Study of B -> D^(*)D_s(J)^(*) Decays andMeasurement of D_s^- and D_s(J)(2460)- Branching Fractions Page: 4 of 8
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4
sUniversity of Victoria, Victoria, British Columbia, Canada V8W 3P6
'9Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
s"University of Wisconsin, Madison, Wisconsin 53706, USA
8 Yale University, New Haven, Connecticut 06511, USA
(Dated: August 15, 2006)
We present branching fraction measurements of twelve B meson decays of the form B
D(*)D(). The results are based on Y(4S) decays in BB pairs. One of the B mesons is fully recon-
structed and the other decays to two charm mesons, of which one is reconstructed, and the mass and
momentum of the other is inferred by kinematics. Combining these results with previous exclusive
branching fraction measurements, we determine B(D- > 7-) = (4.62 + 0.36stat. + 0.51syst.)%,
B(Dsi(2460)- - DS-7r) = (56 + 13stat. + 9syst.)% and B(D i(2460)- > D>-y) = (16 + 4stat. +
3syst. ) %.
PACS numbers: 13.25.Hw, 13.25.FtIn this paper we present the study of charged and
neutral B mesons decaying to two charm mesons, i.e.
B -> DmeasDx [1]. Dmeas represents a fully reconstructed
D(*)+,o or Di*) meson, and the mass and momentum
of the Dx are inferred from the kinematics of the two-
body B decay. This study allows measurements of B
branching fractions without any assumption on the de-
cays of the Dx. Measurements of these two-body branch-
ing fractions can provide tests of the factorization of
the decay amplitudes [2] in the high momentum trans-
fer regime [3]. From two separate classes of events with
Dmeas D>*) and with Dx - D >*) we measure the
branching fraction of D - p7r-, which has important
implications for a wide range of D, and B physics. Fur-
thermore, we select final states with Dx = Dj(2460)-
and combine with the BABAR measurements of B(B ->
D*)+,Dsj(2460)-) x B(Daj(2460)- - D--7r0) and
B(B -> D(*)+,'0Da(2460)-) x B(Dai(2460) ->
D-y) [4], thus extracting for the first time the absolute
branching fractions of this recently observed state [5].
This analysis uses T(4S) -> BB events in which either
a B+ or a B0 meson decays into a fully reconstructed
hadronic final state (Breco). The measurements are based
on an integrated luminosity of 210.5 fb-I1 recorded at
the T(4S) resonance with the BABAR detector at the
PEP-II asymmetric-energy e+e- collider operating near
the T(4S) resonance. An additional 21.7 fb-1 recorded
40 MeV below the resonance (off-resonance) are used to
evaluate backgrounds. The BABAR detector is described
in detail elsewhere [6]. Charged-particle trajectories are
measured by a vertex tracker with 5 double-sided layers
and a 40-layer drift chamber, both operating in a 1.5-T
magnetic field of a superconducting solenoid. Charged-
particle identification is provided by the specific energy
loss (dE/dx) in the tracking devices and by an internally
reflecting ring-imaging Cherenkov detector. Photons are
detected by a CsI(Tl) electromagnetic calorimeter. We
use Monte Carlo simulations (MC) of the BABAR detec-
tor based on GEANT4 [7] to optimize selection criteria
and determine selection efficiencies.
To reconstruct a large sample of B mesons, thehadronic decays Breco - DY+, D*Y+ are selected.
Here, the system Y+ consists of hadrons with a to-
tal charge of +1, composed of niwr n2K n3K0 n4AT,
where n1 + n2 < 5, n3 < 2, and n4 < 2. We re-
construct D* -> bDr-; D*0 -> D0O, D0; D- -
K+7r-r, K+7r-r-, K27r-, K27r-0, K7r-+r ;
73 - K+7r-, K+7r-7r, K+7r-r-r+, K27r+7r-; and
K - r+7r--. The kinematic consistency of Breco can-
didates is checked with two variables, the beam energy-
substituted mass mES s/4 - 4 and the energy dif-
ference AE = EB - I/2. Here fi is the total energy in
the T(4S) center-of-mass (CM) frame, and pB and EB
denote the momentum and energy of the Breco candidate
in the same frame. The resolution on AE is measured to
be o-AE 10 - 35MeV, depending on the decay mode,
and we require AEJ < 3-AE.
For each reconstructed B decay mode, the purity P is
estimated as the ratio of the number of signal events with
mES > 5.27GeV/c to the total number of events in the
same range, and is evaluated on data. We only use modes
for which P exceeds a decay-mode dependent threshold
in the range of 9% to 24%. In events with more than one
Breco we select the decay mode with the highest purity.
On average, we reconstruct one signal Breco candidate in
0.3% (0.5%) of the B0B0 (B+B-) events.
The selected sample of Breco is used as normalization
for the determination of the branching fractions. It is
contaminated by e+e -> qq (q = u, d, s, c) events and
by other T(4S) -> B0B0 or B+B- decays, in which the
Breco is mistakenly reconstructed from particles coming
from both B mesons in the event. To significantly reduce
the e+c -> qq background we require the angle Byj,
defined in the CM frame, between the thrust axis [8] of
the Breco and the thrust axis of all charged and neutral
particles in the event excluding the ones that form the
Breco, to satisfy the requirement Icos EB I < 0.7.
On this signal-enriched sample (Fig. 1), the contribu-
tions from the background are estimated as the sum of
three components: the e+c -> qq, the B0B0, and the
B+B- events. The shapes of these background distribu-
tions are taken from MC simulation. The normalization
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Aubert, B.; Barate, R.; Bona, M.; Boutigny, D.; Couderc, F.; Karyotakis, Y. et al. Study of B -> D^(*)D_s(J)^(*) Decays andMeasurement of D_s^- and D_s(J)(2460)- Branching Fractions, article, May 16, 2006; [Menlo Park, California]. (https://digital.library.unt.edu/ark:/67531/metadc875643/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.