production in p+p and au+au collisions at 200 gev in star rosi reed uc davis

production in p+p and Au+Au collisions at 200 GeV in STAR

Rosi Reed

UC Davis

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Rosi Reed - SJSU 9/16/2010 2

Some Relevant Terms

• Standard Model – Theory that combines 3 out of the 4 fundamental forces

• Quantum Chromo-dynamics (QCD) – The strong force which holds the nucleus together

• Quark Gluon Plasma (QGP) – A hot, dense form of matter with free quarks

• Heavy Ion – Gold ions

• eV – Electron Volt = 1.6 x 10-19 Joules


Goals for this talk

• Introduce Relativistic Heavy Ion physics

• Explain the physics behind the Quark Gluon Plasma (QGP)

• Show how the meson can be used to probe the (QGP)– Measure the temperature


Standard Model

Fermions

Bosons

Describes interactions due to 3 out of 4 of the fundamental forces

Predicted the existence of the W, Z, gluons, top and charm before these particles were observed

http://bccp.lbl.gov/Academy/workshop08/08%20PDFs/chart_2006_4.jpg

Higgs is the only particle predicted that has not be found

Does not include gravity, dark matter, or dark energy


Electro-Magnetic Force• Quantum Electro-dynamics (QED)• 2 charges, + and –• Perturbation theory• Calculations done via Feynman diagrams

• Allows QED calculations to be truncated with very few diagrams

20

21

4 r

QQF

?e- e-

e+ e+

1st Order Contributions 2nd Order Contributions

+

Each multiplies result by 1/137


Strong Force• Quantum-Chromodynamics (QCD)• 3 charges called “colors”• All known stable particles are colorless

– Mesons have a quark and an anti-quark (ex. ) – Baryons have 3 quarks, 1 of each color (ex. protons)

• Only quarks and gluons can feel the QCD force• Mediated by gluons

– Color+anti-color but not colorless!– Spin 1– Mass 0– Can interact with each other!

g

Feynman diagram


Confinement in QCD: a cartoon

• At high energy and small distances, the strength of this force decreases!

• “Asymptotic freedom”• Nobel Prize 2004

http://nobelprize.org/nobel_prizes/physics/laureates/2004/illpres/index.html


Heavy Ion Collisions At STAR we use Gold Ions

Gold is nearly spherical

197 protons and neutrons

Allows us to study the energy range > deconfinement but < Asymptotic freedom

Ions look like “pancakes” due to relativistic length contraction!


Generating a deconfined state

Nuclear Matter(confined)

Hadronic Matter(confined)

Quark Gluon Plasmadeconfined !

Melting protons and neutrons: Hot quarks and gluons in (QCD)• heating• compression deconfined color matter !

Mike Lisa

Would be very cool to “reverse” the animation on the heating/compression slide, showing cooling/decompression.The point would be that even if we went into a QGP, the system would rapidly rehadronize (a process we don’t understand, but must, if we are to understand the strong force) into a hadronic system– hadrons in / hadrons out we will not “see” the QGP, but must infer it from hadronic patterns in the final state


QCD Phase diagram


• Room Temperature: 300 K = 0.025 eV

• Fire: 1000-2000 K: ~0.12 eV

• Sun :– Surface: 5000 K: ~0.4 eV– Corona: 5 x 106 K ~ 400 eV– Core: 15 x 106 K ~ 1 keV

• Heavy ion collision :– Tc ~ 173 MeV : 2 x 1012 K

– Initial T of QGP at STAR = ? > Tc

Heavy ion collisions = HOT matter


RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

Relativistic Heavy Ion Collider (RHIC)

2 km

v = 0.99995c = 186,000 miles/sec


RHIC: Some key results• Goal: Produce matter in the hot phase of QCD.

– What are its properties?– Is the system made up of quarks

and gluons?• Results and interpretation.

– Temperature is high.• All estimates > Tc

– Observation of collective fluid-like behavior of quarks

– High momentum particles aresuppressed

• Matter produced is nearly opaque to quarks and gluons

Sci Am May 2006. by W. Zajc.

STAR White Paper: Nuc Phys A 757 (2005) 102


: a probe of the QGP

• How hot is the matter formed at RHIC?– Is there a way to quantitatively measure

the temperature of the produced matter?

• Yes! Upsilon) production– bb quark Mesons

– Measure production in Heavy Ion collisions compared to proton-proton collisions


Heavy quark bound states• Non-relativistic Quantum

Mechanics– Schrödinger equation– Two particles bound by a linearly

rising potential V(r) ~ kr.

• Bound state of charm-anticharm– Charmonium– J/, ’ (ground state 1s, and excited

state 2s state)– Excited states have different <r>

• Bottom-antibottom– Bottomonium (1S, 2S, 3S)


Suppression of (1S+2S+3S)• Quarkonia = heavy quark+anti-quark meson

(bb,cc)

• b+c quarks are produced early in the collision– Makes them an excellent probe

• Quantifying suppression requires:– Baseline p+p measurement

• Sequential Suppression of the (1S+2S+3S) gives a model dependent temperature– Each state has a different “melting” temperature


Melting of Quarkonia


Measuring TemperatureSequential disappearance of states:

QCD thermometer QGP Properties

A .Mocsy, 417th WE-Heraeus-Seminar,2008

A. Mocsy and P.Petreczky, PRL 99, 211602 (2007)

Theoretical Expectations in 200 GeV Au+Au Collisions:

(1S) does not melt(2S)+J/ are likely to melt(3S)+(2S) will melt

A. Mocsy and P. Petreczky PRD 77 014501 (2008)


Measuringat STAR• (1S)

– m = 9.46 GeV– = 54 keV– BR(e+e-) = 2.5%

• (2S)– m = 10.02 GeV– = 32 keV– BR(e+e-) = 2.0%

• (3S)– m = 10.35 GeV– = 20 keV– BR(e+e-) = 2.2%

Decay channel: e+e−

PDG Values

BR = Branching Ratio = How often decays in that manner

= mass width due to finite lifetime

•Why look at di-elelectron channel?

•Di-lepton channel is clean

•STAR can only measure electrons out of e,,

Mproton = 0.938 GeV

Melectron = 0.511 MeV


Measuringat STAR• Using Einstein’s famous equation (c 1)

– unlike-sign electron pairs Signal + Background– like-sign electron pairs Background

2 22 2 21 2 1 2 1 21 2 2p p E E p p p p M

��222 pmE

Widths are larger than PDG values due to detector resolution

M is the invariant mass


STAR Detectors Tracker (TPC)

Tracking momentum

ionization energy loss electron ID

Calorimeter (BEMC)

Measures Energy

magnet

beam

E/p electron ID )(

c

BvqF


A STAR Event

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A STAR Event


E2 Cluster

E1 Cluster

STAR Trigger pp

Data

Data

AuAu

Rejection~105 in p+pCan sample

full luminosity

pp

DataOne in 109 p+p collisions will have a !


Electron ID

E/p and ionization energy loss (dE/dx) of tracks are used to select e+ and e- tracks

Combination allows greater purity

e

pK

arXiv:1001.2745v2 [nucl-ex]

Contamination

Electrons from will be here


Analysis TechniquesTrack pairs combined into:

e+e- = N+- = Signal + Background Unlike-Sign

e-e-,e+e+ = N--,N++ = Background Like-Sign

Signal calculated as:S = N+--2√N --N++



in p+p 200 GeVarXiv:1001.2745v2 [nucl-ex]arXiv:1001.2745v2 [nucl-ex]

3σ Signal Significance

N(total)= 67±22(stat.)1 b = 10-28 m2

Barn probability of an interaction between particles

At 200 GeV the total inelastic p+p cross-section is 42 mb


STAR vs. theory and world data

STAR 2006 √s=200 GeV p+p ++→e+e- cross section consistent with pQCD and world data trend



Measuring in Au+AuHow many p+p collisions = 1 Au+Au collision?

This will allow us to compare p+p and Au+Au yields directly!

0-60% Centrality

RefMult# charged particles # collisions

RefMult is the observable

# collisions per centrality based on model

Bright Colors = collision


in Au+Au 200 GeV

4 Million Events 4.6 significance95 Signal counts


1S+2S+3S) Ratio 0-60% Centrality

• Yield of (1S+2S+3S)– 78±15(stat:)+17/-22(sys.)

– Evidence that can be measured in heavy ion collisions

• Ratio of Observed/Expected– 0.920±0.35(stat.)+0.06/-0.18

– Indicates little suppression at RHIC energies


Temperature!(1S) = 69.0% of e+e- yield in p+p(2S) = 18.3% of e+e- yield in p+p(3S) = 12.7% of e+e- yield in p+pAssume Ratio of Observed/Expected > 0.2Ratio of (1S+2S+3S) = 0.92 = Some suppression

of the (3S) state T < Tc

Ratio = 0.53 (lower bound) = Complete suppression of the (2S+3S) state T < 2Tc

Ratio = 1.28 (upper bound) T << Tc and some new physics

T = Tc +Tc/-0 = 170 MeV +170/-0 MeV


Conclusions (1S+2S+3S) peak measured

in p+p collisions (1S+2S+3S) peak observed in

Au+Au collisions– Proof that can be measured in Heavy

Ion collisions!

• Temperature is 170 +170/-0 MeV

– Indicates we will be able to set an upper limit!

• Future Measurements– 3x more p+p data from 2009– 4x more Au+Au data from 2010– Improve Temperature Precision

Back-Up

production in p+p and au+au collisions at 200 gev in star rosi reed uc davis

Documents

rosi reed sjsu

e e e e

hot matter slide

star rosi reed uc davis

temperature slide

milessec slide

qcd force

qcd phase diagram slide