Study of the gluon polarization in the proton with a silicon vertex upgrade at RHIC/PHENIX.

Study of the gluon polarization in the proton with a silicon vertex upgrade at RHIC/PHENIX. Manabu Togawa, Kyoto University / RIKEN for the PHENIX collaboration

baseline detector xG(x) GS95 prompt photon cceX bbeX J/ Base line of spin program at PHENIX • Polarized parton distribution in proton. • (longitudinal polarization) - Gluon polarization • pion / hadron ( ref. p0 : Y.Fukao’s talk ) • prompt photon • heavy flavor • Single e ( D -> e + X) • J/Y - Anti-quark polarization • W (require sqrt(s) = 500GeV ) • Transversity (transverse polarization) • pion pair

r = 14.0cm strip r = 10.0cm r = 5.0cm pixel r = 2.5cm With VTX tracker (Barrel part) • Reconstruction of the “jet” axis • Using charged particles in wide rapidity coverage • PHENIX Vertex Tracker (VTX) will be installed in Summer of 2007. • Access to the displaced vertex -heavy flavor tagging • VTX can reveal the detailed collision point. • Looking at the gap between decay and collision point. Beam pipe Barrel (|h|<1.2 and 2p azimuthal coverage)

M.Karliner and R.Robinett. Phys. Lett. B324 (1994) LO analyzing power VTX takes advantage of PHENIXfor gluon polarization =1.1 1.5 2 • Prompt photon • Determine xg,xq • Heavy flavor production • Separate charm and beauty by looking at their life time. For D and B meson, tD < tB • We must separate charm and beauty for gluon polarization since analyzing power is different. low pT higher mass 5 cosq

- From the this formula, • Dg/g can be calculated with • approximation, • for the gluon compton process. (1 arm only) Kensuke Okada Central ARM |h|<0.35 0<f<p Current PHENIX setup (for prompt photon) Prompt photon process (main : gluon compton process ~90%) Prompt photon - We measure the inclusive photon production.

*Assuming that the pT of the prompt photon and recoil jet are balanced. *Assuming that xg< xq With VTX No VTX ( ) RMS = 0.13 xg(true) vs. xg(reconstruct) Jet reconstruction with VTX (For prompt photon)using pythia simulation known by EMCal g (Eg) q (x1,p) qg g (x2,p) qjet q (Ejet) qjet : reconstruct by charged particles using Cone algorithm.

Sergey Butsyk Central ARM |h|<0.35 0<f<p Current PHENIX setup (for heavy quark) in CENTRAL ARM c quark D -> e (+anything) D -> pK J/Y -> e+e- pK(D) or e+e-(J/Y) b quark B -> e (+anything) B -> J/Y + X single electron (main : gluon fusion ~90%) In single electron analysis • back ground. • p0, h Dalitz decay • g conversion ( g -> e+e-) • We can not separate electron • from D and B (J/Y too).

DCA Black : charged particles from collision point Blue : electron from D or B Displaced vertex ( For Heavy production ) • The gap btw decay point and collision can be evaluated with DCA. • Distance of Closest Approach. • DCA of D and B meson are different. • We can separate them. Azimuthal angle Studied by tuned pythia For example cut DCA (mm) Vladimir L. Rykov

Low pT : Determine c first High pT : Determine b first 0.02 Green : Charm Blue : Beauty error estimation ALLDalitz can be evaluated by pi0 -0.02 How to separate D and B Fraction of electron source With DCA cut no DCA cut Red : Dalitz+Conversion Green : Charm Blue : Beauty pT No DCA cut eall(no DCA cut) = eDalitz+ eD + eB With DCA cut eall(DCA cut) = Rdalitz(pT) eDalitz + RD (pT) eD + RB (pT) eB RXXX is electron ratio of “no DCA cut” to “DCA cut” for xxx. (can be estimated by simulation)

Hiroaki Ohnishi Silicon detector Junji Tojo Pixel detector Strip detector (test) test sensor design (Hamamatsu) test hybrid module design (ORNL) • ALICE hybrid • PHENIX sensor delivered in this month • electronics QA done • to be bump-bonded in a month or so SVX4 readout chip (Fermilab)

Summary • VTX is being built to extend capability for PHENIX experiment as an upgrade. • VTX will extend the acceptance of charged particles to the |h|<1.2 and 2p azimuthal coverage. • VTX will be able to reconstruct jet direction. • Determine xg,xq in the prompt photon process • VTX will be able to determine the displaced vertex. • Separate charm and beauty statistically. • ~ 320pb-1 will provide another test of ∆g(x) • We will have VTX detector in 2007 - 2008 RUN.

Back up

r = 14.0cm strip r = 10.0cm r = 5.0cm pixel r = 2.5cm DCA resolution • DCA resolution is dominated most inner 2 layers. DCA resolution pT

*Assuming that xg< xq No VTX ( ) With VTX Cone Algorithm Find cone seed : pt > 1GeV/c xg(true) vs. xg(reconstruct) Barrel VTX coverage |h|<1.2 , 0<f<2p Jet reconstruction (For direct photon) known by EMCal *Assuming that the pT of the prompt photon and recoil jet are balanced. g (Eg) q (x1,p) qg g (x2,p) qjet q (Ejet) qjet : reconstruct by charged particles

x value shift

Gluon shadowing effect

Primary photon ø charged particle Recoil parton Cone Algorithm • Apply pt cut and • first cut : pt > 1.0 (GeV) • Remaining particles (1~3 particles remain) • calculate jet axis taking average • <eta> <ø> -> first jet axis • Second cut • Calculate cone radius R defined as • apply second cut “R<0.5 and pt >1.0” • and calculate jet axis • -> go to “second cut” … iteration

Pythia parameters <kT>=1.5 <mc>=1.25 K-factor=3.5 CTEQ5L Pythia parameters PHENIX: PRL 88(2002)192303 NLO pQCD (M. Mangano et al., NPB405(1993)507) • For charm • Reproduce SPS,FNAL (charm) and ISR (single e) • For bottom PHENIX ISR Pythia parameters <kT>=1.0 (default) <mc>=4.8 (default) K-factor=2.6 GRV94D(NLL,DIS) PYTHIA (single electron)

Rapidity resolution vs.pt Resolution (Qrapidity - JetRapidity) pT

Photon + Jet • PHENIX baseline • prompt photon (inclusive) • asymmetry  gluon polarization • photon’s pTxg s=200GeV, 320pb-1 prompt photon pT>5GeV/c rough xg evaluation 

full NLO + threshold resummation + kT resummation Transversity • Inclusive prompt-photon measurement • Laenen, Sterman & Vogelsang • threshold resummation • necessary to sum up all kinematics of opposite-side jet • kT resummation • Photon + jet • threshold resummation • should not be necessary • kT effect • E706

Study of the gluon polarization in the proton with a silicon vertex upgrade at RHIC/PHENIX.