The hypernuclei program at RHIC-STAR

Jinhui Chen for the STAR CollaborationShanghai Institute of Applied Physics, CAS

The 11th International Conference onHypernuclear and Strange Particle Physics

" HYP2012 " October 1 - 5, 2012Barcelona, Spain

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Introduction & Motivation

Our measurement– Hypertriton invariant yield

– Lifetime measurement

– H-dibaryon search

Conclusion

Outline

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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

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Hypertriton lifetime measurementPrevious measurement (before 1973)Use nuclear emulsion or bubble chamberAccepted events: less than 80

STAR 2010 Measurement

STAR 2012 Measurement

Previous measurement STAR Collaboration, Science 328 (2010)58

Run4 200GeV MB 22M

Run4 200GeV Central 23M

Run7 200GeV MB 68M

Run10 200GeV MB ~223M

Run10 200GeV Central ~199M

Run10&11 low energies

MB ~213M

It is promising to obtain an improved lifetime measurement using the new data

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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

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

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RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

Relativistic Heavy Ion Collider (RHIC)

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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

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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)

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Run10 7.7GeV MB ~4M

Run10 11.5GeV MB ~11M

Run11 19.6GeV MB ~31M

Run11 27GeV MB ~49M

Run10 39GeV MB ~118M

Run10 200GeV MB ~223M

Run10 200GeV Central ~199M

Run7 200GeV MB ~56M

Datasets and event statistics

Datasets and track selection

Analysis method: secondary vertex finding technique•Identify 3He and candidate•Find the V0 position from daughters pairing•Plot the invariant mass dis. of daughters•Combinatorial background analysis

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Daughters identification

Clean (<0.65GeV) and 3He (>2GeV) identification from TPC

STAR preliminary)

/

/ln( th

dxdE

dxdEz

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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

H3ΛStatistics: Run7+Run10+Run11 MB+Central, ~610M events

bin width 4MeV bin width 2MeV

STAR preliminarySTAR preliminary

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Signal in BES(1)

Hypertriton signal from STAR BES at =7.7, 11.5, 19.6GeV

7.7GeV 11.5GeV 19.6GeV

Events ~4M(MB) ~11M (MB) ~31M (MB)3He(anti) 8587(0) 7161(0) 6321(0)

Hypertriton 46±17 41±17 42±14

Details in the analysis

STAR preliminarySTAR preliminary

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Signal in BES(2)

Hypertriton signal from STAR BES at =27, 39, 200GeV

27GeV 39GeV 200GeV

Events ~49M(MB) ~118M(MB) ~223M(MB)3He(anti) 5312(19) 6456(133) 5822(2213)

Hypertriton 46±16 88±21 83±20

Details in the analysis

STAR preliminarySTAR preliminary

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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 preliminarySTAR preliminarySTAR preliminary

STAR preliminary

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New hypertriton lifetime result

STAR 2012 preliminary result:STAR 2010+2012 combined fit:

STAR preliminarySTAR preliminary

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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.

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correlation function

A. Ohnishi, HHI workshop 2012/2

Scattering length (a0) 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.

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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