Results

(GeV)NNs3 4 5 6 7 10 20 30

y=0

/dy

|1

dv

0

0.1

0.2

0.3

10-40 %

Λ Λ p p

+ K - Ks0 K φ (FXT)Λ (FXT)s

0 Kp (FXT) p (E895)

(FXT)+π (FXT)-π

DirectedFlowinSTARFixedtargetExperiment

D. Tlusty, for the STAR Collaboration

The STAR Collaborationdrupal.star.bnl.gov/STAR/presentations

AbstractSomeQGPsignatures,suchasnumber-of-constituent-quarksscalingofv2,canbeseentopersistdownto√sNN =7.7GeV,whileothers,suchassuppressionRCP,showaturn-onbehavior.FixedtargetcollisionsinSTARallowthecenter-of-massenergytogoaslowas4.5GeV.Thiswouldprovideanopportunitytomeasuresuchsignaturesdowntoanenergyrangethat canserveasaclean"control"energyinwhichonlyapurehadrongasisexpected.InthisposterwewillpresentDirectedflowofstrangehadronsK0S and.

References[1] L. Adamczyk et al. (STAR Collaboration), Phys.Rev.Lett.112, 162301(2014)[2] A. M. Poskanzer, S. A. Voloshin, Phys. Rev. C 58, 1671 (1998)[3] P. Chung et al. (E895 Collaboration), Phys. Rev. Lett. 86, 2533 (2001)

Motivation

STARBeamEnergyScan(BES-I)resultssuggestasofteningoftheequationofstate(EOS)whichhintsatcriticalfluctuations

Tohelpclarifythesehints,STARneedstoaccessenergiesbelow7.7GeV whereweexpectnoQGPformation

Henceweneedtoswitchfromthecollidermodetofixed-targetmodeforcollisionsbelow√sNN <7.7GeV atRHIC

Goals of Beam Energy Scan1) Observe the disappearance of QGP

signatures 2) Find evidence of the possible first-order

phase transition 3) Find the possible Critical point

Directed Flow

Experimental Setup

Firstdirectedflowv1 resultsof2015STARFixedtargettestrunwerepresented.

v1ofbothK0S andΛ followthetrendfromtheSTARBeamEnergyScan.

v1ofprotonsisconsistentwiththetrendfromE895experiment[3]

TheFXTprogramextendsBES-IIdownto√𝑠𝑁𝑁 =3.0GeV

Why a Fixed-Target (FXT) Program?¾ STAR Beam Energy Scan (BES-I) results suggest a

softening of the equation of state (EOS) and hints at critical fluctuations

¾ To help clarify these hints, STAR needs to access energies below 7.7 GeV where we expect no QGP formation

¾ At these lower energies the luminosity of RHIC is too low, making it impractical to take data in collider mode

3Kathryn Meehan -- UC Davis -- RHIC & AGS Users Meeting 2016

The goals of BES-I:1) Observe the

disappearance of QGP signatures

2) Find evidence of the possible first-order phase transition

3) Find the possible Critical Point

X. Luo, J. Phys.: Conf. Ser. 599, 012023 (2015). [arXiv:1501.03010].

P. Shanmuganathan for the STAR Collaboration, Quark Matter 2015.

Gold Target Installed for Run 14Run 14 details:

¾ Fixed Target 3.9 GeV data taken concurrently with 14.5 GeV Au + Au collider events

¾ The target foil is held 2 cm below of the beam axis. ¾ The foil is 1 mm thick (4%).

8Kathryn Meehan -- UC Davis -- RHIC & AGS Users Meeting 2016

Out of time pile-upof electron-capture Au halo nuclei

Gold Target Installed for Run 14Run 14 details:

¾ Fixed Target 3.9 GeV data taken concurrently with 14.5 GeV Au + Au collider events

¾ The target foil is held 2 cm below of the beam axis. ¾ The foil is 1 mm thick (4%).

8Kathryn Meehan -- UC Davis -- RHIC & AGS Users Meeting 2016

Out of time pile-upof electron-capture Au halo nuclei

Directed%Flow%(v1)%

•  Directed%flow%describes%the%sideward%mo1on%of%the%par1cles%within%the%reac1on%plane%

•  Generated%during%the%nuclear%passage%1me%(2R/γ%≈%0.1%fm/c)%

•  Therefore%probes%the%very%earliest%stage%of%the%collision%dynamics%

v1 = cos! ! !"RP( )

4%

3.9 GeV Au + Au Test Run

9Kathryn Meehan -- UC Davis -- RHIC & AGS Users Meeting 2016

Excellent PID with Time Projection Chamber (TPC) and Time of Flight (TOF) detectors for fixed target events

e- e+

π- π+

K+

p

dt

e- e+

π-π+

K+

K-

td

p

3He

3.9 GeV Au + Au Test Run

9Kathryn Meehan -- UC Davis -- RHIC & AGS Users Meeting 2016

Excellent PID with Time Projection Chamber (TPC) and Time of Flight (TOF) detectors for fixed target events

e- e+

π- π+

K+

p

dt

e- e+

π-π+

K+

K-

td

p

3He

Directedflowdescribesthesidewardmotionoftheparticleswithinthereactionplane

Generatedduringthenuclearpassagetime(2R/γ ≈0.1fm/c)

Thereforeprobestheveryearlieststageofthecollisiondynamics

Calculatedas

ParticleIdentification(PID)withSTARTimeProjectionChamber(TPC)andTimeofFlight(TOF)- outstandingforFXT

Thetargetfoilwasheld2cmbelowofthebeamaxisThefoilwas1mmthick

Event Plane Reconstruction [2]

= tan�1

Qcentered

y

Qcenteredx

!

Qx

=

X

i

(ylab � yc.m.

)p(i)T

cos �(i)

Qy

=

X

i

(ylab � yc.m.

)p(i)T

sin �(i)

Psi1AEntries 24173Mean 0.009859Std Dev 1.814

/ ndf 2χ 330.4 / 307Prob 0.1714

AΨ3− 2− 1− 0 1 2 30

20

40

60

80

100

Psi1AEntries 24173Mean 0.009859Std Dev 1.814

/ ndf 2χ 330.4 / 307Prob 0.1714

vobserved

1

= hcos(� � Acorrected

)i

centering

⌦cos(

A � R)

↵=

s⌦cos(

A � B)

↵ ⌦cos(

A � C)

↵

hcos(

B � C)i

EventPlaneResolution

=0.85± 0.03forK0S (10-25%)= 0.81± 0.03forΛ (10-30%)

CMy

1− 0.5− 0 0.5 1

1v

0.6−

0.4−

0.2−

0

0.2

0.4

0.6CMy

1− 0.5− 0 0.5 1

1v

0.5−0.4−0.3−0.2−0.1−0

0.10.20.30.40.5

v1

=

vobserved

1

hcos(

A � R)i

K0S(10-25%)

Λ(10-30%)

34th

Reimei Workshop

J-PARC, Tokai, Japan

Daniel Cebra

08/August/2016 Slide 22 of 31

Fixed-Target Program 3.0 to 7.7 GeV

The Fixed-Target Program

will extend the reach of

the RHIC BES to higher B.

Goals:

1) Search for evidence of

the first entrance into

the mixed phase

2) Control

measurements for BES

collider program

searches for Onset of

Deconfinement

3) Control

measurements for

Critical Point searches

K0S orΛ takenfromSubeventB

Summary

STARPreliminary

STARPreliminary

STARPreliminary

STARPreliminary

STARPreliminary

� angle in LAB

R Reaction Plane angle

v1 = hcos(� � R)i

EventplanereconstructedfromprotonsanddeuteronsfromSubeventA

FlatteningusingFourierexpansion

v1ofBothK0S andΛ followthetrendfromtheSTARBeamEnergyScanandprotonsareconsistentwiththetrendfromE895[3]

Opensymbolsarereflected

Opensymbolsarereflected

FittingrangeY=0- 1.5

FittingrangeY=0- 1.5