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
2
Introduction & Motivation
Our measurement– Hypertriton invariant yield
– Lifetime measurement
– H-dibaryon search
Conclusion
Outline
3
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
4
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
5
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
6
RHIC BRAHMSPHOBOS
PHENIXSTAR
AGS
TANDEMS
Relativistic Heavy Ion Collider (RHIC)
7
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
8
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)
9
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
10
Daughters identification
Clean (<0.65GeV) and 3He (>2GeV) identification from TPC
STAR preliminary)
/
/ln( th
dxdE
dxdEz
11
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
12
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
13
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
14
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
15
New hypertriton lifetime result
STAR 2012 preliminary result:STAR 2010+2012 combined fit:
STAR preliminarySTAR preliminary
16
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.
17
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.
18
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