RooFit Code Documentation

class: RooPdf_Bs2JPsiPhi

This is a PDF for use in fitting Bs -> Vector Vector Decays.

It has been written for the Bs -> J/Psi Phi decay to analyse the full three decay angle distribution. It also implements a mode for analysing just the single transversity angle. The choice of three or one angle modes is made through the constructor.

The PDF can handle the following ranges

  • time: arbitrary t1 to t2 in range [0,inf]
  • all angles: full range, no smaller limits allowed

The reference for the three angle distributions is: Dighe, Dunietz, Fleisher /Eur. Phys. Journal C6 , 647-662 (1999)

The definition of phi_s is such that in the SM it is negative, i.e phi_s = - 2 Chi

The PDF is instantiation is:

 !RooPdf_!Bs2JPsiPhi signal (

      //These are fixed parameters used only at construction 
       "name of pdf", 
       "description",
       btype                // Sets whether PDF is for B (=1),  Bbar (=-1) or Untagged (=0)

      //These are RooRealVar parameters which represent the event measurables:
       time,                  // proper time for event decay
       ctheta_tr,           // transversity angle for event decay
       phi_tr,               // phi angle for event decay 
       ctheta_1,           // other angle for event decay 

      // These are the fit parameters 
      gamma,               // average Bs lifetime
      dgam,                  // Bs lifetime difference 
      Rt,                       // Fraction of "transverse" or CP -1 final state
      Rp,                      // Fraction of "parallel" CP +1 final state
      delta1,                // First strong phase  (see reference)
      delta2,                // Second strong phase
      delta_ms,           // Bs mass difference
      phi_s,                 // CP violating phase

      // This is treated as an odd one out for now as it could be a measurable or a fit parameter.
      misTagFraction,         // Mistag fraction in range [0, 0.5]
    ) ;

The relation between the Rt and Rp input parameters and the amplitudes is:

AT^2 = Rt
AP^2 = Rp
AO^2 = 1-Rt-Rp

with AT^2 + AP^2 + AO^2 = 0

Example

The PDF plus an example script should be checked out from cvs

cvs checkout  Analysis/Bs2Jpsiphi/RooPdf

You will find the .h and .cxx class files for the PDF. These allow you to instantiate a standard RooFit RooAbsPdf

There is an example script to run in root (RooMainExample).

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Topic revision: r4 - 2007-11-15 - PeterClarke
 
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