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Spectator response to participants blast

Spectator response to participants blast. New tool for investigation of the momentum- dependent properties of nuclear matter (!?). Vladimir Henzl NSCL-MSU, East Lansing, USA GSI - Darmstadt, Germany. Idea behind the spectator response.

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Spectator response to participants blast

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  1. Spectator response to participants blast New tool for investigation of the momentum- dependent properties of nuclear matter (!?) Vladimir Henzl NSCL-MSU, East Lansing, USAGSI-Darmstadt, Germany

  2. Idea behind the spectator response BUU calculations : 124Sn +124Sn Tlab= 800 MeV/u b = 5 fm L. Shi, P. Danielewicz, R. Lacey, PRC 64 (2001) Spectator response: the spectator is not a passive witness, but rather a victim of violent participants ! • L. Shi, P. Danielewicz, R. Lacey, PRC 64 (2001) • M.V.Ricciardi et al.PRL 90(2003)212302

  3. Spectator responseor „what can we learn from victims“ Theoretical prediction:(Shi, Danielewicz, Lacey, PRC 64 (2001)) PCMS/A = 682 MeV/c Relative spectator momenta appear to be selectively sensitive to the momentum-dependentproperties of the nuclear MF !!! Reacceleration: „... strong enough explosion, when the ordered push may overcome the friction effects, producing a net longitudinal acceleration .“

  4. 1st observation T.Enqvist et al. NPA658(1999)47 V.H. Motivation for new experiments: 1) to improve experimental signature of spec. response 2) to establish correlation of Ares and impact parameter b 3) to study possible dependence of spectator response on incident energy and/or size of the colliding system Proposal of new experimental program: 197Au+197Au @ 0.5 and 1.0 A GeV (... and 197Au+27Al @ 0.5 A GeV) ... aproved and carried out in 2004

  5. The Fragment Separator at GSI-Darmstadt Inverse kinematics: From ToF:  /∆ ≈ 400 A/∆A ≈ 400 (36m) Once mass and charge are identified (A, Z are integer numbers) thevelocity is calculated from B:  /∆ = B/∆B≈ 2000 => veryprecise determination!

  6. The data – general overview • unambiguous identification & precise longitudinal momenta • limited acceptance: ±15mrad, ±1.5% in momentum only one fragment in one reaction measured But if complemented by full acceptance experiments, info on impact parameter b can be partially recovered

  7. Experimental results : longitudinal velocities of the projectile residues • central ridge corresponds to fragmentation • weak shoulders of the distributions correspond to fission. • all three systems yield visible reacceleration of the fragmentation residues • Note: • yields are relative only, colors in each plot adjusted individually • the experiments performed at 500 A MeV did not cover residues with Ares>160

  8. Mean longitudinal velocities of the fragmentation residues • most peripheral collisions yield deceleration mean velocities in agreement with Morrissey systematics. • with decreasing mass loss, velocities level off and increase residues with Ares≤ 85 (or 75 and 70 in the corresponding systems) on average faster than the beam

  9. The reacceleration & its implications • reacceleration is a common feature of rHIC • deviation from Morrissey sys. suggests a threshold nature of the responsible process • reacceleration depends on Ebeam and Atarg • FWHM(vz)PF practically the same for all 3 systems => same „violence“ of the reactions !!! Now:assuming simple spectator-participant model: => dependence of vz on Ebeam and Atarg seems to be too weak Relevant question: Are the experimental observations compatible with the simple „blast wave scenario“ ?? New speculative concept – rocket engine: reacceleration by enhanced backward emission

  10. Experiment vs. Simulations – Au+Au at 1 A GeV • quantitative discrepancy between exp&BUU too large, qualitatively OK for MD MFs but NN cross sections matter !!! • σfree yields better agreement, but still too far in b but in this case also MI MFs reaccelerate !!! Note: in exp b estimated only for Afrag>60

  11. Experiment vs. Simulations – Au+Au at 500 A MeV • limited qualitative agreement only for σfree • momentum dependence and stifness do not really matter Overall agreement bad !!! Note: in exp b estimated only for Afrag>60

  12. Experiment vs. Simulations – Au+Al at 500 A MeV Is there any agreement? Overall, BUU fails to reproduce correct trends of the data Extraction of MD relevant parameters not straight-forward The question: Is at least the reacceleration in exp and BUU of the same nature ? Yes !! Note: in exp b estimated only for Afrag>60

  13. Implications of the calculated results Example:197Au+197Au at 1 A GeV – different results for different σNN • σNN can modify the strength of the blast in BUU • σNN has significant influence on the evolution of spectator mass and its relative momenta but for each in a different way !!! => Aspec and pz/A are not monotonously coupled Strength of the blast influences Aspec, but not the difference in pz/A => Neither in BUU is the blast fully responsible for reacceleration

  14. Summary & Conclusions • longitudinal velocities of fragmentation residues measured in Au+Au @ 0.5, 1 A GeV, Au+Al @ 0.5 A MeV • reacceleration phenomena seen in all systems, its properties suggest the spectator as responsible for its reacceleration • => “rocket engine” scenario instead of the “blast wave” • BUU in limited (dis)agreement with experiment. Results sensitive to momentum dependence and NN cross-sections, • What did we learn about the momentum-dependence ? • mechanism of the reacceleration turns to be more complex than originaly anticipated • reacceleration still sensitive to MD, but refined theory needed for eventual extraction of explicit paramaters • new data and better understanding can guide further experimental and theoretical efforts

  15. CHARMS & re-acceleration (Collaboration for High-Accuracy Experiments on Nuclear Reaction Mechanisms with the FRS) V. Henzl1, J. Benlliure2, P.Danielewicz4, T. Enqvist5,M. Fernandez2, A. Heinz6, D. Henzlova1, A. Junghans7, B. Jurado8, A. Kelic1, J. Pereira2, R. Pleskac1, M. V. Ricciardi1,K.-H. Schmidt1, C. Schmitt1, L.Shi4,J. Taïeb3, A. Wagner7,O. Yordanov1 1GSI, Planckstr. 1, 64291, Darmstadt, Germany 2Universidad de Santiago de Compostela, 15706 Santiago de Compostela, Spain 3CEA/Saclay, 91191 Gif sur Yvette, France 4National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy,Michigan State University, East Lansing, MI 48824, USA 5Department of Physics, University of Jyväskylä, 40014, Finland 6Wright Nuclear Structure Laboratory, Yale University, New Haven, CT 06520, USA 7FZ Rossendorf, Bautzener Landstrasse 128, 01328, Dresden, Germany 8GANIL, 14076 Caen, France

  16. Technical slides

  17. What is momentum dependence ? Local potential (momentum-independent): Nonlocal potential (momentum-dependent): slow particle slow particle U1=U2=f(r) U3U4=f(r,p) fast particle fast particle

  18. Static vs. dynamic properties Aichelin et al. PRL 58(1987)1926 Static properties are studied in dynamical processes !!! Problem: most of the experimental observables are not selective; => the interpretation is influenced by competing phenomena, !!! The results are very often ambiguous !!!

  19. Present knowledge Recent analysis: (Danielewicz et al.) Science 298 (2002) 1592 Attempt to constrain nuclear matter equation of state by results of performed experiments. Only the most extreme models could be excluded by the experiment

  20. Information from full acceptance experiments 238U+Cu @ 1 A GeV - ALADIN fission fragmentation 197Au+197Au @ 1 A GeV - ALADIN fission fragmentation • single, unambiguously identified fragment at FRS ispredominantly largest residue per collision

  21. Information from the Zmax Aladin data:Au+Au @ 400, 600, 800, 1000 A MeV Aladin data:Au+Au @ 600 A MeV • Zbound is a measure of the impact parameter • the largest fragment is well correlated with Zbound (for Zmax>30 ~ Amax>65) Zmax carries information on impact parameter • fragments with Z>20 are produced in reactions with 9fm ≤ b ≤ 15fm (in Au+Au system) • peripheral collisions investigated

  22. Different reaction processes How to distinguish fragmentation and fission? 238U (1 A GeV) + Pb 197Au+197Au @ 1 A GeV (V.H.) fission Fragmentation: heaviest residues fully accepted (A>90) Fission: Only forward and backward component accepted

  23. How to relate Ares and an impact parameter Aladin: • Zmax2 has different (and worse) correlation with Zbound (impact par.) Region of mixing Zmax & Zmax2 can‘t be used to deduceb !

  24. How to understand the calculations Au+Au at 1 A GeV Two crucial observables: spectator mass Aspec and net longitudinal momentum change per spectator nucleon Δpz/A. (like in experiment) THEN:time evolutions of differencies of these quantities for calculations with different parameters or for different systems reveal the characteristics of the involved process.

  25. BUU:Au+Au at 1 A GeV – σin.med vs. σfree 1) Greater σNN => greater mass loss BUT: greater mass loss does not influence velocities !!! 2) Greater σNN => onset of velocity recoverying process for higher b 3) Once the „process“ is on => its strength is independent of σNN

  26. BUU:Au+Au at 500 A MeV – σin.med vs. σfree • Similar behavior as for 1 A GeV system !!! • Once the recovery process is turned on, its strength is same despite different incident beam energy !!! Velocity recoverying process in BUU has a threshold, which depends on energy and σNN, but the process itself not !!!

  27. BUU:500 A MeV – Au+Al vs. Au+Au In Au+Al system abrasion causes greater wound BUT: it does not lead to such a mass loss like in Au+Au !!! Mass loss in Au+Au caused by the participant blast !?! No blast in Au+Al !?! .. but also no recovery of pz/A!!! Can the blast be „only“ an ignitor of the rocket engine ?!?

  28. How to relate Ares and an impact parameter Aladin: • Zmax2 has different (and worse) correlation with Zbound (impact par.) Region of mixing Zmax & Zmax2 can‘t be used to deduceb !

  29. Comparison with ALADIN

  30. Velocity distributions with limited acceptance 43Ca produced in 197Au+27Al @ 1 A GeV • No correction • After correction on beam intensity • After correction for the angular transmission • limited momentum acceptance: Several magnetic field settings need to be combined to get complete velocity distribution (each color = 1 magnetic setting)

  31. Different reaction processes How to distinguish fragmentation and fission? 238U (1 A GeV) + Pb 197Au+197Au @ 1 A GeV (V.H.) fission Fragmentation: heaviest residues fully accepted (A>90) Fission: Only forward and backward component accepted

  32. Info from Zmax and Zmax2

  33. Data vs. Morrissey systematics The measured average longitudinal momentum transfer as a function of the mass of the fragmentation residue in the laboratory frame.

  34. The reacceleration & first implications (op.II) • Let´s consider 2 possible energy pools: • I – participants : EI ~ (Eproj/Aproj)∙AabradedII – spectator : EII ~ Aabraded Relevant question: Are the experimental observations compatible with the simple „blast wave scenario“ ?? • does not seem so ... reacceleration almost independent on the blast Spectator seems to be responsible for the energy fueling its own reacceleration New speculative concept: reacceleration caused by enhanced backward emission => „rocket engine“

  35. The reacceleration & its implications (op.II) • vz ~ const. for systems with different Ebeam for Afrag≈80-130: • vz is same no matter if we compare systems with different Atarget or Ebeam for Afrag<70: • The pace of reacceleration in Au+Al, with smaller Afrag, is slower than in Au+Au Vlad Henzl for CHARMS

  36. Uncertainty of the measurement Deviations of the mean longitudinal velocities of the fragmentation residues from the 3rd degree polynomial fit to the measured data as the function of the mass of the fragmentation residue.

  37. Morrissey systematic D.J.Morrissey – PRC39(1989)460 Many different reactions with Ebeam = 0.4-400 A GeV

  38. Morrissey systematic vs. new data D.J.Morrissey – PRC39(1989)460 Many different reactions with Ebeam = 0.4-400 A GeV But very often projectile or target small, i.e. A< ~20

  39. Correlation of Afrag and <b>

  40. Influence of the limited acceptance

  41. Number of participants according to geometrical model

  42. The reacceleration & first implications (op.II) • Let´s consider 2 possible energy pools: • I – participants : EI ~ (Eproj/Aproj)∙AabradedII – spectator : EII ~ Aabraded Relevant question: Are the experimental observations compatible with the simple „blast wave scenario“ ?? • does not seem so ... reacceleration almost independent on the blast Spectator seems to be responsible for the energy fueling its own reacceleration New speculative concept: reacceleration caused by enhanced backward emission => „rocket engine“

  43. Chapter 1technical slides

  44. Reacceleration in previous experiments Fig. 1.2:Mean values of the velocity distributions of reaction residues, excluding fission, produced in 238U+Pb [Enq99] and 238U+Ti [Ric03] at 1 A GeV in the frame of the projectile. The absolute uncertainty amounts to less than 0.05 cm/ns for each system, 238U + Pb and 238U+Ti, independently.

  45. Chapter 2technical slides

  46. Classic vs. inverse kinematics

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