of 13
Exclusive initial-state-radiation production of the
D

D
,
D


D
, and
D


D

systems
B. Aubert,
1
Y. Karyotakis,
1
J. P. Lees,
1
V. Poireau,
1
E. Prencipe,
1
X. Prudent,
1
V. Tisserand,
1
J. Garra Tico,
2
E. Grauges,
2
L. Lopez,
3a,3b
A. Palano,
3a,3b
M. Pappagallo,
3a,3b
G. Eigen,
4
B. Stugu,
4
L. Sun,
4
M. Battaglia,
5
D. N. Brown,
5
L. T. Kerth,
5
Yu. G. Kolomensky,
5
G. Lynch,
5
I. L. Osipenkov,
5
K. Tackmann,
5
T. Tanabe,
5
C. M. Hawkes,
6
N. Soni,
6
A. T. Watson,
6
H. Koch,
7
T. Schroeder,
7
D. J. Asgeirsson,
8
B. G. Fulsom,
8
C. Hearty,
8
T. S. Mattison,
8
J. A. McKenna,
8
M. Barrett,
9
A. Khan,
9
A. Randle-Conde,
9
V. E. Blinov,
10
A. D. Bukin,
10
A. R. Buzykaev,
10
V. P. Druzhinin,
10
V. B. Golubev,
10
A. P. Onuchin,
10
S. I. Serednyakov,
10
Yu. I. Skovpen,
10
E. P. Solodov,
10
K. Yu. Todyshev,
10
M. Bondioli,
11
S. Curry,
11
I. Eschrich,
11
D. Kirkby,
11
A. J. Lankford,
11
P. Lund,
11
M. Mandelkern,
11
E. C. Martin,
11
D. P. Stoker,
11
S. Abachi,
12
C. Buchanan,
12
H. Atmacan,
13
J. W. Gary,
13
F. Liu,
13
O. Long,
13
G. M. Vitug,
13
Z. Yasin,
13
L. Zhang,
13
V. Sharma,
14
C. Campagnari,
15
T. M. Hong,
15
D. Kovalskyi,
15
M. A. Mazur,
15
J. D. Richman,
15
T. W. Beck,
16
A. M. Eisner,
16
C. A. Heusch,
16
J. Kroseberg,
16
W. S. Lockman,
16
A. J. Martinez,
16
T. Schalk,
16
B. A. Schumm,
16
A. Seiden,
16
L. O. Winstrom,
16
C. H. Cheng,
17
D. A. Doll,
17
B. Echenard,
17
F. Fang,
17
D. G. Hitlin,
17
I. Narsky,
17
T. Piatenko,
17
F. C. Porter,
17
R. Andreassen,
18
G. Mancinelli,
18
B. T. Meadows,
18
K. Mishra,
18
M. D. Sokoloff,
18
P. C. Bloom,
19
W. T. Ford,
19
A. Gaz,
19
J. F. Hirschauer,
19
M. Nagel,
19
U. Nauenberg,
19
J. G. Smith,
19
S. R. Wagner,
19
R. Ayad,
20,
*
A. Soffer,
20,
W. H. Toki,
20
R. J. Wilson,
20
E. Feltresi,
21
A. Hauke,
21
H. Jasper,
21
M. Karbach,
21
J. Merkel,
21
A. Petzold,
21
B. Spaan,
21
K. Wacker,
21
M. J. Kobel,
22
R. Nogowski,
22
K. R. Schubert,
22
R. Schwierz,
22
A. Volk,
22
D. Bernard,
23
G. R. Bonneaud,
23
E. Latour,
23
M. Verderi,
23
P. J. Clark,
24
S. Playfer,
24
J. E. Watson,
24
M. Andreotti,
25a,25b
D. Bettoni,
25a
C. Bozzi,
25a
R. Calabrese,
25a,25b
A. Cecchi,
25a,25b
G. Cibinetto,
25a,25b
P. Franchini,
25a,25b
E. Luppi,
25a,25b
M. Negrini,
25a,25b
A. Petrella,
25a,25b
L. Piemontese,
25a
V. Santoro,
25a,25b
R. Baldini-Ferroli,
26
A. Calcaterra,
26
R. de Sangro,
26
G. Finocchiaro,
26
S. Pacetti,
26
P. Patteri,
26
I. M. Peruzzi,
26,
M. Piccolo,
26
M. Rama,
26
A. Zallo,
26
R. Contri,
27a,27b
E. Guido, M. Lo Vetere,
27a,27b
M. R. Monge,
27a,27b
S. Passaggio,
27a
C. Patrignani,
27a,27b
E. Robutti,
27a
S. Tosi,
27a,27b
K. S. Chaisanguanthum,
28
M. Morii,
28
A. Adametz,
29
J. Marks,
29
S. Schenk,
29
U. Uwer,
29
F. U. Bernlochner,
30
V. Klose,
30
H. M. Lacker,
30
D. J. Bard,
31
P. D. Dauncey,
31
M. Tibbetts,
31
P. K. Behera,
32
X. Chai,
32
M. J. Charles,
32
U. Mallik,
32
J. Cochran,
33
H. B. Crawley,
33
L. Dong,
33
W. T. Meyer,
33
S. Prell,
33
E. I. Rosenberg,
33
A. E. Rubin,
33
Y. Y. Gao,
34
A. V. Gritsan,
34
Z. J. Guo,
34
N. Arnaud,
35
J. Be
́
quilleux,
35
A. D’Orazio,
35
M. Davier,
35
J. Firmino da Costa,
35
G. Grosdidier,
35
F. Le Diberder,
35
V. Lepeltier,
35
A. M. Lutz,
35
S. Pruvot,
35
P. Roudeau,
35
M. H. Schune,
35
J. Serrano,
35
V. Sordini,
35,
x
A. Stocchi,
35
G. Wormser,
35
D. J. Lange,
36
D. M. Wright,
36
I. Bingham,
37
J. P. Burke,
37
C. A. Chavez,
37
J. R. Fry,
37
E. Gabathuler,
37
R. Gamet,
37
D. E. Hutchcroft,
37
D. J. Payne,
37
C. Touramanis,
37
A. J. Bevan,
38
C. K. Clarke,
38
F. Di Lodovico,
38
R. Sacco,
38
M. Sigamani,
38
G. Cowan,
39
S. Paramesvaran,
39
A. C. Wren,
39
D. N. Brown,
40
C. L. Davis,
40
A. G. Denig,
41
M. Fritsch,
41
W. Gradl,
41
A. Hafner,
41
K. E. Alwyn,
42
D. Bailey,
42
R. J. Barlow,
42
G. Jackson,
42
G. D. Lafferty,
42
T. J. West,
42
J. I. Yi,
42
J. Anderson,
43
C. Chen,
43
A. Jawahery,
43
D. A. Roberts,
43
G. Simi,
43
J. M. Tuggle,
43
C. Dallapiccola,
44
E. Salvati,
44
S. Saremi,
44
R. Cowan,
45
D. Dujmic,
45
P. H. Fisher,
45
S. W. Henderson,
45
G. Sciolla,
45
M. Spitznagel,
45
R. K. Yamamoto,
45
M. Zhao,
45
P. M. Patel,
46
S. H. Robertson,
46
M. Schram,
46
A. Lazzaro,
47a,47b
V. Lombardo,
47a
F. Palombo,
47a,47b
S. Stracka, J. M. Bauer,
48
L. Cremaldi,
48
R. Godang,
48,
k
R. Kroeger,
48
D. J. Summers,
48
H. W. Zhao,
48
M. Simard,
49
P. Taras,
49
H. Nicholson,
50
G. De Nardo,
51a,51b
L. Lista,
51a
D. Monorchio,
51a,51b
G. Onorato,
51a,51b
C. Sciacca,
51a,51b
G. Raven,
52
H. L. Snoek,
52
C. P. Jessop,
53
K. J. Knoepfel,
53
J. M. LoSecco,
53
W. F. Wang,
53
L. A. Corwin,
54
K. Honscheid,
54
H. Kagan,
54
R. Kass,
54
J. P. Morris,
54
A. M. Rahimi,
54
J. J. Regensburger,
54
S. J. Sekula,
54
Q. K. Wong,
54
N. L. Blount,
55
J. Brau,
55
R. Frey,
55
O. Igonkina,
55
J. A. Kolb,
55
M. Lu,
55
R. Rahmat,
55
N. B. Sinev,
55
D. Strom,
55
J. Strube,
55
E. Torrence,
55
G. Castelli,
56a,56b
N. Gagliardi,
56a,56b
M. Margoni,
56a,56b
M. Morandin,
56a
M. Posocco,
56a
M. Rotondo,
56a
F. Simonetto,
56a,56b
R. Stroili,
56a,56b
C. Voci,
56a,56b
P. del Amo Sanchez,
57
E. Ben-Haim,
57
H. Briand,
57
J. Chauveau,
57
O. Hamon,
57
Ph. Leruste,
57
J. Ocariz,
57
A. Perez,
57
J. Prendki,
57
S. Sitt,
57
L. Gladney,
58
M. Biasini,
59a,59b
E. Manoni,
59a,59b
C. Angelini,
60a,60b
G. Batignani,
60a,60b
S. Bettarini,
60a,60b
G. Calderini,
60a,60b,
{
M. Carpinelli,
60a,60b,
**
A. Cervelli,
60a,60b
F. Forti,
60a,60b
M. A. Giorgi,
60a,60b
A. Lusiani,
60a,60c
G. Marchiori,
60a,60b
M. Morganti,
60a,60b
N. Neri,
60a,60b
E. Paoloni,
60a,60b
G. Rizzo,
60a,60b
J. J. Walsh,
60a
D. Lopes Pegna,
61
C. Lu,
61
J. Olsen,
61
A. J. S. Smith,
61
A. V. Telnov,
61
F. Anulli,
62a
E. Baracchini,
62a,62b
G. Cavoto,
62a
R. Faccini,
62a,62b
F. Ferrarotto,
62a
F. Ferroni,
62a,62b
M. Gaspero,
62a,62b
P. D. Jackson,
62a
L. Li Gioi,
62a
M. A. Mazzoni,
62a
S. Morganti,
62a
G. Piredda,
62a
F. Renga,
62a,62b
C. Voena,
62a
M. Ebert,
63
T. Hartmann,
63
H. Schro
̈
der,
63
R. Waldi,
63
T. Adye,
64
B. Franek,
64
E. O. Olaiya,
64
F. F. Wilson,
64
S. Emery,
65
L. Esteve,
65
G. Hamel de Monchenault,
65
W. Kozanecki,
65
G. Vasseur,
65
Ch. Ye
`
che,
65
M. Zito,
65
X. R. Chen,
66
H. Liu,
66
W. Park,
66
M. V. Purohit,
66
R. M. White,
66
J. R. Wilson,
66
M. T. Allen,
67
D. Aston,
67
R. Bartoldus,
67
J. F. Benitez,
67
R. Cenci,
67
J. P. Coleman,
67
M. R. Convery,
67
J. C. Dingfelder,
67
J. Dorfan,
67
PHYSICAL REVIEW D
79,
092001 (2009)
1550-7998
=
2009
=
79(9)
=
092001(13)
092001-1
Ó
2009 The American Physical Society
G. P. Dubois-Felsmann,
67
W. Dunwoodie,
67
R. C. Field,
67
A. M. Gabareen,
67
M. T. Graham,
67
P. Grenier,
67
C. Hast,
67
W. R. Innes,
67
J. Kaminski,
67
M. H. Kelsey,
67
H. Kim,
67
P. Kim,
67
M. L. Kocian,
67
D. W. G. S. Leith,
67
S. Li,
67
B. Lindquist,
67
S. Luitz,
67
V. Luth,
67
H. L. Lynch,
67
D. B. MacFarlane,
67
H. Marsiske,
67
R. Messner,
67
D. R. Muller,
67
H. Neal,
67
S. Nelson,
67
C. P. O’Grady,
67
I. Ofte,
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
D. Su,
67
M. K. Sullivan,
67
K. Suzuki,
67
S. K. Swain,
67
J. M. Thompson,
67
J. Va’vra,
67
A. P. Wagner,
67
M. Weaver,
67
C. A. West,
67
W. J. Wisniewski,
67
M. Wittgen,
67
D. H. Wright,
67
H. W. Wulsin,
67
A. K. Yarritu,
67
K. Yi,
67
C. C. Young,
67
V. Ziegler,
67
P. R. Burchat,
68
A. J. Edwards,
68
T. S. Miyashita,
68
S. Ahmed,
69
M. S. Alam,
69
J. A. Ernst,
69
B. Pan,
69
M. A. Saeed,
69
S. B. Zain,
69
S. M. Spanier,
70
B. J. Wogsland,
70
R. Eckmann,
71
J. L. Ritchie,
71
A. M. Ruland,
71
C. J. Schilling,
71
R. F. Schwitters,
71
B. W. Drummond,
72
J. M. Izen,
72
X. C. Lou,
72
F. Bianchi,
73a,73b
D. Gamba,
73a,73b
M. Pelliccioni,
73a,73b
M. Bomben,
74a,74b
L. Bosisio,
74a,74b
C. Cartaro,
74a,74b
G. Della Ricca,
74a,74b
L. Lanceri,
74a,74b
L. Vitale,
74a,74b
V. Azzolini,
75
N. Lopez-March,
75
F. Martinez-Vidal,
75
D. A. Milanes,
75
A. Oyanguren,
75
J. Albert,
76
Sw. Banerjee,
76
B. Bhuyan,
76
H. H. F. Choi,
76
K. Hamano,
76
G. J. King,
76
R. Kowalewski,
76
M. J. Lewczuk,
76
I. M. Nugent,
76
J. M. Roney,
76
R. J. Sobie,
76
T. J. Gershon,
77
P. F. Harrison,
77
J. Ilic,
77
T. E. Latham,
77
G. B. Mohanty,
77
E. M. T. Puccio,
77
H. R. Band,
78
X. Chen,
78
S. Dasu,
78
K. T. Flood,
78
Y. Pan,
78
R. Prepost,
78
C. O. Vuosalo,
78
and S. L. Wu
78
1
Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP), Universite
́
de Savoie, CNRS/IN
2
P
3
,
F-74941 Annecy-Le-Vieux, France
2
Universitat de Barcelona, Facultat de Fisica, Departament ECM, E-08028 Barcelona, Spain
3a
INFN Sezione di Bari, I-70126 Bari, Italy
3b
Dipartimento di Fisica, Universita
`
di Bari, I-70126 Bari, Italy
4
University of Bergen, Institute of Physics, N-5007 Bergen, Norway
5
Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA
6
University of Birmingham, Birmingham, B15 2TT, United Kingdom
7
Ruhr Universita
̈
t Bochum, Institut fu
̈
r Experimentalphysik 1, D-44780 Bochum, Germany
8
University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
9
Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom
10
Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
11
University of California at Irvine, Irvine, California 92697, USA
12
University of California at Los Angeles, Los Angeles, California 90024, USA
13
University of California at Riverside, Riverside, California 92521, USA
14
University of California at San Diego, La Jolla, California 92093, USA
15
University of California at Santa Barbara, Santa Barbara, California 93106, USA
16
University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064, USA
17
California Institute of Technology, Pasadena, California 91125, USA
18
University of Cincinnati, Cincinnati, Ohio 45221, USA
19
University of Colorado, Boulder, Colorado 80309, USA
20
Colorado State University, Fort Collins, Colorado 80523, USA
21
Technische Universita
̈
t Dortmund, Fakulta
̈
t Physik, D-44221 Dortmund, Germany
22
Technische Universita
̈
t Dresden, Institut fu
̈
r Kern- und Teilchenphysik, D-01062 Dresden, Germany
23
Laboratoire Leprince-Ringuet, CNRS/IN
2
P
3
, Ecole Polytechnique, F-91128 Palaiseau, France
24
University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
25a
INFN Sezione di Ferrara, I-44100 Ferrara, Italy
25b
Dipartimento di Fisica, Universita
`
di Ferrara, I-44100 Ferrara, Italy
26
INFN Laboratori Nazionali di Frascati, I-00044 Frascati, Italy
27a
INFN Sezione di Genova, I-16146 Genova, Italy
27b
Dipartimento di Fisica, Universita
`
di Genova, I-16146 Genova, Italy
28
Harvard University, Cambridge, Massachusetts 02138, USA
29
Universita
̈
t Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg, Germany
30
Humboldt-Universita
̈
t zu Berlin, Institut fu
̈
r Physik, Newtonstr. 15, D-12489 Berlin, Germany
31
Imperial College London, London, SW7 2AZ, United Kingdom
32
University of Iowa, Iowa City, Iowa 52242, USA
33
Iowa State University, Ames, Iowa 50011-3160, USA
34
Johns Hopkins University, Baltimore, Maryland 21218, USA
35
Laboratoire de l’Acce
́
le
́
rateur Line
́
aire, IN
2
P
3
/CNRS et Universite
́
Paris-Sud 11, Centre Scientifique d’Orsay,
B. P. 34, F-91898 Orsay Cedex, France
36
Lawrence Livermore National Laboratory, Livermore, California 94550, USA
37
University of Liverpool, Liverpool L69 7ZE, United Kingdom
38
Queen Mary, University of London, London, E1 4NS, United Kingdom
B. AUBERT
et al.
PHYSICAL REVIEW D
79,
092001 (2009)
092001-2
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
Johannes Gutenberg-Universita
̈
t Mainz, Institut fu
̈
r Kernphysik, D-55099 Mainz, Germany
42
University of Manchester, Manchester M13 9PL, United Kingdom
43
University of Maryland, College Park, Maryland 20742, USA
44
University of Massachusetts, Amherst, Massachusetts 01003, USA
45
Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139, USA
46
McGill University, Montre
́
al, Que
́
bec, Canada H3A 2T8
47a
INFN Sezione di Milano, I-20133 Milano, Italy
47b
Dipartimento di Fisica, Universita
`
di Milano, I-20133 Milano, Italy
48
University of Mississippi, University, Mississippi 38677, USA
49
Universite
́
de Montre
́
al, Physique des Particules, Montre
́
al, Que
́
bec, Canada H3C 3J7
50
Mount Holyoke College, South Hadley, Massachusetts 01075, USA
51a
INFN Sezione di Napoli, I-80126 Napoli, Italy
51b
Dipartimento di Scienze Fisiche, Universita
`
di Napoli Federico II, I-80126 Napoli, Italy
52
NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands
53
University of Notre Dame, Notre Dame, Indiana 46556, USA
54
Ohio State University, Columbus, Ohio 43210, USA
55
University of Oregon, Eugene, Oregon 97403, USA
56a
INFN Sezione di Padova, I-35131 Padova, Italy
56b
Dipartimento di Fisica, Universita
`
di Padova, I-35131 Padova, Italy
57
Laboratoire de Physique Nucle
́
aire et de Hautes Energies, IN
2
P
3
/CNRS, Universite
́
Pierre et Marie Curie-Paris6,
Universite
́
Denis Diderot-Paris7, F-75252 Paris, France
58
University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
59a
INFN Sezione di Perugia, I-06100 Perugia, Italy
59b
Dipartimento di Fisica, Universita
`
di Perugia, I-06100 Perugia, Italy
60a
INFN Sezione di Pisa, I-56127 Pisa, Italy
60b
Dipartimento di Fisica, Universita
`
di Pisa, I-56127 Pisa, Italy
60c
Scuola Normale Superiore di Pisa, I-56127 Pisa, Italy
61
Princeton University, Princeton, New Jersey 08544, USA
62a
INFN Sezione di Roma, I-00185 Roma, Italy
62b
Dipartimento di Fisica, 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
CEA, Irfu, SPP, Centre de Saclay, F-91191 Gif-sur-Yvette, France
66
University of South Carolina, Columbia, South Carolina 29208, USA
67
SLAC National Accelerator Laboratory, 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
73a
INFN Sezione di Torino, I-10125 Torino, Italy
73b
Dipartimento di Fisica Sperimentale, Universita
`
di Torino, I-10125 Torino, Italy
74a
INFN Sezione di Trieste, I-34127 Trieste, Italy
74b
Dipartimento di Fisica, Universita
`
di Trieste, I-34127 Trieste, Italy
75
IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
76
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
77
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
78
University of Wisconsin, Madison, Wisconsin 53706, USA
(Received 9 March 2009; published 5 May 2009)
**
Also with Universita
`
di Sassari, Sassari, Italy
{
Also with Laboratoire de Physique Nucle
́
aire et de Hautes Energies, IN
2
P
3
/CNRS, Universite
́
Pierre et Marie Curie-Paris6,
Universite
́
Denis Diderot-Paris7, F-75252 Paris, France
k
Now at University of South Alabama, Mobile, AL 36688, USA
x
Also with Universita
`
di Roma La Sapienza, I-00185 Roma, Italy
Also with Universita
`
di Perugia, Dipartimento di Fisica, Perugia, Italy
Now at Tel Aviv University, Tel Aviv, 69978, Israel
*
Now at Temple University, Philadelphia, PA 19122, USA
EXCLUSIVE INITIAL-STATE-RADIATION PRODUCTION
...
PHYSICAL REVIEW D
79,
092001 (2009)
092001-3
We perform a study of the exclusive production of
D

D
,
D


D
, and
D


D

in initial-state-radiation events,
from
e
þ
e

annihilations at a center-of-mass energy near 10.58 GeV, to search for charmonium and
possible new resonances. The data sample corresponds to an integrated luminosity of
384 fb

1
and was
recorded by the
BABAR
experiment at the PEP-II storage rings. The
D

D
,
D


D
, and
D


D

mass spectra
show clear evidence of several
c
resonances. However, there is no evidence for
Y
ð
4260
Þ!
D


D
or
Y
ð
4260
Þ!
D


D

.
DOI:
10.1103/PhysRevD.79.092001
PACS numbers: 13.66.Bc, 13.87.Fh, 14.40.Gx
I. INTRODUCTION
The surprising discovery of new states decaying to
J=
c

þ


[
1
,
2
] has renewed interest in the field of char-
monium spectroscopy, since the new resonances are not
easy to accommodate in the quark model. In particular, the
BABAR
experiment discovered a new broad state
Y
ð
4260
Þ
,
decaying to
J=
c

þ


in the initial-state-radiation (ISR)
reaction
e
þ
e

!

ISR
Y
ð
4260
Þ
. The quantum numbers
J
PC
¼
1

are inferred from the single virtual-photon
production mechanism. Further structures at
4
:
36 GeV
=c
2
[
3
,
4
] and
4
:
66 GeV
=c
2
[
4
] have been ob-
served in the
c
ð
2
S
Þ

þ


mass distribution from the
reaction
e
þ
e

!

ISR
c
ð
2
S
Þ

þ


. Charmonium states
at these masses would be expected [
5
,
6
] to decay predomi-
nantly to
D

D
,
D


D
,or
D


D

[
7
]. It is peculiar that the
decay rate to the hidden charm final state
J=
c

þ


is
much larger for the
Y
ð
4260
Þ
than for excited charmonium
states [
8
], and that at the
Y
ð
4260
Þ
mass the cross section for
e
þ
e

!
hadrons exhibits a local minimum [
9
]. Several
theoretical interpretations for the
Y
ð
4260
Þ
have been pro-
posed, including unconventional scenarios: quark-
antiquark gluon hybrids [
10
], baryonium [
11
], tetraquarks
[
12
], and hadronic molecules [
13
]. For a discussion and a
list of references see, for example, Ref. [
14
].
This work explores ISR production of
D

D
,
D


D
, and
D


D

final states for evidence of charmonium states and
unconventional structures. This follows an earlier
BABAR
measurement of the
D

D
cross section [
15
]. A study by the
Belle Collaboration of the
D

D
,
D


D
, and
D


D

final states
can be found in Refs. [
16
,
17
]. Recent measurements of the
e
þ
e

cross sections can be found in Ref. [
18
].
We also measure for the first time branching fractions of
high mass charmonium states, other than
Y
ð
4260
Þ
, for
which little information exists [
9
], and compare our mea-
surements with theoretical expectations [
5
,
6
,
14
].
This paper is organized as follows: In Sec.
II
,wegivea
short description of the
BABAR
experiment, and in Sec.
III
,
we describe the data selection. Section
IV
is devoted to the
selection of the
D


D
final state, and in Sec.
V
, we present
the mass resolution, reconstruction efficiency, and mea-
sured cross sections. In Sec.
VI
, we describe the
D


D

cross section measurement, while in Sec.
VII
, we present
the
D

D
data. The description of the fit of the three channels
is described in Sec.
VIII
, while Sec.
IX
is devoted to the
measurements of the ratios of branching fractions. Finally,
in Section
X
, we compute the limit on production of
Y
ð
4260
Þ
decaying to
D


D
and
D


D

, and summarize con-
clusions in Sec.
XI
.
II. THE
BABAR
EXPERIMENT
This analysis is based on a
384 fb

1
data sample re-
corded at the

ð
4
S
Þ
resonance and 40 MeV below the
resonance by the
BABAR
detector at the PEP-II
asymmetric-energy
e
þ
e

storage rings. The
BABAR
de-
tector is described in detail elsewhere [
19
]. We mention
here only the parts of the detector that are used in the
present analysis. Charged particles are detected and their
momenta measured with a combination of a cylindrical
drift chamber and a silicon vertex tracker, both operating
within a 1.5 T magnetic field of a superconducting sole-
noid. The information from a ring-imaging Cherenkov
detector combined with energy-loss measurements in the
silicon vertex tracker and drift chamber provide identifica-
tion of charged kaon and pion candidates. Photon energies
are measured with a CsI(Tl) electromagnetic calorimeter.
III. DATA SELECTION
D

D
candidates are reconstructed in the seven final states
listed in Table
I
.
The
D

0
!
D
0

0
and
D

0
!
D
0

decay modes are
used to form
D

0

D
0
and
D

0

D

0
candidates. The
D
!
D
0

þ
and
D
!
D
þ

0
decay modes are used to form
D
D

and
D
D

candidates. Table
II
summarizes the
full decay chains used to reconstruct the
D


D
and
D


D

candidates.
For all final states, events are retained if the number of
well-measured charged tracks, having a minimum trans-
verse momentum of
0
:
1 GeV
=c
, is exactly equal to the
total number of charged daughter particles. Photons are
identified as electromagnetic clusters that do not have a
TABLE I. List of the reconstructed
D

D
final states.
N Channel First
D
decay mode Second
D
decay mode
1
D
0

D
0
D
0
!
K


þ

D
0
!
K
þ


2
D
0

D
0
D
0
!
K


þ

D
0
!
K
þ



0
3
D
0

D
0
D
0
!
K


þ

D
0
!
K
þ



þ


4
D
0

D
0
D
0
!
K


þ

0

D
0
!
K
þ



þ


5
D
þ
D

D
þ
!
K


þ

þ
D

!
K
þ




6
D
þ
D

D
þ
!
K


þ

þ
D

!
K
þ
K



7
D
þ
D

D
þ
!
K


þ

þ
D

!
K
0
S


B. AUBERT
et al.
PHYSICAL REVIEW D
79,
092001 (2009)
092001-4
spatial match with a charged track, and that have a mini-
mum energy of 30 MeV. Neutral pion candidates are
formed from pairs of photons kinematically fitted with
the

0
mass constraint.
K
0
S
candidates are reconstructed,
with a vertex fit, in the

þ


decay mode. The tracks
corresponding to the charged daughters of each
D
candi-
date are constrained to come from a common vertex.
Additionally, for the
D
0
!
K


þ

0
channel, the
D
0
mass constraint is included in the fit, and for the
D

!
K
0
S


channel, a
K
0
S
mass constraint is imposed.
Reconstructed
D
candidates with a

2
fit probability
greater than 0.1% are retained. Each
D

D
pair is refit to a
common vertex with the constraint that the pair originates
from the
e
þ
e

interaction region. Only candidates with a

2
fit probability greater than 0.1% are retained.
Background

0
candidates from random combinations of
photons and other background channels are suppressed by
requiring no more than one

0
candidate other than those
attributed to the
D
0
and
D

decays. Similarly, we require in
the event no more than one extra photon candidate, having
a minimum energy of 100 MeV, apart from any photon
attributed to
D

or

0
decays.
For
D
decay modes without a

0
daughter, the
D
-candidate momentum is determined from the summed
three-momenta of the decay particles, and its energy is
computed using the nominal
D
mass value [
9
]. For the
D
0
!
K


þ

0
channel, the four-momentum from the
mass-constrained fit is used. Similarly, the
D

momentum
is determined from the summed three-momenta of the
decay particles and its energy is computed using the nomi-
nal
D

mass.
The ISR photon is preferentially emitted at small angles
with respect to the beam axis, and escapes detection in the
majority of ISR events. Consequently, the ISR photon is
treated as a missing particle. We define the squared mass
(
M
2
rec
) recoiling against the
D

D
,
D


D
, and
D


D

systems
using the four-momenta of the beam particles (
p
e

) and of
the reconstructed
D
ð
p
D
Þ
and
D

ð
p
D

Þ
M
2
rec
p
e

þ
p
e
þ

p
D
ðÞ

p

D
ðÞ
Þ
2
:
(1)
This quantity should peak near zero for both ISR events
and for exclusive production of
e
þ
e

!
D


D
or
e
þ
e

!
D


D

. In exclusive production the
D


D
and
D


D

mass
distributions peak at the kinematic limit. Therefore,
we select ISR candidates by requiring
D

D
,
D


D
, and
D


D

invariant masses below
6 GeV
=c
2
and
j
M
2
rec
j
<
1 GeV
2
=c
4
.
We select
D
and
D

candidates based on the candidate
D
mass and the mass difference

m
¼
M
D


M
D
. The
D
and
D

parameters are obtained by fitting the relevant mass
spectra (see Fig.
1
for some

m
distributions) using a
polynomial for the background and a single Gaussian for
the signal. Events are selected within

2
:
5

from the fitted
central values, where

is the Gaussian width. For
D
!
D
0

þ
, the selection criterion has been extended to

6

due to the presence of non-Gaussian tails.
Because of our tolerance of an extra

0
and/or

,an
ambiguity can occur for channels involving a
D

0
, which is
handled as follows. Each combination is considered as a
possible candidate for channels 8–12 and
D
0

D
0
.
Monte Carlo simulations weighted by the
D

D
,
D


D
, and
D


D

measured cross sections [
15
17
], and branching
fractions are used to optimize the selection criteria and
estimate the feedthrough of one channel to the other. A
candidate is rejected if (a) it satisfies all the selection
criteria for an ambiguous channel and (b) this rejection
does not produce any significant loss in the channel under
study and therefore can be classified as background. The
list of channels rejected in case of ambiguities are indi-
cated in the ‘‘Veto’’ column in Table
II
. The table also lists
the fraction of events removed by these cuts in the
j
M
2
rec
j
<
1 GeV
2
=c
4
region.
In the case of multiple
D

0
candidates, such as
D

0

D

0
with both
D

0
!
D
0

, the candidate with
m
ð
D
0

Þ
closest
TABLE II. List of the
D


D
and
D


D

reconstructed final states. The reconstructed
D
0
decay modes are listed in Table
I
for the
D

0

D
and
D

0

D

0
states. The column headed Veto lists ambiguities with the indicated channels, ‘‘Removed’’ indicates the fraction of events
removed by the Veto.
N
Channel
First decay mode
Second decay mode
Veto
Removed %
8
D

0

D
0
D

0
!
D
0

9–12
5.9
9
D

0

D
0
D

0
!
D
0

0
11,12
3.2
10
D

0

D

0
D

0
!
D
0


D

0
!

D
0

9,11
1.1
11
D

0

D

0
D

0
!
D
0

0

D

0
!

D
0

8,10
0.7
12
D

0

D

0
D

0
!
D
0

0

D

0
!

D
0

0
13
D
D

D
!
D
0

þ
,
D
0
!
K


þ
D

!
K
þ




14
D
D

D
!
D
þ

0
,
D
þ
!
K


þ

þ
D

!
K
þ




15
D
D

D
!
D
0

þ
,
D
0
!
K

K
þ
D

!
K
þ




16
D
D

D
!
D
0

þ
,
D
0
!
K


þ
D

!
K
þ
K



17
D
D

D
!
D
þ

0
,
D
þ
!
K


þ

þ
D

!
K
þ
K



18
D
D

D
!
D
0

þ
,
D
0
!
K


þ
D

!

D
0


,

D
0
!
K
þ


19
D
D

D
!
D
þ

0
,
D
þ
!
K


þ

þ
D

!

D
0


,

D
0
!
K
þ


EXCLUSIVE INITIAL-STATE-RADIATION PRODUCTION
...
PHYSICAL REVIEW D
79,
092001 (2009)
092001-5
to the nominal
D

0
mass is accepted. The charged
D


D
and
D


D

modes, also listed in Table
II
, do not require such a
procedure because backgrounds are negligible.
IV. STUDY OF THE
D


D
FINAL STATE
Figure
2
shows the
D


DM
2
rec
distributions after all the
cuts for (a)
D

0

D
0
,
D

0
!
D
0

, (b)
D

0

D
0
,
D

0
!
D
0

0
,
and (c)
D
D

. Clear peaks centered at zero with little
background are observed, providing evidence of an ISR
process.
The number of background events in the
j
M
2
rec
j
<
1 GeV
2
=c
4
is estimated by fitting the
M
2
rec
distribution
for each channel. The fits are performed using a
2
nd
order
polynomial for the background and a signal
M
2
rec
lineshape
obtained from Monte Carlo simulations corresponding to
the relative composition of the data. The event yields are
obtained by subtracting the fitted backgrounds and inte-
grating the resulting
M
2
rec
distributions in the
j
M
2
rec
j
<
1 GeV
2
=c
4
region. The resulting yields and fitted purities,
defined as
P
¼
N
signal
=
ð
N
signal
þ
N
background
Þ
, for each
channel are summarized in Table
III
.
The purity of each reconstructed
D

channel is also
demonstrated in Fig.
1
, where the

m
distribution is shown
for
D


D
candidates with
j
M
2
rec
j
<
1 GeV
2
=c
4
and
D


D
masses below
6 GeV
=c
2
. The final selection of the ISR
candidates is performed applying the

m
selection criteria
described above.
The
D

0

D
0
mass spectrum is shown in Fig.
3(a)
, and the
D
D

mass spectrum is shown in Fig.
3(b)
. Both spectra
show an enhancement near threshold due to the presence of
the
c
ð
4040
Þ
resonance.
The background shape for
D

0

D
0
candidates is explored
using the
M
2
rec
sideband region,
1
:
5
<M
2
rec
<
3
:
5 GeV
2
=c
4
. The
D

0

D
0
mass spectrum for these events,
normalized to the background estimated from the fit to the
M
2
rec
distribution, is presented as the shaded histogram in
Fig.
3(a)
. This background has been fitted with a threshold
function
B
ð
m
Þ¼ð
m

m
th
Þ

þ
m
e

m

m
2

m
3
;
(2)
where
m
th
is the threshold
D

0

D
0
mass. The
D
D

final
state is consistent with having zero background.
V. MASS RESOLUTION, EFFICIENCY, AND
D


D
CROSS SECTION
In order to measure efficiencies and
D


D
mass resolu-
tions, ISR events are simulated at five different values of
the
D


D
invariant masses between 4.25 and
6
:
25 GeV
=c
2
.
These events are simulated using the
GEANT4
detector
simulation package [
20
] and are processed through the
same reconstruction and analysis chain as real events.
The mass resolution is determined from the difference
between generated and reconstructed
D


D
masses. The
D


D
mass resolutions are similar for all channels and
increase with
D


D
mass from 5 to
10 MeV
=c
2
.
The mass-dependent reconstruction efficiency for chan-
nel
i
,

i
ð
m
D


D
Þ
is parameterized by a second-order poly-
nomial, and is multiplied by the decay branching fraction
B
i
[
9
] to define

B
i
ð
m
D


D
Þ¼

i
ð
m
D


D
Þ
B
i
:
(3)
These values are weighted by
N
i
ð
m
D


D
Þ
, the number of
D


D
candidates in channel
i
, to compute the average
efficiency as a function of
m
D


D
,

B
ð
m
D


D
Þ¼
P
n
i
¼
1
N
i
ð
m
D


D
Þ
P
n
i
¼
1
N
i
ð
m
D


D
Þ

B
i
ð
m
D


D
Þ
;
(4)
0
20
40
60
80
-5
0
5
0
25
50
75
100
-5
0
5
0
20
40
60
-5
0
5
FIG. 2. Distribution of
M
2
rec
, the mass recoiling against the
D


D
system, for (a)
D

0
!
D
0

, (b)
D

0
!
D
0

0
, and
(c)
D
D

candidates. The curves are the results from the fits
described in the text.
0
25
50
75
100
0
0.2
0.4
0
25
50
75
100
0.12
0.14
0.16
0
10
20
0.14
0.15
0.16
0
5
10
15
20
0.12
0.14
0.16
FIG. 1 (color online).

m
distributions for
D


D
candidates
after applying the
j
M
2
rec
j
<
1 GeV
2
=c
4
and
m
ð
D


D
Þ
<
6 GeV
=c
2
selections, for (a)
D

0
!
D
0

, (b)
D

0
!
D
0

0
,
(c)
D
!
D
0

þ
with
D
0
!
K


þ
, and (d)
D
!
D
þ

0
with
D
þ
!
K


þ

þ
. The shaded regions indicate the ranges
used to select the
D

candidates.
B. AUBERT
et al.
PHYSICAL REVIEW D
79,
092001 (2009)
092001-6
where
n
is the number of decay modes. In this case, we
have eight
D

0

D
0
channels (1–4 with
D

0
!
D
0

and
D

0
!
D
0

0
) and two
D
D

channels (13, 14).
Representative values of

B
, computed at a mass of
4
:
5 GeV
=c
2
, are displayed in Table
III
. The sample sizes
for the Cabibbo-suppressed decay modes (15, 16, and 17 in
Table
II
) are very small (32 events total) and comprise 14%
of the
D
D

sample. The efficiency for these decay
channels has not been directly computed; instead, these
modes are treated as having the mean efficiency of the
Cabibbo-allowed channels 13 and 14. The ten
D


D
chan-
nels, after correcting for efficiency and branching frac-
tions, have yields that are consistent within the statistical
errors.
The
D


D
cross section is computed using

e
þ
e

!
D


D
ð
m
D


D
Þ¼
dN=dm
D


D

B
ð
m
D


D
Þ
d
L
=dm
D


D
;
(5)
where
dN=dm
D


D
is the background-subtracted yield. The
differential luminosity is computed as [
21
]
d
L
dm
D


D
¼
L
2
m
D


D
s

x
ð
ln
ð
s=m
2
e
Þ
1
Þð
2

2
x
þ
x
2
Þ
;
(6)
where
s
is the square of the
e
þ
e

center-of-mass energy,

is the fine-structure constant,
x
¼
1

m
2
D


D
=s
,
m
e
is the
electron mass, and
L
is the integrated luminosity of
384 fb

1
. The cross sections for
D

0

D
0
,
D
D

, and
combined
D

0

D
0
and
D
D

are shown in Fig.
4
. A clear
c
ð
4040
Þ
resonance is observed.
The systematic uncertainties on the cross sections,
10.9% for
D

0

D
0
and 9.3% for
D
D

, include uncertain-
ties for particle identification, tracking, photon and

0
reconstruction efficiencies, background estimates, branch-
ing fractions, and a potential inaccuracy in the simulation
of extraneous tracks, photon, and

0
candidates. The un-
certainty due to the ISR selection has been estimated by
narrowing the
M
2
rec
allowed range to
0
:
7 GeV
2
=c
4
. All
contributions are added in quadrature. Systematic uncer-
tainties are summarized in Table
IV
.
The
D

0

D
0
and
D
D

cross sections have similar
features and consistent yields. Integrating the cross sec-
tions from threshold to
6 GeV
=c
2
, we obtain

ð
D
D

Þ

ð
D

0

D
0
Þ
¼
0
:
95

0
:
09
stat

0
:
10
syst
;
(7)
consistent with unity. In this calculation systematic errors
TABLE III. Number of ISR candidates and purities for the different channels calculated in the
range
j
M
2
rec
j
<
1 GeV
2
=c
4
. The last column gives the value of the average efficiency

B
at a
mass of
4
:
5 GeV
=c
2
.
Channel
Signal
þ
Background
Purity(%)

B

10

5
D
0

D
0
654
74
:
3

1
:
7
D
þ
D

199
88
:
4

2
:
3
Total
D

D
853
77
:
6

1
:
4
25
D

0

D
0
,
D

0
!
D
0

460
75
:
4

2
:
0
D

0

D
0
D

0
!
D
0

0
422
84
:
4

1
:
8
Total
D

0

D
0
882
79
:
7

1
:
4
4
D
D

228
100
þ
0

3
5
Total
D


D
1110
83
:
6

1
:
1
D

0

D

0
293
69
:
3

3
:
7
D
D

33
100
þ
0

3
Total
D


D

326
72
:
1

2
:
5
1
0
20
40
60
4 4.5 5 5.5 6
0
20
40
60
4 4.5 5 5.5 6
0
5
10
15
4 4.5 5 5.5 6
FIG. 3 (color online). (a)
D

0

D
0
and (b)
D
D

mass spectra.
The shaded histogram in (a) is obtained from the
M
2
rec
sideband
region
1
:
5
<M
2
rec
<
3
:
5 GeV
2
=c
4
normalized to the background
estimated from the fit to the
M
2
rec
distribution. The curve is the
result from the fit described in the text.
EXCLUSIVE INITIAL-STATE-RADIATION PRODUCTION
...
PHYSICAL REVIEW D
79,
092001 (2009)
092001-7
related to the
M
2
rec
selection criteria and tracking efficiency
have been ignored because they largely cancel in the ratio.
VI. STUDY OF THE
D


D

SYSTEM
A similar analysis is carried out for
D


D

channels.
Figure
5
shows the

m
distributions for
D


D

candidates
with
j
M
2
rec
j
<
1 GeV
2
=c
4
and
D


D

masses below
6 GeV
=c
2
. The peak at threshold in Fig.
5(a)
is due to
background from
D

0
!
D
0

0
where one

from the low
momentum

0
is lost.
We select the two
D

candidates and reject candidates
reconstructed in any of the modes listed in the Veto column
in Table
II
. Figure
6
shows the
D

0

D

0
M
2
rec
distributions
for channels 10–12.
The total
D

0

D

0
and
D
D

M
2
rec
distributions are
shown in Fig.
7
. The number of background events for
the
D

0

D

0
channel is estimated by fitting the
M
2
rec
distri-
bution. The fit is performed using a
2
nd
-order polynomial
for the background and a signal
M
2
rec
lineshape obtained
from Monte Carlo simulations that reflect the composition
of the data. The number of ISR candidates and purities are
also summarized in Table
III
. The
D
D

final state has a
background consistent with zero.
Because of the small
D
D

sample size, the charged
and neutral mass spectra are summed in Fig.
8
. The
D


D

mass spectrum shows unresolved peaks at
c
ð
4040
Þ
and
c
ð
4160
Þ
and an enhancement at the position of the
c
ð
4400
Þ
[
9
].
TABLE IV. Systematic errors, given as fractional errors ex-
pressed in %, in the evaluation of the
D


D
cross section.
Effect
D

0

D
0
D
D

Background subtraction
2.6
3.0
Branching fractions
7.4
4.6
M
2
rec
cut
2.2
0.0
Particle identification
1.8
2.1
Tracking efficiency
2.2
3.3
Extraneous tracks
5.7
5.7

0
and

reconstruction efficiency
3.4
3.0
Extraneous

0
and

0.5
0.8
Total
10.9
9.3
0
2.5
5
4
4.5
5
5.5
6
0
2.5
5
4
4.5
5
5.5
6
0
5
10
4
4.5
5
5.5
6
FIG. 4. Cross section for
e
þ
e

!
(a)
D

0

D
0
, (b)
D
D

, and
(c)
D


D
combined. The error bars correspond to statistical errors
only.
0
20
40
60
0
0.2
0.4
0
20
40
60
0.12
0.14
0.16
0
5
10
15
0.14
0.15
0.16
0
2
4
6
0.12
0.14
0.16
FIG. 5 (color online).

m
distributions for
D


D

candidates
after applying the
j
M
2
rec
j
<
1 GeV
2
=c
4
and
m
ð
D


D

Þ
<
6 GeV
=c
2
selections, for (a)
D

0
!
D
0

, (b)
D

0
!
D
0

0
,
(c)
D
!
D
0

þ
with
D
0
!
K


þ
, and (d)
D
!
D
þ

0
with
D
þ
!
K


þ

þ
. The shaded regions indicate the ranges
used to select the
D

signals.
0
10
20
-5
5
0
10
20
30
-5
5
0
5
10
15
20
-5
5
FIG. 6.
M
2
rec
distributions for
D

0

D

0
for (a)
D

0
!
D
0

,

D

0
!

D
0

, (b)
D

0
!
D
0

0
,

D

0
!

D
0

, and
(c)
D

0
!
D
0

0
,

D

0
!

D
0

0
.
B. AUBERT
et al.
PHYSICAL REVIEW D
79,
092001 (2009)
092001-8
The background is explored using events in the
M
2
rec
sideband regions

2
:
5
<M
2
rec
<

1
:
5 GeV
2
=c
4
and
1
:
5
<M
2
rec
<
2
:
5 GeV
2
=c
4
, and fitted using Eq. (
2
). The
D


D

mass spectrum for these events, normalized from the
fit to the
M
2
rec
distribution, is shown as the shaded histo-
gram in Fig.
8
.
The
D


D

cross section is calculated using the same
method used to compute the
D


D
cross section. The result,
summed over the neutral and charged modes, is shown in
Fig.
9
. All systematic uncertaintiesthat have been taken
into account for the
D


D

mode are listed in Table
V
; the
overall uncertainty on the cross section is 12.4%.
The
D


D

cross section distribution exhibits a threshold
enhancement due to the superposition of the
c
ð
4040
Þ
and
c
ð
4160
Þ
resonances.
VII. THE
D

D
MASS SPECTRUM
In the selection of the
D
0

D
0
sample we also apply the
method of resolving ambiguous events having an addi-
tional

0
and/or

. Here, we Veto all events that are
ambiguous with channels 8–12, obtaining a rejection of
7.6% background events in the
j
M
2
rec
j
<
1 GeV
2
=c
4
region.
No such procedure is applied to the
D
þ
D

sample. The
0
10
20
30
4
4.5
5
5.5
6
0
10
20
30
4
4.5
5
5.5
6
FIG. 8 (color online).
D


D

mass spectrum. The shaded his-
togram is obtained from the
M
2
rec
sidebands

2
:
5
<M
2
rec
<

1
:
5
and
1
:
5
<M
2
rec
<
2
:
5 GeV
2
=c
4
. The curve is the result
from the fit described in the text.
0
20
40
60
-5
0
5
0
2
4
6
8
10
-5
0
5
FIG. 7.
M
2
rec
distributions for (a)
D

0

D

0
and (b)
D
D

. The
curve in (a) is the result from the fit described in the text.
0
2.5
5
7.5
10
4 4.5 5 5.5 6
FIG. 9. Cross section
e
þ
e

!
D


D

for combined
D

0

D

0
and
D
D

. Error bars indicate the statistical errors only.
TABLE V. Systematic errors, given as fractional errors ex-
pressed in %, in the evaluation of the
D


D

cross section.
Effect
Fraction (%)
Background subtraction
2.1
Branching fractions
9.3
M
2
rec
cut
1.3
Particle identification
2.8
Tracking efficiency
2.6
Extraneous tracks
5.7

0
and

reconstruction efficiency
4.1
Total
12.4
0
50
100
150
-5
0
5
0
20
40
60
-5
0
5
FIG. 10.
M
2
rec
distribution for (a)
D
0

D
0
and (b)
D
þ
D

. The
curves are the results from the fits described in the text.
0
25
50
75
100
4 4.5 5 5.5 6
0
25
50
75
100
4 4.5 5 5.5 6
FIG. 11 (color online).
D

D
mass distribution. The shaded
histogram is obtained from the
M
2
rec
sideband. The curve is the
result from the fit described in the text.
EXCLUSIVE INITIAL-STATE-RADIATION PRODUCTION
...
PHYSICAL REVIEW D
79,
092001 (2009)
092001-9