Fabrizio's contribution to the IHBD Meeting, 10/09/02

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We have repeated the work done by Franco et al. to determine the parameters alpha and rho (BAD#287, V5). This parameters can be used in the likelihood for the fit to the decay time distribution to take into account the mis-tagging due to tracks from the non-resonstructed D0 used to tag the flavour of the B. alpha and rho are function of the cosine of the angle theta between the tagging track and the soft pion.

We have produced the reduced ntuples for the B->D*pi analysis, with an executable that has been modified by Wolfgang with respect to the original one (IHBDFit/prodKumacs/mkdt1.f) in order to have kaon tagging with the max angle kaon only. Here you can see the cos(theta) distribution for signal events (no CP), BBbar events and data events in the signal region. The distributions we obtain for the kaon tagging have the expected shape, while for lepton tagging we see no difference between the Btag and Dtag events.

  • Maybe some bug in the code ?

    In the case of the kaon tag, we have performed a fit to the cos(theta) distribution of on-resonance data using off-resonance events (rescaled using luminosity), BBbar events (scaled by fitting the on-resonance sample with off-reso and BBbar only in the side-band region), Btag and Dtag signal events. The scaling factor for Btag and Dtag has been found by using a ROOT routine that takes into account the limited statistic in each bin of the distributions (same used by Franco et al.). The ratio between observed cos(theta) distribution and fit result can be found here.

    The distribution of alpha[cos(theta)] and rho[cos(theta)], defined as: 

     H(alpha) = a1*H(Dtag)/(a1*H(Dtag) + a2*H(Btag))
 H(rho)   = b1*H(Dtag)mix/(b1*H(Dtag)mix + b2*H(Dtag)unmixed)
    are then fitted using polinomial functions.

    We are ready to do the same analysis also on the lepton tag sample, once we understand the cos(theta) distributions for Btag and Dtag events in this case.

    All this work has been done with the help of Marco Resa, a summer student who visited Royal Holloway this august.

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    Last Update: 22/04/2002 19:30 PT