Search for CP violation through an amplitude analysis of D0 → K+K−π+π− decays

Abstract

A search for CP violation in the Cabibbo-suppressed D 0 → K + K − π + π − decay mode is performed using an amplitude analysis. The measurement uses a sample of pp collisions recorded by the LHCb experiment during 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb −1 . The D 0 mesons are reconstructed from semileptonic b-hadron decays into D 0 µ − X final states. The selected sample contains more than 160 000 signal decays, allowing the most precise amplitude modelling of this D 0 decay to date. The obtained amplitude model is used to perform the search for CP violation. The result is compatible with CP symmetry, with a sensitivity ranging from 1% to 15% depending on the amplitude considered. JHEP02(2019)126have peculiarities that make them particularly interesting for these studies. They have a rich resonant structure, and the variation of the strong phases over the decay phase space may provide regions with enhanced sensitivity to CP violation. This paper presents a search for CP violation in the individual amplitudes of the decay 1 D 0 → K + K − π + π − , produced in semileptonic decays of b hadrons into D 0 µ − X, where X represents any combination of undetected particles. The charge of the µ − (µ + ) lepton is used to identify D 0 (D 0 ) mesons. The D 0 µ − system is reconstructed in a sample of pp collisions collected by the LHCb experiment in 2011 and 2012 at centre-of-mass energies of 7 and 8 T eV , corresponding to integrated luminosities of 1.0 fb −1 and 2.0 fb −1 , respectively. A CP -averaged decay model is developed through a full amplitude analysis in the fivedimensional phase space of the four-body D 0 decay, where the D 0 and D 0 samples are merged. This model is then used to search for CP violation in a simultaneous fit to the distinct D 0 and D 0 samples.Such an amplitude analysis has already been performed by the CLEO experiment [7] and has been recently updated with the CLEO legacy data [8]. The analysis was based on 3000 signal decays and no CP violation was observed. This paper presents an analysis using a data sample more than 50 times larger. Searches for CP violation in this decay have also been performed by the BaBar [9], LHCb [10] and Belle [11] experiments, which are all compatible with CP symmetry.These studies use a model-independent technique to search for CP violation based on triple products [12]. Similarly the energy test [13] is used to study the D 0 → π + π − π + π − decays [14]. While these techniques are very powerful in evidencing the presence of CP violation, they do not provide any direct information on what generated the observed effect. The technique presented in this paper instead is able to associate any CP violation effect to a specific source in the resonant structure of the decay.Further motivation to study the amplitude structure of this decay mode is given by the determination of the Unitarity Triangle angle γ in B − → DK − decays, where D stands for D 0 or D 0 meson decaying to K + K − π + π − [15], for which the amplitude structure of the D 0 deca...

Averages of $b$-hadron, $c$-hadron, and $τ$-lepton properties as of 2018

“…This implies that the effect originates from a P -odd amplitude, e.g., D 0 → [ρ 0 ρ 0 ] L=1 . A model-dependent search for CP violation has been performed via an amplitude analysis of D 0 → K + K − π + π − decays [1175]. Asymmetries have been measured for 25 contributing amplitudes, with a total uncertainty ranging from 1% to 15%, dominated by the statistical uncertainty.…”

“…Another way to probe P -odd amplitudes is through amplitude analysis using P -odd variables. Usually used is sin Φ, where Φ is the angle between the two decay planes formed with the K + K − and π + π − momenta in the D 0 → K + K − π + π − case [1175]; the sin Φ corresponds to the triple product in fact. The model-independent technique used for the D 0 → π + π − π + π − decays [1174], has been carried out separately for P -odd and P -even contributions, separated out using a triple product.…”

Measurement of the CKM angle γ and $$ {B}_s^0\hbox{-} {\overline{B}}_s^0 $$ mixing frequency with $$ {B}_s^0\to {D}_s^{\mp }{h}^{\pm }{\pi}^{\pm }{\pi}^{\mp } $$ decays

“…For the K 1 (1270) + → ρ(770) 0 K + cascade decay chain, mixing between the ρ(770) 0 and ω(782) 0 states is included [31], with relative magnitude and phase fixed to the values determined in ref. [32]. More details are given in appendix A.…”

Direct CP violation in beauty and charm hadron decays

“…The decay D 0 → K + K − π + π + was also studied very recently by the LHCb collaboration through a full amplitude analysis from the full run I data sample (3 fb −1 ) using semileptonic b-hadron decays into D 0 µ − X final states [282]. The sample has almost 200 thousand candidates with 83% purity.…”