1 / 29

Starting the Energy Scan - First Results from 62.4 GeV Au+Au Collisions

Starting the Energy Scan - First Results from 62.4 GeV Au+Au Collisions. Introduction. High p T . Bulk matter observations. Collective motion. Summary. The story so far.

kquarterman
Download Presentation

Starting the Energy Scan - First Results from 62.4 GeV Au+Au Collisions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Starting the Energy Scan - First Results from 62.4 GeV Au+Au Collisions • Introduction. • High pT. • Bulk matter observations. • Collective motion. • Summary

  2. The story so far. • We have discovered a strongly interacting medium with extremelyhigh energy density which cannot be described in terms of simple hadronic degrees of freedom. Phobos

  3. Nuclear modification factor at 200 GeV Charged Hadrons d2N/dpTd (Au+Au) RAA = NColld2N/dpTd (p+p) High pT suppression and loss of back-to-back signal inAu+Au but not ind+Au showed that effect due to Jet Quenching in final state NOT initial state parton saturation (GCG). BRAHMS Can we turn this effect off? Observed by all 4 experiments

  4. Need for an energy scan Varying the beam energy changes: • Initial state: sNN, Nbin/Npart, Qs(?) • System: , mB, Nch • Partonic: xT, dE/dx • Provide constraints on jet quenching models. • Study the excitation function of baryon transport. • Constrain models for hadron production at intermediate pT. Why 62.4 GeV? • Located (on log scale) mid-way between SPS and RHIC top energies. • Many reference data from ISR.

  5. Ncoll definition Au+Au b ~ 10.5 fm Glauber Monte Carlo Npart “Participants” Npart/2 ~ A L~A1/3 Ncoll= # of NN collisions:~A4/3 “Collisions” At 62.4 GeV Ncoll very different to 200 GeV

  6. First immediate result… Paddle Counter Signal top 50% of cross-section 200 GeV PHOBOS Preliminary 62.4 GeV Significant decrease in maximal multiplicity

  7. Charged hadron spectra and yields PHOBOS Expect 62.4 GeV fit into √s systematics

  8. Jet quenching predictions at 62.4 GeV I. Vitev nucl-th/0404052 Adil & Gyulassy nucl-th/0405036 RAA (p0) ~ 0.5 - 0.3 at pT = 4 GeV

  9. RAA charged particles same results from all 4 experiments BRAHMS Preliminary Maximum significantly higher than at 200 GeV. There is a suppression for most central data Similar shape evolution with centrality

  10. Universal centrality evolution? 62.4 GeV 200 GeV PHOBOS • But, varying the beam energy changes: • Initial state: sNN, Ncoll/Npart • System : , mB, Nch, • Partonic : xT, dE/dx • Energy-independent • Weak function of Npart, pT . • Use central A+A as denominator • Scale with 1/<Npart> • Allows comparison between different experiments nucl-ex/0405003

  11. PID spectra STAR Preliminary p BRAHMS Phenix preliminary p0 W- X-

  12. RAA for p0 for central data Predictions 0.3 - 0.5 at 4 GeV/c Again maximum > 200 GeV STAR Preliminary Charged ISR reference used for p0 Still discrepancy between charged and p0 Large baryon contribution up to at least 4 GeV/c

  13. Rcp of baryons and mesons Stat. Errors Only STAR preliminary STAR Preliminary (stat. errors only) The RCP(baryon) > RCP(meson) at intermediate pT. Problem with limited statistics.

  14. Again, large proton contribution at intermediate pT Small difference as function of centrality (not very peripheral 30-60%) Baryon/meson ratios STAR Preliminary Lessp in central collisions at 62.4 GeV Ratios factor 2-3 higher than in p+p at pT= 2-4 GeV

  15. Ratios at mid-rapidity Clear systematic trend with collision energy Minbias (0-80%) 62.4 GeV STAR Preliminary Stat. Errors Only STAR Preliminary L/L -/ +: 1.017±0.002 K-/K+: 0.835±0.006 p/p: 0.458±0.005 confirm varying y same effect as varying √s. Ratios flat as function of pT

  16. Statistical model results Close to net-baryon free Tch flat with centrality ● p, K,p ● p, K,p ● p, K,p, L, X ● p, K,p, L, X Close to chem. equilibrium ! STAR preliminary Au+Au at √sNN=200GeV and 62 GeV TLQCD~160-170MeV TLQCD~160-170MeV Energy dependence but small Nch dependence…

  17. (In)dependence of mid-rapidity yields Preliminary Preliminary • T, µB, and V all vary with energy, but in such a way as to ensureyields stay ~constant Preliminary

  18. Radial flow Blastwave fit Shape of the mT spectrum depends on mass: Tch Radial flow! p K p STAR Preliminary STAR Preliminary STAR Preliminary Same flow as at 200 GeV

  19. Kaon Slopes Top 5% central collisions

  20. HBT probes space-time evolution of system and system size at freeze-out. Studies at √s=130, 200 GeV yielded similar HBT radii to SPS energies (“HBT puzzle”). Severe challenge to hydrodynamic calculations. At an intermediate energy, a larger expansion time might point to a long-lived mixed phase.  interferometry PRELIMINARY Systematics of central 0-5% Fully consistent Coulomb treatment in kT dependence same results from PHOBOS

  21. HBT from SPS to RHIC No sign of qualitatively different expansion dynamics at 62 GeV. Continues to be a severe challenge submitted to Phys. Rev. C Rapid Communications Same results from STAR

  22. Charged particle correlations PHENIX PRELIMINARY PHENIX PRELIMINARY pT Substantialsignals attributable to elliptic flow (v2 = <cos(2f)>) v2 apparently saturates and is the same as at 200 GeV Jets are going to be a challenge

  23. Longitudinal elliptic flow h’=|h|-ybeam Longitudinal scaling of v2 nucl-ex/0406021

  24. Identified Elliptic Flow sNN = 62.4 GeV Au+Au centrality : 0-84% sNN = 200 GeV Au+Au centrality : 0-92% v2 v2 stat. error only sys. error <15% stat. error only sys. error <20% Charged p,K,p : PRL91, 182301 (2003) p0 : work in progress PHENIX preliminary pT [GeV/c] pT [GeV/c] Although statistics not great again resembles 200 GeV

  25. Quark coalescence? 62.4 GeV Au+Au: PHENIX preliminary 200 GeV Au+Au, charged p,K,p : from PRL p0 : work in progress stat. error only sys. error <20% (62GeV) 15% (200GeV) Coalescence at intermediate pT leads to: v2 /nquark The scaling works as for 200 GeV Au+Au Seems to be slightly lower than 200 GeV for pT/nquark<1 GeV/c pT /nquark [GeV/c]

  26. Summary Many of the results indicate environment similar at 62.4 GeV to 200 GeV but it’s notidentical • Initial energy density lower • Evidence of jet quenching Cronin effect is stronger • HBT radii at ~6 fm • Chemical freeze-out conditions similar to 200 GeV (fn Nch) Baryon chemical potential much higher • Radial flow as strong as at 200 GeV (fn Nch) • Elliptic flow as strong as at 200 GeV (fncentrality) Consistent with Nquark scaling • Elliptic flow appears universal at forward rapidities • Jet contribution much weaker than at 200 GeV As yet un-answered questions: Are the gluon densities the same in both systems? Do they spend the same amount of time in each stage? i.e. do they reach the same freeze-out conditions in the same manner?

  27. back up

  28. Why an energy scan? Varying the beam energy changes: • Initial state: sNN, Ncoll/Npart, Qs(?) • System: , mB, Nch • Partonic: xT, dE/dx Varying the geometry (A,b): • jet quenching • vary overall path length • vary asymmetry • Elliptic (and directed) flow • Study A dependence at fixed eccentricity. Npart eccentricity

  29. p+p references +/-25% uncertainty p0reference p0reference chargedreference

More Related