A study of CP violation in B-+/- -> DK +/- and B-+/- -> D pi(+/-) decays with D -> (KSK +/-)-K-0 pi(-/+) final states

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)

CERN-PH-EP-2014-017 LHCb-PAPER-2013-068 23 May 2014

A study of CP violation in

B ^± → DK ^± and B ^± → Dπ ^± decays with D → K _S ⁰ K ^± π ^∓ final states

The LHCb collaboration^†

Abstract

A first study of CP violation in the decay modes B^±→ [K_S⁰K^±π^∓]Dh^± and B^±→ [K_S⁰K^∓π^±]Dh^±, where h labels a K or π meson and D labels a D⁰ or D⁰ meson, is performed. The analysis uses the LHCb data set collected in pp collisions, corresponding to an integrated luminosity of 3 fb⁻¹. The analysis is sensitive to the CP -violating CKM phase γ through seven observables: one charge asymmetry in each of the four modes and three ratios of the charge-integrated yields. The results are consistent with measurements of γ using other decay modes.

Published in Phys. Lett. B

CERN on behalf of the LHCb collaboration, license CC-BY-3.0.c

†Authors are listed on the following pages.

arXiv:1402.2982v3 [hep-ex] 23 May 2014

LHCb collaboration

R. Aaij⁴¹, B. Adeva³⁷, M. Adinolfi⁴⁶, A. Affolder⁵², Z. Ajaltouni⁵, J. Albrecht⁹, F. Alessio³⁸, M. Alexander⁵¹, S. Ali⁴¹, G. Alkhazov³⁰, P. Alvarez Cartelle³⁷, A.A. Alves Jr²⁵, S. Amato², S. Amerio²², Y. Amhis⁷, L. Anderlini^17,g, J. Anderson⁴⁰, R. Andreassen⁵⁷, M. Andreotti^16,f, J.E. Andrews⁵⁸, R.B. Appleby⁵⁴, O. Aquines Gutierrez¹⁰, F. Archilli³⁸, A. Artamonov³⁵, M. Artuso⁵⁹, E. Aslanides⁶, G. Auriemma^25,n, M. Baalouch⁵, S. Bachmann¹¹, J.J. Back⁴⁸, A. Badalov³⁶, V. Balagura³¹, W. Baldini¹⁶, R.J. Barlow⁵⁴, C. Barschel³⁹, S. Barsuk⁷,

W. Barter⁴⁷, V. Batozskaya²⁸, Th. Bauer⁴¹, A. Bay³⁹, J. Beddow⁵¹, F. Bedeschi²³, I. Bediaga¹, S. Belogurov³¹, K. Belous³⁵, I. Belyaev³¹, E. Ben-Haim⁸, G. Bencivenni¹⁸, S. Benson⁵⁰,

J. Benton⁴⁶, A. Berezhnoy³², R. Bernet⁴⁰, M.-O. Bettler⁴⁷, M. van Beuzekom⁴¹, A. Bien¹¹, S. Bifani⁴⁵, T. Bird⁵⁴, A. Bizzeti^17,i, P.M. Bjørnstad⁵⁴, T. Blake⁴⁸, F. Blanc³⁹, J. Blouw¹⁰, S. Blusk⁵⁹, V. Bocci²⁵, A. Bondar³⁴, N. Bondar³⁰, W. Bonivento^15,38, S. Borghi⁵⁴, A. Borgia⁵⁹, M. Borsato⁷, T.J.V. Bowcock⁵², E. Bowen⁴⁰, C. Bozzi¹⁶, T. Brambach⁹, J. van den Brand⁴², J. Bressieux³⁹, D. Brett⁵⁴, M. Britsch¹⁰, T. Britton⁵⁹, N.H. Brook⁴⁶, H. Brown⁵², A. Bursche⁴⁰, G. Busetto^22,r, J. Buytaert³⁸, S. Cadeddu¹⁵, R. Calabrese^16,f, O. Callot⁷, M. Calvi^20,k,

M. Calvo Gomez^36,p, A. Camboni³⁶, P. Campana^18,38, D. Campora Perez³⁸, A. Carbone^14,d, G. Carboni^24,l, R. Cardinale^19,j, A. Cardini¹⁵, H. Carranza-Mejia⁵⁰, L. Carson⁵⁰,

K. Carvalho Akiba², G. Casse⁵², L. Cassina²⁰, L. Castillo Garcia³⁸, M. Cattaneo³⁸, Ch. Cauet⁹, R. Cenci⁵⁸, M. Charles⁸, Ph. Charpentier³⁸, S.-F. Cheung⁵⁵, N. Chiapolini⁴⁰, M. Chrzaszcz^40,26, K. Ciba³⁸, X. Cid Vidal³⁸, G. Ciezarek⁵³, P.E.L. Clarke⁵⁰, M. Clemencic³⁸, H.V. Cliff⁴⁷, J. Closier³⁸, C. Coca²⁹, V. Coco³⁸, J. Cogan⁶, E. Cogneras⁵, P. Collins³⁸,

A. Comerma-Montells³⁶, A. Contu^15,38, A. Cook⁴⁶, M. Coombes⁴⁶, S. Coquereau⁸, G. Corti³⁸, I. Counts⁵⁶, B. Couturier³⁸, G.A. Cowan⁵⁰, D.C. Craik⁴⁸, M. Cruz Torres⁶⁰, S. Cunliffe⁵³, R. Currie⁵⁰, C. D’Ambrosio³⁸, J. Dalseno⁴⁶, P. David⁸, P.N.Y. David⁴¹, A. Davis⁵⁷, I. De Bonis⁴, K. De Bruyn⁴¹, S. De Capua⁵⁴, M. De Cian¹¹, J.M. De Miranda¹, L. De Paula², W. De Silva⁵⁷, P. De Simone¹⁸, D. Decamp⁴, M. Deckenhoff⁹, L. Del Buono⁸, N. D´el´eage⁴, D. Derkach⁵⁵, O. Deschamps⁵, F. Dettori⁴², A. Di Canto¹¹, H. Dijkstra³⁸, S. Donleavy⁵², F. Dordei¹¹, M. Dorigo³⁹, P. Dorosz^26,o, A. Dosil Su´arez³⁷, D. Dossett⁴⁸, A. Dovbnya⁴³, F. Dupertuis³⁹, P. Durante³⁸, R. Dzhelyadin³⁵, A. Dziurda²⁶, A. Dzyuba³⁰, S. Easo⁴⁹, U. Egede⁵³,

V. Egorychev³¹, S. Eidelman³⁴, S. Eisenhardt⁵⁰, U. Eitschberger⁹, R. Ekelhof⁹, L. Eklund^51,38, I. El Rifai⁵, Ch. Elsasser⁴⁰, S. Esen¹¹, A. Falabella^16,f, C. F¨arber¹¹, C. Farinelli⁴¹, S. Farry⁵², D. Ferguson⁵⁰, V. Fernandez Albor³⁷, F. Ferreira Rodrigues¹, M. Ferro-Luzzi³⁸, S. Filippov³³, M. Fiore^16,f, M. Fiorini^16,f, C. Fitzpatrick³⁸, M. Fontana¹⁰, F. Fontanelli^19,j, R. Forty³⁸, O. Francisco², M. Frank³⁸, C. Frei³⁸, M. Frosini^17,38,g, J. Fu²¹, E. Furfaro^24,l,

A. Gallas Torreira³⁷, D. Galli^14,d, M. Gandelman², P. Gandini⁵⁹, Y. Gao³, J. Garofoli⁵⁹, J. Garra Tico⁴⁷, L. Garrido³⁶, C. Gaspar³⁸, R. Gauld⁵⁵, L. Gavardi⁹, E. Gersabeck¹¹,

M. Gersabeck⁵⁴, T. Gershon⁴⁸, Ph. Ghez⁴, A. Gianelle²², S. Giani’³⁹, V. Gibson⁴⁷, L. Giubega²⁹, V.V. Gligorov³⁸, C. G¨obel⁶⁰, D. Golubkov³¹, A. Golutvin^53,31,38, A. Gomes^1,a, H. Gordon³⁸, M. Grabalosa G´andara⁵, R. Graciani Diaz³⁶, L.A. Granado Cardoso³⁸, E. Graug´es³⁶,

G. Graziani¹⁷, A. Grecu²⁹, E. Greening⁵⁵, S. Gregson⁴⁷, P. Griffith⁴⁵, L. Grillo¹¹, O. Gr¨unberg⁶¹, B. Gui⁵⁹, E. Gushchin³³, Yu. Guz^35,38, T. Gys³⁸, C. Hadjivasiliou⁵⁹, G. Haefeli³⁹, C. Haen³⁸, T.W. Hafkenscheid⁶⁴, S.C. Haines⁴⁷, S. Hall⁵³, B. Hamilton⁵⁸, T. Hampson⁴⁶,

S. Hansmann-Menzemer¹¹, N. Harnew⁵⁵, S.T. Harnew⁴⁶, J. Harrison⁵⁴, T. Hartmann⁶¹, J. He³⁸, T. Head³⁸, V. Heijne⁴¹, K. Hennessy⁵², P. Henrard⁵, L. Henry⁸, J.A. Hernando Morata³⁷, E. van Herwijnen³⁸, M. Heß⁶¹, A. Hicheur¹, D. Hill⁵⁵, M. Hoballah⁵, C. Hombach⁵⁴,

W. Hulsbergen⁴¹, P. Hunt⁵⁵, N. Hussain⁵⁵, D. Hutchcroft⁵², D. Hynds⁵¹, V. Iakovenko⁴⁴, M. Idzik²⁷, P. Ilten⁵⁶, R. Jacobsson³⁸, A. Jaeger¹¹, E. Jans⁴¹, P. Jaton³⁹, A. Jawahery⁵⁸, F. Jing³, M. John⁵⁵, D. Johnson⁵⁵, C.R. Jones⁴⁷, C. Joram³⁸, B. Jost³⁸, N. Jurik⁵⁹, M. Kaballo⁹, S. Kandybei⁴³, W. Kanso⁶, M. Karacson³⁸, T.M. Karbach³⁸, M. Kelsey⁵⁹, I.R. Kenyon⁴⁵, T. Ketel⁴², B. Khanji²⁰, C. Khurewathanakul³⁹, S. Klaver⁵⁴, O. Kochebina⁷, I. Komarov³⁹, R.F. Koopman⁴², P. Koppenburg⁴¹, M. Korolev³², A. Kozlinskiy⁴¹, L. Kravchuk³³, K. Kreplin¹¹, M. Kreps⁴⁸, G. Krocker¹¹, P. Krokovny³⁴, F. Kruse⁹, M. Kucharczyk^20,26,38,k, V. Kudryavtsev³⁴, K. Kurek²⁸, T. Kvaratskheliya^31,38, V.N. La Thi³⁹, D. Lacarrere³⁸, G. Lafferty⁵⁴, A. Lai¹⁵, D. Lambert⁵⁰, R.W. Lambert⁴², E. Lanciotti³⁸, G. Lanfranchi¹⁸, C. Langenbruch³⁸, T. Latham⁴⁸, C. Lazzeroni⁴⁵, R. Le Gac⁶, J. van Leerdam⁴¹, J.-P. Lees⁴, R. Lef`evre⁵,

A. Leflat³², J. Lefran¸cois⁷, S. Leo²³, O. Leroy⁶, T. Lesiak²⁶, B. Leverington¹¹, Y. Li³, M. Liles⁵², R. Lindner³⁸, C. Linn³⁸, F. Lionetto⁴⁰, B. Liu¹⁵, G. Liu³⁸, S. Lohn³⁸, I. Longstaff⁵¹, J.H. Lopes², N. Lopez-March³⁹, P. Lowdon⁴⁰, H. Lu³, D. Lucchesi^22,r, J. Luisier³⁹, H. Luo⁵⁰, E. Luppi^16,f, O. Lupton⁵⁵, F. Machefert⁷, I.V. Machikhiliyan³¹, F. Maciuc²⁹, O. Maev^30,38, S. Malde⁵⁵, G. Manca^15,e, G. Mancinelli⁶, M. Manzali^16,f, J. Maratas⁵, U. Marconi¹⁴, P. Marino^23,t, R. M¨arki³⁹, J. Marks¹¹, G. Martellotti²⁵, A. Martens⁸, A. Mart´ın S´anchez⁷, M. Martinelli⁴¹, D. Martinez Santos⁴², F. Martinez Vidal⁶³, D. Martins Tostes², A. Massafferri¹, R. Matev³⁸, Z. Mathe³⁸, C. Matteuzzi²⁰, A. Mazurov^16,38,f, M. McCann⁵³, J. McCarthy⁴⁵, A. McNab⁵⁴, R. McNulty¹², B. McSkelly⁵², B. Meadows^57,55, F. Meier⁹, M. Meissner¹¹, M. Merk⁴¹,

D.A. Milanes⁸, M.-N. Minard⁴, J. Molina Rodriguez⁶⁰, S. Monteil⁵, D. Moran⁵⁴, M. Morandin²², P. Morawski²⁶, A. Mord`a⁶, M.J. Morello^23,t, R. Mountain⁵⁹, F. Muheim⁵⁰, K. M¨uller⁴⁰,

R. Muresan²⁹, B. Muryn²⁷, B. Muster³⁹, P. Naik⁴⁶, T. Nakada³⁹, R. Nandakumar⁴⁹, I. Nasteva¹, M. Needham⁵⁰, N. Neri²¹, S. Neubert³⁸, N. Neufeld³⁸, A.D. Nguyen³⁹, T.D. Nguyen³⁹,

C. Nguyen-Mau^39,q, M. Nicol⁷, V. Niess⁵, R. Niet⁹, N. Nikitin³², T. Nikodem¹¹, A. Novoselov³⁵, A. Oblakowska-Mucha²⁷, V. Obraztsov³⁵, S. Oggero⁴¹, S. Ogilvy⁵¹, O. Okhrimenko⁴⁴,

R. Oldeman^15,e, G. Onderwater⁶⁴, M. Orlandea²⁹, J.M. Otalora Goicochea², P. Owen⁵³, A. Oyanguren³⁶, B.K. Pal⁵⁹, A. Palano^13,c, F. Palombo^21,u, M. Palutan¹⁸, J. Panman³⁸, A. Papanestis^49,38, M. Pappagallo⁵¹, L. Pappalardo¹⁶, C. Parkes⁵⁴, C.J. Parkinson⁹, G. Passaleva¹⁷, G.D. Patel⁵², M. Patel⁵³, C. Patrignani^19,j, C. Pavel-Nicorescu²⁹, A. Pazos Alvarez³⁷, A. Pearce⁵⁴, A. Pellegrino⁴¹, G. Penso^25,m, M. Pepe Altarelli³⁸,

S. Perazzini^14,d, E. Perez Trigo³⁷, P. Perret⁵, M. Perrin-Terrin⁶, L. Pescatore⁴⁵, E. Pesen⁶⁵, G. Pessina²⁰, K. Petridis⁵³, A. Petrolini^19,j, E. Picatoste Olloqui³⁶, B. Pietrzyk⁴, T. Pilaˇr⁴⁸, D. Pinci²⁵, A. Pistone¹⁹, S. Playfer⁵⁰, M. Plo Casasus³⁷, F. Polci⁸, G. Polok²⁶, A. Poluektov^48,34, E. Polycarpo², A. Popov³⁵, D. Popov¹⁰, B. Popovici²⁹, C. Potterat³⁶, A. Powell⁵⁵,

J. Prisciandaro³⁹, A. Pritchard⁵², C. Prouve⁴⁶, V. Pugatch⁴⁴, A. Puig Navarro³⁹, G. Punzi^23,s, W. Qian⁴, B. Rachwal²⁶, J.H. Rademacker⁴⁶, B. Rakotomiaramanana³⁹, M. Rama¹⁸,

M.S. Rangel², I. Raniuk⁴³, N. Rauschmayr³⁸, G. Raven⁴², S. Redford⁵⁵, S. Reichert⁵⁴, M.M. Reid⁴⁸, A.C. dos Reis¹, S. Ricciardi⁴⁹, A. Richards⁵³, K. Rinnert⁵², V. Rives Molina³⁶, D.A. Roa Romero⁵, P. Robbe⁷, D.A. Roberts⁵⁸, A.B. Rodrigues¹, E. Rodrigues⁵⁴,

P. Rodriguez Perez³⁷, S. Roiser³⁸, V. Romanovsky³⁵, A. Romero Vidal³⁷, M. Rotondo²², J. Rouvinet³⁹, T. Ruf³⁸, F. Ruffini²³, H. Ruiz³⁶, P. Ruiz Valls³⁶, G. Sabatino^25,l,

J.J. Saborido Silva³⁷, N. Sagidova³⁰, P. Sail⁵¹, B. Saitta^15,e, V. Salustino Guimaraes²,

B. Sanmartin Sedes³⁷, R. Santacesaria²⁵, C. Santamarina Rios³⁷, E. Santovetti^24,l, M. Sapunov⁶, A. Sarti¹⁸, C. Satriano^25,n, A. Satta²⁴, M. Savrie^16,f, D. Savrina^31,32, M. Schiller⁴²,

H. Schindler³⁸, M. Schlupp⁹, M. Schmelling¹⁰, B. Schmidt³⁸, O. Schneider³⁹, A. Schopper³⁸, M.-H. Schune⁷, R. Schwemmer³⁸, B. Sciascia¹⁸, A. Sciubba²⁵, M. Seco³⁷, A. Semennikov³¹,

K. Senderowska²⁷, I. Sepp⁵³, N. Serra⁴⁰, J. Serrano⁶, P. Seyfert¹¹, M. Shapkin³⁵, I. Shapoval^16,43,f, Y. Shcheglov³⁰, T. Shears⁵², L. Shekhtman³⁴, O. Shevchenko⁴³,

V. Shevchenko⁶², A. Shires⁹, R. Silva Coutinho⁴⁸, G. Simi²², M. Sirendi⁴⁷, N. Skidmore⁴⁶, T. Skwarnicki⁵⁹, N.A. Smith⁵², E. Smith^55,49, E. Smith⁵³, J. Smith⁴⁷, M. Smith⁵⁴, H. Snoek⁴¹, M.D. Sokoloff⁵⁷, F.J.P. Soler⁵¹, F. Soomro³⁹, D. Souza⁴⁶, B. Souza De Paula², B. Spaan⁹, A. Sparkes⁵⁰, F. Spinella²³, P. Spradlin⁵¹, F. Stagni³⁸, S. Stahl¹¹, O. Steinkamp⁴⁰,

S. Stevenson⁵⁵, S. Stoica²⁹, S. Stone⁵⁹, B. Storaci⁴⁰, S. Stracka^23,38, M. Straticiuc²⁹, U. Straumann⁴⁰, R. Stroili²², V.K. Subbiah³⁸, L. Sun⁵⁷, W. Sutcliffe⁵³, S. Swientek⁹,

V. Syropoulos⁴², M. Szczekowski²⁸, P. Szczypka^39,38, D. Szilard², T. Szumlak²⁷, S. T’Jampens⁴, M. Teklishyn⁷, G. Tellarini^16,f, E. Teodorescu²⁹, F. Teubert³⁸, C. Thomas⁵⁵, E. Thomas³⁸, J. van Tilburg¹¹, V. Tisserand⁴, M. Tobin³⁹, S. Tolk⁴², L. Tomassetti^16,f, D. Tonelli³⁸, S. Topp-Joergensen⁵⁵, N. Torr⁵⁵, E. Tournefier^4,53, S. Tourneur³⁹, M.T. Tran³⁹, M. Tresch⁴⁰, A. Tsaregorodtsev⁶, P. Tsopelas⁴¹, N. Tuning⁴¹, M. Ubeda Garcia³⁸, A. Ukleja²⁸,

A. Ustyuzhanin⁶², U. Uwer¹¹, V. Vagnoni¹⁴, G. Valenti¹⁴, A. Vallier⁷, R. Vazquez Gomez¹⁸, P. Vazquez Regueiro³⁷, C. V´azquez Sierra³⁷, S. Vecchi¹⁶, J.J. Velthuis⁴⁶, M. Veltri^17,h,

G. Veneziano³⁹, M. Vesterinen¹¹, B. Viaud⁷, D. Vieira², X. Vilasis-Cardona^36,p, A. Vollhardt⁴⁰, D. Volyanskyy¹⁰, D. Voong⁴⁶, A. Vorobyev³⁰, V. Vorobyev³⁴, C. Voß⁶¹, H. Voss¹⁰,

J.A. de Vries⁴¹, R. Waldi⁶¹, C. Wallace⁴⁸, R. Wallace¹², S. Wandernoth¹¹, J. Wang⁵⁹, D.R. Ward⁴⁷, N.K. Watson⁴⁵, A.D. Webber⁵⁴, D. Websdale⁵³, M. Whitehead⁴⁸, J. Wicht³⁸, J. Wiechczynski²⁶, D. Wiedner¹¹, L. Wiggers⁴¹, G. Wilkinson⁵⁵, M.P. Williams^48,49,

M. Williams⁵⁶, F.F. Wilson⁴⁹, J. Wimberley⁵⁸, J. Wishahi⁹, W. Wislicki²⁸, M. Witek²⁶,

G. Wormser⁷, S.A. Wotton⁴⁷, S. Wright⁴⁷, S. Wu³, K. Wyllie³⁸, Y. Xie^50,38, Z. Xing⁵⁹, Z. Yang³, X. Yuan³, O. Yushchenko³⁵, M. Zangoli¹⁴, M. Zavertyaev^10,b, F. Zhang³, L. Zhang⁵⁹,

W.C. Zhang¹², Y. Zhang³, A. Zhelezov¹¹, A. Zhokhov³¹, L. Zhong³, A. Zvyagin³⁸.

1Centro Brasileiro de Pesquisas F´ısicas (CBPF), Rio de Janeiro, Brazil

2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil

3Center for High Energy Physics, Tsinghua University, Beijing, China

4LAPP, Universit´e de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France

5Clermont Universit´e, Universit´e Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France

6CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France

7LAL, Universit´e Paris-Sud, CNRS/IN2P3, Orsay, France

8LPNHE, Universit´e Pierre et Marie Curie, Universit´e Paris Diderot, CNRS/IN2P3, Paris, France

9Fakult¨at Physik, Technische Universit¨at Dortmund, Dortmund, Germany

10Max-Planck-Institut f¨ur Kernphysik (MPIK), Heidelberg, Germany

11Physikalisches Institut, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg, Germany

12School of Physics, University College Dublin, Dublin, Ireland

13Sezione INFN di Bari, Bari, Italy

14Sezione INFN di Bologna, Bologna, Italy

15Sezione INFN di Cagliari, Cagliari, Italy

16Sezione INFN di Ferrara, Ferrara, Italy

17Sezione INFN di Firenze, Firenze, Italy

18Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy

19Sezione INFN di Genova, Genova, Italy

20Sezione INFN di Milano Bicocca, Milano, Italy

21Sezione INFN di Milano, Milano, Italy

22Sezione INFN di Padova, Padova, Italy

23Sezione INFN di Pisa, Pisa, Italy

24Sezione INFN di Roma Tor Vergata, Roma, Italy

25Sezione INFN di Roma La Sapienza, Roma, Italy

26Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Krak´ow, Poland

27AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science, Krak´ow, Poland

28National Center for Nuclear Research (NCBJ), Warsaw, Poland

29Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania

30Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia

31Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia

32Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia

33Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia

34Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia

35Institute for High Energy Physics (IHEP), Protvino, Russia

36Universitat de Barcelona, Barcelona, Spain

37Universidad de Santiago de Compostela, Santiago de Compostela, Spain

38European Organization for Nuclear Research (CERN), Geneva, Switzerland

39Ecole Polytechnique F´ed´erale de Lausanne (EPFL), Lausanne, Switzerland

40Physik-Institut, Universit¨at Z¨urich, Z¨urich, Switzerland

41Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands

42Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands

43NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine

44Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine

45University of Birmingham, Birmingham, United Kingdom

46H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom

47Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom

48Department of Physics, University of Warwick, Coventry, United Kingdom

49STFC Rutherford Appleton Laboratory, Didcot, United Kingdom

50School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom

51School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom

52Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom

53Imperial College London, London, United Kingdom

54School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom

55Department of Physics, University of Oxford, Oxford, United Kingdom

56Massachusetts Institute of Technology, Cambridge, MA, United States

57University of Cincinnati, Cincinnati, OH, United States

58University of Maryland, College Park, MD, United States

59Syracuse University, Syracuse, NY, United States

60Pontif´ıcia Universidade Cat´olica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated to ²

61Institut f¨ur Physik, Universit¨at Rostock, Rostock, Germany, associated to¹¹

62National Research Centre Kurchatov Institute, Moscow, Russia, associated to³¹

63Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain, associated to³⁶

64KVI - University of Groningen, Groningen, The Netherlands, associated to⁴¹

65Celal Bayar University, Manisa, Turkey, associated to³⁸

aUniversidade Federal do Triˆangulo Mineiro (UFTM), Uberaba-MG, Brazil

bP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia

cUniversit`a di Bari, Bari, Italy

dUniversit`a di Bologna, Bologna, Italy

eUniversit`a di Cagliari, Cagliari, Italy

fUniversit`a di Ferrara, Ferrara, Italy

gUniversit`a di Firenze, Firenze, Italy

hUniversit`a di Urbino, Urbino, Italy

iUniversit`a di Modena e Reggio Emilia, Modena, Italy

jUniversit`a di Genova, Genova, Italy

kUniversit`a di Milano Bicocca, Milano, Italy

lUniversit`a di Roma Tor Vergata, Roma, Italy

mUniversit`a di Roma La Sapienza, Roma, Italy

nUniversit`a della Basilicata, Potenza, Italy

oAGH - University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications, Krak´ow, Poland

pLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain

qHanoi University of Science, Hanoi, Viet Nam

rUniversit`a di Padova, Padova, Italy

sUniversit`a di Pisa, Pisa, Italy

tScuola Normale Superiore, Pisa, Italy

uUniversit`a degli Studi di Milano, Milano, Italy

1 Introduction

A precise measurement of the unitarity triangle angle γ = arg

−^V_V^udVub∗

cdV_cb^∗



is one of the most important tests of the Cabibbo Kobayashi Maskawa (CKM) mechanism. This parameter can be accessed through measurements of observables in decays of charged B mesons to a neutral D meson and a kaon or pion, where D labels a D⁰ or D⁰ meson decaying to a particular final state accessible to D⁰ and D⁰. Such decays are sensitive to γ through the interference between b → c¯us and b → u¯cs amplitudes. They offer an attractive means to measure γ because the effect of physics beyond the Standard Model is expected to be negligible, thus allowing interesting comparisons with other measurements where such effects could be larger.

The determination of γ using B^± → DK^± decays was first proposed for D decays to the CP -eigenstates K⁺K⁻ and π⁺π⁻ (so-called “GLW” analysis) [1, 2]. Subsequently, the analysis of the K^±π^∓ final state was proposed (named “ADS”) [3,4], where the suppression between the colour favoured B⁻ → D⁰K⁻ and suppressed B⁻ → D⁰K⁻ decays is compensated by the CKM suppression of the D⁰ → K⁺π⁻ decay relative to D⁰ → K⁺π⁻, resulting in large interference. The LHCb collaboration has published the two-body ADS and GLW analyses [5], the Dalitz analysis of the decay B^± → [K_S⁰h^±h^∓]_DK^±, (h = π, K) [6] and the ADS-like analysis of the decay mode B^± → [K^±π^∓π^±π^∓]_DK^± [7], where [X]_D indicates a given final state X produced by the decay of the D meson.

These measurements have recently been combined to yield the result γ = (72.0^+14.7_−15.6)^◦ [8], which is in agreement with the results obtained by the BaBar and Belle collaborations of γ = (69⁺¹⁷₋₁₆)^◦ [9] and γ = (68⁺¹⁵₋₁₄)^◦ [10], respectively. In analogy to studies in charged B meson decays, sensitivity to γ can also be gained from decays of neutral B mesons, as has been demonstrated in the LHCb analysis of B⁰ → [K⁺K⁻]_DK^∗0 decays [11].

The inclusion of additional B^± → DK^±modes can provide further constraints on γ. In this Letter, an analysis of the D → K_S⁰K^±π^∓ final states is performed, the first ADS-like analysis to use singly Cabibbo-suppressed (SCS) decays, as proposed in [12]. The two decays, B^±→ [K_S⁰K^±π^∓]_Dh^± and B^± → [K_S⁰K^∓π^±]_Dh^±, are distinguished by the charge of the K^± from the decay of the D meson relative to the charge of the B meson, so that the former is labelled “same sign” (SS) and the latter “opposite sign” (OS).

In order to interpret CP -violating effects using these three-body decays it is necessary to account for the variation of the D decay strong phase over its Dalitz plot due to the presence of resonances between the particles in the final state. Instead of employing an amplitude model to describe this phase variation, direct measurements of the phase made by the CLEO collaboration are used, which are averaged over large regions of the Dalitz plot [13]. The same CLEO study indicates that this averaging can be employed without a large loss of sensitivity. The use of the CLEO results avoids the need to introduce a systematic uncertainty resulting from an amplitude model description.

The analysis uses the full 2011 and 2012 LHCb pp collision data sets, corresponding to integrated luminosities of 1 and 2 fb⁻¹ and centre-of-mass energies of √

s = 7 TeV and 8 TeV, respectively. The results are measurements of CP -violating observables that can be interpreted in terms of γ and other hadronic parameters of the B^± meson decay.

2 Formalism

The SS decay B⁺→ [K_S⁰K⁺π⁻]_DK⁺ can proceed via a D⁰ or D⁰ meson, so that the decay amplitude is the sum of two amplitudes that interfere,

A(m²_K0

SK, m²_K0

Sπ) = A_D0(m²_K0

SK, m²_K0

Sπ) + r_Be^i(δB+γ)A_D⁰(m²_K0

SK, m²_K0

Sπ), (1)

where A_{D0,D⁰}(m²_K0

SK, m²_K0

Sπ) are the D⁰ and D⁰ decay amplitudes to a specific point in the K_S⁰K⁺π⁻ Dalitz plot. The amplitude ratio rB is ^|A(B_|A(B⁺₊^→D_→D⁰₀^K_K⁺₊^)|_)| = 0.089 ± 0.009 [8] and δ_B is the strong phase difference between the B⁺→ D⁰K⁺ and B⁺→ D⁰K⁺ decays. The calculation of the decay rate in a region of the Dalitz plot requires the evaluation of the integral of the interference term between the two D decay amplitudes over that region.

Measurements have been made by the CLEO collaboration [13], where quantum-correlated D decays are used to determine the integral of the interference term directly in the form of a “coherence factor”, κ_K⁰

SKπ, and an average strong phase difference, δ_K⁰

SKπ, as first proposed in Ref. [14]. The coherence factor can take a value between 0 and 1 and is defined through the expression

κ_K⁰

SKπe^−iδK0SKπ ≡ R A^∗_K0

SK⁻π⁺(m²_K0

SK, m²_Kπ)A_K⁰

SK⁺π⁻(m²_K0

SK, m²_Kπ)dm²_K0

SKdm²_Kπ A^int._K0

SK⁻π⁺A^int._K0 SK⁺π⁻

, (2)

where A^int._K0

SK^±π^∓ = R |A_K⁰

SK^±π^∓(m²_K0

SK, m²_Kπ)|²dm²_K0

SKdm²_Kπ. This avoids the significant modelling uncertainty incurred by the determination of the strong phase difference between the D⁰ and D⁰ amplitudes at each point in the Dalitz region from an amplitude model.

The decay rates, Γ, to the four final states can therefore be expressed as Γ^±_{SS, DK} = z[ 1 + r²_Br²_D+ 2r_Br_Dκ_K⁰

SKπcos(δ_B± γ − δ_K⁰

SKπ) ] Γ^±_{OS, DK} = z[ r²_B+ r²_D + 2rBrDκ_K⁰

SKπcos(δB± γ + δ_K⁰

SKπ) ] (3)

where r_D is the amplitude ratio for D⁰ → K_S⁰K⁺π⁻ with respect to D⁰ → K_S⁰K⁻π⁺ and z is the normalisation factor. Analogous equations can be written for the B^± → Dπ^± system, with r_B^π and δ^π_B replacing r_B and δ_B, respectively. Less interference is expected in the B^± → Dπ^± system where the value of r_B^π is much lower, approximately 0.015 [8].

These expressions receive small corrections from mixing in the charm system which, though accounted for in Sect. 7, are not explicitly written here. At the current level of precision these corrections have a negligible effect on the final results.

Observables constructed using the decay rates in Eq. (3) have a sensitivity to γ that depends upon the value of the coherence factor, with a higher coherence corresponding to greater sensitivity. The CLEO collaboration measured the coherence factor and average strong phase difference in two regions of the Dalitz plot: firstly across the whole Dalitz plot, and secondly within a region ±100 MeV/c² around the K^∗(892)^± resonance, which decays to K_S⁰π^±, where, though the sample size is diminished, the coherence is higher. The measured values are κ_K⁰

SKπ = 0.73 ± 0.08 and δ_K⁰

SKπ = 8.3 ± 15.2^◦ for the whole Dalitz

plot, and κ_K⁰

SKπ = 1.00 ± 0.16 and δ_K⁰

SKπ = 26.5 ± 15.8^◦ in the restricted region. The branching fraction ratio of D⁰ → K_S⁰K⁺π⁻ to D⁰ → K_S⁰K⁻π⁺ decays was found to be 0.592 ± 0.044 in the whole Dalitz plot and 0.356 ± 0.034 in the restricted region [13].

Eight yields are measured in this analysis, from which seven observables are constructed.

The charge asymmetry is measured in each of the four decay modes, defined as A_{SS, DK} ≡

N_SS^DK−−N_SS^DK+

N_SS^DK−+N_SS^DK+ for the B^± → [K_S⁰K^±π^∓]_DK^± mode and analogously for the other modes.

The ratios of B^± → DK^± and B^± → Dπ^±yields are determined for the SS and OS decays, R_{DK/Dπ, SS} and R_{DK/Dπ, OS} respectively, and the ratio of SS to OS B^± → Dπ^± yields, R_SS/OS, is measured. The measurements are performed both for the whole D Dalitz plot and in the restricted region around the K^∗(892)^± resonance.

3 The LHCb detector and data set

The LHCb detector [15] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks. The detector includes a high-precision tracking system consisting of a silicon-strip vertex detector surrounding the pp interaction region, a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubes placed downstream. The combined tracking system provides a momentum measurement with relative uncertainty that varies from 0.4 % at 5 GeV/c to 0.6 % at 100 GeV/c, and impact parameter (IP) resolution of 20 µm for tracks with large transverse momentum. Different types of charged hadrons are distinguished by particle identification (PID) information from two ring-imaging Cherenkov (RICH) detectors [16].

Photon, electron and hadron candidates are identified by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromagnetic calorimeter and a hadronic calorimeter. Muons are identified by a system composed of alternating layers of iron and multiwire proportional chambers.

The trigger consists of a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage, which applies a full event reconstruction.

The software trigger searches for a track with large p_T and large IP with respect to any pp interaction point, also called a primary vertex (PV). This track is then required to be part of a two-, three- or four-track secondary vertex with a high p_T sum, significantly displaced from any PV. A multivariate algorithm [17] is used for the identification of secondary vertices consistent with the decay of a b hadron.

Samples of around two million B^± → [K_S⁰K^∓π^±]_Dπ^± and two million B^± → [K_S⁰K^∓π^±]_DK^± decays are simulated to be used in the analysis, along with similarly-sized samples of B^± → [K_S⁰π⁺π⁻]_Dπ^±, B^± → [K_S⁰K⁺K⁻]_Dπ^± and B^± → [K^±π^∓π⁺π⁻]_Dπ^± decays that are used to study potential backgrounds. In the simulation, pp collisions are generated using Pythia [18] with a specific LHCb configuration [19]. Decays of hadronic particles are described by EvtGen [20], in which final state radiation is generated using Photos [21]. The interaction of the generated particles with the detector and its response are implemented using the Geant4 toolkit [22] as described in Ref. [23].

4 Candidate selection

Candidate B → [K_S⁰K^±π^∓]_DK and B → [K_S⁰K^±π^∓]_Dπ decays are reconstructed in events selected by the trigger and then the candidate momenta are refit, constraining the masses of the neutral D and K_S⁰ mesons to their known values [24] and the B^± meson to originate from the primary vertex [25]. Candidates where the K_S⁰ decay is reconstructed using “long”

pion tracks, which leave hits in the VELO and downstream tracking stations, are analysed separately from those reconstructed using “downstream” pion tracks, which only leave hits in tracking stations beyond the VELO. The signal candidates in the former category are reconstructed with a better invariant mass resolution.

The reconstructed masses of the D and K_S⁰ mesons are required to be within 25 MeV/c² and 15 MeV/c², respectively, of their known values. Candidate B^± → DK^± decays are separated from B^±→ Dπ^± decays by using PID information from the RICH detectors.

A boosted decision tree (BDT) [26, 27] that has been developed for the analysis of the topologically similar decay mode B^± → [K_S⁰h⁺h⁻]_Dh^0± is applied to the reconstructed candidates. The BDT was trained using simulated signal decays, generated uniformly over the D⁰ Dalitz plot, and background candidates taken from the B^± invariant mass region in data between 5700 and 7000 MeV/c². It exploits the displacement of tracks from the decays of long-lived particles with respect to the PV through the use of χ²_IP variables, where χ²_IP is defined as the difference in χ² of a given PV fit with and without the considered track. The BDT also employs the B^± and D candidate momenta, an isolation variable sensitive to the separation of the tracks used to construct the B^± candidate from other tracks in the event, and the χ² per degree of freedom of the decay refit. In addition to the requirement placed on the BDT response variable, each composite candidate is required to have a vector displacement of production and decay vertices that aligns closely to its reconstructed momenta. The cosine of the angle between the displacement and momentum vectors is required to be less than 0.142 rad for the K_S⁰ and D⁰ candidates, and less than 0.0141 rad (0.0100 rad) for long (downstream) B^± candidates.

Additional requirements are used to suppress backgrounds from specific processes.

Contamination from B decays that do not contain an intermediate D meson is minimised by placing a minimum threshold of 0.2 ps on the decay time of the D candidate. A potential background could arise from processes where a pion is misidentified as a kaon or vice versa. One example is the relatively abundant mode B^± → [K_S⁰π⁺π⁻]_Dh^±, which has a branching fraction around ten times larger than the signal. These are suppressed by placing requirements on both the D daughter pion and kaon, making use of PID information. For K_S⁰ candidates formed from long tracks, the flight distance χ² of the candidate is used to suppress background from B^±→ [K^±π^∓π⁺π⁻]_Dh^± decays. Where multiple candidates are found belonging to the same event, the candidate with the lowest value of the refit χ² per degree of freedom is retained and any others are discarded, leading to a reduction in the sample size of approximately 0.3 %.

The B^± invariant mass spectra are shown in Fig. 1 for candidates selected in the whole D Dalitz plot, overlaid with a parametric fit described in Sect. 5. The D Dalitz plots are shown in Fig. 2 for the B^± → DK^± and B^± → Dπ^± candidates that fall within

a nominal B^± signal region in B^± invariant mass (5247–5317 MeV/c²). The dominant K^∗(892)^± resonance is clearly visible within a horizontal band, and the window around this resonance used in the analysis is indicated.

5 Invariant mass fit

In order to determine the signal yields in each decay mode, simultaneous fits are performed to the B^± invariant mass spectra in the range 5110 MeV/c² to 5800 MeV/c² in the different modes, both for candidates in the whole D Dalitz plot, and for only those inside the restricted region around the K^∗(892)^± resonance. The data samples are split according to the year in which the data were taken, the decay mode, the K_S⁰ type and the charge of the B candidate. The fit is parameterised in terms of the observables described in Sect. 2, rather than varying each signal yield in each category independently.

The probability density function (PDF) used to model the signal component is a modified Gaussian function with asymmetric tails, where the unnormalised form is given by

f (m; m₀, α_L, α_R, σ) ≡  exp[−(m − m₀)²/(2σ² + αL(m − m0)²)] for m < m0,

exp[−(m − m₀)²/(2σ²+ α_R(m − m₀)²)] for m > m₀, (4) where m is the reconstructed mass, m₀ is the mean B mass and σ determines the width of the function. The α_L,R parameters govern the shape of the tail. The mean B mass is shared among all categories but is allowed to differ according to the year in which the data were collected. The α_L parameters are fixed to the values determined in the earlier analysis of B^± → [K_S⁰π⁺π⁻]_Dh^± [6]. The α_R parameters are common to the B^± → Dπ^± and B^± → DK^±, SS and OS categories, and are allowed to vary in the fit. Only the width parameters σ(B^± → DK^±) are allowed to vary in the fit. The ratios σ(B^± → Dπ^±)/σ(B^±→ DK^±) are fixed according to studies of the similar mode B^±→ [K_S⁰π⁺π⁻]_Dh^±. The fitted values for σ(B^±→ DK^±) vary by less than 10% around 14 MeV/c². The total yield of B^± → Dπ^± decays is allowed to vary between the different K_S⁰ type and year categories. The yields in the various D decay modes and different charges, and all the B^± → DK^± yields, are determined using the observables described in Sect. 2, rather than being fitted directly.

In addition to the signal PDF, two background PDFs are required. The first background PDF models candidates formed from random combinations of tracks and is represented by a linear function. In the fit within the restricted Dalitz region, where the sample size is significantly smaller, the slope of the linear function fitting the B^± → Dπ^± data is fixed to the value determined in the fit to the whole Dalitz plot. The second background PDF accounts for contamination from partially reconstructed processes. Given that the contamination is dominated by those processes that involve a real D⁰ → K_S⁰K^±π^∓ decay, the PDF is fixed to the shape determined from the more abundant mode B^±→ [K^±π^∓]_Dh^±. The yields of both these background components are free to vary in each data category.

A further significant background is present in the B^± → DK^± samples due to π → K misidentification of the much more abundant B^± → Dπ^± mode. This background is