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Two-particle angular correlations in p+p and d+Au collisions

Two-particle angular correlations in p+p and d+Au collisions. George S.F. Stephans Massachusetts Institute of Technology for the i collaboration. A hint of. Two-particle angular correlations in p+p and d+Au collisions.

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Two-particle angular correlations in p+p and d+Au collisions

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  1. Two-particle angular correlations in p+p and d+Au collisions George S.F. Stephans Massachusetts Institute of Technology for the i collaboration Quark Matter 2005 8-Aug George S.F. Stephans

  2. A hint of Two-particle angular correlations in p+p and d+Au collisions Plus results for fluctuations of rapidity distributions in Au+Au Quark Matter 2005 8-Aug George S.F. Stephans

  3. Collaboration (August 2005) 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 Quark Matter 2005 8-Aug George S.F. Stephans

  4. Sample 2-particle correlation d+Au @ 200 GeV MinBias Raw data  Unique to Phobos  Quark Matter 2005 8-Aug George S.F. Stephans

  5. Dominant physics in raw correlation d+Au @ 200 GeV MinBias Detector effects(-e, etc.)   Quark Matter 2005 8-Aug George S.F. Stephans

  6. Dominant physics in raw correlation d+Au @ 200 GeV MinBias Momentum conservation   Quark Matter 2005 8-Aug George S.F. Stephans

  7. Status of Phobos Results • Why do this in Phobos? • Large  available • Can look at  or   at large || • Work ongoing to remove uninteresting effects. Quark Matter 2005 8-Aug George S.F. Stephans

  8. Change of Topic • In addition to looking at correlations in , Phobos can study essentially all of dN/d either averaged or on event-by-event basis. • Many physics possibilities: • Dependence on energy, system, and centrality • Event-by-event correlations and fluctuations Quark Matter 2005 8-Aug George S.F. Stephans

  9. Extended longitudinal scaling - I Au+Au When effectively viewed in the rest frame of one of the colliding nuclei, dN/d appears to be independent of energy over a very large range of ', denoted “extended longitudinal scaling” (previously “limiting fragmentation”). 19.6 62.4 (Prelim) 130 200 Similar scaling observed for flow: Implies effect is set at an early stage. Quark Matter 2005 8-Aug George S.F. Stephans

  10. dN/d for Cu+Cu • Extended longitudinal scaling is also observed to hold for Cu data. 62.4 200 Cu+Cu Phobos Prelim Quark Matter 2005 8-Aug George S.F. Stephans

  11. Extended longitudinal scaling - II • The shape is a function of centrality but the scaling with energy is repeated for each bin. Quark Matter 2005 8-Aug George S.F. Stephans

  12. Extended longitudinal scaling - III • The factorization of the centrality and energy dependence is quite remarkable. Take the peripheral dN/d, normalize by Npart, divide by the central dN/d, also normalized by Npart Quark Matter 2005 8-Aug George S.F. Stephans

  13. Factorization of Energy and Centrality dN/d for 35-40% over 0-6%, each normalized by Npart Take Periph over Central Quark Matter 2005 8-Aug George S.F. Stephans

  14. Observations on dN/d • Complete factorization of centrality and energy observed in all data studied to date. • It seems inappropriate to separate longitudinal phase space into distinct “fragmentation” and “central” regions governed by different physics. • Differences in particle density will produce variations in final-state effects but the overall shape is set by the initial energy and centrality. “As we discovered on the train, tomorrow never happens, it’s all the same %#&*% day” J. Joplin Quark Matter 2005 8-Aug George S.F. Stephans

  15. Some Related Studies • Do regions of  correlate event-by-event? • P.Steinberg talk last Saturday • Are there events with very large multiplicity? • Does the shape of dN/d vary event-by-event? • These constitute the remainder of this talk… Quark Matter 2005 8-Aug George S.F. Stephans

  16. What we did - I • Used 3% most central event sample in high statistics 200 GeV Au+Au data set. • About 1.96M events pass all quality cuts • Looked at the distribution of the total number of hits in the multiplicity detectors. • Note that these analyses required multiple passes through the entire data sample (not just the 3%), each pass took about 2-4 hours using PROOF and distributed disk storage. • See poster by M. Ballintijn Quark Matter 2005 8-Aug George S.F. Stephans

  17. Results - Ia • There is a tail on the high-total-hit side Cut 570 evts More than one event?? Quark Matter 2005 8-Aug George S.F. Stephans

  18. Could it be pileup? • “Pileup” means a single event in which the data is affected by more than one actual “collision”, including beam-gas and halo from upstream. • Scintillators and Si have different integration times. Result also depends strongly on vertex location and is different for beam gas, beam-beam, halo, etc. • Collisions from different or same bunches. • Rate of each depends on how the beam is distributed into bunches, bunch crossing time, etc. • Pileup within the Si detector integration time, or in the same bunch crossing, estimated at 6000 and 800 events, respectively, out of 2M. Quark Matter 2005 8-Aug George S.F. Stephans

  19. Results - Ib • We found that these events are strongly correlated with the beam rate ➩ Pileup? • Rate of events extrapolated to low luminosity is approximately consistent with zero Quark Matter 2005 8-Aug George S.F. Stephans

  20. What we did - II • Divided dN/d distribution into individual bins and calculated average and variation. • Compared each event to the average and looked for highly unusual events… Quark Matter 2005 8-Aug George S.F. Stephans

  21. Some details - IIa • Normalized each event total to remove remaining fluctuations in total yield. • Binned events in Z&Y vertex location. • X vertex didn’t vary significantly. • Used number of hit pads in bins in  Quark Matter 2005 8-Aug George S.F. Stephans

  22. Some Details - IIb • Compared raw dN/d Quark Matter 2005 8-Aug George S.F. Stephans

  23. Some details - IIc • Important to use the measured variance in each  bin, distributions are not Poisson Quark Matter 2005 8-Aug George S.F. Stephans

  24. Cut Results - IIa • 2 distribution shows a distinct tail 200 evts Quark Matter 2005 8-Aug George S.F. Stephans

  25. Results - IIb • However, these events are also strongly correlated with the beam rate ➩ Pileup again? • Rate of events extrapolated to low luminosity is again approximately consistent with zero Quark Matter 2005 8-Aug George S.F. Stephans

  26. Summary • Many results are in progress for correlations and fluctuations. • Extended longitudinal scaling indicates that mid- and far-from-mid-rapidity cannot be treated as totally distinct. • First event-by-event investigation of total number of hits and overall shape of dN/d in the most central Au+Au collisions @ 200 GeV indicates that both are very stable (at the rate of ~104 or possibly lower). Quark Matter 2005 8-Aug George S.F. Stephans

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