Measurement of vertical bar V-cb vertical bar and the Form-Factor Slope in (B)over-bar -> Dl(-) (nu)over-bar(l) Decays in Events Tagged by a Fully Reconstructed B Meson

TLDR: In this article, a measurement of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar and the form-factor slope rho(2) in (B) over bar -> Dl(-) (nu) over b (l) decays based on 460 X 10(6) B (B)-over bar events recorded at the Gamma(4S) resonance with the BABAR detector is presented.

Abstract: We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar and the form-factor slope rho(2) in (B) over bar -> Dl(-) (nu) over bar (l) decays based on 460 X 10(6) B (B) over bar events recorded at the Gamma(4S) resonance with the BABAR detector. (B) over bar -> Dl(-) (nu) over bar (l) decays are selected in events in which a hadronic decay of the second B meson is fully reconstructed. We measure B(B- -> D(0)l(-) (nu) over bar (l))/B(B- -> Xl(-) (nu) over bar (l)) = (0.255 +/- 0.009 +/- 0.009) and B((B) over bar (0) -> D(+)l(-) (nu) over bar (l))/B((B) over bar (0) -> Xl(-) (nu) over bar (l)) = (0.230 +/- 0.011 +/- 0.011), along with the differential decay distribution in (B) over bar -> Dl(-) (nu) over bar (l) decays. We then determine G(1)vertical bar V-cb vertical bar = 42.3 +/- 1.9 +/- 1.4) X 10(-3) and rho(2) = 1.20 +/- 0.09 +/- 0.04, where G(1) is the hadronic form factor at the point of zero recoil.

Figures

FIG. 1 (color online). Fit to the m2miss distribution in two different w intervals for B ! D0‘ ‘: the data (points with error bars) are compared to the results of the overall fit (sum of the solid histograms). The PDFs for the different fit components are stacked in the order shown in the legend.

TABLE I. Fit results for each sample. The last column reports the result of the B0=B combined fit (hereB refers to B0 decays). We also report signal yields and reconstruction efficiencies integrated over the full w range. Absolute branching fractions (last row) are derived from relative branching fractions using BðB ! X‘ ‘Þ from Ref. [5].

FIG. 2 (color online). (a) Signal yield w distribution obtained summing B ! D0‘ ‘ and B0 ! Dþ‘ ‘ events. The data (d) are compared to the results of the overall fit (histogram). (b) GðwÞjVcbj distribution corrected for the reconstruction efficiency, with the fit result superimposed.

Full text

Measurement of |Vcb| and the Form-Factor Slope
in B[over-bar] -->D#-nu[over-bar] # Decays in
Events Tagged by a Fully Reconstructed B Meson
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Citation BABAR Collaboration et al. “Measurement of |V_{cb}| and the Form-
Factor Slope in B[over -bar]-->Dl^{-} nu [over -bar]_{l} Decays in
Events Tagged by a Fully Reconstructed B Meson.” Physical Review
Letters 104.1 (2010): 011802. ©2010 American Physical Society.
As Published http://dx.doi.org/10.1103/PhysRevLett.104.011802
Publisher American Physical Society
Version Final published version
Citable link http://hdl.handle.net/1721.1/58099
Terms of Use Article is made available in accordance with the publisher's
policy and may be subject to US copyright law. Please refer to the
publisher's site for terms of use.

Measurement of jV
cb
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
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Decays
in Events Tagged by a Fully Reconstructed B Meson
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**
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62
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62
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PRL 104, 011802 (2010)
PHYSICAL REVIEW LETTERS
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8 JANUARY 2010
0031-9007=10=104(1)=011802(7) 011802-1 Ó 2010 The American Physical Society

E. O. Olaiya,
63
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63
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64
L. Esteve,
64
G. Hamel de Monchenault,
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C. C. Young,
65
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M. V. Purohit,
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66
P. R. Burchat,
67
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T. S. Miyashita,
67
S. Ahmed,
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M. S. Alam,
68
J. A. Ernst,
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68
M. A. Saeed,
68
S. B. Zain,
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A. Soffer,
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S. M. Spanier,
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B. J. Wogsland,
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R. Eckmann,
71
J. L. Ritchie,
71
A. M. Ruland,
71
C. J. Schilling,
71
R. F. Schwitters,
71
B. C. Wray,
71
B. W. Drummond,
72
J. M. Izen,
72
X. C. Lou,
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F. Bianchi,
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D. Gamba,
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M. Pelliccioni,
73a,73b
M. Bomben,
74a,74b
L. Bosisio,
74a,74b
C. Cartaro,
74a,74b
G. Della Ricca,
74a,74b
L. Lanceri,
74a,74b
L. Vitale,
74a,74b
V. Azzolini,
75
N. Lopez-March,
75
F. Martinez-Vidal,
75
D. A. Milanes,
75
A. Oyanguren,
75
J. Albert,
76
Sw. Banerjee,
76
B. Bhuyan,
76
H. H. F. Choi,
76
K. Hamano,
76
G. J. King,
76
R. Kowalewski,
76
M. J. Lewczuk,
76
I. M. Nugent,
76
J. M. Roney,
76
R. J. Sobie,
76
T. J. Gershon,
77
P. F. Harrison,
77
J. Ilic,
77
T. E. Latham,
77
G. B. Mohanty,
77
E. M. T. Puccio,
77
H. R. Band,
78
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78
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78
K. T. Flood,
78
Y. Pan,
78
R. Prepost,
78
C. O. Vuosalo,
78
and S. L. Wu
78
(BABAR Collaboration)
1
Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP), Universite
´
de Savoie, CNRS/IN2P3,
F-74941 Annecy-Le-Vieux, France
2
Universitat de Barcelona, Facultat de Fisica, Departament ECM, E-08028 Barcelona, Spain
3a
INFN Sezione di Bari, Dipartimento di Fisica, I-70126 Bari, Italy
3b
Universita
`
di Bari, I-70126 Bari, Italy
4
University of Bergen, Institute of Physics, N-5007 Bergen, Norway
5
Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA
6
University of Birmingham, Birmingham, B15 2TT, United Kingdom
7
Ruhr Universita
¨
t Bochum, Institut fu
¨
r Experimentalphysik 1, D-44780 Bochum, Germany
8
University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
9
Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom
10
Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
11
University of California at Irvine, Irvine, California 92697, USA
12
University of California at Riverside, Riverside, California 92521, USA
13
University of California at San Diego, La Jolla, California 92093, USA
14
University of California at Santa Barbara, Santa Barbara, California 93106, USA
15
University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064, USA
16
California Institute of Technology, Pasadena, California 91125, USA
17
University of Cincinnati, Cincinnati, Ohio 45221, USA
18
University of Colorado, Boulder, Colorado 80309, USA
19
Colorado State University, Fort Collins, Colorado 80523, USA
20
Technische Universita
¨
t Dortmund, Fakulta
¨
t Physik, D-44221 Dortmund, Germany
21
Technische Universita
¨
t Dresden, Institut fu
¨
r Kern-und Teilchenphysik, D-01062 Dresden, Germany
22
Laboratoire Leprince-Ringuet, CNRS/IN2P3, Ecole Polytechnique, F-91128 Palaiseau, France
23
University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
24a
INFN Sezione di Ferrara, Dipartimento di Fisica, I-44100 Ferrara, Italy
24b
Universita
`
di Ferrara, I-44100 Ferrara, Italy
25
INFN Laboratori Nazionali di Frascati, I-00044 Frascati, Italy
26a
INFN Sezione di Genova, Dipartimento di Fisica, I-16146 Genova, Italy
26b
Universita
`
di Genova, I-16146 Genova, Italy
27
Harvard University, Cambridge, Massachusetts 02138, USA
28
Universita
¨
t Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg, Germany
29
Humboldt-Universita
¨
t zu Berlin, Institut fu
¨
r Physik, Newtonstrasse 15, D-12489 Berlin, Germany
30
Imperial College London, London, SW7 2AZ, United Kingdom
31
University of Iowa, Iowa City, Iowa 52242, USA
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32
Iowa State University, Ames, Iowa 50011-3160, USA
33
Johns Hopkins University, Baltimore, Maryland 21218, USA
34
Laboratoire de l’Acce
´
le
´
rateur Line
´
aire, IN2P3/CNRS et Universite
´
Paris-Sud 11, Centre Scientifique d’Orsay,
B.P. 34, F-91898 Orsay Cedex, France
35
Lawrence Livermore National Laboratory, Livermore, California 94550, USA
36
University of Liverpool, Liverpool L69 7ZE, United Kingdom
37
Queen Mary, University of London, London, E1 4NS, United Kingdom
38
University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom
39
University of Louisville, Louisville, Kentucky 40292, USA
40
Johannes Gutenberg-Universita
¨
t Mainz, Institut fu
¨
r Kernphysik, D-55099 Mainz, Germany
41
University of Manchester, Manchester M13 9PL, United Kingdom
42
University of Maryland, College Park, Maryland 20742, USA
43
University of Massachusetts, Amherst, Massachusetts 01003, USA
44
Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139, USA
45
McGill University, Montre
´
al, Que
´
bec, Canada H3A 2T8
46a
INFN Sezione di Milano, Dipartimento di Fisica, I-20133 Milano, Italy
46b
Universita
`
di Milano, I-20133 Milano, Italy
47
University of Mississippi, University, Mississippi 38677, USA
48
Universite
´
de Montre
´
al, Physique des Particules, Montre
´
al, Que
´
bec, Canada H3C 3J7
49
Mount Holyoke College, South Hadley, Massachusetts 01075, USA
50a
INFN Sezione di Napoli, Dipartimento di Scienze Fisiche, I-80126 Napoli, Italy
50b
Universita
`
di Napoli Federico II, I-80126 Napoli, Italy
51
NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands
52
University of Notre Dame, Notre Dame, Indiana 46556, USA
53
Ohio State University, Columbus, Ohio 43210, USA
54
University of Oregon, Eugene, Oregon 97403, USA
55a
INFN Sezione di Padova, Dipartimento di Fisica, I-35131 Padova, Italy
55b
Universita
`
di Padova, I-35131 Padova, Italy
56
Laboratoire de Physique Nucle
´
aire et de Hautes Energies, IN2P3/CNRS, Universite
´
Pierre et Marie Curie-Paris6,
Universite
´
Denis Diderot-Paris7, F-75252 Paris, France
57
University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
58a
INFN Sezione di Perugia, Dipartimento di Fisica, I-06100 Perugia, Italy
58b
Universita
`
di Perugia, I-06100 Perugia, Italy
59a
INFN Sezione di Pisa, Dipartimento di Fisica, I-56127 Pisa, Italy
59b
Universita
`
di Pisa, I-56127 Pisa, Italy
59c
Scuola Normale Superiore di Pisa, I-56127 Pisa, Italy
60
Princeton University, Princeton, New Jersey 08544, USA
61a
INFN Sezione di Roma, Dipartimento di Fisica, I-00185 Roma, Italy
61b
Universita
`
di Roma La Sapienza, I-00185 Roma, Italy
62
Universita
¨
t Rostock, D-18051 Rostock, Germany
63
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
64
CEA, Irfu, SPP, Centre de Saclay, F-91191 Gif-sur-Yvette, France
65
SLAC National Accelerator Laboratory, Stanford, California 94309 USA
66
University of South Carolina, Columbia, South Carolina 29208, USA
67
Stanford University, Stanford, California 94305-4060, USA
68
State University of New York, Albany, New York 12222, USA
69
Tel Aviv University, School of Physics and Astronomy, Tel Aviv, 69978, Israel
70
University of Tennessee, Knoxville, Tennessee 37996, USA
71
University of Texas at Austin, Austin, Texas 78712, USA
72
University of Texas at Dallas, Richardson, Texas 75083, USA
73a
INFN Sezione di Torino, Dipartimento di Fisica Sperimentale, I-10125 Torino, Italy
73b
Universita
`
di Torino, I-10125 Torino, Italy
74a
INFN Sezione di Trieste, Dipartimento di Fisica, I-34127 Trieste, Italy
74b
Universita
`
di Trieste, I-34127 Trieste, Italy
75
IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
76
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
77
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
78
University of Wisconsin, Madison, Wisconsin 53706, USA
(Received 27 April 2009; published 5 January 2010)
PRL 104, 011802 (2010)
PHYSICAL REVIEW LETTERS
week ending
8 JANUARY 2010
011802-3

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element jV
cb
j and the form-
factor slope 
2
in

B ! D‘


‘
decays based on 460  10
6
B

B events recorded at the ð4SÞ resonance
with the BABAR detector.

B ! D‘


‘
decays are selected in events in which a hadronic decay of the
second B meson is fully reconstructed. We measure BðB

! D
0
‘


‘
Þ=BðB

! X‘


‘
Þ¼ð0:255 
0:009  0:009Þ and Bð

B
0
! D
þ
‘


‘
Þ=Bð

B
0
! X‘


‘
Þ¼ð0:230  0:011  0:011Þ, along with the
differential decay distribution in

B ! D‘


‘
decays. We then determine Gð1ÞjV
cb
j¼ð42:3  1:9 
1:4Þ10
3
and 
2
¼ 1:20  0:09  0:04, where Gð1Þ is the hadronic form factor at the point of zero
recoil.
DOI: 10.1103/PhysRevLett.104.011802 PACS numbers: 13.20.He, 12.15.Hh, 12.38.Qk, 14.40.Nd
In the standard model (SM) of electroweak interactions,
the rate of the semileptonic

B ! D‘


‘
decay is propor-
tional to the square of the Cabibbo-Kobayashi-Maskawa
(CKM) [1] matrix element jV
cb
j, which is a measure of the
weak coupling of the b to the c quark. The length of the
side of the unitarity triangle opposite to the well-measured
angle  is proportional to jV
ub
=V
cb
j, making the determi-
nation of jV
cb
j an important test of the SM description of
CP violation. In addition, imprecise knowledge of j V
cb
jis a
significant uncertainty limiting comparison of CP viola-
tion measurements in K-meson decays with those in
B-meson decays [2].
jV
cb
j has been extracted from inclusive semileptonic B
decays [3] and exclusive decays

B ! D‘


‘
and

B !
D

‘


‘
[4]. The results rely on different QCD calcula-
tions. For inclusive decays, the decay rate is predicted by
an expansion in inverse powers of the b-quark mass and in
terms of the strong coupling constant 
S
, while exclusive
decays are expressed in terms of form factors with a
normalization taken from Heavy Quark Symmetry and
nonperturbative QCD calculations. The theoretical uncer-
tainties of these two approaches are independent, and the
measurements have, to a large extent, uncorrelated statis-
tical and systematic uncertainties. This makes the compari-
son of jV
cb
jfrom inclusive and exclusive decays a powerful
test of our understanding of semileptonic decays. The most
recent results differ by more than 2 standard deviations,
with the error on the exclusive measurements larger by a
factor >2 [5]. The

B ! D‘


‘
decay is to a large extent
complementary to the

B ! D

‘


‘
, which depends on
three form factors and therefore requires a full angular
analysis. Improvements in the measurements of the exclu-
sive decay rates are highly desirable, in particular, for

B !
D‘


‘
decays where, at present, the experimental uncer-
tainties dominate. Studies of

B ! D‘


‘
decays have
previously been reported by the Belle [6], CLEO [7],
ALEPH [8], and BABAR [4] Collaborations.
The

B ! D‘


‘
differential decay rate d
D
=dw [9]
depends on the hadronic matrix element describing
strong-interaction effects in

B ! D transitions. In the limit
of very small lepton masses (‘ ¼ e or ), their effect can
be parametrized by a single form factor GðwÞ:
d
D
dw
¼
G
2
F
jV
cb
j
2
48
3
@
M
3
D
ðM
B
þM
D
Þ
2
ðw
2
1Þ
3=2
G
2
ðwÞ; (1)
where G
F
is the Fermi coupling constant, and M
B
and M
D
are the masses of the B and D mesons, respectively. The
variable w denotes the product of the B and D meson
4-velocities V
B
and V
D
, w ¼ V
B
 V
D
¼ðM
2
B
þ M
2
D

q
2
Þ=ð2M
B
M
D
Þ, where q
2
ðp
B
 p
D
Þ
2
, and p
B
and p
D
are the 4-momenta of the B and D mesons.
In the limit of infinite heavy quark masses, GðwÞ co-
incides with the Isgur-Wise function [10]. This function is
normalized to unity at zero recoil, where q
2
is maximum.
Corrections to the heavy quark limit have been calculated
based on unquenched [11] and quenched lattice QCD [12].
Thus jV
cb
j can be extracted by extrapolating the differen-
tial decay rate to w ¼ 1. To reduce the uncertainties asso-
ciated with this extrapolation, constraints on the shape of
the form factor are necessary. Several functional forms
have been proposed [13]. We adopt the parametrization
suggested in Ref. [14], where the nonlinear dependence of
the form factor on w is expressed in terms of a single shape
parameter, the form-factor slope 
2
. In Ref. [12] the form
factor GðwÞ has been computed at a few points above the
zero recoil limit, up to w ¼ 1:2. This allows us to extract
jV
cb
jin a region where the rate is much larger, avoiding the
large extrapolation to w ¼ 1.
In this Letter, we present a measurement of d
D
=dw for

B
0
! D
þ
‘


‘
and B

! D
0
‘


‘
decays from which we
extract GðwÞjV
cb
j at w ¼ 1:0 and at few points with w>
1:0. The analysis is based on data collected with the
BABAR detector [15] at the PEP-II asymmetric-energy
e
þ
e

storage rings. The data consist of 417 fb
1
recorded
at the ð4SÞ resonance, corresponding to approximately
460  10
6
B

B pairs. An additional sample of 40 fb
1
,
collected at a center-of-mass (c.m.) energy 40 MeV below
the ð4SÞ resonance, is used to study background from
e
þ
e

! f

fðf ¼ u; d; s; c; Þ continuum events. We also
use samples of
GEANT4 Monte Carlo (MC) simulated
events that correspond to about three times the data sample
size. The simulation models

B ! D
ðÞ
‘


‘
decays using
calculations based on heavy quark effective theory
(HQET) [14],

B ! D

ð! D
ðÞ
Þ‘


‘
decays using the
ISGW2 model [16], and nonresonant

B ! D
ðÞ
‘


‘
de-
cays using the Goity-Roberts model [17]. The MC simu-
lation includes radiative effects such as bremsstrahlung in
the detector material and final-state radiation modeled by
PHOTOS [18].
PRL 104, 011802 (2010)
PHYSICAL REVIEW LETTERS
week ending
8 JANUARY 2010
011802-4