PROGRAM SUMMARY
Title of program:
TOPAZ0 4.0
Catalogue identifier:
ADIR
Ref. in CPC:
117(1999)278
Operating system: VMS, UNIX
High speed store required:
300K words
Number of bits in a word:
32
Number of lines in distributed program, including test data, etc:
15670
Programming language used: Fortran
Computer: DEC-ALPHA 3000
Other versions of this program:
Cat. Id. Title Ref. in CPC ACNT TOPAZ0 76(1993)328 ADCQ TOPAZ0 2.0 93(1996)120
Nature of physical problem:
An accurate theoretical description of e+e- annihilation processes and
of Bhabha scattering for centre of mass energies at the Z resonance
(LEP 1) and above (LEP 2) is necessary in order to compare theoretical
cross sections and asymmetries with the experimental ones as measured by
the LEP collaborations (realistic observables). In particular a
realistic theoretical description, i.e. a description in which the
effects of experimental cuts, such as maximum acollinearity, energy or
invariant mass and angular acceptance of the outgoing fermions, are
taken into account, allows the comparison of the Minimal Standard Model
predictions with experimental raw data, i.e. data corrected for detector
efficiency but not for acceptance. The program takes into account all
the corrections, pure weak, QED and QCD, which allow for such a
realistic theoretical description. The program offers also the
possibility of computing the Z parameters (pseudo-observables) including
the state-of-the-art of radiative corrections, which is important for
the indirect determination of the fundamental Standard Model parameters.
Method of solution
Same as in the original program. A detailed description of the
theoretical formulation and of a sample of physical results obtained can
be found in ref. [2].
Summary of revisions
The new version of the program TOPAZ0 4.0, includes several
improvements:
1. recently computed two-loop electroweak next-to-leading
O(alpha**2mt**2) corrections [3,4];
2. QCD radiative corrections tothe hadronic decay of the Z, providing
complete corrections of O(alphaalphas) to Gamma(Z -> qqbar) with
q = u, d, s, c and b [5];
3. purely weak boxes for s-channel processes [6];
4. next-to-leading O(alpha**2) and leading O(alpha**3) QED corrections
to the cross section radiator [7,8];
5. improved treatment of the convolution integral for the
forward-backward asymmetry [9].
All the new corrections are relevant for electroweak physics at LEP 1
and/or LEP 2.
Restrictions on the complexity of the problem
Analytic formulas have been developed for an experimental set-up with
symmetrical angular acceptance. Moreover the angular acceptance of the
scattered antifermion has been assumed to be larger than the one of the
scattered fermion. The prediction for Bhabha scattering is understood
to be for the large-angle regime. Initial-state next-to-leading
O(alpha) QED corrections are treated exactly for a cut on the invariant
mass of the event after initial-state radiation, in the soft photon
approximation otherwise. This means that for centre of mass energies
sensibly above the Z0 peak (typically in the LEP 1.5 - LEP 2 regime),
the theoretical accuracy of the C branch is under control (theoretical
error <= 0.3 per cent) when excluding the Z radiative return, whereas
including it the theoretical error can grow up to some per cent
depending on the final state selected [10]. In the same energy range,
large angle Bhabha scattering becomes a t-channel dominated process:
since all the QED corrections implemented are strictly valid for
s-channel processes, this means that large angle Bhabha scattering off
the Z resonance is treated at the leading logarithmic level.
Typical running time
This depends strongly on the particular experimental set-up studied and
on the energy range. As evaluator of realistic observables in seven
energy points around the Z0 peak, between 10 (extrapolated set-up) and
270 (realistic set-up) CPU seconds for HP-UX 9000. Anyway, for the
realistic observables the CPU time depends strongly on being at LEP 1 or
LEP 2, and on the scaling factor SE controlling the accuracy of the
numerical integrations. For the evaluation of pseudo-observables the
program runs much faster.
Unusual features of the program
Subroutines from the library of mathematial subprograms NAGLIB [1] for
the numerical integrations are used in the program.
References
[1] NAG Fortran Library Manual Mark 17 (Numerical Algorithms Group,
Oxford, 1991).
[2] G. Montagna, O. Nicrosini, G. Passarino, F. Piccinini, R. Pittau,
Nucl. Phys. B 401 (1993) 3.
[3] G. Degrassi, S. Fanchiotti, A. Sirlin, Nucl. Phys. B 351 (1991) 49;
G. Degrassi, A. Sirlin, Nucl. Phys. B 352 (1991) 342;
G. Degrassi, P. Gambino, A. Vicini, Phys. Lett. B 383 (1996) 219;
G. Degrassi, P. Gambino, A. Sirlin, Phys. Lett. B 394 (1997) 188.
[4] G. Degrassi, P. Gambino, in preparation.
[5] A. Czarnecki, J.H. Kuhn, Phys. Rev. Lett. 77 (1996) 3955; hep-ph/
9712228;
R. Harlander, T. Seidensticker, M. Steinhauser, hep-ph/971228.
[6] F. Boudjema, B. Mele et al., Standard Model Processes, in: Physics
at LEP2, Vol. 2, G. Alterelli, T. Sjostrand, F. Zwirner, eds.,
CERN Report 96-01 (Geneva, 1996) p. 229.
[7] F. Berends et al., Z Line shape, in: Z Physics at LEP 1, Vol. 1,
G. Altarelli, R. Kleiss, C. Verzegnassi, eds., CERN Report 89-08
(Geneva, 1989) p. 89.
[8] G. Montagna, O. Nicrosini, F. Piccinini, Phys. Lett. B 406 (1997)
243.
[9] M. Bohm, W. Hollik et al., Forward-Backward Asymmetries, in: Z
Physics at LEP 1, Vol. 1, G. Altarelli, R. Kleiss, C. Verzegnassi,
eds., CERN Report 89-08 (Geneva, 1989) p. 203.
[10] G. Montagna, O. Nicrosini, F. Piccinini, Z. Phys. C 76 (1997) 45.