Search

In this paper, I review the status of CP violation in hyperon decay in light of recent progress by BESIII and the anticipated improvements at the super tau-charm facility. I emphasize the complementarity between kaons and hyperons for studying CP violation in |ΔS|=1,2 processes. [ABSTRACT FROM AUTHOR]

A new experimental method to measure muon polarization using a scintillating material has been proposed. One of the key issues for this measurement is the choice of scintillation materials which can maintain the μ + spin polarization for several μ + lifetimes. Thus far, a CeF 3 scintillating crystal has been known to be only a possible candidate and it is highly preferable to find other scintillators whose performance is nearly equivalent to CeF 3. The residual μ + polarization in a 2% cerium-doped LaF 3 scintillating crystal was measured at the J-PARC Material and Life Science Facility (MLF) by applying the longitudinal field (LF) to the LaF 3 material. The polarization was obtained to be 83 and 87 % with LF = 100 and 140 Gauss, respectively, which is high enough to measure the μ + polarization in various experiments. [ABSTRACT FROM AUTHOR]

A new experimental method to search for T-violating transverse muon polarization ( P T ) in the K + → π 0 μ + ν decay has been proposed. In this new experiment, the measurements of the μ + momentum vector, the π 0 momentum vector, and the μ + polarization will be performed by the same electro-magnetic calorimeter. One of main issues is the choice of a scintillation material which can preserve the μ + spin polarization for several μ + lifetimes. A test experiment to measure the μ + polarization in various scintillating crystals was performed at J-PARC Material and Life Science Facility (MLF). We concluded that the μ + polarization in CeF 3 is high enough to perform the new T-violation experiment. [ABSTRACT FROM AUTHOR]

Abstract Femtoscopic correlations between charged pions and kaons for different charge combinations are measured in Pb–Pb collisions at s NN = 2.76 TeV with ALICE at the LHC. The three-dimensional pion-kaon (π − K) correlation functions and double ratios in the out-side-long pair rest frame are studied in different centrality bins. The π − K femtoscopic source size parameter (R out) and emission asymmetry (μ out) are extracted. It is observed that the average source size of the system and the emission asymmetry between pions and kaons increase from peripheral to central events. [ABSTRACT FROM AUTHOR]

Abstract We analyze the recent STAR collaboration results on net-kaon fluctuations in the framework of the Hadron Resonance Gas (HRG) model. Our purpose is to extract the freeze-out temperature and chemical potential as functions of the collision energy. In our HRG model, we use the complete hadron spectrum from the latest PDG list. These results are compared to the freeze-out parameters obtained from a combined analysis of net-electric charge and net-proton fluctuations. At the highest collision energies, kaons need about 10-15 MeV higher freeze-out temperatures than the light hadrons. Predictions for moment ratios of the net-Lambda multiplicity distribution are obtained along the freeze-out lines. Lambda fluctuations are sensitive to the difference in the freeze-out temperatures observed in our analysis. [ABSTRACT FROM AUTHOR]

Abstract The NA48/2 experiment at CERN reports the first observation of the K ± → π ± π 0 e + e − decay from an exposure of 1.7 × 10 11 charged kaon decays recorded in 2003–2004. A sample of 4919 candidates with 4.9% background contamination allows the determination of the branching ratio in the full kinematic region, B R (K ± → π ± π 0 e + e −) = (4.24 ± 0.14) × 10 − 6. The study of the kinematic space shows evidence for a structure dependent contribution in agreement with predictions based on chiral perturbation theory. Several P- and CP-violating asymmetries are also evaluated. [ABSTRACT FROM AUTHOR]

The OKA detector is described, and recently published results of experimental searches for a heavy neutrino and investigations of the Ke3 -decay form factors are reported. Incident-beam characteristics, the detector configuration and its major subsystems, and triggering conditions are discussed. Physical motivations for these experimental studies are provided, and the event-selection procedures are briefly described. [ABSTRACT FROM AUTHOR]

Search for heavy neutral lepton (HNL) production in charged kaon decays using the data collected by kaon experiments NA48/2 and NA62 at CERN are reported. Upper limits are established on the elements of the extended neutrino mixing matrix for heavy neutral lepton mass in the range 130–450 MeV, improving on the results from previous HNL production search. [ABSTRACT FROM AUTHOR]

The J-PARC E36 experiment is searching for lepton universality violation with a stopped kaon beam by measuring the ratio of the K + decay widths Γ ( K e 2 ) ∕ Γ ( K μ 2 ) = Γ ( K + → e + ν e ) ∕ Γ ( K + → μ + ν μ ) . Since the radiative K + → e + ν e γ decays are backgrounds to be removed in this measurement, the radiated γ rays were detected in a CsI(Tl) calorimeter. The energy calibration for the 768 CsI(Tl) modules was performed using mono-chromatic μ + s from the K μ 2 decays. The delayed e + signals from the muon decays were required in order to improve the S/N ratio of the K μ 2 peak by suppressing background events. In addition, a new energy calibration method of the CsI(Tl) calorimeter using stopped cosmic muons has been established. [ABSTRACT FROM AUTHOR]

The QCD axion is one of the most compelling solutions of the strong CP problem. There are major current efforts into searching for an ultralight, invisible axion, which is believed to be the only phenomenologically viable realization of the QCD axion. Visible axions with decay constants at or below the electroweak scale are believed to have been long excluded by laboratory searches. Considering the significance of the axion solution to the strong CP problem, we revisit experimental constraints on QCD axions in the O(10 MeV) mass window. In particular, we find a variant axion model that remains compatible with existing constraints. This model predicts new states at the GeV scale coupled hadronically, and a variety of low-energy axion signatures, such as rare meson decays, nuclear de-excitations via axion emission, and production in e+e- annihilation and fixed target experiments. This reopens the possibility of solving the strong CP problem at the GeV scale. [ABSTRACT FROM AUTHOR]

The status of kaon physics and its prospects are reviewed. A new round of experiment is taking data with the potential of making a significant step in sensitivity on many fronts by the end of the decade. [ABSTRACT FROM AUTHOR]

Kaon flavour physics has played in the 1960s and 1970s a very important role in the construction of the Standard Model (SM) and in the 1980s and 1990s in SM tests with the help of CP violation in KL → ππ decays represented by εK and the ratio ε'/ε. In this millennium, this role has been taken over by Bs,d and D mesons. However, there is no doubt that in the coming years, we will witness the return of kaon flavour physics with the highlights being the measurements of the theoretically clean branching ratios for the rare decays K+ → π+vv and KL → π0vv, and the improved SM predictions for the ratio ε;/ε, for εK and the K0-K0 mixing mass difference ΔMK. Theoretical progress on the decays KL,S → μ+μ- and KL → π0l+l- is also expected. They are all very sensitive to new physics (NP) contributions and the correlations between them should help us to identify new dynamics at very short distance scales. These studies will be enriched when theory on the K → ππ isospin amplitudes ReA0 and ReA2 improves. This paper summarizes several aspects of this exciting field. In particular, we emphasize the role of the Dual QCD approach in getting the insight in the numerical Lattice QCD results on K0-K0 0 mixing and K → ππ decays. [ABSTRACT FROM AUTHOR]

We show how an accidental U ( 1 ) Peccei–Quinn (PQ) symmetry can arise from a discrete A 4 family symmetry combined with a discrete flavour symmetry Z 3 × Z 5 2 , in a realistic Pati–Salam unified theory of flavour. Imposing only these discrete flavour symmetries, the axion solution to the strong CP problem is protected from PQ-breaking operators to the required degree. A QCD axion arises from a linear combination of A 4 triplet flavons, which are also responsible for fermion flavour structures due to their vacuum alignments. We find that the requirement of an accidental PQ symmetry arising from a discrete flavour symmetry constrains the form of the Yukawa matrices, providing a link between flavour and the strong CP problem. Our model predicts specific flavour-violating couplings of the flavourful axion and thus puts a strong limit on the axion scale from kaon decays. [ABSTRACT FROM AUTHOR]

Recent results from OKA setup concerning form factor studies in Ke3 decay are presented. About 5.25 M events obtained for decays of 17.7 GeV/cK+ are selected for the analysis. The linear and quadratic slopes for the decay form factor f+(t) are measured: λ+ = 2.95 ± 0.022 ± 0.018 × 10-2 for the linear slope fit and λ'+ = (2.611 ± 0.035 ± 0.028) × 10-2, λ"+ = (1.91 ± 0.19 ± 0.14) × 10-3 for the quadratic one. The scalar and tensor contributions are compatible with zero. Several alternative parametrizations are tried: the Pole fit parameter is found to be MV = 891 ± 3 MeV; the parameter of the dispersive parametrization is measured to be Λ+ = (2.458 ± 0.018) × 10-2. [ABSTRACT FROM AUTHOR]

NA62 is the last generation kaon experiment at CERN SPS aiming to study the decay K + → π + ν ν ¯ . The goal of the experiment is to measure the decay branching ratio, O ( 10 − 10 ) , with 10% precision collecting about 100 K + → π + ν ν ¯ events in three years of data taking and assuming a 10% signal acceptance. The weak signal and the huge background make the experiment very challenging. The NA62 detector must be able to reject background events from decay channels with branching ratios up to 10 orders of magnitude higher than the signal one and with similar experimental signature. In order to achieve the designed goal, good Particle Identification (PID), kinematic rejection and precise timing are required. The key element of the PID in NA62 is the Ring Imaging Cherenkov detector (RICH) to identify pions and muons and to measure the particle arrival time. After a pilot run in 2014, installation and commissioning of the detector were completed in 2015, when also the first physics run took place. Results on the detector performance will be presented together with preliminary results from the 2015 and 2016 physics runs. [ABSTRACT FROM AUTHOR]

A direct test of the T, CP and CPT symmetries in the neutral kaon system can be performed comparing a transition process i → f to its symmetry conjugated one. The exchange of in and out states required for genuine tests involving the time-reversal T can be performed exploiting the entanglement of the kaon pair produced at a ϕ-factory. In particular, using this method, it would be possible to perform a very clean and fully robust CPT test, which might shed light on possible new CPT-violating mechanisms. It is being implemented with the KLOE-2 experiment at the DAΦNE facility in Frascati, where a statistical sensitivity of O(10-3) on the newly proposed observable quantities could be reached. [ABSTRACT FROM AUTHOR]

The DAΦNE electron-positron collider of the Laboratori Nazionali di Frascati of INFN has made available a unique quality low-energy negatively charged kaons "beam", which is being used to study the kaon-nucleon/nuclei interactions by the SIDDHARTA-2 experiment and the AMADEUS Collaboration. The dynamics of the strong interaction processes in the non-perturbative regime is approached by lattice calculations and effective field theories (ChPT) which are still lacking experimental results in the low-energy regime, fundamental for their good understanding. The studies of kaonic atoms and of the kaonic nuclear processes performed by SIDDHARTA-2 and AMADEUS play in this context a key-role. [ABSTRACT FROM AUTHOR]

The NA62 experiment recorded a large sample of K + → μ + ν μ decays in 2007. A peak search has been performed in the reconstructed missing mass spectrum. In the absence of a signal, limits in the range 2 × 10 − 6 to 10 − 5 have been set on the squared mixing matrix element | U μ 4 | 2 between muon and heavy neutrino states, for heavy neutrino masses in the range 300–375 MeV/ c 2 . The result extends the range of masses for which upper limits have been set on the value of | U μ 4 | 2 in previous production search experiments. [ABSTRACT FROM AUTHOR]

The mass and decay width of the ϕ meson in cold nuclear matter are computed in an effective Lagrangian approach. The medium dependence of these properties are obtained by evaluating kaon–antikaon loop contributions to the ϕ self-energy, employing the medium-modified kaon masses, calculated using the quark-meson coupling model. The loop integral is regularized with a dipole form factor, and the sensitivity of the results to the choice of cutoff mass in the form factor is investigated. At normal nuclear matter density we find a downward shift of the ϕ mass by a few percent, while the decay width is enhanced by an order of magnitude. For a large variation of the cutoff mass parameter, the results for the ϕ mass and the decay width turn out to vary very little. Our results support results in the literature which suggest that one should observe a small downward mass shift and a large broadening of the decay width. In order to explore the possibility of studying the binding and absorption of ϕ mesons in nuclei, we also present the single-particle binding energies and half-widths of ϕ -nucleus bound states for some selected nuclei. [ABSTRACT FROM AUTHOR]

Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x , the relative virtual-photon energy y , and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off an isoscalar 6 LiD target. They cover the kinematic domain 1 ( GeV / c ) 2 < Q 2 < 60 ( GeV / c ) 2 in the photon virtuality, 0.004 < x < 0.4 , 0.1 < y < 0.7 , 0.20 < z < 0.85 , and W > 5 GeV / c 2 in the invariant mass of the hadronic system. The results from the sum of the z -integrated K + and K − multiplicities at high x point to a value of the non-strange quark fragmentation function larger than obtained by the earlier DSS fit. [ABSTRACT FROM AUTHOR]

transitions in a medium followed by decay and regeneration of -component are considered by means of perturbation theory. It is shown that in the previous calculations the problem different from regeneration is solved. [ABSTRACT FROM AUTHOR]

The fixed target experiment NA62 at CERN aims at measuring the ultra-rare decay K + → π + ν ν ¯ , whose branching ratio is of the order of 10 −11 . The main challenges faced by the experiment to achieve a 10% precision measurement are the required beam intensity and background rejection factor. The differential Cherenkov detector KTAG must be able to tag charged kaons in an unseparated hadron beam with an average particle rate of 750 MHz, of which 45 MHz are kaons, with a time precision of at least 100 ps and an efficiency higher than 95%. The additional pion contamination must be kept lower than 10 −4 . The RICH has been designed to separate charged pions from muons in the momentum range 15 < p < 35 GeV / c , contributing to a further muon rejection factor of 100. In order to match the upstream and downstream activity, a time resolution similar to the one of KTAG must be achieved. The RICH is also used as a primitive trigger generator for the level-0 trigger system. The construction and commissioning of both detectors was completed and their performances were studied during the 2014–2015 runs. [ABSTRACT FROM AUTHOR]

The NA62 experiment is designed to measure the (ultra-)rare decay K + → π + ν ν ¯ branching ratio with a precision of ∼ 10 % at the CERN Super Proton Synchrotron (SPS). The L0 Trigger Processor (L0TP) is the lowest level system of the trigger chain. It is hardware implemented using programmable logic. The architecture of the L0TP is completely new for a high energy physics experiment. It is fully digital, based on a standard gigabit ethernet communication between detectors and L0TP Board. The L0TP Board is a commercial development board, Terasic DE4, mounting an Altera Stratix IV FPGA. The primitives generated by sub-detectors are sent asynchronously using the UDP protocol to the L0TP during the entire beam spill period (about 5 seconds). The L0TP realigns in time the primitives coming from 7 different sources and manages the information of the time plus all the characteristics of the event as energy, multiplicity and position of hits in order to select good events with a comparison with preset masks. It should guarantee a maximum latency of 1 ms. The maximum input rate is 10 MHz for each sub-detector, while the design maximum output trigger rate is 1 MHz. A complete trigger-less parasitic acquisition of the primitives is possible using mirroring switches to monitor the L0 behavior. A first version of the L0TP was commissioned during the 2014 NA62 pilot run and it is used in the current data taking. A description of the trigger algorithm is here presented. [ABSTRACT FROM AUTHOR]

A data acquisition system of the OKA experiment on studying rare kaon decays on the U-70 accelerator is described. The basis of the blocked data acquisition system was the high-speed multichannel information system MISS with autonomous controllers that read out the front-end electronics in the sequential data reading mode and buffering data during the accelerator burst. Data stored in the buffer memory are read out and processed at the end of the accelerator burst. The DATE package builds subevents from event fragments and events from subevents via the event building network. The event building network with the star topology is made with 1GbE-interfaces and 24 × 1 Gb E-switch. The GlusterFS cluster file system underlies the distributed storage system. [ABSTRACT FROM AUTHOR]

We propose that three recent anomalies in B meson decays, R D ( ⁎ ) , R K , and P 5 ′ , might be explained by only one vector leptoquark weak triplet state. The constraints on the parameter space are obtained by considering t → b τ + ν data, lepton flavor universality tests in the kaon sector, bounds on the lepton flavor violating decay B → K μ τ , and b → c μ − ν ¯ decays. The presence of such vector leptoquark could be exposed in precise measurements of top semitauonic decays to b quark. The model predicts enhanced decay rate of B → K ν ¯ ν , approximate equality of lepton flavor universality ratios R K ⁎ , R K , and suppressed branching fraction of B s → μ + μ − . [ABSTRACT FROM AUTHOR]

New results on sterile neutrinos searches in kaon decays and neutrino oscillation experiments are presented. [ABSTRACT FROM AUTHOR]