Study of the decay
B
0
!
þ
c
p
þ
and its intermediate states
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
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
D. Kirkby,
10
A. J. Lankford,
10
M. Mandelkern,
10
H. Atmacan,
11
J. W. Gary,
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
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
M. Morii,
26
A. Adametz,
27
U. Uwer,
27
H. M. Lacker,
28
T. Lueck,
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
M. H. Schune,
33
A. Stocchi,
33
G. Wormser,
33
D. J. Lange,
34
D. M. Wright,
34
C. A. Chavez,
35
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
M. Sigamani,
36
G. Cowan,
37
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. Jackson,
40
G. D. Lafferty,
40
E. Behn,
41
R. Cenci,
41
B. Hamilton,
41
A. Jawahery,
41
D. A. Roberts,
41
C. Dallapiccola,
42
R. Cowan,
43
D. Dujmic,
43
G. Sciolla,
43
R. Cheaib,
44
D. Lindemann,
44
P. M. Patel,
44,
§
S. H. Robertson,
44
P. Biassoni,
45a,45b
N. Neri,
45a
F. Palombo,
45a,45b
S. Stracka,
45a,45b
L. Cremaldi,
46
R. Godang,
46,
k
R. Kroeger,
46
P. Sonnek,
46
D. J. Summers,
46
X. Nguyen,
47
M. Simard,
47
P. Taras,
47
G. De Nardo,
48a,48b
D. Monorchio,
48a,48b
G. Onorato,
48a,48b
C. Sciacca,
48a,48b
M. Martinelli,
49
G. Raven,
49
C. P. Jessop,
50
J. M. LoSecco,
50
W. F. Wang,
50
K. Honscheid,
51
R. Kass,
51
J. Brau,
52
R. Frey,
52
N. B. Sinev,
52
D. Strom,
52
E. Torrence,
52
E. Feltresi,
53a,53b
N. Gagliardi,
53a,53b
M. Margoni,
53a,53b
M. Morandin,
53a
M. Posocco,
53a
M. Rotondo,
53a
G. Simi,
53a
F. Simonetto,
53a,53b
R. Stroili,
53a,53b
S. Akar,
54
E. Ben-Haim,
54
M. Bomben,
54
G. R. Bonneaud,
54
H. Briand,
54
G. Calderini,
54
J. Chauveau,
54
O. Hamon,
54
Ph. Leruste,
54
G. Marchiori,
54
J. Ocariz,
54
S. Sitt,
54
M. Biasini,
55a,55b
E. Manoni,
55a,55b
S. Pacetti,
55a,55b
A. Rossi,
55a,55b
C. Angelini,
56a,56b
G. Batignani,
56a,56b
S. Bettarini,
56a,56b
M. Carpinelli,
56a,56b,
{
G. Casarosa,
56a,56b
A. Cervelli,
56a,56b
F. Forti,
56a,56b
M. A. Giorgi,
56a,56b
A. Lusiani,
56a,56c
B. Oberhof,
56a,56b
A. Perez,
56a
G. Rizzo,
56a,56b
J. J. Walsh,
56a
D. Lopes Pegna,
57
J. Olsen,
57
A. J. S. Smith,
57
F. Anulli,
58a
R. Faccini,
58a,58b
F. Ferrarotto,
58a
F. Ferroni,
58a,58b
M. Gaspero,
58a,58b
L. Li Gioi,
58a
M. A. Mazzoni,
58a
G. Piredda,
58a
C. Bu
̈
nger,
59
O. Gru
̈
nberg,
59
T. Hartmann,
59
T. Leddig,
59
H. Schro
̈
der,
59,
§
C. Voß,
59
R. Waldi,
59
T. Adye,
60
E. O. Olaiya,
60
F. F. Wilson,
60
S. Emery,
61
G. Hamel de Monchenault,
61
G. Vasseur,
61
Ch. Ye
`
che,
61
D. Aston,
62
R. Bartoldus,
62
J. F. Benitez,
62
C. Cartaro,
62
M. R. Convery,
62
J. Dorfan,
62
G. P. Dubois-Felsmann,
62
W. Dunwoodie,
62
M. Ebert,
62
R. C. Field,
62
M. Franco Sevilla,
62
B. G. Fulsom,
62
A. M. Gabareen,
62
M. T. Graham,
62
P. Grenier,
62
C. Hast,
62
W. R. Innes,
62
M. H. Kelsey,
62
P. Kim,
62
M. L. Kocian,
62
D. W. G. S. Leith,
62
P. Lewis,
62
B. Lindquist,
62
S. Luitz,
62
V. Luth,
62
H. L. Lynch,
62
D. B. MacFarlane,
62
D. R. Muller,
62
H. Neal,
62
S. Nelson,
62
M. Perl,
62
T. Pulliam,
62
B. N. Ratcliff,
62
A. Roodman,
62
A. A. Salnikov,
62
R. H. Schindler,
62
A. Snyder,
62
D. Su,
62
M. K. Sullivan,
62
J. Va’vra,
62
A. P. Wagner,
62
W. J. Wisniewski,
62
M. Wittgen,
62
D. H. Wright,
62
H. W. Wulsin,
62
C. C. Young,
62
V. Ziegler,
62
W. Park,
63
M. V. Purohit,
63
R. M. White,
63
J. R. Wilson,
63
A. Randle-Conde,
64
S. J. Sekula,
64
M. Bellis,
65
P. R. Burchat,
65
T. S. Miyashita,
65
E. M. T. Puccio,
65
M. S. Alam,
66
J. A. Ernst,
66
R. Gorodeisky,
67
N. Guttman,
67
D. R. Peimer,
67
A. Soffer,
67
S. M. Spanier,
68
J. L. Ritchie,
69
A. M. Ruland,
69
R. F. Schwitters,
69
B. C. Wray,
69
J. M. Izen,
70
X. C. Lou,
70
F. Bianchi,
71a,71b
D. Gamba,
71a,71b
S. Zambito,
71a,71b
L. Lanceri,
72a,72b
L. Vitale,
72a,72b
F. Martinez-Vidal,
73
A. Oyanguren,
73
P. Villanueva-Perez,
73
H. Ahmed,
74
J. Albert,
74
Sw. Banerjee,
74
F. U. Bernlochner,
74
H. H. F. Choi,
74
G. J. King,
74
R. Kowalewski,
74
M. J. Lewczuk,
74
I. M. Nugent,
74
J. M. Roney,
74
R. J. Sobie,
74
N. Tasneem,
74
T. J. Gershon,
75
P. F. Harrison,
75
T. E. Latham,
75
H. R. Band,
76
S. Dasu,
76
Y. Pan,
76
R. Prepost,
76
and S. L. Wu
76
PHYSICAL REVIEW D
87,
092004 (2013)
1550-7998
=
2013
=
87(9)
=
092004(17)
092004-1
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
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
University of Massachusetts, Amherst, Massachusetts 01003, USA
43
Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
44
McGill University, Montre
́
al, Que
́
bec, Canada H3A 2T8
45a
INFN Sezione di Milano, I-20133 Milano, Italy
45b
Dipartimento di Fisica, Universita
`
di Milano, I-20133 Milano, Italy
46
University of Mississippi, University, Mississippi 38677, USA
47
Universite
́
de Montre
́
al, Physique des Particules, Montre
́
al, Que
́
bec, Canada H3C 3J7
48a
INFN Sezione di Napoli, I-80126 Napoli, Italy
48b
Dipartimento di Scienze Fisiche, Universita
`
di Napoli Federico II, I-80126 Napoli, Italy
49
NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands
50
University of Notre Dame, Notre Dame, Indiana 46556, USA
J. P. LEES
et al.
PHYSICAL REVIEW D
87,
092004 (2013)
092004-2
51
Ohio State University, Columbus, Ohio 43210, USA
52
University of Oregon, Eugene, Oregon 97403, USA
53a
INFN Sezione di Padova, I-35131 Padova, Italy
53b
Dipartimento di Fisica, Universita
`
di Padova, I-35131 Padova, Italy
54
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
55a
INFN Sezione di Perugia, I-06100 Perugia, Italy
55b
Dipartimento di Fisica, Universita
`
di Perugia, I-06100 Perugia, Italy
56a
INFN Sezione di Pisa, I-56127 Pisa, Italy
56b
Dipartimento di Fisica, Universita
`
di Pisa, I-56127 Pisa, Italy
56c
Scuola Normale Superiore di Pisa, I-56127 Pisa, Italy
57
Princeton University, Princeton, New Jersey 08544, USA
58a
INFN Sezione di Roma, I-00185 Roma, Italy
58b
Dipartimento di Fisica, Universita
`
di Roma La Sapienza, I-00185 Roma, Italy
59
Universita
̈
t Rostock, D-18051 Rostock, Germany
60
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
61
CEA, Irfu, SPP, Centre de Saclay, F-91191 Gif-sur-Yvette, France
62
SLAC National Accelerator Laboratory, Stanford, California 94309, USA
63
University of South Carolina, Columbia, South Carolina 29208, USA
64
Southern Methodist University, Dallas, Texas 75275, USA
65
Stanford University, Stanford, California 94305-4060, USA
66
State University of New York, Albany, New York 12222, USA
67
Tel Aviv University, School of Physics and Astronomy, Tel Aviv 69978, Israel
68
University of Tennessee, Knoxville, Tennessee 37996, USA
69
University of Texas at Austin, Austin, Texas 78712, USA
70
University of Texas at Dallas, Richardson, Texas 75083, USA
71a
INFN Sezione di Torino, I-10125 Torino, Italy
71b
Dipartimento di Fisica Sperimentale, Universita
`
di Torino, I-10125 Torino, Italy
72a
INFN Sezione di Trieste, I-34127 Trieste, Italy
72b
Dipartimento di Fisica, Universita
`
di Trieste, I-34127 Trieste, Italy
73
IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
74
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
75
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
76
University of Wisconsin, Madison, Wisconsin 53706, USA
(Received 4 February 2013; published 10 May 2013)
We study the decay
B
0
!
þ
c
p
þ
, reconstructing the
þ
c
baryon in the
pK
þ
mode,
using a data sample of
467
10
6
B
B
pairs collected with the
BABAR
detector at the PEP-II
storage rings at SLAC. We measure branching fractions for decays with intermediate
c
baryons to
be
B
½
B
0
!
c
ð
2455
Þ
þþ
p
¼ð
21
:
3
1
:
0
1
:
0
5
:
5
Þ
10
5
,
B
½
B
0
!
c
ð
2520
Þ
þþ
p
¼
ð
11
:
5
1
:
0
0
:
5
3
:
0
Þ
10
5
,
B
½
B
0
!
c
ð
2455
Þ
0
p
þ
¼ð
9
:
1
0
:
7
0
:
4
2
:
4
Þ
10
5
,and
B
½
B
0
!
c
ð
2520
Þ
0
p
þ
¼ð
2
:
2
0
:
7
0
:
1
0
:
6
Þ
10
5
, where the uncertainties are statistical,
systematic, and due to the uncertainty on the
þ
c
!
pK
þ
branching fraction, respectively.
For decays without
c
ð
2455
Þ
or
c
ð
2520
Þ
resonances, we measure
B
½
B
0
!
þ
c
p
þ
non
-
c
¼
ð
79
4
4
20
Þ
10
5
. The total branching fraction is determined to be
B
½
B
0
!
þ
c
p
þ
total
¼
ð
123
5
7
32
Þ
10
5
. We examine multibody mass combinations in the resonant three-particle
c
p
final states and in the four-particle
þ
c
p
þ
final state, and observe different characteristics
for the
p
combination in neutral versus doubly charged
c
decays.
DOI:
10.1103/PhysRevD.87.092004
PACS numbers: 13.25.Hw, 13.60.Rj, 14.20.Lq
*
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, AL 36688, USA.
{
Also with Universita
`
di Sassari, Sassari, Italy.
STUDY OF THE DECAY
...
PHYSICAL REVIEW D
87,
092004 (2013)
092004-3
I. INTRODUCTION
Decays of
B
mesons into final states with baryons
account for
ð
6
:
8
0
:
6
Þ
%
[
1
] of all
B
-meson decays.
Notwithstanding their significant production rate, the
baryon production mechanism in
B
-meson decays is
poorly understood. Theoretical models of
B
-meson bar-
yonic decays are currently limited to rough estimates of the
branching fractions and basic interpretations of the decay
mechanisms [
2
–
6
]. Additional experimental information
may help to clarify the underlying dynamics.
In this paper, we present a measurement of the
B
-meson
baryonic decay
1
B
0
!
þ
c
p
þ
. The
þ
c
baryon is
observed through its decays to the
pK
þ
final state.
The study is performed using a sample of
e
þ
e
annihila-
tion data collected at the mass of the
ð
4
S
Þ
resonance with
the
BABAR
detector at the SLAC National Accelerator
Laboratory. We include a study of the production of this
final state through intermediate
þþ
c
and
0
c
resonances.
The
sPlot
technique [
7
] is used to examine multibody mass
combinations within the
c
p
final states. We account for
background from sources such as
B
!
Dp
p
ð
n
Þ
and
B
!
þ
c
p
, which were not considered in previous
studies [
8
,
9
]. In addition, we extract the four-body
nonresonant branching fraction and examine two- and
three-body mass combinations within the four-body
þ
c
p
þ
final state. The
B
0
!
þ
c
p
þ
decay has
previously been studied by the CLEO [
8
] and Belle [
9
]
Collaborations using data samples of
9
:
17 fb
1
and
357 fb
1
, respectively. The present work represents the
first study of this decay mode from
BABAR
.
Section
II
provides a brief description of the
BABAR
detector and data sample. The basic event selection proce-
dure is described in Sec.
III
. Section
IV
presents the
method used to extract results for channels that proceed
via intermediate
c
baryons. The corresponding results for
channels that do not proceed via
c
baryons are presented
in Sec.
V
. Section
VI
presents the method used to deter-
mine signal reconstruction efficiencies, Sec.
VII
the
branching fraction results, Sec.
VIII
the evaluation of
systematic uncertainties, and Sec.
IX
the final results. A
summary is given in Sec.
X
.
II.
BABAR
DETECTOR AND DATA SAMPLE
The data sample used in this analysis was collected with
the
BABAR
detector at the PEP-II asymmetric-energy
e
þ
e
storage ring at SLAC. PEP-II operates with a
9 GeV
e
and a
3
:
1 GeV
e
þ
beam resulting in a center-
of-mass energy equal to the
ð
4
S
Þ
mass of
10
:
58 GeV
=c
2
.
The collected data sample contains
467
10
6
B
B
pairs,
which corresponds to an integrated luminosity of
426 fb
1
.
The
BABAR
detector [
10
] measures charged-particle
tracks with a five-layer double-sided silicon vertex tracker
(SVT) surrounded by a 40-layer drift chamber (DCH).
Charged particles are identified using specific ionization
energy measurements in the SVT and DCH, as well as
Cherenkov radiation measurements in an internally reflect-
ing ring imaging Cherenkov detector (DIRC). These de-
tectors are located within the 1.5 T magnetic field of a
superconducting solenoid.
Using information from the SVT, the DCH, and the DIRC
for a particular track, the probability for a given particle
hypothesis is calculated from likelihood ratios. The identi-
fication efficiency for a proton is larger than 90%, with the
probability of misidentifying a kaon or pion as a proton
between 3% and 15% depending on the momentum. For a
kaon, the identification efficiency is 90%, with the proba-
bility of misidentifying a pion or proton as a kaon between
5% and 10%. The identification efficiency for a pion is
larger than 95%, with the probability of misidentifying a
kaon or proton as a pion between 5% and 30%.
Monte Carlo (MC) simulated events are produced with
an
e
þ
e
!
B
B
event simulation based on the EvtGen
program [
11
] and an
e
þ
e
!
u
u
,
d
d
,
s
s
,
c
c
event simu-
lation based on the
JETSET
program [
12
]. Generated events
are processed in a
GEANT4
[
13
] simulation of the
BABAR
detector. MC-generated events are studied for generic
background contributions as well as for specific signal
and background modes. Baryonic
B
-meson decays are
generated assuming that their daughters are distributed
uniformly in phase space.
III. EVENT SELECTION
The signal mode is reconstructed in the decay chain
B
0
!
þ
c
p
þ
with
þ
c
!
pK
þ
. All final-state par-
ticles are required to have well-
defined tracks in the SVTand
DCH. Kaons and protons, as well as pions from the
þ
c
decay,
are required to pass likelihood s
electors based on information
from the SVT, DCH, and DIRC. For pion candidates from the
B
0
decay, a well-reconstructed track is required.
To form a
þ
c
candidate, the
p
,
K
, and
þ
candidates
are fitted to a common vertex and a
2
probability greater
than 0.1% is required for the vertex fit. To form a
B
0
candidate, the
þ
c
candidate is constrained to its nominal
mass value and combined with an antiproton and two pions
with opposite charge. The mass constraint value differs
between events from data and MC. For the MC events a
nominal
þ
c
mass of
m
MC
þ
c
¼
2284
:
9 MeV
=c
2
is chosen;
this corresponds to the mass value used in the MC genera-
tion and to the value from fits to reconstructed MC events.
For data,
2
fits are performed on the
m
ð
pK
þ
Þ
invariant
mass distribution to find the nominal
þ
c
mass. The fits are
performed for each of the six distinct
BABAR
run periods.
The results are found to vary between
m
data
þ
c
¼ð
2285
:
55
0
:
18
Þ
MeV
=c
2
and
m
data
þ
c
¼ð
2285
:
62
0
:
22
Þ
MeV
=c
2
,
1
The use of charge conjugate decays is implied throughout this
paper.
J. P. LEES
et al.
PHYSICAL REVIEW D
87,
092004 (2013)
092004-4
where the uncertainties are statistical. All invariant mass
values are found to be consistent. The average result
m
data
þ
c
¼
2285
:
6 MeV
=c
2
is used as the nominal value for
the mass constraint in data.
Only candidates within a
25 MeV
=c
2
mass window
centered on the nominal
þ
c
mass
m
data
þ
c
(or
m
MC
þ
c
for
simulated events) are retained. The entire decay chain is
refitted, requiring that the direct
B
0
daughters originate
from a common vertex and that the
2
probability for the
B
0
vertex fit exceeds 0.1%.
The decays
B
!
Dp
p
ð
n
Þ
with
n
¼
1
, 2, which are
described in more detail in Sec.
IVA
, can contribute a
signal-like background through rearrangement of the
final-state particles and are denoted ‘‘peaking background’’
in the following. To suppress these events, symmetric ve-
toes of
20 MeV
=c
2
around the nominal
D
0
and
D
þ
mass
values [
1
] are applied in the distributions of the invariant
masses
m
ð½
K
þ
þ
c
½
þ
B
0
Þ
,
m
ð½
K
þ
þ
c
½
þ
B
0
Þ
,
and
m
ð½
K
þ
þ
c
Þ
, where subscripts denote the mother
candidate of the particles.
To separate
B
0
signal events from combinatorial
background, two variables are used. The
B
0
invariant
mass is defined as
m
inv
¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
E
2
B
0
p
2
B
0
q
, with the four-
momentum vector of the
B
0
candidate
ð
E
B
0
;
p
B
0
Þ
measured in the laboratory frame. The energy-
substituted mass is defined in the laboratory frame
as
m
ES
¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ð
s=
2
þ
p
i
p
B
0
Þ
2
=E
2
i
p
2
B
0
q
, with
ffiffiffi
s
p
the
center-of-mass energy and
ð
E
i
;
p
i
Þ
the four-momentum
vector of the initial
e
þ
e
system measured in the labo-
ratory frame. For both variables, genuine
B
0
decays are
centered at the
B
0
-meson mass. In MC, these variables
exhibit a negligible correlation for genuine
B
0
mesons.
To suppress combinatorial background,
B
0
candidates
are required to satisfy
m
ES
2½
5
:
272
;
5
:
285
GeV
=c
2
.
Figure
1
shows the
m
inv
distribution after applying all of the
above selection criteria. Th
e dashed lines show sideband
regions
m
inv
2½
5
:
170
;
5
:
230
and
m
inv
2½
5
:
322
;
5
:
382
,
used to study background characteristics; both sideband re-
gions are combined into a single sideband region.
The analysis is separated into two parts: (i) the measure-
ment of the four signal decays via intermediate
c
ð
2455
;
2520
Þ
resonances, i.e.,
B
0
!
c
ð
2455
Þ
þþ
p
,
B
0
!
c
ð
2520
Þ
þþ
p
,
B
0
!
c
ð
2455
Þ
0
p
þ
, and
B
0
!
c
ð
2520
Þ
0
p
þ
, and (ii) the measurement of all other
decays into the four-body final state
þ
c
p
þ
, which
are denoted as
non-
c
signal events
in the following.
IV.
B
0
!
þþ
0
c
p
ANALYSIS
Decays via resonant intermediate states with
c
resonances are studied in the two-dimensional planes
spanned by
m
inv
and the invariant
c
candidate invariant
mass
m
ð
þ
c
þ
Þ
for decays with
c
ð
2455
;
2520
Þ
þþ
and
m
ð
þ
c
Þ
for decays with
c
ð
2455
;
2520
Þ
0
. In the follow-
ing the like-sign
c
invariant mass is denoted as
m
þþ
and the opposite-sign invariant mass as
m
þ
. If both
invariant masses are referred to, we use the notation
m
þ
. For intermediate
c
ð
2455
;
2520
Þ
þþ
;
0
states,
B
½
c
!
þ
c
100%
is assumed [
1
].
We perform fits in both planes
m
inv
:
m
þþ
and
m
inv
:
m
þ
to extract the signal yields for the decays via the
c
resonances. Background contributions are vetoed when
feasible. We distinguish between different signal and re-
maining background contributions by using separate
probability density functions (PDFs) for each signal and
background component. We use analytical PDFs as well as
discrete histogram PDFs. The PDFs are validated using
data from the sideband regions and from MC samples. The
different, combined PDFs are fitted to the
m
inv
:
m
þþ
and
m
inv
:
m
þ
planes and the resulting covariance matrices of
the fits are used to calculate
sPlot
[
7
] distributions of signal
events.
Figures
2(a)
and
2(b)
show the
m
þþ
and
m
þ
distribu-
tions, respectively, after applying the selection criteria as
described in Sec.
III
. Signal contributions from the
c
ð
2455
Þ
þþ
,
c
ð
2520
Þ
þþ
, and
c
ð
2455
Þ
0
resonances
are observed and a contribution from events with a
c
ð
2800
Þ
þþ
resonance is visible. The doubly charged
þþ
c
resonances are seen to contribute larger numbers of
events than the neutral
0
c
resonances. The resonant struc-
tures sit on top of combinatorial background and peaking
background events as well as non-
c
signal events. The
latter are distributed in
m
ð
þ
c
Þ
like combinatorial back-
ground events.
A. Background sources
The main source for combinatorial background events is
other
B
decays, while 20% originate from
e
þ
e
!
c
c
events. Combinatorial events do not exhibit peaking struc-
tures in the distributions of the signal variables under study.
2
GeV/c
inv
m
5.1
5.15
5.2
5.25
5.3
5.35
5.4
5.45
5.5
2
2 MeV/c
1
inv
d
m
dn
0
100
200
300
400
500
600
700
800
FIG. 1 (color online). Distribution of the invariant mass
m
inv
ð
þ
c
p
þ
Þ
for events with
m
ES
in the region
½
5
:
272
;
5
:
285
GeV
=c
2
. The red dotted lines indicate the signal
region and the blue dashed lines the sideband regions. Higher
multiplicity modes, such as
B
!
þ
c
p
þ
, appear for
m
inv
<
5
:
14 GeV
=c
2
.
STUDY OF THE DECAY
...
PHYSICAL REVIEW D
87,
092004 (2013)
092004-5
In contrast, other sources of background do exhibit peaking
structures, and are treated separately.
1.
B
!
Dp
p
ð
n
Þ
Decays of the type
B
!
Dp
p
ð
n
Þ
with
D
!
K
ð
m
Þ
,
where
n
þ
m
¼
3
, can have the same final-state particles
as signal decays. Rearrangement of the final-state particles
can yield a fake
þ
c
candidate, while the
B
0
candidate is
essentially a genuine
B
0
suppressed only by the
þ
c
selec-
tion. Because these events represent fully reconstructed
genuine
B
-meson decays, they are distributed like signal
events in the
m
inv
and
m
ES
variables. Table
I
shows the
relevant decay modes and their misreconstruction rate as
signal. Furthermore, these events can also be misrecon-
structed as higher
c
resonances in the
þ
c
invariant
masses. Figure
3
shows the distributions of the MC-
simulated background modes in the
m
inv
:
m
þþ
and
m
inv
:
m
þ
planes. Additionally,
B
0
!
D
þ
p
p
events
with
D
þ
!
K
þ
þ
have a minimum invariant mass in
m
þþ
of
m
ð
D
þ
p
Þ
2
:
808 GeV
=c
2
and can introduce
background in the study of events with intermediate
c
ð
2800
Þ
þþ
resonances.
From the misreconstruction efficiency determined from
signal MC events and scaled with the measured branching
fractions [
14
],
167
20
background events are expected
to contribute as signal. To suppress these events, veto
regions are set to
20 MeV
=c
2
around the nominal
D
0
and
D
þ
masses [
1
]in
m
ð
K
þ
Þ
,
m
ð
K
þ
þ
Þ
, and
m
ð
K
þ
þ
Þ
, with the resulting suppression rates given
in Table
I
. A systematic uncertainty is assigned to account
for the remaining background events. No distortions are
found in other variables due to the vetoes. Note that
B
0
!
D
0
p
p
þ
events with
D
0
!
K
þ
rearranged to
B
0
!
½
þ
p
½
p
B
0
½
K
þ
D
0
fake
þ
c
do not contribute peaking
background because the selection requirement on
m
ð
pK
þ
Þ
þ
c
effectively vetoes these events.
2.
B
0
!ð
c
c
Þ
K
0
þ
Decays via charmonia, such as
B
0
!ð
c
c
Þ
K
0
þ
with
ð
c
c
Þ!
p
p
and
K
0
!
K
þ
,or
B
0
!ð
c
c
Þ
K
0
with
ð
c
c
Þ!
p
p
þ
, can also produce the same final-
state particles as signal events. We observe no indication of
such contributions in data in the relevant combinations of
B
0
daughters or in signal MC events when scaling the
TABLE I. Efficiencies for reconstructing
B
0
!
Dp
p
ð
n
Þ
events as signal decays by rearranging the final-state particles in
signal-like combinations. In the fake signal reconstruction, the subscript particles denote the actual mother. The quantity
n
expected
gives the number of fake signal events without the
D
-meson veto (see text),
"
Cut
gives the efficiencies of the vetoes, and
n
remaining
gives
the expected number of remaining fake events in the signal regions after applying the vetoes. The
B
0
!
Dp
p
ð
n
Þ
branching fractions
are taken from Ref. [
14
] and the
D
0
=D
þ
branching fractions from Ref. [
1
].
Decay mode
Fake signal
"
B
0
!
þ
c
p
þ
n
expected
"
Cut
n
remaining
B
0
!
D
0
p
p
D
0
!
K
þ
þ
B
0
fake
!½
p
½
p
B
0
½
K
þ
fake
þ
c
þ
D
0
ð
6
:
79
0
:
19
Þ
10
3
26.0
99.3%
0.3
B
0
!
D
þ
p
p
D
þ
!
K
þ
þ
B
0
fake
!½
p
½
p
B
0
½
K
þ
fake
þ
c
þ
D
þ
ð
7
:
28
0
:
17
Þ
10
3
103.0
98.8%
1.0
B
0
!
D
0
p
p
þ
D
0
!
K
þ
B
0
fake
!½
p
½
p
þ
B
0
½
K
fake
þ
c
þ
D
0
ð
4
:
19
0
:
15
Þ
10
3
22.5
96.9%
0.2
B
0
!
D
þ
p
p
þ
D
þ
!
D
0
þ
D
0
!
K
þ
B
0
fake
!
þ
p
½
p
½½
K
þ
D
0
fake
þ
c
þ
D
þ
ð
2
:
44
0
:
12
Þ
10
3
13.4
96.9%
0.1
2
GeV/c
)
+
π
+
c
Λ
m
(
2.6 2.8
3
3.2 3.4 3.6 3.8
4
4.2
2
10 MeV/c
1
)
+
π
+
c
Λ
dm(
dn
0
100
200
300
400
500
600
(a)
2.44 2.46 2.48 2.5 2.52 2.54 2.56 2.58 2.6
2
2 MeV/c
1
0
20
40
60
80
100
120
140
160
180
200
220
(a)
2
GeV/c
)
-
π
+
c
Λ
m
(
2.6 2.8
3
3.2 3.4 3.6 3.8
4
4.2
2
10 MeV/c
1
)
-
π
+
c
Λ
dm(
dn
0
100
200
300
400
500
600
(b)
2.442.46 2.48 2.5 2.52 2.542.56 2.58 2.6
2
2 MeV/c
1
0
20
40
60
80
100
120
140
(b)
FIG. 2 (color online). Event distributions in
m
ð
þ
c
þ
Þ
(a) and
m
ð
þ
c
Þ
(b) for events in the signal region of Fig.
1
. The inserts
show the low invariant mass regions.
J. P. LEES
et al.
PHYSICAL REVIEW D
87,
092004 (2013)
092004-6
misreconstruction efficiencies with the measured branch-
ing fractions [
1
]. We neglect these events, but assign a
corresponding systematic uncertainty (see Sec.
VIII
).
3.
B
!
þ
c
p
Events from
B
!
þ
c
p
decays with
c
ð
2455
Þ
þ
!
þ
c
0
or
c
ð
2520
Þ
þ
!
þ
c
0
are found to have a signal-
like shape in
m
inv
and
m
þþ
. Because of the low-momentum
0
daughters in the
c
ð
2455
;
2520
Þ
þ
center-of-mass sys-
tems, fake
c
ð
2455
;
2520
Þ
þþ
can be generated by replac-
ing the
0
with a
þ
from the
B
þ
. Figure
4
shows the
distributions of MC-generated events. These events cluster
in the
m
inv
signal region as well as in
m
þþ
in the
c
ð
2455
Þ
þþ
and
c
ð
2520
Þ
þþ
signal regions. A correlation
between
m
inv
and
m
þþ
is apparent. No significant struc-
tures are found in MC-generated events with nonresonant
B
!
þ
c
p
0
or with
B
!
c
ð
2800
Þ
þ
p
events
due to the softer momentum constraints on the
0
.
4. Combinatorial background with genuine
c
events
In both MC and data-sideband events, combinato-
rial background events with genuine
c
ð
2455
;
2520
Þ
þþ
;
0
inv
m
5.1
5.15
5.2
5.25
5.3
5.35
5.4
5.45
5.5
2.6
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
+
π
-
π
+
π
-
K
→
0
;
D
p
p
0
D
→
0
B
inv
m
5.1
5.15
5.2
5.25
5.3
5.35
5.4
5.45
5.5
2.6
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
+
π
-
π
+
π
-
K
→
0
;
D
p
p
0
D
→
0
B
inv
m
5.1
5.15
5.2
5.25
5.3
5.35
5.4
5.45
5.5
2.6
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
+
π
+
π
-
K
→
+
;
D
-
π
p
p
+
D
→
0
B
inv
m
5.1
5.15
5.2
5.25
5.3
5.35
5.4
5.45
5.5
2.6
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
+
π
+
π
-
K
→
+
;
D
-
π
p
p
+
D
→
0
B
inv
m
5.1
5.15
5.2
5.25
5.3
5.35
5.4
5.45
5.5
)
+
π
+
c
Λ
m
()
+
π
+
c
Λ
m
()
+
π
+
c
Λ
m
(
)
+
π
+
c
Λ
m
()
+
π
+
c
Λ
m
()
+
π
+
c
Λ
m
(
2.6
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
+
π
-
K
→
0
;
D
-
π
+
π
p
p
0
D
→
0
B
inv
m
5.1
5.15
5.2
5.25
5.3
5.35
5.4
5.45
5.5
2.6
2.8
3
3.2
3.4
3.6
3.8
4
4.2
4.4
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
+
-
K
→
0
;
D
-
+
p
p
0
D
→
0
B
πππ
FIG. 3 (color online). Simulated events with
B
0
!
Dp
p
ð
n
Þ
decays misidentified as signal decays in the
m
inv
:
m
þþ
plane
(left column) and
m
inv
:
m
þ
plane (right column). The MC-generated events are reconstructed as
B
0
!
þ
c
p
þ
. The color scale
indicates the relative contents of a bin compared to the maximally occupied bin.
)
+
π
+
c
Λ
m
(
)
+
π
+
c
Λ
m
(
inv
m
5.1 5.15 5.2 5.25 5.3 5.35 5.4 5.45 5.5
2.6
2.8
3
3.2
3.4
3.6
3.8
4
4.2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
π
+
c
Λ
→
(2455)
+
c
Σ
;
-
π
p
(2455)
+
c
Σ
→
-
B
inv
m
5.1 5.15 5.2 5.25 5.3 5.35 5.4 5.45 5.5
2.6
2.8
3
3.2
3.4
3.6
3.8
4
4.2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
π
+
c
Λ
→
(2520)
+
c
Σ
;
-
π
p
(2520)
+
c
Σ
→
-
B
FIG. 4 (color online). Simulated events with
B
!
c
ð
2455
Þ
þ
p
(left) and
B
!
c
ð
2520
Þ
þ
p
(right) decays, where
þ
c
!
þ
c
0
decays are reconstructed as
þþ
c
!
þ
c
þ
; these events accumulate in the signal regions of
m
inv
and in
m
þþ
. The
MC-generated events are reconstructed as
B
0
!
þ
c
p
þ
. The color scale indicates the relative contents of a bin compared to the
maximally occupied bin.
STUDY OF THE DECAY
...
PHYSICAL REVIEW D
87,
092004 (2013)
092004-7