Experimental Approach to the QCD Phase Diagram Beam Energy Scan at RHIC

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Experimental Approach to the QCD Phase
DiagramBeam 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 _at_ RHIC)
Experimental questions
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QCD diagram is fairly EMPTY K.Rajagopal,
INT, opening talk

• Exploring the rest of QCD phase diagram (T 0,
  m0) by
• - heavy ion collisions
• - lattice calculations (requires m/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
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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 mB0
• 2. Various models find a strong 1st order
  transition at T0 and large mB
• Either the theory is badly broken or there
  must be a critical point.

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Theory
Predictions (models, lattice) for location of CP
M.Stephanov, hep-ph/0402115v1 (March 2006)
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
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Lattice
Several methods on lattice (no agreement so far)

• Reweighting Fodor Katz -gt CP
  
  LR01, LR04
• Imaginary m DElia Lombardo, de
  ForcrandPhilipsen -gt no CP
• Taylor expansion of the pressure Karsh, Gavai
  Gupta, -gt CP LTE03, LTE04
• .
  
  
• mB CP
• Tc(m0)

lt or 2
Theory problem including mBgt0 breaks existing
numerical techniques at a very basic level (the
notorious sign problem)
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hep-lat/0701002v1
Lattice - green points !
mBlt500
Given the very significant theoretical
difficulties, data may lead the study of QCD
phase diagram
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Road Map by K.Rajagopal (INT,Aug.2008 )
Experiment
Photons (PHENIX)
but No need to hit CP(!) signature will be just
as big if you pass anywhere in
mB 100 MeV (HattaIkeda 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 mB !!!
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sQGP at RHIC top energy
RHIC
At RHIC
LHC

• mT-NQ scaling
• partonic collectivity
• deconfinement

RHIC experiments in agreement
hot and dense matter with partonic collectivity
has been formed at RHIC
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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
• properties of hypothesized sQGP
• boundary between hadronic and partonic phases
• possible critical point

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Some indications of something new/not understood
at lower energies NA49 at SPS
non-monotonic K/p behavior,horn, but
dynamical fluctuations quite monotonic?
collapse of proton v2 - signature of phase
transition (Stoecker,Shuryak), but result depends
on analysis technique ?
inconclusive
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INT, Seattle, August 2008 T.Schuster/M.Mitrovski
for NA49/NA61
NA49 Results on the energy dependence of
fluctuations
Onset of deconfinement Critical
Point Charge Fluctuations No
sensitivity No
predictions ltpTgt Fluctuations No
predictions No signal
observed Multiplicity Fluctuations No
sensitivity No signal
observed Hadron Ratio Fluctuations No
quantitative predictions but the structure
seen in the energy dependence of K/p fluctuations
cannot be explained in a hadronic scenario !
Very nice analysis of PbPb 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 mB and T
produces systems with lower freezout temperatures
and higher baryon densities

• -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

advantage of collider geometry !
At fixed target geometry detector acceptance
changes with energy track density at mid-y
increases fast with energy -gt technical
difficulties in tracking
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What should be measured during BES ?
Mainly related to bulk properties yields and
particle ratios T vs mB, particle spactra
(pt, rapidity, ), strangeness production (K/p,
multistrange, ), fluctuations and correlations
of many varietes (K/p,ltptgt, HBT,v2_at_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) -gt increase mB
• 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 gas
• so, K/p fluctuations have more chance than ltptgt
  fluctuations
• -gt lighter ions, shorter time in hadron gas
  phase NA61 argument

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Excellent match with STAR detector capabilities
and existing, well understood STAR analysis
techniques.
STAR after 2010
FTPC
Compatibility of FTPCs and FGT/HFT under
investigation (only issue if run after 2010)
Other anticipated/studied issues triggering and
PID
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Triggering using BBCs
Studies indicate BBCs can be used for triggering
during BES Multiplicity larger than that for pp
BBC is sensitive down to single MIP hitting the
detector
Triggering is not a problem
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Particle Identification in STAR
TPCTOF (completed in 2010)EMCTopology

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

Good quality PID over a broad range 0.2 12
GeV/c
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STARs beam energy scan proposal (PAC 2008)
14 weeks physics1 week commissioning
mBlt500 (Lattice)
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STAR experience with Low Energy RHIC running
2001 19.6 GeV AuAu 2004 22.4 GeV CuCu 2007
9 GeV AuAu 2008 9 (5) GeV AuAu !
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
arXiv0710.0118v2 PHENIX PRC69, 034909
(2004) PHENIX PRL88, 242301 (2002) STAR PRL92,
112301 (2003) STAR PLB595, 143 (2004)
Preliminary
D. Cebra QM2008
Preliminary
Sufficient data to extract ratios, flow velocity,
HBT radii, v2
Data fit into systematics
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2008 low energy run with 9.2 GeV AuAu
Injecting and colliding AuAuvsNN 9.2 GeV, a
few hours -gt 4K good events !
Short test _at_vsNN 5 GeV allowed study of beam
optics
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some preliminary plots from 9.2 GeV analysis
shown by H.Caines at INT, August 2008
primary vertex
Raw multiplicity
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AuAu and AuAl collisions !
Investigated primary vertex location
They are realcollisions.
AuAu collisions
AuBeampipe collisions
Vertex Y
R. Reed
Vertex X
Can see the change in beampipe material and
thickness
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AuAu vsNN9.2 GeV
_
All strange particles up to ?
Raw Yield 0.018/event
Clean PID for p, K, p anti-particles
Invariant mass (pp) GeV/c2
Uncorrected charged particle mid-rapidity pT
spectra out to 4GeV/c. (Not
corrected. Cant extract physics yet)
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• The unique RHIC energy scan program will map the
  QCD diagram
• in ?sNN 5-50 GeV, (corresponding to mB
  600-150 MeV)
• systematic study of collective dynamics and
  fluctuations with p, L, X, W, p, K, K, r, f...
• turning off partonic activities (e.g. v2 of f, W,
  D no NQ scaling, quenching -gt0, )
• but
• experimentalists 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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Experimentalists 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
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If there, a critical point doesnt 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

Correlation lengths expected to reach at most 2
fm (Berdnikov, Rajagopal and Asakawa, Nonaka)
reduces signal amplitude, no sharp discontinuities
Finding evidence for a 1st order phase transition
would immediately narrow location of the critical
point.
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Colliders are a great choice for E-scan
Acceptance
p
NA49
K

• Occupancy for collider detectors is much less
  dependent on beam energy
• Less problems with track merging, charge sharing
  hits etc..

p
K
STAR
Acceptance for collider detectors is totally
independent of beam energy
Better control of systematics
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Luminosity is the key issue
Determined collision rate for 2008 9 GeV AuAu
test to be 1Hz.

• 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 vs)

Expect to reach ?3 rate even at lowest energies
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RHIC run 10 (2010)
(1) Large energy range accessible (2) Collider
geometry (acceptance wont change with ?S, track
density varies slowly) (3) RHIC detectors well
suited (large acceptance), tested understood
STAR PAC 2007 Strawman proposal
Note NA61 _at_ CERN (starting in 2010) 10, 20, 30,
40, 80, 158 GeV/c