Observation of the decay Λ b 0  → pK − μ + μ − and a search for CP violation

Journal of High Energy Physics, Jun 2017

A search for CP violation in the decay Λ b 0  → pK − μ + μ − is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb−1. The Λ b 0  → pK − μ + μ − decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured, \( \Delta {\mathcal{A}}_{CP}\equiv {\mathcal{A}}_{CP}\left({\Lambda}_b^0\to p{K}^{-}{\mu}^{+}{\mu}^{-}\right)-{\mathcal{A}}_{CP}\left({\Lambda}_b^0\to p{K}^{-}J/\psi \right) \) and a \( {a}_{CP}^{\widehat{T}\hbox{-} odd} \), where the latter is based on asymmetries in the angle between the μ + μ − and pK − decay planes. These are measured to be $$ \begin{array}{l}\Delta {\mathcal{A}}_{CP}=\left(-3.5\pm 5.0\left(\mathrm{stat}\right)\pm 0.2\left(\mathrm{syst}\right)\right)\times {10}^{-2},\hfill \\ {}{a}_{CP}^{\widehat{T}\hbox{-} odd}=\left(1.2\pm 5.0\left(\mathrm{stat}\right)\pm 0.7\left(\mathrm{syst}\right)\right)\times {10}^{-2},\hfill \end{array} $$ and no evidence for CP violation is found.

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Observation of the decay Λ b 0  → pK − μ + μ − and a search for CP violation

Accepted: May Observation of the decay search for CP violation A search for CP violation in the decay B physics; CP violation; FCNC Interaction; Hadron-Hadron scattering (ex- - ! pK HJEP06(217)8 The LHCb collaboration 0 b ! pK is presented. This decay is mediated by avour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb 1 . The b0 ! pK time, and two observables that are sensitive to di erent manifestations of CP violation are measured, ACP ACP ( b0 ! pK ACP ( b0 ! pK J= ) and aTb-odd, where CP the latter is based on asymmetries in the angle between the and pK decay planes. + decay is observed for the rst These are measured to be ACP = ( 3:5 aTCbP-odd = ( 1:2 5:0 (stat) 0:2 (syst)) 5:0 (stat) 0:7 (syst)) and no evidence for CP violation is found. 1 Introduction 2 3 4 5 6 7 Detector and simulation Selection of signal candidates Asymmetry measurements Systematic uncertainties Conclusions The LHCb collaboration ter its discovery in the neutral kaon system [ 1 ]. Within the Standard Model of par ticle physics (SM), CPV is incorporated by a single, irreducible weak phase in the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix [ 2, 3 ]. However, the amount of CPV in the SM is insu cient to explain the observed level of matter-antimatter asymmetry in the Universe [4{6]. Therefore, new sources of CPV beyond the SM are expected to exist. Experimental observations of CPV remain con ned to the B- and K-meson systems. Recently, the rst evidence for CPV in b0 ! p + was found at the level of 3:3 standard deviations [7] and a systematic study of CPV in beauty baryon decays has now begun. Among dedicated heavy- avour physics experiments, the LHCb detector [8] is unique in having access to a wide range of decay modes of numerous b-hadron species. Beauty baryons are produced copiously at the LHC, and within the LHCb detector acceptance the production ratio of B0 : b0 : Bs0 particles is approximately 4 : 2 : 1 [9]. The LHCb collaboration has previously searched for CPV in as well as in charmless 0 b ! pKS0 , b0 ! 0 b ! p and J= and 0 b ! h+h transitions [11{13]. . The leading-order transition amplitudes in the SM are described 1The inclusion of charge-conjugate processes is implied throughout this paper, unless stated otherwise. { 1 { Λ0 u b b Vqs μ − μ + s u } u u d } K− p b u d W − Vb∗q νμ W + q Vqs K− p and q represents one of the three up-type quarks u, c or t, the t-quark contribution being dominant. The uu pairs originate from the hadronization process. by the loop diagrams shown in gure 1. In extensions to the SM, new heavy particles could contribute to the amplitudes with additional weak phases, providing new sources of CPV [14, 15]. The limited amount of CPV predicted for the decay and Areco(p) are the reconstruction asymmetries for kaons and protons, mainly due to the di erent interaction cross-sections of particles and antiparticles with the detector material. By measuring the di erence of raw asymmetries between the signal and the Cabibbo0 favoured control mode b ! pK J= (! + metries cancel to a good approximation. No signi cant CPV is expected in the latter decay, since its amplitude is dominated by tree-level CP -conserving diagrams, which leads to ), the production and reconstruction asymACP ACP ( b0 ! pK Araw( b0 ! pK + + ) ) ACP ( b0 ! pK J= ) Araw( b0 ! pK J= ): { 2 { (2.1) (2.2) (2.3) μ + Λ 0 b triple products of the nal-state particle momenta in the A pair of Tb-odd and P -odd observables, A T and AT , is obtained by de ning the Tb-odd b b b0 rest frame C C T b T b p~ + (p~p p~ (p~p p~K ); p~K+ ); and taking the asymmetries A T b N (CT > 0) b N (CT > 0) + N (CT < 0) b b N (CT < 0) b ; A T b N ( C N ( C T > 0) b T > 0) + N ( C b N ( C T < 0) b T < 0) b ; b0 rest frame, as shown in gure 2. sin the where N (N ) is the number of b0 ( b0) signal candidates. These asymmetries are measured from the angular distributions of the decay products, with C [18], where is the angle between the decay planes of the + b T being proportional to Following ref. [18], CP -odd and P -odd observables are de ned as The observables A T are P - and Tb-odd but are not sensitive to CPV e ects [17]. b ACP and aTb-odd are sensitive to di erent manifestations of CPV [17]. CP The CP asymmetry ACP depends on the interference of Tb-even amplitudes, de ned as (2.4) (2.5) (2.6) (2.7) aje exp hi( je + je)i, which have a relative CP -even strong phase 1e 2e and a relative CP ACP / ae1ae2 sin( 1e 2e) sin( e1 e2): tive CP -odd weak phase e1 o 1 , The convention used to de ne strong and weak phases is such that all CPV e ects are encoded in the CP -odd weak phases. phase di erence between the two amplitudes is large. Therefore, ACP is enhanced when the strong On the other hand, aTb-odd de CP h ajo exp i( jo + jo + =2) , which have a relative CP -even strong phase 1e pends on the interference between Tb-even and Tb-odd amplitudes, the latter de ned as 1o and a rela , i (2.8) (2.9) aTCbP-odd / ae1ao1 cos( 1e 1o) sin( e1 o1): As a consequence, aTCbP-odd is enhanced when the strong phase di erence vanishes. It is worth noting that the asymmetries reported in eqs. (2.8), (2.9) are CP -odd, being proportional to an odd function of the weak phase di erence. Furthermore, the observables aTCbP-odd are sensitive to di erent types of CPV e ects from physics beyond the SM [16]. ACP and 3 Detector and simulation The LHCb detector [8, 19] is a single-arm forward spectrometer covering the pseudorapidity range 2 < < 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 of the magnet. The tracking system provides a measurement of momentum, p, of charged particles with a relative uncertainty that varies from 0.5% at low momentum to 1.0% at 200 GeV=c. The minimum distance of a track to a primary vertex (PV), the impact parameter (IP), is measured with a resolution of (15 + 29=pT) m, where pT is the component of the momentum transverse to the beam, in GeV=c. Di erent types of charged hadrons are distinguished using information from two ring-imaging Cherenkov detectors. Photons, electrons and hadrons are identied by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromagnetic calorimeter and a hadronic calorimeter. Muons are identi ed by a system composed of alternating layers of iron and multiwire proportional chambers. The online event selection is performed by a trigger [20], which 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. Simulated signal events are used to determine the e ect of the detector geometry, trigger, reconstruction and selection on the angular distributions of the signal and pK J= control sample. Additional simulated samples are used to estimate the contribution from speci c background processes. In the simulation, pp collisions are generated using Pythia [21, 22] with a speci c LHCb con guration [23]. Decays of hadronic particles are b0 ! { 4 { described by EvtGen [24], in which nal-state radiation is generated using Photos [25]. The interaction of the generated particles with the detector, and its response, are implemented using the Geant4 toolkit [26], as described in ref. [27]. 4 Selection of signal candidates The present analysis is performed using proton-proton collision data corresponding to 1 and 2 fb 1 of integrated luminosity, collected with the LHCb detector in 2011 and 2012, at centre-of-mass energies of 7 and 8 TeV, respectively. The vertex, and are selected using information from the particle identi cation system. The avour is determined from the charge of the kaon candidate, i.e. for positive kaons. Only candidates with reconstructed invariant mass, m(pK the range [5350; 6000] MeV=c2 and a pK invariant mass, m(pK ), below 2350 MeV=c2 are + ), in retained, with the latter requirement being applied to reduce the combinatorial background contribution. The spectrum in the dimuon mass squared, q2, is considered, excluding the resonance regions q2 2 [0:98; 1:10], [8:0; 11:0] and [12:5; 15:0] GeV2=c4 that correspond to the masses of the (1020), J= , and (2S) mesons, respectively. Several background contributions from exclusive decays are identi ed and rejected. b0 for negative and These are Bs0 ! K+K pion is misidenti ed as a proton, and + and B0 ! K muon. These components are e ectively eliminated by tightened particle identi cation requirements combined with selection criteria on invariant masses calculated under the appropriate mass hypothesis (e.g. assigning the kaon mass to the candidate proton to identify possible Bs0 ! K+K + background decays). After these requirements the background contribution from the above decays is negligible. No indication of other speci c background decays is observed. The remaining combinatorial background is suppressed by means of a boosted decision tree (BDT) classi er [28, 29] with an adaptive boosting algorithm [30]. The BDT is constructed from variables that discriminate between signal and background, based on their kinematic, topological and particle identi cation properties, as well as the isolation of the nal-state tracks [31, 32]. Simulated the decay products are uniformly distributed in phase space are used as the signal training sample and a correction for known di erences between data and simulation is applied. Candidates from data in the high mass region, m(pK + ) > 5800 MeV=c2, are used as the background training sample and then removed from the window of the mass t described below. After optimisation of the signi cance, S=pS + B, where S and B are the number of signal and background candidates in the region m(pK the BDT classi er retains only 0:14% of the combinatorial background candidates, with a signal e ciency of 51%. Events in which more than one tion constitute less than 1% of the sample and all candidates are retained; the systematic uncertainty associated with this is negligible. The identical selection is applied to the + ) 2 [5400; 5800] MeV=c2, b0 candidate survives the selec{ 5 { the range [9:0; 10:5] GeV2=c4. 5 Asymmetry measurements b0 ! pK J= , except that the dimuon squared mass is required to be in 0 b 0 avour. For the measurements of the triple-product asymmetries, four subsamples are ACP measurement, the data are divided into two subsamples according to the de ned by the combination of the avour and the sign of C T (or C b T for b b0). The reconstruction e ciencies are studied with simulated events and are found to be equal for all subsamples. The observable ACP can be sensitive to kinematic di erences between the signal and control-mode decays that a ect the cancellation of the detection asymmetries in eq. (2.3). This is taken into account by assigning a weight to each that the resulting proton and kaon momentum distributions match those of the signal decays. These weights are determined from simulation samples for the signal and control modes. No such weighting is required for aTCbP-odd and aTPb-odd, since these observables involve only one decay mode. The asymmetry Araw is determined from a simultaneous extended maximum likelihood unbinned t to the b0 and b0 invariant mass distributions. The A are determined by means of a simultaneous extended maximum likelihood unbinned t to the four subsamples de ned above. The signal model for all ts is the sum of two Crystal Ball functions [33], one with a low-mass power-law tail and one with a high-mass tail, and a Gaussian function, all sharing the same peak position. Only the peak position, the total width of the composite function and the overall normalization are free to vary, with all other shape parameters xed from a t to simulated decays. The background is modelled by an exponential function. The raw asymmetry Araw is incorporated in the t model as ACP is derived from the raw asymmetries measured in the signal and control modes according to eq. (2.3). The asymmetries A and the observables aTb-odd and aTb-odd are computed from A be uncorrelated. Background yields are tted independently for each subsample, while all the signal shape parameters are shared among the subsamples. The invariant mass distributions of with t results superimposed, are shown in and applying the weighting procedure to account for kinematic di erences between signal and Tb and ATb, which are found to { 6 { Λ 0b → pK−J/ψ data and (bottom) b0 ! pK J= candidates, with t results superimposed. Plots refer to the (left) b0 and (right) b0 subsamples. control-mode decays, a value of (2:0 0:7) 10 2 is obtained for the control-mode asymmetry, which yields e ciency-uncorrected from the ts to the data are 600 33 candidates for ACP = ( 4:8 5:0) 10 2. The total signal yields 10 2, and the resulting e ciency-uncorrected parity- and CP -violating 10 2 and aTb-odd = (0:6 CP 5:0) 10 2, where again for the uncertainties are statistical only. 6 Systematic uncertainties The analysis method depends upon the weighting procedure discussed in section 5 to equalise the kinematic distributions of the protons and kaons between the signal and control { 7 { LHCb Λ 0 b → pK+μ −μ + data 5.4 5.5 5.6 5.7 5.8 5.4 5.5 5.6 5.7 5.8 LHCb HJEP06(217)8 5.4 5.5 5.6 5.7 5.8 5.4 5.5 5.6 5.7 5.8 b0 and (bottom) b0 decays divided into the subsamples + subsamples used for the A T and b modes. For ACP , the associated systematic uncertainty is estimated by varying the weights within their uncertainties and taking the largest deviation, 0:15 a systematic uncertainty. No weighting is needed for aTb-odd and aTb-odd, and therefore no 10 2, as systematic uncertainty is assigned. Instead, the e ects of selection and detector acceptance on the triple-product asymmetries are estimated by measuring aTb-odd(pK J= ) on the CP P CP control mode, b0 ! pK J= . A value of (0:5 0:7) 10 2 is obtained. For this mode negligible CPV is expected, and the statistical uncertainty of the measured asymmetry is assigned as the corresponding systematic uncertainty on the observables aTb-odd and aTb-odd. CP P The e ects of the reconstruction e ciency on the measured observables are considered by weighting each event by the inverse of the e ciency extracted from simulated events. This leads to a change in the central values of +1:3 10 2 on ACP , of +0:6 10 2 on aTb-odd and CP within their uncertainties. This amounts to 0:10 10 2 for the ACP observable and P 1:4 10 2 on aTb-odd. A systematic uncertainty is assigned by varying the e ciencies 0:02 10 2 for aTb-odd and aTb-odd. CP P The above e ects are the dominant sources of systematic uncertainties. Other possible sources of systematic uncertainties are considered. The experimental resolution on C is studied with simulated signal events. The e ect of the t model choice is studied by T b tting simulated pseudoexperiments with an alternative t model, in which the Crystal Ball functions are replaced with bifurcated Gaussian functions and the exponential background shape is replaced with a polynomial. Systematic e ects from candidates, and residual physical backgrounds are also studied. These contributions have b0 polarisation [34], multiple negligible impact on the measured asymmetries. 7 Conclusions The rst search for CP violation in the process data sample containing 600 33 signal decays, this representing the rst observation of this b0 decay mode. Two di erent CP -violating observables that are sensitive to di erent manifestations of CP violation, P observable aTb-odd is also measured. The values obtained are ACP and aTb-odd, are measured. The parity-violating CP transitions in B0 and B+ meson decays. The results are compatible with CP and parity conservation and agree with SM predictions for CPV [15, 16], and with experimental results [35, 36] for decays mediated by b ! s + Acknowledgments We express our gratitude to our colleagues in the CERN accelerator departments for the excellent performance of the LHC. We thank the technical and administrative sta at the LHCb institutes. We acknowledge support from CERN and from the national agencies: CAPES, CNPq, FAPERJ and FINEP (Brazil); MOST and NSFC (China); CNRS/IN2P3 (France); BMBF, DFG and MPG (Germany); INFN (Italy); FOM and NWO (The Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MinES and FASO (Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC (United Kingdom); NSF (U.S.A.). We acknowledge the computing resources that are provided by CERN, IN2P3 (France), KIT and DESY (Germany), INFN (Italy), SURF (The Netherlands), PIC (Spain), GridPP (United Kingdom), RRCKI and Yandex LLC (Russia), CSCS (Switzerland), IFIN-HH (Romania), CBPF (Brazil), PL-GRID (Poland) and OSC (U.S.A.). We are indebted to the communities behind the multiple open source software packages on which we depend. Individual groups or members have received support from AvH Foundation (Germany), EPLANET, Marie Sklodowska-Curie Actions and ERC (European Union), Conseil General de Haute-Savoie, Labex ENIGMASS and OCEVU, Region Auvergne (France), RFBR and Yandex LLC (Russia), GVA, XuntaGal and GENCAT (Spain), Herchel Smith { 9 { HJEP06(217)8 Fund, The Royal Society, Royal Commission for the Exhibition of 1851 and the Leverhulme Trust (United Kingdom). Open Access. 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Morello24;t, O. Morgunova68, J. Moron28, A.B. Morris52, R. Mountain61, F. Muheim52, M. Mulder43, M. Mussini15, D. Muller56, J. Muller10, K. Muller42, V. Muller10, P. Naik48, T. Nakada41, R. Nandakumar51, A. Nandi57, I. Nasteva2, M. Needham52, N. Neri22, S. Neubert12, N. Neufeld40, M. Neuner12, T.D. Nguyen41, C. Nguyen-Mau41;n, S. Nieswand9, R. Niet10, N. Nikitin33, T. Nikodem12, A. Nogay68, A. Novoselov37, D.P. O'Hanlon50, A. Oblakowska-Mucha28, V. Obraztsov37, S. Ogilvy19, R. Oldeman16;f, C.J.G. Onderwater70, J.M. Otalora Goicochea2, A. Otto40, P. Owen42, A. Oyanguren69, P.R. Pais41, A. Palano14;d, M. Palutan19, A. Papanestis51, M. Pappagallo14;d, L.L. Pappalardo17;g, W. Parker60, C. Parkes56, G. Passaleva18, A. Pastore14;d, G.D. Patel54, M. Patel55, C. Patrignani15;e, A. Pearce40, A. Pellegrino43, G. Penso26, M. Pepe Altarelli40, S. Perazzini40, P. Perret5, L. Pescatore41, K. Petridis48, A. Petrolini20;h, A. Petrov68, M. Petruzzo22;q, E. Picatoste Olloqui38, B. Pietrzyk4, M. Pikies27, D. Pinci26, A. Pistone20, A. Piucci12, V. Placinta30, S. Playfer52, M. Plo Casasus39, T. Poikela40, F. Polci8, A. Poluektov50;36, I. Polyakov61, E. Polycarpo2, G.J. Pomery48, A. Popov37, D. Popov11;40, B. Popovici30, S. Poslavskii37, C. Potterat2, E. Price48, J.D. Price54, J. Prisciandaro39;40, A. Pritchard54, C. Prouve48, V. Pugatch46, A. Puig Navarro42, G. Punzi24;p, W. Qian50, R. Quagliani7;48, B. Rachwal27, J.H. Rademacker48, M. Rama24, M. Ramos Pernas39, M.S. Rangel2, I. Raniuk45;y, F. Ratnikov35, G. Raven44, F. Redi55, S. Reichert10, A.C. dos Reis1, C. Remon Alepuz69, V. Renaudin7, S. Ricciardi51, S. Richards48, M. Rihl40, K. Rinnert54, V. Rives Molina38, P. Robbe7;40, A.B. Rodrigues1, E. Rodrigues59, J.A. Rodriguez Lopez66, P. Rodriguez Perez56;y, A. Rogozhnikov35, S. Roiser40, A. Rollings57, V. Romanovskiy37, A. Romero Vidal39, J.W. Ronayne13, M. Rotondo19, M.S. Rudolph61, T. Ruf40, P. Ruiz Valls69, HJEP06(217)8 C. Sanchez Mayordomo69, B. Sanmartin Sedes39, R. Santacesaria26, C. Santamarina Rios39, M. Santimaria19, E. Santovetti25;j , A. Sarti19;k, C. Satriano26;s, A. Satta25, D.M. Saunders48, D. Savrina32;33, S. Schael9, M. Schellenberg10, M. Schiller53, H. Schindler40, M. Schlupp10, M. Schmelling11, T. Schmelzer10, B. Schmidt40, O. Schneider41, A. Schopper40, K. Schubert10, M. Schubiger41, M.-H. Schune7, R. Schwemmer40, B. Sciascia19, A. Sciubba26;k, A. Semennikov32, A. Sergi47, N. Serra42, J. Serrano6, L. Sestini23, P. Seyfert21, M. Shapkin37, I. Shapoval45, Y. Shcheglov31, T. Shears54, L. Shekhtman36;w, V. Shevchenko68, B.G. Siddi17;40, R. Silva Coutinho42, L. Silva de Oliveira2, G. Simi23;o, S. Simone14;d, M. Sirendi49, N. Skidmore48, T. Skwarnicki61, E. Smith55, I.T. Smith52, J. Smith49, M. Smith55, H. Snoek43, l. Soares Lavra1, M.D. Sokolo 59, F.J.P. Soler53, B. Souza De Paula2, B. Spaan10, P. Spradlin53, S. Sridharan40, F. Stagni40, M. Stahl12, S. Stahl40, P. Stefko41, S. Stefkova55, O. Steinkamp42, S. Stemmle12, O. Stenyakin37, H. Stevens10, S. Stevenson57, S. Stoica30, S. Stone61, B. Storaci42, S. Stracka24;p, M. Straticiuc30, U. Straumann42, L. Sun64, W. Sutcli e55, K. Swientek28, V. Syropoulos44, M. Szczekowski29, T. Szumlak28, S. T'Jampens4, A. Tayduganov6, T. Tekampe10, G. Tellarini17;g, F. Teubert40, E. Thomas40, J. van Tilburg43, M.J. Tilley55, V. Tisserand4, M. Tobin41, S. Tolk49, 1 Centro Brasileiro de Pesquisas F sicas (CBPF), Rio de Janeiro, Brazil 2 Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil 3 Center for High Energy Physics, Tsinghua University, Beijing, China 4 LAPP, Universite Savoie Mont-Blanc, CNRS/IN2P3, Annecy-Le-Vieux, France 5 Clermont Universite, Universite Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France 6 CPPM, Aix-Marseille Universite, CNRS/IN2P3, Marseille, France 7 LAL, Universite Paris-Sud, CNRS/IN2P3, Orsay, France 8 LPNHE, Universite Pierre et Marie Curie, Universite Paris Diderot, CNRS/IN2P3, Paris, France 9 I. Physikalisches Institut, RWTH Aachen University, Aachen, Germany 10 Fakultat Physik, Technische Universitat Dortmund, Dortmund, Germany 11 Max-Planck-Institut fur Kernphysik (MPIK), Heidelberg, Germany 12 Physikalisches Institut, Ruprecht-Karls-Universitat Heidelberg, Heidelberg, Germany 13 School of Physics, University College Dublin, Dublin, Ireland 14 Sezione INFN di Bari, Bari, Italy 15 Sezione INFN di Bologna, Bologna, Italy 16 Sezione INFN di Cagliari, Cagliari, Italy 17 Sezione INFN di Ferrara, Ferrara, Italy 18 Sezione INFN di Firenze, Firenze, Italy HJEP06(217)8 20 Sezione INFN di Genova, Genova, Italy 21 Sezione INFN di Milano Bicocca, Milano, Italy 22 Sezione INFN di Milano, Milano, Italy 23 Sezione INFN di Padova, Padova, Italy 24 Sezione INFN di Pisa, Pisa, Italy 25 Sezione INFN di Roma Tor Vergata, Roma, Italy 26 Sezione INFN di Roma La Sapienza, Roma, Italy Krakow, Poland Romania 28 AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science, 29 National Center for Nuclear Research (NCBJ), Warsaw, Poland 30 Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, 31 Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia 32 Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia 33 Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia 34 Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia 35 Yandex School of Data Analysis, Moscow, Russia 36 Budker Institute of Nuclear Physics (SB RAS), Novosibirsk, Russia 37 Institute for High Energy Physics (IHEP), Protvino, Russia 38 ICCUB, Universitat de Barcelona, Barcelona, Spain 39 Universidad de Santiago de Compostela, Santiago de Compostela, Spain 40 European Organization for Nuclear Research (CERN), Geneva, Switzerland 41 Institute of Physics, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland 42 Physik-Institut, Universitat Zurich, Zurich, Switzerland 43 Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands 44 Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands 45 NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine 46 Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine 47 University of Birmingham, Birmingham, United Kingdom 48 H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom 49 Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 50 Department of Physics, University of Warwick, Coventry, United Kingdom 51 STFC Rutherford Appleton Laboratory, Didcot, United Kingdom 52 School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 53 School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 54 Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 55 Imperial College London, London, United Kingdom 56 School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 57 Department of Physics, University of Oxford, Oxford, United Kingdom 58 Massachusetts Institute of Technology, Cambridge, MA, United States 59 University of Cincinnati, Cincinnati, OH, United States 60 University of Maryland, College Park, MD, United States 61 Syracuse University, Syracuse, NY, United States 62 Pontif cia Universidade Catolica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated 63 University of Chinese Academy of Sciences, Beijing, China, associated to 3 64 School of Physics and Technology, Wuhan University, Wuhan, China, associated to 3 65 Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China, associated to 2 to 3 68 National Research Centre Kurchatov Institute, Moscow, Russia, associated to 32 69 Instituto de Fisica Corpuscular, Centro Mixto Universidad de Valencia - CSIC, Valencia, Spain, 70 Van Swinderen Institute, University of Groningen, Groningen, The Netherlands, associated to 43 a Universidade Federal do Tria^ngulo Mineiro (UFTM), Uberaba-MG, Brazil b Laboratoire Leprince-Ringuet, Palaiseau, France c P.N. 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Lyu, F. Machefert. Observation of the decay Λ b 0  → pK − μ + μ − and a search for CP violation, Journal of High Energy Physics, 2017, 1-17, DOI: 10.1007/JHEP06(2017)108