BABAR-PUB-07/017
SLAC-PUB-12441
Branching fraction and charge asymmetry measurements in B → J/ψππ decays
B. Aubert,1 M. Bona,1 D. Boutigny,1 Y. Karyotakis,1 J. P. Lees,1 V. Poireau,1 X. Prudent,1 V. Tisserand,1
A. Zghiche,1 J. Garra Tico,2 E. Grauges,2 L. Lopez,3 A. Palano,3 G. Eigen,4 I. Ofte,4 B. Stugu,4 L. Sun,4
G. S. Abrams,5 M. Battaglia,5 D. N. Brown,5 J. Button-Shafer,5 R. N. Cahn,5 Y. Groysman,5 R. G. Jacobsen,5
J. A. Kadyk,5 L. T. Kerth,5 Yu. G. Kolomensky,5 G. Kukartsev,5 D. Lopes Pegna,5 G. Lynch,5 L. M. Mir,5
T. J. Orimoto,5 M. Pripstein,5 N. A. Roe,5 M. T. Ronan,5, ∗ K. Tackmann,5 W. A. Wenzel,5 P. del Amo Sanchez,6
C. M. Hawkes,6 A. T. Watson,6 T. Held,7 H. Koch,7 B. Lewandowski,7 M. Pelizaeus,7 T. Schroeder,7
M. Steinke,7 W. N. Cottingham,8 D. Walker,8 D. J. Asgeirsson,9 T. Cuhadar-Donszelmann,9 B. G. Fulsom,9
C. Hearty,9 N. S. Knecht,9 T. S. Mattison,9 J. A. McKenna,9 A. Khan,10 M. Saleem,10 L. Teodorescu,10
V. E. Blinov,11 A. D. Bukin,11 V. P. Druzhinin,11 V. B. Golubev,11 A. P. Onuchin,11 S. I. Serednyakov,11
Yu. I. Skovpen,11 E. P. Solodov,11 K. Yu Todyshev,11 M. Bondioli,12 S. Curry,12 I. Eschrich,12 D. Kirkby,12
A. J. Lankford,12 P. Lund,12 M. Mandelkern,12 E. C. Martin,12 D. P. Stoker,12 S. Abachi,13 C. Buchanan,13
S. D. Foulkes,14 J. W. Gary,14 F. Liu,14 O. Long,14 B. C. Shen,14 L. Zhang,14 H. P. Paar,15 S. Rahatlou,15
V. Sharma,15 J. W. Berryhill,16 C. Campagnari,16 A. Cunha,16 B. Dahmes,16 T. M. Hong,16 D. Kovalskyi,16
J. D. Richman,16 T. W. Beck,17 A. M. Eisner,17 C. J. Flacco,17 C. A. Heusch,17 J. Kroseberg,17 W. S. Lockman,17
T. Schalk,17 B. A. Schumm,17 A. Seiden,17 D. C. Williams,17 M. G. Wilson,17 L. O. Winstrom,17 E. Chen,18
C. H. Cheng,18 A. Dvoretskii,18 F. Fang,18 D. G. Hitlin,18 I. Narsky,18 T. Piatenko,18 F. C. Porter,18
G. Mancinelli,19 B. T. Meadows,19 K. Mishra,19 M. D. Sokoloff,19 F. Blanc,20 P. C. Bloom,20 S. Chen,20
W. T. Ford,20 J. F. Hirschauer,20 A. Kreisel,20 M. Nagel,20 U. Nauenberg,20 A. Olivas,20 J. G. Smith,20
K. A. Ulmer,20 S. R. Wagner,20 J. Zhang,20 A. M. Gabareen,21 A. Soffer,21 W. H. Toki,21 R. J. Wilson,21
F. Winklmeier,21 Q. Zeng,21 D. D. Altenburg,22 E. Feltresi,22 A. Hauke,22 H. Jasper,22 J. Merkel,22 A. Petzold,22
B. Spaan,22 K. Wacker,22 T. Brandt,23 V. Klose,23 H. M. Lacker,23 W. F. Mader,23 R. Nogowski,23 J. Schubert,23
K. R. Schubert,23 R. Schwierz,23 J. E. Sundermann,23 A. Volk,23 D. Bernard,24 G. R. Bonneaud,24 E. Latour,24
V. Lombardo,24 Ch. Thiebaux,24 M. Verderi,24 P. J. Clark,25 W. Gradl,25 F. Muheim,25 S. Playfer,25
A. I. Robertson,25 Y. Xie,25 M. Andreotti,26 D. Bettoni,26 C. Bozzi,26 R. Calabrese,26 A. Cecchi,26 G. Cibinetto,26
P. Franchini,26 E. Luppi,26 M. Negrini,26 A. Petrella,26 L. Piemontese,26 E. Prencipe,26 V. Santoro,26 F. Anulli,27
R. Baldini-Ferroli,27 A. Calcaterra,27 R. de Sangro,27 G. Finocchiaro,27 S. Pacetti,27 P. Patteri,27 I. M. Peruzzi,27, †
M. Piccolo,27 M. Rama,27 A. Zallo,27 A. Buzzo,28 R. Contri,28 M. Lo Vetere,28 M. M. Macri,28 M. R. Monge,28
S. Passaggio,28 C. Patrignani,28 E. Robutti,28 A. Santroni,28 S. Tosi,28 K. S. Chaisanguanthum,29 M. Morii,29
J. Wu,29 R. S. Dubitzky,30 J. Marks,30 S. Schenk,30 U. Uwer,30 D. J. Bard,31 P. D. Dauncey,31 R. L. Flack,31
J. A. Nash,31 M. B. Nikolich,31 W. Panduro Vazquez,31 P. K. Behera,32 X. Chai,32 M. J. Charles,32 U. Mallik,32
N. T. Meyer,32 V. Ziegler,32 J. Cochran,33 H. B. Crawley,33 L. Dong,33 V. Eyges,33 W. T. Meyer,33 S. Prell,33
E. I. Rosenberg,33 A. E. Rubin,33 A. V. Gritsan,34 Z. J. Guo,34 C. K. Lae,34 A. G. Denig,35 M. Fritsch,35
G. Schott,35 N. Arnaud,36 J. Béquilleux,36 M. Davier,36 G. Grosdidier,36 A. Höcker,36 V. Lepeltier,36
F. Le Diberder,36 A. M. Lutz,36 S. Pruvot,36 S. Rodier,36 P. Roudeau,36 M. H. Schune,36 J. Serrano,36 V. Sordini,36
A. Stocchi,36 W. F. Wang,36 G. Wormser,36 D. J. Lange,37 D. M. Wright,37 C. A. Chavez,38 I. J. Forster,38
J. R. Fry,38 E. Gabathuler,38 R. Gamet,38 D. E. Hutchcroft,38 D. J. Payne,38 K. C. Schofield,38 C. Touramanis,38
A. J. Bevan,39 K. A. George,39 F. Di Lodovico,39 W. Menges,39 R. Sacco,39 G. Cowan,40 H. U. Flaecher,40
D. A. Hopkins,40 P. S. Jackson,40 T. R. McMahon,40 F. Salvatore,40 A. C. Wren,40 D. N. Brown,41 C. L. Davis,41
J. Allison,42 N. R. Barlow,42 R. J. Barlow,42 Y. M. Chia,42 C. L. Edgar,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 G. Blaylock,44
C. Dallapiccola,44 S. S. Hertzbach,44 X. Li,44 T. B. Moore,44 E. Salvati,44 S. Saremi,44 R. Cowan,45 P. H. Fisher,45
G. Sciolla,45 S. J. Sekula,45 M. Spitznagel,45 F. Taylor,45 R. K. Yamamoto,45 S. E. Mclachlin,46 P. M. Patel,46
S. H. Robertson,46 A. Lazzaro,47 F. Palombo,47 J. M. Bauer,48 L. Cremaldi,48 V. Eschenburg,48 R. Godang,48
R. Kroeger,48 D. A. Sanders,48 D. J. Summers,48 H. W. Zhao,48 S. Brunet,49 D. Côté,49 M. Simard,49 P. Taras,49
F. B. Viaud,49 H. Nicholson,50 G. De Nardo,51 F. Fabozzi,51, ‡ L. Lista,51 D. Monorchio,51 C. Sciacca,51
M. A. Baak,52 G. Raven,52 H. L. Snoek,52 C. P. Jessop,53 J. M. LoSecco,53 G. Benelli,54 L. A. Corwin,54
K. K. Gan,54 K. Honscheid,54 D. Hufnagel,54 H. Kagan,54 R. Kass,54 J. P. Morris,54 A. M. Rahimi,54
J. J. Regensburger,54 R. Ter-Antonyan,54 Q. K. Wong,54 N. L. Blount,55 J. Brau,55 R. Frey,55 O. Igonkina,55
http://arxiv.org/abs/0704.1266v1
J. A. Kolb,55 M. Lu,55 R. Rahmat,55 N. B. Sinev,55 D. Strom,55 J. Strube,55 E. Torrence,55 N. Gagliardi,56 A. Gaz,56
M. Margoni,56 M. Morandin,56 A. Pompili,56 M. Posocco,56 M. Rotondo,56 F. Simonetto,56 R. Stroili,56 C. Voci,56
E. Ben-Haim,57 H. Briand,57 J. Chauveau,57 P. David,57 L. Del Buono,57 Ch. de la Vaissière,57 O. Hamon,57
B. L. Hartfiel,57 Ph. Leruste,57 J. Malclès,57 J. Ocariz,57 A. Perez,57 L. Gladney,58 M. Biasini,59 R. Covarelli,59
E. Manoni,59 C. Angelini,60 G. Batignani,60 S. Bettarini,60 G. Calderini,60 M. Carpinelli,60 R. Cenci,60
A. Cervelli,60 F. Forti,60 M. A. Giorgi,60 A. Lusiani,60 G. Marchiori,60 M. A. Mazur,60 M. Morganti,60 N. Neri,60
E. Paoloni,60 G. Rizzo,60 J. J. Walsh,60 M. Haire,61 J. Biesiada,62 P. Elmer,62 Y. P. Lau,62 C. Lu,62 J. Olsen,62
A. J. S. Smith,62 A. V. Telnov,62 E. Baracchini,63 F. Bellini,63 G. Cavoto,63 A. D’Orazio,63 D. del Re,63 E. Di
Marco,63 R. Faccini,63 F. Ferrarotto,63 F. Ferroni,63 M. Gaspero,63 P. D. Jackson,63 L. Li Gioi,63 M. A. Mazzoni,63
S. Morganti,63 G. Piredda,63 F. Polci,63 F. Renga,63 C. Voena,63 M. Ebert,64 H. Schröder,64 R. Waldi,64 T. Adye,65
G. Castelli,65 B. Franek,65 E. O. Olaiya,65 S. Ricciardi,65 W. Roethel,65 F. F. Wilson,65 R. Aleksan,66 S. Emery,66
M. Escalier,66 A. Gaidot,66 S. F. Ganzhur,66 G. Hamel de Monchenault,66 W. Kozanecki,66 M. Legendre,66
G. Vasseur,66 Ch. Yèche,66 M. Zito,66 X. R. Chen,67 H. Liu,67 W. Park,67 M. V. Purohit,67 J. R. Wilson,67
M. T. Allen,68 D. Aston,68 R. Bartoldus,68 P. Bechtle,68 N. Berger,68 R. Claus,68 J. P. Coleman,68 M. R. Convery,68
J. C. Dingfelder,68 J. Dorfan,68 G. P. Dubois-Felsmann,68 D. Dujmic,68 W. Dunwoodie,68 R. C. Field,68
T. Glanzman,68 S. J. Gowdy,68 M. T. Graham,68 P. Grenier,68 C. Hast,68 T. Hryn’ova,68 W. R. Innes,68
M. H. Kelsey,68 H. Kim,68 P. Kim,68 D. W. G. S. Leith,68 S. Li,68 S. Luitz,68 V. Luth,68 H. L. Lynch,68
D. B. MacFarlane,68 H. Marsiske,68 R. Messner,68 D. R. Muller,68 C. P. O’Grady,68 A. Perazzo,68 M. Perl,68
T. Pulliam,68 B. N. Ratcliff,68 A. Roodman,68 A. A. Salnikov,68 R. H. Schindler,68 J. Schwiening,68 A. Snyder,68
J. Stelzer,68 D. Su,68 M. K. Sullivan,68 K. Suzuki,68 S. K. Swain,68 J. M. Thompson,68 J. Va’vra,68 N. van Bakel,68
A. P. Wagner,68 M. Weaver,68 W. J. Wisniewski,68 M. Wittgen,68 D. H. Wright,68 A. K. Yarritu,68 K. Yi,68
C. C. Young,68 P. R. Burchat,69 A. J. Edwards,69 S. A. Majewski,69 B. A. Petersen,69 L. Wilden,69 S. Ahmed,70
M. S. Alam,70 R. Bula,70 J. A. Ernst,70 V. Jain,70 B. Pan,70 M. A. Saeed,70 F. R. Wappler,70 S. B. Zain,70
W. Bugg,71 M. Krishnamurthy,71 S. M. Spanier,71 R. Eckmann,72 J. L. Ritchie,72 A. M. Ruland,72 C. J. Schilling,72
R. F. Schwitters,72 J. M. Izen,73 X. C. Lou,73 S. Ye,73 F. Bianchi,74 F. Gallo,74 D. Gamba,74 M. Pelliccioni,74
M. Bomben,75 L. Bosisio,75 C. Cartaro,75 F. Cossutti,75 G. Della Ricca,75 L. Lanceri,75 L. Vitale,75 V. Azzolini,76
N. Lopez-March,76 F. Martinez-Vidal,76 D. A. Milanes,76 A. Oyanguren,76 J. Albert,77 Sw. Banerjee,77 B. Bhuyan,77
K. Hamano,77 R. Kowalewski,77 I. M. Nugent,77 J. M. Roney,77 R. J. Sobie,77 J. J. Back,78 P. F. Harrison,78
T. E. Latham,78 G. B. Mohanty,78 M. Pappagallo,78, § H. R. Band,79 X. Chen,79 S. Dasu,79 K. T. Flood,79
J. J. Hollar,79 P. E. Kutter,79 Y. Pan,79 M. Pierini,79 R. Prepost,79 S. L. Wu,79 Z. Yu,79 and H. Neal80
(The BABAR Collaboration)
1Laboratoire de Physique des Particules, IN2P3/CNRS et Université de Savoie, F-74941 Annecy-Le-Vieux, France
2Universitat de Barcelona, Facultat de Fisica, Departament ECM, E-08028 Barcelona, Spain
3Università di Bari, Dipartimento di Fisica and INFN, I-70126 Bari, Italy
4University of Bergen, Institute of Physics, N-5007 Bergen, Norway
5Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA
6University of Birmingham, Birmingham, B15 2TT, United Kingdom
7Ruhr Universität Bochum, Institut für Experimentalphysik 1, D-44780 Bochum, Germany
8University of Bristol, Bristol BS8 1TL, United Kingdom
9University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
10Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom
11Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
12University of California at Irvine, Irvine, California 92697, USA
13University of California at Los Angeles, Los Angeles, California 90024, USA
14University of California at Riverside, Riverside, California 92521, USA
15University of California at San Diego, La Jolla, California 92093, USA
16University of California at Santa Barbara, Santa Barbara, California 93106, USA
17University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064, USA
18California Institute of Technology, Pasadena, California 91125, USA
19University of Cincinnati, Cincinnati, Ohio 45221, USA
20University of Colorado, Boulder, Colorado 80309, USA
21Colorado State University, Fort Collins, Colorado 80523, USA
22Universität Dortmund, Institut für Physik, D-44221 Dortmund, Germany
23Technische Universität Dresden, Institut für Kern- und Teilchenphysik, D-01062 Dresden, Germany
24Laboratoire Leprince-Ringuet, CNRS/IN2P3, Ecole Polytechnique, F-91128 Palaiseau, France
25University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
26Università di Ferrara, Dipartimento di Fisica and INFN, I-44100 Ferrara, Italy
27Laboratori Nazionali di Frascati dell’INFN, I-00044 Frascati, Italy
28Università di Genova, Dipartimento di Fisica and INFN, I-16146 Genova, Italy
29Harvard University, Cambridge, Massachusetts 02138, USA
30Universität Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg, Germany
31Imperial College London, London, SW7 2AZ, United Kingdom
32University of Iowa, Iowa City, Iowa 52242, USA
33Iowa State University, Ames, Iowa 50011-3160, USA
34Johns Hopkins University, Baltimore, Maryland 21218, USA
35Universität Karlsruhe, Institut für Experimentelle Kernphysik, D-76021 Karlsruhe, Germany
36Laboratoire de l’Accélérateur Linéaire, IN2P3/CNRS et Université Paris-Sud 11,
Centre Scientifique d’Orsay, B. P. 34, F-91898 ORSAY Cedex, France
37Lawrence Livermore National Laboratory, Livermore, California 94550, USA
38University of Liverpool, Liverpool L69 7ZE, United Kingdom
39Queen Mary, University of London, E1 4NS, United Kingdom
40University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom
41University of Louisville, Louisville, Kentucky 40292, USA
42University of Manchester, Manchester M13 9PL, United Kingdom
43University of Maryland, College Park, Maryland 20742, USA
44University of Massachusetts, Amherst, Massachusetts 01003, USA
45Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139, USA
46McGill University, Montréal, Québec, Canada H3A 2T8
47Università di Milano, Dipartimento di Fisica and INFN, I-20133 Milano, Italy
48University of Mississippi, University, Mississippi 38677, USA
49Université de Montréal, Physique des Particules, Montréal, Québec, Canada H3C 3J7
50Mount Holyoke College, South Hadley, Massachusetts 01075, USA
51Università di Napoli Federico II, Dipartimento di Scienze Fisiche and INFN, I-80126, Napoli, Italy
52NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands
53University of Notre Dame, Notre Dame, Indiana 46556, USA
54Ohio State University, Columbus, Ohio 43210, USA
55University of Oregon, Eugene, Oregon 97403, USA
56Università di Padova, Dipartimento di Fisica and INFN, I-35131 Padova, Italy
57Laboratoire de Physique Nucléaire et de Hautes Energies,
IN2P3/CNRS, Université Pierre et Marie Curie-Paris6,
Université Denis Diderot-Paris7, F-75252 Paris, France
58University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
59Università di Perugia, Dipartimento di Fisica and INFN, I-06100 Perugia, Italy
60Università di Pisa, Dipartimento di Fisica, Scuola Normale Superiore and INFN, I-56127 Pisa, Italy
61Prairie View A&M University, Prairie View, Texas 77446, USA
62Princeton University, Princeton, New Jersey 08544, USA
63Università di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy
64Universität Rostock, D-18051 Rostock, Germany
65Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
66DSM/Dapnia, CEA/Saclay, F-91191 Gif-sur-Yvette, France
67University of South Carolina, Columbia, South Carolina 29208, USA
68Stanford Linear Accelerator Center, Stanford, California 94309, USA
69Stanford University, Stanford, California 94305-4060, USA
70State University of New York, Albany, New York 12222, USA
71University of Tennessee, Knoxville, Tennessee 37996, USA
72University of Texas at Austin, Austin, Texas 78712, USA
73University of Texas at Dallas, Richardson, Texas 75083, USA
74Università di Torino, Dipartimento di Fisica Sperimentale and INFN, I-10125 Torino, Italy
75Università di Trieste, Dipartimento di Fisica and INFN, I-34127 Trieste, Italy
76IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
77University of Victoria, Victoria, British Columbia, Canada V8W 3P6
78Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
79University of Wisconsin, Madison, Wisconsin 53706, USA
80Yale University, New Haven, Connecticut 06511, USA
(Dated: October 30, 2018)
We study the decays B0 → J/ψπ+π− and B+ → J/ψπ+π0, including intermediate resonances,
using a sample of 382 million BB pairs recorded by the BABAR detector at the PEP-II e+e− B
factory. We measure the branching fractions B(B0 → J/ψ ρ0) = (2.7 ± 0.3 ± 0.17) × 10−5 and
B(B+ → J/ψ ρ+) = (5.0± 0.7± 0.31) × 10−5.
We also set the following upper limits at the 90% confidence level: B(B0 → J/ψπ+π−non-
resonant) < 1.2 × 10−5, B(B0 → J/ψ f2) < 4.6 × 10
−6, and B(B+ → J/ψπ+π0 non-resonant)<
4.4×10−6. We measure the charge asymmetry in charged B decays to J/ψ ρ to be −0.11±0.12±0.08.
PACS numbers: 13.25.Hw, 12.15.Hh, 11.30.Er
The decay B0 → J/ψρ0 [1] can in principle be used
to measure the CP violation parameter sin2β. However,
the measurement is not as straightforward as for J/ψK0
[2, 3], because it involves the decay of a pseudoscalar me-
son to two vector mesons, resulting in both CP -odd and
CP -even final states. Furthermore, the decay can pro-
ceed through either a color-suppressed tree diagram, or
a penguin diagram, both shown in Fig. 1, and interfer-
ence between them could result in direct CP violation [4].
Direct CP violation may also occur in B+ → J/ψρ+ de-
cays, where it would manifest itself as a non-zero charge
asymmetry:
ACP =
N(B− → J/ψρ−)−N(B+ → J/ψρ+)
N(B− → J/ψρ−) +N(B+ → J/ψρ+)
. (1)
The large intrinsic width of the ρ meson necessitates an
analysis of a significant portion of the invariant mass
spectrum of the dipion system.
u; 
; t
FIG. 1: Tree and penguin diagrams for the process B0 →
J/ψ ρ0
The branching fraction for B0 → J/ψπ+π− has previ-
ously been measured at BABAR to be (4.6 ± 0.7± 0.6)×
10−5 [5], including a J/ψρ0 component with a branching
fraction of (1.6 ± 0.6 ± 0.4) × 10−5. This measurement
used a data sample containing approximately 56 million
BB pairs, which is a subset of the sample used in this
∗Deceased
†Also with Università di Perugia, Dipartimento di Fisica, Perugia,
Italy
‡Also with Università della Basilicata, Potenza, Italy
§Also with IPPP, Physics Department, Durham University,
Durham DH1 3LE, United Kingdom
analysis. The charged B decay to J/ψρ+ has not pre-
viously been observed, the CLEO collaboration set an
upper limit B(B+ → J/ψρ+) < 7.7 × 10−4 at the 90%
confidence level [6].
The data sample used here contains 382 million BB
pairs collected with the BABAR detector at the PEP-II
asymmetric-energy e+e− storage ring, taken at a center-
of-mass (CM) energy equivalent to the mass of the Υ (4S)
resonance. An additional data sample, corresponding to
an integrated luminosity of 36.8 fb−1, taken at a CM en-
ergy 40MeV below the Υ (4S) resonance, is used to study
backgrounds from continuum qq production, where q =
u, d, s, c.
A detailed description of the BABAR detector can be
found elsewhere [7]. Charged-particle trajectories are
measured by a five-layer silicon vertex tracker (SVT)
and a 40-layer drift chamber (DCH) operating in a
1.5 T solenoidal magnetic field. A detector of internally
reflected Cherenkov light (DIRC) is used for charged
hadron identification. Surrounding this is a CsI(Tl) elec-
tromagnetic calorimeter (EMC), and finally the instru-
mented flux return (IFR) of the solenoid, which consists
of layers of iron interspersed with resistive plate cham-
bers or limited streamer tubes.
The J/ψ meson is reconstructed in decays to l+l−,
where l± refers to a charged lepton, e± or µ±. Elec-
trons are selected on the basis of the ratio of EMC
shower energy to track momentum, and the energy pro-
file of the EMC shower. For J/ψ → e+e−, an attempt
is made to recover energy losses from bremsstrahlung,
by looking for showers in the EMC close to those from
the electron candidates. This procedure increases the
selection efficiency for J/ψ → e+e− candidates by ap-
proximately 30% [8]. The muon selection algorithm uses
a neural network, for which the most important input
is the number of interaction lengths traversed in the
IFR. The lepton pairs are fitted to a common vertex
and the invariant mass of the combination is required to
be in the range 2.98 (3.06) to 3.14GeV/c2 for the e+e−
(µ+µ−) channels. In order to reduce the background
fromB0 → J/ψK∗0(K∗0 → K+π−) decays, charged pion
candidates are required to satisfy stringent particle iden-
tification criteria, based on combined ionization energy
loss (dE/dx) in the DCH and SVT with the Cherenkov
angle measured in the DIRC.
All tracks are required to originate close to the interac-
tion point, and to lie in polar angle ranges where particle
identification efficiency is well measured. The allowed
ranges correspond to the geometric acceptances of the
DIRC for pions, the EMC for electrons, and the IFR for
muons.
Neutral pion candidates are formed by combining pairs
of isolated showers in the EMC. These are required to
spread over a minimum of three crystals, and to have an
energy greater than 200MeV.
To form a B candidate, the reconstructed J/ψ is com-
bined with either a pair of oppositely charged pions, or
a charged pion and a π0, and a kinematic and geomet-
ric fit is used to ensure that all final state particles are
consistent with coming from the same decay point. In
this fit, we constrain the invariant mass of the l+l− and
the γγ to have the nominal mass of the J/ψ and π0,
respectively [9]. The energy difference, ∆E, between
the candidate energy and the single beam energy, ECMbeam,
(both in the CM frame) is expected to be close to zero
for signal events, and is therefore required to be in the
interval −40 to 40MeV (−60 to 80MeV) for B0 (B+)
candidates, corresponding to approximately ±3σ of the
∆E resolution. Note that the range is asymmetric for B+
candidates because the π0 in the final state gives rise to a
tail on the low side of the distribution, due to the EMC
response to photons. For events where more than one
B candidate passes the selection criteria, the candidate
with the smallest value of |∆E| is chosen.
The branching fraction for each signal channel is ob-
tained from:
× ǫsig × B(J/ψ → l+l−)
, (2)
where Nsig and ǫsig are the observed yield and selection
efficiency, respectively, for a specific signal channel, and
is the number of B meson pairs. We assume that
the Υ (4S) decays equally often into neutral and charged
B meson pairs. The J/ψ → l+l− branching fraction is
taken to be (11.87± 0.12)% [9].
We extract the signal yields for the J/ψρ0, J/ψπ+π−
non-resonant, and J/ψf2 channels by performing a fit on
the sample of reconstructed B0 candidates. We also per-
form a similar fit to the sample of charged B candidates
in order to obtain the signal yields for the decay chan-
nels B+ → J/ψρ+ and B+ → J/ψπ+π0 non-resonant.
The fits are two-dimensional, extended, unbinned max-
imum likelihood fits to the distributions of mES and
mππ, Seven event categories are considered: (i) J/ψρ sig-
nal, (ii) J/ψππ non-resonant signal, (iii) J/ψf2 signal,
(iv) J/ψ K0
events, (v) background events that do not
contain a J/ψ (non-J/ψ background), (vi) background
events containing a J/ψ (inclusive J/ψ background), and
(vii) selected background channels that have been stud-
ied in more detail (exclusive J/ψ backgrounds). In the
fit to neutral B candidates, the decay channels that com-
prise category (vii) are J/ψK∗0, J/ψK∗+, J/ψK1(1270),
J/ψK+, J/ψρ+ [10], and J/ψπ+. For the fit to charged
B candidates, the exclusive J/ψ background channels are
J/ψK∗0, J/ψK∗+, J/ψK1(1270), J/ψK
+, J/ψK0
, and
J/ψK0
. In both cases, these decay channels are not in-
cluded in category (vi). Of course, categories (iii) and
(iv) are only present in the fit to neutral B candidates.
A probability density function (PDF) is constructed
for each category, and the sum of these PDFs is used to
fit the data. The likelihood function for the total sam-
ple is the product of the PDF values for each candidate,
multiplied by a Poisson factor:
(N ′)N
Pi, (3)
where N and N ′ are the numbers of observed and ex-
pected events, respectively, and Pi is the value of the
total PDF for event i. For all event categories except
for the exclusive J/ψ background, Pi is a product of one-
dimensional PDFs in mES and mππ.
Fig. 2 shows the mES and mππ distributions for the
data, and the projections of the PDFs for each cate-
gory. The functional forms of these PDFs are as follows.
For the J/ψρ0, J/ψπ+π−, J/ψf2, and J/ψK
compo-
nents, the mES distributions are parametrized by Gaus-
sian functions, all with the same values for the mean and
width, which are allowed to float in the fit. In the fit
to charged B candidates, a Crystal Ball function [11] is
used instead for the mES distributions of the J/ψρ
+ and
J/ψπ+π0 signal components, as the presence of a π0 in
the final state gives rise to a tail on the low mass side of
the peak.
The J/ψ ρ signal component is modeled by a relativis-
tic P -wave Breit-Wigner function [12] in mππ:
Fρ(mππ) =
mππΓ(mππ)P
2Leff+1
((m2ρ −m
2 +m2ρΓ(mππ)
, (4)
where Γ(mππ) = Γ0
1+R2q2
. The pa-
rameter q(mππ) is the pion momentum in the dipion rest
frame, with q0 = q(mρ); P is the J/ψ momentum in the
B rest frame; Leff is the orbital angular momentum be-
tween the J/ψ and the ρ which can be 0, 1 or 2; R is
the radius of the Blatt-Weisskopf barrier factor [13, 14],
which is taken to be (0.5±0.5) fm, and mρ is the ρ meson
mass.
The mππ distribution for the J/ψππ non-resonant sig-
nal is Fππ = q(mππ)P
3, the product of a three-body
phase space factor q(mππ)P and a factor P
2 motivated
by angular momentum conservation.
For the J/ψf2 component, the mππ distribution is de-
scribed by a relativistic D-wave Breit-Wigner, similar to
Eq. 4, but with an extra factor (q/q0)
2 in the expression
for Γ(mππ).
The decays to J/ψK0
are not considered signal for this
analysis. Most of them are removed by the requirement
that all tracks are consistent with coming from the same
vertex. The mππ distribution of the remaining J/ψK
events are modeled by a narrow Gaussian function.
Non-J/ψ background events are modeled by an
ARGUS function [15] in mES. The mππ PDF is the sum
of two Weibull functions [16], and a Breit-Wigner to de-
scribe the ρ component of the continuum background.
The parameters of this PDF are fixed to values obtained
from fits to the J/ψ mass sidebands of the data.
The mES distribution of the inclusive J/ψ background
is an ARGUS function plus a Gaussian at the B mass.
The width of this Gaussian is somewhat wider than that
used for signal components as it represents B candidates
that are not correctly reconstructed. The mππ PDF is a
4th-order polynomial. The PDF parameters for this com-
ponent are fixed to values obtained by fits to a large sam-
ple of B → J/ψ (→ l+l−)X Monte Carlo (MC) simulated
events, with signal events and exclusive J/ψ background
channels removed.
Each of the exclusive J/ψ background channels is mod-
eled by a two-dimensional PDF derived from the distri-
bution of MC events for that decay channel. The nor-
malizations of these PDFs are determined by taking into
account the selection efficiency on MC simulation, and
the world average branching fractions [9].
For the branching fraction fit to neutral B candidates
there are twelve free parameters: the yields of the J/ψρ,
J/ψππ, J/ψf2, J/ψK
, and inclusive J/ψ background
components, the mean and width of the Gaussian used
for the signal distribution in mES, the parameters mρ,
Γ0, and Leff in the ρ lineshape, and the mean and width
of the mππ distribution for the J/ψK
component. All
other parameters are fixed, including those describing
lineshape of the f2(1270), the normalizations and shapes
of the exclusive J/ψ background PDFs, and the shapes
of the inclusive J/ψ and non-J/ψ background PDFs. We
also fix the ratio of non-J/ψ to J/ψ (inclusive plus exclu-
sive) background yields to a value obtained from fitting
to data in the region mES < 5.26 (i.e. lower in mass than
the signal region), and extrapolated to the fit region us-
ing distributions from MC simulation.
The configuration for the chargedB branching fraction
fit is very similar. Here, there are eight free parameters,
since there are no J/ψK0
or J/ψf2 components.
We find from MC simulation studies that correlations
between mES and mππ give rise to small biases in the
numbers of J/ψρ+ and J/ψπ+π0 non-resonant signal can-
didates found in the charged B fit. The sizes of these bi-
ases are evaluated by examining the distribution of resid-
uals (Nobs − Ninput) for a large number of MC exper-
iments, and are listed in Table I. The yields obtained
from the branching fraction fit are therefore corrected to
take account of this by subtracting these quantities from
the fitted yields.
The signal yields and statistical errors obtained from
the branching fraction fits are listed in Table I. We also
list the statistical significances of the observed signals,
−2 ln(LNull/LMax), where LMax is the likelihood from
the fit, and LNull is the value of the likelihood func-
tion when the fit is performed with the signal yield con-
strained to zero events.
We obtain signal efficiencies using samples of MC sig-
nal events, produced in monthly blocks so as to match
variations in detector and background conditions. Par-
ticle identification efficiency is corrected using data con-
trol samples of electrons, muons, and pions. The sizes
of these corrections vary with momentum and polar an-
)2 (GeV/cm
5.2 5.25 5.3
)2 (GeV/cm
5.2 5.25 5.3
)2) (GeV/cπ πm(
0.5 1 1.5 20
)2) (GeV/cπ πm(
0.5 1 1.5 20
)2 (GeV/cESm
5.2 5.25 5.3
)2 (GeV/cESm
5.2 5.25 5.3
)2) (GeV/cπ πm(
0.5 1 1.5 2
)2) (GeV/cπ πm(
0.5 1 1.5 2
FIG. 2: Distributions of (a) mES and (b) mππ for B
J/ψπ+π− candidates. The solid line represents the total PDF,
while the other lines represent (cumulatively, from the bot-
tom of the plot) non-J/ψ background, inclusive J/ψ back-
ground, exclusive J/ψ background, J/ψπ+π− non-resonant
signal, and J/ψ f2 signal. The points with error bars repre-
sent the data and statistical errors. Plots (c) and (d) show
the same distributions for B+ → J/ψπ+π0 candidates. The
sharp spike in (b) corresponds to J/ψK0S events, while the
broader peak is due to J/ψ ρ0 events.
gle, and average corrections are about 1.5% for electrons,
5.9% for muons, and 1.8% for pions. With these correc-
tions applied, about 85% (50%) of electron (muon) pairs,
and about 85% of pions, satisfy their respective particle
identification requirements. A small, energy-dependent
correction (typically about −2% relative) is also applied
to decay modes containing a π0 to account for known
differences in photon detection efficiency between data
and MC simulation. The corrected signal efficiencies are
listed in Table I.
Systematic errors on the branching fraction measure-
ments arise from uncertainties on the signal efficiency, on
the fitted yield, on the number of B0B0 or B+B− events
in the sample, and on the J/ψ → l+l− branching fraction.
The number of BB pairs is known to 1.1% accuracy, and
an additional 1.6% uncertainty is assigned correspond-
ing to the assumption that the Υ (4S) decays 50% of the
time into B0B0 and 50% of the time into B+B− [9]. The
fractional uncertainty on B(J/ψ → l+l−) is 1.0% [9].
The systematic uncertainties on the efficiency are
largely due to imperfect simulation of the detector per-
formance. These effects are studied using various data
control samples. The largest sources of uncertainty are
pion identification efficiency, a 2.0% (3.4%) relative error
for charged (neutral) B decay channels, and π0 efficiency
(3% for charged B decays). Tracking efficiency (1.5%)
and lepton identification efficiency (1.0%) also contribute
TABLE I: Signal yields, detection efficiencies, and branching fractions for the signal decay channels. The fit bias, product of
secondary branching fractions (B(J/ψ → l+l−) and B(π0 → γγ)), and significances of the signals (using statistical uncertainties
only) are also listed. The corrected yields are obtained by subtracting the fit bias from the fitted yields. For the yields,
efficiencies, and branching fractions, the first errors are statistical and the second are systematic. For decay channels where no
significant signal is observed, we quote an upper limit at the 90% confidence level.
Mode Fit bias (events) Corrected yield (events) ǫ(%)
Bi(%) Signif. (σ) B(×10
J/ψ ρ0 0 251.1 ± 27.5 ± 11.2 20.6 ± 0.1± 0.8 11.87 ± 0.12 13.0 2.7± 0.3± 0.2
J/ψπ+π− 0 64.5 ± 35.5 ± 7.7 20.3 ± 0.1± 0.8 11.87 ± 0.12 2.0 < 1.2 (90% C.L.)
J/ψ f2 0 24.4 ± 13.8 ± 1.8 20.3 ± 0.1± 0.8 11.87 ± 0.12 2.0 < 0.46 (90% C.L.)
J/ψ ρ+ −6.8± 1.1 218.5 ± 28.8± 9.5 9.7 ± 0.1 ± 0.4 11.73 ± 0.12 11.6 5.0± 0.7± 0.3
J/ψπ+π0 +8.2± 0.9 −12.7± 27.1 ± 4.7 11.9 ± 0.1± 0.5 11.73 ± 0.12 0 < 0.44 (90% C.L.)
to the uncertainty on the efficiency. The polarization of
the ρ in B → J/ψρ decays is unknown. We use an MC
sample in which the ρ mesons are unpolarized to obtain
the central value of the signal efficiency. We also evaluate
the efficiency using MC data samples with different ρ po-
larizations, and observe a relative variation of 2%, which
is assigned as a systematic uncertainty on the branching
fraction measurement.
We evaluate the impact of the fit procedure by observ-
ing the changes in the yields when varying the PDF pa-
rameters that were fixed in the fit within their uncertain-
ties. The resulting differences are added quadratically for
sets of parameters that are relatively uncorrelated, and
added linearly for highly correlated sets of parameters.
We also repeat the fit using alternative functional forms
for some PDFs, namely the shape of the inclusive J/ψ
background in mππ, and the ρ lineshape, and include the
resulting differences in the yield in the systematic uncer-
tainty. In addition, for the J/ψρ+ and J/ψπ+π0 channels,
systematic uncertainties equal to half of the bias correc-
tions listed in Table I are assigned. The total systematic
uncertainties on the yield vary from 1.8 events for the
J/ψf2 channel, to 11.2 events for the J/ψρ
0 channel.
In order to assess the charge asymmetry Aρ, we per-
form a second fit to the charged B candidate sample. In
this fit, all the shape parameters for the signal and back-
ground components are fixed to values obtained from the
branching fraction fit. This reduces the number of free
parameters and improves the reliability of the fit. We in-
clude terms for the asymmetries in signal and background
components as follows:
Pi = N
(1−QiA
+ NNR ×
(1−QiA
NR)PNRi
(1−QiA
j,i , (5)
where Nρ, NNR, and N
j are the yields for the J/ψρ
signal, the J/ψπ+π0 non-resonant signal, and the dif-
ferent background components j, respectively, Qi is the
charge of the B candidate in event i, and Aρ, ANR, and
j are the corresponding charge asymmetries. The
asymmetry parameters for the exclusive J/ψ background
channels are fixed to world average values [9]. The asym-
metries for the non-J/ψ background and inclusive J/ψ
background components are assumed to be the same
inc = A
non ≡ A
bkg). This fit therefore has six free
parameters: the yields of the J/ψρ+ signal, J/ψπ+π0
non-resonant signal, and inclusive J/ψ background com-
ponents, and the asymmetries Aρ, ANR, and Abkg.
From the charge asymmetry fit, we obtain Aρ =
−0.11 ± 0.12(stat.). The signal and background yields
obtained from this fit are entirely consistent with those
from the branching fraction fit.
A potential contribution to the systematic uncertainty
on the charge asymmetry Aρ could come from differ-
ent pion identification efficiencies for π+ and π−, lead-
ing to different signal selection efficiencies for positively
and negatively charged B candidates. Using data control
samples, this effect is found to be negligible.
The other sources of systematic error on the asymme-
try are potential differences in the backgrounds for posi-
tive and negative B candidates. The parameters describ-
ing the charge asymmetries of the exclusive J/ψ back-
ground channels are varied within their uncertainties [9],
assuming a 10% uncertainty for the J/ψK1(1270) channel
for which no measurement is available. The normaliza-
tions of the exclusive background channels, and the shape
parameters of the inclusive J/ψ background and non-J/ψ
background components are varied in turn, and the fit is
repeated. The resulting changes to the fitted value of
Aρ are added in quadrature, and the total systematic
uncertainty is found to be ±0.08.
In summary, we measure the following branching frac-
tions, where the first error in each case is statistical and
the second is systematic: B(B0 → J/ψρ0) = (2.7± 0.3±
0.2)× 10−5, and B(B+ → J/ψρ+) = (5.0 ± 0.7 ± 0.3) ×
10−5. The signals for B0 → J/ψf2, B
0 → J/ψπ+π−
non-resonant, and B+ → J/ψπ+π0 non-resonant are not
statistically significant, thus we set the following upper
limits at the 90% confidence level: B(B0 → J/ψf2) <
4.6 × 10−6, B(B0 → J/ψπ+π−) < 1.2 × 10−5, and
B(B+ → J/ψπ+π0) < 4.4 × 10−6. These values are cal-
culated by summing the statistical and systematic un-
certainties in quadrature, multiplying the result by 1.28,
and adding it to the central value of the branching frac-
tion. We measure the charge asymmetry defined in Eq. 1
for the decays B± → J/ψρ±, Aρ = −0.11± 0.12± 0.08.
We are grateful for the excellent luminosity and ma-
chine conditions provided by our PEP-II colleagues, and
for the substantial dedicated effort from the comput-
ing organizations that support BABAR. The collaborat-
ing institutions wish to thank SLAC for its support and
kind hospitality. This work is supported by DOE and
NSF (USA), NSERC (Canada), IHEP (China), CEA and
CNRS-IN2P3 (France), BMBF and DFG (Germany),
INFN (Italy), FOM (The Netherlands), NFR (Norway),
MIST (Russia), MEC (Spain), and PPARC (United
Kingdom). Individuals have received support from the
Marie Curie EIF (European Union) and the A. P. Sloan
Foundation.
[1] Charge conjugation is implied throughout this letter un-
less stated otherwise.
[2] BABAR Collaboration, B. Aubert et al., Phys. Rev. Lett.
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[3] Belle Collaboration, K. Abe et al. , Phys. Rev. D 71,
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[7] BABAR Collaboration, B. Aubert et al., Nucl. Instrum.
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[9] W.-M. Yao et al., J. Phys. G 33, 1 (2006).
[10] Note that the J/ψ ρ+ channel which is being measured in
this note is one of the exclusive J/ψ background channels
in the fit to neutral B candidates. For the purpose of
choosing the normalization for this PDF, we assume a
value of (6.0± 6.0) × 10−5 for the branching fraction.
[11] M.J.Oreglia, Ph.D Thesis, SLAC-236(1980), Ap-
pendix D;
J.E.Gaiser, Ph.D Thesis, SLAC-255(1982), Appendix F;
T.Skwarnicki, Ph.D Thesis, DESY F31-86-02(1986), Ap-
pendix E.
The Crystal Ball function can be written as:
CB(m) =
(m−µ)2
m > µ− ασ
(n/α)n exp(−α2/2)
((µ−m)/σ+n/α−α)n
m < µ− ασ
where µ is the mean value, σ is a measure of the width,
and n and α are parameters describing the tail.
[12] J. Pisut and M. Roos, N. Phys. B 6, 325 (1968).
[13] J. M. Blatt and V. F. Weisskopf, Theoretical Nuclear
Physics (Wiley, New York, 1952), p. 361.
[14] Values for the barrier radius can be estimated from qq
meson models (S. Godfrey and N. Isgur, Phys. Rev. D
32, 189 (1985) : figure 12), and by fits to experimental
data (see for example D. Aston et al., Nucl. Phys. B 296,
493 (1988)).
[15] ARGUS Collaboration, H. Albrecht et al., Z. Phys. C 48,
543 (1990).
The ARGUS function can be written as
A(m) = y
1− y2 exp(ξ(1− y
)) y < 1
A(m) = 0 y > 1
where ξ is a shape parameter, y = m/mmax and mmax
is a kinematic limit, equal in this case to half the total
CM energy.
[16] The Weibull function can be written as
W (m) = C V (m−Mon)
(C−1)
exp[−V (m−Mmax)
where V = (C − 1)/(C(Mmax −Mon)
Mmax is the position of the function maximum, Mon is
the lower kinematic cut-off, and C is a shape parameter.
	References

  We study the decays B0 to J/psi pi+pi- and B+ to J/psi pi+pi0, including
intermediate resonances, using a sample of 382 million BBbar pairs recorded by
the BaBar detector at the PEP-II e+e- B factory. We measure the branching
fractions B(B0 ->J/psi rho0) = (2.7 +/- 0.3 +/- 0.17) x 10-5 and B(B+ ->J/psi
rho+) = (5.0 +/- 0.7 +/-0.31) x 10-5.
  We also set the following upper limits at the 90% confidence level: B(B0 ->
J/psi pi+ \pi- non-resonant) < 1.2 x 10-5, B(B0 -> J/psi f_2(1270)) < 4.6 x
10-6, and B(B+ -> J/psi pi+ pi0 non-resonant) < 4.4 x 10-6. We measure the
charge asymmetry in charged B decays to J/psi rho to be -0.11 +/- 0.12 +/-
0.08.

BABAR-PUB-07/017
SLAC-PUB-12441
Branching fraction and charge asymmetry measurements in B → J/ψππ decays
B. Aubert,1 M. Bona,1 D. Boutigny,1 Y. Karyotakis,1 J. P. Lees,1 V. Poireau,1 X. Prudent,1 V. Tisserand,1
A. Zghiche,1 J. Garra Tico,2 E. Grauges,2 L. Lopez,3 A. Palano,3 G. Eigen,4 I. Ofte,4 B. Stugu,4 L. Sun,4
G. S. Abrams,5 M. Battaglia,5 D. N. Brown,5 J. Button-Shafer,5 R. N. Cahn,5 Y. Groysman,5 R. G. Jacobsen,5
J. A. Kadyk,5 L. T. Kerth,5 Yu. G. Kolomensky,5 G. Kukartsev,5 D. Lopes Pegna,5 G. Lynch,5 L. M. Mir,5
T. J. Orimoto,5 M. Pripstein,5 N. A. Roe,5 M. T. Ronan,5, ∗ K. Tackmann,5 W. A. Wenzel,5 P. del Amo Sanchez,6
C. M. Hawkes,6 A. T. Watson,6 T. Held,7 H. Koch,7 B. Lewandowski,7 M. Pelizaeus,7 T. Schroeder,7
M. Steinke,7 W. N. Cottingham,8 D. Walker,8 D. J. Asgeirsson,9 T. Cuhadar-Donszelmann,9 B. G. Fulsom,9
C. Hearty,9 N. S. Knecht,9 T. S. Mattison,9 J. A. McKenna,9 A. Khan,10 M. Saleem,10 L. Teodorescu,10
V. E. Blinov,11 A. D. Bukin,11 V. P. Druzhinin,11 V. B. Golubev,11 A. P. Onuchin,11 S. I. Serednyakov,11
Yu. I. Skovpen,11 E. P. Solodov,11 K. Yu Todyshev,11 M. Bondioli,12 S. Curry,12 I. Eschrich,12 D. Kirkby,12
A. J. Lankford,12 P. Lund,12 M. Mandelkern,12 E. C. Martin,12 D. P. Stoker,12 S. Abachi,13 C. Buchanan,13
S. D. Foulkes,14 J. W. Gary,14 F. Liu,14 O. Long,14 B. C. Shen,14 L. Zhang,14 H. P. Paar,15 S. Rahatlou,15
V. Sharma,15 J. W. Berryhill,16 C. Campagnari,16 A. Cunha,16 B. Dahmes,16 T. M. Hong,16 D. Kovalskyi,16
J. D. Richman,16 T. W. Beck,17 A. M. Eisner,17 C. J. Flacco,17 C. A. Heusch,17 J. Kroseberg,17 W. S. Lockman,17
T. Schalk,17 B. A. Schumm,17 A. Seiden,17 D. C. Williams,17 M. G. Wilson,17 L. O. Winstrom,17 E. Chen,18
C. H. Cheng,18 A. Dvoretskii,18 F. Fang,18 D. G. Hitlin,18 I. Narsky,18 T. Piatenko,18 F. C. Porter,18
G. Mancinelli,19 B. T. Meadows,19 K. Mishra,19 M. D. Sokoloff,19 F. Blanc,20 P. C. Bloom,20 S. Chen,20
W. T. Ford,20 J. F. Hirschauer,20 A. Kreisel,20 M. Nagel,20 U. Nauenberg,20 A. Olivas,20 J. G. Smith,20
K. A. Ulmer,20 S. R. Wagner,20 J. Zhang,20 A. M. Gabareen,21 A. Soffer,21 W. H. Toki,21 R. J. Wilson,21
F. Winklmeier,21 Q. Zeng,21 D. D. Altenburg,22 E. Feltresi,22 A. Hauke,22 H. Jasper,22 J. Merkel,22 A. Petzold,22
B. Spaan,22 K. Wacker,22 T. Brandt,23 V. Klose,23 H. M. Lacker,23 W. F. Mader,23 R. Nogowski,23 J. Schubert,23
K. R. Schubert,23 R. Schwierz,23 J. E. Sundermann,23 A. Volk,23 D. Bernard,24 G. R. Bonneaud,24 E. Latour,24
V. Lombardo,24 Ch. Thiebaux,24 M. Verderi,24 P. J. Clark,25 W. Gradl,25 F. Muheim,25 S. Playfer,25
A. I. Robertson,25 Y. Xie,25 M. Andreotti,26 D. Bettoni,26 C. Bozzi,26 R. Calabrese,26 A. Cecchi,26 G. Cibinetto,26
P. Franchini,26 E. Luppi,26 M. Negrini,26 A. Petrella,26 L. Piemontese,26 E. Prencipe,26 V. Santoro,26 F. Anulli,27
R. Baldini-Ferroli,27 A. Calcaterra,27 R. de Sangro,27 G. Finocchiaro,27 S. Pacetti,27 P. Patteri,27 I. M. Peruzzi,27, †
M. Piccolo,27 M. Rama,27 A. Zallo,27 A. Buzzo,28 R. Contri,28 M. Lo Vetere,28 M. M. Macri,28 M. R. Monge,28
S. Passaggio,28 C. Patrignani,28 E. Robutti,28 A. Santroni,28 S. Tosi,28 K. S. Chaisanguanthum,29 M. Morii,29
J. Wu,29 R. S. Dubitzky,30 J. Marks,30 S. Schenk,30 U. Uwer,30 D. J. Bard,31 P. D. Dauncey,31 R. L. Flack,31
J. A. Nash,31 M. B. Nikolich,31 W. Panduro Vazquez,31 P. K. Behera,32 X. Chai,32 M. J. Charles,32 U. Mallik,32
N. T. Meyer,32 V. Ziegler,32 J. Cochran,33 H. B. Crawley,33 L. Dong,33 V. Eyges,33 W. T. Meyer,33 S. Prell,33
E. I. Rosenberg,33 A. E. Rubin,33 A. V. Gritsan,34 Z. J. Guo,34 C. K. Lae,34 A. G. Denig,35 M. Fritsch,35
G. Schott,35 N. Arnaud,36 J. Béquilleux,36 M. Davier,36 G. Grosdidier,36 A. Höcker,36 V. Lepeltier,36
F. Le Diberder,36 A. M. Lutz,36 S. Pruvot,36 S. Rodier,36 P. Roudeau,36 M. H. Schune,36 J. Serrano,36 V. Sordini,36
A. Stocchi,36 W. F. Wang,36 G. Wormser,36 D. J. Lange,37 D. M. Wright,37 C. A. Chavez,38 I. J. Forster,38
J. R. Fry,38 E. Gabathuler,38 R. Gamet,38 D. E. Hutchcroft,38 D. J. Payne,38 K. C. Schofield,38 C. Touramanis,38
A. J. Bevan,39 K. A. George,39 F. Di Lodovico,39 W. Menges,39 R. Sacco,39 G. Cowan,40 H. U. Flaecher,40
D. A. Hopkins,40 P. S. Jackson,40 T. R. McMahon,40 F. Salvatore,40 A. C. Wren,40 D. N. Brown,41 C. L. Davis,41
J. Allison,42 N. R. Barlow,42 R. J. Barlow,42 Y. M. Chia,42 C. L. Edgar,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 G. Blaylock,44
C. Dallapiccola,44 S. S. Hertzbach,44 X. Li,44 T. B. Moore,44 E. Salvati,44 S. Saremi,44 R. Cowan,45 P. H. Fisher,45
G. Sciolla,45 S. J. Sekula,45 M. Spitznagel,45 F. Taylor,45 R. K. Yamamoto,45 S. E. Mclachlin,46 P. M. Patel,46
S. H. Robertson,46 A. Lazzaro,47 F. Palombo,47 J. M. Bauer,48 L. Cremaldi,48 V. Eschenburg,48 R. Godang,48
R. Kroeger,48 D. A. Sanders,48 D. J. Summers,48 H. W. Zhao,48 S. Brunet,49 D. Côté,49 M. Simard,49 P. Taras,49
F. B. Viaud,49 H. Nicholson,50 G. De Nardo,51 F. Fabozzi,51, ‡ L. Lista,51 D. Monorchio,51 C. Sciacca,51
M. A. Baak,52 G. Raven,52 H. L. Snoek,52 C. P. Jessop,53 J. M. LoSecco,53 G. Benelli,54 L. A. Corwin,54
K. K. Gan,54 K. Honscheid,54 D. Hufnagel,54 H. Kagan,54 R. Kass,54 J. P. Morris,54 A. M. Rahimi,54
J. J. Regensburger,54 R. Ter-Antonyan,54 Q. K. Wong,54 N. L. Blount,55 J. Brau,55 R. Frey,55 O. Igonkina,55
http://arxiv.org/abs/0704.1266v1
J. A. Kolb,55 M. Lu,55 R. Rahmat,55 N. B. Sinev,55 D. Strom,55 J. Strube,55 E. Torrence,55 N. Gagliardi,56 A. Gaz,56
M. Margoni,56 M. Morandin,56 A. Pompili,56 M. Posocco,56 M. Rotondo,56 F. Simonetto,56 R. Stroili,56 C. Voci,56
E. Ben-Haim,57 H. Briand,57 J. Chauveau,57 P. David,57 L. Del Buono,57 Ch. de la Vaissière,57 O. Hamon,57
B. L. Hartfiel,57 Ph. Leruste,57 J. Malclès,57 J. Ocariz,57 A. Perez,57 L. Gladney,58 M. Biasini,59 R. Covarelli,59
E. Manoni,59 C. Angelini,60 G. Batignani,60 S. Bettarini,60 G. Calderini,60 M. Carpinelli,60 R. Cenci,60
A. Cervelli,60 F. Forti,60 M. A. Giorgi,60 A. Lusiani,60 G. Marchiori,60 M. A. Mazur,60 M. Morganti,60 N. Neri,60
E. Paoloni,60 G. Rizzo,60 J. J. Walsh,60 M. Haire,61 J. Biesiada,62 P. Elmer,62 Y. P. Lau,62 C. Lu,62 J. Olsen,62
A. J. S. Smith,62 A. V. Telnov,62 E. Baracchini,63 F. Bellini,63 G. Cavoto,63 A. D’Orazio,63 D. del Re,63 E. Di
Marco,63 R. Faccini,63 F. Ferrarotto,63 F. Ferroni,63 M. Gaspero,63 P. D. Jackson,63 L. Li Gioi,63 M. A. Mazzoni,63
S. Morganti,63 G. Piredda,63 F. Polci,63 F. Renga,63 C. Voena,63 M. Ebert,64 H. Schröder,64 R. Waldi,64 T. Adye,65
G. Castelli,65 B. Franek,65 E. O. Olaiya,65 S. Ricciardi,65 W. Roethel,65 F. F. Wilson,65 R. Aleksan,66 S. Emery,66
M. Escalier,66 A. Gaidot,66 S. F. Ganzhur,66 G. Hamel de Monchenault,66 W. Kozanecki,66 M. Legendre,66
G. Vasseur,66 Ch. Yèche,66 M. Zito,66 X. R. Chen,67 H. Liu,67 W. Park,67 M. V. Purohit,67 J. R. Wilson,67
M. T. Allen,68 D. Aston,68 R. Bartoldus,68 P. Bechtle,68 N. Berger,68 R. Claus,68 J. P. Coleman,68 M. R. Convery,68
J. C. Dingfelder,68 J. Dorfan,68 G. P. Dubois-Felsmann,68 D. Dujmic,68 W. Dunwoodie,68 R. C. Field,68
T. Glanzman,68 S. J. Gowdy,68 M. T. Graham,68 P. Grenier,68 C. Hast,68 T. Hryn’ova,68 W. R. Innes,68
M. H. Kelsey,68 H. Kim,68 P. Kim,68 D. W. G. S. Leith,68 S. Li,68 S. Luitz,68 V. Luth,68 H. L. Lynch,68
D. B. MacFarlane,68 H. Marsiske,68 R. Messner,68 D. R. Muller,68 C. P. O’Grady,68 A. Perazzo,68 M. Perl,68
T. Pulliam,68 B. N. Ratcliff,68 A. Roodman,68 A. A. Salnikov,68 R. H. Schindler,68 J. Schwiening,68 A. Snyder,68
J. Stelzer,68 D. Su,68 M. K. Sullivan,68 K. Suzuki,68 S. K. Swain,68 J. M. Thompson,68 J. Va’vra,68 N. van Bakel,68
A. P. Wagner,68 M. Weaver,68 W. J. Wisniewski,68 M. Wittgen,68 D. H. Wright,68 A. K. Yarritu,68 K. Yi,68
C. C. Young,68 P. R. Burchat,69 A. J. Edwards,69 S. A. Majewski,69 B. A. Petersen,69 L. Wilden,69 S. Ahmed,70
M. S. Alam,70 R. Bula,70 J. A. Ernst,70 V. Jain,70 B. Pan,70 M. A. Saeed,70 F. R. Wappler,70 S. B. Zain,70
W. Bugg,71 M. Krishnamurthy,71 S. M. Spanier,71 R. Eckmann,72 J. L. Ritchie,72 A. M. Ruland,72 C. J. Schilling,72
R. F. Schwitters,72 J. M. Izen,73 X. C. Lou,73 S. Ye,73 F. Bianchi,74 F. Gallo,74 D. Gamba,74 M. Pelliccioni,74
M. Bomben,75 L. Bosisio,75 C. Cartaro,75 F. Cossutti,75 G. Della Ricca,75 L. Lanceri,75 L. Vitale,75 V. Azzolini,76
N. Lopez-March,76 F. Martinez-Vidal,76 D. A. Milanes,76 A. Oyanguren,76 J. Albert,77 Sw. Banerjee,77 B. Bhuyan,77
K. Hamano,77 R. Kowalewski,77 I. M. Nugent,77 J. M. Roney,77 R. J. Sobie,77 J. J. Back,78 P. F. Harrison,78
T. E. Latham,78 G. B. Mohanty,78 M. Pappagallo,78, § H. R. Band,79 X. Chen,79 S. Dasu,79 K. T. Flood,79
J. J. Hollar,79 P. E. Kutter,79 Y. Pan,79 M. Pierini,79 R. Prepost,79 S. L. Wu,79 Z. Yu,79 and H. Neal80
(The BABAR Collaboration)
1Laboratoire de Physique des Particules, IN2P3/CNRS et Université de Savoie, F-74941 Annecy-Le-Vieux, France
2Universitat de Barcelona, Facultat de Fisica, Departament ECM, E-08028 Barcelona, Spain
3Università di Bari, Dipartimento di Fisica and INFN, I-70126 Bari, Italy
4University of Bergen, Institute of Physics, N-5007 Bergen, Norway
5Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA
6University of Birmingham, Birmingham, B15 2TT, United Kingdom
7Ruhr Universität Bochum, Institut für Experimentalphysik 1, D-44780 Bochum, Germany
8University of Bristol, Bristol BS8 1TL, United Kingdom
9University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
10Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom
11Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
12University of California at Irvine, Irvine, California 92697, USA
13University of California at Los Angeles, Los Angeles, California 90024, USA
14University of California at Riverside, Riverside, California 92521, USA
15University of California at San Diego, La Jolla, California 92093, USA
16University of California at Santa Barbara, Santa Barbara, California 93106, USA
17University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064, USA
18California Institute of Technology, Pasadena, California 91125, USA
19University of Cincinnati, Cincinnati, Ohio 45221, USA
20University of Colorado, Boulder, Colorado 80309, USA
21Colorado State University, Fort Collins, Colorado 80523, USA
22Universität Dortmund, Institut für Physik, D-44221 Dortmund, Germany
23Technische Universität Dresden, Institut für Kern- und Teilchenphysik, D-01062 Dresden, Germany
24Laboratoire Leprince-Ringuet, CNRS/IN2P3, Ecole Polytechnique, F-91128 Palaiseau, France
25University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
26Università di Ferrara, Dipartimento di Fisica and INFN, I-44100 Ferrara, Italy
27Laboratori Nazionali di Frascati dell’INFN, I-00044 Frascati, Italy
28Università di Genova, Dipartimento di Fisica and INFN, I-16146 Genova, Italy
29Harvard University, Cambridge, Massachusetts 02138, USA
30Universität Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg, Germany
31Imperial College London, London, SW7 2AZ, United Kingdom
32University of Iowa, Iowa City, Iowa 52242, USA
33Iowa State University, Ames, Iowa 50011-3160, USA
34Johns Hopkins University, Baltimore, Maryland 21218, USA
35Universität Karlsruhe, Institut für Experimentelle Kernphysik, D-76021 Karlsruhe, Germany
36Laboratoire de l’Accélérateur Linéaire, IN2P3/CNRS et Université Paris-Sud 11,
Centre Scientifique d’Orsay, B. P. 34, F-91898 ORSAY Cedex, France
37Lawrence Livermore National Laboratory, Livermore, California 94550, USA
38University of Liverpool, Liverpool L69 7ZE, United Kingdom
39Queen Mary, University of London, E1 4NS, United Kingdom
40University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom
41University of Louisville, Louisville, Kentucky 40292, USA
42University of Manchester, Manchester M13 9PL, United Kingdom
43University of Maryland, College Park, Maryland 20742, USA
44University of Massachusetts, Amherst, Massachusetts 01003, USA
45Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139, USA
46McGill University, Montréal, Québec, Canada H3A 2T8
47Università di Milano, Dipartimento di Fisica and INFN, I-20133 Milano, Italy
48University of Mississippi, University, Mississippi 38677, USA
49Université de Montréal, Physique des Particules, Montréal, Québec, Canada H3C 3J7
50Mount Holyoke College, South Hadley, Massachusetts 01075, USA
51Università di Napoli Federico II, Dipartimento di Scienze Fisiche and INFN, I-80126, Napoli, Italy
52NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands
53University of Notre Dame, Notre Dame, Indiana 46556, USA
54Ohio State University, Columbus, Ohio 43210, USA
55University of Oregon, Eugene, Oregon 97403, USA
56Università di Padova, Dipartimento di Fisica and INFN, I-35131 Padova, Italy
57Laboratoire de Physique Nucléaire et de Hautes Energies,
IN2P3/CNRS, Université Pierre et Marie Curie-Paris6,
Université Denis Diderot-Paris7, F-75252 Paris, France
58University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
59Università di Perugia, Dipartimento di Fisica and INFN, I-06100 Perugia, Italy
60Università di Pisa, Dipartimento di Fisica, Scuola Normale Superiore and INFN, I-56127 Pisa, Italy
61Prairie View A&M University, Prairie View, Texas 77446, USA
62Princeton University, Princeton, New Jersey 08544, USA
63Università di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy
64Universität Rostock, D-18051 Rostock, Germany
65Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
66DSM/Dapnia, CEA/Saclay, F-91191 Gif-sur-Yvette, France
67University of South Carolina, Columbia, South Carolina 29208, USA
68Stanford Linear Accelerator Center, Stanford, California 94309, USA
69Stanford University, Stanford, California 94305-4060, USA
70State University of New York, Albany, New York 12222, USA
71University of Tennessee, Knoxville, Tennessee 37996, USA
72University of Texas at Austin, Austin, Texas 78712, USA
73University of Texas at Dallas, Richardson, Texas 75083, USA
74Università di Torino, Dipartimento di Fisica Sperimentale and INFN, I-10125 Torino, Italy
75Università di Trieste, Dipartimento di Fisica and INFN, I-34127 Trieste, Italy
76IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
77University of Victoria, Victoria, British Columbia, Canada V8W 3P6
78Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
79University of Wisconsin, Madison, Wisconsin 53706, USA
80Yale University, New Haven, Connecticut 06511, USA
(Dated: October 30, 2018)
We study the decays B0 → J/ψπ+π− and B+ → J/ψπ+π0, including intermediate resonances,
using a sample of 382 million BB pairs recorded by the BABAR detector at the PEP-II e+e− B
factory. We measure the branching fractions B(B0 → J/ψ ρ0) = (2.7 ± 0.3 ± 0.17) × 10−5 and
B(B+ → J/ψ ρ+) = (5.0± 0.7± 0.31) × 10−5.
We also set the following upper limits at the 90% confidence level: B(B0 → J/ψπ+π−non-
resonant) < 1.2 × 10−5, B(B0 → J/ψ f2) < 4.6 × 10
−6, and B(B+ → J/ψπ+π0 non-resonant)<
4.4×10−6. We measure the charge asymmetry in charged B decays to J/ψ ρ to be −0.11±0.12±0.08.
PACS numbers: 13.25.Hw, 12.15.Hh, 11.30.Er
The decay B0 → J/ψρ0 [1] can in principle be used
to measure the CP violation parameter sin2β. However,
the measurement is not as straightforward as for J/ψK0
[2, 3], because it involves the decay of a pseudoscalar me-
son to two vector mesons, resulting in both CP -odd and
CP -even final states. Furthermore, the decay can pro-
ceed through either a color-suppressed tree diagram, or
a penguin diagram, both shown in Fig. 1, and interfer-
ence between them could result in direct CP violation [4].
Direct CP violation may also occur in B+ → J/ψρ+ de-
cays, where it would manifest itself as a non-zero charge
asymmetry:
ACP =
N(B− → J/ψρ−)−N(B+ → J/ψρ+)
N(B− → J/ψρ−) +N(B+ → J/ψρ+)
. (1)
The large intrinsic width of the ρ meson necessitates an
analysis of a significant portion of the invariant mass
spectrum of the dipion system.
u; 
; t
FIG. 1: Tree and penguin diagrams for the process B0 →
J/ψ ρ0
The branching fraction for B0 → J/ψπ+π− has previ-
ously been measured at BABAR to be (4.6 ± 0.7± 0.6)×
10−5 [5], including a J/ψρ0 component with a branching
fraction of (1.6 ± 0.6 ± 0.4) × 10−5. This measurement
used a data sample containing approximately 56 million
BB pairs, which is a subset of the sample used in this
∗Deceased
†Also with Università di Perugia, Dipartimento di Fisica, Perugia,
Italy
‡Also with Università della Basilicata, Potenza, Italy
§Also with IPPP, Physics Department, Durham University,
Durham DH1 3LE, United Kingdom
analysis. The charged B decay to J/ψρ+ has not pre-
viously been observed, the CLEO collaboration set an
upper limit B(B+ → J/ψρ+) < 7.7 × 10−4 at the 90%
confidence level [6].
The data sample used here contains 382 million BB
pairs collected with the BABAR detector at the PEP-II
asymmetric-energy e+e− storage ring, taken at a center-
of-mass (CM) energy equivalent to the mass of the Υ (4S)
resonance. An additional data sample, corresponding to
an integrated luminosity of 36.8 fb−1, taken at a CM en-
ergy 40MeV below the Υ (4S) resonance, is used to study
backgrounds from continuum qq production, where q =
u, d, s, c.
A detailed description of the BABAR detector can be
found elsewhere [7]. Charged-particle trajectories are
measured by a five-layer silicon vertex tracker (SVT)
and a 40-layer drift chamber (DCH) operating in a
1.5 T solenoidal magnetic field. A detector of internally
reflected Cherenkov light (DIRC) is used for charged
hadron identification. Surrounding this is a CsI(Tl) elec-
tromagnetic calorimeter (EMC), and finally the instru-
mented flux return (IFR) of the solenoid, which consists
of layers of iron interspersed with resistive plate cham-
bers or limited streamer tubes.
The J/ψ meson is reconstructed in decays to l+l−,
where l± refers to a charged lepton, e± or µ±. Elec-
trons are selected on the basis of the ratio of EMC
shower energy to track momentum, and the energy pro-
file of the EMC shower. For J/ψ → e+e−, an attempt
is made to recover energy losses from bremsstrahlung,
by looking for showers in the EMC close to those from
the electron candidates. This procedure increases the
selection efficiency for J/ψ → e+e− candidates by ap-
proximately 30% [8]. The muon selection algorithm uses
a neural network, for which the most important input
is the number of interaction lengths traversed in the
IFR. The lepton pairs are fitted to a common vertex
and the invariant mass of the combination is required to
be in the range 2.98 (3.06) to 3.14GeV/c2 for the e+e−
(µ+µ−) channels. In order to reduce the background
fromB0 → J/ψK∗0(K∗0 → K+π−) decays, charged pion
candidates are required to satisfy stringent particle iden-
tification criteria, based on combined ionization energy
loss (dE/dx) in the DCH and SVT with the Cherenkov
angle measured in the DIRC.
All tracks are required to originate close to the interac-
tion point, and to lie in polar angle ranges where particle
identification efficiency is well measured. The allowed
ranges correspond to the geometric acceptances of the
DIRC for pions, the EMC for electrons, and the IFR for
muons.
Neutral pion candidates are formed by combining pairs
of isolated showers in the EMC. These are required to
spread over a minimum of three crystals, and to have an
energy greater than 200MeV.
To form a B candidate, the reconstructed J/ψ is com-
bined with either a pair of oppositely charged pions, or
a charged pion and a π0, and a kinematic and geomet-
ric fit is used to ensure that all final state particles are
consistent with coming from the same decay point. In
this fit, we constrain the invariant mass of the l+l− and
the γγ to have the nominal mass of the J/ψ and π0,
respectively [9]. The energy difference, ∆E, between
the candidate energy and the single beam energy, ECMbeam,
(both in the CM frame) is expected to be close to zero
for signal events, and is therefore required to be in the
interval −40 to 40MeV (−60 to 80MeV) for B0 (B+)
candidates, corresponding to approximately ±3σ of the
∆E resolution. Note that the range is asymmetric for B+
candidates because the π0 in the final state gives rise to a
tail on the low side of the distribution, due to the EMC
response to photons. For events where more than one
B candidate passes the selection criteria, the candidate
with the smallest value of |∆E| is chosen.
The branching fraction for each signal channel is ob-
tained from:
× ǫsig × B(J/ψ → l+l−)
, (2)
where Nsig and ǫsig are the observed yield and selection
efficiency, respectively, for a specific signal channel, and
is the number of B meson pairs. We assume that
the Υ (4S) decays equally often into neutral and charged
B meson pairs. The J/ψ → l+l− branching fraction is
taken to be (11.87± 0.12)% [9].
We extract the signal yields for the J/ψρ0, J/ψπ+π−
non-resonant, and J/ψf2 channels by performing a fit on
the sample of reconstructed B0 candidates. We also per-
form a similar fit to the sample of charged B candidates
in order to obtain the signal yields for the decay chan-
nels B+ → J/ψρ+ and B+ → J/ψπ+π0 non-resonant.
The fits are two-dimensional, extended, unbinned max-
imum likelihood fits to the distributions of mES and
mππ, Seven event categories are considered: (i) J/ψρ sig-
nal, (ii) J/ψππ non-resonant signal, (iii) J/ψf2 signal,
(iv) J/ψ K0
events, (v) background events that do not
contain a J/ψ (non-J/ψ background), (vi) background
events containing a J/ψ (inclusive J/ψ background), and
(vii) selected background channels that have been stud-
ied in more detail (exclusive J/ψ backgrounds). In the
fit to neutral B candidates, the decay channels that com-
prise category (vii) are J/ψK∗0, J/ψK∗+, J/ψK1(1270),
J/ψK+, J/ψρ+ [10], and J/ψπ+. For the fit to charged
B candidates, the exclusive J/ψ background channels are
J/ψK∗0, J/ψK∗+, J/ψK1(1270), J/ψK
+, J/ψK0
, and
J/ψK0
. In both cases, these decay channels are not in-
cluded in category (vi). Of course, categories (iii) and
(iv) are only present in the fit to neutral B candidates.
A probability density function (PDF) is constructed
for each category, and the sum of these PDFs is used to
fit the data. The likelihood function for the total sam-
ple is the product of the PDF values for each candidate,
multiplied by a Poisson factor:
(N ′)N
Pi, (3)
where N and N ′ are the numbers of observed and ex-
pected events, respectively, and Pi is the value of the
total PDF for event i. For all event categories except
for the exclusive J/ψ background, Pi is a product of one-
dimensional PDFs in mES and mππ.
Fig. 2 shows the mES and mππ distributions for the
data, and the projections of the PDFs for each cate-
gory. The functional forms of these PDFs are as follows.
For the J/ψρ0, J/ψπ+π−, J/ψf2, and J/ψK
compo-
nents, the mES distributions are parametrized by Gaus-
sian functions, all with the same values for the mean and
width, which are allowed to float in the fit. In the fit
to charged B candidates, a Crystal Ball function [11] is
used instead for the mES distributions of the J/ψρ
+ and
J/ψπ+π0 signal components, as the presence of a π0 in
the final state gives rise to a tail on the low mass side of
the peak.
The J/ψ ρ signal component is modeled by a relativis-
tic P -wave Breit-Wigner function [12] in mππ:
Fρ(mππ) =
mππΓ(mππ)P
2Leff+1
((m2ρ −m
2 +m2ρΓ(mππ)
, (4)
where Γ(mππ) = Γ0
1+R2q2
. The pa-
rameter q(mππ) is the pion momentum in the dipion rest
frame, with q0 = q(mρ); P is the J/ψ momentum in the
B rest frame; Leff is the orbital angular momentum be-
tween the J/ψ and the ρ which can be 0, 1 or 2; R is
the radius of the Blatt-Weisskopf barrier factor [13, 14],
which is taken to be (0.5±0.5) fm, and mρ is the ρ meson
mass.
The mππ distribution for the J/ψππ non-resonant sig-
nal is Fππ = q(mππ)P
3, the product of a three-body
phase space factor q(mππ)P and a factor P
2 motivated
by angular momentum conservation.
For the J/ψf2 component, the mππ distribution is de-
scribed by a relativistic D-wave Breit-Wigner, similar to
Eq. 4, but with an extra factor (q/q0)
2 in the expression
for Γ(mππ).
The decays to J/ψK0
are not considered signal for this
analysis. Most of them are removed by the requirement
that all tracks are consistent with coming from the same
vertex. The mππ distribution of the remaining J/ψK
events are modeled by a narrow Gaussian function.
Non-J/ψ background events are modeled by an
ARGUS function [15] in mES. The mππ PDF is the sum
of two Weibull functions [16], and a Breit-Wigner to de-
scribe the ρ component of the continuum background.
The parameters of this PDF are fixed to values obtained
from fits to the J/ψ mass sidebands of the data.
The mES distribution of the inclusive J/ψ background
is an ARGUS function plus a Gaussian at the B mass.
The width of this Gaussian is somewhat wider than that
used for signal components as it represents B candidates
that are not correctly reconstructed. The mππ PDF is a
4th-order polynomial. The PDF parameters for this com-
ponent are fixed to values obtained by fits to a large sam-
ple of B → J/ψ (→ l+l−)X Monte Carlo (MC) simulated
events, with signal events and exclusive J/ψ background
channels removed.
Each of the exclusive J/ψ background channels is mod-
eled by a two-dimensional PDF derived from the distri-
bution of MC events for that decay channel. The nor-
malizations of these PDFs are determined by taking into
account the selection efficiency on MC simulation, and
the world average branching fractions [9].
For the branching fraction fit to neutral B candidates
there are twelve free parameters: the yields of the J/ψρ,
J/ψππ, J/ψf2, J/ψK
, and inclusive J/ψ background
components, the mean and width of the Gaussian used
for the signal distribution in mES, the parameters mρ,
Γ0, and Leff in the ρ lineshape, and the mean and width
of the mππ distribution for the J/ψK
component. All
other parameters are fixed, including those describing
lineshape of the f2(1270), the normalizations and shapes
of the exclusive J/ψ background PDFs, and the shapes
of the inclusive J/ψ and non-J/ψ background PDFs. We
also fix the ratio of non-J/ψ to J/ψ (inclusive plus exclu-
sive) background yields to a value obtained from fitting
to data in the region mES < 5.26 (i.e. lower in mass than
the signal region), and extrapolated to the fit region us-
ing distributions from MC simulation.
The configuration for the chargedB branching fraction
fit is very similar. Here, there are eight free parameters,
since there are no J/ψK0
or J/ψf2 components.
We find from MC simulation studies that correlations
between mES and mππ give rise to small biases in the
numbers of J/ψρ+ and J/ψπ+π0 non-resonant signal can-
didates found in the charged B fit. The sizes of these bi-
ases are evaluated by examining the distribution of resid-
uals (Nobs − Ninput) for a large number of MC exper-
iments, and are listed in Table I. The yields obtained
from the branching fraction fit are therefore corrected to
take account of this by subtracting these quantities from
the fitted yields.
The signal yields and statistical errors obtained from
the branching fraction fits are listed in Table I. We also
list the statistical significances of the observed signals,
−2 ln(LNull/LMax), where LMax is the likelihood from
the fit, and LNull is the value of the likelihood func-
tion when the fit is performed with the signal yield con-
strained to zero events.
We obtain signal efficiencies using samples of MC sig-
nal events, produced in monthly blocks so as to match
variations in detector and background conditions. Par-
ticle identification efficiency is corrected using data con-
trol samples of electrons, muons, and pions. The sizes
of these corrections vary with momentum and polar an-
)2 (GeV/cm
5.2 5.25 5.3
)2 (GeV/cm
5.2 5.25 5.3
)2) (GeV/cπ πm(
0.5 1 1.5 20
)2) (GeV/cπ πm(
0.5 1 1.5 20
)2 (GeV/cESm
5.2 5.25 5.3
)2 (GeV/cESm
5.2 5.25 5.3
)2) (GeV/cπ πm(
0.5 1 1.5 2
)2) (GeV/cπ πm(
0.5 1 1.5 2
FIG. 2: Distributions of (a) mES and (b) mππ for B
J/ψπ+π− candidates. The solid line represents the total PDF,
while the other lines represent (cumulatively, from the bot-
tom of the plot) non-J/ψ background, inclusive J/ψ back-
ground, exclusive J/ψ background, J/ψπ+π− non-resonant
signal, and J/ψ f2 signal. The points with error bars repre-
sent the data and statistical errors. Plots (c) and (d) show
the same distributions for B+ → J/ψπ+π0 candidates. The
sharp spike in (b) corresponds to J/ψK0S events, while the
broader peak is due to J/ψ ρ0 events.
gle, and average corrections are about 1.5% for electrons,
5.9% for muons, and 1.8% for pions. With these correc-
tions applied, about 85% (50%) of electron (muon) pairs,
and about 85% of pions, satisfy their respective particle
identification requirements. A small, energy-dependent
correction (typically about −2% relative) is also applied
to decay modes containing a π0 to account for known
differences in photon detection efficiency between data
and MC simulation. The corrected signal efficiencies are
listed in Table I.
Systematic errors on the branching fraction measure-
ments arise from uncertainties on the signal efficiency, on
the fitted yield, on the number of B0B0 or B+B− events
in the sample, and on the J/ψ → l+l− branching fraction.
The number of BB pairs is known to 1.1% accuracy, and
an additional 1.6% uncertainty is assigned correspond-
ing to the assumption that the Υ (4S) decays 50% of the
time into B0B0 and 50% of the time into B+B− [9]. The
fractional uncertainty on B(J/ψ → l+l−) is 1.0% [9].
The systematic uncertainties on the efficiency are
largely due to imperfect simulation of the detector per-
formance. These effects are studied using various data
control samples. The largest sources of uncertainty are
pion identification efficiency, a 2.0% (3.4%) relative error
for charged (neutral) B decay channels, and π0 efficiency
(3% for charged B decays). Tracking efficiency (1.5%)
and lepton identification efficiency (1.0%) also contribute
TABLE I: Signal yields, detection efficiencies, and branching fractions for the signal decay channels. The fit bias, product of
secondary branching fractions (B(J/ψ → l+l−) and B(π0 → γγ)), and significances of the signals (using statistical uncertainties
only) are also listed. The corrected yields are obtained by subtracting the fit bias from the fitted yields. For the yields,
efficiencies, and branching fractions, the first errors are statistical and the second are systematic. For decay channels where no
significant signal is observed, we quote an upper limit at the 90% confidence level.
Mode Fit bias (events) Corrected yield (events) ǫ(%)
Bi(%) Signif. (σ) B(×10
J/ψ ρ0 0 251.1 ± 27.5 ± 11.2 20.6 ± 0.1± 0.8 11.87 ± 0.12 13.0 2.7± 0.3± 0.2
J/ψπ+π− 0 64.5 ± 35.5 ± 7.7 20.3 ± 0.1± 0.8 11.87 ± 0.12 2.0 < 1.2 (90% C.L.)
J/ψ f2 0 24.4 ± 13.8 ± 1.8 20.3 ± 0.1± 0.8 11.87 ± 0.12 2.0 < 0.46 (90% C.L.)
J/ψ ρ+ −6.8± 1.1 218.5 ± 28.8± 9.5 9.7 ± 0.1 ± 0.4 11.73 ± 0.12 11.6 5.0± 0.7± 0.3
J/ψπ+π0 +8.2± 0.9 −12.7± 27.1 ± 4.7 11.9 ± 0.1± 0.5 11.73 ± 0.12 0 < 0.44 (90% C.L.)
to the uncertainty on the efficiency. The polarization of
the ρ in B → J/ψρ decays is unknown. We use an MC
sample in which the ρ mesons are unpolarized to obtain
the central value of the signal efficiency. We also evaluate
the efficiency using MC data samples with different ρ po-
larizations, and observe a relative variation of 2%, which
is assigned as a systematic uncertainty on the branching
fraction measurement.
We evaluate the impact of the fit procedure by observ-
ing the changes in the yields when varying the PDF pa-
rameters that were fixed in the fit within their uncertain-
ties. The resulting differences are added quadratically for
sets of parameters that are relatively uncorrelated, and
added linearly for highly correlated sets of parameters.
We also repeat the fit using alternative functional forms
for some PDFs, namely the shape of the inclusive J/ψ
background in mππ, and the ρ lineshape, and include the
resulting differences in the yield in the systematic uncer-
tainty. In addition, for the J/ψρ+ and J/ψπ+π0 channels,
systematic uncertainties equal to half of the bias correc-
tions listed in Table I are assigned. The total systematic
uncertainties on the yield vary from 1.8 events for the
J/ψf2 channel, to 11.2 events for the J/ψρ
0 channel.
In order to assess the charge asymmetry Aρ, we per-
form a second fit to the charged B candidate sample. In
this fit, all the shape parameters for the signal and back-
ground components are fixed to values obtained from the
branching fraction fit. This reduces the number of free
parameters and improves the reliability of the fit. We in-
clude terms for the asymmetries in signal and background
components as follows:
Pi = N
(1−QiA
+ NNR ×
(1−QiA
NR)PNRi
(1−QiA
j,i , (5)
where Nρ, NNR, and N
j are the yields for the J/ψρ
signal, the J/ψπ+π0 non-resonant signal, and the dif-
ferent background components j, respectively, Qi is the
charge of the B candidate in event i, and Aρ, ANR, and
j are the corresponding charge asymmetries. The
asymmetry parameters for the exclusive J/ψ background
channels are fixed to world average values [9]. The asym-
metries for the non-J/ψ background and inclusive J/ψ
background components are assumed to be the same
inc = A
non ≡ A
bkg). This fit therefore has six free
parameters: the yields of the J/ψρ+ signal, J/ψπ+π0
non-resonant signal, and inclusive J/ψ background com-
ponents, and the asymmetries Aρ, ANR, and Abkg.
From the charge asymmetry fit, we obtain Aρ =
−0.11 ± 0.12(stat.). The signal and background yields
obtained from this fit are entirely consistent with those
from the branching fraction fit.
A potential contribution to the systematic uncertainty
on the charge asymmetry Aρ could come from differ-
ent pion identification efficiencies for π+ and π−, lead-
ing to different signal selection efficiencies for positively
and negatively charged B candidates. Using data control
samples, this effect is found to be negligible.
The other sources of systematic error on the asymme-
try are potential differences in the backgrounds for posi-
tive and negative B candidates. The parameters describ-
ing the charge asymmetries of the exclusive J/ψ back-
ground channels are varied within their uncertainties [9],
assuming a 10% uncertainty for the J/ψK1(1270) channel
for which no measurement is available. The normaliza-
tions of the exclusive background channels, and the shape
parameters of the inclusive J/ψ background and non-J/ψ
background components are varied in turn, and the fit is
repeated. The resulting changes to the fitted value of
Aρ are added in quadrature, and the total systematic
uncertainty is found to be ±0.08.
In summary, we measure the following branching frac-
tions, where the first error in each case is statistical and
the second is systematic: B(B0 → J/ψρ0) = (2.7± 0.3±
0.2)× 10−5, and B(B+ → J/ψρ+) = (5.0 ± 0.7 ± 0.3) ×
10−5. The signals for B0 → J/ψf2, B
0 → J/ψπ+π−
non-resonant, and B+ → J/ψπ+π0 non-resonant are not
statistically significant, thus we set the following upper
limits at the 90% confidence level: B(B0 → J/ψf2) <
4.6 × 10−6, B(B0 → J/ψπ+π−) < 1.2 × 10−5, and
B(B+ → J/ψπ+π0) < 4.4 × 10−6. These values are cal-
culated by summing the statistical and systematic un-
certainties in quadrature, multiplying the result by 1.28,
and adding it to the central value of the branching frac-
tion. We measure the charge asymmetry defined in Eq. 1
for the decays B± → J/ψρ±, Aρ = −0.11± 0.12± 0.08.
We are grateful for the excellent luminosity and ma-
chine conditions provided by our PEP-II colleagues, and
for the substantial dedicated effort from the comput-
ing organizations that support BABAR. The collaborat-
ing institutions wish to thank SLAC for its support and
kind hospitality. This work is supported by DOE and
NSF (USA), NSERC (Canada), IHEP (China), CEA and
CNRS-IN2P3 (France), BMBF and DFG (Germany),
INFN (Italy), FOM (The Netherlands), NFR (Norway),
MIST (Russia), MEC (Spain), and PPARC (United
Kingdom). Individuals have received support from the
Marie Curie EIF (European Union) and the A. P. Sloan
Foundation.
[1] Charge conjugation is implied throughout this letter un-
less stated otherwise.
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[9] W.-M. Yao et al., J. Phys. G 33, 1 (2006).
[10] Note that the J/ψ ρ+ channel which is being measured in
this note is one of the exclusive J/ψ background channels
in the fit to neutral B candidates. For the purpose of
choosing the normalization for this PDF, we assume a
value of (6.0± 6.0) × 10−5 for the branching fraction.
[11] M.J.Oreglia, Ph.D Thesis, SLAC-236(1980), Ap-
pendix D;
J.E.Gaiser, Ph.D Thesis, SLAC-255(1982), Appendix F;
T.Skwarnicki, Ph.D Thesis, DESY F31-86-02(1986), Ap-
pendix E.
The Crystal Ball function can be written as:
CB(m) =
(m−µ)2
m > µ− ασ
(n/α)n exp(−α2/2)
((µ−m)/σ+n/α−α)n
m < µ− ασ
where µ is the mean value, σ is a measure of the width,
and n and α are parameters describing the tail.
[12] J. Pisut and M. Roos, N. Phys. B 6, 325 (1968).
[13] J. M. Blatt and V. F. Weisskopf, Theoretical Nuclear
Physics (Wiley, New York, 1952), p. 361.
[14] Values for the barrier radius can be estimated from qq
meson models (S. Godfrey and N. Isgur, Phys. Rev. D
32, 189 (1985) : figure 12), and by fits to experimental
data (see for example D. Aston et al., Nucl. Phys. B 296,
493 (1988)).
[15] ARGUS Collaboration, H. Albrecht et al., Z. Phys. C 48,
543 (1990).
The ARGUS function can be written as
A(m) = y
1− y2 exp(ξ(1− y
)) y < 1
A(m) = 0 y > 1
where ξ is a shape parameter, y = m/mmax and mmax
is a kinematic limit, equal in this case to half the total
CM energy.
[16] The Weibull function can be written as
W (m) = C V (m−Mon)
(C−1)
exp[−V (m−Mmax)
where V = (C − 1)/(C(Mmax −Mon)
Mmax is the position of the function maximum, Mon is
the lower kinematic cut-off, and C is a shape parameter.
	References
