# Presentation: 917300

## Dhevan Gangadharan

**Dhevan Gangadharan**
**UCLA**
**STAR Collaboration**
**DNP meeting**
**10/25/08**

## Outline

-  Examples of Weak Parity Violation
-  The Theory of Parity Violation in the strong interactions
-  The STAR experimental result
-  Outlook/Conclusions

## Examples of Weak Parity Violation

- _Beta decay of Co-60_

- _In flight Pion decay_

- S

- e-

- e-

- Electrons are _***preferentially***_ emitted opposite the spin of the nucleus

- Muons are _***preferentially***_ polarized along the direction of the Pion’s motion

- Wu. et al.
- Physical Review 105(4), 1957

- Garwin. et al.
- Physical Review, **105(4), 1957**

## Spontaneous Parity Violation in Strong Interactions

- This can occur through _*The Chiral Magnetic Effect*_:
-                                                        Kharzeev et al.  arXiv: 0808.3382

- The Chiral Magnetic Effect
- _Ingredient 1of 2_
-  The Vacuum Structure undergoes a Transition

**Sphaleron**

## The Chiral Magnetic Effect

- _Ingredient 2 of 2_
-  A Non-zero background Magnetic field

-  Spectator nucleons create a Magnetic Field

## The Chiral Magnetic Effect

- _As a consequence:_
-  An Electric Field parallel to the Magnetic Field is created

## The Chiral Magnetic Effect

- _The End Result_
-  The Electric Field will cause _charge separation _relative to the reaction plane

- For a given topological charge the E-M current direction has a _***preference.***_
_***This is Parity Violation***_

-  Charge separation represents an E-M current perpendicular to the reaction plane

## Looking for Charge Separation

-  Transitions to -1 Topological charge are just as likely.
-  +1 and -1 states yield opposite E-M currents.
-  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 states.
- Thus, one must use correlation techniques:

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

## The STAR detector at RHIC

- Tracking of particles is done by the TPC (light grey region)
- AuAu 200 GeV collisions used for this analysis.

##  Opposite charge combinations show a distinctly different trend than same charge combinations.

-  This trend is in accord with theory since          should be of opposite sign than

- STAR Preliminary

- More plots of this correlator with different systems and against different variables can be found at            arXiv:0806.0029

## Next.....

-   Rule out non-P violating contributions to our observable (Our correlator is a P-even quantity)
-   Reconstructed particles (Λ, Ξ) can be used to replace particle  _a_ in:
- to determine whether the same asymmetry persists.  This is interesting since in principle  the electric field generated can affect all three constituent quarks before they coalesce.  A Ξ contains 3 negative quarks whereas a Λ contains a mixture of positive and negative quarks.

- Λbar

- Λ

## Conclusions

-   Heavy-Ion collisions might create Spontaneous Parity violating processes in Strong Interactions.
-   The gross quantitative and qualitative features of  the correlation used in this analysis are in accord with theoretical expectations.