Programs in Physics & Physical Chemistry
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|Manuscript Title: NUNUGPV, a Monte Carlo event generator for e+e- -> nu nubar gamma(gamma) events at LEP.|
|Authors: G. Montagna, O. Nicrosini, F. Piccinini|
|Program title: NUNUGPV|
|Catalogue identifier: ADDX_v1_0|
Distribution format: gz
|Journal reference: Comput. Phys. Commun. 98(1996)206|
|Programming language: Fortran.|
|Computer: DEC VAX.|
|Operating system: VMS, UNIX.|
|RAM: 136K words|
|Word size: 32|
|Keywords: Particle physics, Elementary, Qcd, High energy electron Positron collisions, Single-photon events, Radiaive neutrino Counting, Visible photons, Z0 and w bosons, Lep1, Lep2, Corrections qed, Electron structure Functions, Photon transverse Degrees of freedom, Experimental cuts, Monte carlo integration, Event generation, Importance sampling, Multichannel approach.|
Nature of problem:
The radiative neutrino counting and, more in general, the reactions with a single-photon signature, provide a very useful tool for measuring the number of light neutrinos and eventually detecting new-physics signals at the LEP collider . Within the Standard Model (SM), the bulk of the contribution to single-photon events at LEP comes from the production of a neutrino-antineutrino pair accompanied by a large-angle energetic photon, i.e. from the reaction e+e- -> nu nubar gamma. This process has already been studied in the LEP1 energy range using semi- analytical and Monte Carlo codes [3,4,5], which contain assumptions or approximations valid around the Z0 pole. However, in the light of the present data taking at LEP 1.5 (where square root(s) =~ 140 GeV) and in view of the forthcoming experiments at LEP2 (where square root(s) =~ 200 GeV), the approximations employed for the Z0 resonance have to be rediscussed (see, for instance, ref. ), in order to provide reliable predictions with a theoretical error of the order of 1 per cent.
A Monte Carlo integration technique for weighted events is employed to perform the high-dimensional numerical integration in presence of realistic cuts on the observed photons. For experimental simulation, the program can also be used as a true event generator that provides a sample of unweighted events, defined as the components of the three final-state photons, sotred into proper n-tuples. To cure the peaking behaviour of the integrand, the importance-sampling technique  is used, both in the integration and in the generation modes.
Processes originating the same single-photon final state as the signal e+e- -> nu nubar gamma (such as the radiative Bhabha scattering background with the two final-state electrons undetected) are not taken into account in the present version of the program.
None The program uses the random number generator RANLUX  which is included in the program.
As integrator, the code needs about 1 min of ALPHA 3000/700 for generating 10**5 wieghted events; the corresponding relative error on the total corss section is about 5*10**-3. The generation of a sample of 10**4 unweighted events requires about 30 min on the same system.
|||F. James, Comput. Phys. Commun. 79 (1994) 111.|
|||F. Boudjema, B. Mele et al., Standard Model Processes, in Physics at LEP2, G. Altarelli, T. Sjostrand and F. Zwirner eds., CERN Report 96-01, 1996 (to appear); L. Trentadue et al., Neutrino Counting, in Z Physics at LEP1, G. Altarelli, R. Kleiss and C. Verzegnassi eds., CERN Report 89-08, Vol. 1 (1989) p. 129.|
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|||S. Jadach, B.F.L. Ward and Z. Was. Comput. Phys. Commun. 79 (1994) 503.|
|||G. Montagna, O. Nicrosini, F. Piccinini and L. Trentadue, Nucl. Phys. B452 (1995) 161.|
|||F. James, Rep. Prog. Phys. 34 (1980) 1145.|
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