Transcript "Have we seen Local Parity Violation at RHIC?"

Have we seen Local Parity
Violation at RHIC?
●
Introduction
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What the present data tell us
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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 onjecture
Press Release
Think
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J. Liao, BNL workshop, April
2010
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The basic observable
Py (out-of-plane)
Y (out-of-plane)
B
curren
t
X (in-plane)
Px (in-plane)
Momentum
space
Coordinate
space
Charge Separation or
Electric 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
→
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)
Concentrate on same sign pairs for the
moment
Set
Py(out-ofplane)
+
+
Px(inplane)
for both
configurations
Py(out-ofplane)
+
+
Px(inplane)
How to distinguish?
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The STAR measurement
(which not so many discuss)
Add
Py(out-ofplane)
+
+
to the mix
Px(inplane)
Py(out-ofplane)
+
opp.
sign.
same
sign
+
Px(inplane)
Data favor in-plane back-to-back correlation
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J.
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The bottom line
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Using simple math
Same
Charge
out-ofplane
STAR measures for same sign pairs in
Au+Au:
inplane
Therefore:
No out-of-plane correlation for same charge pairs
Opposite
charge:
opp.
Charge
out-ofplane
inplane
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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
?
Implies: “background” correlations are independent of reaction
plane
Two particle
density:
Reaction plane dependence always enters via v2 !
Pt – and eta dependence of v2 needs to be taken into
account
Prominent example: HBT with respect to the reaction
plane
Sources discussed in context of CME:
Clusters (STAR, F. Wang), Resonances (STAR), .Anomaly (Asakawa et al)...
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Pt-dependence
Correlated pairs are
only moderately harder
than
thermal pairs
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Alternative observable
Quadrupol
e
moment
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Reaction plane
angle
Charged
dipole
moment
Charged
dipole
angle
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Extract dipole moment and angle
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J.
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J.
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Correlations can lead to similar dipole angel; but reduce magnitude
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Summary
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Data favor in-plane back-to-back
correlation for same charge
–
●
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CME predicts out of plane
+
Presence of CME requires
fine-tunining: Background = - CME ?
+
Px(inplane)
Need differential information on
–
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Py(out-ofplane)
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 !?
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