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Very Low p T in x

Very Low p T in x. Past, Present, and Prospects. Collaboration (March 2005). Burak Alver , Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel ,

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Very Low p T in x

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  1. Very Low pT in x Past, Present, and Prospects George Stephans

  2. Collaboration (March 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, 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 George Stephans

  3. Au+Au Centrality: 0-15% • 200 GeV Mid-rapidity • (+)/2 Phys. Rev. C70, 051901(R) (2004) • (h+h)/2PLB578 (2004) 297 Kinematic Regions at RHIC Physics Topics: Bulk - Particle production, sets the stage Tail - Jet quenching, probes medium Head - Sensitive to global properties BULK HEAD TAIL George Stephans

  4. Spectrometer The PHOBOS Detector (2001/2002) George Stephans

  5. The Low pT Part George Stephans

  6. The Technique • Simple in principle, Si gives dE/dx which sums to total energy • Combination of dE/dx and ETot gives mass • Complicated in practice • Energy in last plane is unreliable (decays, interactions, etc.) • Need to iterate that energy until (dE/dx)i and Ei consistent • Many corrections: decays, secondaries, ghosts, tracking efficiency, PID efficiency, mis-identified particles, etc. George Stephans

  7. Particle Measurements at Very Low pT For now: Only find particles stopped in the 5th spectrometer plane Reconstruction is based on the analysis of the measured energy depositions in the first 5 layers. Fewer than 5 planes per track leads to more background. Beyond that, magnetic field becomes a serious issue. F E D X[cm] C B A . . Beam pipe 0 10 20 Z [cm] . Single stopping particles from GEANT simulations are used to calibrate the method. Z[cm] George Stephans

  8. Comparison of dE/dx for low momentum pions (red) PR01 data(black) HIJING events George Stephans

  9. Particle Measurements at Very Low pT Summary of data reconstruction + + – Au+AusNN=200 GeV (RHIC Run II) Centrality: 15% most central events Vertex: -7cm < Zvtx < 15cm Event statistics: 2,070,000 Total reconstructed tracks: (+ ) 14,000 (K+K) 1,900 (p+p) 1,000 Dominant background: Feed-down, ghost, mis-identified K& p pT-dependent corrections from 0.69 to 0.78 Use HIJING simulations with yields tuned to our measurements George Stephans

  10. Published Result Au+Au 200 GeV 0-15% PHENIX - open symbols PHOBOS –closed symbols PRC 70 051901 (R) Used PHENIX because 0-15% data published Log scale! Solid curves: Fits to PHENIX only Dashed curves: Extrapolations George Stephans

  11. Published Result (Blown Up) PRC 70 051901 (R) Au+Au 15% central Extrapolation of fit to PHENIX data for pT>0.25 GeV/c George Stephans

  12. Comparison to Cramer et al. Data is (Au+Au 0-15% central Cramer, et al. PRL 94, 102302 & private comm. Fit to modified data Star data, fixed fit PRL curve, data fit problem } { Estimated yield 0-5% nucl-ex 0506008 Phobos 0-15% data George Stephans

  13. Procedure to Estimate 0-5% Yield • PHENIX pion data for pT=250-450 MeV/c • STAR pion data for pT=126-214 MeV/c (estimate 15% numbers using 5-10, 10-20% data) • PHOBOS charged hadron data for pT=250-450 MeV/c • PHOBOS summed charged hadron data • These ratios range from 16.2 to 20.1% • Our extrapolation band spans 15-20% Of course, the final answer is to have the data… George Stephans

  14. Near-Term Future d+Au 200 GEV —Study system size dependence Au+Au 62.4 & 200 GEV — Study energy & centrality dependence ✔Important to determine where any interesting properties “turn off” George Stephans

  15. Far-Term Future Au+Au 200 GEV – high statistics data from RHIC Run 4 • — Study low pT yields vs many event parameters • Could identify negatives using excess energy in last plane • — Attempt to get BE correlationfunction at very low mT • Momentum and angular resolutions are encouraging Cramer, et al. PRL R0 (fm) KT (MeV/c) George Stephans

  16. Far-Term Future Au+Au 200 GEV – high statistics data from RHIC Run 4 We will try, but the reality is that this data set is unlikely to yield usable pair statistics using very low pT stopping particles. There are several other options to explore to see how low in KT Phobos can reach. R0 (fm) KT (MeV/c) George Stephans

  17. Conclusions • i low pT data can play an important role in evaluating model(s) of the exotic systems formed at RHIC • More data for yields will be available soon • Looking forward to detailed comparison to theory(ies) • Very low KT HBT would likely require a dedicated experiment George Stephans

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