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Manuscript Title: PHIPHI: a program for computing radiative Bhabha scattering cross sections at DAPhiNE.
Authors: G. Montagna, F. Piccinini, O. Nicrosini
Program title: PHIPHI
Catalogue identifier: ACPP_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 78(1993)155
Programming language: Fortran.
Computer: DEC VAX.
Operating system: VMS, UNIX.
RAM: 2000K words
Word size: 32
Keywords: Particle physics, Elementary, Qed, Radiative bhabha Scattering (e+e- -> e+e-gamma), Phi-factory daphine, Forward direction, Large angle region, Single and double Tagging cross section, Light spot, Experimental cuts, Mass corrections, Collinear singularities.
Classification: 11.4.

Revision history:
Type Tit le Reference
correction 000ACORRECTION 26/01/94 See below

Nature of problem:
Radiative Bhabha scattering e+e- -> e+e-gamma constitutes a background process to some reactions of relevant interest at the Phi-factory DAPHINE, namely two-photon scattering e+e- -> (gamma gamma) -> e+e-X (X = phi, phi phi, phi**0/eta...) [2]. Since the two-photon processes can be disentangled from the hadronic background due to the annihilation e+e- -> hadrons by equipping the planned detectors with tagging facilities both in the very forward region (0 <= theta <= 20 mrad) and at large angles (8.5 degrees <= theta <= 171.5 degrees) [3], it turns out to be mandatory to predict the total cross sections of the radiative Bhabha scattering in the above kinematical configurations of interest at DAPhiNE.

Solution method:
The tagging cross sections are computed by means of adaptive multi- dimensional numerical integrations of the proper matrix elements over the phase space allowed by experimental cuts. The single and double tagging cross sections at very small angles are computed by integrating the full matrix element for t-channel radiative Bhabha scattering, including all mass corrections terms up to O(m**2) [4], while for small- large and large-large angle double tagging the (s+t)-channel matrix element of ref. [5] is implemented in the program. For the tagging distributions in the forward region the kinematics and the matrix element of ref. [4] are computed in REAL*16 precision in order to exactly evaluate the corresponding very small values of the momentum transfer (of order m**6/E**4) and take care of the cancellations among large partial terms occurring in the calculation of the matrix element.

Unusual features:
REAL*16 declarations are used. All the numerical integrations implemented in the program are performed by means of subroutines from the library of mathematical subprograms NAGLIB [1].

Running time:
Dependent on the required cross section and the experimental cuts. The cross sections for small angle electron single tagging without cuts on positron and photon variables, for light spot in the forward direction and for small-large double tagging are returned very quickly, namely within 0.2 - 2.5 CPU seconds for IBM RISC/350. The total cross sections for large-large angle double tagging typically requires about 180 CPU seconds of IBM RISC/350 and DEC VAXStation 4000-90. The total cross sections for double tagging of electron and positron at very small angle and for coincidence rate of electron and photon in the forward region can be obtained with a relative numerical error of 1 per cent in about 5000 CPU seconds of IBM RISC/350 and about 56 CPU hours for DEC VAXStation 4000-90.

References:
[1] NAG Fortran Library Manual Mark 15 (Numerical Algorithms Group, Oxford, 1991).
[2] F. Anulli et al., The DAPHINE Physics Handbook, Vol. II, pag. 435, L. Maiani, G. Pancheri and N. Paver Eds.
[3] G. Alexander et al., Two-Photon Physics Capabilities of KLOE at DAPHINE, LNF - 93/030(P); KLOE, A General Purpose Detector for DAPHINE, LNF 92/019(R).
[4] M. Greco, G. Montagna, O. Nicrosini and F. Piccinini, Radiative Bhabha Scattering at DAPHINE, submitted to Phys. Lett. B.
[5] F.A. Berends, R. Kleiss, P. De Causmaecker, R. Gastmans, W. Troost and T.T. Wu, Nucl. Phys. B206 (1982) 61 and references therein.

CORRECTION SUMMARY
Manuscript Title: PHIPHI: a program for computing radiative Bhabha scattering cross sections at DAPhiNE. (C.P.C. 78(1993)155).
Authors: G. Montagna, F. Piccinini, O. Nicrosini
Program title: 000ACORRECTION 26/01/94
Catalogue identifier: ACPP_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 79(1994)351
Classification: 11.4.