Reacceleration of the fragmentation residues in the reactions 197 Au+ 197 Au/ 27 Al at 0.5 and 1 A GeV Vladimir Henzl GSI-Darmstadt, Germany NSCL-MSU, Michigan Reviewing the concept of “spectator response to the participant blast”

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

Spectator response or „what can we learn from victims“ Theoretical prediction: (Shi et al. PRC 64 (2001)) Relative spectator momenta appear to be selectively sensitive to the momentum-dependent properties of the nuclear MF !!! P CMS /A = 682 MeV/c Reacceleration: „... strong enough explosion, when the ordered push may overcome the friction effects, producing a net longitudinal acceleration.“ First experimental observation: (T.Enqvist et al., NPA 658 (1999))

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

The data – general overview unambiguous identification & precise longitudinal momenta only one fragment in one reaction measured limited acceptance: ±15mrad, ±1.5% in momentum

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

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

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 E beam and A targ FWHM(v z ) PF practically the same for all 3 systems => same „violence“ of the reactions !!! Now: assuming simple spectator-participant model: Relevant question: Are the experimental observations compatible with the simple „blast wave scenario“ ?? New speculative concept – rocket engine: reacceleration by enhanced backward emission => dependence of  v z  on E beam and A targ seems to be too weak

Summary & Conclusions reacceleration phenomena seen in all systems, its properties suggest the spectator as responsible for its reacceleration => “rocket engine” scenario instead of the “blast wave” longitudinal velocities of fragmentation residues measured in 0.5, 1 A GeV, 0.5 A MeV mechanism of the reacceleration more complex than originaly anticipated new data and better understanding can guide further experimental and theoretical efforts

Morrissey systematic vs. GSI data Many different reactions with E beam = A GeV But very often projectile or target small, i.e. A< ~20 D.J.Morrissey – PRC39(1989)460

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

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

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

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

CHARMS & re-acceleration (Collaboration for High-Accuracy Experiments on Nuclear Reaction Mechanisms with the FRS) V. Henzl 1, J. Benlliure 2, P.Danielewicz 4, T. Enqvist 5, M. Fernandez 2, A. Heinz 6, D. Henzlova 1, A. Junghans 7, B. Jurado 8, A. Kelic 1, J. Pereira 2, R. Pleskac 1, M. V. Ricciardi 1, K.-H. Schmidt 1, C. Schmitt 1, L.Shi 4, J. Taïeb 3, A. Wagner 7, O. Yordanov 1 1 GSI, Planckstr. 1, 64291, Darmstadt, Germany 2 Universidad de Santiago de Compostela, Santiago de Compostela, Spain 3 CEA/Saclay, Gif sur Yvette, France 4 National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA 5 Department of Physics, University of Jyväskylä, 40014, Finland 6 Wright Nuclear Structure Laboratory, Yale University, New Haven, CT 06520, USA 7 FZ Rossendorf, Bautzener Landstrasse 128, 01328, Dresden, Germany 8 GANIL, Caen, France

Technical slides

What is momentum dependence ? U1=U2=f(r)U1=U2=f(r) U 3  U 4 =f(r,p) Local potential (momentum-independent) : Nonlocal potential (momentum-dependent) : slow particle fast particle

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

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

fission Information from full acceptance experiments fission 197 Au A GeV - ALADIN A GeV - ALADIN  single, unambiguously identified fragment at FRS predominantly largest residue per collision  single, unambiguously identified fragment at FRS is predominantly largest residue per collision fragmentation

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

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

How to relate A res and an impact parameter Z max2 has different (and worse) correlation with Z bound (impact par.) Aladin: Region of mixing Z max & Z max2 can‘t be used to deduce b !

How to understand the calculations Au+Au at 1 A GeV Two crucial observables: spectator mass A spec and net longitudinal momentum change per spectator nucleon Δ  p z /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.

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

BUU: Au+Au at 500 A MeV – σ in.med vs. σ free 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 σ NN, but the process itself not !!!

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  p z /A  !!! Can the blast be „only“ an ignitor of the rocket engine ?!?

How to relate A res and an impact parameter Z max2 has different (and worse) correlation with Z bound (impact par.) Aladin: Region of mixing Z max & Z max2 can‘t be used to deduce b !

Comparison with ALADIN

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

Info from Z max and Z max2

 v z  is same no matter if we compare systems with different A target or E beam for A frag <70:  v z  ~ const. for systems with different E beam for A frag ≈80-130: The reacceleration & its implications (op.II) The pace of reacceleration in Au+Al, with smaller A frag, is slower than in Au+Au Vlad Henzl for CHARMS

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. Uncertainty of the measurement

Correlation of A frag and Correlation of A frag and

Influence of the limited acceptance

Fig.7.3: Total number of participants and those arising from the projectile as a function of the impact parameter in the reaction 197 Au+ 197 Au as calculated by the geometrical model. Fig.7.10: Total number of participants and those contributed by the gold projectile and aluminum target as the function of the impact parameter in the reaction 197 Au+ 27 Al as calculated by the geometrical model. Number of participants according to geometrical model

Reacceleration in previous experiments Fig. 1.2: Mean values of the velocity distributions of reaction residues, excluding fission, produced in 238 U+Pb [Enq99] and 238 U+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, 238 U + Pb and 238 U+Ti, independently.