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

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  1. 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 DNP2008

  2. isolatedphotons  q Compton g q  q Annihilation g q Direct photon production-simple theory hard experiment See the classic paper of Fritzsch and Minkowski, PLB 69 (1977) 316-320 yc small-ignore yd 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 DNP2008

  3. Experimental problem is HUGE background from 0, , etc. But this is less of a problem in Au+Au due to suppression of 0 x (1.19)=0.335 /0=0.50 DNP2008

  4. Direct 's in p-p s=200 GeV: Data vs. pQCD p-p p-p PHENIX PRL 98 (2007) 012002 Published results 3<pT<15 GeV/c Preliminary results for 5<pT<24 GeV/c DNP2008

  5. 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 DNP2008

  6. Comparison with other p-p data and pQCD 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 DNP2008

  7. pTt pTa 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 DNP2008

  8. Isolated Direct- away side xE preliminary HP2008 PHENIX isolated-direct--h correlations in s=200GeV p-p collisions xE pTt DNP2008

  9. 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 DNP2008

  10. The Holy Grail: -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) DNP2008

  11. Borghini & Wiedemann, hep-ph/0506218 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 DNP2008

  12. Why use the Hump-backed distribution?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. DNP2008

  13. L3, PLB 259 (1991)199-208  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 DNP2008

  14. Can make the =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. DNP2008

  15. h-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) DNP2008

  16. Extras DNP2008

  17. e+ e- g* q g q = 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 DNP2008

  18. μ = 0.5pT μ = 1.0pT μ = 2.0pT QM2008 direct  in p-p via internal conversion arXiv:0804.4168v1 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  DNP2008