Measurement Of CP Violation Research Articles

Higgs physics at ILC

International Linear Collider (ILC) is a viable option for realization of a future Higgs factory. With proven accelerator technology and technically mature detector design, ILC offers well-understood physics program in the top, EW and Higgs sectors. Clean environment of electron–positron collisions, together with beam polarization of both beams and center-of-mass reach at a TeV scale, will make ILC a precision tool to probe realizations of new physics. The above will be illustrated on examples of fully simulated measurements in the Higgs sector, including Higgs couplings, Higgs self-coupling, CP violation measurements and Higgs exotic decay studies at ILC.

Search for Time-Dependent CP Violation in D0→π+π−π0 Decays

A measurement of time-dependent CP violation in D0→π+π−π0 decays using a pp collision data sample collected by the LHCb experiment in 2012 and from 2015 to 2018, corresponding to an integrated luminosity of 7.7 fb−1, is presented. The initial flavor of each D0 candidate is determined from the charge of the pion produced in the D*(2010)+→D0π+ decay. The decay D0→K−π+π0 is used as a control channel to validate the measurement procedure. The gradient of the time-dependent CP asymmetry ΔY in D0→π+π−π0 decays is measured to be ΔY=(−1.3±6.3±2.4)×10−4, where the first uncertainty is statistical and the second is systematic, which is compatible with CP conservation. © 2024 CERN, for the LHCb Collaboration 2024 CERN

Fast Inclusive Flavour Tagging at LHCb

The task of identifying B meson flavor at the primary interaction point in the LHCb detector is crucial for measurements of mixing and timedependent CP violation. Flavor tagging is usually done with a small number of expert systems that find important tracks to infer the B meson flavor from. Recent advances show that replacing all of those expert systems with one ML algorithm that considers all tracks in an event yields an increase in tagging power. However, training the current classifier takes a long time and it is not suitable for use in real time triggers. In this work we present a new classifier, based on the DeepSet architecture. With the right inductive bias of permutation invariance, we achieve great speedups in training (multiple hours vs 10 minutes), a factor of 4-5 speed-up in inference for use in real time environments like the trigger and less tagging asymmetry. For the first time we investigate and compare performances of these “Inclusive Flavor Taggers” on simulation of the upgraded LHCb detector for the third run of the LHC.

Predicting the baryon asymmetry with degenerate right-handed neutrinos

We consider the generation of a baryon asymmetry in an extension of the Standard Model with two singlet Majorana fermions that are degenerate above the electroweak phase transition. The model can explain neutrino masses as well as the observed matter-antimatter asymmetry, for masses of the heavy singlets below the electroweak scale. The only physical CP violating phases in the model are those in the PMNS mixing matrix, i.e. the Dirac phase and a Majorana phase that enter light neutrino observables. We present an accurate analytic approximation for the baryon asymmetry in terms of CP flavour invariants, and derive the correlations with neutrino observables. We demonstrate that the measurement of CP violation in neutrino oscillations as well as the mixings of the heavy neutral leptons with the electron, muon and tau flavours suffice to pin down the matter-antimatter asymmetry from laboratory measurements.

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.

Phenomenological study of decays* *Supported by the National Natural Science Foundation of China (12175244, 11875262, 11805037, U1832121) and National Key Research and Development Program of China (2020YFA0406301)

The measurement of decay parameters is one of the important goals of particle physics experiments, and the measurement serves as a probe to search for evidence of CP violation in baryonic decays. The experimental results will aid in advancing existing theoretical research and establishing new experimental objectives. In this study, we formulate the asymmetric parameters that characterize parity violation, and then derive formulas for the measurement of CP violation. The formulae for the joint angular distribution of the full decay chain as well as the polarization observable of , , Λ, and are also provided for experiments. Lastly, we evaluated the sensitivity of two asymmetric parameters: (abbreviated as ) and (abbreviated as ) for future experimental measurements.

Earth mover’s distance as a measure of CP violation

We introduce a new unbinned two sample test statistic sensitive to CP violation utilizing the optimal transport plan associated with the Wasserstein (earth mover’s) distance. The efficacy of the test statistic is shown via two examples of CP asymmetric distributions with varying sample sizes: the Dalitz distributions of B0 → K+π−π0 and of D0 → π+π−π0 decays. The windowed version of the Wasserstein distance test statistic is shown to have comparable sensitivity to CP violation as the commonly used energy test statistic, but also retains information about the localized distributions of CP asymmetry over the Dalitz plot. For large statistic datasets we introduce two modified Wasserstein distance based test statistics — the binned and the sliced Wasserstein distance statistics, which show comparable sensitivity to CP violation, but improved computing time and memory scalings. Finally, general extensions and applications of the introduced statistics are discussed.

BAU Production in the SN-Breaking Standard Model

The violation of charge-parity symmetry and the baryon asymmetry of the universe are two of the most significant unresolved problems in physics. This article presents further research on the CP violation problem in the Standard Model with 32 candidate sets of the 10 “natural” parameters that exhibit the same Cabibbo–Kobayashi–Maskawa performance. These parameters are considered “natural” because they consist solely of the Yukawa couplings and the vacuum expectation value of the unique Higgs doublet in the Standard Model. Then, the problems of CP violation and the baryon asymmetry of the universe are investigated by using the Jarlskog measure of CP violation, ΔCP=J(mt2−mc2)(mt2−mu2)(mc2−mu2)(mb2−ms2)(mb2−md2)(ms2−md2)/T12, given that CP symmetry is violated following the breakdown of SN symmetries. Subsequently, numerical tests are performed in a simplified scenario where eight of the ten parameters are assumed to be fixed by two assumptions, and the remaining two parameters are allowed to vary from the S2-symmetric point (x,y)=(−1,1) to their current values in all 32 parameter sets. To estimate the enhancement of CP violation in such processes, a ratio RΔ≡ΔCP/ΔCP(0) is proposed between the running ΔCP and its current value, denoted by ΔCP(0), which is approximately 10−20. In all 32 cases, the three-dimensional plots of RΔ exhibit many regions that stick out of the RΔ=1010 plane, especially in regions very close to (x,y)=(−1,1). These results demonstrate that the SN-breaking Standard Model is already sufficient to violate CP symmetry explicitly and generate a significant amount of baryon asymmetry of the universe. Furthermore, it solves existing problems without creating new ones, at least in the scenario presented in this article.

Predicting neutrino mixing angles using group presentations

By assuming there exist three massive nondegenerate Majorana neutrinos, it is possible to describe neutrino mixing with a residual, unbroken discrete Klein subgroup of a larger spontaneously broken flavor symmetry group. Motivated by forthcoming measurements of leptonic CP violation, we revisit this framework by applying group presentation rules to it. We develop a method that is able to reproduce all previous results in the literature and may also hint at a possible group theoretical origin of CP violation in the Klein symmetry elements. This is due to the explicit appearance of a phase in them. However, for the cases considered in this analysis, it turns out that this phase can be removed. Still, this new method warrants further study.

Zooming into CP violation in B(s)→ hh decays

The LHCb collaboration has recently reported the first observation of CP violation in the penguin-dominated {B}_s^0 → K−K+ decay and further new measurements, indicating differences between the direct CP asymmetries of both the {B}_s^0 → K−K+, {B}_d^0 → π−K+ and the {B}_d^0 → π−π+, {B}_s^0 → K−π+ modes. We show that these puzzling differences can be accommodated through sizeable penguin annihilation and exchange topologies in the Standard Model, and constrain them. Utilising the U-spin symmetry, we extract the angle γ of the unitarity triangle from the CP asymmetries in the {B}_s^0 → K−K+, {B}_d^0 → π−π+ system alone, finding gamma =left({65}_{-7}^{+11}right){}^{circ} , in perfect agreement with the determination from tree-level B → DK decays. The {B}_s^0-{overline{B}}_s^0 mixing phase ϕs can be extracted from CP violation measurements in {B}_s^0 → K−K+ in a clean way. We present a new strategy and extract ϕs = −(3.6 ± 5.4)°. This result is in agreement with the determination from {B}_s^0 → J/ψϕ decays. New CP-violating contributions would influence these determinations differently. Hence it is interesting to keep monitoring both as the experimental picture sharpens.

Two-loop Electroweak Corrections to ϵK

The parameter εK measures CP violation in the neutral kaon system. It is a sensitive probe of new physics and plays a prominent role in the global fit of the Cabibbo-Kobabyashi-Maskawa matrix. As one of the first discovered sources of CP violation, it has been measured in experiment to permil precision. A simple reparametrization of the efFective Hamiltonian has been recently shown to drastically reduce the perturbative errors coming from the charm-quark corrections, making the electroweak corrections relevant. In this proceedings, I will present the two-loop electroweak corrections to ϵK .

ATLAS Measurements of CP Violation and Rare Decay Processes with Beauty Mesons

ATLAS Measurements of CP Violation and Rare Decay Processes with Beauty Mesons

The Upgrade of the LHCb RICH detector

LHCb is one of the four main experiments operating at the LHC and it is dedicated to measurements of CP violation and to the search for new physics beyond Standard Model in the rare decays of hadrons containing heavy quarks. LHCb is currently undergoing a major upgrade in order to increase the operating luminosity to 2 × 1033 cm-2 sec-1 from the start of Run 3 in 2022. The strategy of reading out the detectors at the full rate of 40 MHz without a hardware trigger requires a complete renewal of the data acquisition system.

Measuring CP violation in rare W decays at the LHC* *Supported in part by National Natural Science Foundation of China (11875179, 11775130) and Natural Science Foundation of Shandong Province (ZR2021QA040)

Heavy Majorana neutrinos beyond the standard model can simultaneously explain the origin of tiny neutrino masses and matter-antimatter asymmetry in our Universe. The existence of heavy Majorana neutrinos will also lead to lepton number violation and confirm the possibility of rare lepton-number-violating W decays. With contributions from two different Majorana neutrinos, nonzero CP asymmetry may be generated from the rate difference between W decay and its CP-conjugate process. The aim of this study is to investigate the prospects of measuring CP violation in rare W decays via Majorana neutrinos at the LHC. Our calculations show that the induced CP asymmetry is independent of the Majorana neutrino mass for . Such a CP asymmetry, if observed, would in turn provide unambiguous evidence of new physics beyond the standard model.

ATLAS Results with Beauty Mesons

A broad range of measurements involving BB mesons are performed with the ATLAS experiment at the Large Hadron Collider, of which a selection is discussed in this note. This includes a measurement of the relative B_c^\pmBc± to B^\pmB± production cross section in pppp collisions at a centre-of-mass energy \sqrt{s}s of 8 TeV as well as the latest results on the branching ratios of the rare decays B^0_s\to\mu^+\mu^-Bs0→μ+μ− and B^0\to\mu^+\mu^-B0→μ+μ− using pppp collisions recorded at \sqrt{s}=s= 7, 8 and 13 TeV. Furthermore, accurate measurements of mixing and CP violation in B_s^0 \to J/\psi\, \phiBs0→J/ψϕ decays are performed. The latest results on the CP violating phase \phi_sϕs and other parameters describing the decay obtained at \sqrt{s}=s= 7, 8 and 13 TeV are reported.

Lessons from the LHCb measurement of CP violation in Bs→ K+K−

The LHCb experiment measured the time-dependent CP asymmetries CKK and SKK in Bs→ K+K− decay. Combining with the corresponding CP asymmetries Cππ and Sππ in B → π+π− decay, we find that the size of U-spin breaking in this system is of order 20%. Moreover, the data suggest that these effects are dominated by factorizable contributions. We further study the constraints on new physics contributions to b → uoverline{u}q (q = s, d). New physics that is minimally flavor violating (MFV) cannot be distinguished from the Standard Model (SM) in these decays. However, new physics that is not MFV can mimic large U-spin breaking. Requiring that the U-spin breaking parameters remain below the size implied by the data leads to a lower bound of 5 − 10 TeV on the scale of generic new physics. If the new physics is subject to the selection rules that follow from the Froggatt-Nielsen (FN) mechanism or from General Minimal Flavor Violation (GMFV), the bound is relaxed to 2 TeV.

Direct CP violation and the ΔI= 1/2 rule inK→ππdecay in the Standard Model

We discuss the RBC & UKQCD collaborations’ recent [1] lattice calculation of ϵ′, the measure of direct CP-violation in kaon decays. This result significantly improves on our previous 2015 calculation, with nearly 4× the statistics and more reliable systematic error estimates. We discuss how our results demonstrate the Standard Model origin of the ΔI= 1/2 rule, and present our plans for future calculations.

Improving Hyper-Kamiokande sensitivity to CP violation with high precision near detector electron neutrino cross-section measurements

The next generation long-baseline neutrino oscillation experiment, Hyper-Kamiokande, will consist of a 260 kt underground water Cherenkov detector, placed 295 km from the neutrino source at J-PARC. This is generated by a 1.3 MW proton beam striking a target. In addition, a suite of near detectors, both on and off-axis will be used. With this, Hyper-Kamiokande aims to perform precision measurements of the parameters governing neutrino oscillations, the observation of CP violation being one of the main aims of the experiment. To achieve these goals, Hyper-Kamiokande will require smaller systematic uncertainties than in any previous long-baseline experiment.Many of these systematic uncertainties are related to neutrino-nucleus interactions, and can be constrained by a detector placed close to the beam production point. For this, the Hyper-Kamiokande long-baseline programme includes an Intermediate Water Cherenkov Detector, the IWCD. This is a 500 tonne water Cherenkov detector located 1 km from the beam production point. This detector is able to move within a vertical shaft and span a range of off-axis angles relative to the beam, from 1 to 4 degrees. The combination of large target mass, precise water Cherenkov reconstruction and off-axis angle flux dependence allows for high purity and high statistics electron neutrino and electron antineutrino samples. This paper describes how this detector can be used to constrain the major systematic uncertainty affecting the measurement of CP violation at Hyper-Kamiokande: the electron neutrino and antineutrino interaction cross section.

Two-loop electroweak corrections to the Top-Quark Contribution to \u03f5K

The parameter ϵK measures CP violation in the neutral kaon system. It is a sensitive probe of new physics and plays a prominent role in the global fit of the Cabibbo-Kobabyashi-Maskawa matrix. The perturbative theory uncertainty is currently dominated by the top-quark contribution. Here, we present the calculation of the full two-loop electroweak corrections to the top-quark contribution to ϵK, including the resummation of QED-QCD logarithms. We discuss different renormalization prescriptions for the electroweak input parameters. In the traditional normalization of the weak Hamiltonian with two powers of the Fermi constant GF, the top-quark contribution is shifted by −1%.

Origin of neutrino masses and disappearance ofprimordial antimatter

<p indent="0mm">The standard model (SM) of particle physics has proved to be a huge success in describing the microscopic structures of matter and the behaviors of strong, weak and electromagnetic forces, but it is incomplete in some aspects. For example, the SM itself provides no answer about the origin of tiny neutrino masses, and it fails in accounting for the observed matter-antimatter asymmetry of the Universe. To go beyond the SM, one may wonder whether there exists an intrinsic connection between the solutions to these two fundamental issues in particle physics and cosmology. It is argued that the seesaw mechanism for neutrino mass generation and the associated leptogenesis mechanism for cosmological baryogenesis may pave a way for our deeper understanding of the origin of neutrino masses and mysterious disappearance of primordial antimatter of the Universe. Behind these two mechanisms is the existence of heavy and sterile Majorana neutrinos, which interact with the known (light and active) neutrinos via the Yukawa interactions. The SM contains no right-handed neutrino fields, and hence there is no way to write out a Dirac neutrino mass term. The simplest way to go beyond the SM is to introduce the right-handed neutrino fields and allow for lepton number violation. In this case the right-handed neutrino fields and their charge-conjugate counterparts may constitute a Majorana mass term which, together with the Yukawa interactions between left- and right-handed neutrino fields via the Higgs field, leads us to the origin of tiny Majorana masses for three active neutrinos. Such a seesaw mechanism attributes the smallness of active neutrino masses to the largeness of sterile neutrino masses as compared with the electroweak scale. The lepton-number-violating and CP-violating decays of those heavy degrees of freedom in the early Universe may produce a net lepton-antilepton asymmetry, and the latter may be partly converted into a net baryon-antibaryon asymmetry via the sphaleron process. This is just the leptogenesis mechanism, and it has attracted a lot of attention thanks to the observations of neutrino oscillations in the past decades. The seesaw and leptogenesis scenarios are correlated with each other, and they provide an elegant way of accounting for the cosmological baryon-antibaryon asymmetry and tiny neutrino masses. A pressing question is how to test such a “killing two birds with one stone” picture at low-energy experiments. It seems that a direct test of this picture is extremely difficult or even impossible, but one may always collect various “fossils” of heavy Majorana neutrinos which might have played a crucial role in the early Universe. In this connection it will be greatly helpful to verify the Majorana nature of massive neutrinos by observing the neutrinoless double-beta decays, to measure CP violation in neutrino oscillations and to test unitarity of the 3×3 flavor mixing matrix of three active neutrinos.