of 7
Search for the decay
B

!




B. Aubert,
1
R. Barate,
1
D. Boutigny,
1
F. Couderc,
1
Y. Karyotakis,
1
J. P. Lees,
1
V. Poireau,
1
V. Tisserand,
1
A. Zghiche,
1
E. Grauges,
2
A. Palano,
3
M. Pappagallo,
3
A. Pompili,
3
J. C. Chen,
4
N. D. Qi,
4
G. Rong,
4
P. Wang,
4
Y. S. Zhu,
4
G. Eigen,
5
I. Ofte,
5
B. Stugu,
5
G. S. Abrams,
6
M. Battaglia,
6
A. B. Breon,
6
D. N. Brown,
6
J. Button-Shafer,
6
R. N. Cahn,
6
E. Charles,
6
C. T. Day,
6
M. S. Gill,
6
A. V. Gritsan,
6
Y. Groysman,
6
R. G. Jacobsen,
6
R. W. Kadel,
6
J. Kadyk,
6
L. T. Kerth,
6
Yu. G. Kolomensky,
6
G. Kukartsev,
6
G. Lynch,
6
L. M. Mir,
6
P. J. Oddone,
6
T. J. Orimoto,
6
M. Pripstein,
6
N. A. Roe,
6
M. T. Ronan,
6
W. A. Wenzel,
6
M. Barrett,
7
K. E. Ford,
7
T. J. Harrison,
7
A. J. Hart,
7
C. M. Hawkes,
7
S. E. Morgan,
7
A. T. Watson,
7
M. Fritsch,
8
K. Goetzen,
8
T. Held,
8
H. Koch,
8
B. Lewandowski,
8
M. Pelizaeus,
8
K. Peters,
8
T. Schroeder,
8
M. Steinke,
8
J. T. Boyd,
9
J. P. Burke,
9
N. Chevalier,
9
W. N. Cottingham,
9
T. Cuhadar-Donszelmann,
10
B. G. Fulsom,
10
C. Hearty,
10
N. S. Knecht,
10
T. S. Mattison,
10
J. A. McKenna,
10
A. Khan,
11
P. Kyberd,
11
M. Saleem,
11
L. Teodorescu,
11
A. E. Blinov,
12
V. E. Blinov,
12
A. D. Bukin,
12
V. P. Druzhinin,
12
V. B. Golubev,
12
E. A. Kravchenko,
12
A. P. Onuchin,
12
S. I. Serednyakov,
12
Yu. I. Skovpen,
12
E. P. Solodov,
12
A. N. Yushkov,
12
D. Best,
13
M. Bondioli,
13
M. Bruinsma,
13
M. Chao,
13
S. Curry,
13
I. Eschrich,
13
D. Kirkby,
13
A. J. Lankford,
13
P. Lund,
13
M. Mandelkern,
13
R. K. Mommsen,
13
W. Roethel,
13
D. P. Stoker,
13
C. Buchanan,
14
B. L. Hartfiel,
14
A. J. R. Weinstein,
14
S. D. Foulkes,
15
J. W. Gary,
15
O. Long,
15
B. C. Shen,
15
K. Wang,
15
L. Zhang,
15
D. del Re,
16
H. K. Hadavand,
16
E. J. Hill,
16
D. B. MacFarlane,
16
H. P. Paar,
16
S. Rahatlou,
16
V. Sharma,
16
J. W. Berryhill,
17
C. Campagnari,
17
A. Cunha,
17
B. Dahmes,
17
T. M. Hong,
17
M. A. Mazur,
17
J. D. Richman,
17
W. Verkerke,
17
T. W. Beck,
18
A. M. Eisner,
18
C. J. Flacco,
18
C. A. Heusch,
18
J. Kroseberg,
18
W. S. Lockman,
18
G. Nesom,
18
T. Schalk,
18
B. A. Schumm,
18
A. Seiden,
18
P. Spradlin,
18
D. C. Williams,
18
M. G. Wilson,
18
J. Albert,
19
E. Chen,
19
G. P. Dubois-Felsmann,
19
A. Dvoretskii,
19
D. G. Hitlin,
19
I. Narsky,
19
T. Piatenko,
19
F. C. Porter,
19
A. Ryd,
19
A. Samuel,
19
R. Andreassen,
20
S. Jayatilleke,
20
G. Mancinelli,
20
B. T. Meadows,
20
M. D. Sokoloff,
20
F. Blanc,
21
P. Bloom,
21
S. Chen,
21
W. T. Ford,
21
J. F. Hirschauer,
21
A. Kreisel,
21
U. Nauenberg,
21
A. Olivas,
21
P. Rankin,
21
W. O. Ruddick,
21
J. G. Smith,
21
K. A. Ulmer,
21
S. R. Wagner,
21
J. Zhang,
21
A. Chen,
22
E. A. Eckhart,
22
A. Soffer,
22
W. H. Toki,
22
R. J. Wilson,
22
Q. Zeng,
22
D. Altenburg,
23
E. Feltresi,
23
A. Hauke,
23
B. Spaan,
23
T. Brandt,
24
J. Brose,
24
M. Dickopp,
24
V. Klose,
24
H. M. Lacker,
24
R. Nogowski,
24
S. Otto,
24
A. Petzold,
24
G. Schott,
24
J. Schubert,
24
K. R. Schubert,
24
R. Schwierz,
24
J. E. Sundermann,
24
D. Bernard,
25
G. R. Bonneaud,
25
P. Grenier,
25
S. Schrenk,
25
Ch. Thiebaux,
25
G. Vasileiadis,
25
M. Verderi,
25
D. J. Bard,
26
P. J. Clark,
26
W. Gradl,
26
F. Muheim,
26
S. Playfer,
26
Y. Xie,
26
M. Andreotti,
27
V. Azzolini,
27
D. Bettoni,
27
C. Bozzi,
27
R. Calabrese,
27
G. Cibinetto,
27
E. Luppi,
27
M. Negrini,
27
L. Piemontese,
27
F. Anulli,
28
R. Baldini-Ferroli,
28
A. Calcaterra,
28
R. de Sangro,
28
G. Finocchiaro,
28
P. Patteri,
28
I. M. Peruzzi,
28,
*
M. Piccolo,
28
A. Zallo,
28
A. Buzzo,
29
R. Capra,
29
R. Contri,
29
M. Lo Vetere,
29
M. Macri,
29
M. R. Monge,
29
S. Passaggio,
29
C. Patrignani,
29
E. Robutti,
29
A. Santroni,
29
S. Tosi,
29
G. Brandenburg,
30
K. S. Chaisanguanthum,
30
M. Morii,
30
E. Won,
30
J. Wu,
30
R. S. Dubitzky,
31
U. Langenegger,
31
J. Marks,
31
S. Schenk,
31
U. Uwer,
31
W. Bhimji,
32
D. A. Bowerman,
32
P. D. Dauncey,
32
U. Egede,
32
R. L. Flack,
32
J. R. Gaillard,
32
G. W. Morton,
32
J. A. Nash,
32
M. B. Nikolich,
32
G. P. Taylor,
32
W. P. Vazquez,
32
M. J. Charles,
33
W. F. Mader,
33
U. Mallik,
33
A. K. Mohapatra,
33
J. Cochran,
34
H. B. Crawley,
34
V. Eyges,
34
W. T. Meyer,
34
S. Prell,
34
E. I. Rosenberg,
34
A. E. Rubin,
34
J. Yi,
34
N. Arnaud,
35
M. Davier,
35
X. Giroux,
35
G. Grosdidier,
35
A. Ho
̈
cker,
35
F. Le Diberder,
35
V. Lepeltier,
35
A. M. Lutz,
35
A. Oyanguren,
35
T. C. Petersen,
35
M. Pierini,
35
S. Plaszczynski,
35
S. Rodier,
35
P. Roudeau,
35
M. H. Schune,
35
A. Stocchi,
35
G. Wormser,
35
C. H. Cheng,
36
D. J. Lange,
36
M. C. Simani,
36
D. M. Wright,
36
A. J. Bevan,
37
C. A. Chavez,
37
I. J. Forster,
37
J. R. Fry,
37
E. Gabathuler,
37
R. Gamet,
37
K. A. George,
37
D. E. Hutchcroft,
37
R. J. Parry,
37
D. J. Payne,
37
K. C. Schofield,
37
C. Touramanis,
37
C. M. Cormack,
38
F. Di Lodovico,
38
W. Menges,
38
R. Sacco,
38
C. L. Brown,
39
G. Cowan,
39
H. U. Flaecher,
39
M. G. Green,
39
D. A. Hopkins,
39
P. S. Jackson,
39
T. R. McMahon,
39
S. Ricciardi,
39
F. Salvatore,
39
D. Brown,
40
C. L. Davis,
40
J. Allison,
41
N. R. Barlow,
41
R. J. Barlow,
41
C. L. Edgar,
41
M. C. Hodgkinson,
41
M. P. Kelly,
41
G. D. Lafferty,
41
M. T. Naisbit,
41
J. C. Williams,
41
C. Chen,
42
W. D. Hulsbergen,
42
A. Jawahery,
42
D. Kovalskyi,
42
C. K. Lae,
42
D. A. Roberts,
42
G. Simi,
42
G. Blaylock,
43
C. Dallapiccola,
43
S. S. Hertzbach,
43
R. Kofler,
43
V. B. Koptchev,
43
X. Li,
43
T. B. Moore,
43
S. Saremi,
43
H. Staengle,
43
S. Willocq,
43
R. Cowan,
44
K. Koeneke,
44
G. Sciolla,
44
S. J. Sekula,
44
M. Spitznagel,
44
F. Taylor,
44
R. K. Yamamoto,
44
H. Kim,
45
P. M. Patel,
45
S. H. Robertson,
45
A. Lazzaro,
46
V. Lombardo,
46
F. Palombo,
46
J. M. Bauer,
47
L. Cremaldi,
47
V. Eschenburg,
47
R. Godang,
47
R. Kroeger,
47
J. Reidy,
47
D. A. Sanders,
47
D. J. Summers,
47
H. W. Zhao,
47
S. Brunet,
48
D. Co
ˆ
te
́
,
48
P. Taras,
48
B. Viaud,
48
H. Nicholson,
49
N. Cavallo,
50,†
G. De Nardo,
50
F. Fabozzi,
50,†
C. Gatto,
50
L. Lista,
50
D. Monorchio,
50
P. Paolucci,
50
D. Piccolo,
50
C. Sciacca,
50
M. Baak,
51
H. Bulten,
51
G. Raven,
51
H. L. Snoek,
51
L. Wilden,
51
C. P. Jessop,
52
J. M. LoSecco,
52
T. Allmendinger,
53
G. Benelli,
53
K. K. Gan,
53
K. Honscheid,
53
D. Hufnagel,
53
P. D. Jackson,
53
H. Kagan,
53
R. Kass,
53
PHYSICAL REVIEW D
73,
057101 (2006)
1550-7998
=
2006
=
73(5)
=
057101(7)$23.00
057101-1
©
2006 The American Physical Society
T. Pulliam,
53
A. M. Rahimi,
53
R. Ter-Antonyan,
53
Q. K. Wong,
53
J. Brau,
54
R. Frey,
54
O. Igonkina,
54
M. Lu,
54
C. T. Potter,
54
N. B. Sinev,
54
D. Strom,
54
J. Strube,
54
E. Torrence,
54
F. Galeazzi,
55
M. Margoni,
55
M. Morandin,
55
M. Posocco,
55
M. Rotondo,
55
F. Simonetto,
55
R. Stroili,
55
C. Voci,
55
M. Benayoun,
56
H. Briand,
56
J. Chauveau,
56
P. David,
56
L. Del Buono,
56
Ch. de la Vaissie
`
re,
56
O. Hamon,
56
M. J. J. John,
56
Ph. Leruste,
56
J. Malcle
`
s,
56
J. Ocariz,
56
L. Roos,
56
G. Therin,
56
P. K. Behera,
57
L. Gladney,
57
Q. H. Guo,
57
J. Panetta,
57
M. Biasini,
58
R. Covarelli,
58
S. Pacetti,
58
M. Pioppi,
58
C. Angelini,
59
G. Batignani,
59
S. Bettarini,
59
F. Bucci,
59
G. Calderini,
59
M. Carpinelli,
59
R. Cenci,
59
F. Forti,
59
M. A. Giorgi,
59
A. Lusiani,
59
G. Marchiori,
59
M. Morganti,
59
N. Neri,
59
E. Paoloni,
59
M. Rama,
59
G. Rizzo,
59
J. Walsh,
59
M. Haire,
60
D. Judd,
60
D. E. Wagoner,
60
J. Biesiada,
61
N. Danielson,
61
P. Elmer,
61
Y. P. Lau,
61
C. Lu,
61
J. Olsen,
61
A. J. S. Smith,
61
A. V. Telnov,
61
F. Bellini,
62
G. Cavoto,
62
A. D’Orazio,
62
E. Di Marco,
62
R. Faccini,
62
F. Ferrarotto,
62
F. Ferroni,
62
M. Gaspero,
62
L. Li Gioi,
62
M. A. Mazzoni,
62
S. Morganti,
62
G. Piredda,
62
F. Polci,
62
F. Safai Tehrani,
62
C. Voena,
62
H. Schro
̈
der,
63
G. Wagner,
63
R. Waldi,
63
T. Adye,
64
N. De Groot,
64
B. Franek,
64
G. P. Gopal,
64
E. O. Olaiya,
64
F. F. Wilson,
64
R. Aleksan,
65
S. Emery,
65
A. Gaidot,
65
S. F. Ganzhur,
65
P.-F. Giraud,
65
G. Graziani,
65
G. Hamel de Monchenault,
65
W. Kozanecki,
65
M. Legendre,
65
G. W. London,
65
B. Mayer,
65
G. Vasseur,
65
Ch. Ye
`
che,
65
M. Zito,
65
M. V. Purohit,
66
A. W. Weidemann,
66
J. R. Wilson,
66
F. X. Yumiceva,
66
T. Abe,
67
M. T. Allen,
67
D. Aston,
67
N. Bakel,
67
R. Bartoldus,
67
N. Berger,
67
A. M. Boyarski,
67
O. L. Buchmueller,
67
R. Claus,
67
J. P. Coleman,
67
M. R. Convery,
67
M. Cristinziani,
67
J. C. Dingfelder,
67
D. Dong,
67
J. Dorfan,
67
D. Dujmic,
67
W. Dunwoodie,
67
S. Fan,
67
R. C. Field,
67
T. Glanzman,
67
S. J. Gowdy,
67
T. Hadig,
67
V. Halyo,
67
C. Hast,
67
T. Hryn’ova,
67
W. R. Innes,
67
M. H. Kelsey,
67
P. Kim,
67
M. L. Kocian,
67
D. W. G. S. Leith,
67
J. Libby,
67
S. Luitz,
67
V. Luth,
67
H. L. Lynch,
67
H. Marsiske,
67
R. Messner,
67
D. R. Muller,
67
C. P. O’Grady,
67
V. E. Ozcan,
67
A. Perazzo,
67
M. Perl,
67
B. N. Ratcliff,
67
A. Roodman,
67
A. A. Salnikov,
67
R. H. Schindler,
67
J. Schwiening,
67
A. Snyder,
67
J. Stelzer,
67
D. Su,
67
M. K. Sullivan,
67
K. Suzuki,
67
S. Swain,
67
J. M. Thompson,
67
J. Va’vra,
67
M. Weaver,
67
W. J. Wisniewski,
67
M. Wittgen,
67
D. H. Wright,
67
A. K. Yarritu,
67
K. Yi,
67
C. C. Young,
67
P. R. Burchat,
68
A. J. Edwards,
68
S. A. Majewski,
68
B. A. Petersen,
68
C. Roat,
68
M. Ahmed,
69
S. Ahmed,
69
M. S. Alam,
69
J. A. Ernst,
69
M. A. Saeed,
69
F. R. Wappler,
69
S. B. Zain,
69
W. Bugg,
70
M. Krishnamurthy,
70
S. M. Spanier,
70
R. Eckmann,
71
J. L. Ritchie,
71
A. Satpathy,
71
R. F. Schwitters,
71
J. M. Izen,
72
I. Kitayama,
72
X. C. Lou,
72
S. Ye,
72
F. Bianchi,
73
M. Bona,
73
F. Gallo,
73
D. Gamba,
73
M. Bomben,
74
L. Bosisio,
74
C. Cartaro,
74
F. Cossutti,
74
G. Della Ricca,
74
S. Dittongo,
74
S. Grancagnolo,
74
L. Lanceri,
74
L. Vitale,
74
F. Martinez-Vidal,
75
R. S. Panvini,
76,‡
Sw. Banerjee,
77
B. Bhuyan,
77
C. M. Brown,
77
D. Fortin,
77
K. Hamano,
77
R. Kowalewski,
77
J. M. Roney,
77
R. J. Sobie,
77
J. J. Back,
78
P. F. Harrison,
78
T. E. Latham,
78
G. B. Mohanty,
78
H. R. Band,
79
X. Chen,
79
B. Cheng,
79
S. Dasu,
79
M. Datta,
79
A. M. Eichenbaum,
79
K. T. Flood,
79
M. Graham,
79
J. J. Hollar,
79
J. R. Johnson,
79
P. E. Kutter,
79
H. Li,
79
R. Liu,
79
B. Mellado,
79
A. Mihalyi,
79
Y. Pan,
79
R. Prepost,
79
P. Tan,
79
J. H. von Wimmersperg-Toeller,
79
S. L. Wu,
79
Z. Yu,
79
and H. Neal
80
(
B
A
B
AR
Collaboration)
1
Laboratoire de Physique des Particules, F-74941 Annecy-le-Vieux, France
2
IFAE, Universitat Autonoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain
3
Universita
`
di Bari, Dipartimento di Fisica and INFN, I-70126 Bari, Italy
4
Institute of High Energy Physics, Beijing 100039, China
5
University of Bergen, Institute of Physics, N-5007 Bergen, Norway
6
Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA
7
University of Birmingham, Birmingham, B15 2TT, United Kingdom
8
Ruhr Universita
̈
t Bochum, Institut fu
̈
r Experimentalphysik 1, D-44780 Bochum, Germany
9
University of Bristol, Bristol BS8 1TL, United Kingdom
10
University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
11
Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom
12
Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
13
University of California at Irvine, Irvine, California 92697, USA
14
University of California at Los Angeles, Los Angeles, California 90024, USA
15
University of California at Riverside, Riverside, California 92521, USA
16
University of California at San Diego, La Jolla, California 92093, USA
17
University of California at Santa Barbara, Santa Barbara, California 93106, USA
18
University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064, USA
19
California Institute of Technology, Pasadena, California 91125, USA
20
University of Cincinnati, Cincinnati, Ohio 45221, USA
BRIEF REPORTS
PHYSICAL REVIEW D
73,
057101 (2006)
057101-2
21
University of Colorado, Boulder, Colorado 80309, USA
22
Colorado State University, Fort Collins, Colorado 80523, USA
23
Universita
̈
t Dortmund, Institut fur Physik, D-44221 Dortmund, Germany
24
Technische Universita
̈
t Dresden, Institut fu
̈
r Kern- und Teilchenphysik, D-01062 Dresden, Germany
25
Ecole Polytechnique, LLR, F-91128 Palaiseau, France
26
University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
27
Universita
`
di Ferrara, Dipartimento di Fisica and INFN, I-44100 Ferrara, Italy
28
Laboratori Nazionali di Frascati dell’INFN, I-00044 Frascati, Italy
29
Universita
`
di Genova, Dipartimento di Fisica and INFN, I-16146 Genova, Italy
30
Harvard University, Cambridge, Massachusetts 02138, USA
31
Universita
̈
t Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg, Germany
32
Imperial College London, London, SW7 2AZ, United Kingdom
33
University of Iowa, Iowa City, Iowa 52242, USA
34
Iowa State University, Ames, Iowa 50011-3160, USA
35
Laboratoire de l’Acce
́
le
́
rateur Line
́
aire, F-91898 Orsay, France
36
Lawrence Livermore National Laboratory, Livermore, California 94550, USA
37
University of Liverpool, Liverpool L69 72E, United Kingdom
38
Queen Mary, University of London, E1 4NS, United Kingdom
39
University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom
40
University of Louisville, Louisville, Kentucky 40292, USA
41
University of Manchester, Manchester M13 9PL, United Kingdom
42
University of Maryland, College Park, Maryland 20742, USA
43
University of Massachusetts, Amherst, Massachusetts 01003, USA
44
Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139, USA
45
McGill University, Montre
́
al, Quebec, Canada H3A 2T8
46
Universita
`
di Milano, Dipartimento di Fisica and INFN, I-20133 Milano, Italy
47
University of Mississippi, University, Mississippi 38677, USA
48
Universite
́
de Montre
́
al, Laboratoire Rene
́
J. A. Le
́
vesque, Montre
́
al, Quebec, Canada H3C 3J7
49
Mount Holyoke College, South Hadley, Massachusetts 01075, USA
50
Universita
`
di Napoli Federico II, Dipartimento di Scienze Fisiche and INFN, I-80126, Napoli, Italy
51
NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands
52
University of Notre Dame, Notre Dame, Indiana 46556, USA
53
Ohio State University, Columbus, Ohio 43210, USA
54
University of Oregon, Eugene, Oregon 97403, USA
55
Universita
`
di Padova, Dipartimento di Fisica and INFN, I-35131 Padova, Italy
56
Universite
́
s Paris VI et VII, Laboratoire de Physique Nucle
́
aire et de Hautes Energies, F-75252 Paris, France
57
University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
58
Universita
`
di Perugia, Dipartimento di Fisica and INFN, I-06100 Perugia, Italy
59
Universita
`
di Pisa, Dipartimento di Fisica, Scuola Normale Superiore and INFN, I-56127 Pisa, Italy
60
Prairie View A&M University, Prairie View, Texas 77446, USA
61
Princeton University, Princeton, New Jersey 08544, USA
62
Universita
`
di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy
63
Universita
̈
t Rostock, D-18051 Rostock, Germany
64
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
65
DSM/Dapnia, CEA/Saclay, F-91191 Gif-sur-Yvette, France
66
University of South Carolina, Columbia, South Carolina 29208, USA
67
Stanford Linear Accelerator Center, Stanford, California 94309, USA
68
Stanford University, Stanford, California 94305-4060, USA
69
State University of New York, Albany, New York 12222, USA
70
University of Tennessee, Knoxville, Tennessee 37996, USA
71
University of Texas at Austin, Austin, Texas 78712, USA
72
University of Texas at Dallas, Richardson, Texas 75083, USA
73
Universita
`
di Torino, Dipartimento di Fisica Sperimentale and INFN, I-10125 Torino, Italy
74
Universita
`
di Trieste, Dipartimento di Fisica and INFN, I-34127 Trieste, Italy
75
IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
76
Vanderbilt University, Nashville, Tennessee 37235, USA
77
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
78
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
79
University of Wisconsin, Madison, Wisconsin 53706, USA
80
Yale University, New Haven, Connecticut 06511, USA
(Received 14 July 2005; published 10 March 2006)
BRIEF REPORTS
PHYSICAL REVIEW D
73,
057101 (2006)
057101-3
We search for the rare leptonic decay
B

!




in a sample of
232

10
6
B
B
pairs collected with the
BABAR
detector at the SLAC PEP-II
B
-Factory. Signal events are selected by examining the properties of
the
B
meson recoiling against the semileptonic decay
B

!
D

0


. We find no evidence for a signal
and set an upper limit on the branching fraction of
B

B

!





<
2
:
8

10

4
at the 90% confidence
level. We combine this result with a previous, statistically independent
BABAR
search for
B

!




to
give an upper limit of
B

B

!





<
2
:
6

10

4
at the 90% confidence level.
DOI:
10.1103/PhysRevD.73.057101
PACS numbers: 13.20.He, 14.40.Nd, 14.60.Fg
In the standard model (SM) the purely leptonic decay
B

!




[1] proceeds via the annihilation of the
b
and
u
quarks into a virtual
W
boson. Its amplitude is propor-
tional to the product of the Cabibbo-Kobayashi-Maskawa
(CKM) matrix [2] element
j
V
ub
j
and the
B
meson decay
constant
f
B
. The SM branching fraction is given by [3]
B

B

!





G
2
F
m
B
8

m
2


1

m
2

m
2
B

2
f
2
B
j
V
ub
j
2

B
;
(1)
where
G
F
is the Fermi coupling constant,
m

and
m
B
are
the


lepton and
B

meson masses, and

B
is the
B

lifetime. The branching fractions for
B

!
e


e
and
B

!




are helicity-suppressed by
m
2
=m
2
B
, where
m
is the mass of
e

or


. Using the value of
j
V
ub
j

3
:
67

0
:
47

10

3
[4] and the lattice QCD calculation
of
f
B

0
:
196

0
:
032

GeV
[5], we determine an ex-
pected value of
B

B

!





9
:
3

3
:
9

10

5
.
Currently, our best knowledge of
f
B
comes from theoreti-
cal calculations, with a current theoretical uncertainty of
roughly 16% [5]. Observation of
B

!




could pro-
vide the first direct measurement of
f
B
. The ratio of
B

B

!





and

m
d
, the difference in heavy and light
neutral
B
d
masses [6], can be used to determine the ratio of
CKM matrix elements
j
V
ub
j
=
j
V
td
j
with roughly 4% theo-
retical uncertainties [4,5], dominated by the uncertainties
on the square root of the bag parameter

B
B
p
[5].
No evidence of the
B

!




decay has been reported
to date. The most stringent published experimental limit is
B

B

!





<
4
:
2

10

4
at the 90% confidence level
(C.L.) [7]. Physics beyond the SM, such as supersymmetry
or two-Higgs-doublet models, could enhance
B

B

!





up to the current experimental limits [8].
The data used in this analysis were collected with the
BABAR
detector [9] at the PEP-II asymmetric-energy
e

e

storage ring. The results are based on a data sample
of

231
:
8

2
:
6

10
6
B
B
events, in an integrated lumi-
nosity of
210
:
6fb

1
collected at the


4
S

resonance. An
additional sample of
21
:
6fb

1
was collected at a center-
of-mass (CM) energy approximately 40 MeV below the


4
S

resonance. We used the latter sample to study con-
tinuum events,
e

e

!
q
q

q

u; d; s; c

and
e

e

!




. Charged-particle tracking and
d
E=
d
x
measurements
for particle identification (PID) are provided by a five-layer
double-sided silicon vertex tracker and a 40-layer drift
chamber operated in the 1.5 T magnetic field of a super-
conducting solenoid. A detector of internally reflected
Cherenkov light (DIRC) is used to identify charged kaons
and pions. The energies of neutral particles are measured
by an electromagnetic calorimeter (EMC) consisting of
6580 CsI(Tl) crystals. The magnetic flux return of the
solenoid is instrumented with resistive plate chambers in
order to provide muon identification. A full detector Monte
Carlo (MC) simulation based on
EVTGEN
[10] and
GEANT4
[11] is used to evaluate signal efficiencies and to identify
and study background sources. Beam-related background
and detector noise samples are obtained from random
triggers at regular intervals. These samples are overlaid
on the simulated events with appropriate luminosity
weighting to model these time-varying background
conditions.
Because of the presence of at least two neutrinos in the
final state, the
B

!




decay lacks the kinematic
constraints that are usually exploited in
B
decay searches
in order to reject both continuum and
B
B
backgrounds. The
strategy adopted to search for this decay is to reconstruct
the
B

meson from an


4
S
!
B

B

event in a semi-
leptonic final state, denoted by
B

sl
. All remaining charged
and neutral particles in that event, referred to as the ‘‘-
signal-side’’ particles throughout this paper, are then ex-
amined under the assumption that they are attributable to
the decay of the accompanying
B

(‘‘signal
B
’’).
The
B

sl
is reconstructed in the decay modes
B

sl
!
D

0


(

e
or

). The
D

0
is reconstructed in the
modes
D
0

0
and
D
0

. The
D
0
is reconstructed in four
decay modes:
K



,
K







,
K




0
, and
K
0
S




. All kinematic variables are calculated in the
CM-frame of the


4
S

unless otherwise noted.
Photon candidates are obtained from EMC clusters with
laboratory-frame energy
E

greater than 30 MeV and no
associated charged track. Photon pairs with invariant mass
between 115 and
150 MeV
=c
2
are taken as

0
candidates.
The
D
0
candidates are reconstructed by selecting com-
binations of identified pions and kaons with invariant mass
within
40 MeV
=c
2
of the nominal
D
0
mass [4], except for
the
K




0
mode, where this window is
70 MeV
=c
2
.
Each
D
0
candidate is combined with a soft

0
or

candidate to form a
D

0
. The

0
and

candidates are
required to have momentum less than
450 MeV
=c
.
*
Also with Universita
`
di Perugia, Dipartimento di Fisica,
Perugia, Italy.
Also with Universita
`
della Basilicata, Potenza, Italy.
Deceased.
BRIEF REPORTS
PHYSICAL REVIEW D
73,
057101 (2006)
057101-4
Further, the

candidate must have
E

>
100 MeV
. The
invariant mass difference

M
between the
D

0
and
D
0
is
required to be within the range
135
150 MeV
=c
2
for the
D
0

0
mode, and
130
155 MeV
=c
2
for the
D
0

mode.
The
B

sl
!
D

0


candidates are identified by com-
bining a
D

0
candidate of momentum
p
D

0
>
0
:
5 GeV
=c
with a lepton candidate of momentum
p
>
1
:
0 GeV
=c
.
The lepton candidate must be identified as either an elec-
tron or a muon. The invariant mass
m
D

0
of the
D

0
candidate is required to be greater than
3
:
0 GeV
=c
2
.
Under the assumption that a massless neutrino is the only
missing particle, the cosine of the angle between the direc-
tions of the
B

sl
and the lepton-
D

0
combination is
cos

B
;
D

0
2
E
beam
E
D

0

m
2
B

m
2
D

0
2
j
p
D

0
j

E
2
beam

m
2
B
q
;
(2)
where
E
beam
is the expected
B

meson energy. The energy
and momentum of the
D

0
candidate are
E
D

0
and
p
D

0
,
respectively. Correctly reconstructed candidates populate
the range

1
;
1
, whereas combinatorial backgrounds can
take unphysical values well outside this range. We retain
B

sl
candidates in the wider interval
j
cos

B
;
D

0
j
<
1
:
1
,
allowing for the effects of detector energy and momentum
resolutions. If more than one
D

0
candidate is recon-
structed in an event, the best candidate is selected using a
likelihood based on the simulated
D
0
mass and

M
dis-
tributions. We further require that the sum of the charges of
all the particles in the event (‘‘net charge’’) must be equal
to zero.
The
B

sl
reconstruction efficiency for events containing a
B

!




decay is determined from signal simulation
after verifying that the simulated
B
B
,
u
u
,
d
d
,
s
s
,
c
c
, and




events are consistent with data. This procedure
compensates for differences in the
B

sl
reconstruction effi-
ciency in the low-multiplicity environment of
B

!




events compared with the generic
B

B

environment. The
simulated efficiency is further cross-checked by comparing
the yield of events in which a
B

!
D

0


decay has
been reconstructed in addition to a
B

sl
(‘‘double semilep-
tonic decay’’). In the signal simulation the
B

sl
reconstruc-
tion efficiency is
"
sl

1
:
75

0
:
07

stat
:

0
:
05

syst
:

10

3
. The
D

0


,
D

0
, and
D
0
branching fractions are
factored in
"
sl
.
Events that contain a
B

sl
are examined for evidence of a
B

!




decay. Charged tracks and EMC clusters not
already utilized for the
B

sl
reconstruction are assumed to
originate from the signal candidate
B

decay. We identify
the

lepton in six mutually exclusive channels:
e


e


,






,




,



0


,








, and ‘‘misidenti-
fied lepton.’’ The misidentified-lepton channel selects sig-
nal events from the
e


e


or






signal decays in
which the momentum of the
e

or


from the signal


is
too low to pass the lepton identification criteria. The iden-
tified


modes all together correspond to approximately
81% of all


decays [4].
Signal candidates are searched in events that are re-
quired to possess exactly one signal-side charged track,
except for








candidate events, which must have
three signal-side charged tracks. The signal track from the
e


e


(






) channel is required to be identified as
an electron (a muon), and not to satisfy either muon
(electron) or kaon PID criteria. In the




,



0


,








, and misidentified-lepton channels the signal
track(s) must not satisfy electron, muon, or kaon PID. In
addition, each signal track from the








channel
has to be identified as a pion. For the



0


channel the
signal track is combined with a signal-side

0
candidate,
reconstructed from a signal-side photon pair (
E

>
50 MeV
for each photon) with invariant mass between
100 and
160 MeV
=c
2
. If several signal-side

0
candidates
are reconstructed in an event, the candidate with

in-
variant mass closest to the nominal

0
mass [4] is chosen.
We require that the events in the




and misidentified-
lepton channels contain no signal-side

0
candidates.
Events in the




and misidentified-lepton channels are
distinguished by requiring the momentum of the signal
track to be greater than
1
:
2 GeV
=c
in the former, and
less than
1
:
2 GeV
=c
in the latter.
Further requirements are made on the (total) momentum
of the signal track(s) for some channels:
p
e

<
1
:
4 GeV
=c
for
e


e


, and
p






>
1
:
0 GeV
=c
for








.
We apply constraints on the missing mass
M
miss
of the
event, which is determined by subtracting the total four-
momentum of reconstructed tracks and neutrals from that
for the


4
S

system. This quantity tends to be larger for
events with more neutrinos. Signal events must satisfy
M
miss
>
4 GeV
=c
2
for
e


e


and






,
M
miss
>
3 GeV
=c
2
for




,



0


, and misidentified lepton,
and
M
miss
>
2 GeV
=c
2
for








.
Additional kinematic constraints are applied on the



0


(








) channel, which proceeds mainly
via intermediate


(
a

1
and

0
) resonance(s). In the



0


channel the invariant mass of the



0
must be
between 0.55 and
1
:
0 GeV
=c
2
. For the








chan-
nel the invariant mass of the three-pion system is required
to be within the range
1
:
0
1
:
6 GeV
=c
2
. The




com-
bination of the three-pion system, with invariant mass
closest to the nominal

0
mass [4], is required to have
momentum greater than
0
:
5 GeV
=c
and invariant mass
between 0.55 and
1
:
0 GeV
=c
2
. We further require that
the cosine of the angle between the directions of the


and the



0
(






),
cos

;
had
2
E

E
had

m
2


m
2
had
2
j
p

j j
p
had
j
;
(3)
is within

1
:
1
;
1
:
1
. Here
E
had
,
p
had
, and
m
had
are the
energy, momentum, and invariant mass, respectively, of
the



0
(






). The energy
E

and momentum
p

BRIEF REPORTS
PHYSICAL REVIEW D
73,
057101 (2006)
057101-5
of the


from
B

!




decay are calculated under the
assumption that the
B

is at rest in the CM frame.
Continuum background events contribute to the




,
misidentified-lepton,



0


, and








channels.
To suppress this background we combine five variables in a
linear Fisher discriminant [12]:
p
D

0
,
p
,
cos

B
;
D

0
, the
cosine of the angle between the thrust axis of the decay
products of
B

sl
and the thrust axis of the rest of the event,
and the ratio of the second and zeroth Fox-Wolfram mo-
ments using all the particles in the event [13]. The require-
ment placed on the output of the Fisher discriminant selects
about 93% of signal events and rejects about 37% of
continuum background events. After this requirement the
continuum background in each channel is less than 40% of
the total background.
The sum of the laboratory-frame energies of the neutral
EMC clusters with
E

>
30 MeV
, which are not associ-
ated with either the
B

sl
or the

0
candidate from the



0


channel, is denoted by
E
extra
(Fig. 1). For signal
events the neutral clusters contributing to
E
extra
come only
from hadronic shower fragments, bremsstrahlung, and
beam-related background. This variable peaks near zero
for signal while for background, which contains additional
sources of neutral clusters, it takes on larger values. Signal
events are required to have
E
extra
less than 250 MeV for
e


e


, 150 MeV for






, 300 MeV for




,
170 MeV for misidentified lepton, 250 MeV for



0


, and 200 MeV for








, which are se-
lected based on a MC study to provide the tightest branch-
ing fraction upper limit. The
E
extra
selection region defines
the ‘‘signal region’’ for each channel. The
350
<E
extra
<
1000 MeV
region is defined as the ‘‘sideband’’ for all the
channels.
The efficiencies
"
i
for each

selection channel
i
are
determined using simulated events. Cross-feeds among the

decay channels are taken into account. The systematic
uncertainties in the selection efficiency arise from tracking
efficiency (1.4% per track), particle identification (0.2%–
2.0%),
E
extra
simulation (3.0%–8.0%),

0
reconstruction
(3.3%), and data and MC differences in the output of the
Fisher discriminant (1.0%). Systematic uncertainties due
to the
E
extra
simulation are determined by evaluating the
effect of varying the MC
E
extra
distribution within a range
representing the observed level of agreement with data in
samples containing
B

sl
and up to seven additional tracks.
For a further cross-check the
E
extra
distributions of the data
and MC events for the double semileptonic decays are
compared. The signal selection efficiencies for the six
selection channels are listed in Table I. The total
B

!




selection efficiency is roughly 31%.
The remaining background consists primarily of
B

B

events with correctly reconstructed
B

sl
. For these events
the signal side contains
K
0
L
(’s), neutrino(s), or particles that
pass outside the detector acceptance. For each channel we
estimate the background
b
i
in the signal region using
events in the data sideband and the simulated
E
extra
distri-
bution:
b
i

N
data
SideB

N
MC
SigR
=N
MC
SideB

:
(4)
Here
N
data
SideB
is the number of data events in the sideband,
and
N
MC
SigR
and
N
MC
SideB
are the numbers of MC background
events in the signal region and sideband, respectively.
Background estimation is cross-checked using data and
MC events that satisfy the full signal selection, with the
exception of having two signal-side tracks, or nonzero net
charge, or the

M
of the
D

0
outside the selection region.
The uncertainties in the background estimations are pre-
dominantly statistical; smaller systematic uncertainties
arise from the simulation of the
E
extra
shape in the back-
ground MC.
TABLE I. Efficiency (
"
i
) with statistical and systematic er-
rors, expected background (
b
i
), and observed data candidates
(
n
i
) for each reconstructed

selection channels. The cross-feeds
among the

decay modes are taken into account. The
"
i
values
include the branching fractions of the

decay modes.
Selection
"
i

%

b
i
n
i
e


e


7
:
5

0
:
4

0
:
213
:
4

2
:
4
17






2
:
9

0
:
2

0
:
16
:
2

1
:
7
5




8
:
0

0
:
4

0
:
327
:
7

5
:
0
26



0


2
:
5

0
:
2

0
:
128
:
6

4
:
3
31








1
:
4

0
:
2

0
:
121
:
6

3
:
0
26
Misidentified lepton
9
:
0

0
:
4

0
:
433
:
4

5
:
1
45
FIG. 1 (color online). The distribution of
E
extra
after applying
all other selection criteria, plotted for (a)
e


e


, (b)






,
(c)




, (d) misidentified lepton, (e)



0


, and
(f)








channels. The data and background MC samples
are represented by the points with error bars and solid histo-
grams, respectively. The dotted lines indicate the
B

!




signal distribution from MC. The signal MC events for the
e


e


,






,




, and misidentified-lepton (



0


and








) channels are normalized assuming a branching
fraction of
10

3
(
10

2
) for
B

!




decay.
BRIEF REPORTS
PHYSICAL REVIEW D
73,
057101 (2006)
057101-6