Recent Results on Leading Baryon Production

1
Recent Results on Leading Baryon Production
Maria Carmela Petrucci DESY On behalf of the
ZEUS and H1 collaborations
31 Aug - 6 Sep 2002 Alushta, Crimea

• Introduction and Motivation
• Cross Sections - Comparison to models
• Dijet with Leading Neutrons
• Absorption
• Structure Functions
• Summary

2
Forward Detectors and Data
H1
z
Neutron calorimeter
Proton spectrometer (LPS-FPS)

• Different Sample in Q2
• different g virtuality
• Q2 0 Photoproduction (PHP)
• Q2 gt few GeV
• Deep Inelastic Scattering (DIS)

Data presented ZEUS neutrons and protons
in DIS and PHP H1 neutrons in DIS,
neutron PHP with dijet, proton
in PHP
3
Measured xL sprectra
Cross sections in DIS rate Q2 independent

• Three DIS bins for neutrons
• Q2 gt 125 GeV2
• 40 lt Q2 lt 125 GeV2
• 4 lt Q2 lt 40 GeV2

• Two sample for protons
• DIS Q2 gt 4 GeV2
• Low Q2 (0.1 - 0.74) GeV2

4
Model Comparison (p-n)

• Compare shape and normalization of data
• Standard fragmentation models do not reproduce
  data
• Exchange models describe data
• Protons need multiple processes
• Pomeron, Reggeon, p0 exchange

5
Leading Neutron With Dijet
DIS
PHP

• Compare shape and normalization of data
• Standard fragmentation models do not
• reproduce data
• One-Pion-Exchange describes high En region
• OPE describes ET jet

6
Vertex Factorization
In OPE ep cross section factorizes, can be
written as
Reggeon flux in p
Lepton vertex is independent of baryon vertex
p,IR
Expected leading baryon rate independent of DIS
variables Q2,x
7
Factorization Test in Q2
Neutron with dijet
DIS proton
Leading Baryon production rate is independent
of Q2, xBj
8
Factorization Violation
In One Particle Exchange Model one can violate
factorization via rescattering model (DAlesio
Pirner)
neutron case
DIS g point like PHP g hadron like
rescattering possibile
In OPE ltrnpgt smaller at lower xL more
rescattering at lower xL
9
Test of Factorization Violation
At lower Q2 fewer baryons
ZEUS sees mild factorization violation 20
from PHP to DIS
H1 has much wider increase in the proton yield
from 5 to 10
10
Factorization Violation
lower Q2 lower xL
11
Neutron ratio vs. Q2