The Search for the Critical Point of QCD: STAR Capabilities for Low s NN Running

March 9, 2006 Workshop: Can We Discover the QCD Critical Point at RHIC 1

The Search for the Critical Point of QCD:

STAR Capabilities for Low sNN Running

OUTLINE

• Motivation• Theoretical predictions • Results from SPS and RHIC

• Low sqrt(s) RHIC running• RHIC conditions• RHIC limitations

• STAR Capabilities• Trigger• Physics• Event Rates & requirements

• Summary

Workshop:Can We Discover QCD Critical Point at RHICBrookhaven National Laboratory March 9-10, 2006

Tapan Nayak(for the STAR Collaboration)


Lattice

Neutron STAR

The phase diagram

• SPS top energy is below the curve and RHIC data so far are above.

• It will be worth having a look at the systems produced near the QCD phase boundary.

• RHIC has a unique possibility to scan the full range from AGS to top RHIC energy.


Gavai, Gupta hep-lat/0412035

CRITICAL END POINT

En

erg

y D

ensi

tyTemperature

F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004)

TC ~ 170 15 MeV

C ~ 0.7-1.5 GeV/fm3

Lattice predictions

Lattice calculations suggest that the Critical Point of QGP phase transition may be located at about the SPS energies (c.m. energy of 5-20 GeV/nucleon)


Bjorken estimation of initial energy densityR2

dydz 0

Boost invariant hydrodynamics:

d

dNp

Rdy

dE

Rch

TT

2

31122

Bjorken density as function of #of participants

Assuming Bjorken energy density is similar to that of the lattice calculation: in order to probe the Critical Point (C ~ 0.7-1.5 GeV/fm3) – the c.m. beam energy need to be between 5-20GeV.

Raghunath Sahoo,

Bjorken density as function beam energy

AuAu 10GeV (estimated)

10GeV

STAR

STAR Preliminary


<ßr> (RHIC) = 0.55 ± 0.1 cTKFO (RHIC) = 100 ± 10 MeV

• Rapid change in freeze-out temperature and flow velocity between 2-20GeV

• Explosive Transverse Expansion at RHIC High Pressure

Tth

[GeV

]<

r>

[c]

STA

R

Kinetic freezeout from AGS->RHIC

4.6

Jim Thomas

Get Masashi's latest results from his poster. Use blast wave fits and mean pt.


Elliptic flow: The scaling of v2/ε

The scaling of the strength of the elliptic flow v2 with eccentricity shows that a high degree of collectivity is built up at a very early stage of the collision.

With low energy beam the lower points can be scanned more precisely.


Mohanty, Alam, Sarkar, Nayak, NandiPRC 68 (2003) 021901

Energy dependence of <mT> and temperature

• Rapid rise in <mT> going from AGS to SPS energies and slowing down towards RHIC.

• Step like behavior in the inverse slope parameter in heavy-ions around SPS energies, but not in pp.

Inve

rse

slop

e pa

ram

eter

(M

eV)

4.6


Energy dependence of particle ratio and fluctuations

<K+/+><K/>

Particle Ratio: K/ shows increasing behavior with energy, whereas a horn structure seen in K+/ +

Christof Roland (NA49)

Fluctuation in Ratio: • K/ fluctuations increase towards lower beam energy.• p/ fluctuations are negative, indicating a strong contribution from resonance decays• STAR results are being finalized.

4.6


Beam energy dependence of pion HBT

Debasish Das

Pion rapidity density is proportional to the freezeout volume => Constant Freezeout Volume (freezeout at a constant density).

STARS. Voloshin, QM02

4.6

Jim Thomas

Get Masashi's latest results from his poster. Use blast wave fits and mean pt.


STAR Preliminary

Constant s-Baryon production

at mid-rapidity.

Energy dependence of strange baryon production

s-Baryon production rises

smoothly at mid-rapidity.

STAR Preliminary

Au+AuPb+Pb

Sevil Salur, QM2005


Energy dependence of ratio of strange baryons

Sevil Salur, QM2005

STAR PreliminaryA

nti

-bar

yon

/bar

yon

rat

io

• The ratio of strange to anti-strange baryons goes up with energy.• At RHIC energies the production of strange and anti-strange baryons is equal.


Energy dependence of balance functions

100

shuffling

datashufflingW

preliminary

W

Gary Westfall, STARPanos Christacoglou, NA49

W is a normalized measure of the time of hadronization with respect to uncorrelated data sample.

This is consistent with delayed hadronization at RHIC compared to SPS energies.


<pT> fluctuations

Establishing the scale for studying <pT> fluctuations.

Fractional increase of width of the <pT> distribution w.r.t. to a statistical reference.


fluctuations correlations

200 GeV

Understanding contribution of minijets at low pT

• STAR has the capability to study fluctuations in fine bins of and .

• The localized measures of fluctuation is necessary to understand the underlying structure in an event including the contribution of mini-jets.

• Study of the phase boundary at large sNN has to take the presence of minijets into account.• Minijets might help in our understanding of the phase boundary.


A note on low energy RHIC runningFrom: Wolfram Fischer, BNL C-AD Nov 2005

1. No hard limit for the RHIC collision energy down to c.m. energy of 4.6 GeV/n.

2. The beam and luminosity lifetimes will decrease gradually with the lower energies.

3. Because the ZDC counters will be ineffective – tuning can be done using Beam-Beam-Counters (BBC).

4. Low Energy beam runs including cooling has to be tested in advance.

Details:1. Current regulation of the main dipoles should work even at 50A.2. During RUN-2 with AuAu collisions of 9.8GeV/n beams, luminosity was

delivered at a rate of 1 inv. micro-barn/week. The rates drop with about gamma^3 to gamma^4

3. Operation near AGS transition energy has to be checked.4. Electron cooling at low energies needs study.


MagnetMagnet

CoilsCoils

Central Central TriggerTriggerBarrel Barrel (CTB)(CTB)

ZCalZCal

Time Time Projection Projection

ChamberChamber(TPC)(TPC)

Year 2000Year 2000

Barrel EM Cal Barrel EM Cal (BEMC)(BEMC)

Silicon Vertex Silicon Vertex Tracker (SVT)Tracker (SVT)Silicon Strip Silicon Strip Detector (SSD)Detector (SSD)

FTPCFTPCEndcap EM CalEndcap EM CalFPDFPD

TOFp, TOFrTOFp, TOFr

FPDFPD

Year 2001+Year 2001+

PMD

Large acceptance: 2 coverage at mid-rapidity

The STAR experiment


Hadron identification: STAR Collaboration, nucl-ex/0309012

The STAR experiment (with the inclusion of TOF) is an ideal detection device to search for the Critical Point of QCD and to carry on a systematic study of majority of the physics topics being addressed.

Inclusion of ToF detector

Fabrication of MRPC based Time-of-Flight (ToF) detector for STAR is in progress. It is scheduled to be installed for RHIC RUN-9.

ToF


uRQMD

Particle production at low sNN energies

Pseudo-rapidity distribution of charged particles at 4 different centralities.


Second order event-plane resolution

Event plane resolution in STAR will be better than what was achieved at NA49.

STARTPC Acceptance

sNN = 8.75GeV

Coverage in terms of beam-rapidity increases as we go to lower energies.


STAR Trigger for Low Energy RHIC Running

Trigger Detectors in STAR

ZDCZDC

BBC

BBCBEMC & EEMC

(only a part of the detectors shown)

CTB

FPD FPD

We set up all collision triggers (e.g. ZDC coin., BBC coin., CTB multiplicity, etc) and run them all simultaneously without pre-scales.


STAR uses two BBCs wrapped around the beampipe: one on either side of the TPC. Each counter consists of two rings of hexagonal scintillator tiles: an outer ring composed of large tiles and an inner ring composed of small tiles. Internally, each ring is divided into two separate sub-rings of 6 and 12 tiles each.

Triggering with STAR Beam-Beam Counter (BBC)

Centrality

(b in fm)AuAu Ec.m.= 5 GeV AuAu Ec.m.= 8.75 GeV

BBC Inner 3.3<<5.0

BBC Outer 2.1<<3.3

BBC Inner 3.3<<5.0

BBC Outer 2.1<<3.3

b<3 5 27 12 54

3<b<6 11 30 21 57

6<b<9 22 35 39 40

b>9 44 30 66 8

BBC can effectively be used for triggering for low energy runs.

Table below gives the #of particles within BBC coverage for two c.m. energies and four different centralities:

BBC is sensitive down to single MIP falling on the detector.


STAR physics: option-1 (for low energy RHIC running)

• Particle spectra (pT, (pseudo)-rapidity distributions) • Flow (v1, v2, v4 ….) with charged and identified

hadrons• Strangeness production (k/pi ratio)• Resonance • HBT Radii• Fluctuations (net charge, k/pi ratio, baryon

number….)• Correlations• Formation of Disoriented Chiral Condensates (DCC)

Using PMD–FTPC and BEMC–TPC • Long range (forward-backward) correlations


Required statistics for different observablesAt sNN = 10GeV

Limit for a thorough measurement: 20M events

Very basic measurement: 2M events


BBC Coincidence Rates and Beam-time estimation for option-1

BBC Coincidence Rate for CuCu 20GeV

BBC

ZDC

CuCu 20GeV: beginning of spill: 3000 average over time: ~1000AuAu 20GeV: 1000/4 = 250.Optimistic view: rates scale as 3 This energy scan will take a total of 17

weeks for STAR physics Option-1.

E c.m. BBC Coin Rate

#of days/1M

(1day=12 hr)

#of events needed

#of days of beam

4.6 4 6 10M 60

8 16 1.5 20M 30

12 54 0.5 20M 10

16 100 0.25 20M 5

20 >100 0.25 20M 5

40 >100 0.25 20M 5


STAR physics: Option-2(for low energy RHIC running)

All STAR Physics Option-1 and in addition:• v2 of Omega (centrality dependence)• v2 of phi (centrality dependence)• Jet quenching, Energy loss (RAA and RCP).

For RAA: pp reference will be needed.

E c.m. BBC Coin Rate

#of days/1M

(1day=12 hr)

#of events needed

#of days of beam

4.6 4 6 10M 60

10 30 0.75 50M 38

15 100 0.25 50M 25

20 >100 0.25 50M 25

40 >100 0.25 50M 25

A high statistics energy scan will take total of 25 weeks.

This option is preferable.

> 50M events needed ateach energy.


E c.m. BBBC Coin Rate

#of days/1M(1day=10 hr)

#of events needed

#of days of beam

4.6 570 3 9 5M 45

6.3 470 7 4 5M 20

7.6 410 13 2 5M 10

8.8 380 20 1.5 5M 7.5

12 300 54 0.5 5M 2.5

18 220 >100 0.25 5M 1.5

28 150 >100 0.25 5M 1.5

5M events: 12.5 weeks: JUST enough, Errors factor 2-4 better than NA49

Beam-time estimation for a basic energy scan

Workshop:Can We Discover QCD Critical Point at RHICBrookhaven National Laboratory March 9-10, 2006

• cleanup• vertex• efficiency

• Gunter: 200K 0-5%, minbias:4M

Mar

ch 1

0, 2

006


SummaryP

hys

ics

mea

sure

AGS SPS RHIC

QCD Critical Point

• The QCD phase boundary is worthy of study, including that of the tri-critical point.

• STAR experiment with the inclusion of TOF will be the ideal place for this study.

• Current investigations don’t indicate any problem carrying out this program with the STAR detector.

• The RHIC program looks most promising.

Discoveries Ahead

Energy Density


Thanks to the organizers of the Workshop:

“Can We Discover QCD Critical Point at RHIC”Brookhaven National Laboratory March 9-10, 2006

Thanks to STAR Collaborators and in particular:

Paul SorensenBill Christie Jamie Dunlop Nu XuZhangbu XuPeter Seyboth Tim Hallman

Discoveries Ahead

The Search for the Critical Point of QCD: STAR Capabilities for Low s NN Running

Documents

Transcript of The Search for the Critical Point of QCD: STAR Capabilities for Low s NN Running