High-pT η production in
p+p, d+Au and Au+Au at RHIC

APS / DNP Fall Meeting

Chicago, IL, October 30, 2004

David d’Enterria

Nevis Labs, COLUMBIA University, NY

for the Collaboration

η ...? Why η ?

Goal (1): Compare high pT production for a new hadron species (η) in 3 systs:

p+p (“QCD vacuum”), d+Au (“cold QCD medium”), Au+Au (“hot QCD medium”)

Goal (2): Have under control the 2nd largest hadronic source (η) of decay photon bckgd for direct g and “direct” e± studies.

Factor x4-5 suppression

Perturbative (high pT)

π0 ,h± in central Au+Au

suppressed compared

to expectations of

incoherent parton-

parton scattering.

Consistent with “jet

quenching” in hot/dense

QCD medium.

Q: To what extent is this

suppression “universal”

(magnitude, pT-, centrality-

dependence, ...) for diff.

particle species ?

High pT η spectra (p+p, d+Au at RHIC)

p+p, d+Au η+ X @ √s = 200 GeV (Run-3)

Spectra go up to pT = 12 GeV/c (well in the perturbative regime)

η is the 3rd highest pT identified particle (after π0, g) at RHIC

Preliminary

Preliminary

High pT η spectra (Au+Au at RHIC)

Au+Au η+ X @ √sNN = 200 GeV (Run-2)

Spectra go up to pT = 10 GeV/c (well in the perturbative regime)

Preliminary

High pT η in “cold QCD matter” (d+Au)

η production in d+Au follows (within uncertainties) Ncoll-scaling

for all centralities: No significant “Cronin broadening”

Preliminary

0-20%	20-40%

40-60%	60-88%

High pT η in “hot QCD matter” (Au+Au)

Au+Au central: Strong suppression (RAA~0.2)

Au+Au semi-central: Suppression (RAA~0.4)

Au+Au peripheral: consistent w/ Ncoll scaling (RAA~0.9)

Preliminary

Errors:

Bands: ~15%

abs. uncertainties

Boxes:~8%

pT correlated

Bars: 10--35%

point-to-point

Au+Au η+ X @ √sNN = 200 GeV

High pT meson production: η vs. πo (Au+Au central)

Coincident suppression pattern for π0 and η:

magnitude, pT dependence

Preliminary

High pT meson production: η vs. πo (Au+Au central)

Coincident suppression pattern for π0 and η: magnitude, pT dependence

Agreement with parton energy loss (GLV) predictions in dense medium

(up to the highest pT values measured so far)

Preliminary

GLV RAA π0

dNg/dy = 1100

High pT meson production: η vs. πo (other centralities)

Au+Au semicentral (20 - 60%) Au+Au peripheral (60 - 92%)

Similar suppression pattern for π0 and η:

magnitude, pT-, centrality- dependence

Preliminary

Preliminary

Perturbative η/πo ratio in hadronic collisions (I)

η/πo is approx. constant above pT ~ 2 GeV/c: 0.46 ± 0.03

η/πo “world systematics” [p+p, p+p, π±+p, p+A, A+A @ √s~10 – 540 GeV]

[Systematics by Maike Kaufman & DdE]

Perturbative η/πo ratio in hadronic collisions (II)

[Systematics by Maike Kaufman & DdE]

η/πo = 0.46 ± 0.03

independent of xT=2pT/√s

(within uncertainties)

<η/πo> (>2 GeV/c) as a function of pT

η/πo ratio in p+p and d+Au at RHIC

Approx. flat(*) η/πo ratio above pT= 2 GeV/c.

η/πo ratio at RHIC consistent with “world average”.

“mT scaling” does not reproduce perfectly spectral ratio for pT<2 GeV/c ...

(*) Slow rise with pT consistent w/ data too.

“mT scaling” curve

η/πo = 0.48 ± 0.04

η/πo = 0.40 ± 0.04

Preliminary

Preliminary

Perturbative η/πo ratio in Au+Au at RHIC

Flat η/πo ratio versus pT. No apparent centrality dependence.

η/πo ratio in Au+Au consistent with “world average”.

η/πo ~ 0.40 ± 0.04

“world ratio”

Perturbative η/πo ratio in Au+Au, d+Au, p+p at RHIC

No apparent system-size dependence

η/πo ratio in Au+Au, d+Au consistent with “world average”

d+Au  η+ X

“world ratio”

Perturbative η/πo ratio in Au+Au, d+Au, p+p at RHIC

No apparent collision system dependence:

η/πo ratio in Au+Au, d+Au, p+p consistent with “world average”.

Hot/dense QCD medium suppresses meson yields at high pT

but preserves “universality” (PID-wise) of fragmentation function.

p+p η+ X

“world ratio”

Summary

High pT η measured in the range pT» 2—12 GeV/c in p+p, d+Au, and Au+Au collisions at √s = 200 GeV.

p+p:

- η/πo ~0.48 consistent with 0.46 “world ratio” in hadronic colls.

- “mT scaling” hypothesis not exact for eta's below ~2 GeV/c

d+Au:

- No (or small) “Cronin effect” (RdA~1 for all centralities within uncertainties).

Au+Au:

- Factor x5 suppression in central (0-20%) colls.

- Same suppression pattern for η and π0:

magnitude, pT and centrality dependence.

- Agreement w/ parton energy loss calculations up to highest pT

- η/πo consistent w/ 0.46 “world ratio”: PID universality of FF	preserved in QCD medium.

Backup slides

David d'Enterria

2004-10-28T05:03:52