Research Work of David Cote
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My research work at BaBar is primarly focussed on semileptonic B decays.
More precisely, I've developped several analysis tools that are useful for
measuring the CKM matrix element |Vub| as well as the branching fractions and 
form factors of several exclusive B->Xu l nu decays, where l stands for 
electrons of muons, and Xu stands for one of the pi+, pi0, eta, eta', rho+, 
rho0 or omega mesons. 

For my Ph.D. thesis, I developped an innovative "Loose Neutrino Reconstruction Technique".
With this technique, we reconstruct B meson candidates using the charged pion 
and lepton tracks together with the event's missing momentum as an approximation 
to the signal neutrino momentum. The decay of the second B meson is not explicitly 
reconstructed. The neutrino four-momentum is inferred from the difference between 
the momentum of the colliding-beam particles and the sum of the momenta of all the 
charged and neutral particles detected in a single event. Compared with the tagged 
analyses in which the two B mesons are explicitly reconstructed, the neutrino 
reconstruction approach yields a lower signal purity but a significant increase 
in the signal reconstruction efficiency. The present Loose Neutrino Reconstruction 
Technique also increases the signal efficiency substantially with respect to the 
previous untagged approach by avoiding the tight neutrino quality cuts which ensure 
that the neutrino properties are well taken into account when computing 
q2=(P_lep + P_nu)^2. With our tehcnique, we calculate instead the momentum 
transfer as q2=(P_B - P_pi)^2. In this way, the value of q2 is 
unaffected by any mis-reconstruction of the rest of the event.

With my teamates, I did an analysis of the B0->pilnu channel, based on the Loose
Neutrino Reconstruction Technique, that lead to substential improvements in the 
field and was published in the prestigious Physical Review Letters. Our measurements 
of the branching fraction and of the q2 spectrum of B0->pilnu decay were the most 
precise in the world. We characterized the q2 spectrum of these decays with a complete 
covariance matrix, which allowed improved tests of related QCD calculations. As a 
result, our knowledge of |Vub| is improved, and promised to be even more improved in 
the near future when precise unquenched lattice QCD calculations should become available 
for the B0->pilnu channel. The Loose Neutrino Reconstruction Technique will now be used 
to perform the first studies of the rarer decays B->eta' l nu.

In addition, I'm working on data/MC corrections of K0L detection 
efficiency and energy deposition in BaBar's ElectroMagnetic Calorimeter,
using a D*+/- -> D0 pi+/-, D0->K0 pi+ pi- control sample. This work is 
done as a common service task to the BaBar community. In the past, I've
also worked on synchronization of the machine background between the 
various subsytems in the BaBar simulation software.

My research work lead to the following published documents 
(in some cases for BaBar internal usage only):

 -- "Measurement of the B0 --> pi- l+ nu form-factor shape and branching fraction, 
    and determination of |V(ub)| with a loose neutrino reconstruction technique",
    BaBar Collaboration, Contributed to 33rd International Conference on High Energy 
    Physics (ICHEP 06), Moscow, Russia, Aug. 2006, 25pp, hep-ex/0607060;
    (To be submitted to Physical Review Letters)

 -- "Study of K0L efficiency and reconstruction using data samples",
    M. Bona, D. Cote, G. Cavoto, E. Di Marco, M. Pelliccioni, M. Pierini,
    BAD #1191;

 -- "Reweighting of the form factors in exclusive B->Xlnu decays", 
    D. Cote S. Brunet, P. Taras, B. Viaud, Mai 2004. 10pp. 
    Eur.Phys.J.C38:105-113,2004,
    e-Print Archive: hep-ex/0409046;

 -- "SEMILEPTONIC B DECAYS, B MIXING AND MAGNITUDES OF CKM ELEMENTS AT BABAR"
    D. Cote conference proceeding published in: 
    Frascati Physics Series Vol. XXXVI, DAPHNE 2004: Physics at meson factories ;

 -- "Reweighting of the form factors in exclusive B->Xlnu decays", 
    D. Cote BaBar Analysis Document (BAD) #809 ;

 -- "XSLBtoXulnu: Exclusive semileptonic b -> u skim", 
    D. Cote S. Brunet, M.G. Greene, BAD #740 ;
 
 -- "Improvement of the background mixing for all subsystems in 
    the BaBar Monte Carlo simulation", 
    N.R. Barlow, A.W. Borgland, D. Cote V. Halyo, M. van Hoek, BAD #332.

David Cote, December 8th 2006