Evidence for an Excess of
B
!
D
ðÞ
Decays
J. P. Lees,
1
V. Poireau,
1
V. Tisserand,
1
J. Garra Tico,
2
E. Grauges,
2
A. Palano,
3b,3a
G. Eigen,
4
B. Stugu,
4
D. N. Brown,
5
L. T. Kerth,
5
Yu. G. Kolomensky,
5
G. Lynch,
5
H. Koch,
5
T. Schroeder,
6
D. J. Asgeirsson,
7
C. Hearty,
7
T. S. Mattison,
7
J. A. McKenna,
7
R. Y. So,
7
A. Khan,
8
V. E. Blinov,
9
A. R. Buzykaev,
9
V. P. Druzhinin,
9
V. B. Golubev,
9
E. A. Kravchenko,
9
A. P. Onuchin,
9
S. I. Serednyakov,
9
Yu. I. Skovpen,
9
E. P. Solodov,
9
K. Yu. Todyshev,
9
A. N. Yushkov,
9
M. Bondioli,
10
D. Kirkby,
10
A. J. Lankford,
10
M. Mandelkern,
10
H. Atmacan,
11
J. W. Gary,
11
F. Liu,
11
O. Long,
11
G. M. Vitug,
11
C. Campagnari,
12
T. M. Hong,
12
D. Kovalskyi,
12
J. D. Richman,
12
C. A. West,
12
A. M. Eisner,
13
J. Kroseberg,
13
W. S. Lockman,
13
A. J. Martinez,
13
B. A. Schumm,
13
A. Seiden,
13
D. S. Chao,
14
C. H. Cheng,
14
B. Echenard,
14
K. T. Flood,
14
D. G. Hitlin,
14
P. Ongmongkolkul,
14
F. C. Porter,
14
A. Y. Rakitin,
14
R. Andreassen,
15
Z. Huard,
15
B. T. Meadows,
15
M. D. Sokoloff,
15
L. Sun,
15
P. C. Bloom,
16
W. T. Ford,
16
A. Gaz,
16
U. Nauenberg,
16
J. G. Smith,
16
S. R. Wagner,
16
R. Ayad,
17,
*
W. H. Toki,
17
B. Spaan,
18
K. R. Schubert,
19
R. Schwierz,
19
D. Bernard,
20
M. Verderi,
20
P. J. Clark,
21
S. Playfer,
21
D. Bettoni,
22a
C. Bozzi,
22a
R. Calabrese,
22b,22a
G. Cibinetto,
22b,22a
E. Fioravanti,
22b,22a
I. Garzia,
22b,22a
E. Luppi,
22b,22a
M. Munerato,
22b,22a
L. Piemontese,
22a
V. Santoro,
22a
R. Baldini-Ferroli,
23
A. Calcaterra,
23
R. de Sangro,
23
G. Finocchiaro,
23
P. Patteri,
23
I. M. Peruzzi,
23,
†
M. Piccolo,
23
M. Rama,
23
A. Zallo,
23
R. Contri,
24b,24a
E. Guido,
24b,24a
M. Lo Vetere,
24b,24a
M. R. Monge,
24b,24a
S. Passaggio,
24a
C. Patrignani,
24b,24a
E. Robutti,
24a
B. Bhuyan,
25
V. Prasad,
25
C. L. Lee,
26
M. Morii,
26
A. J. Edwards,
27
A. Adametz,
28
U. Uwer,
28
H. M. Lacker,
29
T. Lueck,
29
P. D. Dauncey,
30
U. Mallik,
31
C. Chen,
32
J. Cochran,
32
W. T. Meyer,
32
S. Prell,
32
A. E. Rubin,
32
A. V. Gritsan,
33
Z. J. Guo,
33
N. Arnaud,
34
M. Davier,
34
D. Derkach,
34
G. Grosdidier,
34
F. Le Diberder,
34
A. M. Lutz,
34
B. Malaescu,
34
P. Roudeau,
34
M. H. Schune,
34
A. Stocchi,
34
G. Wormser,
34
D. J. Lange,
35
D. M. Wright,
35
C. A. Chavez,
36
J. P. Coleman,
36
J. R. Fry,
36
E. Gabathuler,
36
D. E. Hutchcroft,
36
D. J. Payne,
36
C. Touramanis,
36
A. J. Bevan,
37
F. Di Lodovico,
37
R. Sacco,
37
M. Sigamani,
37
G. Cowan,
38
D. N. Brown,
39
C. L. Davis,
39
A. G. Denig,
40
M. Fritsch,
40
W. Gradl,
40
K. Griessinger,
40
A. Hafner,
40
E. Prencipe,
40
R. J. Barlow,
41,
‡
G. Jackson,
41
G. D. Lafferty,
41
E. Behn,
42
R. Cenci,
42
B. Hamilton,
42
A. Jawahery,
42
D. A. Roberts,
42
C. Dallapiccola,
43
R. Cowan,
44
D. Dujmic,
44
G. Sciolla,
44
R. Cheaib,
45
D. Lindemann,
45
P. M. Patel,
45
S. H. Robertson,
45
P. Biassoni,
46b,46a
N. Neri,
46a
F. Palombo,
46b,46a
S. Stracka,
46b,46a
L. Cremaldi,
47
R. Godang,
47,
§
R. Kroeger,
47
P. Sonnek,
47
D. J. Summers,
47
X. Nguyen,
48
M. Simard,
48
P. Taras,
48
G. De Nardo,
49b,49a
D. Monorchio,
49b,49a
G. Onorato,
49b,49a
C. Sciacca,
49b,49a
M. Martinelli,
50
G. Raven,
50
C. P. Jessop,
51
J. M. LoSecco,
51
W. F. Wang,
51
K. Honscheid,
52
R. Kass,
52
J. Brau,
53
R. Frey,
53
N. B. Sinev,
53
D. Strom,
53
E. Torrence,
53
E. Feltresi,
54b,54a
N. Gagliardi,
54b,54a
M. Margoni,
54b,54a
M. Morandin,
54a
M. Posocco,
54a
M. Rotondo,
54a
G. Simi,
54a
F. Simonetto,
54b,54a
R. Stroili,
54b,54a
S. Akar,
55
E. Ben-Haim,
55
M. Bomben,
55
G. R. Bonneaud,
55
H. Briand,
55
G. Calderini,
55
J. Chauveau,
55
O. Hamon,
55
Ph. Leruste,
55
G. Marchiori,
55
J. Ocariz,
55
S. Sitt,
56b,56a
M. Biasini,
56b,56a
E. Manoni,
56b,56a
S. Pacetti,
56b,56a
A. Rossi,
56b,56a
C. Angelini,
57b,57a
G. Batignani,
57b,57a
S. Bettarini,
57b,57a
M. Carpinelli,
57b,57a,
k
G. Casarosa,
57b,57a
A. Cervelli,
57b,57a
F. Forti,
57b,57a
M. A. Giorgi,
57b,57a
A. Lusiani,
57c,57a
B. Oberhof,
57b,57a
E. Paoloni,
57b,57a
A. Perez,
57a
G. Rizzo,
57b,57a
J. J. Walsh,
57a
D. Lopes Pegna,
58
J. Olsen,
58
A. J. S. Smith,
58
A. V. Telnov,
58
F. Anulli,
59a
R. Faccini,
59a
F. Ferrarotto,
59a
F. Ferroni,
59b,59a
M. Gaspero,
59b,59a
L. Li Gioi,
59a
M. A. Mazzoni,
59a
G. Piredda,
59a
C. Bu
̈
nger,
60
O. Gru
̈
nberg,
60
T. Hartmann,
60
T. Leddig,
60
H. Schro
̈
der,
60,
{
C. Voss,
60
R. Waldi,
60
T. Adye,
61
E. O. Olaiya,
61
F. F. Wilson,
61
S. Emery,
62
G. Hamel de Monchenault,
62
G. Vasseur,
62
Ch. Ye
`
che,
62
D. Aston,
63
D. J. Bard,
63
R. Bartoldus,
63
J. F. Benitez,
63
C. Cartaro,
63
M. R. Convery,
63
J. Dorfan,
63
G. P. Dubois-Felsmann,
63
W. Dunwoodie,
63
M. Ebert,
63
R. C. Field,
63
M. Franco Sevilla,
63
B. G. Fulsom,
63
A. M. Gabareen,
63
M. T. Graham,
63
P. Grenier,
63
C. Hast,
63
W. R. Innes,
63
M. H. Kelsey,
63
P. Kim,
63
M. L. Kocian,
63
D. W. G. S. Leith,
63
P. Lewis,
63
B. Lindquist,
63
S. Luitz,
63
V. Luth,
63
H. L. Lynch,
63
D. B. MacFarlane,
63
D. R. Muller,
63
H. Neal,
63
S. Nelson,
63
M. Perl,
63
T. Pulliam,
63
B. N. Ratcliff,
63
A. Roodman,
63
A. A. Salnikov,
63
R. H. Schindler,
63
A. Snyder,
63
D. Su,
63
M. K. Sullivan,
63
J. Va’vra,
63
A. P. Wagner,
63
W. J. Wisniewski,
63
M. Wittgen,
63
D. H. Wright,
63
H. W. Wulsin,
63
C. C. Young,
63
V. Ziegler,
63
W. Park,
64
M. V. Purohit,
64
R. M. White,
64
J. R. Wilson,
64
A. Randle-Conde,
65
S. J. Sekula,
65
M. Bellis,
66
P. R. Burchat,
66
T. S. Miyashita,
66
E. M. T. Puccio,
66
M. S. Alam,
67
J. A. Ernst,
67
R. Gorodeisky,
68
N. Guttman,
68
D. R. Peimer,
68
A. Soffer,
68
P. Lund,
69
S. M. Spanier,
69
J. L. Ritchie,
70
A. M. Ruland,
70
R. F. Schwitters,
70
B. C. Wray,
70
J. M. Izen,
71
X. C. Lou,
71
F. Bianchi,
72b,72a
D. Gamba,
72b,72a
S. Zambito,
72b,72a
L. Lanceri,
73b,73a
L. Vitale,
73b,73a
F. Martinez-Vidal,
74
A. Oyanguren,
74
H. Ahmed,
75
J. Albert,
75
Sw. Banerjee,
75
F. U. Bernlochner,
75
H. H. F. Choi,
75
G. J. King,
75
R. Kowalewski,
75
M. J. Lewczuk,
75
I. M. Nugent,
75
J. M. Roney,
75
R. J. Sobie,
75
N. Tasneem,
75
T. J. Gershon,
1
P. F. Harrison,
1
T. E. Latham,
1
H. R. Band,
77
S. Dasu,
77
Y. Pan,
77
R. Prepost,
77
and S. L. Wu
77
PRL
109,
101802 (2012)
PHYSICAL REVIEW LETTERS
week ending
7 SEPTEMBER 2012
0031-9007
=
12
=
109(10)
=
101802(8)
101802-1
Ó
2012 American Physical Society
(
B
A
B
AR
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, I-70126 Bari, Italy
3b
Dipartimento di Fisica, 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
Ruhr Universita
̈
t Bochum, Institut fu
̈
r Experimentalphysik 1, D-44780 Bochum, Germany
7
University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
8
Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom
9
Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
10
University of California at Irvine, Irvine, California 92697, USA
11
University of California at Riverside, Riverside, California 92521, USA
12
University of California at Santa Barbara, Santa Barbara, California 93106, USA
13
University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064, USA
14
California Institute of Technology, Pasadena, California 91125, USA
15
University of Cincinnati, Cincinnati, Ohio 45221, USA
16
University of Colorado, Boulder, Colorado 80309, USA
17
Colorado State University, Fort Collins, Colorado 80523, USA
18
Technische Universita
̈
t Dortmund, Fakulta
̈
t Physik, D-44221 Dortmund, Germany
19
Technische Universita
̈
t Dresden, Institut fu
̈
r Kern- und Teilchenphysik, D-01062 Dresden, Germany
20
Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, F-91128 Palaiseau, France
21
University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
22a
INFN Sezione di Ferrara, I-44100 Ferrara, Italy
22b
Dipartimento di Fisica, Universita
`
di Ferrara, I-44100 Ferrara, Italy
23
INFN Laboratori Nazionali di Frascati, I-00044 Frascati, Italy
24a
INFN Sezione di Genova, I-16146 Genova, Italy
24b
Dipartimento di Fisica, Universita
`
di Genova, I-16146 Genova, Italy
25
Indian Institute of Technology Guwahati, Guwahati, Assam, 781 039, India
26
Harvard University, Cambridge, Massachusetts 02138, USA
27
Harvey Mudd College, Claremont, California 91711, 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
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, I-20133 Milano, Italy
46b
Dipartimento di Fisica, 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
49a
INFN Sezione di Napoli, I-80126 Napoli, Italy
49b
Dipartimento di Scienze Fisiche, Universita
`
di Napoli Federico II, I-80126 Napoli, Italy
50
NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, Netherlands
PRL
109,
101802 (2012)
PHYSICAL REVIEW LETTERS
week ending
7 SEPTEMBER 2012
101802-2
51
University of Notre Dame, Notre Dame, Indiana 46556, USA
52
Ohio State University, Columbus, Ohio 43210, USA
53
University of Oregon, Eugene, Oregon 97403, USA
54a
INFN Sezione di Padova, I-35131 Padova, Italy
54b
Dipartimento di Fisica, Universita
`
di Padova, I-35131 Padova, Italy
55
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
56a
INFN Sezione di Perugia, I-06100 Perugia, Italy
56b
Dipartimento di Fisica, Universita
`
di Perugia, I-06100 Perugia, Italy
57a
INFN Sezione di Pisa, I-56127 Pisa, Italy
57b
Dipartimento di Fisica, Universita
`
di Pisa, I-56127 Pisa, Italy
57c
Scuola Normale Superiore di Pisa, I-56127 Pisa, Italy
58
Princeton University, Princeton, New Jersey 08544, USA
59a
INFN Sezione di Roma, I-00185 Roma, Italy
59b
Dipartimento di Fisica, Universita
`
di Roma La Sapienza, I-00185 Roma, Italy
60
Universita
̈
t Rostock, D-18051 Rostock, Germany
61
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
62
CEA, Irfu, SPP, Centre de Saclay, F-91191 Gif-sur-Yvette, France
63
SLAC National Accelerator Laboratory, Stanford, California 94309, USA
64
University of South Carolina, Columbia, South Carolina 29208, USA
65
Southern Methodist University, Dallas, Texas 75275, USA
66
Stanford University, Stanford, California 94305-4060, USA
67
State University of New York, Albany, New York 12222, USA
68
Tel Aviv University, School of Physics and Astronomy, Tel Aviv, 69978, Israel
69
University of Tennessee, Knoxville, Tennessee 37996, USA
70
University of Texas at Austin, Austin, Texas 78712, USA
71
University of Texas at Dallas, Richardson, Texas 75083, USA
72a
INFN Sezione di Torino, I-10125 Torino, Italy
72b
Dipartimento di Fisica Sperimentale, Universita
`
di Torino, I-10125 Torino, Italy
73a
INFN Sezione di Trieste, I-34127 Trieste, Italy
73b
Dipartimento di Fisica, Universita
`
di Trieste, I-34127 Trieste, Italy
74
IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
75
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
1
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
77
University of Wisconsin, Madison, Wisconsin 53706, USA
(Received 31 May 2012; published 6 September 2012)
Based on the full
BABAR
data sample, we report improved measurements of the ratios
R
ð
D
ðÞ
Þ¼
B
ð
B
!
D
ðÞ
Þ
=
B
ð
B
!
D
ðÞ
‘
‘
‘
Þ
, where
‘
is either
e
or
. These ratios are sensitive to new physics
contributions in the form of a charged Higgs boson. We measure
R
ð
D
Þ¼
0
:
440
0
:
058
0
:
042
and
R
ð
D
Þ¼
0
:
332
0
:
024
0
:
018
, which exceed the standard model expectations by
2
:
0
and
2
:
7
,
respectively. Taken together, our results disagree with these expectations at the
3
:
4
level. This excess
cannot be explained by a charged Higgs boson in the type II two-Higgs-doublet model.
DOI:
10.1103/PhysRevLett.109.101802
PACS numbers: 13.20.He, 14.40.Nd, 14.80.Da
In the standard model (SM), semileptonic decays of
B
mesons are well-understood processes mediated by a
W
boson [
1
–
3
]. Decays involving the higher mass
lepton are
sensitive to additional amplitudes, such as those involving
an intermediate charged Higgs boson [
4
–
8
], and offer an
excellent opportunity to search for this and other non-SM
contributions.
Our understanding of exclusive semileptonic decays has
greatly improved over the past two decades, thanks to the
development of heavy-quark effective theory and precise
measurements of
B
!
D
ðÞ
‘
‘
[
9
] at the
B
factories
[
10
,
11
]. SM expectations for the relative rates
R
ð
D
ðÞ
Þ¼
B
ð
B
!
D
ðÞ
Þ
=
B
ð
B
!
D
ðÞ
‘
‘
Þ
have less than 6%
uncertainty [
8
]. Calculations [
4
–
8
] based on two-Higgs-
doublet models (2HDM) predict a substantial impact on
the ratio
R
ð
D
Þ
and a smaller effect on
R
ð
D
Þ
. The ratios
R
ð
D
Þ
and
R
ð
D
Þ
are independent of the Cabibbo-
Kobayashi-Maskawa element
j
V
cb
j
and also, to a large
extent, of the parameterization of the hadronic matrix
elements.
The decay
B
!
D
was first observed in 2007 by
the Belle Collaboration [
12
]. Since then, both
BABAR
and
Belle have published improved measurements and have
found evidence for
B
!
D
decays [
13
–
15
].
Although the measured values for
R
ð
D
Þ
and
R
ð
D
Þ
have
consistently exceeded the SM expectations, the significance
PRL
109,
101802 (2012)
PHYSICAL REVIEW LETTERS
week ending
7 SEPTEMBER 2012
101802-3
of the excess has remained low due to the large statistical
uncertainties.
This analysis is an update of an earlier
BABAR
measure-
ment [
13
]. It is based on the full
BABAR
data sample and
includes improvements to the event reconstruction that
increase the signal efficiency by more than a factor of 3.
We analyze data recorded with the
BABAR
detector [
16
]
at a center-of-mass (c.m.) energy of 10.58 GeV, corre-
sponding to the mass of the
ð
4
S
Þ
resonance, which decays
almost exclusively to
B
B
pairs. The data sample comprises
an integrated luminosity of
426 fb
1
and contains
471
10
6
B
B
pairs. An additional sample of
40 fb
1
, taken at a
c.m. energy 40 MeV below the
ð
4
S
Þ
resonance (off-peak
data), is used to study continuum background from
e
þ
e
!
f
f
ð
Þ
pair production with
f
¼
u;d;s;c;
.
We choose to reconstruct only the purely leptonic decays
of the
lepton,
!
e
e
and
!
e
, so that
B
!
D
ðÞ
(signal) and
B
!
D
ðÞ
‘
‘
(normalization)
events are identified by the same particles in the final state.
This leads to the cancellation of various sources of uncer-
tainty in the ratios
R
ð
D
ðÞ
Þ
. Events corresponding to
ð
4
S
Þ!
B
B
decays are selected by reconstructing the
hadronic decay of one of the
B
mesons (
B
tag
), a
D
ðÞ
meson,
and a lepton (
e
or
). Signal and normalization yields are
extracted from a fit to the spectra of two variables: the
invariant mass of the undetected particles
m
2
miss
¼
p
2
miss
¼
ð
p
e
þ
e
p
tag
p
D
ðÞ
p
‘
Þ
2
(where
p
denotes the four-
momenta of the colliding beams, the
B
tag
, the
D
ðÞ
, and the
charged lepton) and the lepton three-momentum in the
B
rest frame
j
p
‘
j
. The
m
2
miss
distribution of decays with a
single missing neutrino peaks at zero, whereas signal
events, which have three missing neutrinos, have a broad
m
2
miss
distribution that extends to about
9 GeV
2
. The ob-
served lepton in signal events is a secondary particle from
the
decay, so its
j
p
‘
j
spectrum is softer than for normal-
ization events.
The
B
tag
reconstruction has been greatly improved with
respect to previous analyses [
17
]. We now reconstruct
B
tag
candidates in 1680 final states. We look for decays of the
type
B
tag
!
SX
, where
S
refers to a seed meson (
D
0
,
D
0
,
D
þ
,
D
þ
,
D
þ
s
,
D
þ
s
,or
J=
c
) reconstructed in 56 different
decay modes and
X
is a charged state decaying to
up to five hadrons (
,
K
,
0
, and
K
0
S
). Two kinematic
variables are used to select
B
tag
candidates:
m
ES
¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
E
2
beam
p
2
tag
q
and
E
¼
E
tag
E
beam
. Here
p
tag
and
E
tag
refer to the c.m. momentum and energy of the
B
tag
,
and
E
beam
is the c.m. energy of a single beam particle. For
correctly reconstructed
B
decays, the
m
ES
distribution is
centered at the
B
-meson mass with a resolution of 2.5 MeV,
while
E
is centered at zero with a resolution of 18 MeV.
We require
m
ES
>
5
:
27 GeV
and
j
E
j
<
0
:
072 GeV
.
We combine each
B
tag
candidate with a
D
ðÞ
meson
candidate and a charged lepton
‘
. Events with additional
charged particles are rejected. The laboratory momentum
of the electron or muon is required to exceed 300 or
200 MeV, respectively.
D
decays are reconstructed in the
following decay modes:
D
0
!
K
þ
,
K
K
þ
,
K
þ
0
,
K
þ
þ
,
K
0
S
þ
;
D
þ
!
K
þ
þ
,
K
þ
þ
0
,
K
0
S
þ
,
K
0
S
þ
þ
,
K
0
S
þ
0
,
K
0
S
K
þ
, with
K
0
S
!
þ
.
For
D
candidates, the decays
D
þ
!
D
0
þ
,
D
þ
0
, and
D
0
!
D
0
0
,
D
0
are used.
In events with more than one reconstructed
B
B
pair, we
select the candidate with the lowest value of
E
extra
, defined
as the sum of the energies of all photon candidates not
associated with the reconstructed
B
B
pair. We further
reject combinatorial background and normalization events
by requiring
q
2
¼ð
p
B
p
D
ðÞ
Þ
2
>
4 GeV
2
and
j
p
miss
j
>
200 MeV
, where
j
p
miss
j
is the missing momentum in the
c.m. frame.
We divide the
B
tag
D
ðÞ
‘
candidates that satisfy the pre-
vious requirements into eight subsamples: four
D
ðÞ
‘
samples, one for each of the types of charm meson recon-
structed (
D
0
‘
,
D
0
‘
,
D
þ
‘
, and
D
þ
‘
), and four
D
ðÞ
0
‘
control samples with the same selection plus an additional
0
. These control samples constrain the poorly understood
B
!
D
ð
‘=
Þ
background (where
D
refers to charm
resonances heavier than the
D
ground state mesons),
which enters the
D
ðÞ
‘
sample predominantly when the
0
from
D
!
D
ðÞ
0
decays is not detected. The
D
ðÞ
0
‘
samples have a very large continuum background,
so we restrict this sample to events with
j
cos
thrust
j
<
0
:
8
, where
thrust
is the angle between the thrust axes of
the
B
tag
and of the rest of the event.
We improve the separation between well-reconstructed
events (signal and normalization) and the various back-
grounds by using boosted decision tree (BDT) selectors
[
18
]. For each of the four
D
ðÞ
‘
samples, we train a BDT
to select signal and normalization events and reject
D
‘
background and charge cross-feed, defined as
D
ðÞ
ð
‘=
Þ
decays reconstructed with the wrong charge. Each BDT
selector relies on the simulated distributions of the follow-
ing variables: (1)
E
extra
; (2)
E
; (3) the reconstructed mass
of the signal
D
meson; (4) the mass difference for the
reconstructed signal
D
:
m
¼
m
ð
D
Þ
m
ð
D
Þ
; (5) the re-
constructed mass of the seed meson of the
B
tag
; (6) the mass
difference for a
D
originating from the
B
tag
,
m
tag
¼
m
ð
D
tag
Þ
m
ð
D
tag
Þ
; (7) the charged particle multiplicity
of the
B
tag
candidate; and (8)
cos
thrust
. For the
D
ðÞ
0
‘
samples, we use similar BDT selectors that are trained to
reject continuum,
D
ðÞ
ð
‘=
Þ
, and other
B
B
events. After
the BDT requirements are applied, the fraction of events
attributed to signal in the
m
2
miss
>
1
:
5 GeV
2
region, which
excludes most of the normalization decays, increases from
2% to 39%. The remaining background is composed of
normalization events (10%), continuum (19%),
D
ð
‘=
Þ
events (13%), and other
B
B
events (19%), primarily from
B
!
D
ðÞ
D
ðÞþ
s
decays with
D
þ
s
!
þ
.
PRL
109,
101802 (2012)
PHYSICAL REVIEW LETTERS
week ending
7 SEPTEMBER 2012
101802-4
As described below, the fit procedure relies on the
Monte Carlo (MC) simulation [
19
–
21
] of the two-
dimensional
m
2
miss
j
p
‘
j
spectra of the different signal
and background contributions. For semileptonic decays,
we parameterize the hadronic matrix elements of the signal
and normalization decays by using heavy-quark effective
theory-based form factors (FFs) [
22
]. For low-mass lep-
tons, there is effectively one FF for
B
!
D‘
‘
, whereas
there are three FFs for
B
!
D
‘
‘
decays, all of which
have been measured with good precision [
23
]. For heavy
leptons, each of these decays depends on an additional FF
which can be calculated by using heavy-quark symmetry
relations or lattice QCD. We use the calculations in Ref. [
7
]
for
B
!
D
and in Ref. [
8
] for
B
!
D
. For the
D
ð
‘=
Þ
background, we consider in the nominal fit only
the four
L
¼
1
states that have been measured [
24
]. We
simulate these decays by using the Leibovich-Ligeti-
Stewart-Wise calculation [
25
].
We validate and, when appropriate, correct the simula-
tions by using three data control samples selected by one of
the following criteria:
E
extra
>
0
:
5 GeV
[
26
],
q
2
4 GeV
2
,
or
5
:
20
<m
ES
<
5
:
26 GeV
. We use off-peak data to
correct the efficiency and the
j
p
‘
j
spectrum of simulated
continuum events. After this correction, the
m
2
miss
and
j
p
‘
j
distributions of the background and normalization events
agree very well with the simulation. However, we find that
small differences in the
E
extra
spectrum and other BDT
input distributions result in a 5%–10% efficiency differ-
ence between selected data and MC samples. We correct
the continuum and
B
B
backgrounds by using the
5
:
20
<
m
ES
<
5
:
26 GeV
control sample. The same correction,
with larger uncertainties, is applied to
D
ð
‘=
Þ
events,
since their simulated
E
extra
spectrum is very similar.
We extract the signal and normalization yields from an
extended, unbinned maximum-likelihood fit to two-
dimensional
m
2
miss
j
p
‘
j
distributions. The fit is per-
formed simultaneously to the four
D
ðÞ
‘
samples and the
four
D
ðÞ
0
‘
samples. The distribution of each
D
ðÞ
‘
sam-
ple is described as the sum of eight contributions:
D
,
D
,
D‘
,
D
‘
,
D
ð
‘=
Þ
, charge cross-feed, other
B
B
, and continuum. The yields for the last three back-
grounds are fixed in the fit to the expected values. A large
fraction of
B
!
D
‘
decays (for
B
¼
B
0
or
B
þ
) is re-
constructed in the
D‘
samples (feed-down). We leave those
two contributions free in the fit and use the fitted yields to
estimate the feed-down rate of
B
!
D
decays. Since
B
!
D
ð
‘=
Þ
decays contributing to the
D
‘
samples are
rare, their rate is fixed to the expected value.
The four
D
ðÞ
0
‘
samples are described by six contri-
butions: The
D
ðÞ
and
D
ðÞ
‘
yields are combined, but
otherwise the same contributions that describe the
D
ðÞ
‘
samples are employed. The four
D
ð
‘=
Þ
yields in the
control samples are free in the fit, but their ratios to the
corresponding
D
ð
‘=
Þ
yields in the
D
ðÞ
‘
samples are
constrained to the expected values.
The fit relies on
8
4
þ
6
4
¼
56
probability density
functions (PDFs), which are determined from MC samples
of continuum and
B
B
events equivalent to 2 and 9 times the
size of the data sample, respectively. The two-dimensional
m
2
miss
j
p
‘
j
distributions are described by using smooth
nonparametric kernel estimators [
27
]. The fit is iterated
to update some of the parameters that depend on the
normalization yields, most importantly the rate of signal
FIG. 1 (color online). Comparison of the data and the fit
projections for the four
D
ðÞ
‘
samples. The insets show the
j
p
‘
j
projections for
m
2
miss
>
1 GeV
2
, which excludes most of
the normalization modes. In the background component, the
region above the dashed line corresponds to charge cross-feed,
and the region below corresponds to continuum and
B
B
.
PRL
109,
101802 (2012)
PHYSICAL REVIEW LETTERS
week ending
7 SEPTEMBER 2012
101802-5
feed-down. This process converges after the first iteration.
We performed MC studies to verify that neither the fit
procedure nor the PDFs produced significant biases in
the results.
Figure
1
shows the
m
2
miss
and
j
p
‘
j
projections of the fit to
the four
D
ðÞ
‘
samples. The fit describes the data well, and
the observed differences are consistent with the statistical
and systematic uncertainties on the signal PDFs and back-
ground distributions.
We extract the branching fraction ratios as
R
ð
D
ðÞ
Þ¼
ð
N
sig
=N
norm
Þ
=
ð
"
sig
="
norm
Þ
, where
N
sig
and
N
norm
refer to the
number of signal and normalization events, respectively,
and
"
sig
="
norm
is the ratio of their efficiencies derived from
simulations. Table
I
shows the results of the fits for the four
individual samples as well as an additional fit in which we
impose the isospin relations
R
ð
D
0
Þ¼
R
ð
D
þ
Þ
R
ð
D
Þ
and
R
ð
D
0
Þ¼
R
ð
D
þ
Þ
R
ð
D
Þ
. The statistical correla-
tions are
0
:
59
for
R
ð
D
0
Þ
and
R
ð
D
0
Þ
,
0
:
23
for
R
ð
D
þ
Þ
and
R
ð
D
þ
Þ
, and
0
:
45
for
R
ð
D
Þ
and
R
ð
D
Þ
. We have
verified that the values of
R
ð
D
ðÞ
Þ
from fits to samples
corresponding to different run periods are consistent. We
repeated the analysis, varying the selection criteria over a
wide range corresponding to changes in the signal-to-
background ratios between 0.3 and 1.3, and also arrive at
consistent values of
R
ð
D
ðÞ
Þ
.
The largest systematic uncertainty affecting the fit results
is due to the poorly understood
B
!
D
ð
‘=
Þ
back-
ground. The PDFs that describe this contribution are im-
pacted by the uncertainty on the branching fractions of the
four
B
!
D
‘
decays, the relative
0
=
efficiency, and
the branching fraction ratio of
B
!
D
to
B
!
D
‘
decays. These effects contribute to an uncertainty of 2.1%
on
R
ð
D
Þ
and 1.8% on
R
ð
D
Þ
. We also repeated the fit
including an additional floating component with the distri-
butions of
B
!
D
ðÞ
‘
, nonresonant
B
!
D
ðÞ
ð
Þ
‘
,
and
B
!
D
ð!
D
ðÞ
Þ
‘
decays. The
B
!
D
ð
‘=
Þ
background is tightly constrained by the
D
ðÞ
0
‘
samples,
and, as a result, all these fits yield similar values for
R
ð
D
ðÞ
Þ
. We assign the observed variation as a systematic
uncertainty: 2.1% for
R
ð
D
Þ
and 2.6% for
R
ð
D
Þ
.
We also account for the impact of the uncertainties
described above on the relative efficiency of the
B
!
D
ð
‘=
Þ
contributions to the signal and
D
ðÞ
0
‘
samples. In addition, the BDT selection introduces an
uncertainty that we estimate as 100% of the efficiency
correction that we determined from control samples.
These effects result in uncertainties of 5.0% and 2.0% on
R
ð
D
Þ
and
R
ð
D
Þ
, respectively.
The largest remaining uncertainties are due to the con-
tinuum and
B
B
backgrounds [4.9% on
R
ð
D
Þ
and 2.7% on
R
ð
D
Þ
] and the PDFs for the signal and normalization
decays (4.3% and 2.1%). The uncertainties in the efficiency
ratios
"
sig
="
norm
are 2.6% and 1.6%; they do not affect the
significance of the signal and are dominated by the limited
size of the MC samples. Uncertainties due to the FFs,
particle identification, final-state radiation, soft-pion re-
construction, and others related to the detector perform-
ance largely cancel in the ratio, contributing only about
1%. The individual systematic uncertainties are added in
quadrature to define the total systematic uncertainty, re-
ported in Table
I
.
There is a positive correlation between some of the
systematic uncertainties on
R
ð
D
Þ
and
R
ð
D
Þ
, and, as a
result the correlation of the total uncertainties is reduced to
0
:
48
for
R
ð
D
0
Þ
and
R
ð
D
0
Þ
,to
0
:
15
for
R
ð
D
þ
Þ
and
R
ð
D
þ
Þ
, and to
0
:
27
for
R
ð
D
Þ
and
R
ð
D
Þ
.
The statistical significance of the signal is determined as
stat
¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
ð
ln
L
Þ
p
, where
ð
ln
L
Þ
is the change in the log-
likelihood between the nominal fit and the no-signal
hypothesis. The statistical and dominant systematic uncer-
tainties are Gaussian. We estimate the overall significance
as
tot
¼
stat
stat
=
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
stat
þ
2
syst
q
, where
stat
is the sta-
tistical uncertainty and
syst
is the total systematic uncer-
tainty affecting the fit. The significance of the
B
!
D
signal is
6
:
8
, the first such measurement exceeding
5
.
To compare the measured
R
ð
D
ðÞ
Þ
with the SM predic-
tions, we have updated the calculations in Refs. [
8
,
31
]
taking into account recent FF measurements. Averaged
over electrons and muons, we find
R
ð
D
Þ
SM
¼
0
:
297
0
:
017
and
R
ð
D
Þ
SM
¼
0
:
252
0
:
003
. At this level of
TABLE I. Results of the isospin-unconstrained (top four rows) and isospin-constrained fits (last two rows). The columns show the
signal and normalization yields, the ratio of their efficiencies,
R
ð
D
ðÞ
Þ
, branching fractions, and
stat
and
tot
, the statistical and total
significances, respectively. Where two uncertainties are given, the first is statistical and the second is systematic. The branching
fractions
B
ð
B
!
D
ðÞ
Þ
are calculated as
R
ð
D
ðÞ
Þ
B
ð
B
!
D
ðÞ
‘
‘
Þ
, by using the average
B
!
D
ðÞ
‘
‘
branching fractions
measured by
BABAR
[
28
–
30
]. The stated branching fractions for the isospin-constrained fit refer to
B
decays.
Decay
N
sig
N
norm
"
sig
="
norm
R
ð
D
ðÞ
Þ
B
ð
B
!
D
ðÞ
Þð
%
Þ
stat
tot
B
!
D
0
314
60
1995
55
0
:
367
0
:
011
0
:
429
0
:
082
0
:
052 0
:
99
0
:
19
0
:
13
5.5
4.7
B
!
D
0
639
62
8766
104
0
:
227
0
:
004
0
:
322
0
:
032
0
:
022 1
:
71
0
:
17
0
:
13
11.3
9.4
B
0
!
D
þ
177
31
986
35
0
:
384
0
:
014
0
:
469
0
:
084
0
:
053 1
:
01
0
:
18
0
:
12
6.1
5.2
B
0
!
D
þ
245
27
3186
61
0
:
217
0
:
005
0
:
355
0
:
039
0
:
021 1
:
74
0
:
19
0
:
12
11.6 10.4
B
!
D
489
63
2981
65
0
:
372
0
:
010
0
:
440
0
:
058
0
:
042 1
:
02
0
:
13
0
:
11
8.4
6.8
B
!
D
888
63 11953
122
0
:
224
0
:
004
0
:
332
0
:
024
0
:
018 1
:
76
0
:
13
0
:
12
16.4 13.2
PRL
109,
101802 (2012)
PHYSICAL REVIEW LETTERS
week ending
7 SEPTEMBER 2012
101802-6
precision, additional uncertainties could contribute [
8
], but
the experimental uncertainties are expected to dominate.
Our measurements exceed the SM predictions for
R
ð
D
Þ
and
R
ð
D
Þ
by
2
:
0
and
2
:
7
, respectively. The combina-
tion of these results, including their
0
:
27
correlation,
yields
2
¼
14
:
6
for 2 degrees of freedom, corresponding
to a
p
value of
6
:
9
10
4
. Thus, the possibility of both the
measured
R
ð
D
Þ
and
R
ð
D
Þ
agreeing with the SM predic-
tions is excluded at the
3
:
4
level [
32
].
Figure
2
shows the effect that a charged Higgs boson of
the type II 2HDM [
7
,
34
] would have on
R
ð
D
Þ
and
R
ð
D
Þ
in terms of the ratio of the vacuum expectation values
tan
v
2
=v
1
and the mass of the charged Higgs
m
H
þ
.
We estimate the effect of the 2HDM on our measurements
by reweighting the simulated events at the matrix element
level for 20 values of
tan
=m
H
þ
over the
½
0
:
05
;
1
GeV
1
range. We then repeat the fit with updated PDF shapes and
"
sig
="
norm
values. The increase in the uncertainty on the
PDFs and the efficiency ratio is estimated for each value of
tan
=m
H
þ
. The other sources of systematic uncertainty are
kept constant in relative terms.
The measured values of
R
ð
D
Þ
and
R
ð
D
Þ
match
the predictions of this particular Higgs model for
tan
=m
H
þ
¼
0
:
44
0
:
02 GeV
1
and
tan
=m
H
þ
¼
0
:
75
0
:
04 GeV
1
, respectively. However, the combination of
R
ð
D
Þ
and
R
ð
D
Þ
excludes the type II 2HDM charged
Higgs boson with a 99.8% confidence level for any value
of
tan
=m
H
þ
. This calculation is valid only for values of
m
H
þ
greater than about
10 GeV
[
4
,
7
]. The region for
m
H
þ
10 GeV
has already been excluded by
B
!
X
s
measurements [
35
], and, therefore, the type II 2HDM is
excluded in the full
tan
m
H
þ
parameter space.
In summary, we have measured the
B
!
D
and
B
!
D
decays relative to the decays to light leptons
B
!
D
ðÞ
‘
‘
. We find
R
ð
D
Þ¼
0
:
440
0
:
058
0
:
042
;
R
ð
D
Þ¼
0
:
332
0
:
024
0
:
018
:
These results supersede the previous
BABAR
results and
have significantly reduced uncertainties. The measured
values are compatible with those measured by the Belle
Collaboration [
12
,
14
,
15
].
The results presented here disagree with the SM at the
3
:
4
level, which, together with the measurements by the
Belle Collaboration, could be an indication of new physics
processes affecting
B
!
D
ðÞ
decays. However, our
results are not compatible with the widely discussed type II
2HDM for any value of
tan
and
m
H
þ
.
We acknowledge M. Mazur for his help throughout the
analysis and S. Westhoff, S. Fajfer, J. Kamenik, and I.
Nis
ˇ
andz
ˇ
ic
́
for their help with the calculation of the charged
Higgs contributions. We are grateful for the excellent
luminosity and machine conditions provided by our PEP-
II colleagues and for the substantial dedicated effort from
the computing organizations that support
BABAR
. The
collaborating institutions thank SLAC for its support and
kind hospitality. This work is supported by DOE and NSF
(USA), NSERC (Canada), CEA and CNRS-IN2P3
(France), BMBF and DFG (Germany), INFN (Italy),
FOM (Netherlands), NFR (Norway), MES (Russia),
MICIIN (Spain), and STFC (United Kingdom).
Individuals have received support from the Marie Curie
EIF (European Union) and the A. P. Sloan Foundation
(USA).
*
Now at the University of Tabuk, Tabuk 71491, Saudi
Arabia.
†
Also with Universita
`
di Perugia, Dipartimento di Fisica,
Perugia, Italy.
‡
Now at the University of Huddersfield, Huddersfield HD1
3DH, United Kingdom.
§
Now at University of South Alabama, Mobile, AL 36688,
USA.
k
Also with Universita
`
di Sassari, Sassari, Italy.
{
Deceased.
[1] P. Heiliger and L. Sehgal,
Phys. Lett. B
229
, 409 (1989)
.
[2] J. G. Korner and G. A. Schuler,
Z. Phys. C
46
, 93 (1990)
.
[3] D. S. Hwang and D. W. Kim,
Eur. Phys. J. C
14
, 271
(2000)
.
[4] M. Tanaka,
Z. Phys. C
67
, 321 (1995)
.
[5] H. Itoh, S. Komine, and Y. Okada,
Prog. Theor. Phys.
114
,
179 (2005)
.
[6] U. Nierste, S. Trine, and S. Westhoff,
Phys. Rev. D
78
,
015006 (2008)
.
[7] M. Tanaka and R. Watanabe,
Phys. Rev. D
82
, 034027
(2010)
.
[8] S. Fajfer, J. F. Kamenik, and I. Nis
ˇ
andz
ˇ
ic
́
,
Phys. Rev. D
85
,
094025 (2012)
.
FIG. 2 (color online). Comparison of the results of this analy-
sis (light gray, blue) with predictions that include a charged
Higgs boson of type II 2HDM (dark gray, red). The SM corre-
sponds to
tan
=m
H
þ
¼
0
.
PRL
109,
101802 (2012)
PHYSICAL REVIEW LETTERS
week ending
7 SEPTEMBER 2012
101802-7