Horace README =============== Horace 2.0 is a new event generator for Drell-Yan processes at hadron colliders developed by C.M. Carloni Calame, G. Montagna, O. Nicrosini and A. Vicini at INFN, Sezione di Pavia, and Dipartimento di Fisica Nucleare e Teorica of the Universita' degli Studi di Pavia (Italy) and at INFN, Sezione di Milano and Dipartimento di Fisica of the Universita' degli Studi di Milano (Italy). For information, updates and citing the code, please refer to the web page http://www.pv.infn.it/hepcomplex/horace.html Compiling the code ------------------------------ Horace is written in the standard FORTRAN 77 language, with a small C function (trapfpe.c) to trap floating point exceptions. A Makefile is provided in order to build the executable file 'HORACE'. By default, the g77 GNU Fortran compiler is used. Please, set in the Makefile file the relevant path variables and set correctly the FFLAGS variable: by default it is strongly tuned for a Pentium4 processor. The HORACE package includes a copy of the libraries LoopTools2 (patched to cover the complex W mass in vertex and box functions) and Cuba-1.2 (for the calculation of the subtraction terms). Running HORACE -------------- The value of the input parameters which have to be provided to the program can be conveniently specified in the file input-test. Input parameters ---------------- new ! HORACE mode: old=only final state QED, new=matched O(alpha) EW and higher orders QED alpha ! order of radiative corrections alpha= exact EW O(alpha) exp = matched EW O(alpha) with h.o. QED born = Born cross-section 2212 ! initial state hadrons: 2212 protons, -2212 antiprotons 2212 1 ! PDF set in HORACE 1 = MRST2004QED 2 = CTEQ6L 3 = LHAPDF (to be activated by the user in the file PDF.f ) 14000. ! CoM energy (GeV) W+andW- ! boson Drell-Yan production possible choices: W+, W-, W+andW-, Z muon ! final state lepton(s) possible choices: muon, electron save-directory/ ! name of the directory where all the data of the ! run will be saved 10000 ! number of events unweighted ! unweightening: possible choices are: weighted, unweighted 15. ! rescaling factor to adjust the efficiency of the unweightening procedure yes ! if events have to be stored (yes/no) read ! mode to include the subtraction terms possible choices are: read, calculate subtractionlhc.dat ! file of subtraction terms 1234234 ! seed for r.n.g. 0 0 ! if apply recombining and smearing routines 0 = no, 1 = yes 2.5 ! maximum lepton rapidity 25. ! minumum lepton pt (GeV) 25. ! minumum missing pt (GeV) 0 ! if apply mt cut (0 = no, 1 = yes) 200. ! mt cut (if previous = 1) If the option unweighted is chosen, the program will generate the requested number of unweighted events (given the unweightening efficiency, a larger number of points will be thrown in the phase-space). If the option weighted is chosen, the program will generate the specified number of points and compute the cross-section and the distributions. The rescaling factor to adjust the efficiency of the unweightening procedure changes the maximum value in the "hit or miss" procedure: if too large the efficiency decreases, if too small a certain number of points could exceed the maximum value and can not be correctly unweighted, introducing a bias in the estimate of the hit or miss cross section. In the result file 'statistics.txt' a recommended value for this parameter is suggested 'a posteriori' and the bias induced by the points which exceed the maximum is evaluated. The rescaling factor must be chosen large enough to make the bias vanish. Nevertheless, a smaller value can increase the efficiency while keeping the bias at a tolerable level. For a given hadronic center-of-mass energy and for a given choice of the pdf factorization scale, the program allows to compute only once the subtraction terms which remove the initial state collinear singularities. When the variable which specifies the subtraction mode is set to 'calculate' the subtraction terms are computed and saved in the file 'subtractionlhc.dat' (which can be set in input). The next time, the program can be run with the subtraction mode 'read', and the grid which interpolates the subtraction terms is read from the file 'subtractionlhc.dat'. We provide also a routine to apply selection cuts to the event sample. By default, we impose cuts on the lepton and neutrino pt and lepton pseudorapidity, the values of which can be set in the input file. A cut on the transverse mass can be also switched on. A photon-electron recombination procedure, as described in the paper hep-ph/0609170, is available together with a simplified smearing procedure, inspired by the experimental D0 and CDF criteria to estimate the detector smearing effects. The user can implement his own cuts by modifying the file cuts.f. The events produced by HORACE can be dumped to an external file (save-directory/dump.events) and can be given as input to standard showering Monte Carlo generators using the Les Houches Interface Accord. User modifiable routines ------------------------ The subroutines the user may need to modify are: -> 'userinterface' (in the file init.f) where the masses and widths of the elementary particles and the values of the coupling constants and of the CKM matrix are defined. -> 'initPDFhorace' (in the file PDF.f) where it is possible to choose, beside the two basic pdf sets (MRST2004QED and CTEQ6L), to use the LHAPDF interface; in this latter case the user needs to 1) uncomment the calls to the routines initPDFsetByName and InitPDF 2) uncomment the calls to the routine evolvePDF(x,s,f) and following lines in the routine pdf_wrapper (in the file PDF.f) 3) define in the Makefile the variable PDFLIB -> 'cuts' (in the file cuts.f) where the experimental cuts are implememted Output files ------------ The output files are saved in the 'save-directory/' directory (which can be set by the user). The files are -> statistics.txt: it is the file where cross sections, statistics information, input parameters, etc. are printed. After the input parameters entered by the user, the weighted integrated cross section is printed. It is subdivided by photon multiplicity: each cross section depends on the 'eps' parameter but the sum does not. After weighted cross section information, the unweighted events statistics is reported. The user must pay attention to the "biases" cross sections: they account for the biases due to negative weights events and unweightening failure due to an under-estimated maximum of the differential cross section. The latter bias is usually negligible, its size is estimated by the corresponding cross section. -> distribution files: in these files some differential distribution are written. The file names should be self-explaining and the data are in the form (e.g. to be plot easily with gnuplot) lower bin edge - differential cross section - corresponding error For the charged-current process, the following distributions are saved: -charged lepton transverse momentum distribution, in different ranges (ptl1, ptl2, ptl3) -missing transverse momentum distribution, in different ranges (ptn1, ptn2, ptn3) -W transverse mass distribution, in different ranges (mtw1, mtw2, mtw3) -charged lepton pseudorapidity distribution (etal) -neutrino pseudorapidity distribution (etan) -W rapidity distribution (yw) -W transverse momentum distribution (ptw) -most energetic photon transverse momentum distribution (with and without rapidity cuts: ptg1, ptg2) -number of detected photons (with and without rapidity cuts: ng1, ng2) -laboratory frame most energetic photon azimuthal angular distribution (ag) - most energetic photon rapidity distribution (etag) -W invariant mass distribution (minv) -> dump.events: the events are dumped by the routine 'evdumpALPGEN' (in the file storage.f) in the same format as the ALPGEN event generator. The weight corresponding to the events is +1 or -1 in case of unweighted generation or the event cross section in case of weighted generation (which can be also negative). Another format for event dumping is also available upon request, together with a reading routine. Enjoy Horace! Alessandro, Carlo, Guido, Oreste