QCD in the Heat Bath: Results from PHENIX Thomas K Hemmick for the PHENIX Collaboration University...

QCD in the Heat Bath:Results from PHENIX

Thomas K Hemmickfor the PHENIX Collaboration

University at Stony Brook

PHENIX Thomas K Hemmick

Overheard at APS ~1992:During a plenary RHI talk at APS, I wound up seated among “real” plasma physicists who made numerous comments about us:

“These guys are stupid…”Always a possibility.

“…why don’t they just shoot a laser through it and then they’d know if its plasma for sure!”

Visible light laser…bad idea.Calibrated probe through QGP…good idea……but not new. (Wang, Gyulassy, …)

The “Calibrated” Plasma ProbeHard scattering processes and products:

Occur at short time scales.Are “calculable” (even by experimentalists) in simple models (e.g. Pythia) with appropriate fudging:

Intrinsic kTK scaling factor.

Find themselves enveloped by the mediumAre “visible” at high pT despite the mediumPromise to be our laser shining (or not) through the dense medium created at RHIC.

QCD and the Heat BathI will make the following artificial divisions:

QCDCharged Hadron + Neutral pion spectra at high pT.Heavy quark production measured via electrons at high pT.J/, direct, +- coming in the future…

Heat BathMultiplicity, ET, …Identified hadrons

Singles, pairsFlow, Hadro-chemistry

Caveat:Short mean free path means that the view of the heat bath is heavily influenced by the latest stage prior to breakup.Nonetheless, initial state information (azimuthal anisotropy) is apparent.

Controlling parameterNature’s variation of the “centrality” controls the heat bath.Size/Energy variation is better, but not yet available.

Pioneering High Energy Nuclear Interaction eXperiment

11 Countries51 Institutions

400+ Collaborators

PHENIX from Above

West Armtracking:

DC,PC1, PC2, PC3electron ID:

RICH, EMCal

PhotonsEMCal

East Armtracking:

DC, PC1, TEC, PC3hadron& electron ID:

RICH,TEC, TOF, EMCphotons:

PHENIX Setup During Year 2001 Run

full heavy ion program and first spin physics including electron & muon pairs

South Armtracking:

MuTrmuon ID:

Other DetectorsVertex

& centrality:ZDC, BBC,MVD

accumulated ~200 106 Au-Au

•The main 2001 data production pass has begun.

•Physics results still from 2000 data set.

Centrality DeterminationZDC measures neutral energy (principally free spectator neutrons) along collision axis.BBC measures produced charged particles within +/-(3.0-3.9).Their joint response is divided into centrality slices :

Each colored band is 5%.Central is at lower right.

The PHENIX trigger accepts 92% of minimum bias events.A Glauber calculation was used to deduce the numbers of participants (Npart) and binary collisions (Nbinary) for each centrality.

0-5%5-10%

cross sectionfraction

Npart Nbinary

0-5 348 10 1009 915-15 271 9 712 6515-30 180 7 406 4230-60 79 5 131 2260-92 14 3 14 5

Transverse Energy Production

Transverse Energy production yields Bjorken Estimate for Energy Density as:

For =1.0 fm/c, this yields ~4.6 GeV/fm3! well above estimated critical value c~0.6-1.2 GeV/fm3

central 2%

PHENIX

~ 1.5X higher than at CERN

Multiplicity rise with Npart is well reproduced by “Saturation” model.This model produces particles via parton-parton scattering.Production is affected by the initial-state gluon distribution which “saturates” as low x gluons fill available space.

Kharzeev & Levin, nucl-th/0108006Schaffner-Bielich et al, nucl-th/0108048

Multiplicity and ET vs. Npart

Multiplicity and ET both rise faster than linearly with the number of participants.This has been parameterized as:

The “Binary Scaling” contribution varies , ~25% in peripheral collisions~50% in central collisions<ET>/<Nch> ~ constant with centrality

12.034.0;28.088.0

dNbinarypart

soft hard

Multiplicity and ET vs. s

Nch and ET evolution very well described by ln(s)Saturation model also quite reasonable here (and especially with the PHOBOS result…).

with quenching

no jet quenchingPHENIX

saturation

Composition of the Heat Bath: PID

Charged hadron ID is achieved via high-res TOF measurement.

True photon pairs show a peak that is absent from mixed sample.Subtracted spectrum can be fitted for 0 yield.

Au+Au @ 200 GeV

Yield vs. Centrality

Yield per participant for all species rises with Npart.Not surprising since the total Nch rises faster than Npart.Integral of , K, p yields in excellent agreement with dNch/d result.

Surprising to me:• Yields of K+, K-, p, p-

bar rise faster with Npart than pion yields.

• The “faster than Npart” character of Nch production also involves a change in relative species abundances favoring K and nucleon production!

Net and Total Baryon DensityTypically we have measure and quote “net baryon” density (b—bbar).Some physical processes will more naturally depend upon the “total baryon” density:

e.g. medium modifications to mesons are predicted to be same for baryonic and anti-baryonic dense matter (Rapp).

Here we calculate both densities:

10288Total baryon density

20.180.4

8.621.4

p – p Participating nucleons (p – p ) A/Z dN( p ) / dy Produced baryons (p, p, n, n )

RHIC(Au-Au)

SPS(Pb-Pb) Caveat:

We don’t measure neutrons!Assume: --(n+p)part=A/Z--nprod = pprod

<pT>: Energy Distribution in Bath

<pT> variation with centrality roughly the same for all species:

~20% rise. and K close to pp production for peripheral collisions.Proton differs from pp significantly at most peripheral bin.

Hadron SpectraHadron spectra stiffen with increasing hadron mass.Well known consequence of collective motion in the final state.Spectra well fitted by “flowing thermal Ansatz:

emperatureFreezeOutTTocitySurfaceVel

mKfmAdmm

)(tanh;

)sinh()cosh()(

Thermal Fit Error ContoursFor each TFO and , a best fit and 2 are found.2

min/dof = 34/40.Contours show 1, 2, 3…Similar T to CERN, higher flow velocity.

118-126 MeV

0.71-0.73

PHENIX Preliminary

Although the result of such a technique is only as good as the assumed functional form, the differences between experiments can be quite instructive.

HBTHBT correlations also reflect underlying collective flow velocities via the kT dependence of the radius parameter.World systematics of HBT nearly universal trend of Rout, Rside???Rout~Rside???Only Rlong variation with s???A real dilemma.

What’s the composition of h+

+h-?PID for charged hadrons run out prior to the pT required for hard processes.Plots w/o renormalization show the species content of hadrons leading into our high pT probe particles.

The stiff slopes (and increased yield) of nucleons cause the high pT spectrum to be more than 50% nucleons!

Where does hard scattering begin?

Initial state Hard scattering should produce a p/ ratio which falls with pT.mT scaling (flow) will producing a rising p/.ISR: Onset of hard processes noted above 2 GeV/c.RHIC: No clear onset of hard scattering is found in the data up to pT = 3 GeV/c !!

mT scaling

pQCDp/

soft/hard transition

measured

Charged Hadron Spectra to High pT

Charged hadron spectra in bins of centrality show a gradual loss in concavity as they evolve from peripheral to central collisions.The loss in concavity is opposite to the effect one might expect comes from the known stiff proton contribution.The protons have a significantly higher slope than pions and become the majority contributor in the range 2-3 GeV/c.

To quantify the shape evolution we can use either pp data or peripheral collisions.

Unfortunately, no pp data at s=130 GeV exist.We choose to interpolate using ISR, UA1, and CDF data.The data establish the parameters of the “Power Law Fit” as a function of s.

These are smoothly interpolated to produce the solid curve in the figure.

Interpolation of pp Data

Spectral comparisonGood fit to peri-collisions using interpolated power law.Power Law overpredicts the central collisions

The discrepancy between the neutral pions and the interpolated power law is more severe than for the charged hadrons.

Difference between h and 0

We subtract the charged nucleon contribution from the all-charged hadron distribution.The result is in reasonable agreement with the neutral pion spectrum demonstrating that the charged part. contamination is principally nucleons.

RaaWe define the nuclear modification factor as:

By definition, processes that scale with Nbinary will produce RAA=1.

ddpdNddp

NNinel

binary

evtTAA

RAA is below 1 for both charged hadrons and neutral pions.

The neutral pions fall below the charged hadrons since they do not suffer proton contamination

RAA--PeripheralWe can also reference RAA using measured peripheral collisions to avoid the systematic error in the pp interpolation.

Again, the central data drops below 1.0 and shown no Cronin!

RAA—0 at RHIC and CERN

WA98 measurements of RAA for 0 show a dramatically different behavior than at RHIC.

RAA influences from “ordinary” effects.

x~2pT/s~0.02

X.N.Wang

soft/hardtransition?

CERN - SPS

Cronin effect: Multiple scatters of the projectile broaden the incoming pT

RAA exceeds 1.0 at high pT e.g. at CERN.

Shadowing?…No.

HIJING prediction for 0

One explanation for the RAA spectrum comes from multiple scattering from a colored medium.The HIJING model using 0.25 GeV/fm energy loss well reproduces the measurement.

Electron IdentificationThe Electromagnetic Calorimeter and RICH were used to select single electrons.Neither device has sufficient identification working alone.The combination shows a clear peak of signal electrons that both fire the RICH and deposit energy equal to their momentum in the EMcal.

0.8 GeV/c < p< 0.9 GeV/c

All charged

With RICH ring

Random background

E/p ratio

Electron SinglesIdentified electron spectra are shown on the left.Low pT single electrons dominantly come from 0 Dalitz decay:0->e+e-

and other neutral meson decays.Our measurements of the 0, +, - spectra determine this background level.Other backgrounds can also be modeled and subtracted as an “electron cocktail”.

Tuning Cocktail SpectraThe pion spectra are fit to an exponential + power law.Dalitz decay is an internal photon conversion.External photons conversions are normalized using a GEANT simulation and modeled as an upscaling to the Dalitz.Heavier meson spectra are assumed to follow mT scaling.Heavier meson yields are normalized by the pp measured ratio at high Pt (consistent w/ thermal).

mT scaling OK

FitData/Fit

Decomposition of Electrons

Green band indicates error (statistical+systematic) in background.Data Shows excess over Cocktail at high pT.

Pythia (after tuning…)

Akiba will show detail about the tuning of Pythia to describe open charm production in pp.The addition of open charm decays ala’ Pythia well describes the electron excess.

Fit the excess as charmThe subtracted spectrum can be used to normalize the charm yield and thereby the cross section.The result is comparable within large error bars to the Pythia calculation.

0 10%cc 380 60 200 b and

Summary-1The RHIC medium is certainly intriguing and exciting:

Particle production scales faster than Npart possibly signaling a hard Nbinary component.Kaon and Nucleon contributions grow in percentage with centrality.Low net baryon density but high total baryon density.Strong radial flow implied by relative slope constants of hadrons.Nucleons begin to be dominant contributors to pT spectra above 2 GeV/c.HBT Rout~Rside???

Probes of the medium yield exciting resultsRAA below 1. Especially dramatic for identified 0 which have no proton background.Charm = Pythia within huge errors. Why?

Summary-2PHENIX has produced a wealth of data and has much more in analysis.The RHIC era opens the hard scattering or QCD toolbox (Pandora box?) in RHI physics.

My wife usually criticises my use of new tools:LMH: “Don’t you ever read the manual?”TKH: “Honey, these tools don’t come with manuals!”

Maybe this week we’ll begin writing the manual for QCD in the RHIC era.

END OF ALL SLIDES

SLIDES BEYOND THIS POINT WILL NOT BE SHOWN

Singles SpectraMost Central Mid-Central Peripheral

Singles==all

Singles mt

Yields

Ratios

Ratios2

ID vs dN/dn

Acceptance

HBT Results

HBT spectra

Charged Particle PID

Pi0 PID

Hard Spectra

Hard Spectra 2

Hard pi0 spectrum

SQRT(s)with quenching

no jet quenchingPHENIX

saturation

PHOBOS

with quenching

SQRT(s)-2

Hard pp

Suppression—Pt

dE/dx-theory

LambdaPHENIX Preliminary

Electron PID

PHENIX RUN 12280 SEQ 0014 EVENT 850

View from North Side

South Side

East Arm West Arm

6 PMT RICH ring2.55 GeV/c track2.5 GeV EMCal hitelectron candidate

RICHPC1

TECPC3

Cocktail

Electron Spectra

Parameters

Pythia

Flow—v2

Thermal

(No QGP phase transition)

2 fm/c20 fm/c

5 fm/c

QCD in the Heat Bath: Results from PHENIX Thomas K Hemmick for the PHENIX Collaboration University...

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