Measurement of the
B
0
!
J=
Branching Fraction
B. Aubert,
1
D. Boutigny,
1
J.-M. Gaillard,
1
A. Hicheur,
1
Y. Karyotakis,
1
J. P. Lees,
1
P. Robbe,
1
V. Tisserand,
1
A. Zghiche,
1
A. Palano,
2
A. Pompili,
2
J. C. Chen,
3
N. D. Qi ,
3
G. Rong,
3
P. Wang,
3
Y. S. Zhu,
3
G. Eigen,
4
I. Ofte,
4
B. Stugu,
4
G. S. Abrams,
5
A. W. Borgland,
5
A. B. Breon,
5
D. N. Brow n ,
5
J. Button-Shafer,
5
R. N. Cahn,
5
E. Charles,
5
M. S. Gill,
5
A.V. Gritsan,
5
Y. Groysman,
5
R. G. Jacobsen,
5
R.W. Kadel,
5
J. Kadyk,
5
L. T. Ker t h ,
5
Yu. G. Kolomensky,
5
J. F. K ra l ,
5
C. LeClerc,
5
M. E. L ev i ,
5
G. Lynch,
5
L. M. Mi r,
5
P. J. Oddone,
5
T. J. Orimoto,
5
M. Pripstein,
5
N. A. Ro e ,
5
A. Romosan,
5
M. T. Ronan,
5
V. G. Shelkov,
5
A. V. Tel nov,
5
W. A . We n z e l ,
5
T. J. Harrison,
6
C. M. Hawkes,
6
D. J. Knowles,
6
S.W. O’Neale,
6
R. C. Penny,
6
A. T. Watson,
6
N. K. Wat son ,
6
T. Deppermann,
7
K. Goetzen,
7
H. Koch,
7
B. Lewandowski,
7
K. Peters,
7
H. Schmuecker,
7
M. Steinke,
7
N. R. Barlow,
8
W. Bhimji,
8
J. T. Boyd,
8
N. Chevalier,
8
P. J. Clark,
8
W. N. Cottingham,
8
C. Mackay,
8
F. F. Wilson,
8
K. Abe,
9
C. Hearty,
9
T. S. Mattison,
9
J. A. McKenna,
9
D. Thiessen,
9
S. Jolly,
10
A. K. McKemey,
10
V. E . B l i n o v ,
11
A. D. Bu k i n ,
11
A. R. Buzykaev,
11
V. B. Golubev,
11
V. N. Ivanchenko,
11
A. A. Korol,
11
E. A. Kravchenko,
11
A. P. Onuchin,
11
S. I. Serednyakov,
11
Yu. I. Skovpen,
11
A. N. Yushkov,
11
D. Best,
12
M. Chao,
12
D. Kirkby,
12
A. J. Lankford,
12
M. Mandelkern,
12
S. McMahon,
12
D. P. Stoker,
12
K. Arisaka,
13
C. Buchanan,
13
S. Chun,
13
D. B. MacFarlane,
14
S. Prell,
14
Sh. Rahatlou,
14
G. Raven ,
14
V. Sharma,
14
J.W. Berryhill,
15
C. Campagnari,
15
B. Dahmes,
15
P. A. Hart,
15
N. Kuznetsova,
15
S. L. L ev y,
15
O. Long,
15
A. Lu,
15
M. A. Ma z u r,
15
J. D. Richman,
15
W. Verkerke,
15
J. Beringer,
16
A. M. Eisner,
16
M. Grothe,
16
C. A. Heusch,
16
W. S. Lockman,
16
T. P u l l i a m ,
16
T. Schalk,
16
R. E. Schmitz,
16
B. A. Schumm,
16
A. Seiden,
16
M. Tu r r i ,
16
W. Wa l k o w i a k ,
16
D. C. Williams,
16
M. G. Wilson,
16
E. Chen,
17
G. P. Dubois-Felsmann,
17
A. Dvoretskii,
17
D. G. H it l i n ,
17
F. C. Porter,
17
A. Ryd,
17
A. Samuel,
17
S. Yang,
17
S. Jayatilleke,
18
G. Mancinelli,
18
B. T. Meadows,
18
M. D. Sokoloff,
18
T. B a r i l l a r i ,
19
P. B l o o m ,
19
W. T. Ford,
19
U. Nauenberg,
19
A. Olivas,
19
P. Rankin,
19
J. Roy,
19
J. G. Smith,
19
W. C . v a n H o e k ,
19
L. Zhang,
19
J. Blouw,
20
J. L. Harton,
20
M. Krishnamurthy,
20
A. Soffer,
20
W. H . To k i ,
20
R. J. Wilson,
20
J. Zhang,
20
D. Altenburg,
21
T. Brandt,
21
J. Brose,
21
T. Colberg,
21
M. Dickopp,
21
R. S. Dubitzky,
21
A. Hauke,
21
E. Maly,
21
R. Mu
̈
ller-Pfefferkorn,
21
S. O t t o ,
21
K. R. Schubert,
21
R. Schwierz,
21
B. Spaan,
21
L. Wilden,
21
D. Bernard,
22
G. R. Bonneaud,
22
F. Brochard,
22
J. Cohen-Tanugi,
22
S. Ferrag,
22
S. T’Jampens,
22
Ch. Thiebaux,
22
G. Vasileiadis,
22
M. Verderi,
22
A. Anjomshoaa,
23
R. Bernet,
23
A. K ha n ,
23
D. L av i n ,
23
F. Muheim,
23
S. Playfer,
23
J. E. Swain,
23
J. Tinslay,
23
M. Falbo,
24
C. Borean,
25
C. Bozzi,
25
L. Piemontese,
25
A. Sa r t i ,
25
E. Treadwell,
26
F. Anulli,
27,
*
R. Baldini-Ferroli,
27
A. Calcaterra,
27
R. de Sangro,
27
D. Falciai,
27
G. Finocchiaro,
27
P. Patteri,
27
I. M. Peruzzi,
27,
*
M. Piccolo,
27
A. Z a l lo ,
27
S. Bagnasco,
28
A. Buzzo,
28
R. Contri,
28
G. Crosetti,
28
M. Lo Vetere,
28
M. Macri,
28
M. R. Monge,
28
S. Passaggio,
28
F. C. Pastore,
28
C. Patrignani,
28
E. Robutti,
28
A. Santroni,
28
S. Tosi,
28
M. Morii,
29
R. Bartoldus,
30
G. J. Grenier,
30
U. Mallik,
30
J. Cochran,
31
H. B. Crawley,
31
J. L a m sa ,
31
W. T. Meyer,
31
E. I. Rosenberg,
31
J. Yi ,
31
M. Davier,
32
G. Grosdidier,
32
A. Ho
̈
cker,
32
H. M. Lacker,
32
S. Laplace,
32
F. Le Diberder,
32
V. Lepeltier,
32
A. M. Lutz,
32
T. C. Petersen,
32
S. Plaszczynski,
32
M. H. Schune,
32
L. Tantot,
32
S. Trincaz-Duvoid,
32
G. Wormser,
32
R. M. Bionta,
33
V. Brigljevic
́
,
33
D. J. Lange,
33
M. Mugge,
33
K. van Bibber,
33
D. M. Wright,
33
A. J. Beva n ,
34
J. R. F r y,
34
E. Gabathuler,
34
R. Gamet,
34
M. George,
34
M. Kay,
34
D. J. Payne,
34
R. J. Sloane,
34
C. Touramanis,
34
M. L. Aspinwall,
35
D. A. Bowerman,
35
P. D. Dauncey,
35
U. Egede,
35
I. Eschrich,
35
G. W. Morton,
35
J. A. Nash,
35
P. Sanders,
35
D. Smith,
35
G. P. Taylor,
35
J. J. Back,
36
G. Bellodi,
36
P. Dixon,
36
P. F. Harrison,
36
R. J. L. Potter,
36
H.W. Shorthouse,
36
P. Strother,
36
P. B. Vidal,
36
G. Cowan,
37
H. U. Flaecher,
37
S. George,
37
M. G. Green,
37
A. Kur up ,
37
C. E. Marker,
37
T. R. McMahon,
37
S. Riccia rdi,
37
F. Salvatore,
37
G. Vaitsas,
37
M. A. Winter,
37
D. Brown,
38
C. L. Davis,
38
J. Allison,
39
R. J. Barlow,
39
A. C. Forti,
39
F. Jackson,
39
G. D. Lafferty,
39
N. Savvas,
39
J. H. Weatherall,
39
J. C. Williams,
39
A. Farbin,
40
A. Jawahery,
40
V. L i l l a r d ,
40
D. A. Roberts,
40
J. R. Schieck,
40
G. Blaylock,
41
C. Dallapiccola,
41
K. T. Flood,
41
S. S. Hertzbach,
41
R. Kofler,
41
V. B. Koptchev,
41
T. B. Moore,
41
H. Staengle,
41
S. Wi l lo cq ,
41
B. Brau,
42
R. Cowan,
42
G. Sciolla,
42
F. Taylor,
42
R. K. Yamamoto,
42
M. Milek,
43
P. M. Patel,
43
F. Palombo,
44
J. M. Bauer,
45
L. Cremaldi,
45
V. Eschenburg,
45
R. Kroeger,
45
J. Reidy,
45
D. A. Sanders,
45
D. J. Summers,
45
C. Hast,
46
P. Taras,
46
H. Nicholson,
47
C. Ca r t a ro ,
48
N. Cava l lo ,
48
G. De Nardo,
48
F. Fabozzi,
48
C. Gatto,
48
L. Lista,
48
P. Paolucci,
48
D. Piccolo,
48
C. Sciacca,
48
J. M. LoSecco,
49
J. R. G. Alsmiller,
50
T. A. Gabriel,
50
J. Brau,
51
R. F rey,
51
M. Iwasaki,
51
C. T. Potter,
51
N. B. Sinev,
51
D. Strom,
51
E. Torrence,
51
F. Colecchia,
52
A. Dorigo,
52
F. Galeazzi,
52
M. Margoni,
52
M. Morandin,
52
M. Posocco,
52
M. Rotondo,
52
F. Simonetto,
52
R. Stroili,
52
C. Voci,
52
M. Benayoun,
53
H. Briand,
53
J. Chauveau,
53
P. D a v i d ,
53
Ch. de la Vaissie
`
re,
53
L. Del Buono,
53
O. Hamon,
53
Ph. Leruste,
53
J. Ocariz,
53
M. Pivk,
53
L. Roos,
53
J. St a rk ,
53
P. F. Manfredi,
54
V. Re,
54
V. Speziali,
54
L. Gladney,
55
Q. H. G uo ,
55
J. Panetta,
55
C. Angelini,
56
G. Batignani,
56
S. Bettarini,
56
M. Bondioli,
56
F. Bucci,
56
G. Calderini,
56
E. Campagna,
56
M. Carpinelli,
56
F. F o r t i ,
56
M. A. Giorgi,
56
A. Lusiani,
56
G. Marchiori,
56
PHYSICAL REVIEW LETTERS
week ending
7 MARCH 2003
V
OLUME
90, N
UMBER
9
091801-1
0031-9007
=
03
=
90(9)
=
091801(7)$20.00
2003 The American Physical Society
091801-1
F. Martinez-Vidal,
56
M. Morganti,
56
N. Neri,
56
E. Paoloni,
56
M. Rama,
56
G. R i z zo ,
56
F. Sandrelli,
56
G. Triggiani,
56
J. Walsh,
56
M. Ha i re ,
57
D. Judd,
57
K. Paick,
57
L. Turnbull,
57
D. E. Wagoner,
57
J. Albert,
58
P. Elmer,
58
C. Lu,
58
V. M i f t a k o v ,
58
J. Olsen,
58
S. F. Schaffner,
58
A. J. S. Smith,
58
A. Tumanov,
58
E.W. Varnes,
58
F. Bellini,
59
G. Cavoto,
58,59
D. del Re,
14 ,59
R. Faccini,
14,59
F. Ferrarotto,
59
F. Ferroni,
59
E. Leonardi,
59
M. A. Mazzoni,
59
S. Morganti,
59
G. Piredda,
59
F. Safai Tehrani,
59
M. Serra,
59
C. Voena,
59
S. Christ,
60
G. Wagner,
60
R. Wa ld i ,
60
T. Adye,
61
N. De G ro ot ,
61
B. Franek,
61
N. I. Geddes,
61
G. P. Gopal,
61
S. M. Xella,
61
R. Aleksan,
62
S. Emery,
62
A. Gaidot,
62
P.-F. Giraud,
62
G. Hamel de Monchenault,
62
W. Kozanecki,
62
M. Langer,
62
G.W. London,
62
B. Mayer,
62
G. Schott,
62
B. Serfass,
62
G. Vasseur,
62
Ch. Yeche,
62
M. Z it o ,
62
M.V. Purohit,
63
A.W. Weidemann,
63
F. X. Yumiceva,
63
I. Adam,
64
D. A st on ,
64
N. Berger,
64
A. M. Boyarski,
64
M. R. Convery,
64
D. P. Coupal,
64
D. Dong,
64
J. Dorfan,
64
W. Dunwoodie,
64
R. C. Field,
64
T. Glanzman,
64
S. J. Gowdy,
64
E. Grauges,
64
T. Haas,
64
T. Hadig,
64
V. Halyo,
64
T. Himel,
64
T. H r y n’ o v a ,
64
M. E. Huffer,
64
W. R. Innes,
64
C. P. Jessop,
64
M. H. Kelsey,
64
P. K i m ,
64
M. L. Kocian,
64
U. Langenegger,
64
D. W. G. S. L eit h ,
64
S. Luitz,
64
V. Luth,
64
H. L. Ly nch ,
64
H. Marsiske,
64
S. Menke,
64
R. Messner,
64
D. R. Muller,
64
C. P. O’Grady,
64
V. E. Ozcan,
64
A. Perazzo,
64
M. Perl,
64
S. Petrak,
64
B. N. Ratcliff,
64
S. H. Robertson,
64
A. Roodman,
64
A. A. Salnikov,
64
T. Schietinger,
64
R. H. Schindler,
64
J. Schwiening,
64
G. Simi,
64
A. Snyder,
64
A. Soha,
64
S. M. Spanier,
64
J. Stelzer,
64
D. Su,
64
M. K. Sullivan,
64
H. A. Tanaka,
64
J. Va’vra,
64
S. R. Wagner,
64
M. Weaver,
64
A. J. R. Weinstein,
64
W. J. Wisniewski,
64
D. H. Wright,
64
C. C. Young,
64
P. R. Burchat,
65
C. H. Cheng,
65
T. I. Meyer,
65
C. Roat,
65
R. Henderson,
66
W. Bugg,
67
H. Cohn,
67
J. M. Izen,
68
I. Kitayama,
68
X. C. Lou,
68
F. Bianchi,
69
M. Bona,
69
D. Gamba,
69
L. Bosisio,
70
G. Della Ricca,
70
S. Dittongo,
70
L. Lanceri,
70
P. Poropat,
70
L. Vitale,
70
G. Vuagnin,
70
R. S. Pa nv i n i ,
71
S.W. Banerjee,
72
C. M. Brown,
72
D. Fortin,
72
P. D. Jackson,
72
R. Kowalewski,
72
J. M. Roney,
72
H. R. Band,
73
S. Dasu,
73
M. Datta,
73
A. M. Eichenbaum,
73
H. Hu,
73
J. R. Johnson,
73
R. Liu,
73
F. Di Lodovico,
73
A. Mohapatra,
73
Y. P a n ,
73
R. Prepost,
73
I. J. Scott,
73
S. J. Sekula,
73
J. H. von Wimmersperg-Toeller,
73
J. Wu,
73
S. L. Wu,
73
Z. Yu,
73
and H. Neal
74
(
BA BAR
Collaboration)
1
Laboratoire de Physique des Particules, F-74941 Annecy-le-Vieux, France
2
Universita
`
di Bari, Dipartimento di Fisica and INFN, I-70126 Bari, Italy
3
Institute of High Energy Physics, Beijing 100039, China
4
University of Bergen, Institute of Physics, N-5007 Bergen, Norway
5
Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720
6
University of Birmingham, Birmingham B15 2TT, United Kingdom
7
Ruhr Universita
̈
t Bochum, Institut fu
̈
r Experimentalphysik 1, D-44780 Bochum, Germany
8
University of Bristol, Bristol BS8 1TL, United Kingdom
9
University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
10
Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom
11
Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
12
University of California at Irvine, Irvine, California 92697
13
University of California at Los Angeles, Los Angeles, California 90024
14
University of California at San Diego, La Jolla, California 92093
15
University of California at Santa Barbara, Santa Barbara, California 93106
16
University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064
17
California Institute of Technology, Pasadena, California 91125
18
University of Cincinnati, Cincinnati, Ohio 45221
19
University of Colorado, Boulder, Colorado 80309
20
Colorado State University, Fort Collins, Colorado 80523
21
Technische Universita
̈
t Dresden, Institut fu
̈
r Kern- und Teilchenphysik, D-01062 Dresden, Germany
22
Ecole Polytechnique, LLR, F-91128 Palaiseau, France
23
University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
24
Elon University, Elon University, North Carolina 27244-2010
25
Universita
`
di Ferrara, Dipartimento di Fisica and INFN, I-44100 Ferrara, Italy
26
Florida A&M University, Tallahassee, Florida 32307
27
Laboratori Nazionali di Frascati dell’INFN, I-00044 Frascati, Italy
28
Universita
`
di Genova, Dipartimento di Fisica and INFN, I-16146 Genova, Italy
29
Harvard University, Cambridge, Massachusetts 02138
30
University of Iowa, Iowa City, Iowa 52242
31
Iowa State University, Ames, Iowa 50011-3160
32
Laboratoire de l’Acce
́
le
́
rateur Line
́
aire, F-91898 Orsay, France
PHYSICAL REVIEW LETTERS
week ending
7 MARCH 2003
V
OLUME
90, N
UMBER
9
091801-2
091801-2
33
Lawrence Livermore National Laboratory, Livermore, California 94550
34
University of Liverpool, Liverpool L69 3BX, United Kingdom
35
University of London, Imperial College, London SW7 2BW, United Kingdom
36
Queen Mary, University of 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
39
University of Manchester, Manchester M13 9PL, United Kingdom
40
University of Maryland, College Park, Maryland 20742
41
University of Massachusetts, Amherst, Massachusetts 01003
42
Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139
43
McGill University, Montre
́
al, Quebec, Canada H3A 2T8
44
Universita
`
di Milano, Dipartimento di Fisica and INFN, I-20133 Milano, Italy
45
University of Mississippi, University, Mississippi 38677
46
Universite
́
de Montre
́
al, Laboratoire Rene
́
J. A. L e
́
vesque, Montre
́
al, Quebec, Canada H3C 3J7
47
Mount Holyoke College, South Hadley, Massachusetts 01075
48
Universita
`
di Napoli Federico II, Dipartimento di Scienze Fisiche and INFN, I-80126, Napoli, Italy
49
University of Notre Dame, Notre Dame, Indiana 46556
50
Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
51
University of Oregon, Eugene, Oregon 97403
52
Universita
`
di Padova, Dipartimento di Fisica and INFN, I-35131 Padova, Italy
53
Universite
́
s Paris VI et VII, Lab de Physique Nucle
́
aire H. E., F-75252 Paris, France
54
Universita
`
di Pavia, Dipartimento di Elettronica and INFN, I-27100 Pavia, Italy
55
University of Pennsylvania, Philadelphia, Pennsylvania 19104
56
Universita
`
di Pisa, Scuola Normale Superiore and INFN, I-56010 Pisa, Italy
57
Prairie View A&M University, Prairie View, Texas 77446
58
Princeton University, Princeton, New Jersey 08544
59
Universita
`
di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy
60
Universita
̈
t Rostock, D-18051 Rostock, Germany
61
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom
62
DAPNIA, Commissariat a
`
l’Energie Atomique/Saclay, F-91191 Gif-sur-Yvette, France
63
University of South Carolina, Columbia, South Carolina 29208
64
Stanford Linear Accelerator Center, Stanford, California 94309
65
Stanford University, Stanford, California 94305-4060
66
TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
67
University of Tennessee, Knoxville, Tennessee 37996
68
University of Texas at Dallas, Richardson, Texas 75083
69
Universita
`
di Torino, Dipartimento di Fisica Sperimentale and INFN, I-10125 Torino, Italy
70
Universita
`
di Trieste, Dipartimento di Fisica and INFN, I-34127 Trieste, Italy
71
Vanderbilt University, Nashville, Tennessee 37235
72
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
73
University of Wisconsin, Madison, Wisconsin 53706
74
Yale University, New Haven, Connecticut 06511
(Received 7 September 2002; published 5 March 2003)
We present a measurement of the branching fraction for the decay of the neutral
B
meson into
the final state
J=
. The data set contains approximately
56
10
6
B
B
pairs produced at the
4
S
resonance and recorded with the
BA BAR
detector at the PEP-II asymmetric-energy
e
e
storage
ring. The result of this analysis is
B
B
0
!
J=
4
:
6
0
:
7
0
:
6
10
5
, where the first
error is statistical and the second is systematic. In addition, we measure
B
B
0
!
J=
0
1
:
6
0
:
6
0
:
4
10
5
.
DOI: 10.1103/PhysRevLett.90.091801
PACS numbers: 13.25.Hw, 11.30.Er, 12.15.Hh
In the standard model, the decay
B
0
!
J=
0
can give
rise to
CP
-violating asymmetries (directly and through
B
0
-
B
0
mixing) [1]. Therefore, it is interesting to study the
decay mode
B
0
!
J=
to understand the
J=
0
component in the final state. Since these decays are
Cabibbo and color suppressed, they could be sensitive to
non-standard-model processes contributing, for example,
through penguin amplitudes. Large non-standard-model
effects could cause the branching fraction to differ sig-
nificantly from the standard model prediction of
B
B
0
!
J=
4
:
8
0
:
8
10
5
[2]. This decay mode
has not previously been observed. CLEO quotes an upper
PHYSICAL REVIEW LETTERS
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limit of
B
B
0
!
J=
0
<
2
:
5
10
4
at the 90% con-
fidence level [4]. Here we present the first measurement of
B
B
0
!
J=
.
The data used in the present analysis were collected at
the PEP-II storage ring with the
BA BAR
detector, de-
scribed in detail elsewhere [5]. Charged particles are
detected, and their momenta measured, with a 40-layer
drift chamber (DCH) and a five-layer silicon vertex
tracker (SVT), both operating in a 1.5 T solenoidal
magnetic field. Surrounding the DCH is a detector of
internally reflected Cherenkov radiation (DIRC), and
outside this is a CsI(Tl) electromagnetic calorimeter
(EMC). The iron flux return of the solenoid is instru-
mented with resistive plate chambers (IFR). The data
sample used for the analysis contains approximately
56
10
6
B
B
pairs, corresponding to a luminosity of
51
:
7fb
1
recorded near the
4
S
resonance. An additional
6
:
4fb
1
, recorded approximately 40 MeV below the
4
S
peak, were used to study continuum backgrounds.
Events containing
B
B
pairs are selected based on track
multiplicity and event topology [6]. At least three tracks
are required to originate near the nominal beam spot,
with polar angle in the range
0
:
41
<
lab
<
2
:
54 rad
,
transverse momentum greater than
100 MeV
=c
, and a
minimum number of DCH hits used in the track fit. To
reduce continuum background the ratio of the second to
zeroth Fox-Wolfram moment,
R
2
H
2
=H
0
, is required to
be less than 0.5. The sum of charged and neutral energy
must be greater than 4.5 GeV in the laboratory frame. The
primary vertex of the event must be within 0.5 cm of the
average measured position of the interaction point in
the plane transverse to the beam line.
The
J=
is reconstructed in the
e
e
and
final
states. Electron candidates must satisfy the requirement
that the ratio of calorimeter energy to track momentum
lies in the range
0
:
75
< E=p <
1
:
3
, the cluster shape and
size are consistent with an electromagnetic shower, and
the energy loss in the DCH is consistent with that for an
electron. If an EMC cluster close to the electron track is
consistent with originating from a bremsstrahlung pho-
ton, it is combined with the electron candidate.
Muon candidates must satisfy requirements on the
number of interaction lengths of IFR iron penetrated
(
N
>
2
), the difference between the measured and ex-
pected interaction lengths penetrated (
j
N
N
exp
j
<
2
),
the position match between the extrapolated DCH track
and the IFR hits, and the average and spread of the
number of IFR strips hit per layer.
Pion candidates are accepted if they originate from
close to the beam spot and are not consistent with being
a kaon. The algorithm uses
dE=dx
information from the
SVT and DCH, and the Cherenkov angle and number of
photons from the DIRC.
Tracks are required to lie in polar-angle ranges where
particle identification efficiency is measured with known
control samples. The allowed ranges correspond approxi-
mately to the geometrical acceptances of the EMC for
electrons, the IFR for muons, and the DIRC for pions.
Identified electron and muon pairs are fit to a common
vertex and must lie in the
J=
invariant mass interval
2.95 (3.06) to
3
:
14 GeV
=c
2
for the
e
e
(
)
channel.
B
0
candidates are formed by combining a
J=
candi-
date with a pair of oppositely charged pion candidates
consistent with coming from a common decay point. We
also require the vertex positions of the lepton and pion
pairs to be consistent. Further selection requirements are
made using two kinematic variables: the difference,
E
,
between the energy of the candidate and the beam energy
E
cm
beam
in the center-of-mass frame and the beam-energy
substituted mass,
m
ES
E
cm
beam
2
p
cm
B
2
q
. After ap-
plying the loose requirements
5
:
2
<m
ES
<
5
:
3 GeV
=c
2
and
j
E
j
<
0
:
12 GeV
, approximately one-quarter of the
events contain more than one
B
0
candidate, from which
we keep the one with the smallest
j
E
j
. The distribution
of the candidates in
E
and
m
ES
is shown in Fig. 1.
For the final signal sample, we require
j
m
ES
5279
:
0 MeV
=c
2
j
<
9
:
9 MeV
=c
2
and
j
E
j
<
39 MeV
,
which correspond to
4
and
3
ranges in the resolutions
for
m
ES
and
E
. After all selection criteria have been
applied, 213 events remain.
An unbinned, extended maximum-likelihood [7]
fit is performed on the invariant mass distribution
of the two pions for the selected events, to determine
the various contributions to the
B
0
!
J=
events. We consider five categories: (i)
B
0
!
J=
0
events;
(ii)
B
0
!
J= K
0
S
K
0
S
!
events;
(iii)
B
0
!
J=
(non-
0
signal)
events;
-0.1
-0.05
0
0.05
0.1
∆
E (GeV)
0
10
20
30
40
5.2
5.225
5.25
5.275
5.3
Events/2.5 MeV/c
2
m
ES
(GeV/c
2
)
FIG. 1 (color online).
Signal for
B
0
!
J=
.The
upper plot shows the distribution of events in the
E
-
m
ES
plane, where the box represents the
fi
nal selection criteria.
The lower plot shows the distribution in
m
ES
of events
with
j
E
j
<
39 MeV
, where the dashed (solid) line corre-
sponds to events in the
K
0
S
(non-
K
0
S
) region in
M
(
0
:
45
–
0
:
55 GeV
=c
2
). The vertical lines represent the
fi
nal
selection.
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