High pT and Direct Production

T.C. Awes, ORNL

International Workshop on RHIC and LHC Detectors Delphi, Greece, June 9, 2003

Theme: “The virtue of ’s and ’s”

To determine if we have produced deconfined QGP we must separately distinguish initial state effects from final state effects.

Once produced, ’s do not interact -> sensitive to: ( yield goes )• initial parton distributions: Intrinsic kT, kT Broadening, Shadowing, Saturation• final state parton/hadron rescatterings: Thermal, Jet/Parton Radiation

Experimental virtues (calorimeter measurement):• Measure and in same detector (get 2 for the price of 1!)• Identified particles to very high pT • ’s abundantly produced• mass provides calibration check

’s will suffer additional final state effects: Rescattering (low pT), Absorption, kT Broadening, Jet/Parton Energy Loss

Highlighted here

PHENIX Electromagnetic Calorimeter

PbSc• Highly segmented lead scintillatorsampling Calorimeter• Module size: 5.5 cm x 5.5 cm x 37 cmPbGl•Highly segmented lead glassCherenkov Calorimeter• Module size: 4 cm x 4 cm x 40 cm

Two Technologies - very important for systematic error understanding!Differences:•Different response to hadrons•Different corrections to get linearenergy response•Different shower overlap corrections

Closer look using the Nuclear Modification Factor RAA

Compare A+A to p-p cross sections

Nuclear Modification Factor:

If no “effects”: R < 1 in regime of soft physics R = 1 at high-pT where hard scattering dominates Suppression: R < 1 at high-pT

AA

AA

AA

AA

AA

AA

q

q

q

q

RHIC Year-1 High-PT Hadrons

hadron spectra out to

pT~4 GeV/c

Nominally expect production through hard scattering, scale spectra from N+N by number of binary collisions

Peripheral reasonably well reproduced; but central significantly below binary scaling

RHIC Headline News…

PHENIX

First observation of large suppression of high pT hadron yields

RHIC Run 2: s=200 GeV/c Au+Au collisions now extend to higher PT

h+ + h-

Au-Au nucl-ex/0304022

PHENIXPreliminary

Also measured high-PT spectra in p+p collisions at 200 GeV/c

p-p hep-ex/0304038

Calculations with different (gluon) FF’s(Regions indicate scale uncertainty)

Spectra for 0 out to 12 GeV/c compared to NLO pQCD predictions. Very good agreement!

No intrinsic kT included.

Good news for Direct measurement!

RAA : High PT Suppression to at least 10 GeV/c

nucl-ex/0304022, submitted to PRL

Binary scaling

Participant scaling

Factor 5

pp

AuAubinaryAuAuAA Yield

NYieldR

/ ⟩⟨=

Large suppression in central AuAu - close to participant scaling at high PT

Centrality Dependence of RAA

More central collisions

D.Kharzeev, E.Levin, L.McLerranhep-ph/0210332

nucl-ex/0304022, submitted to PRL

The suppression increases smoothly with centrality - approximate Npart scaling.

Centrality dependence similar topredictions of Color Glass Condensate- Initial state effect!

p+A and d+A: The control experiments

Nucleus- nucleuscollision

Proton/deuteron nucleuscollision

Nuclear effects other than a dense medium are known to affect hadron spectra (e.g. shadowing, Cronin effect) in p+A and d+A collisions, which do not have a created medium. Could these other influences be causing the suppression of high-PT hadrons in Au+Au collisions? If so, then we should also see suppression of high-PT hadrons in d+Au collisions.

High PT Spectra in d+Au Collisions

PHENIX PRELIMINARYpions neutral 200GeV,s =

dAu min bias + EMC trigger

pT [GeV/c]pT [GeV/c]

Neutral pions are measured with 2 independent Calorimeters – PbSc and PbGl PHENIX Preliminary

1 errors

- 2 results agree within errors

- Not suppressed relative to binary scaling!

Neutral Pion RAA for d+Au: RdA

The dAu results suggest that the created medium is responsible for hadron suppression in Au+Au

“Cronin” enhancement more pronounced in the charged hadron measurement

Possibly a larger effect in protons at medium pT?

Particle ID is important!

PHENIX Preliminary

1 errors

RdA for charged hadrons compared to 0

(h++h-)/2

Data vs Theory : 0

PHENIX Preliminary

0 d+Au (minbias) 200 GeV

0 Au+Au (0-5%) 200 GeV

Au+Au: I. Vitev and M. Gyulassy, hep-ph/0208108, to appear in Nucl. Phys. A; M. Gyulassy, P. Levai and I. Vitev, Nucl. Phys. B 594, p. 371 (2001).

Shadowing

Anti-shadowing d+Au: I. Vitev, nucl-th/0302002 and private communication.

Energy loss + Shadowing + Cronin = flat R

AA

Explains both AuAu and dAu

Nuclear modification factor: Nuclear modification factor: ssNNNN dependence dependence

A.L.S.Angelis PLB 185, 213 (1987)WA98, EPJ C 23, 225 (2002)PHENIX, PRL 88 022301 (2002)D.d'E. PHENIX Preliminary QM2002

CERN: Pb+Pb (sNN

~ 17 GeV), (sNN

~31 GeV): Cronin enhancement

RHIC: Au+Au (sNN

~ 130, 200 GeV): x4-5 suppression with respect to Ncoll

Ncollision

scaling

Npart

scalingR

AA ~ 0.4

RAA

~0.2

RAA

~ 2.0

RAA

~1.5

Is there no energy loss at SPS energies? SPS ~ 0.5*RHIC

and in WA98 at SPS

Fixed Target pA Scaling (Cronin Effect)

• p+p pA High PT Nuclear Enhancement: Cronin effect -> KT Broadening

Large effect at SPS!

•

WA98 Preliminary

p+Pb / p+C

0 Scaling with NColl

(Pb+Pb)central suppressed relative to (Pb+Pb)peripheral

Scales weaker than NColl

Not Cronin-like ! Decreases with pT ? WA98 PRL 81 (1998) 4087 EPJ C23 (2002) 225.

Central suppressed relative to semi-peripheral

Similar to RHIC result!

158 A GeV Pb+Pb

Central Pb+Pb Direct pT Spectrum

• Compare to proton-induced prompt results: Assume hard process - scale

with the number of binary collisions (=660 for central).

Assume invariant yield has form f(xT)/s2 where xT=2pT/s1/2 for s1/2-scaling.

• Factor ~2 variation in p-induced results.

• Similar spectral shape for Pb case, but factor ~2-3 enhanced yield. WA98 nucl-ex/0006007, PRL 85 (2000) 3595.

Direct Comparison to pQCD Calculation

• NLO pQCD calculations factor of 2-5 below s1/2 =19.4 GeV p-induced prompt results.

• But p-induced can be reproduced by effective NLO (K-factor introduced) if intrinsic kT is included.

• Same calculation at s1/2=17.3 GeV reproduces p-induced result scaled to s1/2 =17.3 GeV

• Similar spectrum shape for Pb case, but factor ~2-3 enhanced yield.

WA98 nucl-ex/0006007, PRL 85 (2000) 3595.

Photons - kT Broadening

• pQCD-calculations • Fit intrinsic kT in pp (E704) (Q2

= (2pT)2)

• kT - broadening in Pb+Pb

• Magnitude “consistent“ with expectations from pA

• Hard processes cannot explain excess at low pT

Dumitru et al., hep-ph/0103203.

< kT2 > ~ 1.3 -1.5 GeV2

kT2 ~ 1 GeV2

Direct : Comparison to Model Calculations

• Can be described with EOS with QGP or without QGP

• Many sources of theoretical uncertainty intrinsic kT, p broadening

preequilibrium QM rates: (under control!) HM rates: in-medium masses Hydro evolution: flow

• Need further experimental constraints: Hadron spectra dileptons (CERES,NA50) pA results (WA98) Results from RHIC

P.Houvinen, et al., PLB 535(2002)109.

With pQCD

Without pQCD

Inclusive : Peripheral Au+Au

PbGl and PbSc consistent

Compare with inclusive spectrum calculated via Monte Carlo with measured cross section as input…

()measured / ()simulated : Peripheral

PbGl and PbSc consistent with no excess in peripheral

()measured / ()simulated : Central

No photon excess seen within errorsWorking on better understanding of systematics

1 systematic errors

pQCD Direct predictions for RHIC

pQCD prediction

Plotted here as /Decay (as with

data)

pQCD predictionwith x5 suppression

Expext to see large direct signal,unless also suppressed (CGC)!

Direct : Expectations for RHIC & LHC

• At RHIC & LHC the QM contribution dominates for pT>2-3 GeV/c

• 0 “suppression” = decay suppression Increases Direct/Decay

• For PHENIX: s1/2 =200 GeV:

Two times WA98 central sample in PHENIX MinBias

High pT trigger events another x2 increase

Steffan & Thoma PLB 510 (2001) 98.

Direct at LHC

Large direct rates to ~100 GeV/c,

Large suppression expected,

Direct measurement will provide a powerful probe at LHC.

I.Vitev, M.GyulassyPRL 89 252301 (2002)

Direct (= +jet ) in ALICE EMCalin one Pb+Pb LHC run.

separation and identification up to ~100 GeV/c

PbW04: Very dense: X0 < 0.9 cmGood energy resolution (after 6 years R&D):stochastic 2.7%/E1/2

noise 2.5%/Econstant 1.3%

Photon Spectrometer

PbW04 crystal

• high granularity * 2.2x2.2 cm2 @ 5m

* ~ 18 k channels, ~ 8 m2

* cooled to -25oC

Electromagnetic Calorimeters in ALICE: PHOS

Proposed EMCAL||<0.7 ~ 120o

• large area electromagnetic calorimeter * hadronic energy in TPC + em energy in calorimeter

* trigger on jets, improve energy resolution, -jet coincidences

(PT) ~15%

100 GeV Jet in Central PbPb

Electromagnetic Calorimeters in ALICE: EMCal

Summary and Conclusions

• A strong suppression of hadron production is observed in central Au+Au collisions at RHIC (but protons not suppressed?); possibly due to parton energy loss in medium (not conclusive).

• The hadron production in d+Au collisions shows no strong suppression of high-PT

hadrons. Strongly indicative that suppression effect in Au+Au is due to created QCD medium.

• Suppression also occurs at SPS energies, but much weaker and obscured by large Cronin effect.

• Direct signal observed at SPS in Pb+Pb collisions possibly explained by EOS with QGP, but also consistent with HG. Many ambiguities - poor pQCD description, intrinsic kT effects, etc. Situation will be clearer at RHIC.

• Due to suppression, direct signal at RHIC and LHC should stand out like a beacon!

In fond remembrance of Aris…

USA Abilene Christian University, Abilene, TX Brookhaven National Laboratory, Upton, NY University of California - Riverside, Riverside, CA University of Colorado, Boulder, CO Columbia University, Nevis Laboratories, Irvington, NY Florida State University, Tallahassee, FL Georgia State University, Atlanta, GA University of Illinois Urbana Champaign, IL Iowa State University and Ames Laboratory, Ames, IA Los Alamos National Laboratory, Los Alamos, NM Lawrence Livermore National Laboratory, Livermore, CA University of New Mexico, Albuquerque, NM New Mexico State University, Las Cruces, NM Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY Oak Ridge National Laboratory, Oak Ridge, TN University of Tennessee, Knoxville, TN Vanderbilt University, Nashville, TN

Brazil University of São Paulo, São PauloChina Academia Sinica, Taipei, Taiwan China Institute of Atomic Energy, Beijing Peking University, BeijingFrance LPC, University de Clermont-Ferrand, Clermont-Ferrand Dapnia, CEA Saclay, Gif-sur-Yvette IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay LLR, Ecole Polytechnique, CNRS-IN2P3, Palaiseau SUBATECH, Ecole des Mines de Nantes, CNRS-IN2P3, Univ. NantesGermany University of Münster, MünsterHungary Central Research Institute for Physics (KFKI), Budapest Debrecen University, Debrecen Eötvös Loránd University (ELTE), Budapest India Banaras Hindu University, Banaras Bhabha Atomic Research Centre, BombayIsrael Weizmann Institute, RehovotJapan Center for Nuclear Study, University of Tokyo, Tokyo Hiroshima University, Higashi-Hiroshima KEK, Institute for High Energy Physics, Tsukuba Kyoto University, Kyoto Nagasaki Institute of Applied Science, Nagasaki RIKEN, Institute for Physical and Chemical Research, Wako RIKEN-BNL Research Center, Upton, NY University of Tokyo, Bunkyo-ku, Tokyo Tokyo Institute of Technology, Tokyo University of Tsukuba, Tsukuba Waseda University, Tokyo S. Korea Cyclotron Application Laboratory, KAERI, Seoul Kangnung National University, Kangnung Korea University, Seoul Myong Ji University, Yongin City System Electronics Laboratory, Seoul Nat. University, Seoul Yonsei University, SeoulRussia Institute of High Energy Physics, Protovino Joint Institute for Nuclear Research, Dubna Kurchatov Institute, Moscow PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg St. Petersburg State Technical University, St. PetersburgSweden Lund University, Lund

12 Countries; 57 Institutions; 460 Participants

BACKUP SLIDES

Central/Peripheral Ratio for (Anti)Protons and Pions

- No apparent suppression in proton yields for 2 <pT<4 GeV/c

- Different production mechanism for protons?

Submitted to PRL nucl-ex/030536