Have we seen Local Parity Violation at RHIC?

/home/vkoch/Desktop/INT2010/parity_talk.odp

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Have we seen Local Parity Violation at RHIC?

● Introduction● What the present data tell us● Alternative observable

Based on: Adam Bzdak, VK and Jinfeng Liao, PRC81 031901(R) (2010), [arXiv:0912.5050] J. Liao, VK, and Adam Bzdak, in preparation


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CPT is in good shape

C

P

T

onjecture

ress Release

hink


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J. Liao, BNL workshop, April 2010


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The basic observable

X (in-plane)

Y (out-of-plane) Py (out-of-plane)

Charge Separation orElectric Dipole in Pt Space(along out-of-plane direction)

Complications:• hard to identify direction of magnetic field (reaction plane)P. E-by-E• Direction of dipole either parallel OR anti-parallel to magnetic field

Px (in-plane)

Momentum space

Coordinate space

Bcurrent

→ only variance of parity-odd operator can be observed


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The STAR measurement(which everybody discusses)


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The STAR measurement(a closer look)

Py(out-of-plane)

Px(in-plane)

+

Concentrate on same sign pairs for the moment

+

Set

Py(out-of-plane)

Px(in-plane)

++

for both configurations

How to distinguish?


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The STAR measurement(which not so many discuss)

Py(out-of-plane)

Px(in-plane)

++

Py(out-of-plane)

Px(in-plane)

++

Data favor in-plane back-to-back correlation

Add to the mix

same sign

opp. sign.


8J. Liao


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The bottom line


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Using simple math

STAR measures for same sign pairs in Au+Au:

Therefore:

No out-of-plane correlation for same charge pairs

Opposite charge:

in-plane

in-plane

out-of-plane

out-of-plane

Same Charge

opp. Charge


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Saving the chiral magnetic effect...


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The argument in the STAR papers:Bout, Bin = Background (in and out of plane)P = Parity violating signal

Thus:

The data show

Thus existence of CME would require:

●“Juuuuust right scenario” a.k.a fine tuning !!!●We need to understand the background●We need differential information on


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Do we understand the background

NO!


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How realistic is the assumption ?

Two particle density:

Prominent example: HBT with respect to the reaction plane

Implies: “background” correlations are independent of reaction plane

Reaction plane dependence always enters via v2 !Pt – and eta dependence of v2 needs to be taken into account

Sources discussed in context of CME: Clusters (STAR, F. Wang), Resonances (STAR), .Anomaly (Asakawa et al)...


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Pt-dependence

Correlated pairs areonly moderately harder thanthermal pairs


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Alternative observable

Quadrupolemoment

Reaction planeangle Charged dipole

momentCharged dipoleangle


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Extract dipole moment and angle


18J. Liao


19J. Liao


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Correlations can lead to similar dipole angel; but reduce magnitude


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SummaryPy(out-of-plane)

Px(in-plane)

++

● Data favor in-plane back-to-back correlation for same charge– CME predicts out of plane

● Presence of CME requires fine-tunining: Background = - CME ?

● Need differential information on– Be aware that pt- and eta

dependencemay be differernt● Alternative observable: measure

charge dipole (orientation and magnitude)

● How about proton-proton????


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Conclusion

NO definitive evidence for local parity violation!

Yet !?

Documents

Have we seen Local Parity Violation at RHIC?