Observation of the mass difference between neutral charm-meson eigenstates

• Published in: arXiv.org 2023-08
• Main Authors: collaboration, LHCb, Alexander, M, P Baladron Rodriguez, Baldini, W, Beiter, A, Bertella, C, Bhasin, S, Borsato, M, Buonaura, A, Carus, L, Cattaneo, M, Charles, M, Chavez Barajas, C A, Chen, S, Chobanova, V, Chrzaszcz, M, Cicala, M F, Cobbledick, J L, Coco, V, Contu, A, Currie, R, Dall'Occo, E, De Miranda, J M, Dean, C T, Decamp, D, S Ek-In, Evans, T, Fan, J, S Ferreres Sole, Fini, R A, Fontana, M, Frau, G, Friday, D A, Gabriel, E, Galli, D, Gambetta, S, P Gironella Gironell, Gkougkousis, E L, Golutvin, A, Gorbounov, P, Griffith, P, Hamilton, P M, Hennessy, K, Henry, L, Hilton, M, J Hu, Jost, B, Kenzie, M, Kirn, T, Klimaszewski, K, Kress, F, Krzemien, W, Lancierini, D, Leflat, A, P Li, S Li, Liu, H, M Lucio Martinez, Luo, Y, Massafferri, A, Maurice, E, Mead, J V, Meadows, B, Milanes, D A, Minotti, A, Mitzel, D S, Pawley, C J, M Pepe Altarelli, Petrov, A, Philippov, A, Pietrzyk, G, Poluektov, A, Ponce, S, Pugatch, V, Raab, N V, Rachwal, B, Redi, F, Rudolph, M S, Ryzhikov, A, Sagidova, N, Salomoni, M, Schwemmer, R, Semennikov, A, Simone, S, Soares, M, Stahl, S, Stone, S, Sun, L, Taneja, S, Tuci, G, Usachov, A, M van Veghel, P Vazquez Regueiro, Veltri, M, Veronesi, M, Vos, K, Wilkinson, G, Zhelezov, A, Zheng, Y, Zhou, Y
• Format: Article
• Language: English
• Subjects: Charm (particle physics); Decay; Eigenvectors; Large Hadron Collider; Luminosity; Mesons; Parameters; Particle collisions; Protons
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2106.03744

A measurement of mixing and \(C\!P\) violation in neutral charm mesons is performed using data reconstructed in proton-proton collisions collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4\(\textrm{fb}^{-1}\). A total of \(30.6\) million \(D^{0}\rightarrow K^{0}_{\mathrm{S}}\pi^{+}\pi^{-}\) decays are analyzed using a method optimized for the measurement of the mass difference between neutral charm-meson eigenstates. Allowing for \(C\!P\) violation in mixing and in the interference between mixing and decay, the mass and decay-width differences are measured to be \(x_{C\!P} = \left[3.97\pm0.46\textrm{(stat)}\pm 0.29\textrm{(syst)}\right]\times10^{-3}\) and \(y_{C\!P} = \left[4.59\pm1.20\textrm{(stat)}\pm0.85\textrm{(syst)}\right]\times10^{-3}\), respectively. The \(C\!P\)-violating parameters are measured as \(\Delta x = \left[-0.27\pm0.18\textrm{(stat)}\pm0.01\textrm{(syst)}\right]\times10^{-3}\) and \(\Delta y = \left[0.20\pm0.36\textrm{(stat)}\pm0.13\textrm{(syst)}\right]\times10^{-3}\). This is the first observation of a nonzero mass difference in the \(D^0\) meson system, with a significance exceeding seven standard deviations. The data are consistent with \(C\!P\) symmetry, and improve existing constraints on the associated parameters.