Search for direct CP violation in charm neutral meson decays at LHCb

A search for time-integrated violation of the CP symmetry, ACP(K−K+), in the Cabibbo-suppressed D0 → K−K+ decays is performed at the LHCb detector using proton- proton collisions recorded from 2015 to 2018 at the centre of mass energy of 13 TeV. The data used corresponds to an integrated luminosity of 5.7 fb−1. The flavour of the charm mesons is defined from the charge of the pion in D∗+ → D0π+ and D∗− → D0π− decays. Nuisance asymmetries are constrained from D∗+ → D0(→ K−π+)π+, D+ → KS0π+, D+ → K−π+π+, Ds+ → KS0K+ and Ds+ → φπ+ decays. The ACP(K−K+) asymme- try is measured to be ACP (K−K+) = (6.8 ± 5.4 (stat) ± 1.6 (syst)) · 10−4, in agreement with the previous LHCb results and the current world average. This represents the world’s most precise measurement of this quantity to date. Combining ACP (K−K+) with the time-integrated CP asymmetry difference, ∆ACP = ACP (K−K+)− ACP (π−π+), and the time-dependent CP asymmetry, ∆Y , measured with D0 → K−K+ and D0 → π−π+ decays, the direct CP asymmetries in D0 → K−K+ and D0 → π−π+ decays, adKK and adππ, result to be adKK =(7.7±5.7)·10−4, adππ =(23.2±6.1)·10−4, where the errors include systematic and statistical uncertainties and the correlation be- tween the two values is ρ(adKK,adππ) = 0.88. The values differ from zero for 1.4 and 3.8 standard deviations, respectively. In particular, adππ shows an evidence for direct CP violation in D0 → π−π+ decays.

The AMS-02 Experiment and the Dark Matter Search

AMS-02 is running after great scientific goals since one year and a half: a final setting up for dark matter searches has been achieved, allowing to study the so important antiparticle to particle ratios, which will probably be the first dark matter signals ever corroborated. Even if primary cosmic rays fluxes are subjected to a lot of uncertainties sources, some statements can be done and have been written down about dark matter properties: DM should be a heavy Majorana fermion or Spin 0 or 1 boson, with a mass from about 1 TeV to 10 TeV - unveiling a new TeV-ish search age - which could be able to originate antiparticle fluxes enhancements at high energies, both for positrons and antiprotons. All the observations, direct and indirect, point to these new paradigms or can be traced back to them quite easily. These enhancements perfectly fall into the research window of AMS-02, allowing the experiment to attack each today credible theory. Also an investigation of the Sommerfeld effect-associated dark boson will be possible, in terms of antiparticle to particle ratios substructures. The first great AMS-02 measurement is the positron fraction: an official paper is going to be submitted in few months, where the correct behavior of the apparatus will be reviewed and the full positron fraction rate will be analyzed up to 200 GeV. In this concern, one of the objectives of this work is to test the AMS-02 capability and versatility in doing these dark matter researches, thanks to an orbital temporal (and geomagnetic) stability. The goal has been accomplished: the experiment is very stable in time, so that the temporal error associated to the positron fraction measurement is compatible with zero, offering a beyond belief opportunity to measure CR antiparticle to particle ratios.