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Experimental results from forward rapidities at RHIC

This study presents experimental findings from forward rapidities at the RHIC Bedanga Mohanty Variable Energy Cyclotron Centre in Kolkata. Topics discussed include particle production, longitudinal scaling, nuclear stopping, color glass condensate, and more. The importance of forward rapidity in understanding collision centrality and physics issues is emphasized. Key insights on gluon-to-p fragmentation and critical endpoints in the quark-gluon plasma are also highlighted. The study aims to shed light on the evolution of particle production and the scanning of the phase diagram at varying baryon chemical potentials and temperatures. The results contribute to a deeper understanding of high-energy physics phenomena at forward rapidities.

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Experimental results from forward rapidities at RHIC

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  1. Experimental results from forward rapidities at RHIC Bedanga Mohanty Variable Energy Cyclotron Centre, Kolkata Outline : • Introduction • Particle production • Longitudinal Scaling • Nuclear stopping • Color Glass Condensate • Summary QGP MEET 2006, February 5th – 7th, Kolkata

  2. Y = 0 Y = 1.5 What is pseudorapidity ? Y = 2 Y = 4 forward rapidity: Q small Introduction What is rapidity ? Rapidity as a “relativistic velocity” forward rapidity y>0 Midrapidity :y=0 y=infinity t z QGP MEET 2006, February 5th – 7th, Kolkata

  3. Experimental challenges QGP MEET 2006, February 5th – 7th, Kolkata

  4. Why look at forward rapidity ? Observable look different at forward rapidity Azimuthal distribution Rapidity distribution Physics at forward rapidity interesting Particle ratio Transverse momentum distribution QGP MEET 2006, February 5th – 7th, Kolkata

  5. Forward Detectors at RHIC STAR photon detector STAR Forward TPC STAR Forward p0 detector STAR Forward meson spectrometer PHENIX m stations BRAHMS spectrometers PHOBOS multiplicity array h Physics issues at forward rapidity • Particle production -- Collision centrality -- Pseudorapidity distribution -- Transverse momentum spectra • Longitudinal Scaling -- System size dependence -- Energy dependence -- Centrality dependence -- Identified particle • Baryon production -- Stopping or Transparency -- Energy used for particle production • Color Glass Condensate (initial state) -- Nuclear modification factor -- Correlations QGP MEET 2006, February 5th – 7th, Kolkata

  6. Collisions b sNN/2 sNN/2 Participant spectator Centrality, trigger and forward rapidity All four RHIC experiments have 2 ZDCs • The purpose of ZDCs are • To detect beam neutrons • Measure their total energy (hence multiplicity). • The ZDC coincidence is a minimal bias selection • The neutron multiplicity is also known to be correlated with event geometry or a of measure collision centrality QGP MEET 2006, February 5th – 7th, Kolkata

  7. Evolution of particle production Midrapidity  Forward rapidity  Full rapidity Wounded Nucleon “Scaling” But dN/dh = A Npart + B Ncoll Scaling at forward rapidity different from midrapidity QGP MEET 2006, February 5th – 7th, Kolkata

  8. Gluon to p fragmentation more in KKP than Kretzer Momentum spectra at forward rapidity At higher rapidity and lower pT data prefers Kretzer FF than KKP FF Higher rapidity sensitive to gp fragmentation PDF : CTEQ6 QGP MEET 2006, February 5th – 7th, Kolkata

  9. d2N/dpTd (d+Au) d2N/dpTd (A+A) RdAu = RAA = NColld2N/dpTd (p+p) NColld2N/dpTd (p+p) Ratio of pT spectra at forward rapidity Midrapidity  Forward rapidity At midrapidity, RAA is suppressed and RdAu is enhanced for high pT QGP MEET 2006, February 5th – 7th, Kolkata

  10. Ratio of pT spectra at forward rapidity Midrapidity  Forward rapidity d+ Au collisions at 200 GeV Cronin-like enhancement at =0 Clear suppression as  changes from 0 to 4.0 QGP MEET 2006, February 5th – 7th, Kolkata

  11. Critical endpoint Quark-Gluon Plasma Meson dominated Chiral symmetry restored Hadronic matter Baryon dominated Colour superconductor Chiral symmetry broken B Nuclei Neutron stars Scanning the phase diagram Continuous T 1st order How to scan this phase diagram for a given CM energy ? QGP MEET 2006, February 5th – 7th, Kolkata

  12. Ejiri et al. Tch Fodor-Katz Scanning the phase diagram For a given center of mass energy the phase diagram can be explored by varying centrality (temperature) and rapidity (baryon chemical potential) peripheral central This temperature is Tch As a representation we show the variation of Tfo with centrality Need of higher rapidity measurements QGP MEET 2006, February 5th – 7th, Kolkata

  13. Scanning the phase diagram Baryon chemical potential increases with rapidity QGP MEET 2006, February 5th – 7th, Kolkata

  14. 62.4 ”SPS”-like hadron chemistry radial flow drops by 30% 62.4 RHIC @ y =3 and SPS dn/dy drops by a factor of 3 Recreating the matter at SPS in forward rapidity at RHIC! QGP MEET 2006, February 5th – 7th, Kolkata

  15. Energy for particle production Energy (in GeV) p : 3108 p : 428 K+ : 1628 K- : 1093 + : 5888 - : 6117 • 0 : 6004 • n : 3729 • n : 513 • K0 : 1628 • K0 : 1093 •  : 1879 • : 342 sum: 33.4 TeV produced: 24.8TeV • 35 TeV (EbeamNpart) • of which 25 TeV are • carried by produced particles. • ~ 71 % of the beam energy • Fit , K and p distributions (dN/dy and mT vs y) •  total energy of , K and p • Assume reasonable distribution • for particles we don’t detect (0,n,…) • Calculate the total energy… NB: the method is very sensitive to the tails of the dN/dy dist. (10-15%) QGP MEET 2006, February 5th – 7th, Kolkata

  16. Summary on particle production • Forward rapidity region provides information on collision centrality, it is important to have centrality information from a rapidity region different from where you are studying your physics • Detectors at forward rapidity provides trigger information in experiments at RHIC • Scaling of particle production different at midrapidity and forward rapidity • The ratio of pT spectra in dAu collisions w.r.t pp collisions at high pT decreases from above unity to much below with increase as we move from midrapidity to forward rapidity • Since baryon chemical potential increases as we go from midrapidity to forward rapidity – we can scan the QCD phase diagram • Forward rapidity helps in determining the amount of energy of the beam spend in particle production ~ 72% in central AuAu collisions at RHIC QGP MEET 2006, February 5th – 7th, Kolkata

  17. Longitudinal scaling e-+e+ collisions DELPHI, PLB459 (1999) yjet ln(s/Mj) Mj ~ 1GeV Longitudinal scaling observed in elementary collisions QGP MEET 2006, February 5th – 7th, Kolkata

  18. Over a factor of ~50 variation in √s and Data show limiting fragmentation at high h Longitudinal scaling - I p+p collisions CDF (900) Phys.Rev D 41 (1990) 2330 UA5 (200,546) Z.Phys.C 43 1 (1989) ISR (23.6,45.2) Nucl.Phys B 129 365 (1977) QGP MEET 2006, February 5th – 7th, Kolkata

  19. Data show limiting fragmentation at high hfor beam and target rapidities Longitudinal scaling - II p(d)+A collisions PHOBOS, Phys.Rev. C (2005) QGP MEET 2006, February 5th – 7th, Kolkata

  20. Photons and charged particles follows limiting fragmentation at high h in nucleus-nucleus collisions Longitudinal scaling - III A+A collisions PHOBOS, PRL STAR PMD, PRL 200 GeV 130 GeV Forward physics appears simple – is it ? 19.6 GeV h = h - ybeam QGP MEET 2006, February 5th – 7th, Kolkata

  21. 200GeV 130GeV 19.6GeV Scaling of charged particles centrality dependent that for photons centrality independent Longitudinal scaling - IV Centrality dependence PHOBOS, PRL STAR PMD, PRL How to understand this ? QGP MEET 2006, February 5th – 7th, Kolkata

  22. Study negatively charged and positively charged hadrons separately : Beam protons are +ve charged Study identified particle longitudinal scaling Longitudinal scaling - IV Understanding Centrality dependence STAR PMD+FTPC, PRC • The difference between inclusive charged particles • and inclusive photons may be due to : • Beam remnants • Baryons transport QGP MEET 2006, February 5th – 7th, Kolkata

  23. dNp/dh/0.5Npart Net protons production do not follow energy independent limiting fragmentation p production follows energy independent limiting fragmentation h - ybeam Longitudinal scaling – V Understanding Centrality dependence STAR PMD+FTPC, PRC Beam fragments have some contribution Phys. Rev. Lett. 95 (2005) 062301 STAR nucl-ex/0511026 QGP MEET 2006, February 5th – 7th, Kolkata

  24. peripheral central Longitudinal scaling – VI Extended scaling But thecentralityand energydependence factorizes PHOBOS : Nucl. Phys. A 757 28 (2005) QGP MEET 2006, February 5th – 7th, Kolkata

  25. Longitudinal scaling – VII Predictive power Assuming: dN/dh grows log(s) and linear scaling at high h holds The most central pseudorapidity density at midrapidity in LHC ~ 6x400/2 ~ 1200 Acta Phys.Polon.B35 2873 (2004 ) QGP MEET 2006, February 5th – 7th, Kolkata

  26. z PRL 94, 122303 z Reaction plane (YR) y y x x (defines YR) Drawing by M. Kaneta Longitudinal scaling – VIII Azimuthal Anisotropy Anisotropy is sensitive to EOS …… We observe a simple scaling at high h?! QGP MEET 2006, February 5th – 7th, Kolkata

  27. Summary of scaling studies • Forward rapidity region shows certain universality of particle production. Energy independent behavior observed for e+e-, pp, pA, AA collisions when rapidity shifted by beam rapidity  referred to as Limiting Fragmentation • The longitudinal scaling breaksat forward rapidity for inclusive charged particles when we study it’s centrality dependence in Au+Au collisions at RHIC. It is maintained for inclusive photons • Detailed study reveals that apart from beam remnants, it is the baryons and its transport in rapidity that breaks the scaling • Surprisingly the scaling is restored in energy when we look at the ratio of peripheral to central yields in rapidity shifted by beam rapidity. This extended scaling reflects some kind of factorization in the dependences. • Quantities which crucially depends on the EOS and systems evolution (v2, v1) surprisingly shows longitudinal scaling at forward rapidity QGP MEET 2006, February 5th – 7th, Kolkata

  28. Anti-baryons - all from pair production Baryons - pair production + transported B/B ratio = 1 - Transparent collision B/B ratio ~ 0 - Full stopping, little pair production Measure p/p, L/L , K-/K+ (uud/uud) (uds/uds) (us/us) Baryon stopping and nuclear transparency Landau or Bjorken hydrodynamics QGP MEET 2006, February 5th – 7th, Kolkata

  29. AGS energies : Landau hydrodynamics applicable RHIC energies : Bjorken hydrodynamics applicable Baryon stopping and nuclear transparency Net protons Indication of increasing transparency with energy QGP MEET 2006, February 5th – 7th, Kolkata

  30. 2d 197Au 16O 197Au 197Au 32S Baryon stopping and nuclear transparency Which matters : Target or projectile ? Eur. Phys. J. C2:643 (1998) Projectile size is irrelevant. QGP MEET 2006, February 5th – 7th, Kolkata

  31. 0-20% 20-40% 40-100% Baryon stopping and nuclear transparency Baryon production in dAu collisions at RHIC (stat. Errors only) Difference (~baryon transport) is centrality dependent but…but their ratio (~baryon transport + pair production) is not The increase in baryon stopping with collision centrality is not reflected in a decrease of the anti-baryon to baryon ratio. QGP MEET 2006, February 5th – 7th, Kolkata

  32. Net-baryon after feed-down & neutron corrections Gaussians in pz: 2.03  0.16 2.00  0.10 6 order polynomial Baryon stopping and nuclear transparency Lack of measurement QGP MEET 2006, February 5th – 7th, Kolkata

  33. Baryon stopping and nuclear transparency • Upper limit to rapidity loss? • Energy loss: E = 25.7  2.1 TeV E/nucleon = 72  6 GeV QGP MEET 2006, February 5th – 7th, Kolkata

  34. Summary on baryon production • Net-baryon poor midrapidity region • dN(net-protons)/dy = 7 • Total-baryon rich midrapidity region • dN(all baryons)/dy  65 • Largest observed rapidity loss • <y> = 2 • as large as in pA • Stopping power • central Pb+Pb at RHIC: 72% • central S+S at SPS: 58% • p+p collisions:  50% QGP MEET 2006, February 5th – 7th, Kolkata

  35. From CGC to Quark Gluon Plasma Manifestation of CGC at RHIC • hadron multiplicities • high pT suppression at forward rapidity • Disappearance of back-to-back correlations in azimuthal angles between jets in forward and midrapidity L. McLerran, T. Ludlam, Physics Today, October 2003 QGP MEET 2006, February 5th – 7th, Kolkata

  36. CGC : Hadron multiplicity Multiplicity distribution Consistent with data for pp, dAu and AuAu collisions QGP MEET 2006, February 5th – 7th, Kolkata

  37. Au+Au 0-6% central CGC calculation Q2s0=2 GeV2 Q2=5.3 GeV2 CGC : Longitudinal scaling Consistent with energy independence observed in data at forward rapidity Nucl. Phys. A 757 28 (2005) Phys.Rev.C70 027902 (2004) QGP MEET 2006, February 5th – 7th, Kolkata

  38. CGC : pT spectra p0 • A model that treats Au nucleus as a CGC is consistent with dAu data • The model includes low xBjevolution of the Au wave function Data : G. Rakness, nucl-ex/0501026 D.A. Morozov, , hep-ex/0505024 B. Mohanty (STAR) QM2005 Model: A. Dumitru, A. Hayashigaki, J. Jalilian-Marian, hep-ph/0506308 QGP MEET 2006, February 5th – 7th, Kolkata

  39. Saturation tells us that the Cronin-peak disappears at high h: y=0 As y grows Phys. Rev. D 68 , 094013 (2003) Nucl. Phys. A739, 319 (2004) CGC : Nuclear modification factor Consistent with observations from data QGP MEET 2006, February 5th – 7th, Kolkata

  40. CGC : Nuclear modifiaction factor • CGC model describes RdAu and RCP • Suppression comes in at y > 0.6 D. Kharzeev, Y.V. Kovchegov, K. Tuchin, hep-ph/0405054 (2004) QGP MEET 2006, February 5th – 7th, Kolkata

  41. Other models also explain RdAu Vs. h with only the recombinationof soft and shower partons: no multiple scattering, and no gluon saturation put in explicitly see R. Vogt, hep-ph/0405060 (2004), Phys.Rev. C70 (2004) 064902 Phys.Rev.C 71 024902 (2005) See also R. Vogt, hep-ph/0405060 (2004) QGP MEET 2006, February 5th – 7th, Kolkata

  42. CGC : Back-to-back Correlations Disappearance of back-to-back correlations in dAu collisions predicted by KLM seems to be observed in preliminary STAR data. QGP MEET 2006, February 5th – 7th, Kolkata

  43. v2(h) from CGC+Hydro CGC+Hydro Qualitatively consistent with rapidity dependence of azimuthal anisotropy at RHIC when we use CGC as initial condition for hydrodynamical calculations QGP MEET 2006, February 5th – 7th, Kolkata

  44. Some other forward physics topics I could not cover ………. • Forward Spin Physics • Large Rapidity g-jet may provide interesting corners of phase space to probe gluon polarization (ALL). • Other opportunities are present in diffractive physics and Ultra peripheral collisions. • Lambda polarization has a prominent xf dependence • J/yproduction in PHENIX forward rapidity R. Bellwied, Nucl. Phys. A 698 (2002) 499 QGP MEET 2006, February 5th – 7th, Kolkata

  45. Summary • Detectors at forward rapidity region provides the experiment : centrality and trigger • Forward rapidity region provides rich information on particle production certain universality (species, energy) observed • Forward rapidity region provides information on nuclear stopping, baryon transport and energy for particle production • Forward rapidity provides a chance to scan the QCD phase diagram • Forward rapidity provides the best place to study the possible initial conditions at RHIC : CGC • Forward rapidity provides testing ground for NLO pQCD Measurements at forward rapidity (Kinematical limits and detector constraints) is also an experimental challenge QGP MEET 2006, February 5th – 7th, Kolkata

  46. broaden pT “Cronin effect” Initial state elastic multiple scattering leading to Cronin enhancement (RAA>1) Nuclear shadowing depletion of low-x partons Gluon saturation depletion of low-x gluons due to gluon fusion ”Color Glass Condensate (CGC)” r/ ggg Anti Shadowing Shadowing Suppression due to dominance of projectile valence quarks, energy loss, coherent multiple scattering, energy conservation, parton recombination, ... Initial and final effects - dAu • Initial effects • Wang, Levai, Kopeliovich, Accardi • Especially at forward rapidities: • Eskola, Kolhinen, Vogt, Nucl. Phys. A696 (2001) 729-746 • HIJING • D.Kharzeev et al., PLB 561 (2003) 93 • Others • B. Kopeliovich et al., hep-ph/0501260 • J. Qiu, I, Vitev,hep-ph/0405068 • R. Hwa et al., nucl-th/0410111 • D.E. Kahana, S. Kahana, nucl-th/0406074 QGP MEET 2006, February 5th – 7th, Kolkata

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