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CPLEAR Results on the CP Parameters of Neutral Kaons Decaying to Π+Π−Π0 R

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CPLEAR Results on the CP Parameters of Neutral Kaons Decaying to Π+Π−Π0 R CPLEAR results on the CP parameters of neutral kaons decaying to π+π−π0 R. Adler, A. Angelopoulos, A. Apostolakis, E. Aslanides, G. Backenstoss, P. Bargassa, C P. Bee, O. Behnke, A. Benelli, V. Bertin, et al. To cite this version: R. Adler, A. Angelopoulos, A. Apostolakis, E. Aslanides, G. Backenstoss, et al.. CPLEAR results on the CP parameters of neutral kaons decaying to π+π−π0. Physics Letters B, Elsevier, 1997, 407, pp.193-200. in2p3-00000063 HAL Id: in2p3-00000063 http://hal.in2p3.fr/in2p3-00000063 Submitted on 16 Nov 1998 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN–PPE/97–54 12 May 1997 + 0 CPLEAR results on the CP parameters of neutral kaons decaying to The CPLEAR Collaboration 1 1 11 2 R. Adler 2 , A. Angelopoulos , A. Apostolakis ,E.Aslanides , G. Backenstoss , 9 17 9 11 7;13 P. Bargassa13 ,C.P.Bee,O.Behnke ,A.Benelli ,V.Bertin ,F.Blanc , 15 9 5 9 16 P. Bloch 4 ,P.Carlson ,M.Carroll,J.Carvalho,E.Cawley, S. Charalambous , 3 9 15 14 14 G. Chardin 14 , M.B. Chertok , A. Cody , M. Danielsson , M. Dejardin , J. Derre , 2 16 8 7 11 A. Ealet 11 ,B.Eckart ,C.Eleftheriadis ,I.Evangelou ,L.Faravel ,P.Fassnacht , 5 17 4 10 C. Felder2 , R. Ferreira-Marques ,W.Fetscher , M. Fidecaro , A. Filipˇciˇc , 9 9 9 14 17 D. Francis 3 ,J.Fry, E. Gabathuler , R. Gamet ,D.Garreta ,H.-J.Gerber , 14 9 9 11 A. Go 14 , C. Guyot ,A.Haselden,P.J.Hayman, F. Henry-Couannier , 11 15 13 14 R.W. Hollander6 ,E.Hubert ,K.Jon-And , P.-R. Kettle , C. Kochowski , 6;13 11 2 16 5 P. Kokkas 4 ,R.Kreuger ,R.LeGac , F. Leimgruber , A. Liolios , E. Machado , 8 14 10 3 11 I. Mandi´c10 ,N.Manthos,G.Marel ,M.Mikuˇz , J. Miller ,F.Montanet , 13 17 16 2 A. Muller14 ,T.Nakada, B. Pagels , I. Papadopoulos , P. Pavlopoulos , 5 2 2 3 J. Pinto da Cunha5 , A. Policarpo , G. Polivka ,R.Rickenbach, B.L. Roberts , 1 9 2 17 7 T. Ruf 4 ,L.Sakeliou,P.Sanders,C.Santoni,M.Sch¨afer , L.A. Schaller , 4 14 14 2 12 T. Schietinger2 , A. Schopper , P. Schune ,A.Soares ,L.Tauscher , C. Thibault , 4 8 5 6 F. Touchard 11 , C. Touramanis , F. Triantis ,E.VanBeveren, C.W.E. Van Eijk , 17 13 17 14 10 S. Vlachos2 ,P.Weber , O. Wigger , M. Wolter ,C.Yeche ,D.Zavrtanik and D. Zimmerman 3 Abstract 0 0 K The CPLEAR experiment measured time-dependent decay-rate asymmetries of K and + 0 0 K decaying to in order to study the interference between the decay amplitudes of S 0 — either CP-violating or CP-conserving — and the CP-conserving K decay amplitude. L 0 From the analysis of the complete data set we find for the CP-violating parameter + , +4 +2 3 Re( ) = 2 7 10 ; Im( ) = 2 9 0 +0 + stat. syst. stat. syst. 1 1 3 3 10 Re() = ( +28 7 3 ) 10 ; and for the CP-conserving parameter , stat. syst. 3 )=(10 8 2 ) 10 : Im( stat. syst. From the latter, the branching ratio of the CP- +1:3 +0:5 0 + 0 7 ! B= 2:5 stat: syst: 10 : conserving K decay is deduced to be 1:0 0:6 S (Submitted to Physics Letters B) 1 Introduction 0 The CPLEAR experiment at the Low Energy Antiproton Ring at CERN uses tagged K 0 and K to study CP, T and CPT symmetries in the neutral kaon system. In previous CPLEAR 0 publications, the measurements of the CP-violating parameter + [1] and the value of the CP- + 0 conserving parameter [2], obtained from the analysis of neutral kaons decaying into , 0 were reported for a 25% data sample. In this letter, new measurements of + and based on our complete data set are presented. 0 + 0 ! Interest in the search of the CP-violating amplitude of K extends beyond S 0 the search for CP violation in the K decays. Firstly, increasing experimental precision in the S ' + measurement of the phase, + , of the CP-violating parameter can be fully exploited for an indirect CPT test, only if the precision of the CP-violating parameters of neutral kaons decaying to three pions is improved substantially [3]. Secondly, the measurement of the CP-conserving 0 + 0 ! K amplitude allows the results to be cross-checked with the phenomenological S global fits to all known neutral- and charged-kaon decay rates and to be compared with the predictions of chiral perturbation theories [4–8]. + 0 l +1 (1) l The CP eigenvalue for the final state is given by where is the relative 0 + angular momentum between the two charged pions (or between the and the pair). As the sum of the masses of the three pions is close to the kaon mass, the pions have a low E ( ) l > 0 kinetic energy CM in the kaon rest-frame, and the states with are suppressed by the +0 0 + 0 ! A centrifugal barrier. This implies two contributions to the K decay amplitude : S S + 0 =+1 one from the decay to a state with CP (kinematics-suppressed and CP-allowed), 1 and the other from the decay to a CP = state (kinematics-favoured but CP-suppressed). The +0 0 + 0 ! A l = 0 K decay is dominated by the CP-allowed decay amplitude with and L L 1 CP = . +0 0 0 A K The K decay amplitude interferes with both the CP-conserving decay ampli- S L L 3 ( =+1) 3 ( =1) CP 0 CP K A tude A and the CP-violating decay amplitude . These amplitudes depend S S S 2 + X Y X ' (2m =m )(E ( ) CM on the Dalitz variables and [2], which can be estimated to be K 2 0 E ( )) Y ' (2m =m )(m =3 E ( )) K K CM CM and . The former interference term is antisym- X > 0 X < 0 metric in X , and is observed by separating the events with and . We define the CP-conserving parameter as R R ( =+1) 3( =+1) 3 CP CP dX d Y A dX d Y A (X; Y ) A (X; Y ) (X; Y ) A (X; Y ) X<0 0 X> L S L S R R = : = (1) 2 2 dX d Y jA (X; Y )j dX d Y jA (X; Y )j 0 X<0 X> L L 1) University of Athens, Greece 2) University of Basle, Switzerland 3) Boston University, USA 4) CERN, Geneva, Switzerland 5) LIP and University of Coimbra, Portugal 6) Delft University of Technology, Netherlands 7) University of Fribourg, Switzerland 8) University of Ioannina, Greece 9) University of Liverpool, UK 10) J. Stefan Inst. and Phys. Dep., University of Ljubljana, Slovenia 11) CPPM, IN2P3-CNRS et Universit´e d’Aix-Marseille II, Marseille, France 12) CSNSM, IN2P3-CNRS, Orsay, France 13) Paul-Scherrer-Institut(PSI), Villigen, Switzerland 14) CEA, DSM/DAPNIA CE-Saclay, France 15) KTH-Stockholm, Sweden 16) University of Thessaloniki, Greece 17) ETH-IPP Z¨urich, Switzerland 1 This contribution vanishes when data are integrated over the whole phase space, allowing the observation of the latter interference term through the measurement of the CP-violating param- 0 eter + given by R ( =1) 3 CP (X; Y ) A (X; Y ) dX d Y AL S R = : +0 2 jA (X; Y )j dX d Y L 0 + 0 K R ( ) R ( ) We define the decay rates for an initial decaying to to be + and > 0 X < 0 for X and respectively, where is the decay eigentime. Similarly the decay rates 0 K R ( ) R ( ) for an initial are defined as + and . The time-dependent asymmetry integrated over the whole phase space, h i R ( )+R () [R ()+R ()] + + h i A ( ) = 0 + (2) R ( )+R () +[R ()+R ()] + + =2 = 2 (") 2 e [ ( ) cos (m) ( ) sin (m)] ; 0 +0 Re Re + Im 0 0 0 0 m K K K K " where is the – mass difference, the – decay-width difference and the CP- L S S L 0 0 K K 0 violation parameter in the – mixing, is used to extract the CP-violation parameter + . > 0 X < 0 The two asymmetries obtained by separating the rates for X and , R ( ) R ( ) A ( ) = (3) R ( )+R () =2 = 2 (") 2 e [ ( ) cos (m) ( ) sin(m)] ; 0 +0 Re Re + Im are used to determine the CP-conserving parameter . 2 Data selection The CPLEAR method and detector have been described elsewhere [9]. In this experiment, 0 0 K initial K and are produced in the reactions 0 + + 0 p ! K K pp ! K K ; p (at rest) and (at rest) where the strangeness of the neutral kaon is identified on an event-by-event basis. The results reported in the present paper are based on the complete data set recorded by CPLEAR. The selection criteria are mostly identical to those described in our previous papers [1, 2]. The differences are due to upgrades of our detector in 1994 and 1995. During the 1994 data-taking, the spherical target (radius 7 cm) was replaced by a cylindrical one with a radius of 1.1 cm, filled with gaseous hydrogen at a pressure of 27 bar.
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