Search

PIONEER is a next-generation experiment to measure the charged pion branching ratios to electrons vs. muons Re/μ=Γπ+→e+ν(γ)Γπ+→μ+ν(γ) and pion beta decay (Pib) π+→π0eν. The pion to muon decay (π→μ→e) has four orders of magnitude higher probability than the pion to electron decay (π→eν). To achieve the necessary branching-ratio precision it is crucial to suppress the π→μ→e energy spectrum that overlaps with the low energy tail of π→eν. A high granularity active target (ATAR) is being designed to suppress the muon decay background sufficiently so that this tail can be directly measured. In addition, ATAR will provide detailed 4D tracking information to separate the energy deposits of the pion decay products in both position and time. This will suppress other significant systematic uncertainties (pulse pile-up, decay in flight of slow pions) to μm in thickness or less) with moderate internal signal amplification and great time resolution. To achieve a 100% active region several emerging technologies are being evaluated, such as AC-LGADs and TI-LGADs. A dynamic range from MiP (positron) to several MeV (pion/muon) of deposited charge is expected, the detection and separation of close-by hits in such a wide dynamic range will be a main challenge. Furthermore, the compactness and the requirement of low inactive material of the ATAR present challenges for the readout system, forcing the amplifier chip and digitizer to be positioned away from the active region.

Abstract The BNL-AGS E906 experiment was the first fully electronic experiment to produce and study double hypernuclei with large statistics. Two dominant structures were observed in the correlated π − – π − momentum matrix at (p π − H , p π − L) = (133 , 114) MeV / c and at (114 , 104) MeV / c. In this work we argue that the interpretation of the structure at (133 , 114) MeV / c in terms of Λ 3 H+ Λ 4 H pairs is questionable. We show, that neither a scenario where these single-Λ hypernuclei are produced after capture of a stopped Ξ − by a 9Be nucleus nor interactions of energetic Ξ − with 9Be nuclei in the target material can produce a sufficient amount of such twin pairs. We have therefore explored the conjecture of Avraham Gal that decays of the Image 1 may be responsible for the observed structure. Indeed, the inclusion of Image 1 with a two-body π − branching ratio of 50% in a statistical multifragmentation model allows to describe the E906 data remarkably well. On the other hand, a bound Λ 3 n nucleus would cause a striking structure in the momentum correlation matrix which is clearly inconsistent with the observation of E906. [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]

Appreciable hard X-ray (HXR) and gamma-ray emissions in the 0.04–150 MeV energy range associated with the 2003 October 29 solar flare (X10/3B) were observed at 20:38–20:58 UT by the SONG instrument onboard the CORONAS-F mission. To restore flare gamma-ray spectra we fitted the SONG energy loss spectra with a three-component model of the incident spectrum: (1) a power law in energy, assumed to be due to electron bremsstrahlung; (2) a broad continuum produced by prompt nuclear de-excitation gamma-lines; and (3) a broad gamma-line generated from pion-decay. We also restored spectra from the RHESSI data, compared them with the SONG spectra and found a reasonable agreement between these spectra in the 0.1–10 MeV energy range. The pion-decay emission was observed from 20:44:20 UT and had its maximum at 20:48–20:51 UT. The power-law spectral index of accelerated protons estimated from the ratio between intensities of different components of gamma rays changed with time. The hardest spectrum with a power-law index S  = −3.5 – 3.6 was observed at 20:48–20:51 UT. Time histories of the pion-decay emission and proton spectrum were compared with changes of the locations of flare energy release as shown by RHESSI hard X-ray images and remote and remote Hα brightenings. An apparent temporal correlation between processes of particle acceleration and restructuring of flare magnetic field was found. In particular, the protons were accelerated to subrelativistic energies after radical change of the character of footpoint motion from a converging motion to a separation motion. [ABSTRACT FROM AUTHOR]

A representation of the two-loop contribution to the pion decay constant in SU(3) chiral perturbation theory is presented. The result is analytic up to the contribution of the three (different) mass sunset integrals, for which an expansion in their external momentum has been taken. We also give an analytic expression for the two-loop contribution to the pion mass based on a renormalized representation and in terms of the physical eta mass. We find an expansion of $$F_{\pi }$$ and $$M_{\pi }^2$$ in the strange-quark mass in the isospin limit, and we perform the matching of the chiral SU(2) and SU(3) low-energy constants. A numerical analysis demonstrates the high accuracy of our representation, and the strong dependence of the pion decay constant upon the values of the low-energy constants, especially in the chiral limit. Finally, we present a simplified representation that is particularly suitable for fitting with available lattice data. [ABSTRACT FROM AUTHOR]

The width of three-body single-pion decay process d ⁎ → N N π 0 , ± is calculated by using the d ⁎ wave function obtained from our chiral SU(3) constituent quark model calculation. The effect of the dynamical structure on the width of d ⁎ is taken into account in both the single ΔΔ channel and coupled Δ Δ + C C two-channel approximations. Our numerical result shows that in the coupled-channel approximation, namely, the hidden-color configuration being considered, the obtained partial decay width of d ⁎ → N N π is about several hundred keV, while in the single ΔΔ channel it is just about 2 ∼ 3 MeV . We, therefore, conclude that the partial width in the single-pion decay process of d ⁎ is much smaller than the widths in its double-pion decay processes. Our prediction may provide a criterion for judging different interpretations of the d ⁎ structure, as different pictures for the d ⁎ may result quite different partial decay width. [ABSTRACT FROM AUTHOR]

We evaluate the Λ c Σ c π coupling constant ( G Λ c Σ c π ) and the width of the strong decay Σ c → Λ c π in 2 + 1 flavor lattice QCD on four different ensembles with pion masses ranging from 700 MeV to 300 MeV. We find G Λ c Σ c π = 18.332 ( 1.476 ) s t a t . ( 2.171 ) s y s t . and the decay width Γ ( Σ c → Λ c π ) = 1.65 ( 28 ) s t a t . ( 30 ) s y s t . MeV on the physical quark-mass point, which is in agreement with the recent experimental determination. [ABSTRACT FROM AUTHOR]

The radio galaxy IC310 located in the Perseus Cluster is one of the brightest objects in the radio and X-ray bands, and one of the closest active galactic nuclei observed in very-high energies. In GeV - TeV γ -rays, IC310 was detected in low and high flux states by the MAGIC telescopes from October 2009 to February 2010. Taking into account that the spectral energy distribution (SED) up to a few GeV seems to exhibit a double-peak feature and that a single-zone synchrotron self-Compton (SSC) model can explain all of the multiwavelength emission except for the non-simultaneous MAGIC emission, we interpret, in this work, the multifrequency data set of the radio galaxy IC310 in the context of homogeneous hadronic and leptonic models. In the leptonic framework, we present a multi-zone SSC model with two electron populations to explain the whole SED whereas for the hadronic model, we propose that a single-zone SSC model describes the SED up to a few GeVs and neutral pion decay products resulting from p γ interactions could describe the TeV - GeV γ -ray spectra. These interactions occur when Fermi-accelerated protons interact with the seed photons around the SSC peaks. We show that, in the leptonic model the minimum Lorentz factor of second electron population is exceedingly high γ e ∼ 10 5 disfavoring this model, and in the hadronic model the required proton luminosity is not extremely high ∼10 44 erg/s, provided that charge neutrality between the number of electrons and protons is given. Correlating the TeV γ -ray and neutrino spectra through photo-hadronic interactions, we find that the contribution of the emitting region of IC310 to the observed neutrino and ultra-high-energy cosmic ray fluxes are negligible. [ABSTRACT FROM AUTHOR]

Air-Cherenkov telescopes have mapped the Galactic plane at TeV energies. Here we evaluate the prospects for detecting the neutrino emission from sources in the Galactic plane assuming that the highest energy photons originate from the decay of pions, which yields a straightforward prediction for the neutrino flux from the decay of the associated production of charged pions. Four promising sources are identified based on having a large flux and a flat spectrum. We subsequently evaluate the probability of their identification above the atmospheric neutrino background in IceCube data as a function of time. We show that observing them over the twenty-year lifetime of the instrumentation is likely, and that some should be observable at the 3  σ level with six years of data. In the absence of positive results, we derive constraints on the spectral index and cut-off energy of the sources, assuming a hadronic acceleration mechanism. [ABSTRACT FROM AUTHOR]

The pion branching ratio, $R_{\pi } = \frac { {\Gamma }(\pi ^{+} \rightarrow e^{+} \nu _{e} + \pi ^{+}\rightarrow e^{+} \nu _{e} \gamma )}{\Gamma (\pi ^{+} \rightarrow \mu ^{+} \nu _{\mu } + \pi ^{+} \rightarrow \mu ^{+} \nu _{\mu } \gamma )}$ , provides a sensitive test of lepton universality and constraints on many new physics scenarios. The theoretical uncertainty on the Standard Model prediction of R is 0.02 %, a factor of twenty smaller than the experimental uncertainty. The analysis of a subset of data taken by the PIENU experiment will be presented. The result, R = (1.2344 ± 0.0023( s t a t) ± 0.0019( s y s t)) ⋅ 10 [1], is consistent with the Standard Model prediction and represents a 0.1 % constraint on lepton non-universality. [ABSTRACT FROM AUTHOR]

The PIENU experiment aims to measure the branching ratio of the charged pion decay with precision of < 0.1 %. This measurement is much sensitive to search for massive neutrinos coupled to electrons in ${\pi }^{+}{\rightarrow }e^{+}{\nu }_{e}$ decay. The initial analysis was completed and the upper limit on the neutrino mixing parameter | U | in the neutrino mass range of 0 to 55 MeV/ c was improved by a factor of 1.5, and the sensitivity for the mass range of 68 to 129 MeV/ c was improve by a factor of up to 4. [ABSTRACT FROM AUTHOR]

The differential decay rates of the processes J / ψ → p p ¯ π 0 and J / ψ → p p ¯ η close to the p p ¯ threshold are calculated with the help of the N N ¯ optical potential. The same calculations are made for the decays of ψ ( 2 S ) . We use the potential which has been suggested to fit the cross sections of N N ¯ scattering together with N N ¯ and six pion production in e + e − annihilation close to the p p ¯ threshold. The p p ¯ invariant mass spectrum is in agreement with the available experimental data. The anisotropy of the angular distributions, which appears due to the tensor forces in the N N ¯ interaction, is predicted close to the p p ¯ threshold. This anisotropy is large enough to be investigated experimentally. Such measurements would allow one to check the accuracy of the model of N N ¯ interaction. [ABSTRACT FROM AUTHOR]

We calculate the width of the Roper resonance at next-to-leading order in a systematic expansion of baryon chiral perturbation theory with pions, nucleons, and the delta and Roper resonances as dynamical degrees of freedom. Three unknown low-energy constants contribute up to the given order. One of them can be fixed by reproducing the empirical value for the width of the Roper decay into a pion and a nucleon. Assuming that the remaining two couplings of the Roper interaction take values equal to those of the nucleon, the result for the width of the Roper decaying into a nucleon and two pions is consistent with the experimental value. [ABSTRACT FROM AUTHOR]

Measurements of CP observables in B ± → D K ± and B ± → D π ± decays are presented where the D meson is reconstructed in the final states K ± π ∓ , π ± K ∓ , K + K − , π + π − , K ± π ∓ π + π − , π ± K ∓ π + π − and π + π − π + π − . This analysis uses a sample of charged B mesons from pp collisions collected by the LHCb experiment in 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb − 1 . Various CP -violating effects are reported and together these measurements provide important input for the determination of the unitarity triangle angle γ . The analysis of the four-pion D decay mode is the first of its kind. [ABSTRACT FROM AUTHOR]

We have studied Wigner rotations of different types of Lorentz Transformations according to the nature of movement of one inertial frame relative to the other inertial frame. When the motion is along any arbitrary direction then we can find the formulae for Wigner rotations using the velocity addition formulae for most general, mixed number, quaternion and geometric product Lorentz transformations. Finally we have used simulated data for applying the Wigner rotation formula in pion decay chain and concluded the result. [ABSTRACT FROM AUTHOR]

The PIENU experiment at TRIUMF is aimed at a measurement of the branching ratio R e / μ = Γ ( ( π + → e + ν e ) + ( π + → e + ν e γ ) ) / Γ ( ( π + → μ + ν μ ) + ( π + → μ + ν μ γ ) ) with precision < 0.1 % . Incident pions, delivered at the rate of 60 kHz with momentum 75 MeV/c, were degraded and stopped in a plastic scintillator target. Pions and their decay product positrons were detected with plastic scintillators and tracked with multiwire proportional chambers and silicon strip detectors. The energies of the positrons were measured in a spectrometer consisting of a large NaI(Tℓ) crystal surrounded by an array of pure CsI crystals. This paper provides a description of the PIENU experimental apparatus and its performance in pursuit of R e / μ . [ABSTRACT FROM AUTHOR]

Incoherent η photoproduction on the deuteron is studied, with the main emphasis on the role of final-state interactions. In addition to the previously studied mechanisms of NN and ηN rescatterings, the role of an intermediate pion exchange is considered in detail, where first a pion is photoproduced on one nucleon and then rescatters into an η meson on the other, the spectator nucleon. It is found that the role of this pion-mediated contribution is comparable in size to that of ηN rescattering. Results for total and semi-inclusive differential cross sections and associated polarization observables are presented. In particular, polarization observables show significant sensitivity to final-state interactions. [ABSTRACT FROM AUTHOR]