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Can baryon stopping explain the breakdown of constituent quark scaling and proposed signals of chiral magnetic waves at RHIC?. John Campbell Hot Quarks 2012 – 10/16/12. Outline. NCQ Scaling Breakdown of NCQ Phase Change? Chiral Magnetic Waves? Baryon Stopping? Multi-component coalescence - PowerPoint PPT Presentation
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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”