rhic ags users meeting 12 may brahms highlights ramiro debbe for the brahms collaboration physics...

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RHIC AGS Users Meeting 12 May BRAHMS Highlights Ramiro Debbe for the BRAHMS collaboration Physics Department

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RHIC AGS Users Meeting 12 May

BRAHMS Highlights

Ramiro Debbe

for the BRAHMS collaborationPhysics Department

RHIC AGS Users Meeting 12 May

Outline of presentation

Brief summary of Run04.

Our most recent results submitted for publication.

Hardware additions.

A very preliminary look at Run04 data.

Summary and outlook.

RHIC AGS Users Meeting 12 May

2004 Au + Au Run summary

We have increased our data sample at all angles, this time both spectrometers had specialized triggers.

Achieved ~80% of BUP goal Total recorded luminosity:

170 b-1

140M FS Triggers and 90M MRS Triggers taken

For the first time, we collected data at 2.3° ( y ~4 for pions)

We tried to extend as much as possible the pT coverage at forward angles.

RHIC AGS Users Meeting 12 May

RHIC AGS Users Meeting 12 May

Au+Au at 62.4 GeV Summary

• We have recorded a total ~5 b-1

30% of BUP goal: (~60% of soft-physics goal)

• Recorded luminosity: 5 b-1

• Physics: soft-physics survey Rapidity dependent net-proton

(p-pbar), kaon, pion…

• Some comparison to p+p

RHIC AGS Users Meeting 12 May

2004 p+p run summary

• Good beam (~x2-3 higher rate than run3, almost no background ).• Data taken : ~7M FS Triggers ~4M MRS Triggers. - We collected the missing reference data set for the Forward Spectrometer at 4 degrees positive particles - Increased the size of our data sample at 3 and 12 deg (more data needed) - Transverse spin asymmetry measurements: FS at 2.3 deg. with

being performed as we speak.

RHIC AGS Users Meeting 12 May

Recent Results (leading to publications)

Identified particle production in Au + Au collisions at 200 GeV/per nucleon. nucl-ex/040350 and

nucl-ex/0312023

Charged particle densities in pseudo-rapidity as function of centrality for d + Au at 200 GeV/per nucleon. nucl-ex/04/01025

The evolution of nuclear modification factors for d + Au collisions as function of rapidity and centrality.

nucl-ex/0403005

RHIC AGS Users Meeting 12 May

I have a personal preference for a description of particle production based on two two flat partonic systems interaction at z=0 and t=0

The parton on each system follow a distribution in x that can be translated into a rapidity distribution by:

y = yhadron - ln(1/x)

The shape of the parton distribution defines the shape of produced particle distrib. No need to postulate boost invariance or to fill rapidity gaps as in naïve parton model.

RHIC AGS Users Meeting 12 May

dN/dydN/dyThe measured rapidity distribution for produced mesons has a gaussian shape and the average transverse momentum is almost constant with rapidity.

nucl-ex/040350

RHIC AGS Users Meeting 12 May

Spectra

RHIC AGS Users Meeting 12 May

RHIC AGS Users Meeting 12 May

Stopping

Energy loss 73±6 GeV per nucleon

nucl-ex/0312023

RHIC AGS Users Meeting 12 May

dN/d from d+Au collisions

Our results compared to HIJING and AMPT

Curves from Kharzeev, Levin, Kharzeev, Levin, Nardi NPA730 (2004) 448Nardi NPA730 (2004) 448

RHIC AGS Users Meeting 12 May

Any description of the physics of Au Au collisions at 200 GeV has to reproduce the BRAHMS measurements for all particle species and rapidity coverage.

Our results put stringent conditions on the description of RHIC results:

RHIC AGS Users Meeting 12 May

RdAu ratiosCroninCronin like like enhancement enhancement at at =0.=0.

Clear Clear suppression suppression as as changes changes up to 3.2up to 3.2

Same ratio Same ratio made with made with dn/ddn/d follows the follows the low plow pTT R RdAudAu

RdA d2Nd+Au/dpTd

<Ncoll> d2Nppinel/dpTd

where < < Ncoll> = 7.2> = 7.2±0.3

RHIC AGS Users Meeting 12 May

y1

y

Au dThe suppression of RdA at high rapidities has been seen in low energy fixed target exp.

S. Brodsky and J. Gunion had a description of such triangular shape based on beam fragmentation and string breaking.

Our measurement adds centrality dependence to the picture and beam fragmentation fails to

A saturated system together with quantum evolution can equally describe the trend.

reproduce the data

RHIC AGS Users Meeting 12 May

Cronin enhancement in the MV model

d+Au interactions can be described as coherent multiple scatterings of the deuteron valence quarks with a saturated Au wave function.

Each scattering gets a <kT

2> “kick”.

Cronin in the MV model is a rearrangement of the spectra moving from low pt to higher values around Qs

RHIC AGS Users Meeting 12 May

Quantum Evolution

gluon radiation gluon fusion

Y

dN/d(ln1/x) = s (2N - N2)

The net effect of quantum evolution is the reduction of the number of gluons.

There are two ways to achieve that reduction:

At high rapidity the probability of gluon emission grows as sY and gluon fusion has higher chances of happening to reduce the population.

More central events (higher Npart) start with a higher population of gluons where fusion will also have strong effect.

Kharzeev, Kovchegov and Tuchin Phys. Rev. D 68, 094013

Suppression at all k, suppression even stronger for higher A

dP/dY s

RHIC AGS Users Meeting 12 May

Rcp ratios At At =0 the =0 the central events central events have the ratio have the ratio systematically systematically above that of above that of semi-central semi-central events. We see events. We see a reversal of a reversal of behavior as we behavior as we study events at study events at =3.2=3.2

Rcp

1/<Ncoll central> NABcentral(pT,

1/<Ncoll periph> NAB

periph(pT,)

RHIC AGS Users Meeting 12 May

Hardware additions

We have rearranged our silicon multiplicity detectors to attempt a measurement of the reaction plane of the event.

Together with the information obtained with our spectrometers we will be able to measure first and second Fourier components of the azimuthal distribution for fully identified particles and a wide range of rapidities.

RHIC AGS Users Meeting 12 May

RHIC AGS Users Meeting 12 May

First look at 2004 data

As we already have all our analysis tools in place, and we know that the community expects concrete results.

We will present here very preliminary results that should be seen only as indicators of trends.

RHIC AGS Users Meeting 12 May

PID with the RICH

To compare the yields of anti-protons to those of negative pions we select tracks with p>17 GeV/c

pbarK

-

RHIC AGS Users Meeting 12 May

Anti-Proton/- ratio to probe extent of new medium in rapidity

centralPreliminary

Periph.

~3

RHIC AGS Users Meeting 12 May

Summary and outlook

BRAHMS has now an almost complete description of particle production (, k and p) in rapidity and transverse momentum.

From our net proton distribution we can state that ~70% of the energy has been transferred into particle production.

BRAHMS analysis of the d+Au collisions have opened very exiting possibilities to study parton distribution at small-x. Once again we reiterate the need for another d+Au run in the near future.

We are now busy analyzing the data that we collected.

Many thanks to the C.A.D.

RHIC AGS Users Meeting 12 May

BRAHMS collaborationI. Arsene, I.G. Bearden, D. Beavis, C. Besliu, B. Budick, H. Bøggild, C. Chasman, C. H. Christensen, P. Christiansen, J. Cibor, R. Debbe, E. Enger J. J. Gaardhøje, M. Germinario, K. Hagel, O. Hansen, A. Holme, A.K. Holme, H. Ito, A. Jipa, J.I. Jørdre, F. Jundt, C.E.Jørgensen, R. Karabowicz, E.J. Kim, T. Kozik, T.M. Larsen, J.H. Lee, Y. K.Lee, S. Linda, G. Løvhøjden, R. Lystad, Z. Majka, A. Makeev, M. Mikelsen, M. Murray, J. Natowitz, B. Neumann, B.S. Nielsen, K. Olchanski, D. Ouerdane, R.Planeta, F. Rami, C. Ristea, O. Ristea, D.Roehrich,B. H. Samset, D. Sandberg, S. J. Sanders, R.A.Sheetz, P. Staszel, T.S. Tveter, F.Videbæk, R. Wada,Z. Yin and I. S. Zgura

Brookhaven, Strasbourg, Krakov, Johns Hopkins, NYU, Niels Bohr. Texas A&M, Bergen, Bucharest, Kansas, Oslo

RHIC AGS Users Meeting 12 May

RHIC AGS Users Meeting 12 May

RHIC AGS Users Meeting 12 May

Q2s(A)

Q4s/2

QQss grows with centrality, grows with centrality,

the two boundaries get the two boundaries get farther apart.farther apart.

The effect of ”quantum The effect of ”quantum evolution” is evolution” is proportional to the proportional to the width of the “geometric width of the “geometric scaling” region.scaling” region.