Search for $CP$ violation in ${{{\varXi }} ^+_{c}} \rightarrow {p} {{K} ^-} {{\pi } ^+} $ decays using model-independent techniques

Roel Aaij, Carlos Abellán Beteta, Thomas Ackernley, Bernardo Adeva, Marco Adinolfi, Hossein Afsharnia, Christine Angela Aidala, Salvatore Aiola, Ziad Ajaltouni, Simon Akar, Pietro Albicocco, Johannes Albrecht (+945 others)
A first search for CP violation in the Cabibbosuppressed Ξ + c → pK − π + decay is performed using both a binned and an unbinned model-independent technique in the Dalitz plot. The studies are based on a sample of protonproton collision data, corresponding to an integrated luminosity of 3.0 fb −1 , and collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The data are consistent with the hypothesis of no CP violation. Eur. Phys. J. C (2020) 80:986 imise effects of charged
more » ... article and antiparticle detection asymmetries. Approximately half of the data are collected with each polarity. There is presently no successful method for computing decay amplitudes in multi-body charm decays, which could provide reliable predictions on how the CP asymmetries vary over the phase space of the decay. This situation favours a model-independent approach, which looks for differences between multivariate density distributions for baryons and antibaryons. Therefore, in this article searches for CP V are performed through a direct comparison between the Dalitz plots of Ξ + c and Ξ − c decays using a binned significance (S CP ) method [37] and an unbinned k-nearest neighbour method (kNN) [38] [39] [40] [41] , both of which are model independent. Detector and simulation The LHCb detector [42, 43] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5. It is designed for the study of particles containing b and 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 the 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/ p T ) µm, where p T is the component of the momentum transverse to the beam, in GeV/c. Different types of charged hadrons are distinguished using information from two ring-imaging Cherenkov detectors. Photons, electrons and hadrons are identified by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromagnetic and a hadron calorimeter. Muons are identified by a system composed of alternating layers of iron and multiwire proportional chambers. Samples of simulated events are used to optimise the signal selection, to derive the angular efficiency and to correct the decay-time efficiency. In the simulation, pp collisions are generated using PYTHIA [44] with a specific LHCb configuration [45] . Decays of hadronic particles are described by EVTGEN [46], in which final-state radiation is generated using PHOTOS [47] . The interaction of the generated particles with the detector, and its response, are implemented using the GEANT4 toolkit [48] as described in Ref. [49] .
doi:10.18154/rwth-2020-12123 fatcat:o3t62jv6jvaohbrmh6ca5xvd2u