Generalised area law for hadronic string reinteractions

Here you can find a preprint (hep-ph/9812423) describing the model which has been published in Physics Letters B 452 (1999) 364.

If you use the model please reference J. Rathsman, Physics Letters B 452 (1999) 364. Other relevant references are: A. Edin, G. Ingelman, J. Rathsman, Phys. Lett. B366 (1996) 371; Z. Phys. C75 (1997) 57.

In short the model gives string-reinteractions between two stringpieces with the probabillity

P = R_0 [ 1 - exp( - b dA ) ]

where R_0 is a parameter and dA is the area difference between the two configurations and the area for a string piece between partons i and j is calculated as

A_ij = 2 ( p_i p_j - m_i m_j )

All pairs of stringpieces can have a string-reinteraction with the probabillity given above.

Parameter values

The model is assumed to be universal. Thus it is applicable both in e+e- annihilation, deep inelastic scattering and hadronic collisions. The model has been retuned against data from LEP on charged multiplicity distributions and the momentum distribution of pions (see below). The retuning of the hadronisation gives the following parameter values:

• b = PARJ(42) = 0.45 [GeV^-2]
• Q_0 = PARJ(82) = 2.0 [GeV]
• Q_0^2 = PYPAR(22) = 4.0 [GeV^2]
• R_0 = PARL(7) = 0.10

where the latter has been determined by comparing with the diffractive structurefunction (see below).

Source code

The model has been implemented as a variation of the SCI model in the LSCI routine in LEPTO. To use the new model you choose LST(34)=3 and the parameter values given above. You will also need a slightly modified version of the LEPTO routine. In addition it is proposed that you use version 2 of the seaquark treatment since Q_0 is relatively large, i.e. use LST(35)=2. The parton densities used for the DIS comparisons below where CTEQ4L. To use these parton densities you will probably need a new version of the LWEITS routine in LEPTO.

The model can also be used in AROMA version 2.2.3, by using the latest version of the LSCI routine in LEPTO.

There is also a version for PYTHIA, PYSCI which can be used by having MSTP(188)=3. In addition the following parameter values should be used:

• b = PARJ(42) = 0.45 [GeV^-2]
• Q_0 (final cascade) = PARJ(82) = 2.0 [GeV]
• Q_0 (initial cascade) = PARP(62) = 2.0 [GeV]
• R_0 = PARP(188) = 0.10

You will also need the following routines to run the PYSCI-routine in PYTHIA.

• PYASWI
• PYEVNT
• PYSMALL
• PYSSPA
• PYCSWI
• PYSQTR

Plots

DIS

• F2D3
• Energy-energy correlation
• xp-spectrum in Breit frame current region
• Transverse energy flow
• Pt spectrum of charged particles
• Pt spectrum of charged particles in events with large transverse energy
• Eta spectrum of charged particles with pt>1GeV
• Eta spectrum of all charged particles

e+e- -> Z0 -> qqbar

• Charged particle multiplicity and pion momentum spectra
• Stringeffect and thrust
• Pseudorapidity and pseudorapidity-gaps

e+e- -> W+W- -> qqbar qqbar

• Di-jet mass and charged particle multiplicity