Spontaneous Parity Violation in Strong InteractionsDhevan Gangadharan (UCLA)On behalf of the STAR CollaborationWWND 2009

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Parity and How it’s Violated

•Parity transformation – a spatial inversion of a system’s coordinates.

Two classes of Parity Violation:1. Explicit parity violation

Occurs in Weak Interactions▫ Confirmed

2. Spontaneous parity violation Predicted to occur in Strong Interactions

▫ Not yet confirmed (that’s what we are working on)

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xx

Parity Violation in Weak Interactions

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S

e- e-

Co-60 beta decay

This is an Explicit parity violation because a parity violating term is explicitly seen in the

Weak Lagrangian

S

e-e-

P transformation

Experimentally observed Not Experimentally observed

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Parity Violation in Strong Interactions First Ingredient:

Vacuum Transition

NCS= -2 -1 0 1

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•NCS is the Chern-Simons number and it characterizes the particular gluon field configurations we may create at RHIC.

• The potential energy of the gluon field is periodic in one direction and oscillator-like in all other directions in functional space.

Potential Energy of the Gluon Field

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Parity Violation in Strong InteractionsSecond Ingredient:

An Extremely Large Magnetic Field

• Spectator nuclei create a very large magnetic field in the QGP region.• STAR TPC Magnetic field is only .5 T• Largest steady magnetic field created by man ~ 15 T• Spectator magnetic field @ (1 fm/c and b=4fm) ~ 1012 T = 1 Trillion Tesla

Parity Violation in Strong Interactions

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Ingredient 1 + Ingredient 2 -> Electric field Ey

An Ey will then produce charge separation.

This is Spontaneous parity violationsince the sign of Ey goes according to the spontaneously chosen sign of NCS and is not determined by the initial

conditions of the collision

• Kharzeev et al. arXiv : 0406.125v2

0706.1026v2

0711.0950v1

0808.3382v1

The Chiral Magnetic Effect

De-confinement is a must!

Looking For Charge Separation

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1 1

2

3

,3

sin2cos212

1

n nRPnRPn

TT

nanvdydpp

Nd

pd

dNE

For this analysis we are particularly interested in a1

Looking for Charge Separation•Charge separation is given by a ≠ 0 in

•However, will vanish when averaged over many events because of the equal presence of

+1 and -1 NCS states.

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RPad

dN

sin21

RPsin

Looking for Charge Separation•Thus, one must use correlation techniques:

•This correlator is P-even. It is therefore susceptible to non-parity violating processes.

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c

cRPRPRPRP

cRP

c

vaa

v

v

,2

,2

,2

sinsincoscos

2cos

2cos

S. A. Voloshin, Phys. Rev. C 70, 057901 (2004)

Typically we scale this by v2,c

A Theoretical Prediction for AuAu 130 GeV

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Kharzeev et al.arXiv:

0711.0950v1This plot represents just one possible experimental result and based on some assumptions such as the magnitude of the:1.Vacuum transition rate2.Magnetic field strength

Experimental result in 200 GeV AuAu roughly obeys this trend and order of magnitude

Cuts Applied to Data

•-30 cm < Primary Vertex Z < 30 cm•-1 < eta < 1

•Pt > .15 GeV/c

•Pt < 2 GeV/c for Pt integrated plots•At least 15 TPC hit points required

•#hit points/#possible hit points > .52

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There are many independent STAR analyses on this subject which are consistent with each other. The work presented here represents only a

small selection of our results

Other Contributions to our Correlator

P-even processes may make a Contribution

• Flowing Resonances▫ A resonance may be

flowing elliptically (in-plane) and decay into 2 charged particles which may exhibit charge separation.

• Jets▫ Since they are clusters of

correlated charged particles, jets may fake a signal.

Acceptance Effects may make a

Contribution• Re-Centering

▫ The effect of this type of acceptance correction will be demonstrated in this talk.

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sinsinsin

coscoscos

c 2cos

We take the contribution from flowing resonances to our correlator to be

We estimate the average over resonances from an upper estimate of non-flow azimuthal correlations in 200 GeV AuAu data from .

And the total contribution is found to be less than1% of a1

Background Contributions

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1. Flowing Resonances may fake a signal

001.

2

2cos

ch

resresres

N

f

Too small to fake a signal

ch

cresresresres

resRP

N

vvf

2

2cos

2cos

,2,2

STAR Collaboration, J. Adams et al., Phys. Rev. Lett. 92, 062301 (2004).

fres represents the fraction of charged particles coming from a resonance.

We take the contribution from jets to our correlator to be

We estimate the first term from distributions in 200 GeV AuAu data.

And the total contribution is found to be ≈10-7

Background Contributions

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event

pairs

jet

pairs

event

jet

jetRP N

NN

2cos

2. Jets may fake a signal

trigassocd

dN

038.2cos JetRP

Too small to fake a signal

Our Correlator in Simulated Data

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Preliminary result

•None of these models incorporate correlations generated by the Chiral Magnetic Effect!• Study done by : Evan Finch (Yale), Ilya Selyuzhenkov (Indiana), Sergei Voloshin

(Wayne State)

Acceptance Correction Study in Simulated Data

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Before Re-Centering After Re-Centering

The act of Re-Centering, i.e. , does not remove the signal coscoscos

Centrality Bin Centrality Bin

Study done by Alexei Chikanian (Yale)

Preliminary resultPreliminary result

Acceptance Correction Study with Identified Pions in AuAu200

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Electrons Rejected

Study done by Jim Thomas(LBNL)

Before Corrections After Corrections c 2cos c 2cos

Preliminary result Preliminary result

Conclusions• Heavy Ion Collisions at RHIC might produce

spontaneous parity violation of the strong interactions .

• The magnitude and gross features of a theoretical prediction have been presented. However, more theoretical calculations of the expected signal would be very helpful.

• So far, no P-even processes which could masquerade as the result we see have been identified.

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The STAR parity-v group•Indiana: I. Selyuzhenkov •BNL: V.Dzhordzhadze, R. Longacre, Y. Semertzidis, P. Sorensen •LBNL: J. Thomas •Yale: J. Sandweiss, E. Finch, A.

Chikanian, R. Majka •UCLA: G. Wang, D. Gangadharan •Wayne State: S. Voloshin

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More information about this analysis can be found in Sergei Voloshin’s QM08 Poster

“Probe for the (Strong Interaction) parity violation effects in heavy ion collisions with three particle correlations”