1

Event Generator:Electron and electron-pair simulations for

PHENIX using EXODUS and PYTHIA

Ralf Averbeck,State University of New York at Stony Brook,

PHENIX Upgrade Workshop, Montauk 3/21 - 3/23 2001

PHENIX Upgrade Workshop, Montauk, 3/21/01 2 R. Averbeck, SUNY SB

Outline

Motivation The heart of the simulation package: EXODUS

event generator decay machine acceptance filter

Proof of principle: CERES cocktail Electrons in PHENIX (Au+Au @ 130 GeV): part I Electrons from open charm

Can PYTHIA describe existing open-charm data? PYTHIA extrapolated to RHIC

Electrons in PHENIX (Au+Au @ 130 GeV): part II Summary

PHENIX Upgrade Workshop, Montauk, 3/21/01 3 R. Averbeck, SUNY SB

MotivationSimulation of

phase-space distributions of “all relevant” sources of electrons & electron pairs (or whatever particle species you prefer)

decays acceptance resolution

Valuable for: acceptance studies (e.g. detector upgrades) development of analysis strategies “reference” for data (“cocktail” plots)

THE example: ”GENESIS” generator (CERES)

G. Agakichiev at al.: Eur.Phys.Jour. C4(98)231

PHENIX Upgrade Workshop, Montauk, 3/21/01 4 R. Averbeck, SUNY SB

EXODUS: a “new” cocktail generator

EventBuilder

cc bb DY0 p

Decay Machine

ExperimentFilter

NtuplesASCII

Events

PYTHIA Particle generator

NtuplesASCII

NtuplesASCII

standalone C++ package using ROOT classes

complete separation of particle generator, decay machine, acceptance filter, detector resolution => extremely flexible!

PHENIX Upgrade Workshop, Montauk, 3/21/01 5 R. Averbeck, SUNY SB

EXODUS: particle generator

particle: PID, (E;p), weightstandalone phenomenological generator:

’J/ (, K, p)

needed as input: weight factor (relative to 0): measurement (or model) phase space distributions (pt, y): measurement (or model) mass distributions ()

input distributions provided using “standard” parameterizations (ROOT histograms)

PHENIX Upgrade Workshop, Montauk, 3/21/01 6 R. Averbeck, SUNY SB

Resonance mass distributions ()

2222 )()(

2141

cMmMdm

dN

2)(m

m )(22

22

4

4log5.1exp

e

ec mM

mm

m

M

G.J. Gounaris, J.J. Sakurai:(Phys.Rev.Lett. 21(1968)244

With:

PHENIX Upgrade Workshop, Montauk, 3/21/01 7 R. Averbeck, SUNY SB

Phase space distributions and relative particle weights (Au+Au @ 130 GeV)

Transverse momentum:

)mm96.1

96.1logx13exp(p

dp

dN22

t

tt

UA1 parametrization + mt-scaling

Rapidity:

.constdy

dN 5.0y5.0

relative particle weights from thermal model (J.Stachel QM99): ’ Alternative pt distributions: flat, exponential

Alternative y distribution: 2))()(()(

)(75.0exp

)(

)(75.0exp

m

yy

m

yy

dy

dN

PHENIX Upgrade Workshop, Montauk, 3/21/01 8 R. Averbeck, SUNY SB

Decay machine

Task: first generation => full history (for each event)

Generic decay algorithms: Dalitz, 2- and 3-body decays

Individual decay channels can be activated/deactivated

Propagation of weight factors! Only non-trivial decay: Dalitz

PHENIX Upgrade Workshop, Montauk, 3/21/01 9 R. Averbeck, SUNY SB

Dalitz Decays

Parent -> X + l+l- (masses: M, mx, ml)Lepton pair mass:

)()/(

)/(21

)/(

)/(41

2 22

2

2

22/3 )( mF

Mm

Mm

Mm

MmB

mdm

dN ll 22

22

2

2

))/(1(

)/(4

)/(1

)/(1 )(

Mm

Mm

Mm

MmB

xx

with

(N. Kroll, W.Wada: Phys. Rev. 98(1955)1355)

Electromagnetic form factors from exp. data: Lepton-G

(L.G. Landsberg et al. Phys. Rep. 128(85)301)

Angular distr. of leptons in the virtual photon’s restframe:

2cos1d

dN

PHENIX Upgrade Workshop, Montauk, 3/21/01 10 R. Averbeck, SUNY SB

Proof of principle: p+Be @ 450 GeV/c (CERES)

22 041.0)053.0( ppp mrad6.0 mrad3

GeV/c2.0tp 65.210.2 mrad35ee

Take resolution into account: Take acceptance into account: Generation and decay of 10M primary particles/species:

Reasonable description of data (as did GENESIS)

EXODUS technically OK!

PHENIX Upgrade Workshop, Montauk, 3/21/01 11 R. Averbeck, SUNY SB

momentum resolution: (nominal: )

PHENIX acceptance filter (available from J.Jia)

PHENIX: resolution and acceptance

22p 006.0)p036.0(p 22

p 006.0)p003.0(p

PHENIX Upgrade Workshop, Montauk, 3/21/01 12 R. Averbeck, SUNY SB

Electrons in PHENIX (Au+Au @ 130 GeV): part I

Relative weights from thermal model (except J/ transverse momentum distribution from data (+ mt scaling)

flat rapidity distributions Run1 momentum resolution + full PHENIX acceptance

But what about the contribution from open charm?

PHENIX Upgrade Workshop, Montauk, 3/21/01 13 R. Averbeck, SUNY SB

Open charm production in PYTHIA

Goal: tune PYTHIA to describe existing open-charm data (following P. Braun-Munzinger et al. Eur.Phys.J. C 1(98)123) and extrapolate to RHIC

the surprising truth: data exist only from SPS and FNAL fixed target experiments (srqt(s) < 40 GeV)

parameters available in PYTHIA: parton-distribution function (pdf): MRS(G) mass of charm quark: mc = 1.35 GeV/c2

average intrinsic transverse momentum of partons: <kt

2> = 1.0 (GeV/c)2

K (“fudge” cross section scaling factor): K = 5.2

PHENIX Upgrade Workshop, Montauk, 3/21/01 14 R. Averbeck, SUNY SB

PYTHIA tuning: total D cross sections

PYTHIA describes sqrt(s) dependence

different K factors for charged and neutral Ds!

different PDFs do equally well

different <kt2> work

too

PHENIX Upgrade Workshop, Montauk, 3/21/01 15 R. Averbeck, SUNY SB

PYTHIA tuning: D kinematics

Data: D+, D-, D0, D0, Ds+, Ds

+ (E769 PRL 77(96)2392) Common K factor: 5.2

Different PDFs: different <kt2>:

PHENIX Upgrade Workshop, Montauk, 3/21/01 16 R. Averbeck, SUNY SB

PYTHIA tuning: D-meson correlations

Data: D+, D-, D0, D0, Ds+,

Ds+ (WA92 CERN

PPE/36-180)

PHENIX Upgrade Workshop, Montauk, 3/21/01 17 R. Averbeck, SUNY SB

PYTHIA extrapolation to RHIC

extrapolation to RHIC: reasonably small uncertainty cc cross sections (pp):

380 b (130 GeV)730 b (200 GeV)

PHENIX Upgrade Workshop, Montauk, 3/21/01 18 R. Averbeck, SUNY SB

Electrons in PHENIX (Au+Au @ 130 GeV): part II

Add semi-leptonic decay contributions from open charm to cocktail from light-meson decays:

PHENIX Upgrade Workshop, Montauk, 3/21/01 19 R. Averbeck, SUNY SB

Electrons in PHENIX (Au+Au @ 130 GeV): part II

Expected pair spectrum with nominal resolution:

PHENIX Upgrade Workshop, Montauk, 3/21/01 20 R. Averbeck, SUNY SB

Summary

(Simple) simulation tools are available phenomenological event generator decay machine detector resolution parameterization acceptance filter

and can easily be extended! PYTHIA:

describes existing open-charm data has been extrapolated to RHIC energies has been coupled with EXODUS

In case you want to use the package: GO AHEAD!