Return to central_xsec_howto.txt CVS log | Up to [HallC] / simc_semi |
File: [HallC] / simc_semi / central_xsec_howto.txt
(download)
Revision: 1.1.1.1 (vendor branch), Fri Apr 23 17:13:15 2004 UTC (20 years, 4 months ago) by gaskelld Branch: hallc, MAIN CVS Tags: start, baryon, NoPoltar, HEAD Changes since 1.1: +0 -0 lines simc_semi sources |
March 9, 2004 I have implemented some new flags to help calculate the "central" cross section in simc_semi. The basic idea is that, starting with a model cross section that describes the data well, we can extract the experimental cross section using: sigma_exp = Ndata/Nsimc * sigma_model In simc_semi, we want the cross section at some fixed Q2 and xbj and binning in either z or pt2. The modifications to simc_semi will allow you to dump the "central" cross section event-by-event to the ntuple. The central cross section is given in terms of sigcent = dSigma/( dOmega_e dE_e dOmega_had dE_had) in units of microbarns/MeV**2/sr**2. The fixed Q2 and xbj are taken from the beam energy and central spectrometer settings. If you are binning in z, pt2 is fixed at some constant value that you control in the input file. The z-binning is also determined in the input file where you control z_min, z_max, and the number of bins. Using the same input parameters, you can likewise bin in pt2 and pick some constant z. The new flags of interest are: sigc_flag = 0 ; Set this to 0 to bin in z, or 1 to bin in pt2 sigc_nbin = 10 ; number of bins in z or pt2 for "central" cross section calc sigc_kin_min = 0.31 ; minumum z (or pt2) for central cross section calc sigc_kin_max = 0.43 ; maximum z (or pt2) for central cross section calc sigc_kin_ind = 0.005 ; value for 'independent' variable (pt2 in GeV2 if ; binning in z) The above example is for binning in z. One might use the settings below to bin in pt2. sigc_flag = 1 ; bin in pt2 sigc_nbin = 10 ; number of bins for "central" cross section calc sigc_kin_min = 0.0 ; minumum pt2 for central cross section calc sigc_kin_max = 0.02 ; maximum pt2 for central cross section calc sigc_kin_ind = 0.37 ; value for 'independent' variable, z in this case Some new variables in the ntuple are: sigcent - already defined above. the lab cross section centjac - the "central" jacobian that converts dz dpt2 dphi -> dE_h dOmega_h you can get dSigma/(dOmega_e dE_e dz dPt2 dphi) by taking -> sigcent/centjac zi = E_hadron/nu at the vertex. This is what's used in the model pt2i + the transverse momentum at the vertex If you plot, for example, sigcent vs. zi after running simc in the mode that calculates the z-binned central cross section, you should see a step-like pattern, i.e., a constant cross section for a range in z equal to the bin width. Something like: --- --- --- --- --- Note that if you plot vs. the reconstructed z, the pattern will be smeared around because of multiple scattering, energy loss, etc. To get the cross section as a function of z, one can then define the normalized yields per z-bin of data and Monte Carlo multiplied by the central cross section in each zi bin or sig_exp (z-vertex) = Ndata (z-reconstructed) * sig_model(z-vertex) ----------------------- Nsimc (z-reconstructed)
Analyzer/Replay: Mark Jones, Documents: Stephen Wood |
Powered by ViewCVS 0.9.2-cvsgraph-1.4.0 |