Search for
B
!
K
ð
Þ
and invisible quarkonium decays
J. P. Lees,
1
V. Poireau,
1
V. Tisserand,
1
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
M. Lee,
5
G. Lynch,
5
H. Koch,
6
T. Schroeder,
6
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
D. Kirkby,
10
A. J. Lankford,
10
M. Mandelkern,
10
B. Dey,
11
J. W. Gary,
11
O. Long,
11
G. M. Vitug,
11
C. Campagnari,
12
M. Franco Sevilla,
12
T. M. Hong,
12
D. Kovalskyi,
12
J. D. Richman,
12
C. A. West,
12
A. M. Eisner,
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
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
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
L. Piemontese,
22a
V. Santoro,
22a
R. Baldini-Ferroli,
23
A. Calcaterra,
23
R. de Sangro,
23
G. Finocchiaro,
23
S. Martellotti,
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
M. Morii,
26
A. Adametz,
27
U. Uwer,
27
H. M. Lacker,
28
P. D. Dauncey,
29
U. Mallik,
30
C. Chen,
31
J. Cochran,
31
W. T. Meyer,
31
S. Prell,
31
A. E. Rubin,
31
A. V. Gritsan,
32
N. Arnaud,
33
M. Davier,
33
D. Derkach,
33
G. Grosdidier,
33
F. Le Diberder,
33
A. M. Lutz,
33
B. Malaescu,
33
P. Roudeau,
33
A. Stocchi,
33
G. Wormser,
33
D. J. Lange,
34
D. M. Wright,
34
J. P. Coleman,
35
J. R. Fry,
35
E. Gabathuler,
35
D. E. Hutchcroft,
35
D. J. Payne,
35
C. Touramanis,
35
A. J. Bevan,
36
F. Di Lodovico,
36
R. Sacco,
36
G. Cowan,
37
J. Bougher,
38
D. N. Brown,
38
C. L. Davis,
38
A. G. Denig,
39
M. Fritsch,
39
W. Gradl,
39
K. Griessinger,
39
A. Hafner,
39
E. Prencipe,
39
R. J. Barlow,
40,
‡
G. D. Lafferty,
40
E. Behn,
41
R. Cenci,
41
B. Hamilton,
41
A. Jawahery,
41
D. A. Roberts,
41
R. Cowan,
42
D. Dujmic,
42
G. Sciolla,
42
R. Cheaib,
43
P. M. Patel,
43,
§
S. H. Robertson,
43
P. Biassoni,
44a,44b
N. Neri,
44a
F. Palombo,
44a,44b
L. Cremaldi,
45
R. Godang,
45,
k
P. Sonnek,
45
D. J. Summers,
45
X. Nguyen,
46
M. Simard,
46
P. Taras,
46
G. De Nardo,
47a,47b
D. Monorchio,
47a,47b
G. Onorato,
47a,47b
C. Sciacca,
47a,47b
M. Martinelli,
48
G. Raven,
48
C. P. Jessop,
49
J. M. LoSecco,
49
K. Honscheid,
50
R. Kass,
50
J. Brau,
51
R. Frey,
51
N. B. Sinev,
51
D. Strom,
51
E. Torrence,
51
E. Feltresi,
52a,52b
M. Margoni,
52a,52b
M. Morandin,
52a
M. Posocco,
52a
M. Rotondo,
52a
G. Simi,
52a
F. Simonetto,
52a,52b
R. Stroili,
52a,52b
S. Akar,
53
E. Ben-Haim,
53
M. Bomben,
53
G. R. Bonneaud,
53
H. Briand,
53
G. Calderini,
53
J. Chauveau,
53
Ph. Leruste,
53
G. Marchiori,
53
J. Ocariz,
53
S. Sitt,
53
M. Biasini,
54a,54b
E. Manoni,
54a
S. Pacetti,
54a,54b
A. Rossi,
54a,54b
C. Angelini,
55a,55b
G. Batignani,
55a,55b
S. Bettarini,
55a,55b
M. Carpinelli,
55a,55b,
{
G. Casarosa,
55a,55b
A. Cervelli,
55a,55b
F. Forti,
55a,55b
M. A. Giorgi,
55a,55b
A. Lusiani,
55a,55c
B. Oberhof,
55a,55b
E. Paoloni,
55a,55b
A. Perez,
55a
G. Rizzo,
55a,55b
J. J. Walsh,
55a
D. Lopes Pegna,
56
J. Olsen,
56
A. J. S. Smith,
56
R. Faccini,
57a,57b
F. Ferrarotto,
57a
F. Ferroni,
57a,57b
M. Gaspero,
57a,57b
L. Li Gioi,
57a
G. Piredda,
57a
C. Bu
̈
nger,
58
O. Gru
̈
nberg,
58
T. Hartmann,
58
T. Leddig,
58
C. Voß,
58
R. Waldi,
58
T. Adye,
59
E. O. Olaiya,
59
F. F. Wilson,
59
S. Emery,
60
G. Hamel de Monchenault,
60
G. Vasseur,
60
Ch. Ye
`
che,
60
F. Anulli,
61
D. Aston,
61
D. J. Bard,
61
J. F. Benitez,
61
C. Cartaro,
61
M. R. Convery,
61
J. Dorfan,
61
G. P. Dubois-Felsmann,
61
W. Dunwoodie,
61
M. Ebert,
61
R. C. Field,
61
B. G. Fulsom,
61
A. M. Gabareen,
61
M. T. Graham,
61
C. Hast,
61
W. R. Innes,
61
P. Kim,
61
M. L. Kocian,
61
D. W. G. S. Leith,
61
P. Lewis,
61
D. Lindemann,
61
B. Lindquist,
61
S. Luitz,
61
V. Luth,
61
H. L. Lynch,
61
D. B. MacFarlane,
61
D. R. Muller,
61
H. Neal,
61
S. Nelson,
61
M. Perl,
61
T. Pulliam,
61
B. N. Ratcliff,
61
A. Roodman,
61
A. A. Salnikov,
61
R. H. Schindler,
61
A. Snyder,
61
D. Su,
61
M. K. Sullivan,
61
J. Va’vra,
61
A. P. Wagner,
61
W. F. Wang,
61
W. J. Wisniewski,
61
M. Wittgen,
61
D. H. Wright,
61
H. W. Wulsin,
61
V. Ziegler,
61
W. Park,
62
M. V. Purohit,
62
R. M. White,
62,
**
J. R. Wilson,
62
A. Randle-Conde,
63
S. J. Sekula,
63
M. Bellis,
64
P. R. Burchat,
64
T. S. Miyashita,
64
E. M. T. Puccio,
64
M. S. Alam,
65
J. A. Ernst,
65
R. Gorodeisky,
66
N. Guttman,
66
D. R. Peimer,
66
A. Soffer,
66
S. M. Spanier,
67
J. L. Ritchie,
68
A. M. Ruland,
68
R. F. Schwitters,
68
B. C. Wray,
68
J. M. Izen,
69
X. C. Lou,
69
F. Bianchi,
70a,70b
F. De Mori,
70a,70b
A. Filippi,
70a
D. Gamba,
70a,70b
S. Zambito,
70a,70b
L. Lanceri,
71a,71b
L. Vitale,
71a,71b
F. Martinez-Vidal,
72
A. Oyanguren,
72
P. Villanueva-Perez,
72
H. Ahmed,
73
J. Albert,
73
Sw. Banerjee,
73
F. U. Bernlochner,
73
H. H. F. Choi,
73
G. J. King,
73
R. Kowalewski,
73
M. J. Lewczuk,
73
T. Lueck,
73
I. M. Nugent,
73
J. M. Roney,
73
R. J. Sobie,
73
N. Tasneem,
73
T. J. Gershon,
74
P. F. Harrison,
74
T. E. Latham,
74
H. R. Band,
75
S. Dasu,
75
Y. Pan,
75
R. Prepost,
75
and S. L. Wu
75
(
B
A
B
AR
Collaboration)
PHYSICAL REVIEW D
87,
112005 (2013)
1550-7998
=
2013
=
87(11)
=
112005(13)
112005-1
Ó
2013 American Physical Society
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 SB RAS, 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-44122 Ferrara, Italy
22b
Dipartimento di Fisica e Scienze della Terra, Universita
`
di Ferrara, I-44122 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
Universita
̈
t Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg, Germany
28
Humboldt-Universita
̈
t zu Berlin, Institut fu
̈
r Physik, Newtonstraße 15, D-12489 Berlin, Germany
29
Imperial College London, London, SW7 2AZ, United Kingdom
30
University of Iowa, Iowa City, Iowa 52242, USA
31
Iowa State University, Ames, Iowa 50011-3160, USA
32
Johns Hopkins University, Baltimore, Maryland 21218, USA
33
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
34
Lawrence Livermore National Laboratory, Livermore, California 94550, USA
35
University of Liverpool, Liverpool L69 7ZE, United Kingdom
36
Queen Mary, University of London, London E1 4NS, United Kingdom
37
University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom
38
University of Louisville, Louisville, Kentucky 40292, USA
39
Johannes Gutenberg-Universita
̈
t Mainz, Institut fu
̈
r Kernphysik, D-55099 Mainz, Germany
40
University of Manchester, Manchester M13 9PL, United Kingdom
41
University of Maryland, College Park, Maryland 20742, USA
42
Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139, USA
43
McGill University, Montre
́
al, Que
́
bec, Canada H3A 2T8
44a
INFN Sezione di Milano, I-20133 Milano, Italy
44b
Dipartimento di Fisica, Universita
`
di Milano, I-20133 Milano, Italy
45
University of Mississippi, University, Mississippi 38677, USA
46
Universite
́
de Montre
́
al, Physique des Particules, Montre
́
al, Que
́
bec, Canada H3C 3J7
47a
INFN Sezione di Napoli, I-80126 Napoli, Italy
47b
Dipartimento di Scienze Fisiche, Universita
`
di Napoli Federico II, I-80126 Napoli, Italy
48
NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands
49
University of Notre Dame, Notre Dame, Indiana 46556, USA
50
Ohio State University, Columbus, Ohio 43210, USA
51
University of Oregon, Eugene, Oregon 97403, USA
52a
INFN Sezione di Padova, I-35131 Padova, Italy
52b
Dipartimento di Fisica, Universita
`
di Padova, I-35131 Padova, Italy
J. P. LEES
et al.
PHYSICAL REVIEW D
87,
112005 (2013)
112005-2
53
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
54a
INFN Sezione di Perugia, I-06100 Perugia, Italy
54b
Dipartimento di Fisica, Universita
`
di Perugia, I-06100 Perugia, Italy
55a
INFN Sezione di Pisa, I-56127 Pisa, Italy
55b
Dipartimento di Fisica, Universita
`
di Pisa, I-56127 Pisa, Italy
55c
Scuola Normale Superiore di Pisa, I-56127 Pisa, Italy
56
Princeton University, Princeton, New Jersey 08544, USA
57a
INFN Sezione di Roma, I-00185 Roma, Italy
57b
Dipartimento di Fisica, Universita
`
di Roma La Sapienza, I-00185 Roma, Italy
58
Universita
̈
t Rostock, D-18051 Rostock, Germany
59
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
60
CEA, Irfu, SPP, Centre de Saclay, F-91191 Gif-sur-Yvette, France
61
SLAC National Accelerator Laboratory, Stanford, California 94309, USA
62
University of South Carolina, Columbia, South Carolina 29208, USA
63
Southern Methodist University, Dallas, Texas 75275, USA
64
Stanford University, Stanford, California 94305-4060, USA
65
State University of New York, Albany, New York 12222, USA
66
Tel Aviv University, School of Physics and Astronomy, Tel Aviv 69978, Israel
67
University of Tennessee, Knoxville, Tennessee 37996, USA
68
University of Texas at Austin, Austin, Texas 78712, USA
69
University of Texas at Dallas, Richardson, Texas 75083, USA
70a
INFN Sezione di Torino, I-10125 Torino, Italy
70b
Dipartimento di Fisica Sperimentale, Universita
`
di Torino, I-10125 Torino, Italy
71a
INFN Sezione di Trieste, I-34127 Trieste, Italy
71b
Dipartimento di Fisica, Universita
`
di Trieste, I-34127 Trieste, Italy
72
IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
73
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
74
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
75
University of Wisconsin, Madison, Wisconsin 53706, USA
(Received 1 April 2013; published 5 June 2013)
We search for the flavor-changing neutral-current decays
B
!
K
ðÞ
, and the invisible decays
J=
c
!
and
c
ð
2
S
Þ!
via
B
!
K
ðÞ
J=
c
and
B
!
K
ðÞ
c
ð
2
S
Þ
, respectively, using a data sample of
471
10
6
B
B
pairs collected by the
BABAR
experiment. We fully reconstruct the hadronic decay of one of the
B
mesons in the
ð
4
S
Þ!
B
B
decay, and search for the
B
!
K
ðÞ
decay in the rest of the event. We
observe no significant excess of signal decays over background and report branching fraction upper limits
of
B
ð
B
þ
!
K
þ
Þ
<
3
:
7
10
5
,
B
ð
B
0
!
K
0
Þ
<
8
:
1
10
5
,
B
ð
B
þ
!
K
þ
Þ
<
11
:
6
10
5
,
B
ð
B
0
!
K
0
Þ
<
9
:
3
10
5
, and combined upper limits of
B
ð
B
!
K
Þ
<
3
:
2
10
5
and
B
ð
B
!
K
Þ
<
7
:
9
10
5
, all at the 90% confidence level. For the invisible quarkonium decays, we report
branching fraction upper limits of
B
ð
J=
c
!
Þ
<
3
:
9
10
3
and
B
ð
c
ð
2
S
Þ!
Þ
<
15
:
5
10
3
at
the 90% confidence level. Using the improved kinematic resolution achieved from hadronic reconstruc-
tion, we also provide partial branching fraction limits for the
B
!
K
ðÞ
decays over the full kinematic
spectrum.
DOI:
10.1103/PhysRevD.87.112005
PACS numbers: 13.20.He, 13.20.Gd, 14.40.Nd
I. INTRODUCTION
Flavor-changing neutral-current transitions, such as
b
!
s
, are prohibited in the standard model (SM) at
tree-level. However, they can occur via one-loop box or
electroweak penguin diagrams, as shown in Fig.
1
. They
can occur also in the SM via a quarkonium resonance state
b
!
sc
c
,
c
c
!
, where the
c
c
decay is mediated by a
virtual
Z
0
boson (Fig.
2
). This latter decay process has the
same final state as
b
!
s
with an additional constraint
from the on-shell
c
c
mass. Both the
b
!
s
and
c
c
!
decay rates are expected to be small within the SM, with
*
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, UK.
§
Deceased.
k
Now at University of South Alabama, Mobile, Alabama
36688, USA.
{
Also with Universita
`
di Sassari, Sassari, Italy.
**
Now at Universidad Te
́
cnica Federico Santa Maria,
Valparaiso, Chile 2390123.
SEARCH FOR
B
!
K
ðÞ
AND
...
PHYSICAL REVIEW D
87,
112005 (2013)
112005-3
branching fractions estimated to be
B
ð
B
þ
!
K
þ
Þ¼
B
ð
B
0
!
K
0
Þ¼ð
4
:
5
0
:
7
Þ
10
6
,
B
ð
B
þ
!
K
þ
Þ¼
B
ð
B
0
!
K
0
Þ¼ð
6
:
8
þ
1
:
0
1
:
1
Þ
10
6
[
1
], and
B
ð
J=
c
!
Þ¼ð
4
:
54
10
7
Þ
B
ð
J=
c
!
e
þ
e
Þ
[
2
]. The
b
!
s
rates are predicted with smaller theoretical uncertain-
ties than those in the corresponding
b
!
s‘
þ
‘
modes due
to the absence of long-distance hadronic effects from
electromagnetic penguin contributions.
Various new-physics scenarios exist that could signifi-
cantly enhance the
b
!
s
branching fractions, as well as
modify the expected SM decay distributions of
s
B
q
2
=m
2
B
, where
q
2
is the squared magnitude of the four-
momentum transferred from the
B
meson to the neutrino
pair, and
m
B
is the
B
meson mass. Some of these scenarios
predict massive particles that could contribute additional
loop diagrams with similar amplitudes as those in the SM,
such as nonstandard
Z
0
couplings with supersymmetric
(SUSY) particles [
1
], fourth-generation quarks [
3
], anoma-
lous top-charm transitions [
4
], or a massive U(1) gauge
boson
Z
0
[
1
,
5
]. Since
b
!
s
has two final-state neutri-
nos, other sources of new physics can also contribute to the
experimental signature of a kaon and missing four-
momentum, such as low-mass dark-matter (LDM) candi-
dates [
1
,
6
–
8
], unparticles [
9
], right-handed neutrinos [
5
],
or SUSY particles [
10
]. Models with a single universal
extra dimension also predict higher decay rates [
11
].
The decays
J=
c
!
and
c
ð
2
S
Þ!
provide
additional windows for new-physics searches. In
spontaneously-broken SUSY, a
c
c
resonance can decay
into a pair of goldstinos via either a virtual
Z
0
in the
s
-channel or a
c
-squark exchange in the
t
-channel [
2
]
(Fig.
2
). The contribution of a massive SU(2) gauge boson
Z
0
, introduced in the left-right SUSY model, could sup-
press the decay rates up to an order of magnitude [
2
].
Conversely, a low-mass U(1) gauge boson
U
could en-
hance the invisible decay rates of quarkonium states by
several orders of magnitude by coupling to LDM particles
[
12
,
13
]. The
U
boson could decay into a pair of spin-
1
=
2
Majorana (
), spin-
1
=
2
Dirac (
), or spin-0 (
’’
) LDM
particles.
We search for
B
!
K
and
B
!
K
, and for
J=
c
!
and
c
ð
2
S
Þ!
via
B
!
K
ðÞ
J=
c
and
B
!
K
ðÞ
c
ð
2
S
Þ
, respectively, where
K
ðÞ
signifies a charged or
neutral
K
or
K
meson [
14
]. We use a technique in which
one
B
meson is exclusively reconstructed in a hadronic
final state before looking for a signal decay within the rest
of the event. Since the four-momentum of one
B
meson is
fully determined, the missing mass resolution on the two
final-state neutrinos and the suppression of background are
improved with respect to other reconstruction techniques.
Several previous searches for
B
!
K
and
B
!
K
have been performed by both the
BABAR
and BELLE
collaborations [
15
–
19
]. Currently, the most stringent pub-
lished upper limits at 90% confidence level (CL) are
B
ð
B
þ
!
K
þ
Þ
<
1
:
3
10
5
[
15
] and
B
ð
B
!
K
Þ
<
8
10
5
[
16
]. The
B
ð
B
þ
!
K
þ
Þ
limit was determined
using semileptonic-tag reconstruction, which produces
samples that are statistically larger and independent
of those produced using the hadronic-tag reconstruction
employed in this search. The
B
ð
B
!
K
Þ
limit was a
combination of two
BABAR
analyses, one using
semileptonic-tag reconstruction and the other using
hadronic-tag reconstruction.
A
J=
c
!
search via
c
ð
2
S
Þ!
þ
J=
c
was performed by the BES collaboration, which set
an upper limit at 90% CL of
B
ð
J=
c
!
Þ
<
1
:
2
10
2
B
ð
J=
c
!
þ
Þ
[
20
]. This article presents the
first search for
J=
c
!
using the hadronic-tag recon-
struction of a
B
meson decay. A search for
c
ð
2
S
Þ!
has not been performed previously.
II. THE
BABAR
DETECTOR AND DATA SAMPLE
This search uses a data sample of
471
3
million
B
B
pairs, corresponding to an integrated luminosity of
429 fb
1
collected at the
ð
4
S
Þ
resonance [
21
]. The data
were recorded with the
BABAR
detector [
22
] at the
PEP-II asymmetric-energy
e
þ
e
storage rings. The
charged-particle tracking system consists of a five-layer
double-sided silicon vertex tracker and a 40-layer drift
chamber, both coaxial with a 1.5 T solenoidal magnetic
field. Charged kaons and pions are distinguished by spe-
cific ionization energy-loss measurements from the track-
ing system for lower momentum particles, and by
measurements from a ring-imaging Cherenkov radiation
detector for higher momentum particles. A CsI(Tl) elec-
tromagnetic calorimeter is used to reconstruct photons of
energy greater than 20 MeV and to identify electrons.
Muon identification is provided by the instrumented
flux return of the magnet. Particle identification (PID)
FIG. 2. Lowest-order Feynman diagrams of (from left to right)
the SM decay
c
c
!
, the SUSY decay
c
c
into a pair of
goldstinos (
~
g
) via a
c
-squark in the
t
-channel, and the SUSY
decay
c
c
!
~
g
~
g
via a virtual
Z
0
in the
s
-channel.
FIG. 1. Lowest-order SM Feynman diagrams for
b
!
s
transitions. The virtual top quark provides the dominant contri-
bution in each case.
J. P. LEES
et al.
PHYSICAL REVIEW D
87,
112005 (2013)
112005-4
algorithms are trained to identify charged particle types by
using 36 input parameters including momentum, polar and
azimuthal angles, the Cherenkov angle, and energy-loss
measurements [
23
]. We employ PID criteria that select
K
þ
mesons with an efficiency greater than 85% and with
approximately 1% misidentification probability for pions
and muons.
Signal and background decays are studied using
Monte Carlo (MC) samples simulated with Geant4 [
24
].
The simulation includes a detailed model of the
BABAR
detector geometry and response. Beam-related background
and detector noise are extracted from data and are overlaid
on the MC simulated events. Large MC samples of generic
B
B
and continuum (
e
þ
e
!
þ
or
e
þ
e
!
q
q
, where
q
¼
u
,
d
,
s
,
c
) events provide ten times the number of
ð
4
S
Þ!
B
B
and
e
þ
e
!
c
c
events as in the data sample,
and four times the number of other continuum decays. The
ð
4
S
Þ!
B
B
signal MC samples are generated with one
B
meson decaying via
B
!
K
ðÞ
, with and without the
c
c
resonances, while the other
B
meson decays according to a
model tuned to world averages of allowed decay channels.
The
s
B
distributions for
B
!
K
ðÞ
decays within signal
MC samples are generated initially using a phase-space
model, and then reweighted using the model from Ref. [
1
],
henceforth referred to as ABSW. Within
B
!
K
decays, this model is also used to reweight the helicity-
angle distribution between the signal
B
and the
K
þ
or
K
0
flight directions in the
K
rest frame. The helicity ampli-
tudes for the decay channels
B
!
K
J=
c
and
B
!
K
c
ð
2
S
Þ
are generated using values taken from a
BABAR
measurement [
25
].
III. ANALYSIS METHOD
Event selection for both the
B
!
K
ðÞ
and
B
!
K
ðÞ
c
c
,
c
c
!
searches begins by fully reconstructing
a
B
meson (
B
tag
) in one of many hadronic final states,
B
!
SX
had
, where
S
is a ‘‘seed’’ meson (
D
ðÞþ
,
D
ðÞ
0
,
D
ðÞþ
s
,or
J=
c
) and
X
had
is a collection of at most five mesons,
composed of charged and neutral kaons and pions with a
net charge of
1
. This method, which was used also in
Ref. [
26
], reconstructs additional modes with respect to
previous hadronic-tag
B
!
K
ðÞ
analyses [
16
,
17
], and
results in approximately twice the reconstruction
efficiency. The
D
seeds are reconstructed in the decay
modes
D
þ
!
K
0
S
þ
,
K
0
S
þ
0
,
K
0
S
þ
þ
,
K
þ
þ
,
K
þ
þ
0
,
K
þ
K
þ
,
K
þ
K
þ
0
;
D
0
!
K
þ
,
K
þ
0
,
K
þ
þ
,
K
0
S
þ
,
K
0
S
þ
0
,
K
þ
K
,
þ
,
þ
0
, and
K
0
S
0
. Additional seeds are recon-
structed as
D
þ
!
D
0
þ
,
D
þ
0
;
D
0
!
D
0
0
,
D
0
;
D
þ
s
!
D
þ
s
;
D
þ
s
!
½!
K
þ
K
þ
,
K
0
S
K
þ
; and
J=
c
!
e
þ
e
,
þ
. The
K
0
S
candidates are recon-
structed via their decay to
þ
.
Well-reconstructed
B
tag
candidates are selected
using two kinematic variables:
E
¼
E
B
tag
ffiffiffi
s
p
=
2
and
m
ES
¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
s=
4
~
p
2
B
tag
q
, where
E
B
tag
and
~
p
B
tag
are the energy
and momentum vector of the
B
tag
candidate, respectively,
in the
e
þ
e
center-of-mass (CM) frame and
ffiffiffi
s
p
is the total
energy of the
e
þ
e
system. The value of
E
, which peaks
at zero for correctly reconstructed
B
mesons, is required to
be between
0
:
12
and 0.12 GeV or within two standard
deviations around the mean for a given
X
had
mode, which-
ever is the tighter constraint. If more than one
B
tag
candi-
date is reconstructed, the one in the mode with the highest
purity (fraction of candidates that are correctly recon-
structed within a given
B
tag
decay mode) is chosen. If there
are multiple candidates with the same purity, the one with
the smallest
j
E
j
is selected.
After requiring that the event contains between one and
three charged tracks not used in the
B
tag
reconstruction
(‘‘signal-side’’ tracks), the purity of each mode is recalcu-
lated, and only the
B
tag
modes that have a recalculated
purity greater than 68% are retained. This results in a total
of 448 final states. This purity value was optimized by
maximizing the figure of merit [
27
]
"
sig
i
1
2
n
þ
ffiffiffiffiffiffiffiffiffiffi
N
bkg
i
q
;
(1)
where the number of sigmas
n
¼
1
:
28
corresponds to a
one-sided Gaussian limit at 90% CL,
"
sig
i
is the total signal
efficiency, and
N
bkg
i
is the expected number of background
events, with
i
representing one of the signal decay chan-
nels. All other selection criteria discussed henceforth were
optimized simultaneously using this same figure of merit.
The signal region of the
B
tag
candidate is defined as
5
:
273
<m
ES
<
5
:
290 GeV
=c
2
(Fig.
3
), since correctly re-
constructed
B
mesons produce a peak in this region near
the nominal
B
-meson mass. The
B
tag
candidates that are
incorrectly reconstructed (‘‘combinatorial’’ events), which
result from continuum events or are due to particles
assigned to the wrong
B
meson, produce a distribution
that is relatively uniform below the
m
ES
signal region
and decreases toward the kinematic limit within it.
Approximately 0.3% of signal MC events and 12.0 million
data events contain a
B
tag
that is reconstructed using the
above requirements and found to be within the
m
ES
signal
region.
Since
B
mesons are spin zero and are produced with low
momentum in the CM frame (
0
:
32 GeV
=c
), their decay
products are more isotropically distributed than non-
B
B
background. For example,
j
cos
T
j
, where
T
is the angle
in the CM frame between the
B
tag
thrust [
28
] axis and the
thrust axis of all other particles in the event, has a uniform
distribution for
B
B
events but peaks near one for contin-
uum events. Continuum background is suppressed by using
a multivariate likelihood selector based on six event-shape
variables. These consist of
j
cos
T
j
, the cosine of the angle
between
~
p
B
tag
and the beam axis, the magnitude of the
B
tag
SEARCH FOR
B
!
K
ðÞ
AND
...
PHYSICAL REVIEW D
87,
112005 (2013)
112005-5
thrust, the component of the
B
tag
thrust along the beam
axis, the angle between the missing momentum vector
(
~
p
miss
) and the beam axis, and the ratio of the second-to-
zeroth Fox-Wolfram moment [
29
] computed using all
charged and neutral particles in the event. The multivariate
selector requires
L
B
Q
j
P
B
ð
x
j
Þ
Q
j
P
B
ð
x
j
Þþ
Q
j
P
q
ð
x
j
Þ
>
53%
;
(2)
where
P
q
ð
x
j
Þ
and
P
B
ð
x
j
Þ
are probability density functions
determined from MC that describe continuum and signal-
like
B
B
events, respectively, for the six event-shape vari-
ables
x
j
. The
L
B
requirement, which was optimized with
other selection criteria using Eq. (
1
), also improves the
agreement between data and MC by suppressing unmod-
eled continuum backgrounds.
In the sample of selected
B
tag
candidates, signal events
are chosen such that a single
K
ðÞ
candidate can be recon-
structed within the rest of the event and no additional
charged tracks remain in the event. The sum of the
K
ðÞ
and
B
tag
candidate charges must equal zero. Since signal
decays have two final-state neutrinos, these events are
required to have missing energy greater than zero, where
the missing energy is defined as the CM energy minus all
detected calorimeter deposits from charged and neutral
particles in the event. For
B
!
K
ðÞ
, the signal decays
are reconstructed in six channels:
B
þ
!
K
þ
;
B
0
!
K
0
where
K
0
!
K
0
S
;
B
þ
!
K
þ
, where
K
þ
!
K
þ
0
and
K
þ
!
K
0
S
þ
; and
B
0
!
K
0
, where
K
0
!
K
þ
and
K
0
!
K
0
S
0
.For
c
c
!
, the same
six signal channels are employed with an additional re-
quirement that the
K
ðÞ
momentum is consistent with a
two-body decay, either
B
!
K
ðÞ
J=
c
or
B
!
K
ðÞ
c
ð
2
S
Þ
.
The
J=
c
and
c
ð
2
S
Þ
mesons then decay into a pair
of neutrinos, thus yielding the same final states as for
B
!
K
ðÞ
.
We reconstruct
K
0
S
!
þ
decay candidates using
two tracks of opposite charge, which originate from a
common vertex and produce an invariant mass within
7 MeV
=c
2
of the nominal
K
0
S
mass [
30
]. The PID for
each track must be inconsistent with that for an electron,
muon, or kaon. The
0
candidates are reconstructed from
pairs of photon candidates with individual energies greater
than 30 MeV, a total CM energy greater than 200 MeV, and
a
invariant mass between 100 and
160 MeV
=c
2
. All
K
þ
candidates must satisfy the PID criteria for a kaon.
Reconstructed
K
candidates are required to have an
invariant mass within
70 MeV
=c
2
of the nominal
K
mass [
30
]. A
K
þ
!
K
0
S
þ
candidate combines a
K
0
S
candidate with a track that satisfies the PID criteria for a
pion. If more than one
K
þ
!
K
0
S
þ
candidate can be
reconstructed in an event, the one with the mass closest
to the nominal
K
þ
mass is chosen. A
K
0
!
K
þ
candidate combines one track that satisfies the PID criteria
for a kaon with one that is inconsistent with the PID criteria
for an electron, muon, or kaon. In an event containing a
K
þ
(
K
0
S
) candidate and no additional signal-side tracks,
K
!
K
þ
0
(
K
0
S
0
) candidates are reconstructed if the invariant
mass of a
0
candidate and the
K
þ
(
K
0
S
) candidate falls
within the
K
mass window; otherwise the event is con-
sidered for the
K
þ
(
K
0
S
) signal channel. If more than one
K
þ
!
K
þ
0
or
K
0
!
K
0
S
0
candidate can be recon-
structed, the one with the highest energy
0
candidate is
chosen.
Once the
B
tag
and
K
ðÞ
are identified, the signal events
are expected to contain little or no additional energy within
the calorimeter. However, additional energy deposits can
result from beam-related photons, hadronic shower frag-
ments that were not reconstructed into the primary particle
deposit, and photons from unreconstructed
D
!
D=
0
transitions in the
B
tag
candidate. Only deposits with energy
greater than 50 MeV in the rest frame of the detector are
considered, and the sum of all such additional energy
deposits (
E
extra
) is required to be less than a threshold value
(
E
i
). The values of
E
i
, given in Table
I
and depicted in
Fig.
4
, were optimized with the other selection criteria but
TABLE I. Threshold values
E
i
for the
E
extra
variable in each of
the signal channels, determined using Eq. (
1
). The channels in
brackets refer to the
K
decay products.
Channel
K
þ
K
0
½
K
þ
0
½
K
0
S
þ
½
K
þ
½
K
0
S
0
E
i
[GeV] 0.11 0.28 0.18
0.29
0.31
0.33
]
2
[GeV/c
ES
m
5.2
5.21 5.22 5.23 5.24 5.25 5.26 5.27 5.28 5.29
)
2
Entries/(1 MeV/c
0
5
10
15
20
25
30
35
3
10
×
Sideband Region
Region
Signal
FIG. 3 (color online). The
m
ES
distribution for the
B
tag
candi-
dates in data (points) and in the expected combinatorial back-
ground as predicted by the MC (shaded). This distribution
includes only the charged and neutral
B
tag
candidates that pass
the purity restrictions, the multivariate continuum suppression,
and a requirement of one to three signal-side tracks. The data
within the
m
ES
sideband region is used to extrapolate the
expected number of combinatorial background events within
the signal region.
J. P. LEES
et al.
PHYSICAL REVIEW D
87,
112005 (2013)
112005-6
were allowed to differ between signal channels. For
events within the
K
þ
signal channel, calorimeter deposits
identified as kaon shower fragments are not included in the
E
extra
sum. A fragment candidate is defined as a neutral
calorimeter deposit whose momentum vector, when
compared to that of the signal track, is separated by
polar and azimuthal angles (relative to the beam axis
and in the rest frame of the detector) of
and
, respectively, such that
r
clus
<
15
, where
r
clus
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ð
Þ
2
þ
2
3
ð
Q
K
8
Þ
2
q
and
Q
K
¼
1
is the
K
charge. The
r
clus
and fragment candidate definitions were
optimized using studies of truth information in the signal
MC samples. The recovery of these kaon shower fragments
improves the final signal efficiency in the
K
þ
channel by
about 13%. This procedure was explored for the other
signal tracks, but the effect was small.
The searches for
B
!
K
ðÞ
and for
c
c
!
via
B
!
K
ðÞ
c
c
diverge in the final step of the signal selection,
which involves restricting the kinematics of the decay.
The value of
s
B
is calculated as
ð
p
B
sig
p
K
ðÞ
Þ
2
=m
2
B
, where
p
K
ðÞ
is the four-momentum of the
K
ðÞ
candidate, and
p
B
sig
is the expected signal
B
four-momentum with an energy of
ffiffiffi
s
p
=
2
, the nominal
B
-meson mass, and a momentum vector
pointing opposite the
B
tag
momentum. For
B
!
K
ðÞ
,
the signal region optimized for maximum SM sensitivity is
0
<s
B
<
0
:
3
for all six signal channels. This corresponds
to a
K
ðÞ
momentum greater than about 1.8
ð
1
:
7
Þ
GeV
=c
in
the signal
B
rest frame for
B
!
K
(
B
!
K
) events.
Partial branching fractions over the full
s
B
spectrum are
also provided for sensitivity to new-physics scenarios that
modify the kinematic distributions for
B
!
K
ðÞ
.For
c
c
!
via
B
!
K
ðÞ
c
c
, the invariant mass of the two
neutrinos
m
ffiffiffiffiffiffiffiffiffiffiffiffi
s
B
m
2
B
q
is expected to correspond to the
mass of the
J=
c
(
3
:
097 GeV
=c
2
) meson or to that of the
c
ð
2
S
Þ
(
3
:
686 GeV
=c
2
) meson. Signal events are selected
within three standard deviations around the nominal
c
c
masses, which results in windows of
3
:
044
<m
<
3
:
146
ð
3
:
019
<m
<
3
:
175
Þ
GeV
=c
2
for the
B
!
KJ=
c
(
B
!
K
J=
c
) channels, and
3
:
650
<m
<
3
:
724
ð
3
:
627
<
m
<
3
:
739
Þ
GeV
=c
2
for the
B
!
K
c
ð
2
S
Þ
(
B
!
K
c
ð
2
S
Þ
) channels.
To avoid experimenter bias, all the above selection
criteria and values were optimized using the MC before
looking at any data events within the
E
extra
and
m
ES
signal
regions.
IV. BACKGROUND AND BRANCHING
FRACTION EXTRACTION
The total number of background events
N
bkg
i
in the
signal region has two components:
N
peak
i
is the number of
expected background events having a correctly recon-
structed
B
tag
candidate and hence peaking within the
m
ES
signal region, and
N
comb
i
is the number of expected com-
binatorial background events, including both continuum
events and
B
B
events with an incorrectly reconstructed
B
tag
candidate. To reduce the dependence on MC simula-
tions, the number of
N
comb
i
events is extrapolated directly
from the observed data events within the
m
ES
sideband
region, defined as
5
:
200
<m
ES
<
5
:
265 GeV
=c
2
and de-
picted in Fig.
3
. The shape of the combinatorial
m
ES
distribution is estimated using MC samples of continuum
events and of
B
B
events reconstructed with the wrong
charge.
The number of
N
peak
i
events is estimated from generic
B
B
MC samples. Over half of
N
peak
i
is found to be from
B
!
D
ðÞ
‘
(
‘
¼
e
or
) decays in which no lepton can-
didate is identified in the event and the
K
ðÞ
is a daughter of
the
D
or
D
meson. One particular peaking background in
the
B
!
K
ðÞ
search is
B
þ
!
þ
, with
þ
!
K
ðÞþ
, which has the same final state as the signal decay
[
31
]. Exclusive
B
þ
!
þ
MC samples, assuming a
branching fraction of
ð
1
:
65
0
:
34
Þ
10
4
[
30
], indicate
that this background constitutes less than 15 (5)% of the
total background in the
B
þ
!
K
þ
(
B
þ
!
K
þ
)
channel.
[GeV]
extra
E
Entries/(0.25 GeV)
0
10
20
+
K
[GeV]
extra
E
0
5
10
15
0
K
[GeV]
extra
E
0
5
10
15
+
K*
[GeV]
extra
E
0
0.1
0.2
0.3
0.4
0.5
0.6
0
5
10
15
20
0
K*
FIG. 4 (color online). The
E
extra
distribution over the full
s
B
spectrum in the (from top to bottom)
K
þ
,
K
0
,
K
þ
, and
K
0
channels after applying all other signal selection criteria. The
expected combinatorial (shaded) plus
m
ES
-peaking (solid) back-
ground contributions are overlaid on the data (points). The
B
!
K
ðÞ
signal MC distributions (dashed) have arbitrary normal-
ization. Both the
B
!
K
ðÞ
and
c
c
!
searches select
events to the left of the vertical line that corresponds to the
E
i
value of that channel, as given in Table
I
.
SEARCH FOR
B
!
K
ðÞ
AND
...
PHYSICAL REVIEW D
87,
112005 (2013)
112005-7
Since both
N
peak
i
and
"
sig
i
are determined from MC
samples, we normalize the MC yields to the data to account
for differences between data and MC, such as from the
B
tag
reconstruction and the modeled branching fractions of
B
tag
modes within the MC. This normalization is performed
before applying the full signal selection in order to have a
large background-to-signal ratio; looser
K
ðÞ
mass win-
dows and
E
extra
selection requirements are used such that
the number of background events is approximately 60 times
larger than the final background contribution, over the full
s
B
spectrum. The peaking background component in the
B
B
MC is then normalized to the number of data events
that peak within the
m
ES
signal region. This peaking yield
normalization is performed separately for charged and
neutral
B
tag
candidates, and results in the scaling of all
signal and background MC samples by
1
:
027
0
:
039
ð
1
:
017
0
:
044
Þ
for charged (neutral)
B
tag
candidates.
The signal branching fractions are calculated using
B
i
¼
N
obs
i
ð
N
peak
i
þ
N
comb
i
Þ
"
sig
i
N
B
B
;
(3)
where
N
B
B
¼
471
10
6
is the total number of
B
meson
pairs in the data sample and
N
obs
i
is the number of data
events within the signal region. The total signal efficiency
"
sig
i
includes that of the
B
tag
reconstruction and is deter-
mined separately for each of the signal channels
i
. Since
misreconstructed events from other signal channels con-
tribute to
N
peak
i
, the branching fractions of all signal chan-
nels are determined simultaneously by inverting a
6
6
efficiency matrix
"
ij
, which describes the probability that a
signal event of process
i
is reconstructed in signal channel
j
. Branching fraction limits and uncertainties are computed
using a mixed frequentist-Bayesian approach described in
Ref. [
32
], with the systematic uncertainties on
N
bkg
i
and
"
sig
i
modeled using Gaussian distributions. To combine the
results of signal decay channels, we find the
B
i
value that
maximizes a likelihood function defined as the product of
the Poisson probabilities of observing
N
obs
i
events.
V. SYSTEMATIC STUDIES
To verify the modeling of
"
sig
i
and
N
bkg
i
, a control sample
of
B
!
D‘
events is selected. In place of a signal
K
candidate, the events are required to contain a recon-
structed
D
0
!
K
þ
,
D
!
K
þ
,or
D
!
K
0
S
candidate with an invariant mass within
35 MeV
=c
2
of
the nominal
D
-meson mass values [
30
]. The event must
have one additional track that satisfies the PID criteria of
either an electron or muon. All other reconstruction and
signal selection requirements are retained. The resulting
yields in the data agree with MC expectations, assuming
the well-measured branching fractions of
B
!
D‘
[
30
],
within the 7% (12%) statistical uncertainty of the data in
the
0
<s
B
<
0
:
3
(
J=
c
or
c
ð
2
S
Þ
mass) region.
The control sample is used to determine the systematic
uncertainties due to the MC modeling of the
E
extra
variable
within data. Additional uncertainties on
N
peak
i
and
"
sig
i
are
due to the
K
0
S
and
K
mass reconstruction windows, the
0
reconstruction, and the uncertainties in the branching frac-
tions [
30
] of the dominant backgrounds contributing to
N
peak
i
. The uncertainty on
N
comb
i
is dominated by the side-
band data statistics. Other systematic uncertainties, such as
those from PID, tracking,
B
tag
reconstruction,
N
B
B
, and the
assumption that charged and neutral
B
B
pairs are produced
at equal rates, are all accounted for by the normalization of
the MC peaking yields. Because the peaking yield in data
depends on the extrapolated shape of the combinatorial
B
tag
background, the normalization scale factors are
TABLE II. Summary of systematic uncertainties that are
shared by the
B
!
K
ðÞ
,
J=
c
!
, and
c
ð
2
S
Þ!
searches. All values are relative uncertainties in %. The channels
in brackets refer to the
K
decay products.
Source
K
þ
½
K
þ
0
½
K
0
S
þ
K
0
½
K
þ
½
K
0
S
0
"
sig
i
normalization 3.5 3.5
3.5 8.9 8.9
8.9
N
bkg
i
normalization
2.3 2.3
2.3 6.0 6.0
6.0
K
0
S
reconstruction
1.4 1.4
1.4
K
reconstruction
2.8
2.8
2.8
2.8
0
reconstruction
3.0
3.0
E
extra
4.5 6.0
6.5 6.0 6.0
6.5
TABLE III. Summary of systematic uncertainties that differ
between the
B
!
K
ðÞ
,
J=
c
!
, and
c
ð
2
S
Þ!
searches, and the total systematic uncertainties for each signal
channel. All values are relative uncertainties in %. The total
systematic uncertainties are determined by adding in quadrature
each relevant uncertainty, including those listed in Table
II
.
Source
K
þ
½
K
þ
0
½
K
0
S
þ
K
0
½
K
þ
½
K
0
S
0
B
!
K
ðÞ
N
peak
i
B
’s
2.8 2.8
2.8
2.8
2.8
2.8
s
B
resolution
3.6 3.6
3.6
3.6
3.6
3.6
Total
N
peak
i
syst. 6.8 8.9
8.8
9.7
10.0
10.9
Total
N
comb
i
syst. 2.3 2.3
2.3
6.0
6.0
6.0
Total
"
sig
i
syst. 6.7 8.8
8.8 11.4 11.7
12.4
J=
c
!
N
peak
i
B
’s
3.5 3.5
3.5
3.5
3.5
3.5
m
resolution 1.1 2.1
0.4
0.7
0.3
1.3
Total
N
peak
i
syst. 6.2 8.6
8.4
9.3
9.6
10.5
Total
N
comb
i
syst. 2.3 2.3
2.3
6.0
6.0
6.0
Total
"
sig
i
syst. 5.8 8.3
8.0 10.8 11.1
11.9
c
ð
2
S
Þ!
N
peak
i
B
’s
2.8 2.8
2.8
2.8
2.8
2.8
m
resolution 0.8 2.4
1.0
0.9
1.8
3.1
Total
N
peak
i
syst. 5.8 8.5
8.1
9.1
9.5
10.7
Total
N
comb
i
syst. 2.3 2.3
2.3
6.0
6.0
6.0
Total
"
sig
i
syst. 5.8 8.4
8.1 10.9
11.2 12.2
J. P. LEES
et al.
PHYSICAL REVIEW D
87,
112005 (2013)
112005-8
re-evaluated by varying the method used to extrapolate this
shape. The resulting variations on the final
N
bkg
i
and
"
sig
i
values are taken as the systematic uncertainties due to the
normalization.
Due to the approximately 1.0% resolution on the
s
B
measurement around
s
B
¼
0
:
3
, an uncertainty is evaluated
within the
B
!
K
ðÞ
signal region. Similarly, the reso-
lution on
m
contributes to uncertainties within the
J=
c
!
and
c
ð
2
S
Þ!
signal regions. Only the
systematic uncertainties due to the
N
peak
i
branching frac-
tions and to
s
B
or
m
differ between the
B
!
K
ðÞ
,
J=
c
!
, and
c
ð
2
S
Þ!
searches. The systematic
uncertainties are summarized in Tables
II
and
III
; the
former lists the uncertainties shared by the searches, while
the latter lists those that differ.
VI. RESULTS FOR
B
!
K
ðÞ
Figure
5
shows the observed data yields, expected back-
ground contributions, and SM signal distributions over the
full
s
B
spectrum. Tables
IV
and
V
summarize the number
of observed data events within the
s
B
signal region (
0
<
s
B
<
0
:
3
), expected backgrounds,
B
!
K
ðÞ
signal effi-
ciencies, branching fraction central values, and branching
fraction limits at the 90% CL. Combining the signal chan-
nels, we determine upper limits of
B
ð
B
!
K
Þ
<
3
:
2
10
5
and
B
ð
B
!
K
Þ
<
7
:
9
10
5
. Since we see a
small excess over the expected background in the
K
þ
channel, we report a two-sided 90% confidence interval.
However, the probability of observing such an excess
within the signal region, given the uncertainty on the
background, is 8.4% which corresponds to a one-sided
Gaussian significance of about
1
:
4
. Therefore, this excess
is not considered significant.
Using the same procedure as when combining signal
decay channels, the
B
!
K
branching fraction central
values are combined with a previous semileptonic-tag
BABAR
analysis that searched within a statistically inde-
pendent data sample [
15
]. We obtain combined
BABAR
upper limits at the 90% CL of
B
ð
B
þ
!
K
þ
Þ
<
1
:
6
10
5
;
B
ð
B
0
!
K
0
Þ
<
4
:
9
10
5
;
and
B
ð
B
!
K
Þ
<
1
:
7
10
5
:
(4)
The combined central value is
B
ð
B
!
K
Þ¼
ð
0
:
8
þ
0
:
7
0
:
6
Þ
10
5
, where the uncertainty includes both
Entries/(0.1)
0
5
10
15
ν
ν
+
K
→
+
B
0
5
10
15
ν
ν
0
K
→
0
B
0
5
10
15
ν
ν
+
K*
→
+
B
B
s
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
5
10
15
20
ν
ν
0
K*
→
0
B
FIG. 5 (color online). The
s
B
distribution for (from top to
bottom)
B
þ
!
K
þ
,
B
0
!
K
0
,
B
þ
!
K
þ
, and
B
0
!
K
0
events after applying the full signal selection. The ex-
pected combinatorial (shaded) plus
m
ES
-peaking (solid) back-
ground contributions are overlaid on the data (points). The signal
MC distributions (dashed) are normalized to branching fractions
of
20
10
5
for
B
þ
!
K
þ
and
50
10
5
for the other
channels. Events to the left of the vertical lines are selected to
obtain SM-sensitive limits, while the full spectra are used to
determine partial branching fractions.
TABLE IV. Expected
B
!
K
background yields
N
bkg
i
¼
N
peak
i
þ
N
comb
i
, signal efficiencies
"
sig
i
, number of observed data events
N
obs
i
, resulting branching fraction upper limits at 90% CL, and the combined upper limits and central values, all within the
0
<s
B
<
0
:
3
region. Uncertainties are statistical and systematic, respectively. The channels in brackets refer to the
K
decay products.
B
þ
!½
K
þ
0
B
þ
!½
K
0
S
þ
B
0
!½
K
þ
B
0
!½
K
0
S
0
N
peak
i
1
:
2
0
:
4
0
:
11
:
3
0
:
4
0
:
15
:
0
0
:
8
0
:
50
:
2
0
:
2
0
:
0
N
comb
i
1
:
1
0
:
4
0
:
00
:
8
0
:
3
0
:
02
:
0
0
:
5
0
:
10
:
5
0
:
3
0
:
0
N
bkg
i
2
:
3
0
:
5
0
:
12
:
0
0
:
5
0
:
17
:
0
0
:
9
0
:
50
:
7
0
:
3
0
:
0
"
sig
i
ð
10
5
Þ
4
:
9
0
:
2
0
:
46
:
0
0
:
2
0
:
512
:
2
0
:
3
1
:
41
:
2
0
:
1
0
:
1
N
obs
i
3372
Limit
<
19
:
4
10
5
<
17
:
0
10
5
<
8
:
9
10
5
<
86
10
5
B
ð
B
þ
=
0
!
K
þ
=
0
Þð
3
:
3
þ
6
:
2
þ
1
:
7
3
:
6
1
:
3
Þ
10
5
ð
2
:
0
þ
5
:
2
þ
2
:
0
4
:
3
1
:
7
Þ
10
5
Limit
<
11
:
6
10
5
<
9
:
3
10
5
B
ð
B
!
K
Þð
2
:
7
þ
3
:
8
þ
1
:
2
2
:
9
1
:
0
Þ
10
5
Limit
<
7
:
9
10
5
SEARCH FOR
B
!
K
ðÞ
AND
...
PHYSICAL REVIEW D
87,
112005 (2013)
112005-9