of 7
V
OLUME
87, N
UMBER
16
PHYSICAL REVIEW LETTERS
15 O
CTOBER
2001
Measurement of
J



c
Production in Continuum
e
1
e
2
Annihilations near
p
p
p
s
5
10
.
6GeV
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. Palano,
2
G. P. Chen,
3
J. C. Chen,
3
N. D. Qi,
3
G. Rong,
3
P. Wang,
3
Y. S. Zhu,
3
G. Eigen,
4
P. L. Reinertsen,
4
B. Stugu,
4
B. Abbott,
5
G. S. Abrams,
5
A. W. Borgland,
5
A. B. Breon,
5
D. N. Brown,
5
J. Button-Shafer,
5
R. N. Cahn,
5
A. R. Clark,
5
Q. Fan,
5
M. S. Gill,
5
A. Gritsan,
5
Y. Groysman,
5
R. G. Jacobsen,
5
R. W. Kadel,
5
J. Kadyk,
5
L. T. Kerth,
5
S. Kluth,
5
Yu. G. Kolomensky,
5
J. F. Kral,
5
C. LeClerc,
5
M. E. Levi,
5
T. Liu,
5
G. Lynch,
5
A. B. Meyer,
5
M. Momayezi,
5
P. J. Oddone,
5
A. Perazzo,
5
M. Pripstein,
5
N. A. Roe,
5
A. Romosan,
5
M. T. Ronan,
5
V. G. Shelkov,
5
A. V. Telnov,
5
W. A. Wenzel,
5
P. G. Bright-Thomas,
6
T. J. Harrison,
6
C. M. Hawkes,
6
A. Kirk,
6
D. J. Knowles,
6
S. W. O’Neale,
6
R. C. Penny,
6
A. T. Watson,
6
N. K. Watson,
6
T. Deppermann,
7
K. Goetzen,
7
H. Koch,
7
J. Krug,
7
M. Kunze,
7
B. Lewandowski,
7
K. Peters,
7
H. Schmuecker,
7
M. Steinke,
7
J. C. Andress,
8
N. R. Barlow,
8
W. Bhimji,
8
N. Chevalier,
8
P. J. Clark,
8
W. N. Cottingham,
8
N. De Groot,
8
N. Dyce,
8
B. Foster,
8
A. Mass,
8
J. D. McFall,
8
D. Wallom,
8
F. F. Wilson,
8
K. Abe,
9
C. Hearty,
9
T. S. Mattison,
9
J. A. McKenna,
9
D. Thiessen,
9
B. Camanzi,
10
S. Jolly,
10
A. K. McKemey,
10
J. Tinslay,
10
V. E. Blinov,
11
A. D. Bukin,
11
D. A. Bukin,
11
A. R. Buzykaev,
11
M. S. Dubrovin,
11
V. B. Golubev,
11
V. N. Ivanchenko,
11
A. A. Korol,
11
E. A. Kravchenko,
11
A. P. Onuchin,
11
A. A. Salnikov,
11
S. I. Serednyakov,
11
Yu. I. Skovpen,
11
V. I. Telnov,
11
A. N. Yushkov,
11
D. Best,
12
A. J. Lankford,
12
M. Mandelkern,
12
S. McMahon,
12
D. P. Stoker,
12
A. Ahsan,
13
K. Arisaka,
13
C. Buchanan,
13
S. Chun,
13
J. G. Branson,
14
D. B. MacFarlane,
14
S. Prell,
14
Sh. Rahatlou,
14
G. Raven,
14
V. Sharma,
14
C. Campagnari,
15
B. Dahmes,
15
P. A. Hart,
15
N. Kuznetsova,
15
S. L. Levy,
15
O. Long,
15
A. Lu,
15
J. D. Richman,
15
W. Verkerke,
15
M. Witherell,
15
S. Yellin,
15
J. Beringer,
16
D. E. Dorfan,
16
A. M. Eisner,
16
A. Frey,
16
A. A. Grillo,
16
M. Grothe,
16
C. A. Heusch,
16
R. P. Johnson,
16
W. Kroeger,
16
W. S. Lockman,
16
T. Pulliam,
16
H. Sadrozinski,
16
T. Schalk,
16
R. E. Schmitz,
16
B. A. Schumm,
16
A. Seiden,
16
M. Turri,
16
W. Walkowiak,
16
D. C. Williams,
16
M. G. Wilson,
16
E. Chen,
17
G. P. Dubois-Felsmann,
17
A. Dvoretskii,
17
D. G. Hitlin,
17
S. Metzler,
17
J. Oyang,
17
F. C. Porter,
17
A. Ryd,
17
A. Samuel,
17
M. Weaver,
17
S. Yang,
17
R. Y. Zhu,
17
S. Devmal,
18
T. L. Geld,
18
S. Jayatilleke,
18
G. Mancinelli,
18
B. T. Meadows,
18
M. D. Sokoloff,
18
P. Bloom,
19
M. O. Dima,
19
S. Fahey,
19
W. T. Ford,
19
F. Gaede,
19
D. R. Johnson,
19
A. K. Michael,
19
U. Nauenberg,
19
A. Olivas,
19
H. Park,
19
P. Rankin,
19
J. Roy,
19
S. Sen,
19
J. G. Smith,
19
W. C. van Hoek,
19
D. L. Wagner,
19
J. Blouw,
20
J. L. Harton,
20
M. Krishnamurthy,
20
A. Soffer,
20
W. H. Toki,
20
R. J. Wilson,
20
J. Zhang,
20
T. Brandt,
21
J. Brose,
21
T. Colberg,
21
G. Dahlinger,
21
M. Dickopp,
21
R. S. Dubitzky,
21
E. Maly,
21
R. Müller-Pfefferkorn,
21
S. Otto,
21
K. R. Schubert,
21
R. Schwierz,
21
B. Spaan,
21
L. Wilden,
21
L. Behr,
22
D. Bernard,
22
G. R. Bonneaud,
22
F. Brochard,
22
J. Cohen-Tanugi,
22
S. Ferrag,
22
E. Roussot,
22
S. T’Jampens,
22
Ch. Thiebaux,
22
G. Vasileiadis,
22
M. Verderi,
22
A. Anjomshoaa,
23
R. Bernet,
23
A. Khan,
23
F. Muheim,
23
S. Playfer,
23
J. E. Swain,
23
M. Falbo,
24
C. Borean,
25
C. Bozzi,
25
S. Dittongo,
25
M. Folegani,
25
L. Piemontese,
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
Y. Xie,
27
A. Zallo,
27
S. Bagnasco,
28
A. Buzzo,
28
R. Contri,
28
G. Crosetti,
28
P. Fabbricatore,
28
S. Farinon,
28
M. Lo Vetere,
28
M. Macri,
28
M. R. Monge,
28
R. Musenich,
28
M. Pallavicini,
28
R. Parodi,
28
S. Passaggio,
28
F. C. Pastore,
28
C. Patrignani,
28
M. G. Pia,
28
C. Priano,
28
E. Robutti,
28
A. Santroni,
28
M. Morii,
29
R. Bartoldus,
30
T. Dignan,
30
R. Hamilton,
30
U. Mallik,
30
J. Cochran,
31
H. B. Crawley,
31
P.-A. Fischer,
31
J. Lamsa,
31
W. T. Meyer,
31
E. I. Rosenberg,
31
M. Benkebil,
32
G. Grosdidier,
32
C. Hast,
32
A. Höcker,
32
H. M. Lacker,
32
V. Lepeltier,
32
A. M. Lutz,
32
S. Plaszczynski,
32
M. H. Schune,
32
S. Trincaz-Duvoid,
32
A. Valassi,
32
G. Wormser,
32
R. M. Bionta,
33
V. Brigljevic
́
,
33
O. Fackler,
33
D. Fujino,
33
D. J. Lange,
33
M. Mugge,
33
X. Shi,
33
K. van Bibber,
33
T. J. Wenaus,
33
D. M. Wright,
33
C. R. Wuest,
33
M. Carroll,
34
J. R. Fry,
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
N. J. W. Gunawardane,
35
R. Martin,
35
J. A. Nash,
35
P. Sanders,
35
D. Smith,
35
D. E. Azzopardi,
36
J. J. Back,
36
P. Dixon,
36
P. F. Harrison,
36
R. J. L. Potter,
36
H. W. Shorthouse,
36
P. Strother,
36
P. B. Vidal,
36
M. I. Williams,
36
G. Cowan,
37
S. George,
37
M. G. Green,
37
A. Kurup,
37
C. E. Marker,
37
P. McGrath,
37
T. R. McMahon,
37
S. Ricciardi,
37
F. Salvatore,
37
I. Scott,
37
G. Vaitsas,
37
D. Brown,
38
C. L. Davis,
38
J. Allison,
39
R. J. Barlow,
39
J. T. Boyd,
39
A. C. Forti,
39
J. Fullwood,
39
F. Jackson,
39
G. D. Lafferty,
39
N. Savvas,
39
E. T. Simopoulos,
39
J. H. Weatherall,
39
A. Farbin,
40
A. Jawahery,
40
V. Lillard,
40
J. Olsen,
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
C. S. Lin,
41
T. B. Moore,
41
H. Staengle,
41
S. Willocq,
41
J. Wittlin,
41
B. Brau,
42
R. Cowan,
42
G. Sciolla,
42
F. Taylor,
42
R. K. Yamamoto,
42
D. I. Britton,
43
M. Milek,
43
P. M. Patel,
43
J. Trischuk,
43
F. Lanni,
44
F. Palombo,
44
J. M. Bauer,
45
162002-1
0031-9007

01

87(16)

162002(7)$15.00
© 2001 The American Physical Society
162002-1
V
OLUME
87, N
UMBER
16
PHYSICAL REVIEW LETTERS
15 O
CTOBER
2001
M. Booke,
45
L. Cremaldi,
45
V. Eschenburg,
45
R. Kroeger,
45
J. Reidy,
45
D. A. Sanders,
45
D. J. Summers,
45
J. P. Martin,
46
J. Y. Nief,
46
R. Seitz,
46
P. Taras,
46
V. Zacek,
46
H. Nicholson,
47
C. S. Sutton,
47
C. Cartaro,
48
N. Cavallo,
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
T. Handler,
50
J. Brau,
51
R. Frey,
51
M. Iwasaki,
51
N. B. Sinev,
51
D. Strom,
51
F. Colecchia,
52
F. Dal Corso,
52
A. Dorigo,
52
F. Galeazzi,
52
M. Margoni,
52
G. Michelon,
52
M. Morandin,
52
M. Posocco,
52
M. Rotondo,
52
F. Simonetto,
52
R. Stroili,
52
E. Torassa,
52
C. Voci,
52
M. Benayoun,
53
H. Briand,
53
J. Chauveau,
53
P. David,
53
Ch. de la Vaissi
è
re,
53
L. Del Buono,
53
O. Hamon,
53
F. Le Diberder,
53
Ph. Leruste,
53
J. Lory,
53
L. Roos,
53
J. Stark,
53
S. Versill
é
,
53
P. F. Manfredi,
54
V. Re,
54
V. Speziali,
54
E. D. Frank,
55
L. Gladney,
55
Q. H. Guo,
55
J. H. Panetta,
55
C. Angelini,
56
G. Batignani,
56
S. Bettarini,
56
M. Bondioli,
56
M. Carpinelli,
56
F. Forti,
56
M. A. Giorgi,
56
A. Lusiani,
56
F. Martinez-Vidal,
56
M. Morganti,
56
N. Neri,
56
E. Paoloni,
56
M. Rama,
56
G. Rizzo,
56
F. Sandrelli,
56
G. Simi,
56
G. Triggiani,
56
J. Walsh,
56
M. Haire,
57
D. Judd,
57
K. Paick,
57
L. Turnbull,
57
D. E. Wagoner,
57
J. Albert,
58
C. Bula,
58
P. Elmer,
58
C. Lu,
58
K. T. McDonald,
58
V. Miftakov,
58
S. F. Schaffner,
58
A. J. S. Smith,
58
A. Tumanov,
58
E. W. Varnes,
58
G. Cavoto,
59
D. del Re,
59
R. Faccini,
14,59
F. Ferrarotto,
59
F. Ferroni,
59
K. Fratini,
59
E. Lamanna,
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
R. Waldi,
60
T. Adye,
61
B. Franek,
61
N. I. Geddes,
61
G. P. Gopal,
61
S. M. Xella,
61
R. Aleksan,
62
G. De Domenico,
62
S. Emery,
62
A. Gaidot,
62
S. F. Ganzhur,
62
P.-F. Giraud,
62
G. Hamel de Monchenault,
62
W. Kozanecki,
62
M. Langer,
62
G. W. London,
62
B. Mayer,
62
B. Serfass,
62
G. Vasseur,
62
Ch. Y
è
che,
62
M. Zito,
62
N. Copty,
63
M. V. Purohit,
63
H. Singh,
63
F. X. Yumiceva,
63
I. Adam,
64
P. L. Anthony,
64
D. Aston,
64
K. Baird,
64
E. Bloom,
64
A. M. Boyarski,
64
F. Bulos,
64
G. Calderini,
64
R. Claus,
64
M. R. Convery,
64
D. P. Coupal,
64
D. H. Coward,
64
J. Dorfan,
64
M. Doser,
64
W. Dunwoodie,
64
R. C. Field,
64
T. Glanzman,
64
G. L. Godfrey,
64
S. J. Gowdy,
64
P. Grosso,
64
T. Himel,
64
M. E. Huffer,
64
W. R. Innes,
64
C. P. Jessop,
64
M. H. Kelsey,
64
P. Kim,
64
M. L. Kocian,
64
U. Langenegger,
64
D. W. G. S. Leith,
64
S. Luitz,
64
V. Luth,
64
H. L. Lynch,
64
G. Manzin,
64
H. Marsiske,
64
S. Menke,
64
R. Messner,
64
K. C. Moffeit,
64
R. Mount,
64
D. R. Muller,
64
C. P. O
Grady,
64
M. Perl,
64
S. Petrak,
64
H. Quinn,
64
B. N. Ratcliff,
64
S. H. Robertson,
64
L. S. Rochester,
64
A. Roodman,
64
T. Schietinger,
64
R. H. Schindler,
64
J. Schwiening,
64
V. V. Serbo,
64
A. Snyder,
64
A. Soha,
64
S. M. Spanier,
64
A. Stahl,
64
J. Stelzer,
64
D. Su,
64
M. K. Sullivan,
64
M. Talby,
64
H. A. Tanaka,
64
A. Trunov,
64
J. Va
vra,
64
S. R. Wagner,
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
D. Kirkby,
65
T. I. Meyer,
65
C. Roat,
65
R. Henderson,
66
W. Bugg,
67
H. Cohn,
67
E. Hart,
67
A. W. Weidemann,
67
T. Benninger,
68
J. M. Izen,
68
I. Kitayama,
68
X. C. Lou,
68
M. Turcotte,
68
F. Bianchi,
69
M. Bona,
69
B. Di Girolamo,
69
D. Gamba,
69
A. Smol,
69
D. Zanin,
69
L. Lanceri,
70
A. Pompili,
70
G. Vuagnin,
70
R. S. Panvini,
71
C. M. Brown,
72
A. De Silva,
72
R. Kowalewski,
72
J. M. Roney,
72
H. R. Band,
73
E. Charles,
73
S. Dasu,
73
F. Di Lodovico,
73
A. M. Eichenbaum,
73
H. Hu,
73
J. R. Johnson,
73
R. Liu,
73
J. Nielsen,
73
W. Orejudos,
73
Y. Pan,
73
R. Prepost,
73
I. J. Scott,
73
S. J. Sekula,
73
J. H. von Wimmersperg-Toeller,
73
S. L. Wu,
73
Z. Yu,
73
H. Zobernig,
73
T. M. B. Kordich,
74
and H. Neal
74
(The
BABAR
Collaboration)
1
Laboratoire de Physique des Particules, F-74941 Annecy-le-Vieux, France
2
Università 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 Universität Bochum, Institut für 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 Universität Dresden, Institut für Kern-und Teilchenphysik, D-01062 Dresden, Germany
22
Ecole Polytechnique, F-91128 Palaiseau, France
23
University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
162002-2
162002-2
V
OLUME
87, N
UMBER
16
PHYSICAL REVIEW LETTERS
15 O
CTOBER
2001
24
Elon College, Elon College, North Carolina 27244-2010
25
Universit
à
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
Universit
à
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
Acc
é
l
é
rateur Lin
é
aire, F-91898 Orsay, France
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, 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, Montr
é
al, Quebec, Canada H3A 2T8
44
Universit
à
di Milano, Dipartimento di Fisica and INFN, I-20133 Milano, Italy
45
University of Mississippi, University, Misssissippi 38677
46
Universit
é
de Montreal, Laboratoire Ren
é
J. A. Levesque, Montr
é
al, Quebec, Canada H3C 3J7
47
Mount Holyoke College, South Hadley, Massachusetts 01075
48
Universit
à
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
Universit
à
di Padova, Dipartimento di Fisica and INFN, I-35131 Padova, Italy
53
Universit
é
s Paris VI et VII, LPNHE, F-75252 Paris, France
54
Universit
à
di Pavia, Dipartimento di Elettronica and INFN, I-27100 Pavia, Italy
55
University of Pennsylvania, Philadelphia, Pennsylvania 19104
56
Universit
à
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
Universit
à
di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy
60
Universit
ä
t Rostock, D-18051 Rostock, Germany
61
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom
62
DAPNIA, Commissariat
à
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
Universit
à
di Torino, Dipartimento di Fiscia Sperimentale and INFN, I-10125 Torino, Italy
70
Universit
à
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 8 June 2001; published 27 September 2001)
The production of
J

c
mesons in continuum
e
1
e
2
annihilations has been studied with the
BA BA R
de-
tector at energies near the
Y

4
S

resonance. The mesons are distinguished from
J

c
production in
B
de-
cays through their center-of-mass momentum and energy. We measure the cross section
e
1
e
2
!
J

c
X
to be
2.52
6
0.21
6
0.21
pb. We set a
90%
C.L. upper limit on the branching fraction for direct
Y

4
S

!
J

c
X
decays at
4.7
3
10
2
4
.
DOI: 10.1103/PhysRevLett.87.162002
PACS numbers: 13.65. +i, 12.38.Qk, 13.25.Gv, 14.40.Gx
The development of nonrelativistic QCD (NRQCD) rep-
resents a signi
fi
cant advance in the theory of the produc-
tion of heavy quarkonium (
q
̄
q
) states [1]. In particular,
it provides an explanation [2] for the cross section for
162002-3
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c

2
S

production observed by CDF [3], which is a fac-
tor of 30 larger than expected from previous models. The
enhancement is attributed to the production of a
c
̄
c
pair
in a color octet state, which then evolves into the charmo-
nium (
c
̄
c
) meson along with other light hadrons. A similar
contribution is expected in NRQCD for
J

c
production in
e
1
e
2
annihilation [4,5], but is absent in the color singlet
model [6].
Signi
fi
cant continuum
J

c
production
as distinct
from production in
B
decay at the
Y

4
S

resonance
has
not been observed previously in
e
1
e
2
annihilation below
the
Z
resonance. It therefore represents a good test of
NRQCD. In particular, matrix elements extracted from
different
J

c
production processes should be consistent
[7]. In addition, momentum, polarization, and particularly
the angular distributions of the
J

c
distinguish between
theoretical approaches [8]. Despite NRQCD
s successes,
it is not clear whether it correctly explains [9] the CDF
measurements of
J

c
polarization [10], or measurements
of
J

c
photoproduction at HERA [11,12].
The study reported here uses
20.7
fb
2
1
of data col-
lected at the
Y

4
S

resonance (10.58 GeV) and
2.59
fb
2
1
collected at 10.54 GeV, below the threshold for the
B
̄
B
creation. The luminosity-weighted center-of-mass (c.m.)
energy is 10.57 GeV.
The data were collected with the
BABAR
detector [13]
located at the PEP-II collider at the Stanford Linear Ac-
celerator Center. PEP-II collides 9 GeV electrons with
3.1 GeV positrons to create a center of mass moving along
the
z
axis with a Lorentz boost of
bg

0.56
.
The momenta and trajectories of charged particles are
reconstructed with two detector systems located in a 1.5-T
solenoidal magnetic
fi
eld: a
fi
ve-layer, double-sided sili-
con vertex tracker (SVT) and a 40-layer drift chamber
(DCH). The
fi
ducial volume covers the polar angular re-
gion
0.41
,u,
2.54
rad, 86% of the solid angle in the
c.m. frame.
The energies of electrons and photons are measured in a
CsI(Tl) electromagnetic calorimeter (EMC) in the
fi
ducial
volume
0.41
,u,
2.41
rad, 84% of the solid angle in the
c.m. frame. The instrumented
fl
ux return is used to detect
muons. The DIRC, a unique Cherenkov radiation detection
device, distinguishes charged particles of different masses.
J

c
mesons are reconstructed via decays to electron
or muon pairs.
The leptons must form high-quality
tracks with
0.41
,u,
2.41
rad:
they must have
p
t
.
0.1
GeV

c
and momentum below
10
GeV

c
, have
at least 12 hits in the DCH, and approach within 10 cm
of the beam spot in
z
and within 1.5 cm of the beam line.
The beam spot rms size is approximately 0.9 cm in
z
,
120
m
m horizontally and 5.6
m
m vertically.
One electron candidate must have an energy deposit in
the EMC of at least 75% of its momentum. The other
must have between 89% and 120%, and must also have an
energy deposition in the DCH and a signal in the DIRC
consistent with expectations for an electron. Both must
satisfy criteria on the shape of the EMC deposit. If pos-
sible, photons radiated by electrons traversing material
prior to the DCH are combined with the track.
Muon candidates must deposit less than 0.5 GeV in the
EMC (2.3 times the minimum-ionizing peak), penetrate
at least two interaction lengths
l
of material, and have
a pattern of hits consistent with the trajectory of a muon.
We require that the material traversed by one candidate
be within 1
l
of that expected for a muon; for the other
candidate, this is relaxed to 2
l
.
The mass of the
J

c
candidate is calculated after con-
straining the two lepton candidates to a common origin.
To reject interactions with residual gas in the beam pipe
or with the beam pipe wall, we construct an event vertex
using all tracks in the
fi
ducial volume and require it to
be located within 6 cm of the beam spot in
z
and within
0.5 cm of the beam line. To suppress a substantial back-
ground from radiative Bhabha

e
1
e
2
g

events in which
the photon converts to an
e
1
e
2
pair,
fi
ve tracks are re-
quired in events with a
J

c
!
e
1
e
2
candidate.
At this point, the data include
J

c
mesons both from
our signal
continuum-produced
J

c
mesons and
J

c
mesons from the decay of continuum-produced
c

2
S

and
x
cJ
mesons
and from other known sources. We apply
additional selection criteria to suppress these other sources
based on their kinematic properties.
The most copious background,
B
!
J

c
X
, is elimi-
nated by requiring the
J

c
momentum in the c.m. frame

p


to be greater than
2
GeV

c
, above the kinematic
limit for
B
decays. This requirement is dropped for data
recorded below the
Y

4
S

resonance.
Other background sources include initial-state radiation
(ISR) production of
J

c
mesons,
e
1
e
2
!
g
J

c
,or
of the
c

2
S

, with
c

2
S

!
J

c
X
.
ISR production
of lower-mass
Y
resonances is negligible.
Two pho-
ton production of the
x
c
2
can produce
J

c
mesons
via
x
c
2
!
g
J

c
. Because the out-going electron and
positron are rarely reconstructed, this process, similar
to the ISR
J

c
production, contains only two tracks.
We therefore require three high-quality tracks with
0.41
,u,
2.54
rad.
The remaining background is primarily ISR
c

2
S

de-
cays to
J

cp
1
p
2
, plus some ISR
J

c
events in which
the ISR photon converts. To suppress these, we require the
visible energy
E
to be greater than 5 GeV, and the ratio of
the second to the zeroth Fox-Wolfram moment [14],
R
2
,
to be less than 0.5. Both are calculated from tracks and
neutral clusters in the
fi
ducial volume. Figure 1, which
displays the visible energy and
R
2
distributions for our
signal and for simulated ISR background, motivates these
criteria.
The ISR distributions in Fig. 1 are obtained from a full
detector simulation. All selection criteria are applied, other
than the one on the quantity being plotted. ISR kinemat-
ics ensures
E
,
5
GeV when the photon is outside the
fi
ducial volume unless it interacts in material and deposits
additional energy in the detector. The rate of such inter-
actions is not accurately simulated and so is obtained by a
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FIG. 1.
J

c
signal events observed as a function of visible
energy
E
in the (a)
e
1
e
2
and (b)
m
1
m
2
fi
nal states;
R
2
dis-
tribution for (c)
e
1
e
2
and (d)
m
1
m
2
. The histogram is the
predicted ISR background that has been subtracted from data;
the
fi
lled histogram is the ISR component only. A requirement
of
$
5
tracks is applied to the
e
1
e
2
sample; applying it to the
m
1
m
2
sample produces the dashed histogram. Event preselec-
tion requires
E
.
4
GeV and
R
2
,
0.95
.
comparison to data for
E
,
5
GeV. Approximately 3.5%
of the
J

c
meson events that satisfy all criteria are from
this background; an additional

1.6%
are ISR events with
the photon in the
fi
ducial volume. Systematic errors on
the remaining backgrounds are estimated from a compari-
son between simulation and data for
E
,
5
GeV and for
events in which the ISR photon is reconstructed.
J

c
production as a function of
E
is obtained in the
data by
fi
tting the dilepton mass distribution in 1-GeV
wide energy intervals after applying all other selection cri-
teria. The
fi
t uses a polynomial function for the back-
ground distribution. The
J

c
mass function is obtained
from a complete simulation of
B
!
J

c
X
events, con-
volved with a Gaussian distribution to match the resolution
of
12
MeV

c
2
observed in data in a sample of approxi-
mately
14000
B
!
J

c
X
events. The signal distribution
in
E
is obtained by subtracting the ISR backgrounds from
the data distribution.
A similar process is used for
R
2
. Figures 1(c) and 1(d)
show there is little signal above
R
2
of 0.5. In this respect,
the continuum
J

c
events are more similar to
B
̄
B
events,
in which the energy is distributed spherically, than
c
̄
c
events, which tend to be jetlike.
The mass distributions of the selected
J

c
candidates
show clear signals for both
e
1
e
2
and
m
1
m
2
fi
nal states,
both on and below resonance (Fig. 2).
To determine the production cross section, we perform
mass
fi
ts in
15
p

- cos
u

bins, where
u

is the polar angle of
the candidate in the c.m. frame. This allows us to correct
(a)
121
±
26 J/
ψ
Entries / 10 MeV/c
2
(b)
156
±
25 J/
ψ
e
+
e
-
Mass (GeV/c
2
)
(c)
799
±
62 J/
ψ
(d)
879
±
52 J/
ψ
μ
+
μ
-
Mass (GeV/c
2
)
0
50
100
0
200
400
2.5
3
3
3.25
FIG. 2. Mass distribution of
J

c
candidates reconstructed in
data recorded below the
Y

4
S

resonance in the (a)
e
1
e
2
and
(b)
m
1
m
2
fi
nal states. Mass distributions for
p

.
2
GeV

c
in data at the
Y

4
S

resonance in (c)
e
1
e
2
and (d)
m
1
m
2
fi
nal
states. The number of
J

c
mesons extracted by a
fi
t to the
distribution is shown on each graph.
for the variation of ef
fi
ciency with
p

and cos
u

. The cross
section is given by
s
e
1
e
2
!
J

c
X

X
i
,
j

N
ij
2
B
ij

e
R
ij
?e
E
?
B
J

c
!

1

2
?
L
i
,
(1)
where the sum is over three
p


i

and
fi
ve cos
u


j

bins.
N
ij
is the number of
J

c
mesons in the bin, where
electrons and muons are analyzed separately, but off-
and on-resonance data are combined. The sum of the
yields from the 15
fi
ts agrees to within 1% with the yields
in Fig. 2.
B
ij
is the ISR background,
B
J

c
!

1

2
is the
J

c
!
e
1
e
2
or
m
1
m
2
branching fraction [15], and
L
i
is the integrated luminosity
sum of on plus off res-
onance for
p

.
2
GeV

c
, off resonance only for
p

,
2
GeV

c
.
The reconstruction ef
fi
ciency
e
R
ij
(acceptance, track
quality, and lepton identi
fi
cation) is calculated in each
bin with simulated unpolarized
J

c
mesons uniformly
distributed in
p

and cos
u

. The ef
fi
ciency decreases with
increasing
p

and cos
u

due to acceptance. The average
e
R
ij
is 0.63 for
J

c
!
e
1
e
2
and 0.48 for
J

c
!
m
1
m
2
,
where the difference is due to lepton identi
fi
cation.
Particle identi
fi
cation ef
fi
ciency is veri
fi
ed in data by
comparing the number of
J

c
mesons in
B
decays in
which one or both leptons satisfy the requirements. The
ef
fi
ciency of the track-quality selection is studied by com-
paring tracks found in the SVT and DCH.
The components of
e
E
, the event selection ef
fi
ciency,
are determined as follows. We estimate the ef
fi
ciency of
the requirements on the number of high-quality tracks,
primary vertex location, and total energy to be the average
of simulated
c
̄
c
and
B
̄
B
events, and the uncertainty to be
one-half the difference. We use
B
̄
B
events for
R
2
.
The ef
fi
ciency of the
fi
ve track requirement applied to
e
1
e
2
candidates is 0.67, obtained by comparing the net
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J

c
yield, in both
e
1
e
2
and
m
1
m
2
fi
nal states, in events
passing and failing the requirement. Overall,
e
E

0.59
for
e
1
e
2
and 0.89 for
m
1
m
2
.
The calculations of the
J

c
X
cross section from the
e
1
e
2
and
m
1
m
2
fi
nal states are consistent: the ratio
s

m
1
m
2

s

e
1
e
2

is
0.93
6
0.11
for
p

.
2
GeV

c
.
The two values are combined, accounting for common sys-
tematic errors, to obtain
s
e
1
e
2
!
J

c
X

2.52
6
0.21
6
0.21
pb
,
(2)
where the
fi
rst error is statistical and the second system-
atic. With existing values for matrix elements, color singlet
cross section estimates range from 0.45 to 0.81 pb [4
6],
while NRQCD cross sections, including a color octet com-
ponent, range from 1.1 to 1.6 pb [4,5].
The dominant component of the 8.3% systematic error
is a 7.2% uncertainty on
e
E
common to both the
e
1
e
2
and
m
1
m
2
cases and a 4.9% uncertainty due to the
fi
ve track
requirement. Other contributions include 2.4% due to track
quality cuts; 1.5% from the luminosity; 1.8% (electrons) or
1.4% (muons) from particle identi
fi
cation; and 1.2% from
the ISR background.
The statistical error is dominated by the uncertainty
on the contribution below
p

of
2
GeV

c
. Restricting
the measurement to
p

.
2
GeV

c
gives
s
e
1
e
2
!
J

c
X

1.87
6
0.10
6
0.15
pb.
In determining the cross sections, we assume that
there are no
J

c
mesons from direct
Y

4
S

decays.
We quantify this statement using the
p

.
2
GeV

c
component. We scale the off-resonance event yield to the
on-resonance luminosity and subtract it from the
on-resonance yield. The excess, attributable to
Y

4
S

decays, is consistent with zero:
2
120
6
179
e
1
e
2
events and
176
6
138
m
1
m
2
, in a sample of

22.7
6
0.4

3
10
6
Y

4
S

decays.
Using the average recon-
struction
ef
fi
ciency
for
p

.
2
GeV

c
(0.62
for
e
1
e
2
and 0.45 for
m
1
m
2
), we obtain
B
Y

4
S

!
J

c
X


1.5
6
2.2
6
0.1

3
10
2
4
. A Bayesian 90% con
fi
dence
level upper limit with a uniform prior above zero is
B
Y

4
S

!
J

c
X
,
4.7
3
10
2
4

90%
C.L.

,
(3)
for
J

c
with
p

.
2
GeV

c
. This result disagrees with a
previous publication [16]. In NRQCD, the expected par-
tial width is similar to that for the
Y

1
S

[5,17], implying
a branching fraction of a few
3
10
2
6
. Note that a true
branching fraction of
10
2
4
would correspond to an effec-
tive cross section of 0.10 pb.
Production and decay properties of the
J

c
have also
been studied. The
p

distribution is obtained by dividing
the sample into
500
MeV

c
wide intervals,
fi
tting the re-
sulting mass distribution, subtracting predicted ISR back-
grounds, correcting for the reconstruction ef
fi
ciency, and
normalizing for different luminosities (Fig. 3).
The distribution of the signal in cos
u

has been extracted
and
fi
t with
1
1
A
?
cos
2
u

. Both NRQCD and color sin-
glet calculations predict a
fl
at distribution

A

0

at low
p

. At high momentum, NRQCD predicts
0.6
,
A
,
1.0
p* (GeV/c)
Entries / 500 MeV/c
0
500
1000
012345
FIG. 3. Center-of-mass
momentum distribution of
J

c
mesons produced in continuum
e
1
e
2
annihilation.
while the color singlet model predicts
A

2
0.8
[8]. We
measure the distribution separately for low and high mo-
mentum mesons, selecting
p


3.5
GeV

c
as the bound-
ary. We proceed as for the
p

distribution, with mass
fi
ts performed in cos
u

intervals of width 0.4. The dis-
tributions are then normalized to the unit area [Fig. 4(a)].
We
fi
nd
A

0.05
6
0.22
for
p

,
3.5
GeV

c
and
A

1.5
6
0.6
for
p

.
3.5
GeV

c
, clearly favoring NRQCD.
Finally, we obtain the helicity angle
u
H
distribution for
the two
p

ranges by
fi
tting mass distributions in intervals
of width 0.4 in cos
u
H
[Fig. 4(b)]. The helicity is the angle,
measured in the rest frame of the
J

c
, between the posi-
tively charged lepton daughter and the direction of the
J

c
measured in the c.m. frame. Fitting the function
3

1
1
a
cos
2
u
H

2

a1
3

, we obtain a
J

c
polarization
a

2
0.46
6
0.21
for
p

,
3.5
GeV

c
and
a

2
0.80
6
0.09
for
p

.
3.5
GeV

c
.
a

0
indicates an unpolar-
ized distribution,
a

1
transversely polarized, and
a

2
1
longitudinally polarized.
In
summary,
we
measure
the
cross
section
s
e
1
e
2
!
J

c
X

2.52
6
0.21
6
0.21
pb.
Restricting to
p

.
2
GeV

c
,we
fi
nd
1.87
6
0.10
6
0.15
pb.
The
total cross section and the angular distribution favor the
NRQCD calculation over the color singlet model. We
set a 90% C.L. upper limit on the branching fraction
Y

4
S

!
J

c
X
of
4.7
3
10
2
4
.
We are grateful for the excellent luminosity and ma-
chine conditions provided by our PEP-II colleagues. The
Signal / 0.4
p*
<
3.5 GeV/c
p*
>
3.5 GeV/c
(a)
cos
θ
(b)
0.1
0.2
0.3
0.1
0.2
0.3
0.4
-1
-0.5
0
0.5
1
FIG. 4. (a) Production angle (cos
u

) distribution for
J

c
mesons produced in continuum
e
1
e
2
annihilation; (b) helicity
(cos
u
H
) distribution. Solid curve is the
fi
tto
p

,
3.5
GeV

c
;
dashed curve is for
p

.
3.5
GeV

c
.
162002-6
162002-6
V
OLUME
87, N
UMBER
16
PHYSICAL REVIEW LETTERS
15 O
CTOBER
2001
collaborating institutions wish to thank SLAC for its sup-
port and kind hospitality. This work is supported by DOE
and NSF (U.S.A.), NSERC (Canada), IHEP (China), CEA
and CNRS-IN2P3 (France), BMBF (Germany), INFN
(Italy), NFR (Norway), MIST (Russia), and PPARC
(United Kingdom).
Individuals have received support
from the Swiss NSF, A. P. Sloan Foundation, Research
Corporation, and Alexander von Humboldt Foundation.
*Also with Universit
à
di Perugia, Perugia, Italy.
Also with Universit
à
della Basilicata, Potenza, Italy.
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