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Ramiro Debbe Physics Department

Forward Light Hadrons. RHIC-II Forward and pA Workshop. Ramiro Debbe Physics Department. Outline of the presentation. Brief description of the BRAHMS setup. Charged particle production as function of rapidity and centrality. Particle identification:

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Ramiro Debbe Physics Department

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  1. Forward Light Hadrons RHIC-II Forward and pA Workshop Ramiro Debbe Physics Department RHIC-II 29-Apr-2005

  2. Outline of the presentation • Brief description of the BRAHMS setup. • Charged particle production as function of rapidity and centrality. • Particle identification: • RdAu for anti-protons and - at =3.2 • Composition of h+ at =3.2 • Results from p+p collisions. • Summary RHIC-II 29-Apr-2005

  3. The BRAHMS Detector MRS GeometricalAcc.:0.8 msr FFS BFS p/p = 0.0018p [GeV/c] RHIC-II 29-Apr-2005

  4. TMA BB BB ZDC ZDC INEL Event characterization The centrality of the collision for the results that will be presented is defined as fractions of the total multiplicity measured with the TMA in -2<<2 The centrality of Au-Au collisions can also be defined with the ZDC and BB or TMA correlations. Our triggers are defined with the ZDC and BB, p+p and d+Au collisions were triggered with the INEL detectors. RHIC-II 29-Apr-2005

  5. I have a personal preference for the ~direct connection between gluon distributions in the colliding ions and the distribution of produced particles. For d+Au collisions, multiplicity densities show “cascading” in Au side and dAu = pp at d frag. side. Already seen at lower energies. RHIC-II 29-Apr-2005

  6. The reach “into” the target wave function pT From Guzey, Strikman, and Vogelsang. Most of the data collected at 4 degrees would have x2~0.01 x2 Energy and momentum conservation xL = xa - xb =(2MT/√s)sinh y ka + kb = k, xaxb = MT2/s A solution to this system is: xa = (MT/√s) ey xb = (MT/√s) e-y where y is the rapidity of the (xL,, k) system RHIC-II 29-Apr-2005

  7. Acceptance and d+Au and p+p Spectra PRL 93 242303 (nucl-ex/0403005) RHIC-II 29-Apr-2005

  8. Modification of pt spectra as function of rapidity In both p+p and d+Au systems the distributions get softer at higher rapidities, beyond a trivial thermal behavior. RHIC-II 29-Apr-2005

  9. RdAu ratios Croninlike enhancement at =0. Clear suppression as  changes up to 3.2 Same ratio made with dn/d follows the low pT RdAu 1 d2Nd+Au/dpTdh RdA= <Ncoll> d2Nppinel/dpTdh where < Ncoll> = 7.2±0.3 RHIC-II 29-Apr-2005

  10. Rcp 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 1/<Ncollcentral> NABcentral(pT,h) Rcp= 1/<Ncoll periph> NABperiph(pT,h) RHIC-II 29-Apr-2005

  11. d+Au particle abundances The ratios proton/pion from dAu collisions measured at mid-rapidity are consistent with “fragmentation in vacuum” RHIC-II 29-Apr-2005

  12. Using ratios to obtain the RdAu of identified negative particles. RHIC-II 29-Apr-2005

  13. Use of theBRAHMSRICHto identify particles We make use of already produced spectra and RdAu factors and use the RICH at high momentum to bypass the long process of invariant yield extraction. 17 GeV/c Above the selected momentum threshold the RICH is ~94% efficient. RHIC-II 29-Apr-2005

  14. RdAufor anti-protons and pions (min bias) d Au Preliminary p p RHIC-II 29-Apr-2005

  15. Difference between h+ and h- in dAu at ~3 But pQCD calculations that do well reproducing 0 would have at most a 10% difference not the factors ~3 we measure. • proton Our measurement is showing that the difference is driven by the protons.  kaon RHIC-II 29-Apr-2005

  16. BRAHMS results from p+p collisions The ratio of particle to anti-particle measured in p+p collisions is remarkably similar to the one we measured in Au+Au collisions. RHIC-II 29-Apr-2005

  17. Comparison of NLO pQCD and measurement at  = 0 Work done by Marco van Leeuwen STAR Calculations by W. Vogelsang RHIC-II 29-Apr-2005

  18. Measured h- at 4 degrees and a NLO pQCD calculation NLO pQCD calc. From W. Vogelsang Frag. Function: modified KKP is an attempt to reproduce h- BRAHMS data RHIC-II 29-Apr-2005

  19. Spectra for identified particles at =2.2 RHIC-II 29-Apr-2005

  20. Comparison of particle ratios measured in p+p collisions and simulated with PYTHIA For protons we find a remarkable difference that may indicate other processes besides parton fragmentation. =3.2 =3.2 We measure a small excess of kaons and see an emerging trend that suffers from low statistics at high pt. RHIC-II 29-Apr-2005

  21. Summary • Inclusive charged particle production in dAu compared to scaled pp shows a suppression that depends on rapidity and the centrality of the collisions. • First results that include particle identification in dAu collisions show particle abundances consistent with “fragmentation in the vacuum”. • Different “Cronin effect” of baryons and mesons is also seen at forward rapidities. • NLO pQCD describes pp inclusive pt distributions up to the highest rapidities measured. • We see that PYTHIA fails to describe the baryons (protons) at forward rapidity. RHIC-II 29-Apr-2005

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