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A Strange Perspective – Preliminary Results from the STAR Detector at RHIC

A Strange Perspective – Preliminary Results from the STAR Detector at RHIC. Science is a wonderful thing if one does not have to earn one's living at it – Einstein (1879—1955). The STAR Collaboration. Brazil: Universidade de Sao Paolo China: IHEP - Beijing, IPP - Wuhan

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A Strange Perspective – Preliminary Results from the STAR Detector at RHIC

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  1. A Strange Perspective – Preliminary Results from the STAR Detector at RHIC Science is a wonderful thing if one does not have to earn one's living at it – Einstein (1879—1955)

  2. The STAR Collaboration Brazil: Universidade de Sao Paolo China:IHEP - Beijing, IPP - Wuhan England:University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt Poland:Warsaw University, Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR–Dubna, IHEP-Protvino U.S. Labs:Argonne, Berkeley, Brookhaven National Labs U.S. Universities:Arkansas, UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton, Indiana, Kent State, MSU, CCNY, Ohio State, Penn State, Purdue,Rice, Texas A&M, UT Austin, Washington, Wayne State, Yale Spokesperson: John Harris Institutions: 36 Collaborators: 415 Students: ~50

  3. QCD Quarks confined within hadrons via strong force v(r) = a/r + s*r At large r -second term dominates At small r -Coulomb-like part dominates However a function of q( mtm transfer) and a -> 0 faster than q (or 1/r) -> infinity (called asymptotic freedom) This concept of asymptotic freedom among closely packed coloured objects (q and g) has led to one of the most exciting predictions of QCD !! The formation of a new phase of matter where the colour degrees of freedom are liberated. Quarks and gluons are no longer confined within colour singlets. The Quark-Gluon Plasma!

  4. Don’t Panic!!! - New Scientist most dangerous event in human history: - ABC News –Sept ‘99 "Big Bang machine could destroy Earth" -The Sunday Times – July ‘99 No… the experiment will not tear our region of space to subatomic shreds. - Washington Post – Sept ‘99 the risk of such a catastrophe is essentially zero. – B.N.L. – Oct ‘99 Apocalypse2 – ABC News – Sept ‘99 Will Brookhaven Destroy the Universe? – NY Times – Aug ‘99

  5. The Phase Space Diagram TWO different phase transitions at work! – Particles roam freely over a large volume – Masses change Calculations show that these occur at approximately the same point Two sets of conditions: High Temperature High Baryon Density Lattice QCD calc. Predict: Deconfinement transition Chiral transition Tc ~ 150-170 MeV ec ~ 0.5-0.7 GeV/fm

  6. Why are we interested in Strangeness? Tfireball < Tc(170MeV) Hadron gas Hard to make S  0 particles p + N  L + K (Ethresh  530MeV) p + K L + N (Ethresh  1420MeV) Mtm phase space suppressed Need to create 3 qq pairs (initially there are no q) with similar momenta in a region already containing many quarks. Tfireball >Tc(170MeV) QGP Easy to make s quarks E=2ms ( 300MeV) Free gluons g-g fusion - dominate ss creation faster reaction time than qq Pauli blocking may aid creation of ss quarks ( probably not true at high T, too many states). _ _ _ _ _ _ _

  7. Introduction Chemical content – Yields When is Strangeness Produced –Resonances Flow – How much and when does it start? Thermal Freeze-out –Radii and Inverse slopes Chemical Freeze-out - Ratios

  8. Previous Strangeness Highlights Enhancement W > X > L > h SPS s=17GeV WA97 |s| Evidence of strangeness enhancement between pA and AA collisions at the SPS – Not reproducible by models

  9. Strangeness Highlights (2) Multi-Strange Particles appear to freeze out at a cooler temperature/ earlier or have less flow SPS AGS AGS and SPS > 1 Need to consider p absorption _

  10. The CERN announcement • Strangeness was one of the corner stones of the CERN announcement. • Have numerous pointers that there is evidence of a new state of matter even at SPS energies so why RHIC? • Still a large baryon number so need models to understand what’s going on. • Those models can probably be tuned to reproduce the experimental data but would require more “knobs” • So want to go to “cleaner” system • Less baryon number (only look at produced particles) • Closer to the region where QCD predictions work – Definite theory not models • Higher energies – further across phase transition boundary – In new regime for longer and more frequently

  11. Welcome to BNL- RHIC!

  12. Year 2000, The STAR Detector (Year-by-Year) Time Projection Chamber Silicon Vertex Tracker * FTPCs (1 +1) Endcap Calorimeter Vertex Position Detectors Barrel EM Calorimeter + TOF patch year 2001, year-by-year until 2003, installation in 2003 Magnet Coils TPC Endcap & MWPC ZCal ZCal Central Trigger Barrel RICH * yr.1 SVT ladder

  13. STAR Pertinent Facts Field: 0.25 T (Half Nominal value) (slightly worse resolution at higher p, lower pt acceptance) TPC: Inner Radius – 50cm (pt>75 MeV/c) Length – ± 200cm ( -1.5< h < 1.5) Events: ~300,000 “Central” Events –top 8% multiplicity ~160,000 “Min-bias” Events L3-Real time display

  14. Needle in the Hay-Stack! How do you do tracking in this regime? Solution: Build a detector so you can zoom in close and “see” individual tracks high resolution Clearly identify individual tracks Good tracking efficiency Pt (GeV/c)

  15. Particle ID Techniques - dE/dx Resolution: dE/dx No calibration 9 % With calibration 7.5% Design 6.7% Even identified anti-3He ! dE/dx PID range: ~ 0.7 GeV/c for K/ ~ 1.0 GeV/c for K/p

  16. Particle ID Techniques - Topology X+ Decayvertices Ks p + + p - L  p + p - L  p + p + X-  L + p - X+L + p + W  L + K- L Vo “kinks”: K  + 

  17. Finding V0s proton Primary vertex pion

  18. High Pt K+ & K- Identification Via “Kinks” m+/- nm K+/-

  19. Particle ID Techniques Combinatorics K* combine all K+ and p- pairs (x 10-5) f from K+ K- pairs dn/dm m inv (GeV) background subtracted Breit-Wigner fit Mass & width consistent w. PDG m inv dn/dm K+ K- pairs same event dist. mixed event dist. m inv Combinatorics Ks p+ + p-f  K+ + K- L  p + p-L  p + p+

  20. STAR STRANGENESS! (Preliminary) K+ W-+ L̅ W̅+ f K0s L X- X̅+ K*

  21. Triggering/Centrality • “Minimum Bias” ZDC East and West thresholds set to lower edge of single neutron peak. ~30K Events |Zvtx| < 200 cm • “Central” CTB threshold set to upper 15% REQUIRE: Coincidence ZDC East and West REQUIRE: Min. Bias + CTB over threshold

  22. The Collisions The End Product

  23. Baryon Stopping/Transport 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) _ _ _ _ - - - - - - - -

  24. _ p/p Ratio Ratio is flat as function of pt and y Slight fall with centrality Phys. Rev. Lett March 2001 Ratio = 0.65 ±0.03(stat) ±0.03(sys) Still finite baryon number

  25. Strange Baryon Ratios Reconstruct: Reconstruct: _ _ ~0.84 L/ev, ~ 0.61 L/ev ~0.006 X-/ev, ~0.005 X+/ev STAR Preliminary Ratio = 0.73 ± 0.03 (stat) Ratio = 0.82 ± 0.08 (stat)

  26. Preliminary L̅/ Ratio _ L/L= 0.73  0.03 (stat) Central events |y|<0.5 Ratio is flat as a function of pt and y

  27. L and L̅ from mixed event Studies _ L/L= 0.77  0.07 (stat) Good cross-check with standard V0 analysis. Low pt measurement where there is no V0 analysis High efficiency (yields are ~10X V0 analysis yields) Background determined by mixed event STAR preliminary The ratio is in agreement with “standard” analysis

  28. Anti-baryon/Baryon Ratios versus s _ _ ¯ _ _ _ _ _ Baryon-pair production increases dramatically with s – still not baryon free Pair production is larger than baryon transport STAR preliminary 2/3 of protons from pair production , yet pt dist. the same – Another indication of thermalization

  29. Particle Freeze-out Conditions time 3. freeze-out Kinetic Freeze out: elastic scattering stops 2. hot / dense 1.formation ChemicalFreeze out: inelastic scattering stops

  30. K+/K- Ratio - Nch Kinks dE/dx STAR preliminary STAR preliminary • K+/K-= 1.08±0.01(stat.)± 0.06(sys.) (dE/dx). (The kink method is systematically higher.) K+/K- constant over measured centrality

  31. K-/p-Ratios STAR preliminary K-/p-ratio is enhanced by almost a factor of 2 in central collisions when compared to peripheral collisions SPS

  32. _ K0* and K0* Identification First measurement in heavy ion collisions Short lifetime (ct =4fm) – sensitive to the evolution of the system?

  33. K0*/h- Represents a 50% increase compared to K0*/p measured in pp at the ISR. Strangeness Enhancement? Also look at K*/K From spin counting K*/K = vector meson/meson = V/(V+P) =0.75 e+e-(LEP)K*/K = 0.32 ±0.02 pp (ISR)K*/K = 0.6 ± .09 ± .03 Au-Au (STAR)= 0.42

  34. Comparing to SPS K+/K-(kink) = 1.2 ± K+/K-(dE/dx) = 1.08 ±0.01 (stat.)± 0.06 (sys.) K-/p- =0.15 ± 0.02 (stat.) K*/h-= 0.06 ± 0.006 (stat.)± 0.01 (sys.) K*/h-= 0.058 ± 0.006 (stat.)± 0.01 (sys.) ¯ p/p = 0.6  0.02 (stat.)  0.06 (sys.) ¯ ¯ / = 0.73 ± 0.03 (stat.) X/X = 0.82 ± 0.08 (stat.) ¯

  35. Simple Model Measure D=1.08± 0.08 Assume fireball passes through a deconfined state can estimate particle ratios by simple quark-counting models No free quarks so all quarks have to end up confined within a hadron Predict D=1.12 Predict D=1.12 System consistent with having a de-confined phase

  36. Particle Ratios and Chemical Content mj= Quark Chemical Potential T = Temperature Ej – Energy required to add quark gj– Saturation factor Use ratios of particles to determine m, Tchand saturation factor

  37. Chemical Fit Results Not a 4-yields fit! s  1 2  1.4 Thermal fit to preliminary data: Tch (RHIC) = 0.19 GeV  Tch (SPS) = 0.17 GeV q (RHIC) = 0.015 GeV << q (SPS) = 0.12-0.14 GeV s (RHIC) < 0.004 GeV  s (SPS)

  38. Chemical Freeze-out early universe LEP/ SppS 250 RHIC quark-gluon plasma 200 SPS AGS Lattice QCD deconfinement chiral restauration 150 Chemical Temperature Tch [MeV] thermal freeze-out 100 SIS hadron gas 50 neutron stars atomic nuclei 0 200 400 600 800 1000 1200 0 Baryonic Potential B [MeV] P. Braun-Munzinger, nucl-ex/0007021

  39. Kinetic Freeze-out and Radial Flow 1/mt d2N/dydmt Look at mt = (pt2 + m2 )distribution A thermal distribution gives a linear distribution dN/dmt  e-(mt/T) mt Slope = 1/T If there is transverse flow Slope = 1/Tmeas ~ 1/(Tfo+ 0.5mo<vt>2) Want to look at how energy distributed in system. Look in transverse direction so not confused by longitudinal expansion

  40. Increase with collision centrality  consistent with radial flow. mt slopes vs. Centrality mid-rapidity Tp = 565 MeV TK = 300 MeV Tp = 190 MeV

  41. Radial Flow: mt - slopes versus mass Naïve: T = Tfreeze-out + m  r 2 where  r  = averaged flow velocity • Increased radial flow at RHIC ßr (RHIC)  ßr (SPS/AGS) = 0.6c = 0.4 - 0.5cTfo (RHIC)  Tfo (SPS/AGS) = 0.1-0.12 GeV = 0.12-0.14 GeV

  42. f Identification STAR Preliminary No evidence of mass modification

  43. Inverse slope for L Hyperons Some evidence that a single exponential fit is not the best fit to the data 15% Most Central e(-mt/T) As L/L ratio is flat as a function of pt can infer that the Lslope is the same – backed up by fitting to corrected spectrum T=352±6(stat) MeV Same slope as f

  44. Radial Flow and Strange Particles Neither the L or the proton are corrected for feed-down. Correction would drive the p slope up. What about p absorption/annihilation? Lower momentum  more collisions  more absorption/annihilation. STAR Preliminary _ Do not follow “radial flow systematics” early kinetic freeze out?

  45. Measuring the Source “Size” (HBT) 1D: overall rough “size” y1 x1 K y2 ~1 m x2 Rout Rside ~5 fm 3D decomposition of relative momentum provides handle on shape and time as well as size

  46. K0s-K0s Correlations • No coulomb repulsion • No 2 track resolution • Few distortions from resonances • K0s is not a strangeness eigenstate - unique interference term that provides additional space-time information l = 0.7 ±0.5 R = 6.5 ± 2.3 K0s Correlation will become statistically meaningful once we have ~10M events

  47. Mapping out “Soft Physics” Regime Net-baryon  0 at mid-rapidity! ( y = y0-ybeam ~ 5 ) Chemical parameters Chemical freeze-out appears to occur at same ~T as SPS Strangeness saturation similar to SPS Kinetic parameters Higher radial flow than at SPS Thermal freeze out same as at SPS Strange Particles The f and L do not seem to flow with the other particles. Reduced rescattering for the kaons from f decay and/or f/L feel less flow What have we “learnt” so far More than we ever hoped for after the first run !!!

  48. This Year – RICH,TOF Patch,SVT,FTPC RICH and TOF: Increase K identification in pt over a limited geometric acceptance Centered at mid-rapidity they provide complimentary pt coverage TOF patch 0.3< pt <1.5 GeV/c RICH 1.1 < pt < 3.0 GeV/c Overlaps with the TPC kink and dE/dx measurement kink pt < 5 GeV, dE/dx pt < 0.8 GeV SVT: Increased efficiency for all strange particles and resonances due to improved tracking Should measure spectra for all particles this year. HBT with strange particles Exotica FTPC: Strange particles at high y

  49. The Silicon Vertex Tracker Radii – 6,10 15 cm Length ±12.4 cm ± 18.6 cm ± 21.7cm (-1 < h < 1)

  50. SVT STAR detector gets new silicon heart – CERN Courier SVT installed and operational April 2001!! 91% live (out of 103,680 channels)

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