Transcript nexus: < 1 - Duke Physics

Strange Particles
from NEXUS 3
(Basic ideas, baryon production in pp)
hep-ph/0007198
Physics Reports 350 (2001) 93-289
hep-ph/0102194
Phys. Rev. Lett. 86 (2001) 3506
NEXUS 3 : Consistent treatment
of multiple scattering
Fuming Liu
Sergej Ostapchenko
Tanguy Pierog
Klaus Werner
Hajo Drescher
Michael Hladik
Joerg Aichelin
Marcus Bleicher
SUBATECH, Nantes
Problems with the
String Model Approach
Particle production in pp scattering via string fragmentation
pp ==> 2 strings
Strings decay into chains of hadrons
Not enough multiplicity fluctuations ==>
Two Pairs of strings
In general: n pairs of strings
Probability of n pairs ?
Gribov Regge : Pomeron (= pair of strings)
2
/2
...
String model -- Gribov-Regge
String model: first and subsequent pairs
are of different nature
Gribov-Regge: all Pomerons are identical
String model: energy-momentum is properly shared
among strings
Gribov-Regge: energy-sharing is not considered
inconsistent
And …
traditional string models fail badly
when it comes to
strange baryon production in pp ...
The new approach
Aim:
connecting properly string model
and Gribov-Regge Theory
… and the parton model
Extending work by Gribov, Kaidalov, Capella ...
Basic Features
Result of a pp collisions: 2 remnants and n Pomerons
(all identical)
Pomeron = 2 strings
Energy-momentum properly shared
Same formalism for particle production and probability calculations
Notations
Consider parton-parton scattering
Elastic
amplitude
T2 2
Unitarity: 2 ImT22 
Inelastic
amplitude
T2  X

X
T2* X T2 X  cut diagram 
Inelastic scattering in pp:
Amplitude:
remnant
Squared amplitude
=> interference terms:
=> Symbolic notation
Inelastic scattering in AB:
TAB X  T
(i )
AB X
(Elastic and
inelastic elem.
Interactions)
i
Squaring amplitude
 sum over many
interference terms
expressed via cut and
uncut elementary
diagrams
full energy
conservation!!
remnant
Pomerons: multiplicity proportional to number of binary collisions
Remnants: multiplicity proportional to participants
Pomeron-Pomeron
Interactions
 • Diffraction
• Screening
• Shadowing
• Saturation
• Increasing mult. fluctuations
• Solving F2-tot puzzle
Hadronization
Multiple scattering theory determines
how many Pomerons are involved
in each nucleon-nucleon interaction
and the momenta of each Pomeron.
Then:
Pomeron  strings
Strings  hadrons
From Pomerons to Strings
In the multiple scattering theory
a dashed line represents
a cut Pomeron
The complicated hadronic
structure is “hidden”
What is the precise structure
of a cut Pomeron?
Pomeron = 2 strings
pp scattering:
1 Pomeron
2 Pomerons
Projectile
remnant
strings
Target
remnant
Crucial: separation of Pomerons and remnants
otherwise completely wrong baryon yields
(FM Liu, M Bleicher, J Aichelin, T. Pierog, KW et al)
etc
q, q-bar
or qq qq-bar
(sea quarks)
Baryon ratios in pp at 158 GeV
3
Traditional string models
NEXUS: < 1
Antibaryon/baryon ratios
at RHIC (pp -1<y<1):
NEXUS:
data (A.Billmeier,STAR):
proton: 0.81
Lambda: 0.895
Xi:
0.95
Omega: 0.94
(0.81 +)
(0.89 +- 0.03)
(0.97 +- 0.04)
(0.90 +- 0.19)
Why does the conventional string model
give more antiomegas than omegas?
A string end flavor u or d prevents the production of omegas
NEXUS : projectile/target flavor is in the remnants
not in the strings
Leading
particles
(mainly
from
remnants)
Data:
NA49
Baryon spectra
in pp at 158 GeV
Theory:
NEXUS
(FM Liu et al)
Summary
Consistent multiple scattering formalism
=> separation remnants - Pomerons (strings)
=> antibaryon/baryon ratios R < 1
contrary to conventional string models
strings: R = 1
remnants: R < 1