RHIC AGS Users Meeting 12 May BRAHMS Highlights Ramiro Debbe for the BRAHMS collaboration Physics 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 p T coverage at forward angles.

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/ and nucl-ex/  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/

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 = y hadron - 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/dy The 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

Stopping Energy loss 73±6 GeV per nucleon nucl-ex/

RHIC AGS Users Meeting 12 May dN/d  from d+Au collisions Our results compared to HIJING and AMPT Kharzeev, Levin, Nardi NPA730 (2004) 448 Curves from Kharzeev, Levin, Nardi 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 R dAu ratios Cronin like enhancement at  =0. Clear suppression as  changes up to 3.2 Same ratio made with dn/d  follows the low p T R dAu R dA   d 2 N d+Au /dp T d  d 2 N pp inel /dp T d  <> = 7.2 where = 7.2±0.3

RHIC AGS Users Meeting 12 May y1y1 y Au d The suppression of R dA 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 “kick”. Cronin in the MV model is a rearrangement of the spectra moving from low pt to higher values around Q s

RHIC AGS Users Meeting 12 May Quantum Evolution gluon radiation gluon fusion Y dN/d(ln1/x) =  s (2N - N 2 ) 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  s Y and gluon fusion has higher chances of happening to reduce the population. More central events (higher N part ) start with a higher population of gluons where fusion will also have strong effect. Kharzeev, Kovchegov and Tuchin Phys. Rev. D 68, Suppression at all k, suppression even stronger for higher A dP/dY  s

RHIC AGS Users Meeting 12 May R cp ratios At  =0 the central events have the ratio systematically above that of semi-central events. We see a reversal of behavior as we study events at  =3.2 R cp   1/ N AB central (p T,  1/ N AB periph (p T,  )

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

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 pbar K --

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 collaboration I. 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

Q 2 s (A) Q4s/2Q4s/2 Q s grows with centrality, the two boundaries get farther apart. The effect of ”quantum evolution” is proportional to the width of the “geometric scaling” region.