1. Anti-hypernuclei production and search for P-odd domain formation at RHIC Gang Wang ( for the STAR Collaboration ) UCLA A colored and flavored system in collision...

2. 2 Outline N Z S Exotic particleExotic phenomenon

3. 3 No one has ever observed any anti- hypernucleus before us (STAR). The first hypernucleus was discovered by Danysz and Pniewski in 1952, formed in a cosmic ray interaction in a balloon-flown emulsion plate. M. Danysz and J. Pniewski, Phil. Mag. 44 (1953) 348 M. Danysz and J. Pniewski, Phil. Mag. 44 (1953) 348   p +  - (64%);   n +  0 (36%) What is a hypernucleus? Hypernuclei of lowest A A nucleus containing at least one hyperon in addition to nucleons.

4. 4 Hypernuclei: ideal lab for YN and YY interaction – Baryon-baryon interaction with strangeness sector – Input for theory describing the nature of neutron stars Coalescence mechanism for production: depends on overlapping wave functions of Y+N at final stage Anti-hypernuclei and hypernuclei ratios: sensitive to anti-matter and matter profiles in HIC Extension of the nuclear chart into anti-matter with S [1] [1] W. Greiner, Int. J. Mod. Phys. E 5 (1995) 1 Why (anti-)hypernuclei?

5. 5 International Hyper-nuclear network PANDA at FAIR 2012~ Anti-proton beam Double  -hypernuclei  -ray spectroscopy MAMI C 2007~ Electro-production Single  -hypernuclei  -wavefunction JLab 2000~ Electro-production Single  -hypernuclei  -wavefunction FINUDA at DA  NE e + e - collider Stopped-K - reaction Single  -hypernuclei  -ray spectroscopy (2012~) J-PARC 2009~ Intense K - beam Single and double  -hypernuclei  -ray spectroscopy  HypHI at GSI/FAIR Heavy ion beams Single  -hypernuclei at extreme isospins Magnetic moments SPHERE at JINR Heavy ion beams Single  -hypernuclei BNL Heavy ion beams Anti-hypernuclei Single  -hypernuclei Double  -hypernuclei

6. 6 RHIC PHENIX STAR AGS TANDEMS Animation M. Lisa Relativistic Heavy Ion Collider (RHIC)

7. 7 Relativistic Heavy-ion Collisions initial stage pre-equilibrium QGP and hydrodynamic expansion hadronization and freeze-out  New state of matter: QGP RHIC creates hot and dense matter, containing equilibrium in phase space population of u, d and s: ideal source of hypernuclei about equal numbers of q and anti-q: ideal source of anti-nuclei RHIC white paper: Nucl. Phys. A 757

8. 8 STAR Detector STAR consists of a complex set of various detectors, a wide range of measurements and a broad coverage of different physics topics.

9. 9 Event display STAR TPC: an effectively 3-D ionization camera with over 50 million pixels.

10. 10 3  H mesonic decay, m=2.991 GeV/c 2, B.R. 0.25 Data-set used, Au+Au 200 GeV ~67M year 2007 minimum-bias ~22M year 2004 minimum-bias ~23M year 2004 central, |V Z |<30cm Tracks level: standard STAR quality cuts, i.e., not near edges of acceptance, good momentum & dE/dx resolution. Data-set and track selection Secondary vertex finding technique DCA of v0 to PV < 1.2 cm DCA of p to PV > 0.8 cm DCA of p to 3 He < 1.0 cm Decay length > 2.4 cm QM09 proceeding: arXiv:0907.4147

11. 11 3 He & anti- 3 He selection Select pure 3 He sample: 3 He: 5810 counts anti- 3 He: 2168 counts condition: -0.2 2 GeV/c … Theory curve: Phys. Lett. B 667 (2008) 1

12. 12 signal from the data Signal observed from the data (bin-by-bin counting): 157 ± 30 Mass: 2.989 ± 0.001 ± 0.002 GeV; Width (fixed): 0.0025 GeV. Projection on anti-hypertriton yield: =157*2168/5810= 59 ± 11 STAR Collaboration, Science 328 (2010) 58

13. 13 Signal observed from the data (bin-by-bin counting): 70 ± 17 Mass: 2.991 ± 0.001 ± 0.002 GeV; Width (fixed): 0.0025 GeV. signal from the data Projection on anti-hypertriton yield: 59 ± 11 STAR Collaboration, Science 328 (2010) 58

14. 14 Combined the signal Combined hyperT and anti-hyperT signal : 225 ± 35 It provides a >6  significance for discovery. STAR Collaboration, Science 328 (2010) 58

15. 15 Measure the lifetime ps We measure   = 267 ± 5 ps PDG value   = 263 ± 2 ps PDG: Phys. Lett. B 667 (2008) 1 STAR Collaboration, Science 328 (2010) 58

16. 16 Production rate Tabulated ratios favor coalescence Coalescence => 0.45 ~ 0.77*0.77*0.77

17. 17 A case for energy scan RHIC is carrying out Beam Energy Scan as we speak. Baryon-strangeness correlation via hypernuclei: a viable experimental signal to search for the onset of deconfinement. model calculation: S. Zhang et al, Phys. Lett. B684, 224(2010) Baryon-strangeness correlation: PRL 95 (2005) 182301, PRC 74 (2006) 054901, PRD 73 (2006) 014004. Phase diagram plot: arXiv:0906.0630 STAR Collaboration, Science 328 (2010) 58

18. 18 The measured lifetime is ps, consistent with free  lifetime (263 ps) within uncertainty. Consistency check has been done on analysis; 157 candidates, with significance better than 5  has been observed for first time; 70 candidates, with significance ~4 . Summary I The / ratio is measured as 0.49 ± 0.18 ± 0.07, and 3 He / 3 He is 0.45 ± 0.02 ± 0.04, favoring coalescence. RHIC is the best anti-matter machine ever built!

19. 19 Outlook Lifetime: –10 times more data within this year Production rate: –baryon-strangeness correlation –a case for energy scan –establish a trend from AGS-SPS-RHIC-LHC 3 L H  d+p+p channel measurement: d-identification via ToF. Search for other hypernucleus: 4 L H, 4 L He, 4 LL H, 3 X H, Search for anti-α AGS-E906, Phys. Rev. Lett. 87, 132504 (2001)

20. 20 Looking into a mirror, you see someone else… It’s a parity violation?! Parity transformation: A spatial inversion of the coordinates. Origins of parity violation: 1. Global parity violation Occurs in weak interactions  Confirmed 2. Local parity violation Predicted in strong interactions  we are working on it… Kharzeev, PLB 633 260 (2006) [hep-ph/0406125]; Kharzeev, McLerran, Warringa, NPA 803 227 (2008); Kharzeev, Zhitnitsky, NPA 797 67 (2007); Fukushima, Kharzeev, Waringa, PRD 78, 074033. Parity violation

21. 21 P/CP invariance are (globally) preserved in strong interactions: neutron EDM (electric dipole moment) experiments: Θ<10 −11 Pospelov, Ritz, PRL83:2526 (1999) Baker et al., PRL97:131801 (2006) In heavy-ion collisions, the formation of (local) meta-stable P-odd domains is not forbidden. The strong magnetic field (B~10 15 T) could induce electric field (E~θB), and manifest the P-odd domains with charge separation w.r.t Reac.plane. Kharzeev, PLB633:260 (2006) Kharzeev, McLerran, Warringa, NPA803:227 (2008) Local P violation in strong interactions

22. 22 Charge separation in strong interactions A direct measurement of the P-odd quantity “a” should yield zero. S. Voloshin, PRC 70 (2004) 057901 Directed flow: vanishes if measured in a symmetric rapidity range Non-flow/non-parity effects: largely cancel out P-even quantity: still sensitive to charge separation

23. 23 Factorization If the event plane or the third particle has non-flow correlations with the first two particles, we can NOT safely factorize the above equation. S. Voloshin, PRC 70 (2004) 057901

24. 24 STAR ZDC-SMD SMD is 8 horizontal slats & 7 vertical slats located at 1/3 of the depth of the ZDC New knowledge of the direction of the impact parameter vector Minimal, if any, non-flow/non-parity effects Worse resolution than from TPC… can be overcome with statistics ZDC side view Scintillator slats of Shower Max Detector Transverse plane of ZDC

25. 25 Approach With the EP from ZDC, the 3-particle non-flow/non-parity correlations (independent of the reaction plane) will be basically eliminated as a source of background. As a systematic check, I also calculate directly The results on the following slides are based on Au+Au collisions at 200 GeV, taken in RHIC run2007, except otherwise specified.

26. 26 Results with different event planes STAR Preliminary The correlator using ZDC event plane is consistent with that using TPC event plane. Lost in the medium?

27. 27 Different charge combinations The + + and – – combinations are consistent with each other. STAR Preliminary

28. 28 What do we know about the position R n after n steps? R n follows a Gaussian distribution: mean = 0, and rms = Our measurement of PV is like R n 2, expected to be n. Compared with going in one fixed direction, where R n 2 = n 2, the "random-walk" measurement is diluted by a factor ~ n ~ N ch. Dilution effect In the quark-gluon medium, there could be multiple P-odd domains. The net effect is like a random walk, but one-dimensional.

29. 29 Dilution effect STAR Preliminary The factor N part is used to compensate for dilution effect. Weaker B field Non-zero Radial flow? Thin medium

30. 30 Systematic check: v 1 {ZDC-SMD} STAR Preliminary S. Voloshin, PRC 70 (2004) 057901 If v 1 (η) is not anti- symmetric around η= 0, then this term won’t vanish. STAR Preliminary v 1 (η) crosses zero for both charges in the TPC region.

31. 31 The average magnitude of is ~ 10 -4. Its corresponding contribution to the correlator,, will be safely negligible. STAR Preliminary Systematic check: a 1 {ZDC-SMD} S. Voloshin, PRC 70 (2004) 057901

32. 32 Systematic check: η gap STAR Preliminary The same-sign correlation approaches zero when the η gap increases.

33. 33 Systematic check: p T gap The non-zero same-sign correlator for p T gap > 200 MeV/c indicates that we are safe from HBT or Coulomb effects. STAR Preliminary

34. 34 More checks from TPC EP We have looked at lower beam energy (62 GeV) and/or smaller system (Cu+Cu), to see qualitatively similar results. STAR Collaboration, arXiv:0909.1717

35. 35 Summary II The formation of (local) meta-stable P-odd domains in heavy-ion collisions is predicted to lead to charge separation w.r.t the reaction plane. P-even correlator has been measured with event planes from both STAR TPC and ZDC; and the results are consistent! The gross feature of the correlator meets the expectation for the picture of local Parity Violation: charge separation, suppression of OS by opacity, weaker OS signal in central collisions, OS&LS symmetry in peripheral collisions... STAR has checked the possible effects on v 1, a 1,η gap, and p T gap.

36. 36 Interpretations - + Ψ RP + - Out-of-Plane Charge Separation Interpretation 1: Ψ RP Flowing “structures” Interpretation 2: X X X X X X X = unknown structure Implies Local P-violation of strong interactions Does Not Imply P violation of the strong interactions

37. 37 Interpretation 2 -+ Ψ RP +- charge conservation/cluster + v 2 Scenario 1: Scenario 2: Need some investigation -+ Ψ RP +- -+ charge conservation/cluster + v 1 symmetry fluctuation STAR Collaboration, PRL103 (2009)251601

38. 38 Alternative measurements These observables contain all possible (mixed) harmonic terms, while the correlator observables previously shown contain only one. Charge asymmetry correlation

39. 39 Alternative measurements STAR preliminary d+Au Same-sign: - δ‹A 2 › UD > δ ‹A 2 › LR - meets LPV expectation - δ ‹A 2 › < 0 in central collisions Oppo-sign: - aligned (‹A + A - › > 0) - local charge conservation? - ‹A + A - › UD > ‹A + A - › LR - contradicts LPV expectation? - not dominantly RP-related Different observables have different sensitivities to the charge separation, and suffer different backgrounds. No real reaction plane here!

40. 40 Outlook With zero net charge, the neutral particles are expected to be much less affected by the electric field. Λ, K s 0 et al. Beam energy below QGP threshold Beam Energy Scan Isobaric couple of spherical nuclei : different magnetic fields: Neodymium(144,60)- Samarium(144,62) et al. body-body U+U collisions Deformed nuclei can provide the collisions with zero magnetic field and large v 2 to test the theory. CP-violating decays η→π + π - et al. R. Millo and E. V. Shuryak, arXiv:0912.4894

41. 41 Back-up

42. 42 Systematic check: EP resolution