1. The hypernuclei program at RHIC-STAR Jinhui Chen for the STAR Collaboration Shanghai Institute of Applied Physics, CAS The 11 th International Conference on Hypernuclear and Strange Particle Physics " HYP2012 " October 1 - 5, 2012 Barcelona, Spain

2. 2 Introduction & Motivation Our measurement – Hypertriton invariant yield – Lifetime measurement – H-dibaryon search Conclusion Outline

3. 3 Introduction & Motivation Hypernuclei: ideal lab for YN and YY interaction – Baryon-baryon interaction with strangeness sector – Input for theory describing the nature of neutron stars Binding energy and lifetime are sensitive to the Y-N interaction Previous measurement on hypertriton lifetime shows large statistical uncertainties Search for H-dibaryon via  correlation, provide sensitive constrains on Y-Y interaction

4. 4 Hypertriton lifetime measurement Previous measurement (before 1973) Use nuclear emulsion or bubble chamber Accepted events: less than 80 STAR 2010 Measurement STAR 2012 Measurement Previous measurement STAR Collaboration, Science 328 (2010)58 Run4 200GeVMB22M Run4 200GeVCentral23M Run7 200GeVMB68M Run10 200GeVMB~223M Run10 200GeVCentral~199M Run10&11 low energies MB~213M It is promising to obtain an improved lifetime measurement using the new data

5. 5 Relativistic heavy-ion collisions initial stage pre-equilibrium QGP and hydrodynamic expansion hadronization and freeze-out  Initial condition of collisions  New state of matter : QGP  Hadronization and hadronic interaction RHIC creates hot and dense matter, containing dozens of hyperons in central events : ideal source of hypernuclei studies. RHIC white paper: Nucl. Phys. A 757

6. 6 RHIC BRAHMS PHOBOS PHENIX STAR AGS TANDEMS Relativistic Heavy Ion Collider (RHIC)

7. 7 STAR Detector TPC: effectively 3-D ionization camera with over 50 million pixels. STAR: a complex set of various detectors, a wide range of measurements and a broad coverage of different physics topics. STAR-TPC: NIMA 499 (2003) 659 STAR-detector: NIMA 499 (2003) 624

8. 8 Event display A beautiful event in the STAR TPC that includes the production and decay of a antihypertriton candidate. (Data taken from Run4 Au+Au 200GeV MB collision)

9. 9 Run10 7.7GeVMB~4M Run10 11.5GeVMB~11M Run11 19.6GeVMB~31M Run11 27GeVMB~49M Run10 39GeVMB~118M Run10 200GeVMB~223M Run10 200GeVCentral~199M Run7 200GeVMB~56M Datasets and event statistics Datasets and track selection Analysis method: secondary vertex finding technique Identify 3 He and  candidate Find the V0 position from daughters pairing Plot the invariant mass dis. of daughters Combinatorial background analysis

10. 10 Daughters identification Clean  ( 2GeV) identification from TPC STAR preliminary

11. 11 signal from the data Signal observed from the data (bin-by-bin counting [2.986,2.996]GeV): 602±63, significance:9.6  Background estimation: rotated background Statistics: Run7+Run10+Run11 MB+Central, ~610M events bin width 4MeV bin width 2MeV STAR preliminary

12. 12 Signal in BES(1) Hypertriton signal from STAR BES at =7.7, 11.5, 19.6GeV 7.7GeV11.5GeV19.6GeV Events~4M(MB)~11M (MB)~31M (MB) 3 He(anti)8587(0)7161(0)6321(0) Hypertriton46±1741±1742±14 Details in the analysis STAR preliminary

13. 13 Signal in BES(2) Hypertriton signal from STAR BES at =27, 39, 200GeV 27GeV39GeV200GeV Events~49M(MB)~118M(MB)~223M(MB) 3 He(anti)5312(19)6456(133)5822(2213) Hypertriton46±1688±2183±20 Details in the analysis STAR preliminary

14. 14 Measure the lifetime Measure the hypertriton signal in different L/βγ bins: 2-5-8-11-41cm Combined datasets: run10 7.7,11.5,39,200GeV MB, run10 200GeV central, run11 19.6, 27GeV MB STAR preliminary

15. 15 New hypertriton lifetime result STAR 2012 preliminary result: STAR 2010+2012 combined fit: STAR preliminary

16. 16  correlation function Type of ΛΛ interaction:  Meson exchange models: Nijmegen model D, F, Soft Core (89, 97)  Quark cluster model interaction: fss2  Phenomenological model: Ehime  interaction  attractive Inclusive  correlations: feed down contributions included in theoretical models. STAR preliminary Correlation functions for 0-40% Au+Au collisions at = 200GeV Shah IV Mon.

17. 17  correlation function A. Ohnishi, HHI workshop 2012/2 Scattering length (a 0 ) is negative in most fits Current fit from different potential models to data gives indication towards non-existence of bound H-dibaryon Shah IV Mon.

18. 18 A statistically improved lifetime ps is obtained The hypertriton and antihypertriton signals are reconstructed for each RHIC BES energy Over 600 hypertriton and antihypertriton particles are reconstructed in heavy-ion collisions at RHIC, with a significance of 9.6  Conclusion The H-dibaryon search: current fit from different potential models to data gives no indication towards the existence of bound H-dibaryon