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First Observation of an Anti-Hypernucleus

First Observation of an Anti-Hypernucleus. Xin Dong for the STAR Collaboration. Science 328, 58 (2010). Outline. Introduction Measurements on (anti-)Hypernuclei at STAR and signal Lifetime Production rate Conclusions and Outlook. Hypernucleus.

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First Observation of an Anti-Hypernucleus

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  1. First Observation of an Anti-Hypernucleus Xin Dong for the STAR Collaboration Science 328, 58 (2010)

  2. Outline • Introduction • Measurements on (anti-)Hypernuclei at STAR • and signal • Lifetime • Production rate • Conclusions and Outlook

  3. Hypernucleus What is a hypernucleus? Nucleus which contains at least one hyperon in addition to nucleons Hypernucleus of lowest A Hypertriton • 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)

  4. 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 • At low energies • (cosmic ray / Kaon beam stopped in nuclear emulsion or bubble chamber) • hypernucleus production via • L or Kcapture • direct strangeness exchange reaction. • 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) No anti-hypernucleus has been observed before.

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

  6. Relativistic Heavy Ion Collider (RHIC) STAR

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

  8. Topological Recon. of (anti-)Hypernuclei Secondary vertex finding technique TPC track projection error ~ 0.5 cm • 3LH 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, • |VZ|<30cm Secondary decay

  9. 3He & anti-3He selection 3He t d p K  • Select pure 3He sample: 3He: 5810 counts • anti-3He: 2168 counts • Selection condition: |z|<0.2, p>2 GeV/c

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

  11. Signal Signal counts: 157 ± 30 Mass: 2989 ± 1± 2 MeV Width: 2.5 MeV Expected anti-hypertriton yield: = 59±11

  12. Signal Signal counts: 70±17 Mass: 2991±1±2 MeV Width: 2.5 MeV

  13. Lifetime Measurement We measure tL= 267±5 ps PDG value is tL= 263±2 ps ps

  14. Production Rate Coalescence => 0.45 ~ (0.77)3 Favoring coalescence

  15. Conclusions First observation of an anti-hypernucleus with 70 candidates, with significance ~4s. The measured lifetime is ps, consistent with free Llifetime (263 ps) within uncertainty. The measured / ratio is 0.49±0.18±0.07, and 3He / 3He is 0.45±0.02 ±0.04. These ratios favor coalescence production of light (hyper-)nuclei.

  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. 3LHd+p+ • Search for other hypernuclei: 4H, double -hypernuclues • Search for anti-

  17. BackUp

  18. Hypernuclei and Neutron stars S=-2 S=-1 S=0 J.M. Lattimer and M. Prakash, Science 304, 536 (2004)

  19. Topological Recon. of Weak Decays TPC track projection error ~ 0.5 cm Weak decay particles c ~ 2 - 10 cm Ks0    STAR, PRC 77 (2008) 54901

  20. Combined Signal Combined hypertriton and anti-hypertriton signal : 225±35; It provides a >6s significance for discovery.

  21. Yield to measure B/S Correlation In the coalescence model: A=2:  baryon density <rB> A=3:  <rB2>, <rBrL> H. Sato Phys. Lett. B 98 (1981) 153 Baryon-strangeness correlation: PRL 95 (2005) 182301, PRC 74 (2006) 054901, PRD 73 (2006) 014004. model: PLB 684 (2010) 224 Baryon-strangeness correlation via hypernuclei: a viable experimental signal to search for the onset of deconfinement.

  22. World Map of Hypernucleus Labs

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