Observation of a Broad Structure in the
J= Mass Spectrum around 4:26 GeV=c
2
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
PRL 95, 142001 (2005)
PHYSICAL REVIEW LETTERS
week ending
30 SEPTEMBER 2005
0031-9007=05=95(14)=142001(7)$23.00 142001-1 © 2005 The American Physical Society
T. Allmendinger,
53
G. Benelli,
53
K. K. Gan,
53
K. Honscheid,
53
D. Hufnagel,
53
P. D. Jackson,
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H. Kagan,
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R. Kass,
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T. Pulliam,
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A. M. Rahimi,
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R. Ter-Antonyan,
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Q. K. Wong,
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J. Brau,
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R. Frey,
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O. Igonkina,
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M. Lu,
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C. T. Potter,
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N. B. Sinev,
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D. Strom,
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J. Strube,
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E. Torrence,
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F. Galeazzi,
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M. Margoni,
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M. Morandin,
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M. Posocco,
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M. Rotondo,
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F. Simonetto,
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R. Stroili,
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C. Voci,
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M. Benayoun,
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H. Briand,
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J. Chauveau,
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P. David,
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L. Del Buono,
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Ch. de la Vaissie
`
re,
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O. Hamon,
56
M. J. J. John,
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Ph. Leruste,
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J. Malcle
`
s,
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J. Ocariz,
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L. Roos,
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G. Therin,
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P. K. Behera,
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L. Gladney,
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Q. H. Guo,
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J. Panetta,
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M. Biasini,
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R. Covarelli,
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S. Pacetti,
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M. Pioppi,
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C. Angelini,
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G. Batignani,
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S. Bettarini,
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F. Bucci,
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G. Calderini,
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M. Carpinelli,
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R. Cenci,
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F. Forti,
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M. A. Giorgi,
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A. Lusiani,
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G. Marchiori,
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M. Morganti,
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N. Neri,
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E. Paoloni,
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M. Rama,
59
G. Rizzo,
59
J. Walsh,
59
M. Haire,
60
D. Judd,
60
D. E. Wagoner,
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J. Biesiada,
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N. Danielson,
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P. Elmer,
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Y. P. Lau,
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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,
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F. Ferroni,
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M. Gaspero,
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L. Li Gioi,
62
M. A. Mazzoni,
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S. Morganti,
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G. Piredda,
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F. Polci,
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F. Safai Tehrani,
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C. Voena,
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H. Schro
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G. Wagner,
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R. Waldi,
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T. Adye,
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N. De Groot,
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B. Franek,
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G. P. Gopal,
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E. O. Olaiya,
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F. F. Wilson,
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R. Aleksan,
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S. Emery,
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A. Gaidot,
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S. F. Ganzhur,
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P.-F. Giraud,
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G. Graziani,
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G. Hamel de Monchenault,
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M. Legendre,
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G. W. London,
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A. M. Boyarski,
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J. P. Coleman,
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M. R. Convery,
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M. Cristinziani,
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J. C. Dingfelder,
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D. Dong,
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J. Dorfan,
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D. Dujmic,
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W. Dunwoodie,
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S. Fan,
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R. C. Field,
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T. Glanzman,
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S. J. Gowdy,
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T. Hadig,
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V. Halyo,
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C. Hast,
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T. Hryn’ova,
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W. R. Innes,
67
M. H. Kelsey,
67
P. Kim,
67
M. L. Kocian,
67
D. W. G. S. Leith,
67
J. Libby,
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A. A. Salnikov,
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R. H. Schindler,
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J. Schwiening,
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J. Stelzer,
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D. Su,
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M. K. Sullivan,
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K. Suzuki,
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J. M. Thompson,
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J. Va’vra,
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M. Weaver,
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W. J. Wisniewski,
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M. Wittgen,
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D. H. Wright,
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A. K. Yarritu,
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K. Yi,
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C. C. Young,
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A. J. Edwards,
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S. A. Majewski,
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B. A. Petersen,
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C. Roat,
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S. Ahmed,
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M. S. Alam,
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J. A. Ernst,
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M. A. Saeed,
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F. R. Wappler,
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S. B. Zain,
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W. Bugg,
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M. Krishnamurthy,
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S. M. Spanier,
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R. Eckmann,
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J. L. Ritchie,
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A. Satpathy,
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R. F. Schwitters,
71
J. M. Izen,
72
I. Kitayama,
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X. C. Lou,
72
G. Williams,
72
S. Ye,
72
F. Bianchi,
73
M. Bona,
73
F. Gallo,
73
D. Gamba,
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M. Bomben,
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L. Bosisio,
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C. Cartaro,
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F. Cossutti,
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G. Della Ricca,
74
S. Dittongo,
74
S. Grancagnolo,
74
L. Lanceri,
74
L. Vitale,
74
F. Martinez-Vidal,
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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,
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R. J. Sobie,
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J. J. Back,
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P. F. Harrison,
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T. E. Latham,
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G. B. Mohanty,
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H. R. Band,
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X. Chen,
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B. Cheng,
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S. Dasu,
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M. Datta,
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A. M. Eichenbaum,
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K. T. Flood,
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M. Graham,
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J. J. Hollar,
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J. R. Johnson,
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P. E. Kutter,
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H. Li,
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R. Liu,
79
B. Mellado,
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A. Mihalyi,
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Y. Pan,
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R. Prepost,
79
P. Tan,
79
J. H. von Wimmersperg-Toeller,
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S. L. Wu,
79
Z. Yu,
79
and H. Neal
80
(BABAR 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
Dipartimento di Fisica and INFN, Universita
`
di Bari, I-70126 Bari, Italy
4
Institute of High Energy Physics, Beijing 100039, China
5
Institute of Physics, University of Bergen, 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
Institut fu
¨
r Experimentalphysik 1, Ruhr Universita
¨
t Bochum, D-44780 Bochum, Germany
9
University of Bristol, Bristol BS8 1TL, United Kingdom
10
University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
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
Institute for Particle Physics, University of California at Santa Cruz, Santa Cruz, California 95064, USA
19
California Institute of Technology, Pasadena, California 91125, USA
PRL 95, 142001 (2005)
PHYSICAL REVIEW LETTERS
week ending
30 SEPTEMBER 2005
142001-2
20
University of Cincinnati, Cincinnati, Ohio 45221, USA
21
University of Colorado, Boulder, Colorado 80309, USA
22
Colorado State University, Fort Collins, Colorado 80523, USA
23
Institut fu
¨
r Physik, Universita
¨
t Dortmund, D-44221 Dortmund, Germany
24
Institut fu
¨
r Kern- und Teilchenphysik, Technische Universita
¨
t Dresden, D-01062 Dresden, Germany
25
Ecole Polytechnique, LLR, F-91128 Palaiseau, France
26
University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
27
Dipartimento di Fisica and INFN, Universita
`
di Ferrara, I-44100 Ferrara, Italy
28
Laboratori Nazionali di Frascati dell’INFN, I-00044 Frascati, Italy
29
Dipartimento di Fisica and INFN, Universita
`
di Genova, I-16146 Genova, Italy
30
Harvard University, Cambridge, Massachusetts 02138, USA
31
Physikalisches Institut, Universita
¨
t Heidelberg, 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, London E1 4NS, United Kingdom
39
Royal Holloway and Bedford New College, University of London, 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
Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
45
McGill University, Montre
´
al, Quebec H3A 2T8, Canada
46
Dipartimento di Fisica and INFN, Universita
`
di Milano, I-20133 Milano, Italy
47
University of Mississippi, University, Mississippi 38677, USA
48
Laboratoire Rene
´
J. A. Le
´
vesque, Universite
´
de Montre
´
al, Montre
´
al, Quebec H3C 3J7, Canada
49
Mount Holyoke College, South Hadley, Massachusetts 01075, USA
50
Dipartimento di Scienze Fisiche and INFN, Universita
`
di Napoli Federico II, I-80126 Napoli, Italy
51
National Institute for Nuclear Physics and High Energy Physics, NIKHEF, 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
Dipartimento di Fisica and INFN, Universita
`
di Padova, I-35131 Padova, Italy
56
Laboratoire de Physique Nucle
´
aire et de Hautes Energies, Universite
´
s Paris VI et VII, F-75252 Paris, France
57
University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
58
Dipartimento di Fisica and INFN, Universita
`
di Perugia, I-06100 Perugia, Italy
59
Dipartimento di Fisica, Scuola Normale Superiore and INFN, Universita
`
di Pisa, I-56127 Pisa, Italy
60
Prairie View A&M University, Prairie View, Texas 77446, USA
61
Princeton University, Princeton, New Jersey 08544, USA
62
Dipartimento di Fisica and INFN, Universita
`
di Roma La Sapienza, 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
Dipartimento di Fisica Sperimentale and INFN, Universita
`
di Torino, I-10125 Torino, Italy
74
Dipartimento di Fisica and INFN, Universita
`
di Trieste, 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 V8W 3P6, Canada
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
PRL 95, 142001 (2005)
PHYSICAL REVIEW LETTERS
week ending
30 SEPTEMBER 2005
142001-3
(Received 28 June 2005; published 28 September 2005)
We study initial-state radiation events, e
e
!
ISR
J= , with data collected with the BABAR
detector. We observe an accumulation of events near 4:26 GeV=c
2
in the invariant-mass spectrum of
J= . Fits to the mass spectrum indicate that a broad resonance with a mass of about 4:26 GeV=c
2
is
required to describe the observed structure. The presence of additional narrow resonances cannot be
excluded. The fitted width of the broad resonance is 50 to 90 MeV=c
2
, depending on the fit hypothesis.
DOI: 10.1103/PhysRevLett.95.142001 PACS numbers: 14.40.Gx, 13.25.Gv, 13.66.Bc
Recent observations of the X3872, decaying into
J= [1– 4], and the Y3940, decaying into !J=
[5], have renewed experimental interest in charmonium
spectroscopy. We have previously reported a search for
direct X3872 production in e
e
annihilation through
initial-state radiation (ISR): e
e
!
ISR
X [6]. No signal
is observed, suggesting that the X3872 is not a 1
state,
just as expected for a narrow state well above the D
D
threshold. In this Letter, we present a study of the e
e
!
ISR
J= process across the charmonium mass
range.
We use data collected with the BABAR detector [7] at
the PEP-II asymmetric-energy e
e
storage rings, located
at the Stanford Linear Accelerator Center (SLAC). These
data represent an integrated luminosity of 211 fb
1
col-
lected at
s
p
10:58 GeV, near the peak of the 4S
resonance, plus 22 fb
1
collected approximately 40 MeV
below this energy.
Charged-particle momenta are measured in a tracking
system consisting of a five-layer double-sided silicon ver-
tex tracker (SVT) and a 40-layer central drift chamber
(DCH), both situated in a 1.5 T axial magnetic field. An
internally reflecting ring-imaging Cherenkov detector
(DIRC) with quartz bar radiators provides charged-particle
identification. A CsI electromagnetic calorimeter (EMC) is
used to detect and identify photons and electrons, while
muons are identified in the instrumented magnetic flux
return system (IFR).
Electron candidates are identified by the ratio of the
shower energy deposited in the EMC to the momentum,
the shower shape, the specific ionization in the DCH, and
the Cherenkov angle measured by the DIRC. Muons are
identified by the depth of penetration into the IFR, the IFR
cluster geometry, and the energy deposited in the EMC.
Pion candidates are selected based on a likelihood calcu-
lated from the specific ionization in the DCH and SVT, and
the Cherenkov angle measured in the DIRC. Photon can-
didates are identified with clusters in the EMC that have a
shape consistent with an electromagnetic shower but with-
out an associated charged track.
A candidate J= meson is reconstructed via its decay to
e
e
or
. The lepton tracks must be well recon-
structed, and at least one must be identified as an electron
or a muon. An algorithm to associate and combine the
energy from bremsstrahlung photons with nearby electron
tracks is used when forming a J= ! e
e
candidate. An
e
e
(
) pair with an invariant mass within
33
95
33
40
MeV=c
2
of the nominal J= mass is taken as a J=
candidate and is combined with a pair of oppositely
charged tracks that are identified as pions.
Following an observation of an enhancement in the
J= mass spectrum during an earlier search for
ISR X3872 production in a 124 fb
1
subsample of the
available data, we chose to exclude the mass region from
4.2 to 4:4 GeV=c
2
from consideration during optimization
of the selection criteria with the full sample to avoid the
introduction of statistical or other biases in the analysis of
this region. Radiative production of the 2S serves as a
clean benchmark process [8] for a data-driven optimiza-
tion. Selection criteria are chosen to maximize N=3=2
B
p
[9], where N is the total number of
ISR
2S,
2S!
J= candidates in the 20 MeV=c
2
J= mass range that brackets the 2S mass, and
B is the number of events in the
J= mass regions
3:8; 4:2 GeV=c
2
and 4:4; 4:8 GeV=c
2
, scaled to the
width of the originally observed peak. Simulated ISR
events are validated with the 2S data and are used to
extrapolate the selection criteria to the excluded mass
region as appropriate for small kinematic differences due
to the higher mass.
Radiative e
e
!
ISR
J= events are character-
ized by a small mass recoiling against the
J=
system and by low missing transverse momentum. These
properties are reflected in (1), (2), and (3) of the selection
criteria: (1) there must be no additional well-reconstructed
charged tracks in the event; (2) the transverse component
of the visible momentum in the e
e
center-of-mass
frame, including the ISR photon when it is reconstructed,
must be less than 2:5 GeV=c; (3) the inferred value of the
square of the mass recoiling against the
J= combi-
nation (m
2
Rec
) must be within 1:04; 3:27 GeV
2
=c
4
for
J= ! e
e
candidates and 1:04; 1:25 GeV
2
=c
4
for
J= !
candidates; (4) cos
‘
, where
‘
is the angle
between the ‘
momentum in the J= rest frame and the
J= momentum in the e
e
center-of-mass frame, must
satisfy jcos
‘
j < 0:90. In addition, (5) for the e
e
mode,
cos
, where
is the angle between the
momentum
and the J= momentum in the
rest frame, is re-
quired to be less than 0.90 to reject background from
misidentified low momentum e
in the forward region of
the detector. We do not require the ISR photon to be
PRL 95, 142001 (2005)
PHYSICAL REVIEW LETTERS
week ending
30 SEPTEMBER 2005
142001-4
detected in the EMC since it is produced preferentially
along the beam direction.
Candidate
‘
‘
tracks are refitted, constrained
to a common vertex, while the lepton pair is kinemati-
cally constrained to the J= mass. The resulting
J= mass-resolution function is well described by
a Cauchy distribution [10] with a full width at half maxi-
mum of 4:2 MeV=c
2
for the 2S and 5:3 MeV=c
2
at
4:3 GeV=c
2
.
The
J= invariant-mass spectrum for candidates
passing all criteria is shown in Fig. 1 as points with error
bars. Events that have an e
e
(
) mass in the J=
sidebands 2:76; 2:95 or 3:18; 3:25 (2:93; 3:01 or
3:18; 3:25) GeV=c
2
but pass all the other selection crite-
ria are represented by the shaded histogram after being
scaled by the ratio of the widths of the J= mass window
and sideband regions. An enhancement near 4:26 GeV=c
2
is clearly observed; no other structures are evident at the
masses of the quantum number J
PC
1
charmonium
states, i.e., the 4040, 4160, and 4415 [11], or the
X3872. The Fig. 1 inset includes the 2S region with a
logarithmic scale for comparison; 11 802 110 2S
events are observed, consistent with the expectation of
12 142 809 2S events. We search for sources of back-
grounds that contain a true J= and peak in the
J=
invariant-mass spectrum. The possibility that one or both
pion candidates are misidentified kaons is checked by
reconstructing the K
K
J= and K
J= final states;
we observe featureless mass spectra. Similar studies of ISR
events with a
J= candidate plus one or more addi-
tional pions reveal no structure that could feed down to
produce a peak in the
J= mass spectrum. Two-
photon events are studied directly by reversing the require-
ment on the missing mass; the number of events inferred
for the signal region is a small fraction of those observed
and their mass spectrum shows no structure. Hadronic
e
e
! q
q events produce J= at a rate that is surpris-
ingly large [12–15], but no structure is observed for this
background.
We evaluate the statistical significance of the enhance-
ment using unbinned maximum likelihood fits to the
J= mass spectrum. To evaluate the goodness of
fit, the fit probability is determined from the
2
and the
number of degrees of freedom for bin sizes of 5, 10, 20, 40,
and 50 MeV=c
2
. Bins are combined with higher mass
neighbors as needed to ensure that no bin is predicted to
have fewer than seven entries. We try first-, second-, and
third-order polynomials as null-hypothesis fit functions.
The
2
-probability estimates for these fits range from
10
16
to 10
11
. No substantial improvement is obtained
by including 4040, 4160,or 4415 [11] terms in
the fit. We conclude that the structure near 4:26 GeV=c
2
is
statistically inconsistent with a polynomial background.
Henceforth, we refer to this structure as the Y4260.
It is important to test the ISR-production hypothesis
because the J
PC
1
assignment for the Y4260 fol-
lows from it. The ISR photon is reconstructed in 24 8%
of the Y4260 events, in agreement with the 25% observed
for ISR 2Sevents. Kinematic distributions for the signal
are obtained by subtracting scaled distributions for events
with
J= mass in the regions 3:86; 4:06 GeV=c
2
and 4:46; 4:66 GeV=c
2
from those with
J= mass
in the signal region, defined as 4:16; 4:36 GeV=c
2
. The
distribution of m
2
Rec
is shown in Fig. 2, along with corre-
sponding distributions for ISR 2S data events and for
)
4
/c
2
(GeV
2
Rec
m
05
4
/c
2
Events / 0.1 GeV
-10
0
10
20
FIG. 2. The distribution of m
2
Rec
. The points represent the
data events passing all selection criteria except that on m
2
Rec
and having a
J= mass near 4260 MeV=c
2
, minus the
scaled distribution from neighboring
J= mass regions
(see text). The solid histogram represents ISR Y Monte Carlo
events, and the dotted histogram represents the ISR 2S data
events.
)
2
) (GeV/cψJ/
-
π
+
πm(
3.8 4 4.2 4.4 4.6 4.8 5
2
Events / 20 MeV/c
0
10
20
30
40
)
2
) (GeV/cψJ/
-
π
+
πm(
3.8 4 4.2 4.4 4.6 4.8 5
2
Events / 20 MeV/c
0
10
20
30
40
)
2
) (GeV/cψJ/
-
π
+
πm(
3.8 4 4.2 4.4 4.6 4.8 5
2
Events / 20 MeV/c
0
10
20
30
40
)
2
) (GeV/cψJ/
-
π
+
πm(
3.8 4 4.2 4.4 4.6 4.8 5
2
Events / 20 MeV/c
0
10
20
30
40
3.6 3.8 4 4.2 4.4 4.6 4.8 5
1
10
2
10
3
10
4
10
FIG. 1 (color online). The
J= invariant-mass spec-
trum in the range 3:8–5:0 GeV=c
2
and (inset) over a wider
range that includes the 2S. The points with error bars repre-
sent the selected data and the shaded histogram represents the
scaled data from neighboring e
e
and
mass regions
(see text). The solid curve shows the result of the single-
resonance fit described in the text; the dashed curve represents
the background component.
PRL 95, 142001 (2005)
PHYSICAL REVIEW LETTERS
week ending
30 SEPTEMBER 2005
142001-5
