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Searches for States of Exotic Hot and Cold Quark Matter

Searches for States of Exotic Hot and Cold Quark Matter. James Nagle Columbia University. Outline. Motivations for Studying Heavy Ion Collisions Creation of Hot Quark-Gluon Plasma Creation of Cold Strange Quark Matter Probes of these Phenomena Strange Anti-baryon Production

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Searches for States of Exotic Hot and Cold Quark Matter

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  1. Searches for States of Exotic Hot and Cold Quark Matter James Nagle Columbia University

  2. Outline Motivations for Studying Heavy Ion Collisions Creation of Hot Quark-Gluon Plasma Creation of Cold Strange Quark Matter Probes of these Phenomena Strange Anti-baryon Production Antideuteron Production Search for Strange Quark Matter (Strangelets) Experimental Results Experiment E878 and E864 at the Brookhaven AGS Conclusions What are the Answers?

  3. Dense Nuclear Matter A gold nucleus has a volume of ~1400 fm3 The individual nucleons are ~ 4.6 fm3 x 197 ~ 65% of the total volume occupied! Baryon = 3 Quarks However, if you compress a nucleus to ten times nuclear matter density, the individual nucleons overlap. It becomes unclear to which proton or neutron a quark belongs.

  4. Phase Transitions Deconfinement Normally quarks are bound together (confined) in particles such as protons and neutrons. QCD (the theory of strong interactions) states that there can be no free individual quarks. However, QCD predicts that at high density (5 to 10 ro) and high temperature (~ 150-200 MeV ~ 1012oF), the quarks are no longer confined, but form a plasma of quarks. u u u u u d u d d u d d d u u d

  5. Chiral Symmetry If the individual nucleons disappear, and the system is a plasma of individual quarks, one expects that the quarks will act as nearly massless objects. This transition to nearly massless quarks is called the restoration of approximate Chiral Symmetry. The up and down quark are expected to have masses of ~ 5 MeV, while the strange quark is reduced to a mass of ~ 150 MeV. Up Down Strange Charm Bottom Top

  6. Heavy Ion Collisions 1) Collision of Nuclei 2) Compressed and Heated Nuclear Matter ? Quark Phase ? Chiral Symmetry 3) Expansion and Cooling

  7. Enhanced Antibaryons What measurable effects might result in heavy ion collisions from a hot plasma state with nearly massless quarks? It will be easier to produce antibaryons (such as antiprotons) in a plasma. The production of strange antibaryons (such as antilambdas) will be even more enhanced in part due to Pauli blocking of light quark pair production. Quark - Antiquark baryon antibaryon Quark - Antiquark Anti-Strange Quark U. Heinz et al., Nucl. Phys. 12 (1986) 1237. J. Ellis et al., Phys. Lett. B 233 (1989) 233. P. Koch, B. Muller, J. Rafelski, Phys. Rep.142, 167 (1986).

  8. What Happens Next? s s s s Plasma has enhanced s s content, but no net strangeness s s s s s s s s s s s s s Strangeness Separation K0 K+ s s s s s s s s K+ (u s) K+ Bubbles of Hot Strange QM Cools into Cold Lump of Strange Quark Matter C.Greiner et al. Phys. Rev. Lett. 58 (1987) 1825. C.Greiner and H. Stocker, Phys. Rev. D 44 (1991) 3517.

  9. Strange Quark Matter The existence of quark states with more than three quarks is allowed in QCD. The stability of such quark matter states has been studied with lattice QCD and phenomenologicalbag models, but is not well constrained by theory. The addition of strange quarks to the system allows the quarks to be in lower energy states despite the additional mass penalty. Quark MatterStrange Quark Matter u d u d s Energy Level Strange Quark Mass There is additional stability from reduced Coulomb repulsion. SQM is expected to have low Z / A.

  10. Strange Quark Matter Stability Strange Quark Matter detection for mass > 10 GeV would be a smoking gun signature of hot quark plasma formation ! Also, theorists have speculated that strange quark matter might exist in the core of neutron stars and other astrophysical objects. E. Witten proposed that large lumps of strange quark matter might be even more stable than nuclear matter (55Fe) and thus could exist as remnants from the Big Bang and help to explain the Dark Matter question.

  11. Where is the Experiment? Brookhaven National Laboratory Accelerator: AGS (Alternating Gradient Synchrotron) Experiment E878 and E864

  12. E864 Collaboration G. De Cataldo, N. Giglietto, A. Raino, P. Spinelli University of Bari/INFN C.B. Dover Brookhaven National Laboratory K.N. Barish, H.Z. Huang University of California, Los Angeles J.L. Nagle Columbia University J.C. Hill, R.A. Hoverstein, B.P. Libby, F.K. Wohn Iowa State University P. Haridas, I.A. Pless, G.Van Buren Massachusetts Institute of Technology T.A. Armstrong, R.A. Lewis, G.A. Smith, W.S. Toothacker Pennsylvania State University R.R. Davies, A.S. Hirsch, N.T. Porile, A. Rimai, R.P. Scharenberg, M.L. Tincknell Purdue University M.S.Z Rabin University of Massachusetts S.V. Greene, T. Miller, J.D. Reid, A. Rose Vanderbilt University S.J. Bennett, T.M. Cormier, P. Dee, P. Fachini, B. Kim, M.G. Munhoz, C.A. Pruneau, K.H. Zhao Wayne State University A. Chikanian, S. Batsouli, S.D. Coe, G.E. Diebold, L.E. Finch, N.K. George, B.S. Kumar, J.G. Lajoie, R.D. Majka, J.K. Pope, F.S. Rotondo, J. Sandweiss, A.J. Slaughter Yale University

  13. E864 Details Overall Design • Multi-purpose detector • Measures mass from momentum and velocity • High data rate (samples 105 interactions/sec) Specifics Six planes of Straw Tube tracking chambers Time-of-Flight Hodoscopes with s(time) ~ 120-150 ps Hadronic Calorimeter for independent mass measurement with energy resolution ~ 40%/sqrt(E) and s(time) ~ 400 ps High Mass Trigger (requiring late-energy in calorimeter)

  14. E864 Pictures Time-of-Flight Detectors Simon Bennett and the Calorimeter

  15. E864 Particle Identification Excellent Antiproton Signal to Noise Ratio Good Z=2 Identification Neutral Particle Measurement Using the Hadronic Calorimeter

  16. E864 Antiproton Data The production level increases for more central collisions. Accepted in Phys. Rev. C Excellent agreement for the 10% most central data between independent analysis efforts. Note: different triggers, different magnetic fields, different people (J.G. Lajoie, J.N.) T.A. Armstrong et al., Phys. Rev. Lett. 79, 3351 (1997). J.L. Nagle et al., J. Phys. G: Nucl. Phys. 23 2145 (1997).

  17. Data Comparison E864 (1996) E864 (1995) E878 There is no statistically significant disagreement for the most peripheral collisions. The two data sets disagree to a significant extent for more central collisions.

  18. Do the Experiments Measure the Same Thing? Number of strange anti-quarks There are many particles which decay into antiprotons at various distances from the interaction target. Target Incoming Au beam L p p

  19. Decay Contributions E878 has a very small opening aperture and thus the relative acceptance for L and S0 is ~ 14% for S+ ~11%. No calculations for |S|=2,3 objects has been done. E864 has a large opening aperture and thus the relative acceptance for all these decay products is ~ 100%. E878 ~ p E864 ~ p + frac(L,S,X,W)

  20. Ratio of Strange Antibaryons to Antiprotons Peripheral Collisions are consistent with elementary particle collisions ratios for strange antibaryons. However, for more central collisions there is a significant enhancement. Strange Antibaryons / Antiprotons

  21. Other Preliminary Results Two other experiments (E877 and E866) have measured antiprotons and have calculated their relative acceptance for strange antibaryons. So far the picture is consistent!

  22. Other Measurements and Other Systems Si + Au central collisions L--> p + p+ Indicate significant enhancement Preliminary - Exp. 859 (Y. Wu) Au + Au central collisions Awaiting final results! Pb + Pb central collisions at CERN SPS (higher energy) L--> p + p+ NA35, NA49, WA97 and also X and W WA97

  23. Model Comparisons E859 and NA49 results are preliminary Published theoretical results

  24. More on Thermal Models In a simple model assuming chemical and thermal equilibrationin the hadron phase, Y/p > 2 is obtained in some parameter space…. Although there are serious questions about the model assumptions. Temp. = 120 MeV m(up) = 200 MeV Strangeness chemical potential set by conservation of strangenes.

  25. More on Transport Models The annihilation probability is large due to the strong attraction between the proton and antiproton. Escape path Calculations indicate antiproton losses on the order of 90-95% Extreme calculation with no annihilation for strange antibaryons in RQMD yield Y/p ~ 3 This has a dramatic effect of Pt distribution

  26. Why does the QGP model work so well? The QGP model predictions were published well before any strange antibaryon results for Au + Au and Pb + Pb were available The QGP model assumes that in the deconfined state ms = 0 independent of temperature and baryon density Now the problem is when we apply hadrochemistry in the Grand Canonical Ensemble how do be conserve strangeness????? If hadronization occurs quickly the relative abundances of mesons and baryons stays fixed “because processes which convert mesons into baryon-antibaryon pairs are relatively slow.” Thus, the model fixes the meson to baryon ratio in order to conserve strangeness.

  27. What have we learned? Very interesting results indicating large enhancement of strange antibaryons. Presently, these yields are difficult to explain in a purely hadronic picture. Enhancement easily understood in quark plasma model; however, a consistent picture is still lacking. Direct measurement of L is needed with pt dependence. (E866/E917 analysis is far along...) Also, more comparisons with data at higher energies (CERN and RHIC)!

  28. What about Antideuterons? No statistically significant signal observed Set upper limit on coalescence parameter Coalescence if antiproton and antineutron close in phase space; therefore antiprotons from weak decay of strange antibaryons do NOT contribute

  29. Preliminary Mass Distribution Preliminary Data Analysis of Gene Van Buren True measure of the coalescence rate gives… 1) Information about strange antibaryons 2) Information about the spatial distribution and collective flow of antinucleons J.L. Nagle et al., Phys. Rev. Lett. 73 (1994) 1219. J.L. Nagle et al., Phys. Rev. C 53 (1996) 367. H. Sorge, J.L. Nagle and S.Kumar, Phys. Lett. B 355 (1995).

  30. What else is there? Many other interesting observations: First Neutron Yields Coalescence of Light Nuclei up to A=7 First Reconstruction of Unstable Nuclei A= 1 2 3 4 5 6 7 Evan Finch, Zhangbu Xu, Nigel George

  31. Search for Z< 0 Objects We identify over 50,000antiprotons from tracking and observe a number of Z=-1 high mass candidates. However, using the hadronic calorimeter reveals these candidates as background...

  32. Strange Quark Matter Limits E878 Limits E864 Published E864 Final Limits Strangelets/Event < 10-9 Lifetimes> 50 ns uuuuuu dddddd ssssss T.A. Armstrong et al, Phys. Rev. Lett. 79, 3612 (1997). T.A. Armstrong et al,. Nucl. Phys. A 625, 494 (1997).

  33. SQM Production Mechanisms Coalescence QGP Distillation Strange and non-strange nucleons combine into composite objects in near final-state interaction. Only viable for low mass range Plasma charges up with net strangeness and cools off into meta-stable SQM droplet. Only mechanism for high mass QGP Prediction A. Baltz et al., Phys. Lett. B 325, 7 (1994) H. Crawford et al., Phys. Rev. D 45, 857 (1992). H.C. Liu and G.L. Shaw, Phys. Rev. D 30, 1137 (1984).

  34. What is the Experiment Doing Now? Cold Quark Matter Search • Final strange quark matter limits • We recorded over 280 Million events for the reconstruction of H4L (bound state of p-n-n-L) decaying to 4He + p • Think about future experiments at JHF Hot Quark Matter Search • Final antiproton results in Phys. Rev. C • Working on antideuteron invariant yields • Look forward to results from E866/E917 and E896 and more theoretical developments • RHIC results on strange antibaryons should be very exciting!

  35. Hot Cold No Strangelets 10-9 Intriguing Strange Antibaryon Signal

  36. Neutral Candidates Candidates understood to result from overlapping neutron showers and neutrons originating from secondary Au interactions in the target.

  37. Other Ideas and Explanations Antiprotons can be converted to strange antibaryons by associated production. p + p L + K However, cascade models such as RQMD include such processes and only get ratios for L/p ~ 0.4. Strange antibaryons might have a lower annihilation probability than antiprotons One expects the cross section to be somewhat lower due to less available phase space and possibly other reasons (quark content). L initial final p

  38. RQMD/Coalescence Au + Au central collisions

  39. RQMD/Coalescence Calculation for Antideuterons Good agreement with existing published deuteron and antideuteron data. J.L. Nagle et al., Phys. Rev. Lett. 73 (1994) 1219. J.L. Nagle et al., Phys. Rev. C 53 (1996) 367. H. Sorge, J.L. Nagle and S.Kumar, Phys. Lett. B 355 (1995). Awaiting new data at CERN from NA44 in Pb + Pb

  40. Antideuteron Tracking Results No statistically significant signal above background.

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