1 / 25

J T , k T and the fragmentation in pp collisions at s NN =200 GeV

This study investigates the jet kinematics and angular width in pp collisions at √sNN=200 GeV, focusing on the fragmentation process. The analysis includes the near-side and away-side correlation peaks, intrinsic transverse momentum kT, jet transverse fragmentation momentum jT, associated yield, and fragmentation function. The results shed light on the medium-induced fragmentation function softening and the suppression of high-pT particles in the QCD medium.

kimberlydiaz
Download Presentation

J T , k T and the fragmentation in pp collisions at s NN =200 GeV

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Jan RakUniversity of New Mexico JT , kT and the fragmentation in pp collisions at sNN=200 GeV • Jet kinematics from the angular width of the near and away-side correlation peak • Intrinsic transverse momentum kT • Jet transverse fragmentation momentum jT • Associated yield • Fragmentation function from the combined fit to the inclusive pTand and associated xE distributions • Conditional fragmentation - zt  pTa correlation • AuAu low pT correlation function • Distortions of back-to-back peak – Mach shock waves?

  2. Scattered partons radiate energy in colored medium • suppression of high-pT particles • effective kT broadening X.N. Wang nucl-th/0302077 Medium induced fragmetation function softening Partonic jets as a probe of QCD medium Particle production @ RHIC s=200 GeV • dnch/dh|h=0= 670, Ntotal ~ 750092% of (15,000)all quarks from vacuum !

  3. jet fragmentation transverse momentum Partons have to materialize (fragment) in colorless world jet jT jet fragmentation transverse momentum - constant value independent on fragment’s pT is characteristic of jet fragmentation (jT-scaling). kT (intrinsic + NLO radiative corrections)carries the information on the parton interaction with QCD medium. kT, jT

  4. o - h correlation functions 1.5<pT<2.0 Fit = const + Gauss(0)+Gauss() 3.0<pT<4.0 d+Au Intra-jet pairs angular width : N jT Inter-jet pairs angular width : A jT  kT

  5. p2out =  p2Tasin2  2 k2Ty z2a  2 k2Tyz2tx2hxh= pTa /pTt Feynman, Field, Fox and Tannenbaum (see Phys. Lett. 97B (1980) 163) xE = two particle equivalent of the fragmentation variable z. Jet kinematics

  6. Near and away-side angular width 1.4<pTa<2.4 GeV/c Unlike N, the value of A is not vanishing for large values of pTt reflecting the fact that the magnitude of the away-side angle is driven by kT.

  7. jT with associated and trigger pT However, the  j2Ty analysis done at s=62 GeV explicitly neglected zt. This may explain the slightly larger value seen by CCOR collaboration.

  8. 1.4<pTa<2.4 GeV/c Assumption: For fixed pTt the parton momentum (jet energy) is fixed, pTa samples the different region of fragmentation at fix Q2 zt kT should be constant THIS IS CLEARLY WRONG ztkT “puzzle”

  9. xE variable - two particle equivalent of the fragmentation variable z.  Simple relation Fragmentation Function from xE distribution In order to understand the (anti)correlation of zt kT with pTt and pTaone has to explore the fragmentation under the condition of detection of an associated particle.

  10. CCOR (ISR) s = 63 GeV see A.L.S. Angelis, Nucl Phys B209 (1982) Correct +- 1/xE  -5.3 xE in pp collisions 1/xE  -5.8 to –7.8

  11. The shape of the xE distributions does not vary, unlike the pTa distributions, with pTt. This supports the the idea of D(z) =dn/dz  dn/dxE. However, the scaling is not perfect ! It has nothing to do with pQCD scaling violation, but maybe it has something to do with the ztkT “puzzle” ? Is the z=xEzt valid assumption? xE “scaling”

  12. By selecting events with differentpassoc the probability distribution of mother parton is changing.  Trigger parton distribution is affected as well ! zassoc ztrig Monte Carlo Di-jet fragmentation

  13. Global fit to the inclusive and associated distribs.

  14. Fragmentation function and z  These are preliminary results from QM04 – final are under collaboration review. QM04 PHENIX preliminary pythia The QM analysis did not account for “conditioanl fragmentation. The D(z)  exp(-z/z) assumption is also not well justified.

  15. “flow” pairs : [1+2v22 cos(2)] Intra-jet pairs angular width : N |jTy| Inter-jet pairs angular width : A |jTy|  |kTy| z CARTOON flow+jet flow N A Azimuthal correlation function in AuAu Two particle azimuthal correlation function Unavoidable source of two particle correlations in HI – elliptic flow

  16. Phys.Rev.Lett.92:032301,2004 (3.0pTtrigg5.0)(1.5pTassoc3.0) pp <z><|kTy|> pp <|jTy|> There seems to be significant broadening of the away-side correlation peak which persists also at somewhat higher pT range. AuAu |jTy|and z |kTy| from CF (2.5pTtrigg4.0)(1.0pTassoc2.5)

  17. Jet correlation in Au+Au h-h correlation Intermediate pT correlation • Jet pair fraction is small • Jet shape is strongly distorted at away side PHENIX preliminary

  18. Medium modification • Assume Zero jet yield at minimum • Systematics dominated by v2 Away side is strongly distorted 2 dip at . Jet interact with flowing medium • hep-ph/0411315 Shuryak • nucl-th/0312065, S. Voloshin • hep-ph/0411341 Armesto,Salgado,Wiedemann

  19. Preliminary Novel behavior of away <pT> <pT> more robust than correlation functions. Novel dip structure observed in central AA. Energy loss effect? Mach shock wave?

  20. Summary • The angular width of the near and away-side correlation has been measured. Formulae for jT and kT we discussed. We found • j2T = 0.58 GeV/c by 15% small then at lower s measurement. This may be attributed to the neglecting the z. • Associated pTa and xE distributions were analyzed. The (anti)correlation between trigger z and pTa has been discussed. The method of extraction the D(z) parameters from the combined fit to the inclusive and associated pTa distributions was presented. Similar analysis of AuAu data is under way. • Intermediate pT ( 2 GeV/c) correlation function in AuAu data develops significant distortion of back-to-back peak with the dip around at 180 deg. Associated pTa reveals similar structure. Some speculation about Mach shock waves, however, there is no reasonable calculation supporting this interpretation.

  21. |pout|2 (GeV2/c2) CCOR j2T from |pout|2 CCOR coll. PL 97B (1980)

  22. = effective final state parton distribution Inclusive fragmentation = 0 fragmentation function

  23. associated “double” fragmentation With the condition of seeing associated particle, the parton spectrum on the away-side is biased: It is now evident why xE distributions do not scale perfectly! At fixed trigger pt the xE distribution is a folding of D(z)fq and not just D(z)!

  24. kT-smearing Associated parton distribution fa = kTftand the final formula for invariant cross section is Correlation fcn between b2b parotns gaussian for kt>0 or delta function for kT=0

  25. 4 < pTtrig < 6 GeV/c 2.5 < pTtrig < 3 GeV/c 0.3<pTassoc<0.8 GeV/c 0.8<pTassoc<1.3 GeV/c 1.3<pTassoc<1.8 GeV/c STAR sees the same? Shape varies with pT and becomes broader and double peaked at large pTa. Effect is more pronounced for lower pTt! Vitev, hep-ph/0501255: should not have peak structure.

More Related