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Particle production in nuclear collisions over a broad centrality range

Particle production in nuclear collisions over a broad centrality range. Aneta Iordanova University of Illinois at Chicago for the PHOBOS collaboration. Phobos Collaboration. Burak Alver , Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts,

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Particle production in nuclear collisions over a broad centrality range

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  1. Particle production in nuclear collisions over a broad centrality range Aneta Iordanova University of Illinois at Chicago for the PHOBOS collaboration

  2. Phobos Collaboration Burak Alver, Birger Back,Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel, Wit Busza (Spokesperson), Zhengwei Chai, Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Ian Harnarine, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane, Piotr Kulinich, Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Eric Richardson, Christof Roland, Gunther Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith, Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Artur Szostak, Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Donald Willhelm, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Shaun Wyngaardt, Bolek Wysłouch ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER Aneta Iordanova

  3. Aneta Iordanova

  4. PHOBOS detector Aneta Iordanova

  5. Relativistic heavy ion collisions at PHOBOS • Au+Au • √sNN = 19.6, 56, 62.4, 130 and 200 GeV • Cu+Cu • √sNN = 22.4, 62.4 and 200 GeV • d+Au • √sNN = 200 GeV Cu+Cu All-inclusive count, Including tests Au+Au d+Au Au+Au Aneta Iordanova

  6. “White Paper”: nucl-ex/0410022, Nucl. Phys. A 757, 28 PHOBOS observations • We have created a state of matter at RHIC with high energy-density, that is nearly net-baryon free and interacting very strongly. • Transition to this high-energy state of matter does not create abrupt changes in observables at RHIC energies. • The data exhibit many “simple” scaling behaviors. • The data exhibit a remarkable factorization of collision energy and geometry. Aneta Iordanova

  7. Outline • Description of a heavy ion collision • Control parameters • Energy • Colliding system size (centrality Npart) • Species • Global features of charged particle production (observables) • dNch/dh shapes (particle distributions in h) • Particle distributions in pT • Observed scaling and factorization • Limiting fragmentation (Extended longitudinal scaling) • Mid-rapidity factorization Aneta Iordanova

  8. A description of a collision • Two high energy nuclei collide • Produce particles with different properties • emission angle (h distribution) • momentum (pT distribution) • species (PID spectra and particle ratios) • We can define some terminology • for the collision • for the particles Aneta Iordanova

  9. definition for collisions Centrality of the collision • Centrality • Describes the interacting volume of the collision • Simplest case: p+A collisions • Consider the “A” as a continuous sphere of matter Proton passes through a very low density region Proton passes through a medium density region Proton passes through a high density region Aneta Iordanova

  10. definition for collisions Centrality of the collision • The nucleus is not continuous matter • Discrete nucleons • Have different density of nucleons dependent on distance from center • Use this as a basis to classify collisions in A+A collisions Aneta Iordanova

  11. definition for collisions Classifying centrality:Impact parameter • Impact parameter, b • distance between colliding nuclei, perpendicular to the beam-axis • large b are classified as PERIPHERAL • small b are classified as CENTRAL b CANNOT measure impact parameter: MUST derive it from models and connect with a measured quantity from data Aneta Iordanova

  12. definition for collisions Classifying centrality:geometry of the collision/system size • The geometrical overlap • number of interacting nucleons (participants) Spectators → nucleons outside overlap volume Participants (Npart) → nucleons inside overlap volume Npart/2 ~ A characteristic nuclear size Number of participants = Number of wounded nucleons (3d) nucleus distribution based on measurement Aneta Iordanova

  13. definition for collisions Measuring centrality: A+A collisions • Data • Divide data based on the number of particles produced in a region of phase space • This signal is from the “paddle” counters • 3.2<|η|<4.5 Aneta Iordanova

  14. definition for collisions Measuring centrality: A+A collisions • Monte-Carlo simulations • simulate the same signal from the paddles • correlate this to the (known) number of participants • find the average Npart (wounded nucleons) associated with a given fraction of cross section MC Aneta Iordanova

  15. definition for collisions Centrality datasets Aneta Iordanova

  16. definition for particles η = ±3 η = ±1 Angular distribution ofproduced charged particles • Particles are produced predominantly at small angles • they all go down the interaction axis • Particles can be assigned an “angle” − pseudorapidity (η) • similar to the characteristic velocity − rapidity (y) PHOBOS Data m«p, then E≈p Aneta Iordanova

  17. definition for particles θ and η distributions η = ±1 • η is logarithmic! • ~450 → η=1 • This is a little confusing at first sight • it seems that ALL the particles are at 900 • they are not! • PHOBOS cannot measure y over whole region – requires particle identification η = ±3 Aneta Iordanova

  18. Data comparison of Au+Au and Cu+Cu

  19. Au+Au : PRL 91, 052303 (2003) dN/dh distribution 19.6 GeV 62.4 GeV 130 GeV 200 GeV Charged hadron dNch/dh distribution centrality preliminary Au+Au data • With energy: • Height increases • Width increases (in h space) • With centrality(0-50% central): • Height increases Aneta Iordanova

  20. dN/dh distribution Mid-rapidity dNch/dh versus energy • Central Au+Au collisions • produce higher multiplicity than p+p collisions per colliding pair • slower particle production versus energy than expected 6% central collisions, Npart ~ 340 Aneta Iordanova

  21. Au+Au : PRL 91, 052303 (2003) d+Au : arxiv nucl-ex/0409021 dN/dh distribution 19.6 GeV 62.4 GeV 130 GeV 200 GeV Charged hadron dNch/dh distribution centrality preliminary Au+Au data preliminary preliminary Cu+Cu data d+Au • With species: • Same systematic trends Aneta Iordanova

  22. dN/dh distribution midcentral central Cu+Cu Preliminary 15-25%, Npart = 61 Au+Au 45-55%, Npart = 56 Cu+Cu Preliminary 3-6%, Npart = 100 Au+Au 35-40%, Npart = 99 Comparison of Au+Au and Cu+Cu 200 GeV • For the same collision system size (Npart) dNch/d shape is very similar for • central Cu+Cu with mid-central Au+Au collisions • mid-central Cu+Cu with peripheral Au+Au collisions Aneta Iordanova

  23. dN/dh distribution All at √s = 200 GeV Comparison of Au+Au, d+Au and p+p collisions at 200 GeV • Scale by Npart/2 • allows for a direct comparison to p+p • i.e. normalized to 1 participating pair • Multiplicity obtained at the same center-of-mass energy is similar in p+p and d+Au • Multiplicity is larger for Au+Au collisions at the same energy d+Au : PRL 93, 082301 (2004) Aneta Iordanova

  24. d+Au : arxiv nucl-ex/0409021 p+p : 2004 J.Phys.G 30 S1133-1137 dN/dh distribution 2 dNch Npart dη Comparison of d+Au and p+p • More detailed comparison of d+Au and p+p shows • more peripheral collisions tend toward p+p shape • limiting slopes in d+Au and p+p are the same, but offset PHOBOS d+Au and p+p Data at √s = 200 GeV 3 2 1 0 -6 -4 -2 0 2 4 6 η Aneta Iordanova

  25. scaling limiting fragmentation

  26. limiting fragmentation Limiting Fragmentation • Term for particles produced at high η. • particles produced close to the beam rapidity of one of the colliding nuclei • same “Limiting” distribution of charged-particles in this region independent of energy Center-of-mass System Aneta Iordanova

  27. limiting fragmentation Au+AudNch/dη vs η 19.6 62.4 (Prelim) 130 200 ybeam~5.37 ybeam~4.90 ybeam~4.20 ybeam~3.05 • ybeam grows with energy • Shift each η by ybeam • Scaling by Npart/2 • Distributions are relatively the same • <Npart> ~ same for each energy for 0-6% central Aneta Iordanova

  28. limiting fragmentation Au+Au dNch/dη vs η–ybeam • Region of ‘overlap’ • for each energy • close to rapidity of one projectile • Expected • narrow fragmentation region • Observed • extended longitudinal scaling • Fragmentation Region • grows with energy Aneta Iordanova

  29. limiting fragmentation Cu+Cu dNch/dη vs η–ybeam • Extended longitudinal scaling is also observed to hold for Cu+Cu data 62.4 200 Cu+Cu preliminary Aneta Iordanova

  30. limiting fragmentation Centrality Dependence Au+Au • Centrality • data divided into distinct multiplicity bins • Central 0-6% • Npart ~ 340 • Peripheral 35-40% • Npart ~ 100 Aneta Iordanova

  31. limiting fragmentation Centrality + Energy Dependence Au+Au • Observations • reduction at η~0 • increase at η>ybeam • important observation for the total yield Aneta Iordanova

  32. limiting fragmentation Smaller systems • This observation is not peculiar to Au+Au • first observed in p+p • also in d+Au and new Cu+Cu • All exhibit similar features Aneta Iordanova

  33. limiting fragmentation p+p • Collection of many data over a factor of ~50 in √s • reasonable Limiting Fragmentation agreement! • η’ = η-ybeam CDF (900) → Phys.Rev D41 7(1990) 2332 UA5 (200,546) → Z.Phys.C 43 (1989) 1 ISR (23.6,45.2) → Nucl.Phys B129 365 (1977) Aneta Iordanova

  34. limiting fragmentation d+Au 50-70% Centrality, PHOBOS data d+Au data from nucl-ex/0409021 p+Em referenced therein Aneta Iordanova

  35. limiting fragmentation d+Au • Limiting fragmentation in both • projectile rest frame • target rest frame • Centrality/system size dependence • systematic comparison with lower energy data • Limiting fragmentation in each centrality bin Aneta Iordanova

  36. scaling universality of total charged

  37. “Universality” of total chargein e++e-, p+p and A+A collisions • Total charged particles produced scale differently in A+A and p+p collisions arxiv nucl-ex/0301017, submitted to PRL Aneta Iordanova

  38. “Universality” of total chargein e++e-, p+p and A+A collisions • e++e- scale as p+p after consideration of the “leading hadron” • reduce √s by ½ Aneta Iordanova

  39. “Universality” of total chargein e++e-, p+p and A+A collisions • In this regime all data are consistent • Can examine this more closely by dividing by e++e- • e++e- fit Aneta Iordanova

  40. “Universality” of total chargein e++e-, p+p and A+A collisions • All data are consistent with e++e- • Scaling breaks down for low energy A+A Aneta Iordanova

  41. factorization at midrapidity in energy and centrality

  42. Mid-rapidity factorization Mid-rapidity dNch/dh • Information about the created matter →energy density • Particle production in A+A: interplay between collision centrality (geometry) and collision energy? • balance of binary/soft processes Aneta Iordanova

  43. Mid-rapidity factorization PHOBOS Au+Au Measured pseudorapidity density per participant pair as a function of Npart • Multiplicity in Au+Au collisions (dNch/dh) per participant pair (Npart/2) higher than the corresponding values for inelastic p+p • Percentile cross-section • 0-50% for 200, 130 and 62.4 GeV • 0-40% for 19.6 GeV 90 % C.L. 200 GeV (UA5) 19.6 and 62.4 GeV (ISR) Aneta Iordanova

  44. Mid-rapidity factorization Divide by the corresponding p+pmultiplicity • Compare particle production in Au+Au to p+p collisions • multiplicity per pair is ~40% higher • Remarkable similarities between the data sets • similar centrality dependence • observed level above value of 1 (participant scaling) Aneta Iordanova

  45. Participant Scaling Participants − in overlap region • Participant scaling • multiplicity in Au+Au proportional to number of participating pairs (Npart/2) • every pair is equivalent to 1 p+p collision, produces the same number of particles as p+p at this energy • multiplicity from coherent “soft” collisions dNch(Au+Au)/dh = dNch(p+p)/dh x Npart/2 “Wounded Nucleon Model” Aneta Iordanova

  46. Collision Scaling • Collision scaling • multiplicity proportional to Ncoll • each collision contributes with a multiplicity of 1 p+p collision • multiplicity from binary collisions projectile “nucleon” dNch(Au+Au)/dh = dNch(p+p)/dh x Ncoll Aneta Iordanova

  47. Mid-rapidity factorization Divide by the corresponding p+p • Remarkable similarities between all data sets • similar Npart dependence • observed level above participant scaling depends on the p+p reference • Data is dominated by Npart scaling • closer to Npart than Ncoll Aneta Iordanova

  48. Mid-rapidity factorization Midrapidity Ratios • Define a ratio 200/19.6 for midrapidity data • similar for other energies Aneta Iordanova

  49. Mid-rapidity factorization Midrapidity Ratios 200/19.6 Phys.Rev.C70 021902(R) 2004 200/62.4 Preliminary 200/130 Phys.Rev.C65 061901(R) 2002 • Data ratio 200/X • no centrality (geometry) dependence • Models • HIJING • disagrees with data • Saturation Model (KLN) • flat centrality dependence as in data HIJING PHOBOS 200/19.6 KLN Saturation 200/62.4 200/130 Cu+Cu preliminary Au+Au HIJING:Comput.Phys.Commun. 83 (1994) 307,v 1.35 KLN:Phys.Lett.B523 79 (2001) & arXiv:hep-ph/0111315 Aneta Iordanova

  50. factorization at midrapidity versus pT

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