Hump backed distribution without jet reconstruction in direct hadron correlation
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Hump-backed distribution without jet reconstruction in direct- -hadron correlation. M. J. Tannenbaum Brookhaven National Laboratory Upton, NY 11973 USA. DNP 2008 Oakland, CA October 26, 2008. isolated photons. . q. Compton. g. q. . q. Annihilation. g. q.

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Hump backed distribution without jet reconstruction in direct hadron correlation
Hump-backed distribution without jet reconstruction in direct--hadron correlation

M. J. Tannenbaum

Brookhaven National Laboratory

Upton, NY 11973 USA

DNP 2008 Oakland, CA October 26, 2008


Direct photon production simple theory hard experiment

isolated direct-photons









Direct photon production-simple theory hard experiment

See the classic paper of Fritzsch and Minkowski, PLB 69 (1977) 316-320




Analytical formula for -jet cross section for a photon at pT, yc (and parton (jet) at pT, yd):

fg(x) and F2(x) are g and q pdf’s in nuclei A,B


Experimental problem is HUGE background from direct-0, , etc. But this is less of a problem in Au+Au due to suppression of 0

x (1.19)=0.335



Direct direct-'s in p-p s=200 GeV: Data vs. pQCD



PHENIX PRL 98 (2007) 012002

Published results 3<pT<15 GeV/c

Preliminary results for 5<pT<24 GeV/c


Direct direct-'s in p-p are Isolated

Fraction of inclusive photon spectrum

PHENIX PRL 98 (2007) 012002

Fragmentation photons <10% of direct  for pT > 6 GeV/c in agreement with GRV


Comparison with other p p data and pqcd
Comparison with other p-p data and pQCD direct-

P. Aurenche et al Phys. Rev. D 73, 094007 (2006)

PHENIX direct photon p-p data clarifies longstanding data/theory puzzle

PHENIX PRL 98 (2007) 012002


2 particle correlations kinematics

p direct-Tt


pout=pT sin

is the jet fragmentation variable: zt and za

is a typical Fragmentation Function, b~ 8-11 at RHIC

Due to the steeply falling spectrum, the trigger fragment e.g.0 is biased towards large zt, , while unbiased

xE pTt

2-particle Correlations: Kinematics

From Feynman, Field and Fox: the xE distribution corrected for <zt> measures the unbiased fragmentation function

Wrong for a fragment! Correct for direct- zt=1


Hp2008 phenix isolated direct h correlations in s 200gev p p collisions


Isolated Direct- away side xE


HP2008 PHENIX isolated-direct--h correlations in s=200GeV p-p collisions

xE pTt


0 h and isol h x e distributions are different
direct-0-h and isol--h xE distributions are different

Modulo kT, the xE distribution opposite the direct- IS the fragmentation function of a jet of pT=-pT


The holy grail h correlations in au au
The Holy Grail: direct--h correlations in Au+Au

X-N. Wang and Z. Huang PRC 55, 3047 (1997)

MJT-should scale the z axis to see the energy loss (not take the ratio)


Prediction of jet shape in vacuum and medium

Borghini & Wiedemann, hep-ph/0506218 direct-

Prediction of Jet shape in vacuum and medium

Would be much easier to understand if they also plotted z in addition to =ln(1/z): e.g =3.0z=0.050


Why use the hump backed distribution is better than z
Why use the Hump-backed distribution? direct-Is  better than z?

  • Evolution is predictable in MLLA QCD and is signature for coherence for small values of z<0.1. [Dokshitzer, et al, RMP60, 373(1988)]

  • Emphasizes the increase in emission of fragments at small z due to the medium induced depletion of the number of fragments at large z.

  • An extra benefit for LHC (apart from the very low z) is that it was assumed by Borghini&Wiedemann that full jet reconstruction would be required in order to find the energy of the jet.

  • However, it was shown at LEP that if the energy of the jet were known, e.g. for dijet events at a precisely known s in e+e- collisions, then both z and =ln(1/z) distributions could be obtained without jet reconstruction.


From single inclusive 0 at z 0 l3 thank you sam ting

L3, PLB 259 (1991)199-208 direct-

 from single inclusive 0 at Z0--L3. Thank you Sam Ting

We should be able to do this from -0 or -h away side correlations in p-p (almost there, convert xE plot to ) and Au+Au to get a Tannenbaum,Ting,Wang,Wiedemann (in alphabetical order) plot


Can make the ln 1 z plot from h correlations tannenbaum ting wiedemann wang plot
Can make the direct-=ln(1/z) plot from -h correlations Tannenbaum-Ting-Wiedemann-Wang plot

Is this (linear) plot better for observing or measuring the medium effect in Au+Au than the plot in the standard fragmentation variable z? We need the -h correlations in Au+Au to decide.


h direct--h correlations in Au+Au: Away-side yield vs xEpTa/pTt is steeper in Au+Au than p-p indicating energy loss

h(4<pTt<5 GeV/c)--h

PHENIX AuAu PRC 77, 011901(R)(2008)



Extras direct-


Qm2005 direct in auau via internal conversion

e direct-+






= Kroll-Wada

QM2005-direct  in AuAu via internal conversion

Kroll Wada PR98(1955) 1355

PHENIX NPA774(2006)403

Eliminating the 0 background by going to 0.2<mee<0.3 GeV enables direct  signal to be measured for 1<pT <3 GeV/c in Au+Au. It is exponential, does that mean it is thermal. We must see whether p-p direct  turns over as pT 0 as in Drell-Yan or exponential like for 0


Qm2008 direct in p p via internal conversion

μ direct- = 0.5pT

μ = 1.0pT

μ = 2.0pT

QM2008 direct  in p-p via internal conversion


Lowest pT direct  ever measured in p-p (and Au+Au). Curves are pQCD extrapolated (W.Vogelsang)

This is a major discovery, p-p result turns over as pT0, follows the same function B(1+pT2/b)-n used in Drell Yan [Ito, et al, PRD23, 604 (1981)] . Fit to Au+Au is [A e-pT/T + TAA Bpp(1+pT2/bpp)-npp]. Significance of exponential (thermal?) is > 3 