Abstract
Differences in the behaviour of matter and antimatter have been observed in K and B meson decays, but not yet in any baryon decay. Such differences are associated with the non-invariance of fundamental interactions under the combined charge-conjugation and parity transformations, known as CP violation. Here, using data from the LHCb experiment at the Large Hadron Collider, we search for CP-violating asymmetries in the decay angle distributions of Λb0 baryons decaying to pπ−π+π− and pπ−K+K− final states. These four-body hadronic decays are a promising place to search for sources of CP violation both within and beyond the standard model of particle physics. We find evidence for CP violation in Λb0 to pπ−π+π− decays with a statistical significance corresponding to 3.3 standard deviations including systematic uncertainties. This represents the first evidence for CP violation in the baryon sector.
Highlights
Di erences in the behaviour of matter and antimatter have been observed in K and B meson decays, but not yet in any baryon decay
The asymmetry between matter and antimatter is related to the violation of the CP symmetry (CPV), where C and P are the charge-conjugation and parity operators
CP violation is accommodated in the standard model (SM) of particle physics by the Cabibbo–Kobayashi–Maskawa (CKM) mechanism that describes the transitions between up- and down-type quarks[1,2], in which quark decays proceed by the emission of a virtual W boson and where the phases of the couplings change sign between quarks and antiquarks
Summary
AT , and are, by construction, largely insensitive to particle–antiparticle production asymmetries and detector-induced charge asymmetries[26]. The LHCb detector[29,30] is designed to collect data of b-hadron decays produced from proton–proton collisions at the Large Hadron Collider. It instruments a region around the proton beam axis, covering the polar angles between 10 and 250 mrad, where approximately 24% of the b-hadron decays occur[31]. Simulated samples of Λ0b signal modes and control samples are used in this analysis to verify the experimental method and to study certain systematic effects These simulated events model the experimental conditions in detail, including the proton–proton collision, the decays of the particles, and the response of the detector. It consists of a hardware stage, based on information from the NATURE PHYSICS | VOL 13 | APRIL 2017 | www.nature.com/naturephysics
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