Evidence of
B
þ
!
þ
decays with hadronic
B
tags
J. P. Lees,
1
V. Poireau,
1
V. Tisserand,
1
J. Garra Tico,
2
E. Grauges,
2
A. Palano,
3a,3b
G. Eigen,
4
B. Stugu,
4
D. N. Brown,
5
L. T. Kerth,
5
Yu. G. Kolomensky,
5
G. Lynch,
5
H. Koch,
6
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,
22a,22b
G. Cibinetto,
22a,22b
E. Fioravanti,
22a,22b
I. Garzia,
22a,22b
E. Luppi,
22a,22b
M. Munerato,
22a,22b
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,
24a,24b
E. Guido,
24a,24b
M. Lo Vetere,
24a,24b
M. R. Monge,
24a,24b
S. Passaggio,
24a
C. Patrignani,
24a,24b
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,
32
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,
40
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,
46a,46b
N. Neri,
46a
F. Palombo,
46a,46b
S. Stracka,
46a,46b
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,
49a,49b
D. Monorchio,
49a,49b
G. Onorato,
49a,49b
C. Sciacca,
49a,49b
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,
54a,54b
N. Gagliardi,
54a,54b
M. Margoni,
54a,54b
M. Morandin,
54a
M. Posocco,
54a
M. Rotondo,
54a
G. Simi,
54a,54b
F. Simonetto,
54a,54b
R. Stroili,
54a,54b
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,
55
M. Biasini,
56a,56b
E. Manoni,
56a,56b
S. Pacetti,
56a,56b
A. Rossi,
56a,56b
C. Angelini,
57a,57b
G. Batignani,
57a,57b
S. Bettarini,
57a,57b
M. Carpinelli,
57a,57b,
¶
G. Casarosa,
57a,57b
A. Cervelli,
57a,57b
F. Forti,
57a,57b
M. A. Giorgi,
57a,57b
A. Lusiani,
57a,57c
B. Oberhof,
57a,57b
E. Paoloni,
57a,57b
A. Perez,
57a
G. Rizzo,
57a,57b
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,59b
F. Ferrarotto,
59a
F. Ferroni,
59a,59b
M. Gaspero,
59a,59b
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
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,
72a,72b
D. Gamba,
72a,72b
S. Zambito,
72a,72b
L. Lanceri,
73a,73b
L. Vitale,
73a,73b
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,
76
P. F. Harrison,
76
T. E. Latham,
76
E. M. T. Puccio,
76
H. R. Band,
77
S. Dasu,
77
Y. Pan,
77
R. Prepost,
77
and S. L. Wu
77
PHYSICAL REVIEW D
88,
031102(R) (2013)
RAPID COMMUNICATIONS
1550-7998
=
2013
=
88(3)
=
031102(9)
031102-1
Ó
2013 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 de 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, The Netherlands
J. P. LEES
et al.
PHYSICAL REVIEW D
88,
031102(R) (2013)
RAPID COMMUNICATIONS
031102-2
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
76
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
77
University of Wisconsin, Madison, Wisconsin 53706, USA
(Received 8 July 2012; published 8 August 2013)
We present a search for the decay
B
þ
!
þ
using
467
:
8
10
6
B
B
pairs collected at the
ð
4
S
Þ
resonance with the
BABAR
detector at the SLAC PEP-II
B
-Factory. We select a sample of events with one
completely reconstructed
B
in the hadronic decay mode (
B
!
D
ðÞ
0
X
and
B
!
J=
c
X
). We
examine the rest of the event to search for a
B
þ
!
þ
decay. We identify the
þ
lepton in the following
modes:
þ
!
e
þ
,
þ
!
þ
,
þ
!
þ
and
þ
!
þ
. We find an excess of events with respect
to the expected background, which excludes the null signal hypothesis at the level of
3
:
8
(including
systematic uncertainties) and corresponds to a branching fraction value of
B
ð
B
þ
!
þ
Þ¼
ð
1
:
83
þ
0
:
53
0
:
49
ð
stat
Þ
0
:
24
ð
syst
ÞÞ
10
4
.
DOI:
10.1103/PhysRevD.88.031102
PACS numbers: 13.20.
v, 13.25.Hw
The study of the purely leptonic decay
B
þ
!
þ
[
1
]isof
particular interest to test the predictions of the Standard
Model (SM) and to probe new physics effects. It is sensitive
to the product of the
B
meson decay constant
f
B
, and the
absolute value of the Cabibbo-Kobayashi-Maskawa matrix
element
j
V
ub
j
[
2
]. In the SM the branching fraction is given by
B
ð
B
þ
!
þ
Þ¼
G
2
F
m
B
m
2
8
1
m
2
m
2
B
2
f
2
B
j
V
ub
j
2
B
þ
;
(1)
where
G
F
is the Fermi constant,
m
B
and
m
are the
B
þ
meson
and
lepton masses, respectively, and
B
þ
is the
B
þ
lifetime.
*
Deceased.
†
Present address: University of Tabuk, Tabuk 71491, Saudi
Arabia.
‡
Also at Universita
`
di Perugia, Dipartimento di Fisica,
Perugia, Italy.
§
Present address: University of Huddersfield, Huddersfield
HD1 3DH, United Kingdom.
∥
Present address: University of South Alabama, Mobile,
Alabama 36688, USA.
¶
Also at Universita
`
di Sassari, Sassari, Italy.
EVIDENCE OF
B
þ
!
þ
DECAYS
...
PHYSICAL REVIEW D
88,
031102(R) (2013)
RAPID COMMUNICATIONS
031102-3
Using the lattice QCD calculation of
f
B
¼ð
189
4
Þ
MeV
[
3
], and the
BABAR
measurement of
j
V
ub
j
from charmless
semileptonic
B
exclusive decays [
4
], the predicted SM value
of the brancing fraction is
B
SM
ð
B
þ
!
þ
Þ¼ð
0
:
62
0
:
12
Þ
10
4
.Ifweusethe
BABAR
measurement of
j
V
ub
j
from inclusive charmless semileptonic B decays [
5
], the SM
prediction is
B
SM
ð
B
þ
!
þ
Þ¼ð
1
:
18
0
:
16
Þ
10
4
.
The process is sensitive to possible extensions of the
SM. For instance, in two-Higgs doublet models (2HDM)
[
6
] and in minimal supersymmetric extensions [
7
], it can
be mediated by a charged Higgs boson. A branching frac-
tion measurement can, therefore, also be used to constrain
the parameter space of new physics models.
The data used in this analysis were collected with the
BABAR
detector at the PEP-II storage ring. The sample
corresponds to an integrated luminosity of
426 fb
1
at the
ð
4
S
Þ
resonance. The sample contains
ð
467
:
8
5
:
1
Þ
10
6
B
B
decays (
N
B
B
). The detector is described in detail
elsewhere [
8
]. Charged particle trajectories are measured
in the tracking system composed of a five-layer double-
sided silicon vertex tracker and a 40-layer drift chamber,
operating in a 1.5 T solenoidal magnetic field. A
Cherenkov detector is used for charged
K
discrimi-
nation, a CsI calorimeter for photon and electron identi-
fication, and the flux return of the solenoid, which consists
of layers of iron interspersed with resistive plate chambers
or limited streamer tubes, for muon and neutral hadron
identification.
We use a Monte Carlo (MC) simulation based on
GEANT4
[
9
] to estimate signal selection efficiencies and
to study backgrounds. In MC simulated signal events, one
B
þ
meson decays as
B
þ
!
þ
and the other decays in
any final state. The
B
B
and continuum MC samples are
equivalent to approximately 3 times and 1.5 times the data
sample, respectively. Beam-related background and detec-
tor noise are sampled from data and overlaid on the simu-
lated events.
We reconstruct an exclusive decay of one of the
B
mesons in the event (which we refer to as the tag-
B
) and
examine the rest of the event for the experimental signature
of
B
þ
!
þ
. The tag-
B
reconstruction can be performed
by looking at both hadronic
B
decays and semileptonic
B
decays. Published results from both
BABAR
and Belle are
summarized in Table
I
.
We reconstruct the tag-
B
candidate in the set of hadronic
decays
B
!
M
0
X
, where
M
0
denotes a
D
ðÞ
0
or a
J=
c
,
and
X
denotes a system of hadrons with total charge
1
composed of
n
1
,
n
2
K
,
n
3
0
,
n
4
K
0
S
where
n
1
þ
n
2
5
,
n
2
,
n
3
and
n
4
2
. We reconstruct the
D
0
as
D
0
!
K
þ
,
K
þ
0
,
K
þ
þ
,
K
0
S
0
,
K
0
S
þ
,
K
0
S
þ
0
,
K
þ
K
,or
þ
. We reconstruct the
D
0
meson as
D
0
!
D
0
0
,
D
0
, and the
J=
c
meson via their
decays
J=
c
!
e
þ
e
,
þ
. Two kinematic variables
are used to discriminate between correctly reconstructed
tag-
B
candidates and misreconstructed events: the beam
energy-substituted mass
m
ES
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
s=
4
p
2
B
q
, and the en-
ergy difference
E
E
B
ffiffiffi
s
p
=
2
, where
ffiffiffi
s
p
is the total
energy in the
ð
4
S
Þ
center-of-mass (CM) system and
p
B
and
E
B
respectively denote the momentum and the energy
of the tag-
B
candidate in the CM. The resolution on
E
is
measured to be
E
¼
10
–
35 MeV
, depending on the
decay mode; we require
j
E
j
<
3
E
. Events with a
tag-
B
candidate arise from two possible classes with differ-
ent
m
ES
distributions. One class includes signal events with
a correctly reconstructed tag-
B
, and background events
from
ð
4
S
Þ!
B
þ
B
with a correctly reconstructed
tag-
B
. All these events are characterized by an
m
ES
distribution peaked at the nominal
B
mass (signal and
peaking background). The other classes of events consist
of continuum background,
e
þ
e
!
q
q
(
q
¼
u
,
d
,
s
,
c
)
and
e
þ
e
!
þ
, and combinatorial background,
ð
4
S
Þ!
B
0
B
0
or
B
þ
B
in which the tag-
B
is misrecon-
structed. These events are characterized by a smooth
m
ES
distribution.
If multiple tag-
B
candidates are reconstructed in the
event, we select the one with the lowest value of
j
E
j
.
After the reconstruction of the tag-
B
, we require the pres-
ence of only one well-reconstructed track (signal track),
with charge opposite to that of the tag-
B
. The purity
P
of
each reconstructed tag-
B
decay mode is estimated as
the ratio of the number of peaking events with
m
ES
>
5
:
27 GeV
to the total number of events in the same range.
The yield in data is determined by means of an extended
unbinned maximum likelihood fit to the
m
ES
distribution,
as shown in Fig.
1
. We use a phenomenologically moti-
vated threshold function (ARGUS function [
14
]) as proba-
bility density function (PDF) to describe the continuum
and combinatorial background components in the fit, while
for the correctly reconstructed tag-
B
component we use a
Gaussian distribution plus an exponential tail for the PDF
(Crystal Ball function) [
15
]. We use only events with
the tag-
B
reconstructed in decay modes with
P
>
0
:
1
.
Combinatorial and continuum background distributions
in any discriminating variable are estimated from a side-
band in
m
ES
(
5
:
209 GeV
<m
ES
<
5
:
260 GeV
) and are
extrapolated into the signal region (
m
ES
>
5
:
270 GeV
)
using the results of a fit to an ARGUS function. The
peaking
B
þ
B
background shape is determined from
B
þ
B
MC, after subtraction of the combinatorial
TABLE I. Published results for
B
þ
!
þ
from
BABAR
and
Belle collaborations.
Experiment
Tag
Branching fraction (
10
4
Þ
BABAR
Hadronic [
10
]
1
:
8
þ
0
:
9
0
:
8
0
:
4
0
:
2
BABAR
Semileptonic [
11
]
1
:
7
0
:
8
0
:
2
Belle
Hadronic [
12
]
0
:
72
þ
0
:
27
0
:
25
0
:
11
Belle
Semileptonic [
13
]
1
:
54
þ
0
:
38
þ
0
:
29
0
:
37
0
:
31
J. P. LEES
et al.
PHYSICAL REVIEW D
88,
031102(R) (2013)
RAPID COMMUNICATIONS
031102-4
component to avoid double counting. The efficiency of the
tag-
B
reconstruction in presence of a
B
þ
!
þ
decay is
estimated with signal MC as
tag
¼ð
2
:
8
0
:
1
Þ
10
3
.
The signal-side
lepton is reconstructed in four decay
modes:
þ
!
e
þ
,
þ
!
þ
,
þ
!
þ
, and
þ
!
þ
, totaling approximately 70% of all
decays.
We separate the event sample into four categories using
particle identification criteria applied to the signal track
(
e
þ
,
þ
, and
þ
). The
þ
!
þ
sample is obtained by
associating the signal track
þ
with a
0
reconstructed
from a pair of neutral clusters with an invariant mass
between
115 MeV
=c
2
and
155 MeV
=c
2
.
In order to remove the
e
þ
e
!
þ
background, we
impose
mode dependent requirements on the ratio be-
tween the 2nd and the 0th Fox-Wolfram moments R2 [
16
]
calculated using all the tracks and neutral clusters of the
event. This preserves 90% of the
B
þ
!
þ
signal.
To reject continuum background, we use the absolute
value of
cos
TB
, the cosine of the angle in the CM frame
between the thrust axis [
17
] of the tag-
B
and the thrust axis
of the remaining charged and neutral candidates in the
event. For correctly reconstructed tag-
B
candidates the
j
cos
TB
j
distribution is expected to be uniform, while
for jet-like
e
þ
e
!
q
q
continuum events it peaks strongly
at 1. In order to reject background from events with a
correctly reconstructed tag-
B
, we study the distribution
of several discriminating variables exploiting the different
kinematics between the signal and background of the
remaining reconstructed candidates. We use the missing
momentum polar angle in the laboratory frame
~
p
miss
¼
~
p
CM
~
p
tag
B
~
p
trk
P
neut
~
p
i
, where
~
p
CM
is the total mo-
mentum of the beams,
~
p
tag
B
is the reconstructed momen-
tum of the tag-
B
, and
~
p
trk
is the reconstructed track
momentum, and the sum is extended on all the neutral
candidates reconstructed in the calorimeter not assigned to
the tag-
B
. For the
þ
!
þ
mode, we combine
p
trk
(where the star denotes the CM frame) and the cosine of
the angle between
~
p
miss
and the beam axis (
cos
miss
)ina
likelihood ratio
L
P
¼
L
S
ð
p
trk
;
cos
miss
Þ
ð
L
S
ð
p
trk
;
cos
miss
Þþ
L
B
ð
p
trk
;
cos
miss
ÞÞ
;
(2)
where the signal (S) and background (B) likelihoods
have been obtained from the product of the PDFs of
the two discriminating variables:
L
S
ð
p
trk
;
cos
miss
Þ¼
P
S
ð
p
trk
Þ
P
S
ð
cos
miss
Þ
and
L
B
ð
p
trk
;
cos
miss
Þ¼
P
B
ð
p
trk
Þ
P
B
ð
cos
miss
Þ
. Similarly, for the
þ
!
þ
mode we
combine four discriminating variables in the likelihood
ratio
L
P
:
cos
miss
, the invariant mass of the
0
candidate,
the
þ
candidate momentum, and the invariant mass of
the
þ
0
pair used to make the
þ
candidate. The PDFs
used in the likelihood ratio for the signal and background
are determined from signal and
B
þ
B
MC samples,
respectively.
The most powerful discriminating variable is
E
extra
,
defined as the sum of the energies of the neutral clusters
not associated with the tag-
B
or with the signal
0
from the
þ
!
þ
mode, and passing a minimum energy require-
ment (60 MeV). Signal events tend to peak at low
E
extra
.
Background events, which contain additional sources of
neutral clusters, tend to be distributed at higher values. The
signal region in data is kept blind until the end of the
analysis chain when we extract the signal yield, meaning
that we do not use events in data with
E
extra
<
400 MeV
during the selection optimization procedure and for the
evaluation of background shapes.
We optimize the selection requirements, including those
on the purity
P
of the tag-
B
and the minimum energy of the
neutral clusters, minimizing the expected uncertainty in the
branching fraction fit. In order to estimate the uncertainty,
which includes the statistical and the dominant systematic
sources, we run 1000 MC simulated pseudo experiments
extracted from the background and signal expected
E
extra
distributions for a set of possible selection requirements,
assuming a signal branching fraction of
1
:
8
10
4
[
10
].
Table
II
summarizes the signal selection requirements
and Fig.
2
shows the
E
extra
distribution with all the selec-
tion requirements applied. The background events populat-
ing the low
E
extra
region are mostly semileptonic
B
decays
for the leptonic modes. For the
þ
!
þ
mode the
background is composed mostly of charmless hadronic
B
FIG. 1 (color online). Fit to the
m
ES
distribution in data. Dots
are data, the upper curve is the global fit result and the lower
curve represents the fitted combinatorial and continuum
background.
TABLE II. Optimized signal selection criteria for each
mode.
Variable
e
þ
þ
þ
þ
P
>
10%
Cluster energy (MeV)
>
60
R
2
<
0
:
57
<
0
:
56
<
0
:
56
<
0
:
51
j
cos
TB
j
<
0
:
95
<
0
:
90
<
0
:
65
<
0
:
8
L
P
>
0
:
30
>
0
:
45
EVIDENCE OF
B
þ
!
þ
DECAYS
...
PHYSICAL REVIEW D
88,
031102(R) (2013)
RAPID COMMUNICATIONS
031102-5
decays and semileptonic
B
decays with a muon in the final
state. For the
þ
!
þ
mode the backgrounds are
charmed hadronic
B
decays, semileptonic
B
decays with
a muon in the final state and a small fraction with a
.
We use an extended unbinned maximum likelihood fit to
the measured
E
extra
distribution to extract the
B
þ
!
þ
branching fraction. The likelihood function for the
N
k
candidates selected in one of the four reconstructed
decay modes
k
is
L
k
¼
e
ð
n
s;k
þ
n
b;k
Þ
N
k
!
Y
N
k
i
¼
1
f
n
s;k
P
s
k
ð
E
i;k
Þþ
n
b;k
P
b
k
ð
E
i;k
Þg
;
(3)
where
n
s;k
is the signal yield,
n
b;k
is the background yield,
E
i;k
is the
E
extra
value of the
i
th event,
P
s
k
is the PDF of
signal events, and
P
b
k
is the PDF of background events.
The background yields in each decay mode are permitted
to float independently of each other in the fit, while the
signal yields are constrained to a single branching ratio via
the relation
n
s;k
¼
N
B
B
k
B
;
(4)
where
k
is the reconstruction efficiency of the signal
B
þ
!
þ
decay in the
k
reconstructed
decay mode,
and
B
is the
B
þ
!
þ
branching fraction. The parame-
ters
N
B
B
and
k
are fixed in the fit while
B
is allowed to
vary. The reconstruction efficiencies
k
, which include
signal cross-feeds among
reconstruction modes and
branching fractions, are obtained from MC-simulated sig-
nal events (see Table
III
). Since the tag-
B
reconstruction
efficiency is included in
k
and is estimated from the signal
MC, we apply a correction factor of
R
data
=
MC
¼
0
:
926
0
:
010
to take into account data/MC differences. This is
derived from the ratio of the peaking component of the
m
ES
distribution for the hadronic tag-
B
in data and in MC
simulated events.
The signal PDF is an histogram obtained from a high
statistics signal sample of MC simulated data. We use a
sample of fully reconstructed events to correct the signal
PDF for data/MC disagreement. In addition to the recon-
structed tag-
B
, a second
B
is reconstructed in the hadronic
or the semileptonic decay mode using tracks and neutral
clusters not assigned to the tag-
B
. In order to estimate the
correction to the signal PDF, we compare the distribution
of
E
extra
in this double tagged event sample from experi-
mental data and MC simulations. The MC distributions are
normalized to the experimental data and the comparison is
shown in Fig.
3
. We extract the correction function by
taking the ratio of the two distributions and fitting it with
a second order polynomial.
TABLE III. Reconstruction efficiency
k
, measured branching
fractions, and statistical uncertainty obtained from the fit with all
the modes separately and constrained to the same branching
fraction. The
decay mode branching fractions are included in
the efficiencies.
Decay mode
k
ð
10
4
Þ
Signal yield
B
ð
10
4
Þ
þ
!
e
þ
2
:
47
0
:
14
4
:
1
9
:
10
:
35
þ
0
:
84
0
:
73
þ
!
þ
2
:
45
0
:
14
12
:
9
9
:
71
:
12
þ
0
:
90
0
:
78
þ
!
þ
0
:
98
0
:
14
17
:
1
6
:
23
:
69
þ
1
:
42
1
:
22
þ
!
þ
1
:
35
0
:
11
24
:
0
10
:
03
:
78
þ
1
:
65
1
:
45
Combined
62
:
1
17
:
31
:
83
þ
0
:
53
0
:
49
[GeV]
extra
E
0
0.2
0.4
0.6
0.8
/100 MeV
evt
N
0
50
100
150
200
250
300
(a)
[GeV]
extra
E
0
0.2
0.4
0.6
0.8
/100 MeV
evt
N
0
20
40
60
80
100
120
140
(b)
[GeV]
extra
E
0
0.2
0.4
0.6
0.8
/100 MeV
evt
N
0
20
40
60
80
100
120
(c)
[GeV]
extra
E
0
0.2
0.4
0.6
0.8
/100 MeV
evt
N
0
2
4
6
8
10
(d)
[GeV]
extra
E
0
0.2
0.4
0.6
0.8
/100 MeV
evt
N
0
5
10
15
20
25
(e)
FIG. 2 (color online).
E
extra
distribution in data (points with
error bars) with all selection requirements applied and fit results
overlaid. The hatched histogram is the background and the
dashed component is the best-fit signal excess distribution.
Plot (a) shows all
decay modes fitted simultaneously. Lower
plots show the projection of the simultaneous fit result on the
four analyzed
decay modes: (b)
þ
!
e
þ
, (c)
þ
!
þ
,
(d)
þ
!
þ
, (e)
þ
!
þ
.
J. P. LEES
et al.
PHYSICAL REVIEW D
88,
031102(R) (2013)
RAPID COMMUNICATIONS
031102-6
We determine the PDF of the combinatorial background
from the
m
ES
sideband. The normalization of this
component in the signal region is obtained by fitting the
m
ES
distribution after the selection has been applied. The
shape of the peaking background is taken from
B
þ
B
MC.
The two background components are added together
into a single histogram background PDF. We estimate
the branching fraction by minimizing
ln
L
, where
L
¼
4
k
¼
1
L
k
, and
L
k
is given in Eq. (
3
). The projections
of the fit results are shown in Fig.
2
.
We observe an excess of events with respect to the
expected background level and measure a branching frac-
tion of
B
ð
B
þ
!
þ
Þ¼ð
1
:
83
þ
0
:
53
0
:
49
Þ
10
4
, where the
uncertainty is statistical. Table
III
summarizes the results
from the fit. We evaluate the significance of the observed
signal, including only statistical uncertainty, as
S
¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2ln
ð
L
s
þ
b
=
L
b
Þ
p
, where
L
s
þ
b
and
L
b
denote the obtained
maximum likelihood values in the signal and background,
and the background only hypotheses, respectively. We find
S
¼
4
:
2
.
Additive systematic uncertainties are due to the uncer-
tainties in the signal and background
E
extra
PDF shapes
used in the fit. To estimate the systematic uncertainty
in the background PDF shape we repeat the fit of the
branching fraction with 1000 variations of the background
PDFs, varying each bin content within its statistical uncer-
tainty. We use the range of fitted branching fractions cover-
ing 68% of the distribution as systematic uncertainty
yielding an overall contribution of 10%. We correct the
systematic effects of disagreements between data and MC
E
extra
distributions for signal events using a sample of
completely reconstructed events in data and MC, as al-
ready described. To estimate the related systematic uncer-
tainties, we vary the parameters of the second-order
polynomial defining the correction within their uncertainty
and repeat the fit to the
B
þ
!
þ
branching fraction. We
observe a 2.6% variation that we take as the systematic
uncertainty on the signal shape. Including the effects of
additive systematic uncertainties, the significance of the
result is evaluated as
3
:
8
.
Multiplicative systematic uncertainties on the efficiency
stem from the uncertainty in the tag-
B
efficiency correction
(5.0%), estimated by comparing the ratio of double tags
yield in data and in MC simulation with the same ratio for
single tags, electron identification (2.6%), muon identifi-
cation (4.7%), charged kaon veto (0.4%), estimated from
experimental data control samples, and the finite signal
MC statistics (0.8%). Table
IV
summarizes the systematic
uncertainties. The total systematic uncertainty is obtained
by combining all sources in quadrature.
In summary, we have measured the branching fraction of
the decay
B
þ
!
þ
using a tagging algorithm based on
the reconstruction of hadronic
B
decays using a data sam-
ple of
467
:
8
10
6
B
B
pairs collected with the
BABAR
detector at the PEP-II
B
-Factory. We measure the branch-
ing fraction to be
B
ð
B
þ
!
þ
Þ¼ð
1
:
83
þ
0
:
53
0
:
49
ð
stat
Þ
0
:
24
ð
syst
ÞÞ
10
4
, excluding the null hypothesis by
3
:
8
(including systematic uncertainty). This result super-
sedes our previous result using the same technique [
10
].
The improvements in the statistical and systematic uncer-
tainties are due to the cumulative effect of several factors,
which we briefly list in the following, for the interested
reader. We improved the tag-B reconstruction algorithm,
considering more decay modes with the effect of increas-
ing the efficiency by a factor 2, at the cost of a larger
background of misreconstructed tag-
B
s. We performed a
multivariate analysis choosing the variables and the selec-
tion level by an optimisation procedure aiming at the
smallest uncertainty, by means of Monte Carlo pseudo-
experiments. To extract the signal yield, the previous
analysis used a cut and count method, while we fit the
signal yield maximising a likelihood built from the most
discriminating variable. Finally, the present analysis took
advantage of a more recent version of the reconstruction
software and data Monte Carlo studies to assess systematic
uncertainties.
The result is statistically consistent with recent
Belle measurement using a similar tag-
B
reconstruction
FIG. 3 (color online).
E
extra
distribution for double tagged
events. The ‘‘signal’’
B
is reconstructed in hadronic decays
(left plot) or semileptonic decays (right plot). Points are data
and boxes are MC simulation.
TABLE IV. Contributions to systematic uncertainty on the
branching fraction.
Source of systematics
B
uncertainty (%)
Additive
Background PDF
10
Signal PDF
2.6
Multiplicative
Tag-
B
efficiency
5.0
B
counting
1.1
Electron identification
2.6
Muon identification
4.7
Kaon identification
0.4
Tracking
0.5
MC statistics
0.6
Total
13
EVIDENCE OF
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þ
!
þ
DECAYS
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031102-7
technique [
12
], and with the other measurement from Belle
using semileptonic tag-
B
s[
13
]. Combining this result with
the other
BABAR
measurement of
B
ð
B
þ
!
þ
Þ
derived
from a statistically independent sample [
11
], we obtain
B
ð
B
þ
!
þ
Þ¼ð
1
:
79
0
:
48
Þ
10
4
, where both sta-
tistical and systematic uncertainties are combined in
quadrature.
Our measurement of the branching fraction
B
ð
B
þ
!
þ
Þ
exceeds the prediction of the SM determined using the
values of
j
V
ub
j
extracted from exclusive semileptonic
events and from inclusive semileptonic events by
2
:
4
and
1
:
6
, respectively. We also determine, separately for
the exclusive and inclusive
j
V
ub
j
BABAR
measurements,
90% C.L. exclusion regions in the parameter space of the
2HDM- type II
ð
m
H
þ
;
tan
Þ
, where
m
H
þ
is the charged
Higgs mass and
tan
is the ratio of the vacuum expecta-
tion values of the two Higgs doublets. We find that, taking
j
V
ub
j
from the exclusive measurement, most of the parame-
ters space is excluded at 90% C.L. Using the higher value
of
j
V
ub
j
from the inclusive measurement, the constraints
are less stringent but already set a lower limit at the TeV
scale for high
tan
. The same implications on 2HDM are
supported by a recent
BABAR
study of the
B
ð
B
!
D
ðÞ
Þ
decays [
18
]. Figure
4
shows a comparison between the
measured
B
ð
B
þ
!
þ
Þ
branching fraction with the pre-
diction of the 2HDM as a function of
tan
=m
H
þ
and the
exclusion plots in the
ð
m
H
þ
;
tan
Þ
plane for the exclusive
and inclusive measurements of
j
V
ub
j
.
We are grateful for the extraordinary contributions of our
PEP-II colleagues in achieving the excellent luminosity and
machine conditions that have made this work possible. The
success of this project also relies critically on the expertise
and dedication of the computing organizations that support
BABAR
. The collaborating institutions wish to thank SLAC
for its support and the kind hospitality extended to them.
This work is supported by the U.S. Department of Energy
and National Science Foundation, the Natural Sciences and
Engineering Research Council (Canada), the Commissariat
a
`
l’Energie Atomique and Institut National de Physique
Nucle
́
aire et de Physique des Particules (France), the
Bundesministerium fu
̈
r Bildung und Forschung and
Deutsche Forschungsgemeinschaft (Germany), the Istituto
Nazionale di Fisica Nucleare (Italy), the Foundation for
Fundamental Research on Matter (The Netherlands), the
Research Council of Norway, the Ministry of Education and
Science of the Russian Federation, Ministerio de Ciencia e
Innovacio
́
n (Spain), and the Science and Technology
Facilities Council (United Kingdom). Individuals have re-
ceived support from the Marie-Curie IEF program
(European Union), the A. P. Sloan Foundation (USA) and
the Binational Science Foundation (USA-Israel).
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FIG. 4 (color online). Top plot: Comparison between the mea-
sured
B
ð
B
þ
!
þ
Þ
branching fraction (horizontal band) with
the prediction of the 2HDM as a function of
tan
=m
H
þ
, using
exclusive (red/light gray) or inclusive (blue/dark gray)
j
V
ub
j
measurement. Bottom plots: 90% and 99% C.L. exclusion
regions in the
ð
m
H
þ
;
tan
Þ
plane using the exclusive (left) and
inclusive (right) measurements of
j
V
ub
j
.
J. P. LEES
et al.
PHYSICAL REVIEW D
88,
031102(R) (2013)
RAPID COMMUNICATIONS
031102-8
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EVIDENCE OF
B
þ
!
þ
DECAYS
...
PHYSICAL REVIEW D
88,
031102(R) (2013)
RAPID COMMUNICATIONS
031102-9