Jet Probes at RHIC

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Jet Probes at RHIC

• Justin Frantz
• Stony Brook University
• FRIF Workshop on QCD Power Corrections
• January 13, 2006

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The Heavy Ion/QGP Mission

• in the context of this workshop
• See qs/gs outside of pQCD
• (Often delicate) NP effects in pQCD jet event
  shape
• Lattice QCD predicts deconfinement phase change
  ? a Quark Gluon Plasma
• Specifically, observe collective behavior of many
  q/gs in this plasma?
• Larger Scale observables
• Temperature, Pressure, Density
• Also how does it modify particle physics?
• Chiral symmetry restoration?
• Color screening melts J/Psi?
• aS modified _at_ finite Temp.

Lattice Calculation
Energy Density / T4
pion gas
T/TC
TC estimates 170 MeV
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RHIC

• The Relativistic Heavy Ion Collider QGP Search

STAR
NYC
RHIC

• Collides AuAu, pp, dAu, CuCu, at energies vs
  , 20, 62, 130, 200, 400, 500 GeV
• Polarized proton beams, Spin program ? probe
  gluon spin structure

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Highlights of Basic Results

• Runs 1/yr 2001-2006 interesting yield of
  results
• Requisite Densities
• Thermalization success of statistical models w/
  T in the critical range
• Hydrodynamic Flow Too large for ideal QGP but
  evidence against hadron gas
• Baryon/Meson flow vs pT follows (common!) quark
  number scaling instead of mass scaling
• Hydro-models with only hadrons fail to reproduce
• Hadron cross sections (esp. strange) too small to
  build it up
• Large Baryon Excess at soft-hard transition
  energies (p/p 1)
• Recombination of quarks promising way to explain
• Strongly interacting QGP
  (sQGP) perfect liquid

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Hard Scattering Probes
AuAu ? gdirect X
AuAu ? p0 X
pp ? p0 X

• Hard scattering in AuAu ? pQCD (works well in
  pp)
• Insert into HI medium, observe differences
• E.g. high pT hadron and direct photon production
• High pT spectral shapes clearly power law as
  expected for all centralities
• And same shape same as pp

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RAA

• Ratio of AA/ scaled pp
• Scaling factor number of equiv NN crossings
  (Ncoll)
• FLAT
• Prediction jet energy loss leads to suppression
  effect for fragmentation products
• But not for EM direct photons
• Energy loss models depend on dN/dygluons
• Many models LPM effect, Modified D(z)
• ? Density!
• DE E was surprise (just E shift - like NP?)

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Elliptic Flow (v2)

• In semi-central events initial state spacial f
  anisotropy ? momentum space
• v2 second Fourier harmonic w/ w.r.t the
  (measured) global reaction plane
• 2 Kinds
• At low pT (soft), hydrodynamic (of quarks we
  believe)
• At high pT, energy loss of jet partons traversing
  the matter

PHENIX
dN/d?
Incl. Hadrons
pT 3-4 GeV/c
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Di-Jet Di-Hadron Correlations

• Huge Soft background (dN/dh 1000)
• Jet Finding difficult (Impossible?) in HI
  environment
• Rely on 2-particle opening angle (azimuthal)
  correlations
• 2 categories in pT Trigger (high pT) Assoc

6 5 4 3 2 1
Nearside Awayside
STAR
200 GeV pTtrig 5-10, pTassoc 1-2 GeV/c
h-h
AuAu
pp
PHENIX
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Experimental Method Flow Subtraction

• Assume 2-source correlation Flow Jet
• Main source of systematic error
• b0 determined by Zero Yield At Minimum (ZYAM),
  other methods

PHENIX p0h pTtrig 5-10 GeV/c pTassoc 3-5
GeV/c
Note scale
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First Results (High x Low pT)

• Jet suppression of awayside shape
• Nearside per trigger yield same
• Absolute NS yield suppressed
• At low pT, recovered

4-6 x 2-4 GeV/c
0.2
0.1
0.0
0
p
w/ pT,assoc ? 0.2 GeV/c
0
p
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High x High Re-emergence

• Low/No Background (Flow Sub. Unimportant)
• Clear emergence of jet structure at the away-side
• Away side width consistent with constant
• Away side yield suppressed

STAR Preliminary
8 lt pT(trig) lt 15 GeV/c
pT(assoc)gt6 GeV/c
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Really Weird! Low x Low

• Large modication on the awayside!
• Cone/ Volcano shape
• Medium response to the jets?
• Explained by
• Mach cone sound wave
• Color cerenkov cone
• Bending jets
• If Mach Cone, size ? vsound ? direct measure of
  matter property

2.5-4 GeV/c trig
STAR
1-2.5 GeV/c assoc
PHENIX
p
0
Df
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How Robust is The Volcano?

• Still questions about robustness (oversubtraction
  in v2?)
• Look _at_ trigger w.r.t. RP
• Over subtraction? opposite effect

In plane
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IAA etc.

• Looking for best way to analyze extracted jet
  (f-integrated) yields
• Good parameter pT, zT,xE ?
• IAA ratio of integrated per-trigger yield in
  AA/pp
• How does it fit together with RAA? Better
  quantity? Still open

An Eloss model Wang et. al.
Phys. Lett. B579 (2004) 299308.
STAR Awayside IAA ( RAA !)
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Direct g-Jet

• In central AuAu high suppression effect ? higher
  purity of direct g
• Complement of jet-jet Eloss
• Probes interior of collision volume
• Eg proxy for Ejet
• Extraction of gdirect-jet from ginclusive
  correlations underway

pp 200 GeV
gdir-jet
jet-jet
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Jet Event Shapes _at_ RHIC
What am I doing _at_ this workshop?

• Good things _at_ RHIC
• Not just AA pp, pA, polarized pp ( lots!)
• Dectectors optimized for soft physics (Good E,p
  resolution/ PID above 50 MeV) in addition to
  hard
• Bad things
• As hh, central rapidity restriction
• Ambiguity of Q/vs12
• In AuAuwell e.g. no jet finding (jets
  modified!)etc
• From your standpoint
• For pp, best source of low Q? (mid-h x ranges
  like Tevatron/LHC, but lower s)
• AuAu Interesting modification to hadronization
  could Power Correction frameworks say anything
  sensible? How about in dAu ?
• From HI experimentalist standpoint
• Want to use jets to probe medium event shapes
  are a natural goal

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Energy Energy Correlations

• Instead of muliplicity correlations, energy flow,
  correlations (combining info in all pT bins)
• No jet finding neccesary
• auto-convolution of JCEF ?other shape observable
  as correlations?
• Sensitive to aS , NP effects (plasma?)

(p c)
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EEC in hh?

• EEC never measured in hh?
• Structure Fn complication x1x2 distribution of Q
• But theory work says it should be possible
• Basham, Et al Use Tranverse EEC(f)
• Gale et. al. QGP multiple scatt. ? large effects
  to TEEC (hep-ph/9406208)
• Measured and used in DIS
  _at_ HERA (1 S.F.)

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EEC in AA

• 2 EECs in AA? sQGP has its own? (beyond
  flow?)
• Large flow harmonic contribution
• Extract Jet EEC
• Large underlying ET (shape
  distorting)
• Combinatoric pair subtraction
• PHENIX ½ f solid ang. ? missed ET even pp

Lokhtin et al., hep-ph/0402108
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Effect of Inaccurate ET

• Pythia study of EEC (200 GeV pp)

In PHENIX
ET (GeV)
Q (GeV)
Q (GeV)
Ratio to Blue (Arbitrary Norm)
EEC w/ Phenix ET Denom
EEC(f) A.U.
EEC w/ real Phx Acc
Q 10-15 GeV/c
EEC w/ true Q in Denom
EEC w/ ET in Denom
Df
Df
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Idea EEC Direct-Gamma Events

• Similar to the DIS t-channel
• Does it probe the same properties? (g/q jet)
• Ever done before?
• Two varieties
• only charged particles-Eg only
• Including neutral (w/ direct g)
• Is one better?

2Eg TRIG (GeV)
PYTHIA direct g events
Q (GeV)
PYTHIA direct g events Eg 10-15 GeV
EEC(f) A.U.
f
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Conclusions

• Interesting time at RHIC
• Jet/Hard observables continue to provide key
  information
• We see jet modification!
• Can we use traditional event shape?
• same perturbative inspired frameworks?
• Need help from theorists
• What can be calculated?
• What can be learned?

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Flat RAA? (Energy Loss)

• Example of using hard scattering probes

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Understanding RAA(Npart, ??)

• Can we find a consistent description of
  centrality and ?? dependence of RAA?
• Define with
• Perform survival-weighted average over all
  production points, emission directions.
• Survival weighting

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Energy Loss Calculations