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Can baryon stopping explain the breakdown of constituent quark scaling and proposed signals of

chiral magnetic waves at RHIC?

John CampbellHot Quarks 2012 – 10/16/12

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Outline

• NCQ Scaling• Breakdown of NCQ– Phase Change?– Chiral Magnetic Waves?– Baryon Stopping?

• Multi-component coalescence– Formalism– UrQMD Simulations

• Comparison of CMW and MCC to data• Summary

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Number of Constituent Quark (NCQ) Scaling

The “NCQ” scaling pattern of hadron at RHIC indicates flowing quarks, which then coalesce.

Low : Ordered by mass, consistent with Hydro

Intermediate : Ordered by baryon/meson

Scale each by Number of Constituent Quarks n, and

the curves all line up!

This Should break down at low if quarks are no longer dynamical degrees of freedom.

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What could cause NCQ to break down?• Maybe: Phase transition occurs!

• No partonic DoF → No NCQ• But no specific predictions...

• Maybe: Chiral Magnetic Waves occur! • Induced quadrupole moment gives negative particles

an in-plane boost• predict for negative particles always more than for

positive particlesBurnier, et al. Phys.Rev.Lett. 107 (2011) 052303

• Certainly: Baryon stopping occurs!• Data: At BES energies, ~50% of light

quarks at midrapidity are transported from the entrance channel

• what effect could this have...?

Midrapidity yields of common particles from central Pb+Pb collisions measured by the NA49/SPS Collaboration

6.41 GeV

J. Dunlop et. al., Phys.Rev. C84 (2011) 044914

At lower BES energies, ~50% of quarks are transported from the entrance channel!

Fractions of down (up) quarks

transported to midrapidity from

the entrance channel

8.86 GeVMore stopping…

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Basic Idea• Multi-component coalescence (MCC)

model:• two populations of quarks with

different flows• transported (stopped) quarks

with • produced quarks with

• hadronization by quark coalescence

What does MCC predict?• Hadron has two components: from

transported quarks and from produced quarks. In pions, for example:

∆ 𝑣2❑𝜋≡𝑣2

❑𝜋−

−𝑣2❑𝜋+¿=(𝑣2❑𝑇− 𝑣2

❑𝑃 ) ( 𝑋 𝑑𝑇− 𝑋𝑢𝑇 )¿

positive in MCC scenario

transported () quarks

produced () quarks

produced () quarks

Fractions of down (up) quarks transported to midrapidity from the

entrance channel

specific prediction

Multi-component coalescence

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MCC vs. CMWWhat does MCC predict?• Species dependence for sign of

What does CMW predict?• Negative particles get a boost: , regardless of

species

• is proportional to the Charge Asymmetry. The proportionality constant is the (positive) quadrople moment of the plasma.

∆ 𝑣2❑𝜋 ≈ 𝑟 𝐴±r > 0

∆ 𝑋𝑇≡ 𝑋𝑑𝑇− 𝑋𝑢𝑇 𝐴±≡𝑁+¿−𝑁−

𝑁+¿+𝑁 −¿¿

Prevalence of down quarks to be stopped over up quarks Charge Asymmetry

∆ 𝑣2❑𝜋=(𝑣2❑𝑇−𝑣2❑𝑃 )∆ 𝑋𝑇

• For pions, CMW and MCC give similar predictions: , in agreement with preliminary data

• CMW model goes further: predicts a positive correlation between and

• MCC model goes further: predicts a positive correlation between and

• To compare the two, we must examine the correlation between and

Why might it be a positive correlation? Well increased baryon stopping will…• Inject charge to midrapidity INCREASING • Enrich the down quark population more than the up quark population INCREASING • (event-by-event fluctuations of number of stopped baryons)

How are and correlated?

UrQMD: Pb+Pb, • Simulations show that and have a

strong negative correlation!• This means that MCC predicts a

negative correlation between and

• Negative slope and non-zero intercept• Can check with data!

∆ 𝑋𝑇

+¿∆ 𝑋𝑇

𝐴±

¿𝐴±

∆ 𝑣2❑𝜋 ∆ 𝑣2❑𝜋

Why might it be a negative correlation? But increased isospin will…• Inject charge to midrapidity INCREASING • Enrich the up quark population more than the down quark population DECREASING • (event-by-event fluctuations of isospin of stopped baryons)

• Surely both fluctuations occur. Which type dominates?

8𝐴±

∆ 𝑋𝑇

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Preliminary Data

STAR Preliminary

Shusu Shi for the STAR collaborationQuark Matter 2012

“Event Anisotropy v2 in Au+Au Collisions at √sNN = 7.7 – 62.4 GeV with STAR”

At low energies we see the same species dependence as predicted by

Multi-Component Coalescence!

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Preliminary Data

Gang Wang for the STAR collaborationQuark Matter 2012

“Search for Chiral Magnetic Effects in High-Energy Nuclear Collisions”

Preliminary data show a positive correlation between and , as predicted by Chiral Magnetic Waves

∆ 𝑣2❑𝜋 ≈𝑟 𝐴±r > 0

Summary• NCQ scaling implies partonic degrees of freedom→QGP• Can Baryon Stopping explain NCQ breakdown? Yes! ... but so

can Phase Change and Chiral Magnetic Waves• Neither explanation explains data fully

Phase ChangeNo specific predictions

Baryon Stopping + MCC

Species dependence for :

and are negatively correlated:

Chiral Magnetic Waves

, regardless of species:

and are positively correlated:

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Backup Slide – Slope Parameter at different energies

Gang Wang for the STAR collaborationQuark Matter 2012

“Search for Chiral Magnetic Effects in High-Energy Nuclear Collisions”