ALPGEN

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V1.1 vs V1 update. The following things have been changed/debugged/added:

Earlier bug reports/fixes for V1:

• July 3rd: A problem with the most recent gcc 3.1 compiler has been pointed out by Gustaaf Brooijmans (D0). The problem appears when using the optimization flag -O2 or higher (-O3), and goes away with lower optimization (-O1, -O). While we are trying to understand the origin of the problem, users willing to compile with gcc 3.1 are advised to select the following compilation option: FCFLAGS = -O1 -Wall -fugly-complex -fno-second-underscore -fno-backslash -fno-automatic -finit-local-zero -Wunused -Wno-globals -ffast-math
  • July 8: a fix to the above gcc 3.1 compilation problem has been introduced in the subroutine gammamat contained in the file alplib/Asu3.f. This is now part of the default library, alpgen.tar.gz
  • July 12: the above problem has been identified as a compiler bug. While GNU fixes it, the fix indicated in the previous point is confirmed as a temporary solution.
• July 15th: a bug in the storing of Z+jet events was found by P.Richardson. The information on the type of Z decay products was not passed correctly to Herwig. The following routines have been updated, and can be found at the end of the library: herlib/atoher.f, zjetlib/zjets.f
• July 17th: after a warning by E.Collins, a typo was found in the Z+jet phase space. This had an impact on the cross-sections for the low multiplicities (1 and 2 jet) final states. The routine zjetlib/zjets.f has been updated, and can be found at the end of the library.
• July 22th: the assignement of the lepton code (electron vs neutrino) has been fixed in the W+jets code. The change has no impact on the cross sections without lepton cuts. The routine wjetlib/wjets.f has been updated, and can be found at the end of the library.

Recent items incorporated in V1.1:

• The PYTHIA, LesHouches compliant, interface has been added (courtesy of Andrea Messina, Univ of Roma I). It appears in the directory /pylib. Its functionality is similar to HERWIG's
• The Fortran90 implementation is now available for ALL hard processes.
• The defaults for the selection of EW parameters have been changed. All processes now have as a default the parameter iewopt=3. This means that the input parameters are MW(80.41), MZ(91.188) and GFermi (1.16639d-5). Output parameters are: sin2(thetaW)=0.2224, 1/aem=132.4, g=0.65316.
• Wqq and Wjet:
  • A missing 4-quark subprocess has been added: q' g->W q q qbar (bug reported by Soushi Tsuno, KEK)
  • The array ni in the common book was wrongly declared as integer
• Zqq and Zjet:
  • The lepton-type information was wrongly written to output in the case of Z-> nu nubar events, making it impossible to process unweighted events (bug reported by Mike Seymour).
  • A typo in the equation for the Z width, resulting in incorrect leptonic BR's for the Z, has been fixed.
  • The b quark mass was wrongly set in final states with more than one heavy quark pair
  • The Q scale parametrizations now include the options iqopt=0-5, with: (0) mZ^2+pt[ll]^2, (1) mZ^2, (2) mZ^2+sum(ptjet^2), (3) m[ll]^2+pt[ll]^2, (4) m[ll]^2, (5) m[ll]^2+sum(ptjet^2). The difference between (0-2) and (3-5) consists in forcing the numerical value of Q to be linked to the input value of mZ (in the first case), or to the actual invariant mass of the dilepton pair (m[ll]) in the second case. This last option is more suitable in the case of runs away from the Z mass peak region.