Measurement Of CP Violation Research Articles

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.

A Review of CP Violation Measurements in Charm at LHCb

The LHCb experiment has been able to collect the largest sample ever produced of charm-hadron decays, performing a number of measurements of observables related to CP violation in the charm sector. In this document, the most recent results from LHCb on the search of direct CP violation in D0→Ks0Ks0, D(s)+→h+π0 and D(s)+→h+η decays are summarised, in addition to the most precise measurement of time-dependent CP asymmetry in D0→h+h− decays and the first observation of mass difference between neutral charm-meson eigenstates.

Archiver System Management for Belle II Detector Operation

The Belle II experiment is a high-energy physics experiment at the SuperKEKB electron-positron collider. Using Belle II data, high precision measurement of rare decays and CP-violation in heavy quarks and leptons can be performed to probe New Physics. In this paper, we present the archiver system used to store the monitoring data of the Belle II detector and discuss in particular how we maintain the system that archives the monitoring process variables of the subdetectors. We currently save about 26 thousand variables including the temperature of various subdetectors components, status of water leak sensors, high voltage power supply status, data acquisition status, and luminosity information of the colliding beams. For stable data taking, it is essential to collect and archive these variables. We ensure the availability and consistency of all the variables from the subdetector and other systems, as well as the status of the archiver itself are consistent and regularly updated. To cope with a possible hardware failure, we prepared a backup archiver that is synchronized with the main archiver.

Probing the \u2206U = 0 rule in three body charm decays

CP violation in charm decay was observed in the decays D0→ P±P∓ of a D0 meson to two pseudoscalars. When interpreted within the SM, the results imply that the ratio of the relevant rescattering amplitudes has a magnitude and phase that are both of O(1). We discuss ways to probe similar ratios in D0→ V±P∓ decays, where V is a vector that decays to two pseudoscalars, from the Dalitz-plot analysis of time-integrated three-body decays. Compared to two-body decays, three-body decays have the advantage that the complete system can be solved without the need for time-dependent CP violation measurements or use of correlated {D}^0-{overline{D}}^0 production. We discuss the decays D0→ π+π−π0 and D0→ K+K−π0 as examples by considering a toy model of only two overlapping charged resonances, treating the underlying pseudo two-body decays in full generality.

Mixing and CP Violation in the Charm System

In recent years charm physics has undergone a renaissance, which has been catalyzed by an unexpected and impressive set of experimental results from the B factories, the Tevatron, and LHCb. The existence of [Formula: see text] oscillations is now well established, and the recent discovery of CP violation in D0 decays has further renewed interest in the charm sector. In this article, we review the current status of charm-mixing and CP-violation measurements and assess their agreement with theoretical predictions within the Standard Model and beyond. We look forward to the great improvements in experimental precision that can be expected over the coming two decades and to the prospects for corresponding advances in theoretical understanding.

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.

Measurement of CP Violation in the Decay B^{+}→K^{+}π^{0}.

A measurement of CP violation in the decay B^{+}→K^{+}π^{0} is reported using data corresponding to an integrated luminosity of 5.4 fb^{-1} collected with the LHCb experiment at a center-of-mass energy of sqrt[s]=13 TeV. The CP asymmetry is measured to be 0.025±0.015±0.006±0.003, where the uncertainties are statistical, systematic, and due to an external input. This is the most precise measurement of this quantity. It confirms and significantly enhances the observed anomalous difference between the direct CP asymmetries of the B^{0}→K^{+}π^{-} and B^{+}→K^{+}π^{0} decays, known as the Kπ puzzle.

2020 global reassessment of the neutrino oscillation picture

We present an updated global fit of neutrino oscillation data in the simplest three-neutrino framework. In the present study we include up-to-date analyses from a number of experiments. Concerning the atmospheric and solar sectors, besides the data considered previously, we give updated analyses of IceCube DeepCore and Sudbury Neutrino Observatory data, respectively. We have also included the latest electron antineutrino data collected by the Daya Bay and RENO reactor experiments, and the long-baseline T2K and NOνA measurements, as reported in the Neutrino 2020 conference. All in all, these new analyses result in more accurate measurements of θ13, θ12, Delta {m}_{21}^2 and left|Delta {m}_{31}^2right| . The best fit value for the atmospheric angle θ23 lies in the second octant, but first octant solutions remain allowed at ∼ 2.4σ. Regarding CP violation measurements, the preferred value of δ we obtain is 1.08π (1.58π) for normal (inverted) neutrino mass ordering. The global analysis still prefers normal neutrino mass ordering with 2.5σ statistical significance. This preference is milder than the one found in previous global analyses. These new results should be regarded as robust due to the agreement found between our Bayesian and frequentist approaches. Taking into account only oscillation data, there is a weak/moderate preference for the normal neutrino mass ordering of 2.00σ. While adding neutrinoless double beta decay from the latest Gerda, CUORE and KamLAND-Zen results barely modifies this picture, cosmological measurements raise the preference to 2.68σ within a conservative approach. A more aggressive data set combination of cosmological observations leads to a similar preference for normal with respect to inverted mass ordering, namely 2.70σ. This very same cosmological data set provides 2σ upper limits on the total neutrino mass corresponding to Σmν< 0.12 (0.15) eV in the normal (inverted) neutrino mass ordering scenario. The bounds on the neutrino mixing parameters and masses presented in this up-to-date global fit analysis include all currently available neutrino physics inputs.

Bargmann invariants, geometric phases and recursive parametrization with Majorana fermions

A generalized connection between the quantum mechanical Bargmann invariants and the geometric phases was established for the Dirac fermions. We extend that formalism for the Majorana fermions by defining proper quantum mechanical ray and Hilbert spaces. We then relate both the Dirac and Majorana type Bargmann invariants to the rephasing invariant measures of CP violation with the Majorana neutrinos, assuming that the neutrinos have lepton number violating Majorana masses. We then generalize the recursive parametrization for studying any unitary matrices to include the Majorana fermions, which could be useful for studying the neutrino mixing matrix.

Effects of the violation of the equivalence principle at DUNE

A number of different effects of the violation of the Equivalence Principle (VEP), taken as sub-leading mechanism of neutrino flavor oscillation, are examined within the framework of the DUNE experiment. We study the possibility of obtaining a misleading neutrino oscillation parameter region caused by our unawareness of VEP. Additionally, we evaluate the impact on the measurement of CP violation and the distinction of neutrino mass hierarchy at DUNE. Besides, limits on VEP for a wide variety of textures of the matrix that connects neutrino gravity eigenstates to flavor eigenstates are imposed. An extra-task of our study is to set limits on Hamiltonian added terms considering different energy dependencies ($E^n$, with $n=0,1,2,3$) that can be associated to the usual Lorentz violating terms defined in the Standard Model Extension Hamiltonian. In order to understand our results, approximated analytical three neutrino oscillation probability formulae are derived.

Direct CP violation and the ΔI=1/2 rule in K→ππ decay from the standard model

We present a lattice QCD calculation of the $\Delta I=1/2$, $K\to\pi\pi$ decay amplitude $A_0$ and $\varepsilon'$, the measure of direct CP-violation in $K\to\pi\pi$ decay, improving our 2015 calculation of these quantities. Both calculations were performed with physical kinematics on a $32^3\times 64$ lattice with an inverse lattice spacing of $a^{-1}=1.3784(68)$ GeV. However, the current calculation includes nearly four times the statistics and numerous technical improvements allowing us to more reliably isolate the $\pi\pi$ ground-state and more accurately relate the lattice operators to those defined in the Standard Model. We find ${\rm Re}(A_0)=2.99(0.32)(0.59)\times 10^{-7}$ GeV and ${\rm Im}(A_0)=-6.98(0.62)(1.44)\times 10^{-11}$ GeV, where the errors are statistical and systematic, respectively. The former agrees well with the experimental result ${\rm Re}(A_0)=3.3201(18)\times 10^{-7}$ GeV. These results for $A_0$ can be combined with our earlier lattice calculation of $A_2$ to obtain ${\rm Re}(\varepsilon'/\varepsilon)=21.7(2.6)(6.2)(5.0) \times 10^{-4}$, where the third error represents omitted isospin breaking effects, and Re$(A_0)$/Re$(A_2) = 19.9(2.3)(4.4)$. The first agrees well with the experimental result of ${\rm Re}(\varepsilon'/\varepsilon)=16.6(2.3)\times 10^{-4}$. A comparison of the second with the observed ratio Re$(A_0)/$Re$(A_2) = 22.45(6)$, demonstrates the Standard Model origin of this "$\Delta I = 1/2$ rule" enhancement.

Hyper-Kamiokande

A next generation water Cherenkov detector Hyper-Kamiokande to be built in Japan is described. The main goals of this project include a sensitive measurement of CP violation in neutrino oscillations, a search for proton decay and study of solar, atmospherics and astrophysical neutrinos. Key features of the Hyper-Kamiokande detector are described. The main emphasis is put on large photosensors. The recent progress in development of near neutrino detectors is also presented.

Progress on the Electromagnetic Calorimeter Trigger Simulation at the Belle II Experiment

The Belle II experiment at KEK in Japan has started real data taking from April 2018 to probe a New Physics beyond the Standard Model by measuring CP violation precisely and rare weak decays of heavy quark and lepton. The experiment is performed at the high luminosity SuperKEKB e^+ e^- collider with 80 x 10^34 cm^-2 s^-1 as an ultimate instantaneous luminosity. In order to develop and test an appropriate trigger algorithm under much higher luminosity and beam background environment than previous KEKB collider, a detail simulation study of the Belle II calorimeter trigger system is very crucial to operate Belle II Trigger and DAQ system in stable. We report preliminary results on various trigger logics and their efficiencies using physics and beam background Monte Carlo events with a Belle II Geant4-based analysis framework called Basf2.

Measurement of CP violation in B0\u2192 D\u2217\xb1D\u2213 decays

The decay-time-dependent CP asymmetry in B0→ D∗±D∓ decays is mea- sured using a data set corresponding to an integrated luminosity of 9 fb−1 recorded by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The CP parameters are measured asSD∗D=−0.861±0.077stat±0.019syst,ΔSD∗D=0.019±0.075stat±0.012syst,CD∗D=−0.059±0.092stat±0.020syst,ΔCD∗D=−0.031±0.092stat±0.016syst,AD∗D=0.008±0.014stat±0.006syst.\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$ {\\displaystyle \\begin{array}{c}{S}_{D\\ast D}=-0.861\\pm 0.077\\left(\\mathrm{stat}\\right)\\pm 0.019\\left(\\mathrm{syst}\\right),\\\\ {}\\varDelta {S}_{D\\ast D}=0.019\\pm 0.075\\left(\\mathrm{stat}\\right)\\pm 0.012\\left(\\mathrm{syst}\\right),\\\\ {}{C}_{D\\ast D}=-0.059\\pm 0.092\\left(\\mathrm{stat}\\right)\\pm 0.020\\left(\\mathrm{syst}\\right),\\\\ {}{\\varDelta C}_{D\\ast D}=-0.031\\pm 0.092\\left(\\mathrm{stat}\\right)\\pm 0.016\\left(\\mathrm{syst}\\right),\\\\ {}{\\mathcal{A}}_{D\\ast D}=\\kern0.75em 0.008\\pm 0.014\\left(\\mathrm{stat}\\right)\\pm 0.006\\left(\\mathrm{syst}\\right).\\end{array}} $$\\end{document}The analysis provides the most precise single measurement of CP violation in this decay channel to date. All parameters are consistent with their current world average values.

Measurement of CP violation and mixing in [formula omitted] in ATLAS

An overview of a measurement of time-dependent CP asymmetry parameters in Bs0→J/ψ(μ+μ−)ϕ(K+K−) decays using 80.5 fb−1 of integrated luminosity collected with the ATLAS detector from 13 TeV pp collisions at the LHC is presented. A manifestation of the CP violation is an interference between direct and mixing-mediated Bs0 decays, producing a common final state. In the Standard Model, it is characterized by a phase shift ϕs related to the CKM matrix. In the case of Bs0→J/ψϕ, this shift is predicted to be small, ϕs=−0.0363−0.0015+0.0016 rad. New physics can enhance ϕs whilst satisfying all existing constraints. Results presented in this talk are compatible with those obtained from 19.2 fb−1 of 7 TeV and 8 TeV data as well as with the Standard Model predictions and other LHC measurements.

Caliope: a search for CPT-violation in o-ps

CALIOPE, or CP(T) Aberrant Leptons in ortho-Positronium Experiment, is a tabletop search for fundamental symmetry violations, including CP- and CPT-violation, in ortho-positronium (o-Ps). We use a tagged 22Na source adjacent to a cylinder of aerogel to generate o-Ps at the center of a cylindrical array of 24 NaI(Tl) bars. We search for CPT - violating angular correlations in the gamma rays emitted in the decay of o-Ps. With an angular acceptance of 75% of 4π, and the ability to acquire statistics over a longer period of time, CALIOPE will improve upon the limit set by previous experiments. The experimental setup can also be used in a search for CP-violation in o-Ps with the addition of an electromagnet. We describe the design of the experiment, results from a characterization of the systematics for the CPT- and CP-violating measurements, and a demonstration of the DAQ.

Constraint on the solar Δm2 using 4000 days of short baseline reactor neutrino data

There is a well known 2$\sigma$ tension in the measurements of the solar $\Delta m^2$ between KamLAND and SNO/Super-KamioKANDE. Precise determination of the solar $\Delta m^2$ is especially important in connection with current and future long baseline CP violation measurements. Reference \cite{Seo:2018rrb} points out that currently running short baseline reactor neutrino experiments, Daya Bay and RENO, can also constrain solar $\Delta m^2$ value as demonstrated by a GLoBES simulation with a limited systematic uncertainty consideration. In this work, the publicly available data, from Daya Bay (1,958 days) and RENO (2,200 days) are used to constrain the solar $\Delta m^2$. Verification of our method through $\Delta m^2_{ee}$ and $\sin^2 \theta_{13}$ measurements is discussed in Appendix A. Using this verified method, reasonable constraints on the solar $\Delta m^2$ are obtained using above Daya Bay and RENO data, both individually and combined. We find that the combined data of Daya Bay and RENO set an upper limit on the solar $\Delta m^2$ of 18 $\times 10^{-5}$ eV$^2$ at the 95% C.L., including both systematic and statistical uncertainties. This constraint is slightly more than twice the KamLAND value. As this combined result is still statistics limited, even though driven by Daya Bay data, the constraint will improve with the additional running of this experiment.

A comparative study between ESSnuSB and T2HK in determining the leptonic CP phase

In this paper, we perform a comparative analysis between the future proposed long-baseline experiments ESSnuSB and T2HK in measuring the leptonic CP phase [Formula: see text]. In particular, we study the effect of the neutrino mass ordering degeneracy and the leptonic mixing angle [Formula: see text] octant degeneracy in the measurement of leptonic CP violation and precision for both experiments. Since the ESSnuSB (T2HK) experiment probes the second (first) oscillation maximum to study neutrino oscillations, the effect of these degeneracies are significantly different in both experiments. Our main conclusion is that for the ESSnuSB experiment, the information on the neutrino mass ordering does not play a major role in the determination of [Formula: see text], which is not the case for the T2HK experiment. However, the information on the true octant compromises the CP sensitivity of the ESSnuSB experiment as compared to T2HK if [Formula: see text] lies in the lower octant. These conclusions are true for both the 540 km and 360 km baseline options for the ESSnuSB experiment. In addition, we investigate the effect of different running times in neutrino and antineutrino modes and the effect of [Formula: see text] precision in measuring [Formula: see text].

Measurement of CP violation in the {B}_s^0to phi phi decay and search for the B0\u2192 \u03d5\u03d5 decay

A measurement of the time-dependent CP-violating asymmetry in {B}_s^0to phi phi decays is presented. Using a sample of proton-proton collision data corresponding to an integrated luminosity of 5.0 fb−1 collected by the LHCb experiment at centre-of-mass energies sqrt{s} = 7 TeV in 2011, 8 TeV in 2012 and 13 TeV in 2015 and 2016, a signal yield of around 9000 {B}_s^0to phi phi decays is obtained. The CP-violating phase {phi}_s^{soverline{s}s} is measured to be −0.073 ± 0.115(stat) ± 0.027(syst) rad, under the assumption it is independent of the helicity of the ϕϕ decay. In addition, the CP-violating phases of the transverse polarisations under the assumption of CP conservation of the longitudinal phase are measured. The helicity-independent direct CP-violation parameter is also measured, and is found to be |λ| = 0.99 ± 0.05(stat) ± 0.01(syst). In addition, T-odd triple-product asymmetries are measured. The results obtained are consistent with the hypothesis of CP conservation in overline{b}to overline{s}soverline{s}s transitions. Finally, a limit on the branching fraction of the B0 → ϕϕ decay is determined to be mathcal{B}left({B}^0to phi phi right)<2.7times {10}^{-8} at 90 % confidence level.

Scalar Nonstandard Interactions in Neutrino Oscillation.

The scalar nonstandard interactions (NSI) can also introduce matter effect for neutrino oscillation in a medium. Especially the recent Borexino data prefer nonzero scalar NSI, η_{ee}=-0.16. In contrast to the conventional vector NSI, the scalar type contributes as a correction to the neutrino mass matrix rather than the matter potential. Consequently, the scalar matter effect is energy independent while the vector one scales linearly with neutrino energy. This leads to significantly different phenomenological consequences in reactor, solar, atmospheric, and accelerator neutrino oscillations. A synergy of different types of experiments, especially those with matter density variation, is necessary to identify the scalar NSI and guarantee the measurement of CP violation at accelerator experiments.