Gang Wang ( for the STAR Collaboration )
UCLA
A colored and flavored system in collision ...

Exotic particle
S
Z
Exotic phenomenon
N
2

A nucleus containing at least one hyperon in addition to nucleons.
Hypernuclei of lowest A

3
H ( n


3
H ( n
 p p



)

)
No one has ever observed any antihypernucleus before us (STAR).
  p +

(64%);
  n +

0 (36%)
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
3

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
4

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

PHENIX
STAR
RHIC
AGS
TANDEMS
Animation M. Lisa
6

initial stage QGP and hydrodynamic expansion pre-equilibrium hadronization and freeze-out
CYM & LGT
 New state of matter: QGP
PCM & clust. hadronization
RHIC creates hot and dense matter, containing
NFD equilibrium in phase space population of u, d and s:
NFD & hadronic TM ideal source of hypernuclei string & hadronic TM ideal source of anti-nuclei
RHIC white paper: Nucl. Phys. A 757
7

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

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

3

H mesonic decay, m=2.991 GeV/ c 2 , B.R. 0.25

3
H
 3
H e
  

3
H
 3
He
  
 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.
QM09 proceeding: arXiv:0907.4147
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
10

3
3
z
 ln( dE dE
/ dx th
)
/ dx
Theory curve: Phys. Lett. B 667 (2008) 1
Select pure 3 He sample: 3 He: 5810 counts anti3 He: 2168 counts condition: 0.2 < z < 0.2 & dca < 1.0 cm & p > 2 GeV/c …
11

STAR Collaboration, Science 328 (2010) 58
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
3
Λ
H
 3
Λ
H
 3
H e/
3
He 59 ± 11
12

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

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

 
182
 89
45

STAR Collaboration, Science 328 (2010) 58
27 ps
We measure

PDG value


= 267 ± 5 ps

= 263 ± 2 ps
PDG: Phys. Lett. B 667 (2008) 1
15

N

(N
MB eve
N
MB part

N central eve
N central part
)/2
Coalescence =>

3
H
/

3
H

( p / p )( n / n )(

/

)
3
H e
3
/
He

( p / p )
2
( n / n )
0.45 ~ 0.77*0.77*0.77
Tabulated ratios favor coalescence
16

STAR Collaboration, Science 328 (2010) 58
Phase diagram plot: arXiv:0906.0630
RHIC is carrying out Beam Energy Scan as we speak.
Baryon-strangeness correlation: PRL 95
(2005) 182301 , PRC 74 (2006) 054901 ,
PRD 73 (2006) 014004.
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)
17

3
Λ
H has been observed for first time; 70 candidates, with significance ~ 4 s
.
H candidates, with significance better than 5 s .
157
 
182

45

27 ps , consistent with free
 lifetime (263 ps) within uncertainty.
The
Λ
H /
Λ
H ratio is measured as 0.49 ± 0.18 ± 0.07
3 He / 3 He is 0.45 ± 0.02 ± 0.04
, favoring coalescence.
, and
RHIC is the best anti-matter machine ever built!
18

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,
AGS-E906, Phys. Rev. Lett. 87, 132504 (2001)
Search for anti-α
19

Looking into a mirror, you see someone else…
It’s a parity violation?
!
Parity transformation :
A spatial inversion of the coordinates. x
  x
Origins of parity violation:
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.
1.
Global parity violation
Occurs in weak interactions
 Confirmed
2.
Local parity violation
Predicted in strong interactions
 we are working on it…
20

  
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.
dN d

 
1

2 a

 sin
  
RP

Kharzeev, PLB633:260 (2006)


Kharzeev, McLerran, Warringa, NPA803:227 (2008)
21

dN

 
1

2 a

 sin

   
RP
 d
A direct measurement of the P -odd quantity
“a” should yield zero.
S. Voloshin, PRC 70 (2004) 057901
Non-flow/non-parity effects: largely cancel out
Directed flow: vanishes if measured in a symmetric rapidity range
P-even quantity: still sensitive to charge separation
22

S. Voloshin, PRC 70 (2004) 057901 cos(


 


2

RP
)
 cos(


 


2

EP
)
EP resolution cos(


 


2


)
 v
2 ,

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.
23

• 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
SMD is 8 horizontal slats &
7 vertical slats located at
1/3 of the depth of the ZDC
ZDC side view
Transverse plane of
ZDC
Scintillator slats of
Shower Max Detector
24

cos(

1
 
2

2

RP
 cos(

1
 cos(


2
  east

  west
)
)

) east west
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 a
1

  
RP

   full
full
The results on the following slides are based on Au+Au collisions at 200 GeV, taken in RHIC run2007, except otherwise specified.
25

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

The + + and – – combinations are consistent with each other.
27

In the quark-gluon medium, there could be multiple P-odd domains.
The net effect is like a random walk , but one-dimensional.
What do we know about the position R n
R n after n steps?
follows a Gaussian distribution: mean = 0, and rms = n
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
.
28

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

1
S. Voloshin, PRC 70 (2004) 057901
STAR Preliminary
If v
1
( η ) is not antisymmetric around
η
= 0, then this term won’t vanish.
STAR Preliminary v
1
( η ) crosses zero for both charges in the TPC region.
30

1
S. Voloshin, PRC 70 (2004) 057901
The average
< magnitude of a
1
> is ~ 10 -4 .
STAR Preliminary
Its corresponding contribution to the correlator,
<a
1
><a
1
>, will be safely negligible.
31

The same-sign correlation approaches zero when the
η gap increases.
32

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

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

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.
35

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

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

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

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

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

41

42