Measuring jet properties from p  — h correlation in dAu and pp

Measuring jet properties from p— h correlation in dAu and pp Jiangyong Jia Columbia University, Nevis Labs For the PHENIX Collaborations Introduction study of jet shape study of fragmentation function conclusion

Hard-scattering and Jet fragmentation Leading hadron Q2 • Properties of di-jet system • The spread of the hadrons around the jet axis and relative orientation of the two jets – jT, kT, Pout • The multiplicity of hadrons – fragmentation function D(z) • They can be accessed with two particle correlation in Df. • We present the result for leading p— h correlation from dAu and pp collisions Jiangyong Jia

p— h azimuthal distribution Jet shape jT, kT is given by the near side and far side width Jet multiplicity is given by the area under the peak PHENIX identify p at pT> 4.7 GeV/c Trigger pion 5-10 GeV/c dAu pp PHENIX preliminary 1-2 GeV/c 0.4-1 GeV/c 2-3 GeV/c 3-5 GeV/c Jiangyong Jia

Jet shape Df Pout jT is fragmentation momentum • Near side correlation • Far side correlation kT is parton initial momentum RMS of jT kT can be extracted from the jet width More direct way is via the projection of assoc to trigger : Pout Pout = pT,assoc sin(Df) Jiangyong Jia

Relation jT and kT to Pout Near side Pout depends on jT Far side Pout also depends on kT Multiple scattering in dAu would broaden the Pout distribution p+p p+p d+A Jiangyong Jia

Pout distribution Pout distribution carries more information than just RMS of jT, kT. Far side Pout is broader than near side due to kT Radiative tails pp PHENIX preliminary Jiangyong Jia

Pout dAu central vs pp 0.8-1.6 (GeV/c)2 in central collisions C~ 0.2-0.4 1(GeV/c)2 <1(GeV/c)2 7(GeV/c)2 W.Volgelsang, hep-ph/0312320 • No sensitivity to broadening? PHENIX preliminary PHENIX preliminary Jiangyong Jia

Jet multiplicity  Conditional yield Fragmentation function Correlation method give per trigger yield • Study any modification of jet multiplicity in dAu • Multiple scattering, modification of PDF, etc.. Jiangyong Jia

Jet Yield PHENIX preliminary dAu minbias Far Near pp PHENIX preliminary PHENIX preliminary • 1/Ntrig dNh/dpT • pT from 0.4-5 GeV/c. Near Far • 1/Ntrig dNh/dxE • xE from 0.1-0.7 • Near side yield is related to di-hadron fragmentation function. • Far side is closer to single fragmentation function. • No difference between dAu and pp within errors Jiangyong Jia

Scale dependence • Plot the far side CY for fixed xE ranges. • No apparent scale dependence. PHENIX preliminary PHENIX preliminary • Study the CY as function of trigger pT (thus the Q2) PHENIX preliminary PHENIX preliminary Jiangyong Jia

Jet multiplicity: centrality dependence • No change in jet multiplicity is seen within errors PHENIX preliminary PHENIX preliminary • 1/Ntrig dNh/dpT • pT from 0.4-5 GeV/c. • as function of centrality and compare with pp • Modification of jet multiplicity in dAu Jiangyong Jia

Conclusion • The di-jet decay kinematics are studied with p— h correlation • Pout distribution are very similar between dAu and pp, indicating no significant broadening in cold nuclear medium • CY distribution are also similar between dAu and pp, indicating no significant increase in jet multiplicity in dAu relative to pp. Jiangyong Jia

pidentification RICH detects p at pT> 4.7 GeV/c EMCal is used to reject high pT background from conversion Remaining background is less than 5%. Turn on around 6 GeV/c Jiangyong Jia

pRcp Up to 16 GeV/c Jiangyong Jia

Two particle azimuth correlation method • In ideal acceptance, real pair distribution is • Real distribution is modulated by pair acceptance function Acc(Df, Dh). • Pair acceptance function can be determined from event mixing technique • Real/mix gives the acceptance corrected CY (modulo constant background l). • Fit with a double gauss + constant to extract the Near side and far side yield. Jiangyong Jia

Pair acceptance function ACC in PHENIX Single particle acceptance Pair acceptance in Dh Pair acceptance in Df Shape from overlapping four triangles: west1-west2, east1-east2, west1-east2, east1-west2 Triangle results from convoluting two flat distribution effi is 100% at Df=0, Dh=0 Average is 25% Jiangyong Jia

The corrections • The mathematical framework is detailed in nucl-ex/0409024 • The normalization factor can be determined experimentally. The near side peaks in both Df and Dh. Far side is very broad in Dh (almost flat in |Dh|<1) • Correct near side jet yield to full jet yield |Dh|< • Correct far side jet yield to yield in |Dh|<0.7 • Procedure has been verified with MC simulation Jiangyong Jia

Normalization for 2D and 1D CY Detected triggers Underling triggers Mix normalized to pair phase space Acceptance+ efficiency • 1D CY can be obtained by integrating out Dh . Single particle efficiency in full azimuth and 1 unit h Pair cuts and two track resolution Fraction of jet yield falls in h acceptance Can be calculated analytically assuming Gauss shape • 2D CY Jiangyong Jia

Is kT in dAu sensitive to broadening? • Seems radiation contribution dominate over the broadening I.Vitev hep-ph/0310274 10% difference between dAu and pp for 4.5 GeV trigger • Radiation contribution is even stronger at higher pT Pythia the sensitivity on broadening decreases as pT increases. p-h correlation Jiangyong Jia sfar not very sensitive to additional broadening

kT Broadening in dAu 1(GeV/c)2 0.9(GeV/c)2 7(GeV/c)2 Au W.Volgelsang, hep-ph/0312320 d 0.8-1.6 (GeV/c)2 in central collisions C~ 0.2-0.4 • Presence of cold medium can broaden the jet kT • However, radiation contribution seems dominate over broadening Small difference between dAu and pp pythia hep-ph/0310274 I.Vitev the sensitivity on broadening decreases as pT increases. Jiangyong Jia

Jet shape Df Pout p+p p+A • jT is fragmentation momentum • Pout is projection of assoc to trigger • Pout = pT,assoc sin(Df) • Near side correlation • Far side correlation jets have intrinsic pT Jiangyong Jia

Measuring jet properties from p  — h correlation in dAu and pp