1. Direct photon and high-pT  0 correlations with ALICE DongJo,Kim Jyväskylä University, Finland

2. 10-Jun-15DongJo Kim2 Motivation pQCD jet quenching : Similar suppression pattern of high-p T electrons from semi-leptonic D and B mesons decays; PRL 91, 172302 (2003) No broadening of the associated correlation peak (nucl-ex/051000) in contrast to “standart picture” e.g. Phys. Lett. B630, 78 (2005) Induced gluon radiation should violate the x T scaling, not seen in  0 seen in h . E.g. Brodsky, Pirner and Raufeisen, hep-ph/0510315. Why NLO pQCD work without k T ? Detailed understanding of “unmodified” parton properties in p+p is crucial p+p data @ RHIC and LHC Fragmentation function D(z) Jet shape  j T  jet fragmentation transverse momentum  k T  parton transverse momentum

3. 10-Jun-15DongJo Kim3 pQCD quenching - modification of D(z) Fragmentation strongly modified at p T hadron ~1-5 GeV even for the highest energy jets  = ln( E Jet / p hadron ) p T hadron ~2 GeV for E jet =100 GeV Borghini and Wiedemann, hep-ph/0506218 MLLA: parton splitting+coherence  angle-ordered parton cascade Theoretically controlled, experimentally verified approach Medium effects introduced at parton splitting

4. 10-Jun-15DongJo Kim4 Width of Away-Side Peaks - where is broadening ? away-side widths similar for central and peripheral d+Au 0.24+-0.07 rad Au+Au 20-40% 0.20+-0.02 rad Au+Au 0-5% 0.22+-0.02 rad Where is the jet broadening at RHIC? How about LHC? STAR nucl-th/0308028 Leading Particle Reconstructed Jet STAR nucl-ex/0604018 8 < p T (trig) < 15 GeV/c I. Vitev

5. 10-Jun-15DongJo Kim5 k T physics Reference to heavy ion: Broadening in the “punch through” - high-pT ? Broadening in the “Mach cone” - low-pT ? Understanding of (p)QCD phenomena  k 2 T  evolution with  s.  k 2 T  associated to direct photons. Resummation techniques Vogelsang,Sterman,Keusza Nucl Phys A721,591(2003). NLO physics - p out distribution.

6. 10-Jun-15DongJo Kim6 Hard scattering – k T Longitudinal jet transverse acoplanar in P L  P T space acoplanar in P X  P Y space Longitudinal jet k T measures the accoplanarity of the two back-to-back jets in transverse plane

7. 10-Jun-15DongJo Kim7 Origin of k T Intrinsic k T “fermi motion” Soft QCD NLO radiation. As an example - J/  production.  p T  J/  =1.8  0.23  0.16 GeV/c Phys. Rev. Lett. 92, 051802, (2004). Power law tail @ large value of p T,pair Gussian @ p T,pair  0 Leading-Log resummation Vogelsang,Sterman,Keusza Nucl Phys A721,591(2003)

8. 10-Jun-15DongJo Kim8 Soft Gaussian + hard power law D. Boer and W. Vogelsang, Phys. Rev. D69 (2004) 094025 J. Qiu and I. Vitev, Phys. Lett. B570 (2003) 161 radiative tails STAR p+p Phys. Rev., 1981, D23, 604

9. 10-Jun-15DongJo Kim9  o - h  correlation functions p+p  s=200 GeV d+Au Corrected for acceptance NN AA  N   j T  jet fragmentation transverse mom.  F   k T  parton transverse momentum Y A  folding of D(z) and final state PDF. p + p  jet + jet  p out

10. 10-Jun-15DongJo Kim10 Trigger bias There are ALWAYS two types of trigger biases when correlating p Ttrigger  p Tassoc z-bias; steeply falling/rising D(z) & PDF(1/z)  z trig   z assoc  Selecting events with p Tt > p Ta forces k T vector toward trigger jet: hat-x h bias kTkT

11. 10-Jun-15DongJo Kim11 Trigger associated spectra are insensitive to D(z) LEP data M.J. Tannenbaum Approximation - Incomplete Gamma function when assumed power law for final state PDF and exp for D(z)

12. 10-Jun-15DongJo Kim12  k 2 T ,  z t  in p+p @ 200 GeV ISR We gave up an effort to extract fragmentation function from di-hadron data, direct photon analysis under way. For D(z) the LEP date were used. PHENIX Iterative solution for each p T bin by varying  k 2 T  Systematic errors comes from unknown ratio gluon/quark jet => D(z) slope.

13. 10-Jun-15DongJo Kim13 NLO at work at RHIC. Good agreement with NLO pQCD Phys.Rev.Lett.91:241803,2003 p+p  0 +X p+p  direct +Xp+p  0 +X

14. 10-Jun-15DongJo Kim14 High p T : ref. for HI, resummation, detailed NLO tests High p T : ref. for HI, resummation, detailed NLO tests PHENIX measured  p T  pair =3.36  0.09  0.43GeV/c extrapolation to LHC  k 2 T  =34 GeV 2 /c 2

15. 10-Jun-15DongJo Kim15 LO pQCD and inclusive yield LO gets the data only when Gaussian smearing of order of  k 2 T  3 GeV/c used. P. Levai

16. 10-Jun-15DongJo Kim16 Trigger  associated spectra are sensitive to D(z)  z trig   z assoc  Di-hadron correlations Direct photon correlations D(z t )  (z t ) No trigger bias - associated spectra reflect the actual Fragmentation Function

17. 10-Jun-15DongJo Kim17 Direct photon measurement hep-ph/0311131 Very Challenging measurement:  /   < 0.1 in accessible kinematic region CTEQ5

18. 10-Jun-15DongJo Kim18 How to construct direct  -h yield i.Construct inclusive  -h yield ii.Construct decay  -h yield via: –Pair by pair weighted summation method convolutes all  0 -h pair contributions from higher p T Weight reflects the probability from kinematics for a  0 at given p T to decay into a photon in a given p T range iii.Subtraction via:

19. 10-Jun-15DongJo Kim19  -h correl. fcn. in p+p @ √s = 200 GeV comparison to PYTHIA

20. 10-Jun-15DongJo Kim20 Pythia CKIN(3) Triggered  0 yield CKIN(3) values correspond to minimum of hard 2  2 process. Effectively similar effect as online tower threshold cut. The only thing which is not correct is the absolut normalization (xsection). This can be done by matching renormalization in the overlap region (if there is such a region.) I show 200 GeV p+p data because we know them best.

21. 10-Jun-15DongJo Kim21 Pythia 200 GeV  0 yield Kinematical limit 100 GeV/c! Below 20 GeV/c the spectrum is power law with n=7 (n=8 in the case of invariant xsection). Phase space factor at pT>20 GeV/c turned the pQCD power low in “non perturbative” exponential.

22. 10-Jun-15DongJo Kim22 Cross Check to go for correlations PYTHIA6.323CTEQ5

23. 10-Jun-15DongJo Kim23 High pT Direct  ’s : for cross check… LO q+g  q+  (Compton scattering) >> q+q  g+  (Annihilation process) @high energy, only the compton process is relevant NLO bremsstrahlung, fragmentation

24. 10-Jun-15DongJo Kim24 @high pT (Ktmode=1,ckin3=8) 16<pT t <20 GeV pT a : 2,3,4,5,7,8,10,15,20GeV

25. 10-Jun-15DongJo Kim25 X E distributions : k T effect (I) There is no difference from  0 -h with  2 = 3 GeV kT effect is quite clear

26. 10-Jun-15DongJo Kim26 PYTHIA  -h @ 200GeV PHENIX  0 -h @ 200GeV k T makes x E slope steeper in lower pT but it is not much in higher pT Caution : “fitting” is not finalized yet for this study Looking at p+p data with strict isolation cuts etc X E distributions : k T effect (II)

27. 10-Jun-15DongJo Kim27 Conclusion and perspectives High pT  0 suppressionin HI itself poorly informs us on how exactly the produced medium affects the propagation and the hadronization of high-energy quarks and gluons. From  0 -h correlation is not sensitive on the determination of fragmentation –PHENIX measured  p T  pair =3.36  0.09  0.43GeV/c –extrapolation to LHC  k 2 T  =34 GeV 2 /c 2 –But Trigger bias Need  -h correlation PHENIX used “substraction” method, agreed with PYTHIA –Need more detail study PYTHIA shows kT effect is stronger in low pT < 4, and almost no effect in high pT Data are being looked at with more strict isolation cuts etc.