1. X. Dong 1 May 10, 2010 NSD Monday Morning Meeting First Observation of an Anti-Hypernucleus Xin Dong for the STAR Collaboration Science 328, 58 (2010)

2. May 10, 2010 NSD Monday Morning MeetingX. Dong 2  Introduction  Measurements on (anti-)Hypernuclei at STAR and signal Lifetime Production rate  Conclusions and Outlook Outline

3. May 10, 2010 NSD Monday Morning MeetingX. Dong 3 Hypernucleus Hypernucleus production in the laboratory  is an Ideal probe to study the Y-N interaction;  provides information on Equation-of-State of neutron stars. Configurations of neutron stars: (depending on the Y-N interaction length) Hyperons / Meson condensates / Strange quark matter J.M. Lattimer and M. Prakash, Science 304, 536 (2004) What is a hypernucleus? Nucleus which contains at least one hyperon in addition to nucleons Hypernucleus of lowest A Hypertriton

4. May 10, 2010 NSD Monday Morning MeetingX. Dong 4  In high energy heavy-ion collisions: (AGS/BNL … ) – (anti-)nucleus/hypernucleus production by coalescence (wave functions overlap between two or more particles/nuclei in phase space and they re-combine into one particle/nucleus)  At low energies (cosmic ray / Kaon beam stopped in nuclear emulsion or bubble chamber) hypernucleus production via –  or K capture – direct strangeness exchange reaction. How are (anti-)hypernuclei produced First hypernucleus discovered by Danysz and Pniewski in 1952 from a cosmic ray interaction in nuclear emulsion. M. Danysz and J. Pniewski, Phil. Mag. 44 (1953) 348 No anti-hypernucleus has been observed before.

5. May 10, 2010 NSD Monday Morning MeetingX. Dong 5 Particle/Nucleus production at RHIC Anti-particles and particles are nearly equally produced. Chance to find anti-hypernuclei at RHIC! 3 He/ 3 He ratio 10 -11 (AGS) 10 -3 (SPS) 0.5 (RHIC) STAR white paper, NPA 757, 102 (2005)

6. May 10, 2010 NSD Monday Morning MeetingX. Dong 6 Relativistic Heavy Ion Collider (RHIC) STAR

7. May 10, 2010 NSD Monday Morning MeetingX. Dong 7 Solenoidal Tracker At RHIC (STAR) Time Projection Chamber BEMC Time Projection Chamber (TPC): |  |<1, 2  in azimuth Tracking, particle identification via dE/dx Full Barrel TOF in year2010

8. May 10, 2010 NSD Monday Morning MeetingX. Dong 8 3  H mesonic decay, B.R. 25%, c  ~ 7 cm Data-sets used, Au+Au 200 GeV ~ 67M year 2007 minimum-bias ~ 22M year 2004 minimum-bias ~ 23M year 2004 central, |V Z |<30cm Secondary vertex finding technique Topological Recon. of (anti-)Hypernuclei TPC track projection error ~ 0.5 cm Secondary decay

9. May 10, 2010 NSD Monday Morning MeetingX. Dong 9 Select pure 3 He sample: 3 He: 5810 counts anti- 3 He: 2168 counts Selection condition: |z| 2 GeV/c 3 He & anti- 3 He selection  K p d t 3 He

10. May 10, 2010 NSD Monday Morning MeetingX. Dong 10 refmult = 217 vertexX = -0.17 vertexY = 0.46 vertexZ = -21.60 mass = 2.99164 pt = 4.60 He3pt = 4.34 pionpt = 0.28 runid = 5017004 eventid = 1844 decayL = 21.25 dca = 0.50 dca1to2 = 0.48 …… A Candidate Event Display

11. May 10, 2010 NSD Monday Morning MeetingX. Dong 11 Signal counts: 157 ± 30 Mass: 2989 ± 1± 2 MeV Width: 2.5 MeV Signal Expected anti-hypertriton yield: = 59±11

12. May 10, 2010 NSD Monday Morning MeetingX. Dong 12 Signal counts: 70±17 Mass: 2991±1±2 MeV Width: 2.5 MeV Signal

13. May 10, 2010 NSD Monday Morning MeetingX. Dong 13 ps We measure   = 267±5 ps PDG value is   = 263±2 ps Lifetime Measurement

14. May 10, 2010 NSD Monday Morning MeetingX. Dong 14 Production Rate Coalescence => 0.45 ~ (0.77) 3 Favoring coalescence

15. May 10, 2010 NSD Monday Morning MeetingX. Dong 15 The measured lifetime is ps, consistent with free  lifetime (263 ps) within uncertainty. First observation of an anti-hypernucleus with 70 candidates, with significance ~4 . The measured / ratio is 0.49±0.18±0.07, and 3 He / 3 He is 0.45±0.02 ±0.04. Conclusions These ratios favor coalescence production of light (hyper-)nuclei.

16. May 10, 2010 NSD Monday Morning MeetingX. Dong 16 Outlook  Hypertriton Data samples with larger statistics to allow precision measurements on Lifetime - binding energy Production rate - baryon-strangeness correlation  Other channels, e.g.    d+p+   Search for other hypernuclei: 4  H, double  -hypernuclues  Search for anti- 

17. May 10, 2010 NSD Monday Morning MeetingX. Dong 17 BackUp

18. May 10, 2010 NSD Monday Morning MeetingX. Dong 18 Hypernuclei and Neutron stars S=-1 S=-2 S=0 J.M. Lattimer and M. Prakash, Science 304, 536 (2004)

19. May 10, 2010 NSD Monday Morning MeetingX. Dong 19 Topological Recon. of Weak Decays TPC track projection error ~ 0.5 cm Weak decay particles c  ~ 2 - 10 cm Ks0Ks0    STAR, PRC 77 (2008) 54901

20. May 10, 2010 NSD Monday Morning MeetingX. Dong 20 Combined hypertriton and anti-hypertriton signal : 225±35; It provides a >6  significance for discovery. Combined Signal

21. May 10, 2010 NSD Monday Morning MeetingX. Dong 21 In the coalescence model: A=2:  baryon density A=3: , H. Sato Phys. Lett. B 98 (1981) 153 Yield to measure B/S Correlation Baryon-strangeness correlation via hypernuclei: a viable experimental signal to search for the onset of deconfinement. model: PLB 684 (2010) 224 Baryon-strangeness correlation: PRL 95 (2005) 182301, PRC 74 (2006) 054901, PRD 73 (2006) 014004.

22. May 10, 2010 NSD Monday Morning MeetingX. Dong 22 World Map of Hypernucleus Labs