Forward and high pt physics at RHIC with BRAHMS

November 8 2004

Ericeira Jens Jørgen Gaardhøje, Niels Bohr Institute 1

Forward and high pt physics at RHIC with BRAHMS

Stopping in Au+Au at √s=200, 62.4 GeV

Rapidity dependence of high pt suppression of hadrons at √s=200 GeV

Au+Au and d+Au at η=0 Au+Au at η=2.2, 3.2 d+Au at η= 0 to 3.2 (CGC?)

Energy dependence of high pt suppression of hadrons at √s=62.4 GeV

in Au+Au at η= 0, 1

Flavor dependence in Au+Au and d+Au

Rapidity dependence of particle production in p+p collisions

November 8 2004


The BRAHMS experiment

November 8 2004


Excellent Hadron Identification by TOF and RICH

m2=p2( t2 / L2 -1)

D

p

KD

FS 4 deg

November 8 2004


Transparency and beam energy loss at RHIC

BRAHMS PRL 93 (2004) 102301

November 8 2004


Net Protons at 62.4 GeV

BRAHMS preliminary

0-5%

y

dN(p-pbar)/dy

November 8 2004


Rapidity and energy loss at RHIC

Rapidity loss saturates!

But Energy loss increases strongly

dE(baryon)=75GeV

ΔE(tot)=26TeV

Out of available

35 TeV

Relative rapidity loss :

35% < y/yb < 44%

November 8 2004


Total relativistic energy

Produced particles

in -3<y<+3

carry about

9 TeV of total energy

E = mt cosh(y)

mt=(pt2+m2)1/2

November 8 2004


pt21

RAA

0

The smoking gun of QGP? Jet Quenching, high pt suppression.

ddp/d/N

ddp/NdR

TNN2NN

inelbin

T2

AA

Soft Hard (jets)

BRAHMS: PRL 91 (2003) 072305

November 8 2004


Test: Absence of suppression at midrapidity in d+Au?

q

q

AuD

PRL 91 (2003) 072305

1/5

Absence of high pt suppression at midrapidity rules out initial

state effects .

November 8 2004


What does theory have to say?

HIJING: pQCD (hard) + strings (soft),shadowing, very schematic jet quenching (1992)

Vitev-Gyulassy: pQCD (hard), no softCronin kT broadening, shadowing and (GLV) jet quenching

Cassing et al: pQCD (hard) + strings (soft)kT broadening, shadowing and energy loss (pre-hadronic and hadronic)

Hirano-Nara: pQCD (hard) + hydro (soft)Cronin kT broadening, shadowing and (GLV) jet quenching

November 8 2004


High pt suppression persists at forward rapidity

Large high pt suppression also at forward rapidity.

Longitudinally extended medium, boost invariance, CGC or …?

Not quantitatively understood.

November 8 2004


Energy loss by stimulated gluon emission in QGP ?

q

q

q

q

QCD: <E> g ln(1/L) dz

<L2>

November 8 2004


RAuAu for hadrons at η=3.2 (4degrees)RHIC run IV

BRAHMS: preliminary

RCP indicates strong high pt suppression at very forward rapidities in

Au+Au

RCP= RdAu (0-20%) / (60-80%)

RdAu (30-50%) / (60-80%)

November 8 2004


RAuAu @ 62.4 GeVη=0 and η=0.95

November 8 2004


No sudden transition…..

√Snn (GeV)

?

November 8 2004


Color Glass CondensateThe fundamental state of the colliding nuclei?

X= p(parton) /p(nucleon)

AuD

Measure at large y on D side:

Probes small x in Au

detector

November 8 2004


Color Glass Condensate in d+Au collisions?

BRAHMS accepted PRL nucl-ex / 0403005

November 8 2004


Centrality dependence … in d+Au

RCP= RdAu (0-20%) / (60-80%)

RdAu (30-50%) / (60-80%)

Most central to peripheral ratio is most enhanced at midrapidity and most suppressed at forward rapidity

This centrality inversion is consistent with the CGC model.

November 8 2004


’High pt’ spectra are different for baryons and mesons in Au+Au

Very different from p+p and e++e-

Hadronic flow or partonic mechanism?

Qualitative agreement with parton recombination models, but need results from run IV for higher pt

November 8 2004


How does it look in d+Au ? Identified hadrons at 4 degrees (η=3.2)

π

K

p

PID with RICH

At eta= 3.2

P-bar : 10%

Π- : 80%

November 8 2004


RdAu at η=3.2(min.bias) Baryon meson difference in d+Au

Strong Difference between

mesons (pions) and Baryons

(anti-p) persists at forward rapidity

in d+Au collisions

BRAHMS preliminary

Flow?

Isospin?

Need to understand

November 8 2004


The hadron spectrum for d+Au at η=3.2

But many protons at forward rapidity

Excess of h+ over h-

November 8 2004


Difference understandable from relative abundances

h+ = 0.8h-( 1 + p/+ + K/+)

November 8 2004


p+p at 200GeVParticle ratios vs rapidity

PYTHIA misses 200GeV protons

BRAHMS, nucl-ex/0409002, Submitted to Phys. Lett. B (2004)

November 8 2004


Proton/pion in p+p at η=3.2vs. Pythia (vs. 6.303)

November 8 2004


Summary

Large high pt suppression at midrapidity in Au+Au. Gluon radiation energy loss?

No suppression in d+Au => no initial state effects. Large effect (factor 5).

Strong high pt suppression in Au+Au persists at forward rapidities- need quantitative understanding.

Reduced high pt suppression in Au+Au at 62.4 GeV

Decrease in R(dAU) from η=0 to η=3.2 and centrality dependence inversion. Consistency with CGC picture.

Baryon/mesons difference sseen at midrapidty in Au+Au is also present in d+Au at forward rapidity.

Pythia does not reproduce protons in p+p.

=== > BRAHMS whitepaper on RHIC discoveries: Nucl-ex/0410020, subm. Nucl. Phys. A

November 8 2004


Extra material

November 8 2004


Is a unified picture emerging?

November 8 2004


New Physics?

November 8 2004


I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J. Bondorf7, J.Brzychczyk4, B. Budick6, H. Bøggild7, C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1, J. J. Gaardhøje7, M. Germinario7, K. Grotowski4, K. Hagel8, O.

Hansen7, A. Holm7, A.K. Holme12, H. Ito1, E. Jacobsen7, A. Jipa10, J. I. Jordre9, F. Jundt2, E. Johnson11, C. E. Jørgensen7,T. Keutgen9, E. J. Kim11, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5, G. Løvhøjden12, Z. Majka3, A. Makeev8, B. McBreen1, M. Murray11, J. Natowitz8, B.S.Nielsen7, K. Olchanski1, D. Ouerdane7, R.Planeta4, F. Rami2, D. Roehrich9, B. H.

Samset12, S. J. Sanders11, D. Sandberg7,I. S. Sgura10, R.A.Sheetz1, Z.Sosin3, P. Staszel7,3, T.S. Tveter12, F.Videbæk1, R. Wada8 and A.Wieloch3.

1Brookhaven National Laboratory, USA 2IReS and Université Louis Pasteur, Strasbourg, France

3Jagiellonian University, Cracow, Poland 4Institute of Nuclear Physics, Cracow, Poland 5Johns Hopkins University, Baltimore, USA

6New York University, USA 7Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark 8Texas A&M University, College Station. USA

9University of Bergen, Norway 10University of Bucharest, Romania

11University of Kansas, Lawrence,USA 12 University of Oslo Norway

BRAHMS Intl. collaboration

November 8 2004


At lower energy the opposite is seen :High pt enhancement

CERN- SPS

(snn=17 GeV)

High p_t enhancement seen when compared to p+p scaled by N_binary.

Cronin effect:

quark mult scattering

November 8 2004


p+p reference at 62.4 GeV: a problem

November 8 2004


Transverse spin asymmetry for pions using polarized p+p collisions

STAR PRL 92,06230(2004)D.L.Adams (E704) Phys.Lett B264,462(1991);

Phys.ReV D53, 4747 (1996). FNAL704

AANN = (s+ - s-) / (s+ + s-) = (s+ - s-) / (s+ + s-)

November 8 2004


First results at high XF

<ε >~ -0.035 AN = -0.08 +- 0.005 +- [0.015]

0.17 < xF < 0.32

< ε >~ +0.022 AN = +0.05 +- 0.005 +- [0.015]

0.17 < xF < 0.32

BRAHMS preliminary

AANN = = εε /P P=0.40 - 0.45 /P P=0.40 - 0.45

εε = (N+ /L+ - N-/L-) / (N+ /L+ + N-/L-) = (N+ /L+ - N-/L-) / (N+ /L+ + N-/L-)

= (N+ - L*N-) / (N+ + L*N-) with L = L+ / L-= (N+ - L*N-) / (N+ + L*N-) with L = L+ / L-

π+

November 8 2004


BRAHMS whitepaperon RHIC discoveries

Conclusion: …There is no doubt that the experiments at RHIC have revealeda plethora of new phenomena that for the most part have come as asurprise. In this sense it is clear that the matter that iscreated at RHIC differs from anything that has been seen before.What name to give it must await our deeper understanding of thismatter.

Nucl-ex/0410020, subm. Nucl. Phys. A

Forward and high pt physics at RHIC with BRAHMS

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