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Register a new userOn model-independent searches for direct CP violation in multi-body decays
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Techniques for performing model-independent searches for direct CP violation in three and four-body decays are discussed. Comments on the performance and the optimisation of a binned chisquare approach and an unbinned approach, known as the energy test, are made. The use of the energy test in the presence of background is also studied. The selection and treatment of the coordinates used to describe the phase-space of the decay are discussed. The conventional model-independent techniques, which test for P-even CP violation, are modified to create a new approach for testing for P-odd CP violation. An implementation of the energy test using GPUs is described.
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Model-independent techniques for CP violation searches in multi-body charm decays are discussed. Examples of recent analyses from BaBar and LHCb are used to illustrate the experimental challenges involved.
Since the discovery of CP violation more than 5 decades ago, this phenomenon is still attracting a lot of interest. Among the many fascinating aspects of this subject, this review is dedicated to direct CP violation in non-leptonic decays. The advances within the last decade have been enormous, driven by the increasingly large samples of b- and c-hadron decays, and have led to very interesting results such as large CP asymmetries in charmless B decays and the observation of direct CP violation in the charm sector. We address the quest for understanding the origin of strong phases, the importance of final state interactions and the relation with CPT symmetry, and different approaches to measure direct CP violation in these decays. The main experimental results and their implications are then discussed.
A first search for $CP$ violation in the Cabibbo-suppressed $Xi_c^+rightarrow pK^-pi^+$ 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 proton-proton collision data, corresponding to an integrated luminosity of $3.0~{rm fb^{-1}}$, and collected by the LHCb experiment at centre-of-mass energies of $7$ and $8~rm TeV$. The data are consistent with the hypothesis of no $CP$ violation.
Using a data sample corresponding to an integrated luminosity of 0.35 $mathrm{fb}^{-1}$ collected by LHCb in 2011, we report the first evidence of CP violation in the decays of $B^0_s$ mesons to $K^pm pi^mp$ pairs, $A_{CP}(B^0_s rightarrow K pi)=0.27 pm 0.08,mathrm{(stat)} pm 0.02,mathrm{(syst)}$, with a significance of 3.3$sigma$. Furthermore, we report the first observation of CP violation in $B^0$ decays at a hadron collider, $A_{CP}(B^0 rightarrow Kpi)=-0.088 pm 0.011,mathrm{(stat)} pm 0.008,mathrm{(syst)}$, with a significance exceeding 6$sigma$.
We report the first lattice QCD calculation of the complex kaon decay amplitude $A_0$ with physical kinematics, using a $32^3times 64$ lattice volume and a single lattice spacing $a$, with $1/a= 1.3784(68)$ GeV. We find Re$(A_0) = 4.66(1.00)(1.26) times 10^{-7}$ GeV and Im$(A_0) = -1.90(1.23)(1.08) times 10^{-11}$ GeV, where the first error is statistical and the second systematic. The first value is in approximate agreement with the experimental result: Re$(A_0) = 3.3201(18) times 10^{-7}$ GeV while the second can be used to compute the direct CP violating ratio Re$(varepsilon/varepsilon)=1.38(5.15)(4.59)times 10^{-4}$, which is $2.1sigma$ below the experimental value $16.6(2.3)times 10^{-4}$. The real part of $A_0$ is CP conserving and serves as a test of our method while the result for Re$(varepsilon/varepsilon)$ provides a new test of the standard-model theory of CP violation, one which can be made more accurate with increasing computer capability.
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