?

• directedflow• femtoscopy

ØDoweobserveacriticalpoint?• fluctuationanalyses• dielectrons?

ØDoweobservechiralsymmetryrestoration?• dielectrons andlow-massvectormesons

• RHICBeamEnergyScan(PhaseI)• carriedoutin2010-2014• coveredenergiesfrom√sNN=7.7to64GeV

• STARhaspublished16papersbasedonBES-I• fourpaperssubmitted• fiveinpreparation

Darmstadt- 3/18/17 CBM/STARJointWorkshop- BulkSpectra 2

STARBES-IPapersPublished1. PRC86(2012)054908– v2 ofh±

2. PRL110(2013)142301- v2 ofparticlesvs.antiparticles,v2 ofφ3. PRC88(2013)014902– PIDv24. PRL112(2014)032302– net-phighermoments5. PRL112(2014)162301– v1 ofp,pbar,π6. PRL113(2014)052302– chargeseparationalongmagn.field7. PRL113(2014)092301– net-chargehighermoments8. PLB750(2015)64– LMRdielectron at19.6GeV9. PRC92(2015)014904– πHBT10. PRC92(2015)021901– Kπ,p-π,Kp fluctuations11. PRL114(2015)– chargeasymmetrydependenceofπv2 andpossibleCMW12. PRC93(2016)014907 † – centralitydependenceofPIDv213. PRC 93(2016)021903– Ω andφ spectra14. PRC 94(2016)024909– chargebalancefunctions15. PRC 94(2016)034908– v2 oflightnuclei16. PRL116(2016)112302 † – v3ofh±

Submitted1. EnergydependenceofJ/ψ production(39– 200GeV)

arXiv:1607.07517

2. BESglobalΛ polarization†

3. BES3-particlemixedharmonic †

arXiv:1701.06496and1701.06497

4. BESbulkproperties(π/K/pspectra)arXiv:1701.07065

InPreparation1. BESRCP – inGPC‡†

2. BESnet-kaon– inGPC †

3. BESdielectron- inGPC4. BEShypertriton lifetime– readyforGPC5. BESstrangeness– readyforGPC

†includesrun-14√sNN=14.5GeV‡God-ParentCommittee:internalSTAReditorialboard


SelectedResultsfromBESPhase-I

MostmeasurementslimitedbystatisticsandsystematicsØProposalforaBESPhaseIIwithmorestatisticsandnewdetectors

BulkBehaviorChiralVorticalEffectCriticalPoint

PRL112(2014)

PhaseTransition

PRL112(2014)

EnergyLossPenetratingProbes


BeamEnergyScanPhase-IIThe Beam Energy Scan at the Relativistic Heavy Ion Collider 32

Table 2. Event statistics (in millions) needed for Beam Energy Scan Phase-II for various observables.Collision Energy (GeV) 7.7 9.1 11.5 14.5 19.6µB (MeV) in 0-5% central collisions 420 370 315 260 205

Observables

RCP up to pT = 5 GeV/c – 160 125 92Elliptic Flow (f mesons) 100 150 200 200 400Chiral Magnetic Effect 50 50 50 50 50Directed Flow (protons) 50 75 100 100 200Azimuthal Femtoscopy (protons) 35 40 50 65 80Net-Proton Kurtosis 80 100 120 200 400Dileptons 100 160 230 300 400Required Number of Events 100 160 230 300 400

3.1.1. RCP of identified hadrons up to pT = 5 GeV/c High-pT suppression is seen as anindication of the energy loss of leading partons in a colored medium. Therefore, the RAA

measurements are one of the clearest signatures for the formation of the quark-gluon plasma.Because there was not a comparable p+ p energy scan, the BES analysis has had to resortto RCP measurements as a proxy. Still the study of the shape of RCP(pT ) will allow usto quantitatively address the evolution of the phenomenon of jet-quenching to lower beamenergies. A very clear change in behavior as a function of beam energy is seen in thesedata (see Figs. 12 and 13); at the lowest energies (7.7 and 11.5 GeV) there is no evidence ofsuppression for the highest pT values that are reached. However, it should be noted that forthese energies the BES-I measurements are only able to reach 3-4 GeV/c for inclusive hadronsand 2-3 GeV/c for identified hadrons. Typically, one considers pT of 5 GeV/c and above to bedominated by partonic behavior. Therefore, although the BES-I RCP results are suggestive ofa disappearance of this QGP signature, they are not conclusive. The pT reach expected in theproposed BES Phase-II measurements will be crucial in drawing definitive conclusions aboutevidence for the creation of QGP at a given collision energy.

Although the BES-I spectra do not reach high enough pT to extend into the purely hard-scattering regime, they do allow us to make detailed projections of how many events would beneeded to reach a given pT for a given beam energy. We propose to acquire about 400 tracksin the pT range of 4-5 GeV/c for the 11.5, 14.5, and 19.6 GeV energies. At the lower energiesof 7.7 and 9.1 GeV, there is simply not enough kinematic reach to get out to 4-5 GeV/c. Theserequired numbers of events are listed in Table 2

We have used the yields of identified particles measured in BES-I to make projections ofthe expected errors for the RCP measurements with increased statistics expected to be availablein BES Phase-II. For each particle species, energy, and centrality, we have used a exponentialextrapolation (note that this is a more conservative estimate than the power law extrapolation)to estimate the expected number of particles to be measured in each pT bin based on theexpected number of events at each energy shown in Table 2. From this expected number ofparticles per bin, we can estimate the statistical error for the central and peripheral bins andpropagate these to estimate the expected error on the RCP measurements. These projected

STAR

Note59

8


StrongendorsementbyNSACLongRangePlan2015:Ø“TrendsandfeaturesinBES-Idataprovidecompellingmotivationfor[…]experimentalmeasurementswithhigherstatisticalprecisionfromBES-II”

26

2. Quantum Chromodynamics: The Fundamental Description of the Heart of Visible Matter

The trends and features in BES-I data provide compelling

motivation for a strong and concerted theoretical

response, as well as for the experimental measurements

with higher statistical precision from BES-II. The goal

of BES-II is to turn trends and features into definitive

conclusions and new understanding. This theoretical

research program will require a quantitative framework

for modeling the salient features of these lower energy

heavy-ion collisions and will require knitting together

components from different groups with experience

in varied techniques, including LQCD, hydrodynamic

modeling of doped QGP, incorporating critical

fluctuations in a dynamically evolving medium, and more.

Experimental discovery of a critical point on the QCD

phase diagram would be a landmark achievement. The

goals of the BES program also focus on obtaining a

quantitative understanding of the properties of matter

in the crossover region of the phase diagram, where it

is neither QGP nor hadrons nor a mixture of the two, as

these properties change with doping.

Additional questions that will be addressed in this

regime include the quantitative study of the onset

of various signatures of the presence of QGP. For

example, the chiral symmetry that defines distinct

left- and right-handed quarks is broken in hadronic

matter but restored in QGP. One way to access the

onset of chiral symmetry restoration comes via BES-II

measurements of electron-positron pair production in

collisions at and below 20 GeV. Another way to access

this, while simultaneously seeing quantum properties

of QGP that are activated by magnetic fields present

early in heavy collisions, may be provided by the slight

observed preference for like-sign particles to emerge

in the same direction with respect to the magnetic field.

Such an effect was predicted to arise in matter where

chiral symmetry is restored. Understanding the origin

of this effect, for example by confirming indications that

it goes away at the lowest BES-I energies, requires the

substantially increased statistics of BES-II.

NEW MICROSCOPES ON THE INNER WORKINGS OF QGPTo understand the workings of QGP, there is no

substitute for microscopy. We know that if we had a

sufficiently powerful microscope that could resolve the

structure of QGP on length scales, say a thousand times

smaller than the size of a proton, what we would see

Figure 2.10: The top panel shows the increased statistics anticipated at BES-II; all three lower panels show the anticipated reduction in the uncertainty of key measurements. RHIC BES-I results indicate nonmonotonic behavior of a number of observables; two are shown in the middle panels. The second panel shows a directed flow observable that can encode information about a reduction in pressure, as occurs near a transition. The third panel shows the fluctuation observable understood to be the most sensitive among those measured to date to the fluctuations near a critical point. The fourth panel shows, as expected, the measured fluctuations growing in magnitude as more particles in each event are added into the analysis.

are quarks and gluons interacting only weakly with each

other. The grand challenge for this field in the decade

to come is to understand how these quarks and gluons

conspire to form a nearly perfect liquid.

Microscopy requires suitable messengers that reveal

what is happening deep within QGP, playing a role

analogous to light in an ordinary microscope. The

26

2. Quantum Chromodynamics: The Fundamental Description of the Heart of Visible Matter

The trends and features in BES-I data provide compelling

motivation for a strong and concerted theoretical

response, as well as for the experimental measurements

with higher statistical precision from BES-II. The goal

of BES-II is to turn trends and features into definitive

conclusions and new understanding. This theoretical

research program will require a quantitative framework

for modeling the salient features of these lower energy

heavy-ion collisions and will require knitting together

components from different groups with experience

in varied techniques, including LQCD, hydrodynamic

modeling of doped QGP, incorporating critical

fluctuations in a dynamically evolving medium, and more.

Experimental discovery of a critical point on the QCD

phase diagram would be a landmark achievement. The

goals of the BES program also focus on obtaining a

quantitative understanding of the properties of matter

in the crossover region of the phase diagram, where it

is neither QGP nor hadrons nor a mixture of the two, as

these properties change with doping.

Additional questions that will be addressed in this

regime include the quantitative study of the onset

of various signatures of the presence of QGP. For

example, the chiral symmetry that defines distinct

left- and right-handed quarks is broken in hadronic

matter but restored in QGP. One way to access the

onset of chiral symmetry restoration comes via BES-II

measurements of electron-positron pair production in

collisions at and below 20 GeV. Another way to access

this, while simultaneously seeing quantum properties

of QGP that are activated by magnetic fields present

early in heavy collisions, may be provided by the slight

observed preference for like-sign particles to emerge

in the same direction with respect to the magnetic field.

Such an effect was predicted to arise in matter where

chiral symmetry is restored. Understanding the origin

of this effect, for example by confirming indications that

it goes away at the lowest BES-I energies, requires the

substantially increased statistics of BES-II.

NEW MICROSCOPES ON THE INNER WORKINGS OF QGPTo understand the workings of QGP, there is no

substitute for microscopy. We know that if we had a

sufficiently powerful microscope that could resolve the

structure of QGP on length scales, say a thousand times

smaller than the size of a proton, what we would see

Figure 2.10: The top panel shows the increased statistics anticipated at BES-II; all three lower panels show the anticipated reduction in the uncertainty of key measurements. RHIC BES-I results indicate nonmonotonic behavior of a number of observables; two are shown in the middle panels. The second panel shows a directed flow observable that can encode information about a reduction in pressure, as occurs near a transition. The third panel shows the fluctuation observable understood to be the most sensitive among those measured to date to the fluctuations near a critical point. The fourth panel shows, as expected, the measured fluctuations growing in magnitude as more particles in each event are added into the analysis.

are quarks and gluons interacting only weakly with each

other. The grand challenge for this field in the decade

to come is to understand how these quarks and gluons

conspire to form a nearly perfect liquid.

Microscopy requires suitable messengers that reveal

what is happening deep within QGP, playing a role

analogous to light in an ordinary microscope. The

http://science.energy.gov/~/media/np/nsac/pdf/2015LRP/2015_LRPNS_091815.pdf

Studying the Phase Diagram of QCD Matter at RHIC A STAR white paper summarizing the current understanding and describing future plans 01 June 2014

DedicatedsecondphaseoftheBESprogram,proposedin2014

BESIIFixedTargetModeProposaltoextendCMSenergyrangefrom7.7downto3GeVØ increaseμB rangefrom420MeVto720MeV


Expect1-2daysdedicatedbeamtimeperenergy≈50Mevents/day

ColliderEnergy

Fixed-TargetEnergy

Single-beamAGeV

Center-of-MassRapidity

μB(MeV)

62.4 7.7 30.3 2.10 420

39 6.2 18.6 1.87 487

27 5.2 12.6 1.68 541

19.6 4.5 8.9 1.52 589

14.5 3.9 6.3 1.37 633

11.5 3.5 4.8 1.25 666

9.1 3.2 3.6 1.13 699

7.7 3.0 2.9 1.05 721

TheSTARUpgradesandBESPhaseIIEndcap TOF

iTPC Upgrade:• RebuildstheinnersectorsoftheTPC• Continuouscoverage• ImprovesdE/dx• Extendsh coveragefrom1.0to1.5• LowerspT cut-offfrom125MeV/cto60MeV/c

EPDUpgrade:• Improvestrigger• Reducesbackground• AllowsabetterandindependentreactionplanemeasurementcriticaltoBESphysics

EndcapTOFUpgrade:• Rapiditycoverageiscritical• PIDath =1.1to1.5• Improvesthefixedtargetprogram• ProvidedbyCBMatFAIR


An Event Plane Detector for STAR

EPD East/West 24 sectors each 16 radial segments 2.1<|�|<5.1

16 channels WLS to clear fiber connector

G10 mechanical support in four quadrants

Clear fiber to SiPM connector on FEE board

May 2016

https://drupal.star.bnl.gov/STAR/system/files/EPD_Construction_Pro

posal.pdf

Physics Program for the STAR/CBM eTOF Upgrade

The STAR CollaborationThe CBM Collaboration eTOF Group

(Dated: September 19, 2016)

arX

iv:1

609.

0510

2v1

[nuc

l-ex]

16

Sep

2016

arXiv:1609.05102v1

A Proposal for STAR Inner TPC Sector Upgrade (iTPC)

The STAR Collaboration June 9th, 2015

STARNote619

iTPC +eTOF :AcceptanceConsiderations

spaceforendcapTOFmodules

Darmstadt- 3/18/175 of 20

Daniel Cebra 8/19/2016

Outer Sectors 32 pad rows

Inner Sectors 13 or 40 pads rows

η=0.96

η=1.9

η=1.5 190

126 120

60

210

-200

cm

LT

η=0

η=1.0

η=1.09

η=1.62

Barrel TOF

eTO

F

PseudoRapidity Considerations

eTOF: Z = -270 cm Rmin = 110 cm Rmax = 220 cm

-270

Note: There is and acceptance gap between bTOF and wTOF

Motivation is to mount eTOF modules at as large a Z and radius as possible Î limit is magnet iron

η=0.9

η=1.6

η=1.1

η=1.6

CBM/STARJointWorkshop- BulkSpectra 8

Note:ThereisanacceptancegapbetweenBTOFandeTOF

iTPC +eTOF :PIDinColliderMode

π K p e

• LowerpT limit– fromtracklengthoftheTPC(multiplescattering);• forBTOFlowerpT limitfromminimaltrackrigidity

• HighpT limit– fromtheTOFtimeresolution(σTOF =100and80ps ranges)


BES-II:IdentifiedParticlev2• BES-I:clearindicationsofbaryon-mesonsplittingathigherenergiesfor√sNN ≥19.6GeV

• NCQscalingseenforhigherenergies

• scalingindicationofpartonicbehavior

Øφ mesonmaynotfollowtrendsbelow19.6GeV

ØNeedmorestatistics:• forenergiesbelow√sNN ≤11.5GeVlimitedbystatistics

• improvestatisticsforφ mesonat7.7and11.5GeV

ØiTPC/EPD:improveEPresolutionDarmstadt- 3/18/17 CBM/STARJointWorkshop- BulkSpectra 10

STAR,PRC93(2016)014907

EPDConstructionProposalSTAR,PRC88(2013)014902

• Directedflowexpectedtobesensitivetoearlyevolutionofcollision

• modelswithexplicit1st orderphasetransitionpredictdipofv1 slopewithdouble-signchange

• net-protonsproxyfortransportedprotons

• BES-I:Minimuminnet-protonv1 slope• interplaybetweenbaryonstoppingandsoftEOSØBES-II:improvestatisticsØBES-II:improvedevent-planeresolutionfromEPD

• includeΛ baryons

• Forwardv1 measurementsasafunctionofcentralityØBES-II:improvementsduetoextendediTPC coverage

STAR,PRL112(2014)032302BES-II:DirectedFlowMeasurements


BES-I:BulkSpectraandFreeze-outParameters• Statistical-thermalmodelsincombinationwithmeasuredparticleyieldsallowtheextractionofchemical(Tchem,μB)andkinetic(Tkin,β)freeze-outparameters.

ØTkin andTchem arecomparablefor√sNN ≤7GeV

• Strongercollectivityathigherbeamenergies

• CentralcollisionsshowlowerTkin andhigherβ

arXiv:1701.07065


BES-II:BulkSpectraandFreeze-outParametersØiTPC :LoweringthelowerpT cut-offfrom125to60MeV/c

• Reducethemagnitudeofextrapolationby~2x

• Reduceuncertaintyonfinalyields

arXiv:1701.07065


LowpT Yieldw/oiTPC

Low pT YieldwithiTPC

pion 35% 18%

kaon 17% 8%

proton 13% 5%

YieldErrorw/oiTPC

YieldErrorwithiTPC

pion 9% 5%

kaon 7% 4%

proton 14% 6%

BES-II:π-/π+ RatiosLoweringpT cut-offto60MeV/c:

• AllowforstudyofCoulombpotentialofthesourceØrelatestobaryonstopping• … protonsbring(net)positivechargetointeractionregion

• MeasureCoulombenhancementforofπ-/π+ ratiosforpT<100MeV/c


D.Cebra,etal. arXiv:1408.1369

3

10

10 2

10

10 2

10

10 2

0 0.1 0.2 0 0.1 0.2 0 0.1 0.2 0.3mt-m0 (GeV/c2)

π-

π+

Au+Au 1 AGeVKaoS

Au+Au 2 AGeVE895

Au+Au 4 AGeVE895

Au+Au 6 AGeVE895

Au+Au 8 AGeVE895

Au+Au 10.8 AGeVE866

Pb+Pb 20 AGeVNA49

Pb+Pb 30 AGeVNA49

Au+Au 42 AGeVSTAR

1/(2πm

t)dN

2 /dm

tdy

((G

eV/c

2 )-2)

FIG. 1. The mid-rapidity mt�m0 spectra are shown for neg-ative (solid symbols) and positive (open symbols) pions fromcentral Au+Au and Pb+Pb collisions at 1.0 [14], 2.0 [20],4.0 [20], 6.0 [20], 8.0 [20], 10.8 [16], 20 [28], 30 [28], and42 [29] AGeV. The Coulomb distortion is exhibited by thedivergence of the spectra at low mt �m0. The spectra are fitwith a Bose-Einstein function modified by Coulomb acceler-ation due to the e↵ective potential from Eqn. (4). A singletemperature parameter is used at each bombarding energy tosimultaneously fit the ⇡� (solid) and the ⇡+ (dashed).

final pion ratio as a function of Ef is given by:

Rf (Ef ) =Ef � VC

Ef + VC

p(Ef � VC)2 �m

2

p(Ef + VC)2 �m

2

n

+(Ef � VC)

n

�(Ef + VC)

(2)where the n±(E) are the pion emission functions describ-ing the initial ⇡± spectrum. In general, the pion emissionfunctions in heavy-ion collisions are best represented bya Bose-Einstein distribution, so that:

n

+(Ef � VC)

n

�(Ei + VC)=

A

+(e(Ef+VC)/T⇡ � 1)

A

�(e(Ef�VC)/T⇡ � 1)(3)

where T⇡ is the slope parameter and the A

± are the am-plitudes characteristic of the initial pion distributions.The initial pion ratio, Ri, is defined as A

+

/A

�. Inreference [19], E877 replaced Eqn. (3) with a constant‘overall’ pion ratio, R

0. If one assumes a Maxwell-Boltzmann distribution for the initial pion spectra, then

R

0 = Rie2VC/T⇡ . However, using a Bose-Einstein form

for the initial pion spectra results in an energy depen-dent emission function ratio, n+(Ef �VC)/n

�(Ei+VC),that can not be approximated with a constant R0.The assumption of a static source is not valid for

heavy-ion collisions. During the course of the interac-tion, the protons, which carry the bulk of the sourcecharge, are emitted simultaneously with the pions. Thusthe charged source is expanding during the course of theCoulomb interaction. Therefore, the low momentum pi-ons do not experience the full Coulomb potential butrather a reduced potential. This reduced Coulomb po-tential, as a function of pion momentum, can be cal-culated by integrating the proton emission function upto a maximum kinetic energy corresponding to the pion

velocity, Emax

=q

(mpp⇡/m⇡)2 +m

2

p � mp. Assuming

that the proton emission function is given by a Maxwell-Boltzmann distribution with a characteristic slope pa-rameter Tp, the e↵ective Coulomb potential is:

V

e↵

= VC(1� e

�Emax

/Tp) (4)

The mid-rapidity pion ratios for beam energies 1 to158 AGeV are shown in Fig. 2 (references to the exper-imental data are given in the figure caption). The dataare fit to the ratio function as given in Eqn. (2). The twocurves in each panel correspond to either a fixed VC or aV

e↵

given by Eqn. (4). For these fits, we have fixed theslope parameters of the pion and proton initial distribu-tions to the values given in Table I. The pion initial slopeparameters were fixed by simultaneously fitting the ⇡

+

and ⇡

� spectra in the range 0 < mt �m

0

< 0.5 GeV/c2

to Coulomb-modified Bose-Einstein distributions.

1

2⇡mt

d

2

N

dydmt(Ef ) = (Ef⌥Veff )

p(Ef ⌥ Veff )2 �m

2

A

±

(e(Ef⌥Veff )/T⇡ � 1)(5)

where Ef = mtcoshy, A± is a normalization constant,

and Veff is given by Eqn. (4). These fits are shownby the solid (⇡�) and dashed (⇡+) curves in Fig. 1. Thepion slope parameters used in this analysis are lower thanthose reported previously [14, 16, 20] at each beam energybecause this analysis focuses on the mt �m

0

region be-low 0.5 GeV/c2, whereas the published slope parameterscome from fits to higher mt �m

0

regions of the spectra.The proton slope parameters given in Table I were de-termined using Maxwell-Boltzmann fits to spectra datafrom previous publications [26, 45–53]. For this analysis,the fit range was limited to 0.25 < mt�m

0

< 1.0 GeV/c2.The slope parameters used in this analysis are similar tothose cited by the authors of the original studies.The fits to the pion ratio data in Fig. 2 were achieved

with two free parameters, the Coulomb potential, VC ,and the initial pion ratio, Ri. It is evident that the lowmt�m

0

data points are better fit by the e↵ective poten-tial (solid curve) than by a fixed VC (dashed curve). Themagnitude of the correction due to the e↵ective Coulombpotential of Eqn. (4) is determined by the proton slope

5

5

10

15

20

25

30

35

sNN (GeV)

0

0.1

0.2

0.3

(dN

/dy)

y=0/N

part

dN/dy

Cou

lom

b Po

tent

ial V

C (M

eV)

VC

Initi

al P

ion

Rat

io (R

i)

0

0.2

0.4

0.6

0.8

1

2 3 4 5 6 7 8 9 10 20

FIG. 3. The top panel shows in solid symbols the Coulombpotential (VC) extracted from the fits to the pion ratiodata shown in Fig. 2 as a function of center-of-mass energy(psNN ). In open symbols the normalized net-proton rapid-

ity densities are shown, (dN/dy)y=0/Npart; their axis label ison the right-hand side. The curve in this panel is an empir-ical fit to the net-proton dN/dy data. The proton rapiditydensity results are from references [29, 47, 49, 51, 52]. Thelower panel shows the initial pion ratio, (Ri), extracted fromthe pion ratio fits as a function of center-of-mass energy. Thefit to the data illustrates a smooth transition from pion pro-duction exclusively through the � resonance channel at thelowest collision energies to thermal production at the highestenergies.

the trend. The VC values track the decrease in net-protondN/dy. This suggests that the VC is primarily measuringthe charge of the net-charge of the interaction region andthe implication is that the emission radius remains un-changed across the range of bombarding energies consid-ered. This final conclusion is consistent with the trendsobserved for the sidewards pion source radius (Rside) asmeasured in two-pion femtoscopy. In those femtoscopystudies, Rside is observed to be approximately 5 fm forall

psNN from 2.5 to 200 GeV [55].

The monotonic increase in the initial pion ratio, Ri,with beam energy seen in the lower panel of Fig. 3 sug-gests a change in the pion production mechanism. Atthe lowest reported energies, Ri is slightly below 0.5.This ratio value is expected if all pions were created

in first-chance nucleon-nucleon collisions that proceededthrough the � resonance. This value is determined bythe neutron-to-proton ratio in the the central interactionregions of Au+Au collisions. From the numbers of par-ticipating protons and neutrons, the relative numbers ofpp, np, and nn collisions can be calculated. As the crosssections for the various N + N ! N + N

0 + ⇡ channelsare known [41], one can calculate the expected ⇡

+

/⇡

�

ratio. From Glauber Monte Carlo models using �NN =45 mb (which is applicable for center-of-mass energiesaround 2.5 GeV), we estimate that for the 0-5% centralAu+Au data there should be 136 and 218 participatingprotons and neutrons respectively. Using the pion pro-duction cross sections from [41], we estimate a ⇡

+

/⇡

�

ratio of 0.47. It is also possible to estimate the relativeyields of ⇡+ and ⇡

�, assuming that all pions are createdthough an intermediary � resonance. Using the isospinof the initial and final states, one can calculate the rel-ative production ratios for the various charge states ofthe � resonance and the relative decay ratios of the �+

and the �0. Using the same number of participatingprotons and neutrons indicated above and the analysiswhich exclusively requires production through � reso-nance channel in first chance collisions, we expect an Ri

of 0.46. Both of these methodologies reproduce the Ri

value extracted using the pion spectra from SIS [14, 15]at 1 AGeV (

psNN = 2.33) suggesting that ⇡ produc-

tion proceeds primarily through the � resonance at thisenergy.The increase in Ri with beam energy suggests that an

increasingly larger fraction of pions are formed in isospinindependent direct production. Direct production of pionpairs would lead to an equal number of ⇡+ and ⇡

�. Thisconjecture is illustrated by the curve in the lower panelof Fig. 3. The curve assumes that the cross sections for⇡ production through the � channel remain unchangedwith

psNN . For center-of-mass energies above 2.33 GeV,

the cross section for ⇡ pair production (�NN!NN⇡+⇡�)is linearly proportional to (

psNN -2.33) GeV. The func-

tional form of the curve is given by:

f(x) =0.47 +A(log(x)� log(2.33))

1.0 +A(log(x)� log(2.33))(6)

where the numerator represents the yield ⇡

+, the denom-inator the yield of ⇡�, x is the

psNN , and A is the slope

of the isospin dependent pion production. The quali-tative agreement between the curve and the observed Ri

values suggests that production through isospin indepen-dent channels becomes increasingly important with col-lision energy.

III. CONCLUSIONS

We have presented a comprehensive study of the lowmt �m

0

pion ratios for central Au+Au and Pb+Pb col-lisions from 1 to 158 AGeV. The spectra and ratios are

ØDecreaseofVC indicativeofexpansionofsourceorreductioninbaryonstopping

BES-II:BulkSpectraandRapidityDependenceiTPC allowsmeasurementsthatextendtolargerrapidities

• protonrapiditytoy=1.6(70%ofyieldat19.6GeV)• RHICwillrunlongerbunches⟹displacedverticesouttoy=2.3(90%ofyieldat19.6GeV)

ØSTAR::fromamid-rapiditytoa4πdetectorExpecttoimproveconstraintsonthermodynamics

• AtNA49:fromy=0to1.2:• nochangeinprotonyields,but~50%changeinanti-protons

• indicatorforchangesinμB• factorof2indN/dy ⟹ ΔμB ≈50MeV

ØFurtherincluderapiditydependenceinthecolliderphysicsprogra

• dileptons,directedflow,ellipticflow,fluctuations,…


STAR,arXiv:1609.05102

BES-I:NuclearModification• LHC/RHIC@200GeVhigh-pT suppression• BES-1:disappearanceofhigh-pTsuppression

• enhancementandsuppressionmechanismscompete

• evidentsuppressionathighbeamenergies• noevidencebelow14.5GeV

STAR@QM2015

CMS, EPJ C72 (2012) 1945


Investigatecompetingenhancementandsuppressionasafunctionofcentrality

Y 𝑁"#$% = '()*+,--'./'0 12314"5728

Observethatmostcentraldatafor√sNN ≥14.5GeVturnover⇒ suppression

200GeVdecreasesmonotonically7.7and11.5GeVincreasemonotonically

STAR@QM2015

BES-I:StrangenessRCP• Ks0 RCP increaseswithdecreasingbeamenergiesØ Effectfrompartonic energylosslessimportantatlower√sNN

• CNMeffectstakeoveratcollisionsenergies

• RCP differencesbetweenparticleslesspronouncedatsmallcollisionsenergies

• √sNN =7.7,11.5GeVcomparedto√sNN ≥19.6GeVØ indicativeofdifferentpropertiesofsystem

whengoingtolowerenergies


STAR@SQM2016

BESStrangeness:Ω andφ Production

• Coalescenceandrecombinationmodelsfor200GeV:

• Ω uptopT =6GeV/cdominatedbythermalquarkrecombination

• recombinationforφ upto4GeV/c• expectstraightline ofN(Ω + Ω;)/2N(φ)vs pT withdeviations~4GeV/c

• BESmeasurements• ratiosfor19.6– 39GeVfollow200GeV• at√sNN =11.5GeVturndownatpT =2GeV/c• Ω andφ havesmallhadroniccrosssections

Ø earlyturn-downoriginatesfrompartonic phase?

ØNeedfurtherstudybelow19.6GeV• increasestatistics• improvesystematics

STAR,PRC93021903(2016)


StrangenessBaryon-to-MesonRatio:Λ;/𝐾?@

• EnhancementofΛ;/𝐾?@ ratiosatintermediatepTØ duetoparton recombinationandcollectivity

• Separationofcentral(0-5%●)andperipheral(40-60%□)

Ølessobviousfor√sNN ≤14.5GeV• lessbaryonenhancement⟹ possiblechangeofmediumproperties

ØNeedmorestatisticsatlowercollisionenergies

17�Strangeness in Quark Matter, 27 June - 1 July 2016

Ø  The separation of central (0-5%) and peripheral (40-60%) collisions in the ratio less obvious when collision energy ≤ 14.5 GeV: less baryon enhancement

-> possible change of medium property Ø  Need more statistics at lower

beam energies �

/KS0 Ratio

0 1 2 3 40

0.2

0.4

0.6

0.8

139GeV

STAR Preliminary0 1 2 3 40

0.2

0.4

0.6

0.8

127GeV

STAR Preliminary

0 1 2 3 40

0.2

0.4

0.6

0.8

119.6GeV

STAR Preliminary0 1 2 3 40

0.2

0.4

0.6

0.8

1 0-5%5-10%10-20%20-30%30-40%40-60%60-80%

14.5GeV

STAR Preliminary

0 1 2 3 40

0.1

0.2

0.3

11.5GeV

STAR Preliminary

0 1 2 3 40

0.1

0.2

0.3

7.7GeV

STAR Preliminary

(GeV/c)TP

0 s/K

Λ

Enhancement of baryon at intermediate pT in central collisions: parton recombination �

Λ


STAR@SQM2016

“… (issuesandimprovements)”thesecondpartofthetitle


Somethoughtson…

Timetopublication

BES-I:2010/2011(+2014)• FirstGPCswithinayear.Great!

ü DetectorcalibrationandproductionQA• Increasedcomplexity⟹moretimebeforeGPCisformed

• complex/newalgorithms;mayneedmoreQA• realisticdetectorsimulationsforcorrections,

incl.efficiencycalculations(embedding)Ø but,alsodangerofattritioninanalysisteam

• Resourcecompetition:BESinvolvesmany(small)datasets

Ø but,embeddinginprinciplestillneededforeachrunningcondition

BES-II:2019/2020Howtospeed-uptime-to-publication?• canweimproveproductionturn-around?

• e.g.calibrationsproceduresfamiliar– involveHLT?Ø newdetectors:iTPC,EPD,andETOF-

reconstruction/calibrationreadiness

• picoDST distributionacrossinstitutes?Ø Identifyearlyanalysisteams

• encouragemultipleindependentteams• test-drivereconstruction+analysis chains• setupPWGstructuresforQAcross-checkandcombination• encourageearlypaperdrafts

ü continueactiveinternaltrackingofGPCs(fromGPCtojournal)


2012 2013 2014 2015 2016 2017

published 1 2 4 4 5(1) -

submitted 1 3 5 5 3 3

GPC 3 7 3 5(1) 6(5)

(run-14)

ShortSummary…

• BES-IIProposalcallsformorestatisticsandnewdetectors• iTPC,EPD,andETOFdetectorupgradesareallwellunderway• severalday-onebulk-spectratopicsaregettinginthestartingblocks

• significantimprovementsinuncertainties• enablenewmeasurements

• Encouragemultiple,independentanalysisteams• importantinternalQAchecksbetweenteams• prepare(skeleton)paperdraftsearlyon


Backup


07/01/2016 Alexander Schmah - STAR Upgrades 15

The Event Plane Detector

TPC

EPD

• Large eta coverage 2.1< |η|< 5.1 compared to TPC (|η|<1.0), • Installed at z position +/- 375 cm • High η (radial, 16) and azimuthal (24) segmentation • Good timing resolution (~ 1 ns) " Adds mid-rapidity independent event plane and centrality determination. Also used as trigger detector for BES-II.

More details: see talk by Jinlong Zhang η = 1

η = 2.1

η = 5.1

EventPlaneDetector:coverage


Jinlong ZhangAlexSchmahatSQM2016

An Event Plane Detector for STAR

EPD East/West 24 sectors each 16 radial segments 2.1<|�|<5.1

16 channels WLS to clear fiber connector

G10 mechanical support in four quadrants

Clear fiber to SiPM connector on FEE board

May 2016

https://drupal.star.bnl.gov/STAR/system/files/EPD_Construction_

Proposal.pdf

7.7 11.5 bulk spectra day-one physics and plans · bulk spectra day-one physics and plans frank...

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