CP Violation Parameter Research Articles

Matter asymmetries in the ZN dark matter-companion models

A class of ZN≥3-symmetric WIMP dark matter models that are characterized by the semi-annihilation into the companion of dark matter has been proposed in ref. [1], providing a mechanism to evade the stringent direct detection constraint. In this work, we point out that such models naturally provide the three Sakharov elements necessary for dark matter asymmetry, and moreover this asymmetry can be transferred to the visible sector with a proper link to the leptonic or quark sector. In our minimal Z3 example, the migration to the leptonic sector is via the asymmetric companion decay into neutrinos, and the lepton asymmetry can be further transferred to the quark sector. The CP violation parameter is restrained in this model. Thus, we explore the thermal motion effect of dark matter and find that it gives an enhancement to the CP violation parameter, which is studied for the first time. A preliminary numerical analysis based on the Boltzmann equations shows that both correct relic density of dark matter and baryon asymmetry can be accommodated.

New graph-neural-network flavor tagger for Belle II and measurement of sin 2ϕ1 in B0→J/ψKS0 decays

We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral B mesons produced in ϒ(4S) decays. It improves previous algorithms by using the information from all charged final-state particles and the relations between them. We evaluate its performance using B decays to flavor-specific hadronic final states reconstructed in a 362 fb−1 sample of electron-positron collisions collected at the ϒ(4S) resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of (37.40±0.43±0.36%), where the first uncertainty is statistical and the second systematic, which is 18% better than the previous Belle II algorithm. Demonstrating the algorithm, we use B0→J/ψKS0 decays to measure the mixing-induced and direct CP violation parameters, S=(0.724±0.035±0.009) and C=(−0.035±0.026±0.029). Published by the American Physical Society 2024

Measurement of CP asymmetries in B0→KS0KS0KS0 decays at Belle II

We report a measurement of decay-time-dependent charge-parity (CP) asymmetries in B0→KS0KS0KS0 decays. We use 387×106 BB¯ pairs collected at the ϒ(4S) resonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the CP-violating parameters S and C from a fit to the distribution of the decay-time difference between the two B mesons. The resulting confidence region is consistent with previous measurements in B0→KS0KS0KS0 and B0→(cc¯)K0 decays and with predictions based on the standard model. Published by the American Physical Society 2024

Maximising CP Violation in naturally aligned Two-Higgs Doublet Models

The Two-Higgs Doublet Model (2HDM) is a well-motivated theoretical framework that provides additional sources of CP Violation (CPV) beyond the Standard Model (SM). After studying the vacuum topology of a general (convex) 2HDM potential, we unambiguously identify three origins of CPV: (i) Spontaneous CPV (SCPV), where the vacuum manifold has at least two degenerate CPV minima disconnected by domain walls, (ii) Explicit CPV (ECPV) with one single CPV ground state, and (iii) Mixed Spontaneous and Explicit CPV (MCPV), where the theory possesses more than one non-degenerate CPV local minimum. Most importantly, we define a novel complex parameter rCP whose norm and phase control the three different realisations of CPV, at least at the tree level. In all these scenarios, only two CPV phases can be made independent, as any third CPV parameter will always be constrained via the CP-odd tadpole condition. Since ECPV vanishes in 2HDMs where SM Higgs alignment is achieved naturally through accidental continuous symmetries, we analyse the possibility of maximising CPV through soft and explicit breaking of these symmetries. We derive upper limits on key CPV parameters that quantify the degree of SM misalignment from constraints due to the non-observation of an electron Electric Dipole Moment (EDM). Finally, we delineate the CP-violating parameter space of the so-constrained naturally aligned 2HDMs that can further be probed at the CERN Large Hadron Collider (LHC).

Measurement of CP Violation in B^{0}→K_{S}^{0}π^{0} Decays at Belle II.

We report a measurement of the CP-violating parameters C and S in B^{0}→K_{S}^{0}π^{0} decays at Belle II using a sample of 387×10^{6} BB[over ¯] events recorded in e^{+}e^{-} collisions at a center-of-mass energy corresponding to the ϒ(4S) resonance. These parameters are determined by fitting the proper decay-time distribution of a sample of 415 signal events. We obtain C=-0.04_{-0.15}^{+0.14}±0.05 and S=0.75_{-0.23}^{+0.20}±0.04, where the first uncertainties are statistical and the second are systematic.

Averages of b -hadron, c -hadron, and τ -lepton properties as of 2021

This paper reports world averages of measurements of b-hadron, c-hadron, and τ-lepton properties obtained by the Heavy Flavor Averaging Group using results available before April 2021. In rare cases, significant results obtained several months later are also used. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays, and Cabibbo-Kobayashi-Maskawa matrix elements.97 MoreReceived 25 June 2022Accepted 20 September 2022DOI:https://doi.org/10.1103/PhysRevD.107.052008Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBound statesChiral perturbation theoryElectroweak interactionFlavor changing neutral currentsForm factorsHadron mixingLattice QCDParticle decaysParticle interactionsParticle mixing & oscillationsQuark mixingParticles & Fields

Kaon processes in general 2HDM

We discuss new physics (NP) contributions to kaon mixing parameter εK , direct CP violation parameter ε′/ε of K → ππ, and rare decays , and KL,S → μ+μ− in the context of general two Higgs doublet model. We focus on contributions of top quark related exotic couplings, and show that simultaneous presence of flavor conserving and flavor violating interactions can lead to large NP effects in kaon sector, while being consistent with the stringent constraints from B physics observables such as mixing, Bs → μ+μ−, and b → sγ. We stress on the importance of correlations between εK , and Bs → μ + μ − that can be exploited to distinguish the parameter space corresponding to a light (sub-TeV) or heavy (TeV) scale charged Higgs boson.

Probing Higgs CP properties at the CEPC in the e^{+} e^{-} rightarrow Z H rightarrow l^{+} l^{-}H using optimal variables

In the Circular Electron Positron Collider (CEPC), a measurement of the Higgs CP mixing through e^{+} e^{-} rightarrow Z H rightarrow l^{+} l^{-}(e^{+} e^{-} /mu ^{+} mu ^{-}) H(rightarrow b bar{b} / c bar{c} / g g) process is presented, with 5.6 text{ ab}^{-1}e^{+} e^{-} collision data at the center-of-mass energy of 240 textrm{GeV}. In this study, the CP-violating parameter tilde{c}_{Z gamma } is constrained between the region of -0.30 and 0.27 and tilde{c}_{Z Z} between -0.06 and 0.06 at 68% confidence level. This study demonstrates the great potential of probing Higgs CP properties at the CEPC.

Strange processes in general two Higgs doublet model

In the general two Higgs doublet model (g2HDM) that has extra Yukawa couplings, we analyze their New Physics (NP) contributions to kaon mixing parameter εK, direct CP violation parameter ε′/ε, and rare {K}^{+}to {pi}^{+}nu overline{nu} , {K}_Lto {pi}^0nu overline{nu} , and KL,S→ μ+μ− decays. We study correlations between these observables, and call special attention to a unique complementarity of kaon mixing and rare Kto pi nu overline{nu} decays in probing the exotic Higgs mass spectrum of g2HDM. The importance of kaon physics in probing NP vis-à-vis B physics is stressed. One unexpected feature we uncover is the special sensitivity of {K}^{+}to {pi}^{+}nu overline{nu} to TeV scale charged Higgs boson.

Minimizing the phase structure of quark mass matrices

Fritzsch–Xing matrices are a particular class of texture 4 zero hermitian quark mass matrices, known to be successful in accommodating the quark mixing data. In the present work, it is shown that these texture 4-zero matrices with only one phase parameter, unlike the usually considered two phase parameters, are not only consistent with the latest experimental quark mixing data, but also predict the CP violation parameters, J and corresponding phase delta , in agreement with the recent global analyses. We also show that the mass matrix elements do not exhibit a strong hierarchy and there is a strong correlation between some of the mass matrix elements of up and down sector. A precision measurement of delta as well as small quark masses would have the potential to constrain the phase structure of the matrices further.

Charge parity violation parameters in neutral beauty meson decays into charmonium and strange kaon mesons

The most precise measurement of decay-time-dependent CP violation in the decays of [Formula: see text] and [Formula: see text] was reported by LHCb collaboration with the values of [Formula: see text] and [Formula: see text] [Formula: see text]. In this study, the parameters of CP violation in these decay modes have been calculated under the factorization approach. In these decays, CP violation in the interference of mixing and decay has has arisen from decay-time-dependent asymmetry. This type of CP violation has been characterized by [Formula: see text]. We have estimated the parameters of [Formula: see text] and [Formula: see text] for the [Formula: see text] decay and [Formula: see text] and [Formula: see text] correspond to the [Formula: see text] decay which are compatible with the experimental values approved by the LHCb collaboration. In the following, we have obtained the value of [Formula: see text]. Finally, we have calculated the total amplitude and obtained comparable results with the experimental values for the branching ratios of both decays.

Power corrections to the CP-violation parameter εK

We present the calculation of the short-distance power corrections to the CP-violation parameter εK coming from dimension-8 operators in the ∆S = 2 effective Hamiltonian. A first estimate of this contribution, obtained for large-Nc and in the chiral limit, was provided in ref. [1]. Here we evaluate and include the mathcal{O}left({m}_K^2/{m}_c^2right) and mathcal{O}left({Lambda}_{mathrm{QCD}}^2/{m}_c^2right) contributions that, a priori, could induce mathcal{O} (1) corrections to previous estimates, as mK is numerically of order ΛQCD. Our computation shows that there are several dimension-8 operators besides the one considered before. Their effect on εK, however, accidentally cancels out to a large extent, leaving the final correction at the level of 1%.

Dirac masses and mixings in the (geo)SM(EFT) and beyond

We report a set of exact formulae for computing Dirac masses, mixings, and CP-violation parameter(s) from 3×3 Yukawa matrices Y valid when YY† → U†YY†U under global mathrm{U}{(3)}_{Q_L} flavour symmetry transformations U. The results apply to the Standard Model Effective Field Theory (SMEFT) and its ‘geometric’ realization (geoSMEFT). We thereby complete, in the Dirac flavour sector, the catalogue of geoSMEFT parameters derived at all orders in the sqrt{2leftlangle {H}^{dagger }Hrightrangle } /Λ expansion. The formalism is basis-independent, and can be applied to models with decoupled ultraviolet flavour dynamics, as well as to models whose infrared dynamics are not minimally flavour violating. We highlight these points with explicit examples and, as a further demonstration of the formalism’s utility, we derive expressions for the renormalization group flow of quark masses, mixings, and CP-violation at all mass dimension and perturbative loop orders in the (geo)SM(EFT) and beyond.

Observation of the Mass Difference between Neutral Charm-Meson Eigenstates.

A measurement of mixing and CP 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 fb^{-1}. A total of 30.6 million D^{0}→K_{S}^{0}π^{+}π^{-} decays are analyzed using a method optimized for the measurement of the mass difference between neutral charm-meson eigenstates. Allowing for CP violation in mixing and in the interference between mixing and decay, the mass and decay-width differences are measured to be x_{CP}=[3.97±0.46(stat)±0.29(syst)]×10^{-3} and y_{CP}=[4.59±1.20(stat)±0.85(syst)]×10^{-3}, respectively. The CP-violating parameters are measured as Δx=[-0.27±0.18(stat)±0.01(syst)]×10^{-3} and Δy=[0.20±0.36(stat)±0.13(syst)]×10^{-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 CP symmetry and improve existing constraints on the associated parameters.

Weak value amplification in high energy physics: A case study for precision measurement of CP violation in B meson decays

The technique of weak value amplification, proposed by Aharonov et al. in 1988, has been applied for various fields of physics for the purpose of precision measurement, which is made possible by exploiting the freedom of `postselection' specifying actively the final state in the physical process. Here we report for the first time the feasibility of utilizing the technique of weak value amplification in high energy particle physics, especially in measuring the CP-violating parameters in B meson decays, where the effective lifetime of the decay mode is expected to be prolonged statistically due to the postselection. Our analysis shows that, when adopted in the Belle II experiment at the SuperKEKB collider, the effective lifetime may be prolonged up to 2.6 times, and that the measurement precision of the CP-violating parameters will also be improved by its effect.

The history of LHCb

In this paper, we describe the history of the LHCb experiment over the last three decades, and its remarkable successes and achievements. LHCb was conceived primarily as a {b} -physics experiment, dedicated to CP violation studies and measurements of very rare {{b}} decays; however, the tremendous potential for {c} -physics was also clear. At first data taking, the versatility of the experiment as a general-purpose detector in the forward region also became evident, with measurements achievable such as electroweak physics, jets and new particle searches in open states. These were facilitated by the excellent capability of the detector to identify muons and to reconstruct decay vertices close to the primary {{p}} {{p}} interaction region. By the end of the LHC Run 2 in 2018, before the accelerator paused for its second long shut down, LHCb had measured the CKM quark mixing matrix elements and CP violation parameters to world-leading precision in the heavy-quark systems. The experiment had also measured many rare decays of {b} and {c} quark mesons and baryons to below their Standard Model expectations, some down to branching ratios of order 10^{-9}. In addition, world knowledge of {{b}} and {{c}} spectroscopy had improved significantly through discoveries of many new resonances already anticipated in the quark model, and also adding new exotic four and five quark states. The paper describes the evolution of the LHCb detector, from conception to its operation at the present time. The authors’ subjective summary of the experiment’s important contributions is then presented, demonstrating the wide domain of successful physics measurements that have been achieved over the years.

Matter-antimatter asymmetry and non-inertial effects

We investigate non-inertial effects on CP-violating processes using a model, based on the framework of quantum field theory in curved spacetimes, devised to account for the decay of accelerated particles. We show that the CP violation parameter for the decay of accelerated kaons into two pions decreases very slightly as very high accelerations are achieved, implying decreased asymmetry between matter and antimatter in this regime. We discuss the relationship between these results and cosmological processes surrounding matter-antimatter asymmetry and argue that, due to the connection between non-inertial and thermal phenomena established by the Unruh effect, this kind of computation may prove useful in furthering the understanding of thermodynamical effects in curved spacetimes.

Measurement of time-dependent CP violation parameters in B0→KS0KS0KS0 decays at Belle

We measure the time-dependent CP violation parameters in B0→KS0KS0KS0 decays using 772×106BB¯ pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. The obtained mixing-induced and direct CP asymmetries are −0.71±0.23 (stat)±0.05 (syst) and 0.12±0.16 (stat)±0.05 (syst), respectively. These values are consistent with the Standard Model predictions. The significance of CP violation differs from zero by 2.5 standard deviations.Received 3 November 2020Accepted 15 January 2021DOI:https://doi.org/10.1103/PhysRevD.103.032003Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Physical SystemsBottom mesonsQuark mixingTechniquesLepton collidersParticle decaysParticle mixing & oscillationsParticles & Fields

Noninertial effects on CP‐violating systems

AbstractAn analysis of accelerated kaon decays based on the Unruh effect shows a slight decrease in a CP violation parameter for very high accelerations as a consequence of the previously known increase in decay rates for noninertial systems. Its consequences regarding the understanding of the relation between thermal and noninertial phenomena are briefly discussed.

Perturbative QCD predictions for the decay Bs0→SS(a0(980),f0(980),f0(500))

In this work, we calculate the branching ratios and CP violations of the B^{0}_{s}\rightarrow a_{0}(980)a_{0}(980) decay modes with both charged and neutral a_{0}(980) mesons and B^{0}_{s}\rightarrow f_{0}(980)(f_{0}(500))f_{0}(980)(f_{0}(500)) for the first time in the pQCD approach. Considering the recent observation of the BESIII collaboration that provide a direct information about the constituent two-quark components in the corresponding a_{0}(980) wave functions, we regard the scalar mesons a_{0}(980), f_{0}(980) and f_{0}(500) as the q\bar{q} quark component in our present work, and then make predictions of these decay modes. The branching ratios of our calculations are at the order of the 10^{-4}\sim10^{-6} when we consider the mixing scheme. We also calculate the CP violation parameters of these decay modes. The relatively large branching ratios make it easily to be tested by the running LHC-b experiments, and it can help us to understand both the inner properties and the QCD behavior of the scalar meson.