production in p+p and au+au collisions at 200 gev in star
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production in p+p and Au+Au collisions at 200 GeV in STAR
Rosi Reed
UC Davis
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 for STAR
• eV – Electron Volt = 1.6 x 10-19 Joules
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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
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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 been found
Does not include gravity, dark matter, or dark energy
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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 = 1/40ħc
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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• Each multiplies result by ~1
– QCD is not perturbative at low energies• Mediated by gluons
– Color+anti-color but not colorless!
– Spin 1– Mass 0– Can interact with each other!
g
Feynman diagram
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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
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Heavy Ion Collisions At STAR we use Gold Ions
Gold is nearly spherical
197 protons and neutrons
Allows us to study the energy range
E > Edeconfinement
E < EAsymptotic freedom
Ions look like “pancakes” due to relativistic length contraction!
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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 !
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QCD Phase diagram
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• 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
• Temperature of deconfinement
– Initial T of QGP at STAR = ? > Tc
Heavy ion collisions = HOT matter
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RHIC BRAHMSPHOBOS
PHENIXSTAR
AGS
TANDEMS
Relativistic Heavy Ion Collider (RHIC)
2 km
v = 0.99995c = 186,000 miles/sec
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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
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: 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
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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)
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Suppression of (1S+2S+3S)• Quarkonia = heavy quark+anti-quark meson• 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
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Melting of Quarkonia
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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)
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STAR Detectors Tracker (TPC)
Tracking momentum
ionization energy loss electron ID
Calorimeter (BEMC)
Measures Energy
magnet
beam
E/p electron ID )(
c
BvqF
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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%
PDG Values
Decay channel: e+e−
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
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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
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A STAR Event
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A STAR Event
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E2 Cluster
E1 Cluster
STAR Trigger pp
Data
Data
AuAu
Rejection~105 in p+pCan sample
full luminosity
One in 109 p+p collisions will have a !
pp
Data
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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
Contamination
Electrons from will be here
Phys. Rev. D 82 (2010) 12004
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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++
Phys. Rev. D 82 (2010) 12004
Rosi Reed - SJSU 9/16/2010 27
in p+p 200 GeV
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
Phys. Rev. D 82 (2010) 12004
Phys. Rev. D 82 (2010) 12004
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STAR vs. theory + world data
STAR 2006 √s=200 GeV p+p ++→e+e- cross section consistent with pQCD and world data trend
Phys. Rev. D 82 (2010) 12004
Rosi Reed - SJSU 9/16/2010 29
Measuring in Au+AuHow many p+p collisions = 1 Au+Au collision?
0-60% Centrality
RefMult# charged particles # collisions
RefMult is the observable
# collisions per centrality based on model
Bright Colors = collision
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in Au+Au 200 GeV
4 Million Events 4.6 significance95 Signal counts
First Heavy Ion Measurement!
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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
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Temperature!
Ratio of (1S+2S+3S) =
0.92Some suppression of (3S)T =0.8 Tc
0.53 (lower bound) Suppression of (2S+3S) T = 1.2 Tc
1.28 (upper bound) T << Tc not physical
140 < T < 210 MeV
S. Digal, P. Petreczky, and H. Satz, Phys. Rev. D 64, 094015 (2001)
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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 140 < T < 210 MeV– Indicates we will be able to set an
upper limit with more statistics!
• Future Measurements– 3x more p+p data from 2009– 4x more Au+Au data from 2010– Improve Temperature Precision
Phys. Rev. D 82 (2010) 12004
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