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Observation of a New D_s Meson Decaying to D K at a Mass of 2.86 GeVc^2

a r X i v :h e p -e x /0607082v 3 26 O c t 2006

BABAR-PUB-06/044

SLAC-PUB-11993

Observation of a New D s Meson Decaying to DK at a Mass of 2.86GeV /c 2

B.Aubert,1R.Barate,1M.Bona,1D.Boutigny,1F.Couderc,1Y.Karyotakis,1J.P.Lees,1V.Poireau,1V.Tisserand,1A.Zghiche,1E.Grauges,2L.Lopez,3A.Palano,3J.

C.Chen,4N.

D.Qi,4G.Rong,4P.Wang,4Y.S.Zhu,4G.Eigen,5I.Ofte,5B.Stugu,5G.S.Abrams,6M.Battaglia,6D.N.Brown,6J.Button-Shafer,6

R.N.Cahn,6E.Charles,6M.S.Gill,6Y.Groysman,6R.G.Jacobsen,6J.A.Kadyk,6L.T.Kerth,6Yu.G.Kolomensky,6G.Kukartsev,6G.Lynch,6L.M.Mir,6T.J.Orimoto,6M.Pripstein,6N.A.Roe,6M.T.Ronan,6W.A.Wenzel,6P.del Amo Sanchez,7M.Barrett,7K.E.Ford,7T.J.Harrison,7A.J.Hart,7C.M.Hawkes,7S.E.Morgan,7A.T.Watson,7T.Held,8H.Koch,8B.Lewandowski,8M.Pelizaeus,8K.Peters,8T.Schroeder,8M.Steinke,8J.T.Boyd,9J.P.Burke,9W.N.Cottingham,9D.Walker,9T.Cuhadar-Donszelmann,10

B.G.Fulsom,10

C.Hearty,10N.S.Knecht,10T.S.Mattison,10J.A.McKenna,10A.Khan,11P.Kyberd,11

M.Saleem,11D.J.Sherwood,11L.Teodorescu,11V.E.Blinov,12A.D.Bukin,12V.P.Druzhinin,12V.B.Golubev,12

A.P.Onuchin,12S.I.Serednyakov,12Yu.I.Skovpen,12E.P.Solodov,12K.Yu Todyshev,12D.S.Best,13M.Bondioli,13M.Bruinsma,13M.Chao,13S.Curry,13I.Eschrich,13D.Kirkby,https://www.wendangku.net/doc/3913538750.html,nkford,13P.Lund,13M.Mandelkern,13R.K.Mommsen,13W.Roethel,13D.P.Stoker,13S.Abachi,14C.Buchanan,14S.D.Foulkes,15J.W.Gary,15O.Long,15

C.Shen,15K.Wang,15L.Zhang,15H.K.Hadavand,16E.J.Hill,16H.P.Paar,16S.Rahatlou,16V.Sharma,16J.W.Berryhill,17C.Campagnari,17A.Cunha,17B.Dahmes,17T.M.Hong,17

D.Kovalskyi,17J.D.Richman,17T.W.Beck,18A.M.Eisner,18C.J.Flacco,18C.A.Heusch,18J.Kroseberg,18W.S.Lockman,18G.Nesom,18T.Schalk,18B.A.Schumm,18A.Seiden,18P.Spradlin,18D.C.Williams,18M.G.Wilson,18J.Albert,19

E.Chen,19A.Dvoretskii,19

F.Fang,19D.

G.Hitlin,19I.Narsky,19T.Piatenko,19F.C.Porter,19A.Ryd,19A.Samuel,19G.Mancinelli,20B.T.Meadows,20K.Mishra,20M.D.Sokolo?,20F.Blanc,21P.C.Bloom,21S.Chen,21W.T.Ford,21J.F.Hirschauer,21A.Kreisel,21M.Nagel,21U.Nauenberg,21A.Olivas,21

W.O.Ruddick,21J.G.Smith,21K.A.Ulmer,21S.R.Wagner,21J.Zhang,21A.Chen,22E.A.Eckhart,22

A.So?er,22W.H.Toki,22R.J.Wilson,22F.Winklmeier,22Q.Zeng,22D.D.Altenburg,23E.Feltresi,23A.Hauke,23H.Jasper,23A.Petzold,23

B.Spaan,23T.Brandt,24V.Klose,https://www.wendangku.net/doc/3913538750.html,cker,24W.F.Mader,24R.Nogowski,24J.Schubert,24K.R.Schubert,24R.Schwierz,24J.E.Sundermann,24A.Volk,24D.Bernard,25G.R.Bonneaud,25P.Grenier,25,?https://www.wendangku.net/doc/3913538750.html,tour,25Ch.Thiebaux,25M.Verderi,25P.J.Clark,26W.Gradl,26F.Muheim,26S.Playfer,26A.I.Robertson,26Y.Xie,26M.Andreotti,27D.Bettoni,27

C.Bozzi,27R.Calabrese,27G.Cibinetto,27E.Luppi,27M.Negrini,27A.Petrella,27L.Piemontese,27E.Prencipe,27F.Anulli,28R.Baldini-Ferroli,28A.Calcaterra,28R.de Sangro,28G.Finocchiaro,28S.Pacetti,28P.Patteri,28I.M.Peruzzi,28,?M.Piccolo,28M.Rama,28

A.Zallo,28A.Buzzo,29R.Capra,29R.Contri,29M.Lo Vetere,29M.M.Macri,29M.R.Monge,29S.Passaggio,29C.Patrignani,29E.Robutti,29A.Santroni,29S.Tosi,29G.Brandenburg,30K.S.Chaisanguanthum,30M.Morii,30J.Wu,30R.S.Dubitzky,31J.Marks,31S.Schenk,31U.Uwer,31D.J.Bard,32W.Bhimji,32D.A.Bowerman,32P.D.Dauncey,32U.Egede,32R.L.Flack,32J.A.Nash,32M.

B.Nikolich,32W.Panduro Vazquez,32P.K.Behera,33X.Chai,33M.J.Charles,33U.Mallik,33N.T.Meyer,33V.Ziegler,33J.Cochran,34H.B.Crawley,34L.Dong,34

V.Eyges,34W.T.Meyer,34S.Prell,34E.I.Rosenberg,34A.E.Rubin,34A.V.Gritsan,35A.G.Denig,36

M.Fritsch,36G.Schott,36N.Arnaud,37M.Davier,37G.Grosdidier,37A.H¨o cker,37F.Le Diberder,37V.Lepeltier,37

A.M.Lutz,37A.Oyanguren,37S.Pruvot,37S.Rodier,37P.Roudeau,37M.H.Schune,37A.Stocchi,37

W.F.Wang,37G.Wormser,37C.H.Cheng,https://www.wendangku.net/doc/3913538750.html,nge,38D.M.Wright,38C.A.Chavez,39I.J.Forster,39J.R.Fry,39E.Gabathuler,39R.Gamet,39K.A.George,39D.E.Hutchcroft,39D.J.Payne,39K.C.Scho?eld,39C.Touramanis,39A.J.Bevan,40F.Di Lodovico,40W.Menges,40R.Sacco,40G.Cowan,41H.U.Flaecher,41D.A.Hopkins,41P.S.Jackson,41T.R.McMahon,41S.Ricciardi,41F.Salvatore,41A.C.Wren,41D.N.Brown,42

C.L.Davis,42J.Allison,43N.R.Barlow,43R.J.Barlow,43Y.M.Chia,43C.L.Edgar,43G.

https://www.wendangku.net/doc/3913538750.html,?erty,43M.T.Naisbit,43J.C.Williams,43J.I.Yi,43C.Chen,44W.D.Hulsbergen,44A.Jawahery,https://www.wendangku.net/doc/3913538750.html,e,44

D.A.Roberts,44G.Simi,44G.Blaylock,45C.Dallapiccola,45S.S.Hertzbach,45X.Li,45T.B.Moore,45S.Saremi,45H.Staengle,45R.Cowan,46G.Sciolla,46S.J.Sekula,46M.Spitznagel,46F.Taylor,46R.K.Yamamoto,46H.Kim,47S.

E.Mclachlin,47P.M.Patel,47S.H.Robertson,https://www.wendangku.net/doc/3913538750.html,zzaro,48V.Lombardo,48

F.Palombo,48J.M.Bauer,49L.Cremaldi,49V.Eschenburg,49R.Godang,49R.Kroeger,49D.A.Sanders,49D.J.Summers,49H.W.Zhao,49S.Brunet,50D.C?o t′e ,50M.Simard,50P.Taras,50F.B.Viaud,50H.Nicholson,51N.Cavallo,52,?

G.De Nardo,52

F.Fabozzi,52,?C.Gatto,52L.Lista,52D.Monorchio,52P.Paolucci,52D.Piccolo,52C.Sciacca,52M.Baak,53

G.Raven,53H.L.Snoek,53C.P.Jessop,54J.M.LoSecco,54T.Allmendinger,55G.Benelli,55K.K.Gan,55

K.Honscheid,55D.Hufnagel,55P.D.Jackson,55H.Kagan,55R.Kass,55A.M.Rahimi,55R.Ter-Antonyan,55 Q.K.Wong,55N.L.Blount,56J.Brau,56R.Frey,56O.Igonkina,56M.Lu,56R.Rahmat,56N.B.Sinev,56

D.Strom,56J.Strube,56

E.Torrence,56A.Gaz,57M.Margoni,57M.Morandin,57A.Pompili,57M.Posocco,57 M.Rotondo,57

F.Simonetto,57R.Stroili,57C.Voci,57M.Benayoun,58J.Chauveau,58H.Briand,58P.David,58 L.Del Buono,58Ch.de la Vaissi`e re,58O.Hamon,58B.L.Hart?el,58M.J.J.John,58Ph.Leruste,58J.Malcl`e s,58 J.Ocariz,58L.Roos,58

G.Therin,58L.Gladney,59J.Panetta,59M.Biasini,60R.Covarelli,60C.Angelini,61 G.Batignani,61S.Bettarini,61F.Bucci,61G.Calderini,61M.Carpinelli,61R.Cenci,61F.Forti,61M.A.Giorgi,61 A.Lusiani,61G.Marchiori,61M.A.Mazur,61M.Morganti,61N.Neri,61E.Paoloni,61G.Rizzo,61J.J.Walsh,61

M.Haire,62D.Judd,62D.E.Wagoner,62J.Biesiada,63N.Danielson,63P.Elmer,https://www.wendangku.net/doc/3913538750.html,u,63C.Lu,63

J.Olsen,63A.J.S.Smith,63A.V.Telnov,63F.Bellini,64G.Cavoto,64A.D’Orazio,64D.del Re,64E.Di Marco,64 R.Faccini,64F.Ferrarotto,64F.Ferroni,64M.Gaspero,64L.Li Gioi,64M.A.Mazzoni,64S.Morganti,64

G.Piredda,64F.Polci,64F.Safai Tehrani,64C.Voena,64M.Ebert,65H.Schr¨o der,65R.Waldi,65T.Adye,66N.De Groot,66B.Franek,66E.O.Olaiya,66F.F.Wilson,66R.Aleksan,67S.Emery,67A.Gaidot,67S.F.Ganzhur,67

G.Hamel de Monchenault,67W.Kozanecki,67M.Legendre,67G.Vasseur,67Ch.Y`e che,67M.Zito,67X.R.Chen,68

H.Liu,68W.Park,68M.V.Purohit,68J.R.Wilson,68M.T.Allen,69D.Aston,69R.Bartoldus,69P.Bechtle,69

N.Berger,69R.Claus,69J.P.Coleman,69M.R.Convery,69M.Cristinziani,69J.C.Dingfelder,69J.Dorfan,69

G.P.Dubois-Felsmann,69D.Dujmic,69W.Dunwoodie,69R.C.Field,69T.Glanzman,69S.J.Gowdy,69

M.T.Graham,69V.Halyo,69C.Hast,69T.Hryn’ova,69W.R.Innes,69M.H.Kelsey,69P.Kim,69

D.W.G.S.Leith,69S.Li,69S.Luitz,69V.Luth,69H.L.Lynch,69D.B.MacFarlane,69H.Marsiske,69R.Messner,69

D.R.Muller,69C.P.O’Grady,69V.

E.Ozcan,69A.Perazzo,69M.Perl,69T.Pulliam,69B.N.Ratcli?,69

A.Roodman,69A.A.Salnikov,69R.H.Schindler,69J.Schwiening,69A.Snyder,69J.Stelzer,69D.Su,69

M.K.Sullivan,69K.Suzuki,69S.K.Swain,69J.M.Thompson,69J.Va’vra,69N.van Bakel,69M.Weaver,69 A.J.R.Weinstein,69W.J.Wisniewski,69M.Wittgen,69D.H.Wright,69A.K.Yarritu,69K.Yi,69C.C.Young,69

P.R.Burchat,70A.J.Edwards,70S.A.Majewski,70B.A.Petersen,70C.Roat,70L.Wilden,70S.Ahmed,71 M.S.Alam,71R.Bula,71J.A.Ernst,71V.Jain,71B.Pan,71M.A.Saeed,71F.R.Wappler,71S.B.Zain,71 W.Bugg,72M.Krishnamurthy,72S.M.Spanier,72R.Eckmann,73J.L.Ritchie,73A.Satpathy,73C.J.Schilling,73 R.F.Schwitters,73J.M.Izen,74X.C.Lou,74S.Ye,74F.Bianchi,75F.Gallo,75D.Gamba,75M.Bomben,76 L.Bosisio,76C.Cartaro,76F.Cossutti,76G.Della Ricca,76S.Dittongo,https://www.wendangku.net/doc/3913538750.html,nceri,76L.Vitale,76V.Azzolini,77 F.Martinez-Vidal,77Sw.Banerjee,78B.Bhuyan,78C.M.Brown,78D.Fortin,78K.Hamano,78R.Kowalewski,78 I.M.Nugent,78J.M.Roney,78R.J.Sobie,78J.J.Back,79P.F.Harrison,https://www.wendangku.net/doc/3913538750.html,tham,79G.B.Mohanty,79

M.Pappagallo,79H.R.Band,80X.Chen,80B.Cheng,80S.Dasu,80M.Datta,80K.T.Flood,80J.J.Hollar,80 P.E.Kutter,80B.Mellado,80A.Mihalyi,80Y.Pan,80M.Pierini,80R.Prepost,80S.L.Wu,80Z.Yu,80and H.Neal81

(The B A B A R Collaboration)

1Laboratoire de Physique des Particules,F-74941Annecy-le-Vieux,France

2Universitat de Barcelona,Facultat de Fisica Dept.ECM,E-08028Barcelona,Spain

3Universit`a di Bari,Dipartimento di Fisica and INFN,I-70126Bari,Italy

4Institute of High Energy Physics,Beijing100039,China

5University of Bergen,Institute of Physics,N-5007Bergen,Norway

6Lawrence Berkeley National Laboratory and University of California,Berkeley,California94720,USA

7University of Birmingham,Birmingham,B152TT,United Kingdom

8Ruhr Universit¨a t Bochum,Institut f¨u r Experimentalphysik1,D-44780Bochum,Germany

9University of Bristol,Bristol BS81TL,United Kingdom

10University of British Columbia,Vancouver,British Columbia,Canada V6T1Z1

11Brunel University,Uxbridge,Middlesex UB83PH,United Kingdom

12Budker Institute of Nuclear Physics,Novosibirsk630090,Russia

13University of California at Irvine,Irvine,California92697,USA

14University of California at Los Angeles,Los Angeles,California90024,USA

15University of California at Riverside,Riverside,California92521,USA

16University of California at San Diego,La Jolla,California92093,USA

17University of California at Santa Barbara,Santa Barbara,California93106,USA 18University of California at Santa Cruz,Institute for Particle Physics,Santa Cruz,California95064,USA

19California Institute of Technology,Pasadena,California91125,USA

20University of Cincinnati,Cincinnati,Ohio45221,USA

21University of Colorado,Boulder,Colorado80309,USA

22Colorado State University,Fort Collins,Colorado80523,USA

23Universit¨a t Dortmund,Institut f¨u r Physik,D-44221Dortmund,Germany

24Technische Universit¨a t Dresden,Institut f¨u r Kern-und Teilchenphysik,D-01062Dresden,Germany 25Ecole Polytechnique,Laboratoire Leprince-Ringuet,F-91128Palaiseau,France

26University of Edinburgh,Edinburgh EH93JZ,United Kingdom

27Universit`a di Ferrara,Dipartimento di Fisica and INFN,I-44100Ferrara,Italy

28Laboratori Nazionali di Frascati dell’INFN,I-00044Frascati,Italy

29Universit`a di Genova,Dipartimento di Fisica and INFN,I-16146Genova,Italy

30Harvard University,Cambridge,Massachusetts02138,USA

31Universit¨a t Heidelberg,Physikalisches Institut,Philosophenweg12,D-69120Heidelberg,Germany

32Imperial College London,London,SW72AZ,United Kingdom

33University of Iowa,Iowa City,Iowa52242,USA

34Iowa State University,Ames,Iowa50011-3160,USA

35Johns Hopkins University,Baltimore,Maryland21218,USA

36Universit¨a t Karlsruhe,Institut f¨u r Experimentelle Kernphysik,D-76021Karlsruhe,Germany

37Laboratoire de l’Acc′e l′e rateur Lin′e aire,IN2P3-CNRS et Universit′e Paris-Sud11,

Centre Scienti?que d’Orsay,B.P.34,F-91898ORSAY Cedex,France

38Lawrence Livermore National Laboratory,Livermore,California94550,USA

39University of Liverpool,Liverpool L697ZE,United Kingdom

40Queen Mary,University of London,E14NS,United Kingdom

41University of London,Royal Holloway and Bedford New College,Egham,Surrey TW200EX,United Kingdom

42University of Louisville,Louisville,Kentucky40292,USA

43University of Manchester,Manchester M139PL,United Kingdom

44University of Maryland,College Park,Maryland20742,USA

45University of Massachusetts,Amherst,Massachusetts01003,USA 46Massachusetts Institute of Technology,Laboratory for Nuclear Science,Cambridge,Massachusetts02139,USA

47McGill University,Montr′e al,Qu′e bec,Canada H3A2T8

48Universit`a di Milano,Dipartimento di Fisica and INFN,I-20133Milano,Italy

49University of Mississippi,University,Mississippi38677,USA

50Universit′e de Montr′e al,Physique des Particules,Montr′e al,Qu′e bec,Canada H3C3J7

51Mount Holyoke College,South Hadley,Massachusetts01075,USA

52Universit`a di Napoli Federico II,Dipartimento di Scienze Fisiche and INFN,I-80126,Napoli,Italy

53NIKHEF,National Institute for Nuclear Physics and High Energy Physics,NL-1009DB Amsterdam,The Netherlands 54University of Notre Dame,Notre Dame,Indiana46556,USA

55Ohio State University,Columbus,Ohio43210,USA

56University of Oregon,Eugene,Oregon97403,USA

57Universit`a di Padova,Dipartimento di Fisica and INFN,I-35131Padova,Italy 58Universit′e s Paris VI et VII,Laboratoire de Physique Nucl′e aire et de Hautes Energies,F-75252Paris,France 59University of Pennsylvania,Philadelphia,Pennsylvania19104,USA

60Universit`a di Perugia,Dipartimento di Fisica and INFN,I-06100Perugia,Italy 61Universit`a di Pisa,Dipartimento di Fisica,Scuola Normale Superiore and INFN,I-56127Pisa,Italy

62Prairie View A&M University,Prairie View,Texas77446,USA

63Princeton University,Princeton,New Jersey08544,USA

64Universit`a di Roma La Sapienza,Dipartimento di Fisica and INFN,I-00185Roma,Italy

65Universit¨a t Rostock,D-18051Rostock,Germany

66Rutherford Appleton Laboratory,Chilton,Didcot,Oxon,OX110QX,United Kingdom

67DSM/Dapnia,CEA/Saclay,F-91191Gif-sur-Yvette,France

68University of South Carolina,Columbia,South Carolina29208,USA

69Stanford Linear Accelerator Center,Stanford,California94309,USA

70Stanford University,Stanford,California94305-4060,USA

71State University of New York,Albany,New York12222,USA

72University of Tennessee,Knoxville,Tennessee37996,USA

73University of Texas at Austin,Austin,Texas78712,USA

74University of Texas at Dallas,Richardson,Texas75083,USA

75Universit`a di Torino,Dipartimento di Fisica Sperimentale and INFN,I-10125Torino,Italy

76Universit`a di Trieste,Dipartimento di Fisica and INFN,I-34127Trieste,Italy

77IFIC,Universitat de Valencia-CSIC,E-46071Valencia,Spain

78University of Victoria,Victoria,British Columbia,Canada V8W3P6

79Department of Physics,University of Warwick,Coventry CV47AL,United Kingdom

80University of Wisconsin,Madison,Wisconsin53706,USA

81Yale University,New Haven,Connecticut06511,USA

(Dated:February5,2008)

We observe a new D s meson with mass(2856.6±1.5stat.±5.0syst.)MeV/c2and width(48±7stat.±

10syst.)MeV/c2decaying into D0K+and D+K0S.In the same mass distributions we also observe

a broad structure with mass(2688±4stat.±3syst.)MeV/c2and width(112±7stat.±36syst.)

MeV/c2.To obtain this result we use240fb?1of data recorded by the B A B A R detector at the

PEP-II asymmetric-energy e+e?storage rings at the Stanford Linear Accelerator Center running

at center-of-mass energies near10.6GeV.

PACS numbers:14.40.Lb,13.25.Ft,12.40.Yx

The spectrum of known c

s state and a broad structure observed in the decay channels D0K+and D+K0S.This analysis is based on a240fb?1data sample recorded near theΥ(4S)resonance by the B A B A R detector at the PEP-II asymmetric-energy e+e?storage rings.

The B A B A R detector is described in detail elsewhere

[3]. Charged particles are detected and their momenta mea-sured by a combination of a cylindrical drift chamber (DCH)and a silicon vertex tracker(SVT),both oper-ating within a1.5T solenoidal magnetic?eld.A ring-imaging Cherenkov detector(DIRC)is used for charged-particle identi?cation.Photon energies are measured with a CsI electromagnetic calorimeter.We use infor-mation from the DIRC and energy-loss measurements in the SVT and DCH to identify charged kaon and pion candidates.

We observe three inclusive processes[4]:

e+e?→D0K+X,D0→K?π+(1) e+e?→D0K+X,D0→K?π+π0(2) e+e?→D+K0S X,D+→K?π+π+,K0S→π+π?(3) For channels(1)and(2)we perform a vertex?t for the

K?π+and require aχ2probability greater than0.1%. For theπ0in channel(2),we consider the photons that emanate from the K?π+vertex,perform a?t with the π0mass constraint,and require aχ2probability greater than1%.The combinatorial background is reduced by requiring theπ0laboratory momentum to be greater than 350MeV/c.

To purify the D0sample in channel(2),its quasi-two body decays[5]K?πand Kρare used,allowing ranges of±50MeV/c2around the K?mass for Kπand±100 MeV/c2around theρmass forππ.

For channel(3),we?t two pions with the same charge and a kaon of the opposite charge to a common vertex to form the D+candidate,and require aχ2probability greater than0.1%.We obtain the K0S sample with a FIG.1:(a)K?π+,(b)K?π+π0and(c)K?π+π+mass distributions for all candidate events to channels(1),(2)and (3)respectively.The shaded regions indicate the de?nition of signal and sidebands regions.

?t that constrains the mass and require aχ2probability greater than2%.K0S candidates are retained only if their decay lengths are greater than0.5cm.

For all three channels,the D candidate is combined with an identi?ed K,requiring a vertex?tχ2probability greater than0.1%,and constraining the vertex to be in the e+e?luminous region.To reduce combinatorial back-ground from the continuum(e+e?→qˉq,q=u,d,s,c) and B-meson decays,each DK candidate must have a

FIG.2:The DK invariant mass distributions for (a)D 0K ?π+K +,(b)D 0K ?π+π0K +and (c)D +K ?π+π+K 0

s .

The shaded histograms are for the D -mass sideband regions.The dotted histogram in (a)is from e +e ?

→c ˉc Monte Carlo simulations incorporating previously known D s states with an arbitrary normalization.The insets show an expanded view of the 2.86GeV /c 2region.The solid curves are the ?tted background threshold functions from the three separate ?ts described in the text.

momentum p ?in the e +e ?center-of-mass frame greater than 3.5GeV /c .

Figs.1(a),(b)and (c)show the K ?π+,K ?π+π0,and K ?π+π+invariant mass distributions,respectively.All distributions show pronounced peaks at the D mass,with signal yields of about 950,000,790,000,and 430,000events.Fits using a polynomial and a single Gaussian give σ=7.6,12.6,6.0MeV /c 2for the three widths.We de?ne the signal region by ±2σfrom the ?tted D mass and establish sidebands at (?6σ,?4σ)and (4σ,6σ).In the signal regions,the signal-to-background ratios are 4.1,1.2,and 2.2respectively.

Selecting events in the D signal regions,Fig.2shows the D 0K +invariant mass distributions for channels (1)

and (2),and the D +K 0

S invariant mass distribution for channel (3).To improve mass resolution,the nominal D mass and the reconstructed 3-momentum are used to calculate the D energy for channels (1)and (3).Since channel (2)has a poorer D 0resolution,each K ?π+π0candidate is kinematically ?t with a D 0mass constraint and we require a χ2probability greater than 0.1%.

We ?nd that the fraction of events having more than one DK combination per event is 0.9%for channels (1)and (3)and 3.4%for channel (2).In the rest of the paper,we use the term re?ection to describe enhancements pro-duced by two or three body decays of narrow resonances where one of the decay products is missed.

The three mass spectra in Fig.2present similar fea-tures.

?A single bin peak at 2.4GeV /c 2due to a re?ection from the decays of the D s 1(2536)+to D ?0K +or

D ?+K 0

S in which the π0or γfrom the D ?decay is missed.This state,if J P =1+,cannot decay to DK .

?A prominent narrow signal due to the D s 2(2573)+.?A broad structure peaking at a mass of approxi-mately 2.7GeV /c 2.

?An enhancement around 2.86GeV /c 2.This can be seen better in the expanded views shown in the insets of Fig.2.

In the following we examine di?erent background sources:combinatorial,possible re?ections from D ?de-cays,and particle misidenti?cation.

Backgrounds come both from events in which the can-didate D meson is correctly identi?ed and from events in which it is not.The ?rst case can be studied combin-ing a reconstructed D meson with a kaon from another ˉD

meson in the same event,using data with fully recon-structed D ˉD

pairs or Monte Carlo simulations.No signal near 2.7or 2.86GeV /c 2is seen in the DK mass plots for these events.The second case can be studied using the D mass sidebands.The shaded regions in Fig.2show the DK mass spectra for events in the D sideband regions normalized to the estimated background in the signal re-gion.No prominent structure is visible in the sideband mass spectra.

We examined the possibility that the features at2.7

and2.86GeV/c2could be a re?ection from D?or other higher mass resonances.Candidate DK pairs where the

D is a D?-decay product are identi?ed by forming Dπand Dγcombinations and requiring the invariant-mass

di?erence between one of those combinations and the D

to be within±2σof the known D??D mass di?erence. No signal near2.7or2.86GeV/c2is seen in the DK mass

plots for these events.Events belonging to these possi-

ble re?ections(except for the D?0→D0γevents,which could not be isolated cleanly)have been removed from the mass distributions shown in Fig.2(corresponding to ≈8%of the?nal sample).

We use a Monte Carlo simulation to investigate the

possibility that the2.7or2.86GeV/c2signals could be

due to re?ections from other charmed states.This simu-lation includes e+e?→cˉc events and all known charmed states and decays.The Monte Carlo events were gener-ated using a detailed detector simulation and subjected to the same reconstruction and event-selection procedure as was used for the data.The D0K+e?ective mass dis-tribution for these Monte Carlo events is shown(dotted) in Fig.2(a)for channel(1).The normalization is ar-bitrary.No peak is found in the2.7and2.86GeV/c2 D0K+signal regions.We note that the simulation un-derestimates the size of the D s1(2536)+re?ection and the D s2(2573)+signal relative to the background.No such discrepancy is found in the study of the D0π+?nal state, therefore we attribute this e?ect to a poor knowledge of the strange-charmed meson cross sections.In order to improve the data-Monte Carlo comparison,the events having a D s1(2536)+and D s2(2573)+in the?nal state have been scaled up by factors5and2respectively.

We checked the possibility that the structures at

2.7and2.86GeV/c2are due to misidentifying pions

as kaons by assigning the kaon mass to the pion in D0π+data events.We observe no structure near2.7or 2.86GeV/c2in the resulting D0K+invariant mass dis-tribution.Monte Carlo simulations and tests using the data show that these structures also do not originate from protons misidenti?ed as kaons from high mass charmed baryon decays.

Wrong sign D0K?mass distributions for channels(1)

and(2)have also been examined and we?nd no signal

in either mass spectrum.

A more detailed study in channel(1)of the2.7GeV/c2

structure shows a broad structure in this mass region for

events from the D0sidebands in which the DK candidate has a very low p?(p?<3GeV/c).This is not seen in channels(2)or(3)however.We conclude that the assignment of the2.7GeV/c2structure to a re?ection remains inconclusive.

By comparing the reconstructed mass distributions for

the DK system with those generated with Monte Carlo simulations,we obtain the mass resolutions.The resolu-tions are similar in the three channels,increasing linearly from1.7MeV/c2at a mass of2.5GeV/c2,to3.5MeV/c2 at a mass of2.86GeV/c2.

In the following discussion we label as D sJ(2860)+ the structure in the2.86GeV/c2mass region and as X(2690)+the structure observed in the2.7GeV/c2mass

region.We?t to the three DK mass spectra shown in Fig.2from 2.42GeV/c2to 3.1GeV/c2(exclud-ing the D s1(2536)+re?ection)using a binnedχ2min-imization.The background for the three DK mass dis-tributions is described by a threshold function:(m?m th)αe?βm?γm2?δm3where m th=m D+m K.A?t to the Monte Carlo distribution shown in Fig.2(a)us-ing this background expression and one spin-2relativis-tic Breit-Wigner for the D s2(2573)+gives a good?t with32%χ2probability.In the?t to the data,the D s2(2573)+and D sJ(2860)+peaks are described with relativistic Breit-Wigner lineshapes where spin-2is as-sumed for the D s2(2573)+and spin0is used for the D sJ(2860)+.We?nd that the D sJ(2860)+parameters are insensitive to the choice of the spin.The best de-scription of the X(2690)+structure is obtained using a Gaussian distribution.The results from the?ts are sum-marized in Table I.Table II summarizes theχ2proba-bilities,the number of D sJ(2860)+events(with statisti-cal and systematic errors)and the D sJ(2860)+statistical signi?cances from the three separate?ts to the DK mass spectra.

The?ts give consistent values for the parameters of the three structures.We notice a smaller width of the D s2(2573)+in the D+

K?π+π+

K0s channel which we at-tribute to the uncertainty in the description of the back-ground.We compute also the ratios of the yields of D sJ(2860)+with respect to D s2(2573)+?nding agree-ment,within statistical errors,between the three chan-nels.

The presence of resonant structures can be visually enhanced by subtracting the?tted background threshold function from the data.Fig.3shows the background-

subtracted D0

K?π+

K+,D0

K?π+π0

K+,and D+

K?π+π+

K0s invariant mass distributions in the2.86GeV/c2mass re-gion.Fig.3(d)shows the sum of the three mass spectra. We also?t to the three distributions simultaneously. The parameters from this?t are labelled DK A in Table I. If we remove the D sJ(2860)+,theχ2increases by108 units while the number of degrees of freedom increases by?ve.

As a systematic test,we repeated the?ts varying the lower p?cut on the DK system from3.50to3.75and to 4.00GeV/c.We also restricted the?t to the D sJ(2860)+ only and replaced the threshold function which represents the background with a polynomial.Fits have also been performed without removing the events associated to D?re?ections and modifying the spin of D s2(2573)+.The systematic uncertainties take into account the variation of the resonance parameters among the three di?erent ?nal states and the resonance parameterizations.The

FIG.3:Fitted background-subtracted DK invariant mass distributions for (a)D 0K ?π+K +,(b)D 0K ?π+π0K +,(c)D +K ?π+π+K 0

s ,and (d)the sum of all modes in the 2.86GeV /c 2mass region.The curves are the ?tted functions described in the text.

TABLE I:Results from the ?ts to the total DK mass spectra of

Fig.2.Quantities are in units of MeV /c 2.Errors are statistical only.Simultaneous ?ts of the three mass spectra are labelled with DK A and DK B .

D 0K ?π+K +2572.4±0.427.6±0.52687±441±52855.4±2.037±826/20D 0K ?π+π0K +2572.3±0.528.4±0.92682±552±52860.8±4.052±1433/20D +K ?π+π+K 0s 2572.6±0.921.9±1.12684±750±72856.6±8.081±2526/21DK A

2572.3±0.327.1±0.62684±348±22856.6±1.547±7100/72DK B 2572.3±0.327.0±0.52688±4112±72857.6±1.9

38±7

112/72

Channel

χ2

D sJ (2860)+

Statistical probability (%)

events

signi?cance

uncertainty on the mass scale is estimated to be of the order of 1MeV /c 2.

We obtain the mass and width of D s 2(2573)+:m (D s 2(2573)+)=(2572.2±0.3±1.0)MeV /c 2Γ(D s 2(2573)+)=(27.1±0.6±5.6)MeV /c 2,where the ?rst errors are statistical and the second sys-

tematic.For the new state we ?nd

m (D sJ (2860)+)=(2856.6±1.5±5.0)MeV /c 2

Γ(D sJ (2860)+)=(47±7±10)MeV /c 2.

Since the assignment of the X (2690)+as a re?ection is inconclusive,the three mass spectra have also been ?t including the X (2690)+as an additional resonance (Breit-Wigner,rather than Gaussian shape).This gives ?t DK B shown in Table I.The resulting resonance pa-rameters are:

m (X (2690)+)=(2688±4±3)MeV /c 2Γ(X (2690)+)=(112±7±36)MeV /c 2.

In summary,in 240fb ?1of data collected by the

B A B A R experiment,we observe a new D +

s state in the inclusive DK mass distribution near 2.86GeV /c 2in three independent channels.The decay to two pseu-doscalar mesons implies a natural spin-parity for this state:J P =0+,1?,....It has been suggested that this

new state could be a radial excitation of D ?

sJ (2317)[6]although other possibilities cannot be ruled out.In the same mass distributions we also observe a broad enhance-

ment around2.69GeV/c2which it is not possible to as-sociate to any known re?ection or background.

We are grateful for the excellent luminosity and ma-chine conditions provided by our PEP-II colleagues,and for the substantial dedicated e?ort from the comput-ing organizations that support B A B A R.The collabo-rating institutions wish to thank SLAC for its sup-port and kind hospitality.This work is supported by DOE and NSF(USA),NSERC(Canada),IHEP(China), CEA and CNRS-IN2P3(France),BMBF and DFG(Ger-many),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.

?Also at Laboratoire de Physique Corpusculaire,Clermont-Ferrand,France

?Also with Universit`a di Perugia,Dipartimento di Fisica, Perugia,Italy

?Also with Universit`a della Basilicata,Potenza,Italy

[1]B.Aubert et al.,Phys.Rev.Lett.90,242001(2003);

D.Besson et al.,Phys.Rev.D68,032002(2003);

Y.Mikami et al.,Phys.Rev.Lett.92,012002(2004);

B.Aubert et al.,Phys.Rev.D69,031101(2004).

[2]S.Godfrey and N.Isgur,Phys.Rev.D32,189(1985);

S.Godfrey and R.Kokoski,Phys.Rev.D43,1679(1991);

N.Isgur and M.B.Wise,Phys.Rev.Lett.66,1130(1991);

M.Di Pierro and E.Eichten,Phys.Rev.D64,114004 (2001);

T.Matsuki,T.Morii,and K.Sudoh,hep-ph/0605019.

T.Matsuki,T.Morii,and K.Sudoh,hep-ph/0610186.

See,however,T.Matsuki,T.Morii,Phys.Rev.D56,5646 (1997)for a prediction that correctly anticipated the low masses.

[3]B.Aubert et al.,Nucl.Instr.Meth.A479,1(2002).

[4]Charge-conjugate reactions are implied throughout.

[5]S.Kopp et al.,Phys.Rev.D6*******(2001).

[6]E.van Beveren and G.Rupp,hep-ph/0606110.

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