Grazyna Odyniec

Experimental Approach to the QCD Phase Diagram

Beam Energy Scan at RHIC

Grazyna Odyniec/LBNL

IV International Workshop on Correlations and Femtoscopy Krakow, September 10-14, 2008

Outline :

QCD phase diagram - #1 single figure

Lattice and HI exp. (BES @ RHIC)

Experimental questions

IV International Workshop on Correlations and Femtoscopy, Krakow, September 10-14, 2008 2

Grazyna Odyniec

Exploring the rest of QCD phase diagram (T =0, =0) by:- heavy ion collisions- lattice calculations (requires /T not too large)

“Locate” the CP (:= second order point where a line of 1st order transition ends) either- via experimental detection of signatures- via lattice calculations

Stress on plural !

- need agreement of several signatures

- need agreement of different calculations

“QCD diagram is fairly EMPTY …”K.Rajagopal, INT, opening talk

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Grazyna Odyniec

QCD phase diagram

M.Stephanov, hep-ph/0402115v1 (March 2006)Theory at the “edges” is believed to be

well understood:

1. Lattice QCD finds a rapid, but smooth, crossover at large T and B~0

2. Various models find a strong 1st order transition at T~0 and large B

Either the theory is badly broken or there must be a critical point.

IV International Workshop on Correlations and Femtoscopy, Krakow, September 10-14, 2008 4

Grazyna Odyniec

Theory

M.Stephanov, hep-ph/0402115v1 (March 2006)

Predictions (models, lattice) for location of CP

be careful !

this figure is of great historical interest but it does not represent the span of theories that are currently given strong credibility

Lattice

IV International Workshop on Correlations and Femtoscopy, Krakow, September 10-14, 2008 5

Grazyna Odyniec

Lattice

• Reweighting : Fodor + Katz -> CP LR01, LR04• Imaginary : D’Elia + Lombardo, de Forcrand+Philipsen -> no CP• Taylor expansion of the pressure: Karsh, Gavai Gupta, -> CP LTE03, LTE04• …. B CP

Tc(=0) < or ~ 2

Several methods on lattice (no agreement so far):

Theory problem: including B>0 “breaks” existing numerical techniques at a very basic level (the notorious “sign problem”)

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Grazyna Odyniec

hep-lat/0701002v1

Given the very significant theoretical difficulties, data may lead the study of QCD phase diagram …

Lattice - green points !

B<500

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but

No need to hit CP(!) – signature will be just as big if you pass anywhere in

B ~ 100 MeV

(Hatta+Ikeda model, estimate is both crude and uncertain, it would be good to get it on lattice)

Focusing of trajectories that pass near the critical point = NO need to take very small steps in B !!!

Experiment

+ Photons (PHENIX)

Road Map by K.Rajagopal (INT,Aug.2008 ):

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“sQGP” at RHIC top energy

LHC

RHIC

RHIC experiments in agreement

(1) mT-NQ scaling

(2) partonic collectivity

(3) deconfinement

At RHIC:

hot and dense matter with partonic collectivity has been formed at RHIC

IV International Workshop on Correlations and Femtoscopy, Krakow, September 10-14, 2008 9

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Beam Energy Scan at RHIC: sNN ~ 5-50 GeVexperimental window to QCD phenomenology

at finite temperature and baryon number density

At RHIC : indications of sQGP found

but remain unknown:

(1) properties of hypothesized sQGP

(2) boundary between hadronic and partonic phases

(3) possible critical point

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Some indications of something new/not understood at lower energies – NA49 at SPS

40A GeV

pro

ton

v2 NA49 PRC

collapse of proton v2 - signature of phase transition (Stoecker,Shuryak), but result depends on analysis technique … ?

inconclusive

non-monotonic K+/+

behavior,“horn”, but dynamical fluctuations quite monotonic…?

Grazyna Odyniec

NA49 Results on the energy dependence of fluctuations:

Onset of deconfinement Critical Point

Charge Fluctuations: No sensitivity No predictions<pT> Fluctuations: No predictions No signal observedMultiplicity Fluctuations: No sensitivity No signal observedHadron Ratio Fluctuations: No quantitative predictions

• but the structure seen in the energy dependence of K/π fluctuations cannot be explained in a hadronic scenario !

INT, Seattle, August 2008

T.Schuster/M.Mitrovski for NA49/NA61:

Very nice analysis of Pb+Pb at sqrt(S)= 6.3, 7.6, 8.8, 13.3, 17.3 GeV

no dependence on sqrt(S)

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BES at RHIC - access to large range of B and T

advantage of collider geometry !At fixed target geometry:

detector acceptance changes with energy

track density at mid-y increases fast with energy

-> technical difficulties in tracking

-explore a broad region of the QCD phase diagram

-look for the evidence of ordered transition

-study the evolution with beam energy of the unusual medium properties found at RHIC

-do any of the partonic properties change or “turn off” ?

-new surprises in unexplored region …

produces systems with lower freezout temperatures and higher baryon densities

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What should be measured during BES ?Mainly related to bulk properties

yields and particle ratios T vs

particle spactra (pt, rapidity, …),

strangeness production (K/, multistrange, …),

fluctuations and correlations of many varietes (K/,<pt>, HBT,v2@CP,…)

flow (v1,v2,v4, …) with charged and identified particles,

signals of parity violation,

“lumpy”(“clumpy” ?) final state

prospect of data will “encourage” theorists to be more specific

Search for : - disappearance of partonic activities

- fluctuations, correlations turn on and off signature of deconfinement

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The Signature !

decrease sqrt (S) -> increase B

The signature is a CHANGE (not observable itself) = rise and then fall of Gaussian e-by-e fluctuations of: …. …. Note, number fluctuations will better survive the late time hadron gasso, K/ fluctuations have more chance than <pt> fluctuations

-> lighter ions, shorter time in hadron gas phase – NA61 argument

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Grazyna Odyniec

Excellent match with STAR detector capabilities

Compatibility of FTPCs and FGT/HFT under investigation (only issue if run after 2010)

and existing, well understood STAR analysis techniques.

STAR after 2010 :

FTPC

Other anticipated/studied issues: triggering and PID

IV International Workshop on Correlations and Femtoscopy, Krakow, September 10-14, 2008 16

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Triggering using BBCs

impact parameter

AuAu @ 5 GeV AuAu @ 8.75 GeV

BBC Inner BBC Outer BBC Inner BBC Outer

0<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 is sensitive down to single MIP hitting the detector

Studies indicate BBCs can be used for triggering during BES

Multiplicity larger than that for p+p

Triggering is not a problem

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Particle Identification in STAR

• TOF alone: (,K) up to 1.6 GeV/c, p up to 3 GeV/c• TOF+TPC(dE/dx, topology) up to 12 GeV (NIMA 558 (419) 2006)

log10(p)

log

10(d

E/d

x)

TPC+TOF (completed in 2010)+EMC+Topology

Good quality PID over a broad range: ~ 0.2 – 12 GeV/c

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STAR’s beam energy scan proposal (PAC 2008)

√sNN (GeV)

μB (MeV)

Rate (Hz)

EventsDuratio

n (days)

5.0 550 0.5 Test 7

6.1 491 1.4 1M 23

7.7 410 2.7 2M 20

8.6 385 4 2M 15

12.3 300 10 5M 15

17.3 229 25 10M 12

27 151 30 10M 7

39 112 50 10M 6

14 weeks physics+1 week commissioning

B<500 (Lattice)

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STAR experience with Low Energy RHIC running 2001: 19.6 GeV Au+Au2004: 22.4 GeV Cu+Cu2007: 9 GeV Au+Au 2008: 9 (5) GeV Au+Au !

E802 PRL81, 2650 (1998)E866 PLB476, 1 (2000)E917 PLB490, 53 (2000)NA44 PLB471, 6 (1999)WA98 PRC67, 104906 (2003)NA49 PRC66, 054902 (2002)NA49 EPJC33, S621 (2004)NA49 arXiv:0710.0118v2PHENIX PRC69, 034909 (2004)PHENIX PRL88, 242301 (2002)STAR PRL92, 112301 (2003)STAR PLB595, 143 (2004)

Preliminary

Preliminary

Sufficient data to extract ratios, flow velocity, HBT radii, v2

Data fit into systematics

D. Cebra QM2008

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Grazyna Odyniec

2008: low energy run with 9.2 GeV Au+Au

Injecting and colliding Au+Au√sNN = 9.2 GeV, a few hours -> 4K good events !

Short test @√sNN = 5 GeV allowed study of beam optics

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some preliminary plots from 9.2 GeV analysis

Raw multiplicity

STAR preliminary

primary vertex

shown by H.Caines at INT, August 2008

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Vertex Z (cm)

Au+Al Au+Al

Au+Be

Au+Au and Au+Al collisions !V

ert

ex Y

Vertex X

Au+Au collisions

Au+Beampipe collisions

Investigated primary vertex location:They are “real”collisions.

R. Reed

Can see the change in beampipe material and thickness

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Au+Au √sNN=9.2 GeV

Uncorrected charged particle mid-rapidity p

T spectra out to ~4GeV/c.

(Not corrected. Can’t extract physics yet)

STAR preliminary

Clean PID for π, K, p + anti-particles

All strange particles up to Λ _

Raw Yield 0.018/event

Preliminary

Invariant mass (pπ) [GeV/c2]

Preliminary

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• The unique RHIC energy scan program will map the QCD diagram in sNN =5-50 GeV, (corresponding to B ~ 600-150 MeV)

– systematic study of collective dynamics and fluctuations with p, , , , , K, K*,, – turning off partonic activities (e.g. v2 of , D – no NQ scaling, quenching ->0, …)

but …• experimentalist’s questions:

Can we get as quantitative as possible about critical line shape and use hydro or something else to connect freeze-out point to it ?

Can we try to predict freezout versus sqrt(s) with and without CP ?…

?

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Experimentalist’s request to the community of correlations/fluctuations experts :

other signals of the first order phase transition and CP new analysis techniques, tools (correlations, fluctuations, ?)

We will study all of them with the data. First run soon.

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THANKS !

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ETRA SLIDES

IV International Workshop on Correlations and Femtoscopy, Krakow, September 10-14, 2008 28

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If there, a critical point doesn’t hide…Image courtesy of C.Nonaka

•Hydro predicts that the evolution of the system is attracted to the critical point.

•Effect observed already for liquid-gas nuclear transition

•Focusing causes broadening of signal region - No need to run at exactly Critical Point energy

Finding evidence for a 1st order phase transition would immediately narrow location of the critical point.

Correlation lengths expected to reach at most 2 fm (Berdnikov, Rajagopal and Asakawa,

Nonaka): reduces signal amplitude, no sharp discontinuities

IV International Workshop on Correlations and Femtoscopy, Krakow, September 10-14, 2008 29

Grazyna Odyniec

Colliders are a great choice for E-scanAcceptance

Acceptance for collider detectors is totally independent of beam energy

• Occupancy for collider detectors is much less dependent on beam energy

• Less problems with track merging, charge sharing hits etc..

π

K

STAR

Better control of systematics

Kπ

NA49

IV International Workshop on Correlations and Femtoscopy, Krakow, September 10-14, 2008 30

Grazyna Odyniec

Luminosity is the key issue

Rate can be increased by:

•factor 2 by adding more bunches - only 56 used for tests (max 120).

•factor 3-6 by operating with higher charge in bunches.

•factor few by running in continuous injection mode

•electron cooling in RHIC (?) (not helpful at lower √s)

Image courtesy of T.Satogata

Tota

l Event

Rate

[H

z]

γ3

Expect to reach γ3 rate even at lowest energies

Determined collision rate for 2008 9 GeV Au+Au test to be ~1Hz.

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RHIC run 10 (2010)

sNN [pft]

GeV [GeV/c]

B

[MeV]<BBC Rate>

[Hz]

Days/

Mevent

# events # beam days

4.6 [9.6] 570 3 9 5M 45

6.3 [18.8] 470 7 4 5M 20

7.6 [27.9] 410 13 2 5M 10

8.8 [37.7] 380 20 1.5 5M 7.5

12 [71.0] 300 54 0.5 5M 2.5

18 [161] 220 >100 0.25 5M 1.5

28 [391] 150 >100 0.25 5M 1.5

(1) Large energy range accessible(2) Collider geometry (acceptance won’t change with S, track density varies slowly)(3) RHIC detectors well suited (large acceptance), tested & understood

STAR PAC 2007 Strawman proposal:

Note: NA61 @ CERN (starting in 2010): 10, 20, 30, 40, 80, 158 GeV/c