anti-hypernuclei production and search for p-odd domain formation at rhic

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

Outline

N

Z

S

Exotic particle Exotic phenomenon

3

No one has ever observed any anti-

hypernucleusbefore us (STAR).

The first hypernucleus was discovered by Danysz and Pniewski in 1952The first hypernucleus was discovered by Danysz and Pniewski in 1952,, formed in a cosmic ray interaction in a balloon-flown emulsion plate. formed in a cosmic ray interaction in a balloon-flown emulsion plate. M. Danysz and J. Pniewski, M. Danysz and J. Pniewski, Phil. Mag. 44 (1953) 348Phil. 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.

)(

)(3

3

pnH

pnH

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?

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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 DANE• 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

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RHICPHENIX

STAR

AGS

TANDEMS

Animation M. Lisa

Relativistic Heavy Ion Collider (RHIC)

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Relativistic Heavy-ion Collisions

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

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

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STAR Detector

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

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Event display

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

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3H mesonic decay, m=2.991 GeV/c2, 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,

|VZ|<30cm

Tracks level: standard STAR quality cuts, i.e. , not near edges of acceptance, good momentum & dE/dx resolution.

Data-set and track selection

HeH

eHH33

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Secondary vertex finding technique

DCA of v0 to PV < 1.2 cmDCA of p to PV > 0.8 cmDCA of p to 3He < 1.0 cmDecay length > 2.4 cm

QM09 proceeding: arXiv:0907.4147

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3He & anti-3He selection

)/

/ln( th

dxdE

dxdEz

Select pure 3He sample: 3He: 5810 counts

anti-3He: 2168 counts

condition: -0.2 < z < 0.2 & dca < 1.0 cm & p > 2 GeV/c …

Theory curve: Phys. Lett. B 667 (2008) 1

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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 ± 11Hee/HHH 333Λ

3Λ

STAR Collaboration, Science 328 (2010) 58

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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


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Combined the signal

Combined hyperT and anti-hyperT signal : 225 ± 35

It provides a >6 significance for discovery.


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Measure the lifetime

27182 8945 ps

We measure = 267 ± 5 ps PDG value = 263 ± 2 psPDG: Phys. Lett. B 667 (2008) 1


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Production rate

Tabulated ratios favor coalescence

)/)(n/n)(p/p(HH33 /

Coalescence =>

0.45 ~ 0.77*0.77*0.77

)n/n()p/p(He3

eH23 /

)/2NNN(NN centralpart

centraleve

MBpart

MBeve

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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


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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

H3Λ

H3Λ

H3Λ

H3Λ The / ratio is measured as 0.49 ± 0.18 ± 0.07, and

3He / 3He is 0.45 ± 0.02 ± 0.04, favoring coalescence.

27182 8945

RHIC is the best anti-matter machine ever built!

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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

3LHd+p+p channel measurement: d-identification via ToF.

Search for other hypernucleus: 4LH, 4

LHe, 4LLH, 3

XH,

Search for anti-α

AGS-E906, Phys. Rev. Lett. 87, 132504 (2001)

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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…

xx

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

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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~1015 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)

RPad

dN

sin21

Local P violation in strong interactions

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Charge separation in strong interactions

RPad

dN

sin21

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

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,2

)2cos(

resolution

)2cos()2cos(

v

EPEP

RP

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

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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

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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.

)cos(

)cos()2cos( 21

21westeast

westeastRP

fullfullRPa EP_Res/)sin()sin(1

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Results with different event planesSTAR Preliminary

The correlator using ZDC event plane is consistent with that using TPC event plane.

Lost in the medium?

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Different charge combinations

The + + and – – combinations are consistent with each other.

STA

R P

reliminary

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What do we know about the position Rn after n steps? Rn follows a Gaussian distribution: mean = 0, and rms =

Our measurement of PV is like Rn2, expected to be n.

Compared with going in one fixed direction, where Rn2 = n2,

the "random-walk" measurement is diluted by a factor ~ n ~ Nch.

Dilution effectIn the quark-gluon medium, there could be multiple P-odd domains. The net effect is like a random walk, but one-dimensional.

n

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Dilution effect

STAR Preliminary

The factor Npart is used to compensate for dilution effect.

Weaker B field

Non-zero Radial flow?

Thin medium

outin BB

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Systematic check: v1{ZDC-SMD}

STAR Preliminary

S. Voloshin, PRC 70 (2004) 057901

If v1 (η) is not anti-symmetric around η= 0, then this term won’t vanish.

STAR Preliminary

v1 (η) crosses zero for both charges in the TPC region.

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The average magnitude of

<a1> is ~ 10-4.

Its corresponding contribution to the correlator,

<a1><a1>, will be safely negligible.STAR Preliminary

Systematic check: a1{ZDC-SMD} S. Voloshin, PRC 70 (2004) 057901

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Systematic check: η gapST

AR

Prelim

inary

The same-sign correlation approaches zero when the η gap increases.

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Systematic check: pT gap

The non-zero same-sign correlator for pT gap > 200 MeV/c indicates that we are safe from HBT or Coulomb effects.

STA

R P

reliminary

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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

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Summary IIThe 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 v1, a1,η gap, and pT gap.

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Interpretations

-

+

ΨRP

+

-

Out-of-Plane Charge Separation

Interpretation 1:

ΨRP

Flowing “structures”

Interpretation 2:

X

XX

XX

X

X = unknown structure

Implies Local P-violation of strong interactions

Does Not Imply P violation of the

strong interactions

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Interpretation 2

-+ ΨRP+ -

charge conservation/cluster + v2

Scenario 1: Scenario 2:

Need some investigation

-+ ΨRP+ --+

charge conservation/cluster + v1 symmetry fluctuation

STAR Collaboration, PRL103 (2009)251601

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Alternative measurements

These observables contain all possible (mixed) harmonic terms, while the correlator observables previously shown contain only one.

Charge asymmetry correlation

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Alternative measurements

STAR preliminary

d+Au

Same-sign:- δ‹A2›UD > δ‹A2›LR

- meets LPV expectation- δ‹A2› < 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!

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OutlookWith zero net charge, the neutral particles are expected to be much less affected by the electric field.

Λ, Ks0 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 v2 to test the theory.

CP-violating decays η→π+π- et al.R. Millo and E. V. Shuryak, arXiv:0912.4894

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Back-up

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Systematic check: EP resolution

anti-hypernuclei production and search for p-odd domain formation at rhic

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