Hadron production in hard scattering

Event Generator GEANT

JETSET:Single particle production in hard scattering

High probability to detect leading hadron in the forward detector

The primary hadrons produced in string fragmentation come from the string as a whole, rather than from an individual parton.

- Before- After quarkTarget remnant

DIS:Q2>1GeV2

W2>4 GeV2 (10)y<0.85

LUND Fragmentation Functions

LUND Fragmentation Functions

HERMES

low PT

high PT

PDF side: gaussian <kT2>

212 2212 2 0

10 2 2

0

( , )( , )1 ( , )( , )

( , )

hf ff

h

hf f fDIS

f ff

fD ze dxq x QdN z Qe dxq x Q D

dzN e dxq x Q

Q

z

MC:MC:PYTHIA in combination with JETSET; PDF:CTEQ-6PYTHIA in combination with JETSET; PDF:CTEQ-6

DATA:DATA:unpolarised p-targetunpolarised p-target

QQ2 2 > 1GeV> 1GeV22, W, W22>10 GeV>10 GeV22, z>0.2, 2<p, z>0.2, 2<phh<15GeV<15GeV

HERMES: Fragmentation and Multiplicities

Tuning of JETSET FF parameters to multiplicities in acceptanceTuning of JETSET FF parameters to multiplicities in acceptance

PT

+

-

+

-

-

+

-

+

Mu

ltip

lici

ties

z PT

HERMESHERMES-MCTune-2Tune-3JETSET-std

CLAS data vs LUND-MC

CLAS data (4.3GeV) and LUND-MC comparison

0.5<z<0.8

LUND-MC tuned at higher energies

QQ2 2 > 1GeV> 1GeV22, W, W22>4 GeV>4 GeV22, z>0.5,y<0.85, z>0.5,y<0.85

LUND event-II

Lund ID

ep -> e’+ -> e’ pK→

Particle number in the event

Parent and first daughter line numbers

p

K*+

charge and status

px py pz

Momentum in GeV, E m Vx Vy Vz,

Vertex in cm

K

Exclusive + at 6 GeV

PYTIA-6

+ 2

Exclusive production background from PYTHIA

Pions from string (direct) present the lower limit for current fragmentation events

Filled (open) symbols represent pions from exclusive (all) vector mesons.

electron

0 sample “clean” at large z (non-string pions are mainly from semi-inclusive +, )

GEANT simulation

Angular acceptance for charged tracks for CLAS+IC configuration

Maximum angle ~50o

Minimum angle ~14o

13o

50o

Background studies for CLAS with IC

CLAS data

GEANT+backgroundtarget

IC edgeshielding

Background accounting procedure tested with e1dvcs

CLAS GEANT-MC + background consistent with data

Acceptance moments from MC

generatedreconstructed

Extract acceptance moments from MC

CLASHERMES

3 methods to analize the azimuthal moments

fit

I

II

III

Different methods have different sensitivity to acceptance corrections

LUND MC with Long. Pol. Target: SSA for +

sin and sin2 moments arising from the Collins effect added in MC using predictions from Efremov et al.Phys.Rev.D67:063511,2003

Simulated and reconstructedSSA moments consistent

distributions from MC vs 5.7 CLAS data.Fiducial cuts on e,+ and smearing applied.

CLAS-Data

Summary

Monte-Carlo generators have become an essential tool for feasibility studies, simulation of anticipated physics and background rates, acceptance and other corrections.

Detailed simulation of processes of interest is crucial to keep under control systematic errors due to, both detector and physics background contributions

LUND-MC combined with GEANT-simulation of detector response provide test of procedures for global analysis and extraction of physics observables.

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