Beam energy dependences of baryon
productions and hadron freeze-out
properties at RHIC-PHENIX

Tatsuya Chujo
University of Tsukuba(for the PHENIX Collaboration)

INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoBaryon/Meson anomaly at RHIC
PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004),
PRC 74, 024904 (2006)“Baryon anomaly (or enhancement)
at RHIC”.
• In Au+Au √sNN = 200 GeV central
collisions:• RCP (or RAA)
• Pions: Strong suppression ofyields above pT ~ 2 GeV/c, due tojet quenching.
• Protons: No suppression atintermediate pT (2-5 GeV/c).
• p/π and p/π ratios• More (anti) baryons than pions atintermediate pT (2-5 GeV/c).
• Strong centrality dependence.

Inspired extensive theoretical works
to explain the data.
2INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoParticle type dep. of elliptic flow (v2)
• Complicated particle
type dependent
structure at low pT (<1.5 GeV/c) is welldescribed by thehydro model.
• How about at theintermediate pT?
3INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoQuark Number Scaling of v2
nucl-ex/0703024 (PHENIX)* KET = mT - m•••Shown a clear Baryon / Meson splitting at the intermediate pT region.
φ meson’s v2 follows the meson data points.
Number of constituent quark scaling (n =2 for mesons, n =3 for baryons)
works, suggested the pressure developed at quark level, not hadronic level.
4

INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoPHENIX White Paper (WP) says…
Nucl. Phys. A 757 (2005) 184-283, PHENIX Collaboration

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoAfter the publication of WP…
• PHENIX high pT PID detectorupgrades:– Aerogel Cherenkov• Fully installed in 2005, working.

– TOF West (MRPC)• installed in 2006, started datataking in 2007.

• New data sets:

TOF.W installation (2006. July)– High statistics data:• Au+Au 200 GeV (2004)• Cu+Cu 200 GeV (2005)• p+p 200 GeV (2005,2006)– Lower beam energy data:• Au+Au 62 GeV (2004)• Cu+Cu 22, 62 GeV (2005)• p+p 62 GeV (2006)
INPC 2007, Tokyo, Japan (June 3-8, 2007)

6T.ChujoExploring the QCD phase diagram
by changing √s at RHIC
• Where is the onset ofbaryon anomaly at RHIC?
• How p/π+ and p/π− ratios
and RAA evolve as afunction of √s (or µB) andcolliding system?

Figure from “Future Science at theRelativistic heavy ion Collider (Aug. 25, 2006 version)”,by RHIC II Science Working Groups• The lower beam energy
data taken at RHIC so far
can provide the excitation
function of baryonproductions.
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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoPID charged pT spectra analysis in PHENIX•••

PHENIX detector:• Drift Chamber, Pad Chamber 1 (PC1),
Beam-Beam Counter (BBC) and TOF
for PID charged analysis.
Collision centrality:• Subdivided minimum bias triggered
events, based on BBC charge (62GeV), or the number of PC1 hit (22GeV).
Corrections:• Geometrical acceptance, in flight decay.
• No weak decay feed-down correction
applied.

1/βCharged particle identification by TOF
Cu+Cu @ 22.5 GeV

8INPC 2007, Tokyo, Japan (June 3-8,Charge2007) x Momentum (GeV/c)

T.ChujoExperimental Results:√s dependence of baryonproductions

PID spectra at lower √sNN

π0 pT spectrain Cu+Cu 22.5 GeV 10
INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√s dep. of p/π- ratio (central)* No weak decay feed-down correction applied.

p+p 62.4 GeV, set thebaseline for HI data.
New PHENIX dataagrees with ISR data.

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√s dep. of p/π- ratio (central)

Cu+Cu 22.5 GeV, p/π−ratio in central agreeswith p+p.

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√s dep. of p/π- ratio (central)

Cu+Cu 62.4 GeV, p/π−ratio larger thanthose in p+p and
Cu+Cu 22.5 GeV.

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√s dep. of p/π- ratio (central)

Cu+Cu 200 GeV,
similar to those in
Cu+Cu 62.4 GeV.

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√s dep. of p/π- ratio (central)

Au+Au 62 GeV, p/πis unchanged from
Cu+Cu 200 GeV

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√s dep. of p/π- ratio (central)

Au+Au 200 GeV,
p/π- isenhanced.

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√s dep. of p/π- ratio (peripheral)

Peripheral collisions for allsystems
Conversing to the same line

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoCentrality dep. of p/π- (22 GeV vs. 62 GeV)

0.3

* No weak decay feed-down correction applied.

• In 22.5 GeV Cu+Cu: weak centrality dependence, p/π- ratios are ~0.3-0.4 at pT = 2GeV/c, which is close to the value in p+p.
• In 62.4 GeV Cu+Cu: p /π- ratio in central collisions reaches R=~0.6 at pT = 2 GeV/c,
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decreasing towards the peripheral events.
INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoComparison with SPS data
T. Schuster, A. Laszlo (NA49)
nucl-ex/0606005(Pb+Pb 17.2 GeV)
(Au+Au 200 GeV)
(Au+Au 200 GeV)

Pb+Pb 17.2 GeV (central)

0.25
01.0
pT (GeV/c)

2.0

3.0

SPS Pb+Pb: consistent with Cu+Cu 22.5 GeV p/π.
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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujop/π- ratio (central): summary• Increasing as afunction of √s.

• Indicates theonset of baryon
enhancement is inbetween 22 GeVand 62 GeV.

* No weak decay feed-down correction applied.

20INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√sNN dep. RAA for antiprotons (by ISR fit)
Nuclear Modification Factor

RAA (pT ) =yield ( AuAu ) Ncoll
yield ( pp)• Used ISR data at
23 GeV and 63 GeV(Alper. NPB 100,237) for p+p
reference.
• Similar RAA for all
three systems.
* Note:p+p 62.4 GeV p+p data has
been measured by PHENIX,still working on the trigger bias
and cross section seen in thedetector. Here we use ISR fit
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to obtain RAA.

* No weak decay feed-down correction applied.

INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√sNN dep. RAA for charged pions (by ISR fit)
• Used ISR fit (nuclex/0411049, D.
d’Enteria) for p+p
parameterization.
• Moderate suppression
for Au+Au 62.4 GeV.

Error notations:- Error bars: statistical error for HI spectra- Boxes:1) sys. error for p+p reference.
2) sys. error for HI spectra.
- Lines: Ncoll error (1σ.)• Greater than unity for
Cu+Cu 62/22 GeV (pT >2.0 GeV/c).

* No weak decay feed-down correction applied.

22INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujoπ0 at 22.5 GeV (centrality dep.)

Little centrality dependence
Baldo Sahlmüller (QM06)
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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoSPS (17 GeV) vs. RHIC (22 GeV)
• Same behavior for similar Npart (63 at WA98,67.8 at PHENIX)

Blattnig parameterization
used for WA98 data (S.
Blattnig et. al., Phys.Rev.
D62 (2000) 094030 / D.
D’Enterria, Phys. Lett. B596 (2004) 32))

Baldo Sahlmüller (QM06)
INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo24

Conclusions•••

pT spectra for antiproton and pions at √sNN = 22.5 and 62.4 GeV in Au+Au(Cu+Cu) have been studied to search for the onset of baryon enhancement atRHIC.
Only antiprotons in Cu+Cu 22.5 GeV system seems to be different fromothers:– Little centrality dependence in p/π− ratio at the intermediate pT.
– Central 0-10% p/π− ratio agrees with the value in p+p collisions.
– Neutral pion’s RAA : no suppression and consistent with SPS data. Littlecentrality dependence.
62 GeV Cu+Cu/Au+Au data:– p/π- ratio: baryon enhancement still exists in central Au+Au 62 GeV andCu+Cu 62 GeV.
–RAA (by ISR fit, limited pT < 2.5 ~ 3.0 GeV/c)•••

π: moderate suppression in Au+Au 62 GeV, unity for Cu+Cu 62 GeV.
p: small differences between Cu+Cu and Au+Au, close to one.

Data indicates that an onset of baryon anomaly at RHIC is in
between 22 GeV and 62 GeV.
25INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoOutlook•

PHENIX high pT PID upgrade(Physics):– Jet correlations of PID particles,
to study the origin of the baryonenhancement.
– Detailed study of fragmentation
mechanisms of p, p at high pT (>5 GeV/c).
– Λ, Λ spectra and v2 high pT (> 5GeV/c).

•RHIC-II program:– Exploring QCD phase diagram indetail by the beam energyscan(√sNN = 5 - 65 GeV) andspecies scan, to study the bulk
properties of produced QCD
matter, near the critical end
point, which maybe accessible inRHIC-II.
INPC 2007, Tokyo, Japan (June 3-8, 2007)

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T.Chujo27
INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoBackup Slides

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo√sNN dep. of p/π+ ratio (central)• decreasing

as a functionof √s.

* No weak decay feed-down correction applied.

29
INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoRAA for protons (by ISR fit)

• Used ISR data at
63 GeV (Alper. NPB100, 237) for p+preference.
• Largest RAA forCu+Cu 22.5 GeV.
• RAA for Au+Au
62.4 GeV is smaller
than that in Cu+Cu
62.4 GeV.

* No weak decay feed-down correction applied.

30
INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoReference data (p+p 62.4 GeV)
•p+p parameterization at 62.4 GeV: Fit to existing (ISR) data atsimilar energies (D.d'Enterria. J.Phys.G31, S491 (2005))

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoReference data (p+p 62.4 GeV)
• Problem: data sets inconsistent => large error

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.ChujoReference data (p+p 22.5 GeV)
•p+p parameterization at 22.4 GeV: Fit to existing data at similarenergies (D.d'Enterria. J.Phys.G31, S491 (2005))

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INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujoπ0 RAA vs. √sNN

D. d’Enterria, nucl-ex/0504001
INPC 2007, Tokyo, Japan (June 3-8, 2007)

T.Chujo34