Experimental Observables to study the nuclear symmetry energy with Heavy Ion Collision

Transcription

1 Experimental Observables to study the nuclear symmetry energy with Heavy Ion Collision Heavy Ion Meeting April 13, 212 Pohang, Korea Betty Tsang The National Superconducting Cyclotron Laboratory Michigan State University

2 Density Dependence of Symmetry Energy B a Aa A Z( Z 1) a C A 2/3 V S 1/ 3 E/A (,) = E/A (,) + 2 S(); = ( n - p )/ ( n + p ) = (N-Z)/A ( A 2Z) A a sym 2 B.A. Brown, PRL 85 (2) 5296

3 V asy (MeV) 1 5 E/A (,) = E/A (,) + 2 S() = ( n - p )/ ( n + p ) = (N-Z)/A Two observables: n/p ratios and isospin diffusion stiff Li et al., PRL 78 (1997) 1644 soft Neutron Proton Tsang et al., PRL 92 (24) 6271 Projectile 124 Sn u = / o Y(n)/Y(p); t/ 3 He, p + /p - Target 112 Sn Isospin Diffusion; low, E beam

4 B sym B o sym K L S E sym B sym P E L B 3 3 Symmetry energy constraints from HIC arxiv: g i 1

5 B sym B o sym K L S E sym B sym P E L B 3 3 Symmetry energy constraints from HIC arxiv: g i 1 HIC has been successful in obtaining constraints on the symmetry energy at.3</ O <1

6 Summary Symmetry Energy constraints for.3</ o <1 are consistent even though different experimental techniques and theories are involved. 3n force is needed in the description of EoS of pure n-matter. arxiv:

7 Challenges: Constraints on the density dependence of symmetry energy at supra normal density Xiao et al., PRL12, 6252 (29) Russotto et al., PL B697 (211) 471

8 HIC has been successful in obtaining constraints on the symmetry energy at.3</ O <1 Lessons learned from LE measurements: 1. HI collision dynamics are complex but prove to be sensitive to density dependence of symmetry energy. 2. Need multiple observables to verify results and to add credibility to the constraints 3. Problems still remain, e.g. How to extract results to T=; Control of input parameters in transport models. 4. Provide guidance to the experiments at high energy Talk Outline 1. Review of LE experimental observables 2. Discussions of HE experimental observables and experiments at RIKEN, KoRIA & FRIB

9 How to obtain the information about EoS? Both astrophysical and laboratory observables can constrain the EoS, (,T,) or P(,T,) indirectly. Experiments: Accelerator: Projectile, target, energy Detectors: Information of emitted particles identity, spatial info, energy, yields construct observables What are the experimental challenges? What are the theory challenges? Models Input: Projectile, target, energy. Simulate the collisions with the appropriate physics Success depends on the comparisons of observables.

10 Challenges for Experimentalists Ideally: Projectile and targets Unlimited variations of beam and target isospin. High beam intensity and thick target to get statistics Detectors (perfect vision) 1% geometrical and energy/velocity and particle coverage and resolutions. Perfect identifications of n, pions and charged particles. Perfect determination of centrality Bounded by law of physics Isospin observables depends on the isospin of target and projectile, centrality and incident energy In Reality: Projectile and targets Limited varieties even with FRIB, RIKEN and KoRIA Beam intensities drop >x1 for each nucleon away from stability Detectors (blurred vision) Much less than 1% coverage Limited dynamic range in the detection of particles types Limited energy range of detected particles due to thresholds etc Difficulties in the detection of n, p etc Uncertainties in impact parameter selections due to smearing

11 Theoretical challenges Interpretation depends on comparison of data to models Nuclear collisions many, many-body problem Transport models: Describe dynamical evolution of the collision process Self consistent mean field n-n collisions, Pauli exclusion Uncertainties Semi-classical Approximations needed to make computation feasible. Advantages Symmetry energy included in the nuclear EOS for infinite nuclear matter at various densities from the beginning of collision. Statiscal Model Assumptions Describe longer time scale decays from single source. nuclear mass, level densities decay rates Uncertainties Source parameters: A o, Z o, E o, V o, J Information obtained is for finite nuclei, not for infinite nuclear matter Advantages fast turn around Production of very rare isotopes possible provide lots of physics insights quickly, Include some structure effects

12 Theoretical challenges Interpretation depends on comparison of data to models Nuclear collisions many, many-body problem Transport models: Describe dynamical evolution of the collision process Self consistent mean field n-n collisions, Pauli exclusion Uncertainties Semi-classical Approximations needed to make computation feasible. Advantages Symmetry energy included in the nuclear EOS for infinite nuclear matter at various densities from the beginning of collision. Theory must predict how reaction evolves from initial contact to final observables Wish lists Realistic sequential decay models Consistent results from different models Inclusions of cluster formation Standardization of transport model parameters s NN, m*, momentum dependence mean fields, Pauli Blocking. Include surface properties of nuclei Descriptions of pions

13 Density Dependence of Symmetry Energy Density region sampled depends on reaction mechanisms (impact parameter) & beam energy Stiff Soft Observab les: ρ<ρ o : Isospin diffusion, n/p ratios. flow and observables from NS. ρ>ρ o : HIC the only game in town: n/p, t/ 3 He, flow, p + /p - ratio

14 Heavy Ion collision: 124 Sn+ 124 Sn, E/A=5 MeV b= fm multifragmentation Reaction mechanism of fragment productions depends on impact parameters Charged fragments (Z=3-2) are formed at subnormal density Impact parameter selection is a must! b=7 fm Neck fragments S()=12.5(/ o ) 2/3 +19(/ o ) g i

15 Hubble ST Proton Number Z Strategies used to study the symmetry energy with Heavy Ion collisions below E/A=1 MeV Isospin degree of freedom B a Aa A Z( Z 1) a C 2/3 V S 1/ 3 2 A ( A 2Z) a sym A Neutron Number N Crab Pulsar Vary the N/Z compositions of projectile and targets 124 Sn+ 124 Sn, 124 Sn+ 112 Sn, 112 Sn+ 124 Sn, 112 Sn+ 112 Sn Measure N/Z compositions of emitted particles n & p yields isotopes yields isospin diffusion

16 Strategies used to study the symmetry energy with Heavy Ion collisions below E/A=1 MeV At E/A>1 MeV, ρ>ρ o Strategies should be similar but observables maybe different Vary the N/Z compositions of projectile and targets 124 Sn+ 124 Sn, 124 Sn+ 112 Sn, 112 Sn+ 124 Sn, 112 Sn+ 112 Sn Measure N/Z compositions of emitted particles n & p yields isotopes yields isospin diffusion

17 1 E/A (,) = E/A (,) + 2 S() = ( n - p )/ ( n + p ) = (N-Z)/A Two observables: n/p ratios and isospin diffusion Li et al., PRL 78 (1997) 1644 V asy (MeV) 5 stiff soft Neutron Proton u = / o Double Ratio 124 Sn+ 124 Sn;Y(n)/Y(p) 112 Sn+ 112 Sn;Y(n)/Y(p) Data : Famiano et al. PRL 97 (26) 5271 minimize systematic errors

18 n/p double yield ratios and flow ratios 5 A.MeV Sn+Sn 4 A.MeV Au + Au P. Russotto et al., PLB 697, 471 (211) Data : Famiano et al. PRL 97 (26) 5271 Theorists frustration: large experimental uncertainties! Results from better designed experiments are coming!

19 Famiano et al n/p Experiment 124 Sn+ 124 Sn; 112 Sn+ 112 Sn; E/A=5 MeV Scattering Chamber

20 Complicated Experimental Layout Wall A Wall B LASSA charged particles Miniball impact parameter Courtesy Mike Famiano Neutron walls neutrons Forward Array time start Proton Veto scintillators

21 Large scintillation arrays at great distance (TOF) Experimental challenges in detecting n and p γ yield 5 MeV Small Si-CsI arrays close to target (DE-E) protons H 12 MeV n q CM (deg) neutrons Rejected He TOF Many more particles detected by the neutron detectors in 124 Sn+ 124 Sn reactions than n s Different coverage in geometry and energy for particles E CM (MeV)

22 t/ 3 He Double Ratios (central collisions) Detection of t/ 3 He are better controlled but still have cut off problems at high energy due to statistics and detector limitations. More suitable for experiments at higher beam energy

23 Lessons learned?? n/p signal seems to persist above E/A=12 MeV (Good news) Use same detectors to detect both neutrons and protons by implementing good veto counters. Detect p & n in separate experiments Better detectors to detect high energy t & 3He

24 Other Observables: SN/SZ Ratios (complementary to n/p) SN/SZ trends are similar for each element except for Be due to lack of 8Be which is unstable

25 Other Observables: SN/SZ double ratios DR does not solve the problem with 8Be Clear demonstration of the need for sequential decay corrections Need observables that are insensitive to sequential decays

26 Degree of isospin diffusion Experimental Observable : Isospin Diffusion Projectile 124 Sn Isospin diffuse through low-density neck region Symmetry energy drives system towards equilibrium. stiff EOS small diffusion; R i >> Target 112 Sn soft EOS fast equilibrium; R i Advantages stiff Sequential decays and non diffusion effects normalized by the symmetric systems soft R i 2 x AB ( x x AA x x AA BB BB ) / 2

27 Isotope distributions and isospin diffusions The main effect of changing the asymmetry of the projectile spectator remnant is to shift the isotopic distributions of the products of its decay This can be described by the isoscaling parameters and : Y2 N, Z Cexp( N Z) Y N, Z 1 and are related to the nucleon chemical potentials Isospin diffusionri() no diffusion R i ()

28 .4g i 1 Comparison with theory ImQMD model describes np ratios and g i two isospin diffusion measurements: S()=12.5(/ o ) 2/ (/ o ).4g i 1.45g i.95 Success of isospin diffusion can be attributed to its relative insensitivity to sequential decays. Experiment is difficult as it requires: A+A; B+B; A+B or B+A This observable is predicted to diminish and disappear at high energy

29 B sym B o sym K L S E sym B sym P E L B 3 3 Symmetry energy constraints from HIC, GDR, FRDM and IAS

30 Constraints on the density dependence of symmetry energy n,p squeeze-out Heavy Ion Collisions Au+Au p + /p - ratios

31 facility Probe Beam Energy Travel (k) $ year density MSU 9- RIBF 12, FRIB 2, KoRIA? MSU n, p,t,3he < o GSI n, p, t, 3He / o MSU iso-diffusion 5 21/211 < o RIKEN iso-diffusion < o MSU p +,p o RIKEN n,p,t, 3 He,p +,p o GSI n, p, t, 3He o FRIB n, p,t, 3 He, p +,p o FAIR K + /K - 8-1? o GSI 1 FAIR Symmetry Energy Project International collaboration to determine the symmetry energy over a range of density Require: New Detectors (TPC), & theory support

32 Nuclear Symmetry Energy (NuSym) collaboration Determination of the Equation of State of Asymmetric Nuclear Matter MSU: B. Tsang & W. Lynch, G. Westfall, P. Danielewicz, E. Brown, A. Steiner Texas A&M University : Sherry Yennello, Alan McIntosh Western Michigan University : Michael Famiano RIKEN, JP: TadaAki Isobe, Atsushi Taketani, Hiroshi Sakurai Kyoto University: Tetsuya Murakami Tohoku University: Akira Ono GSI, Germany: Wolfgang Trautmann, Yvonne Leifels Daresbury Laboratory, UK: Roy Lemmon INFN LNS, Italy: Giuseppe Verde, Paulo Russotto GANIL, France: Abdou Chbihi CIAE, PU, CAS, China: Yingxun Zhang, Zhuxia Li, Fei Lu, Y.G. Ma, W. Tian Korea University, Korea: Byungsik Hong The Time projection chamber is being built in the US to measure p+/p- & light charge particles in RIKEN

33 Isospin Observables in HIC at supra-normal densities E/A=5-1 MeV Neutron/proton and t/ 3 He and light isotopes energy spectra & flow RIBF, FRIB, KoRIA E/A>15 MeV π + /π - spectra π + /π - flow Preliminary data shows: n/p remains robust at E/A=12 MeV. May be able to extend measurements to E/A~2 MeV

34 A new isospin observable π- generated from n+n collisions π+ generated from p+p Collisions of neutron rich nuclei: N(π-)>N(π+) π- multiplicity dependent on density dependence of EOS Different transport codes make different predictions!

35 New Detector(s) At beam energy > 1 A.MeV, fragment production decreases. Observables are: n/p ratios, flow, t/3he ratios, flow, p+/ p- ratios Properties of the Time projection chamber (TPC) Particle identification (de/dx track rigidity) Charged pions, Proton, Light ions (t, 3He) Centrality Determination (b): momentum measurement Reaction plane determination Ability to measure large number of multiple particles

36 RIKEN Superconducting Magnet 3T with 2m dia. pole (designed resolution 1/7) 8cm gap (vertical) TPC Large Vacuum Chamber Rotational Stage

37 SAMURAI-TPC The SAMURAI Time Projection Chamber (TPC) tracks the light charged particles and pions after the heavy ion collisions. SAMURAI Dipole Magnet TPC in the Vacuum Chamber

38 The SAMURAI TPC Since the field cage is where the magic happens, we want to maximize the height of the field cage. The height is limited by the magnet chamber to 8 cm, but by minimizing the height of other parts we can maximize the field cage height Reentrant Lid and Electronics Field Cage Target mechanism Outside enclosure Voltage step down Bottom plate for enclosure Rail Structure

39 Summary Success at low energy HIC program suggests paths forward to higher energy program to determine the density dependence of symmetry energy at high density important program in any nuclear science LR plans. HIC is the only way on earth to create nuclear matter with ρ>ρ o. Challenges remains: New detectors to measure new observables. TPC to detect p s. Extension of current observables to high energy (n,/p, t/3he ) HIC experiments are complicated, need advance planning and floor place/footprint in new facilities. Much work remains exciting time to join the international effort! n,p squeeze-out Au +A u p + /p - ratios

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41 Production of p s in HIC E beam <29 A.MeV, sub-threshold p s are produced from collective effects of nucleons & Fermi motion, E beam <3 GeV p are produced via delta resonances Resonance states are generated through n-n collisions Pion yields are directly related to the n & p chemical potentials In neutron-rich matter, Y(p - )>Y(p + ) Y(p - )/Y(p + ) is an observable to study the symmetry energy

42 ASY-EOS May AMeV 96 Zr AMeV 96 Ru AMeV ~ 5x1 7 Events for each system Krakow array Beam Line Chimera TofWall MicroBall target Russotto & Lemmon Shadow Bar Land (not splitted