1. DNP2008 M. J. Tannenbaum 1/14/15 M. J. Tannenbaum Brookhaven National Laboratory Upton, NY 11973 USA DNP 2008 Oakland, CA October 26, 2008 Hump-backed distribution without jet reconstruction in direct-  -hadron correlation

2. DNP2008 M. J. Tannenbaum 2/14/15 Direct photon production-simple theory hard experiment See the classic paper of Fritzsch and Minkowski, PLB 69 (1977) 316-320 q qg  q q g  isolated photons Compton Annihilation small-ignore Analytical formula for  -jet cross section for a photon at p T, y c (and parton (jet) at p T, y d ): f g (x) and F 2 (x) are g and q pdf’s in nuclei A,B ycyc ydyd

3. DNP2008 M. J. Tannenbaum 3/14/15 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

4. DNP2008 M. J. Tannenbaum 4/14/15 Direct  's in p-p  s=200 GeV: Data vs. pQCD Published results 3<p T <15 GeV/c PHENIX PRL 98 (2007) 012002 p-p Preliminary results for 5<p T <24 GeV/c

5. DNP2008 M. J. Tannenbaum 5/14/15 Direct  's in p-p are Isolated Fraction of inclusive photon spectrum PHENIX PRL 98 (2007) 012002 Fragmentation photons 6 GeV/c in agreement with GRV

6. DNP2008 M. J. Tannenbaum 6/14/15 P. Aurenche et al Phys. Rev. D 73, 094007 (2006) PHENIX direct photon p-p data clarifies longstanding data/theory puzzle Comparison with other p-p data and pQCD PHENIX PRL 98 (2007) 012002

7. DNP2008 M. J. Tannenbaum 7/14/15 2-particle Correlations: Kinematics x E p Tt p out =p T sin  p Tt p Ta is the jet fragmentation variable: z t and z a 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 z t,, while unbiased From Feynman, Field and Fox: the x E distribution corrected for measures the unbiased fragmentation function Wrong for a fragment! Correct for direct-  z t =1

8. DNP2008 M. J. Tannenbaum 8/14/15 HP2008 PHENIX isolated-direct-  -h correlations in  s=200GeV p-p collisions Isolated Direct-  away side x E preliminary  x E p Tt

9. DNP2008 M. J. Tannenbaum 9/14/15  0 -h and isol-  -h x E distributions are different Modulo k T, the x E distribution opposite the direct-  IS the fragmentation function of a jet of p T =-p T 

10. DNP2008 M. J. Tannenbaum 10/14/15 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)

11. DNP2008 M. J. Tannenbaum 11/14/15 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 Borghini & Wiedemann, hep-ph/0506218

12. DNP2008 M. J. Tannenbaum 12/14/15 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.

13. DNP2008 M. J. Tannenbaum 13/14/15  from single inclusive  0 at Z 0 --L3. Thank you Sam Ting L3, PLB 259 (1991)199-208 We should be able to do this from  -  0 or  -h away side correlations in p-p (almost there, convert x E plot to  ) and Au+Au to get a Tannenbaum,Ting,Wang,Wiedemann (in alphabetical order) plot

14. DNP2008 M. J. Tannenbaum 14/14/15 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.

15. DNP2008 M. J. Tannenbaum 15/14/15 h  -h  correlations in Au+Au: Away-side yield vs x E  p Ta /p Tt is steeper in Au+Au than p-p indicating energy loss h  (4<p Tt <5 GeV/c )--h  PHENIX AuAu PRC 77, 011901(R)(2008)

16. DNP2008 M. J. Tannenbaum 16/14/15 Extras

17. DNP2008 M. J. Tannenbaum 17/14/15 QM2005-direct  in AuAu via internal conversion Kroll Wada PR98(1955) 1355 q  g q e+e+ e-e- PHENIX NPA774(2006)403  signal to be measured for 1<p T <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 p T  0 as in Drell-Yan or exponential like for Eliminating the  0 background by going to 0.2<m ee <0.3 GeV enables direct  signal to be measured for 1<p T <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 p T  0 as in Drell-Yan or exponential like for  0 = Kroll-Wada

18. DNP2008 M. J. Tannenbaum 18/14/15 QM2008 direct  in p-p via internal conversion μ = 0.5p T μ = 1.0p T μ = 2.0p T Lowest p T 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 p T  0, follows the same function B(1+p T 2 /b) -n used in Drell Yan [Ito, et al, PRD23, 604 (1981)]. Fit to Au+Au is [A e -p T /T +  T AA  B pp (1+p T 2 /b pp ) -n pp ]. Significance of exponential (thermal?) is > 3  arXiv:0804.4168v1