Rightarrow Pp Research Articles

Neutrinoless double- β decay in effective field theory: The light-Majorana neutrino-exchange mechanism

We present the first chiral effective theory derivation of the neutrinoless double beta-decay $nn\rightarrow pp$ potential induced by light Majorana neutrino exchange. The effective-field-theory framework has allowed us to identify and parameterize short- and long-range contributions previously missed in the literature. These contributions can not be absorbed into parameterizations of the single nucleon form factors. Starting from the quark and gluon level, we perform the matching onto chiral effective field theory and subsequently onto the nuclear potential. To derive the nuclear potential mediating neutrinoless double beta-decay, the hard, soft and potential neutrino modes must be integrated out. This is performed through next-to-next-to-leading order in the chiral power counting, in both the Weinberg and pionless schemes. At next-to-next-to-leading order, the amplitude receives additional contributions from the exchange of ultrasoft neutrinos, which can be expressed in terms of nuclear matrix elements of the weak current and excitation energies of the intermediate nucleus. These quantities also control the two-neutrino double beta-decay amplitude. Finally, we outline strategies to determine the low-energy constants that appear in the potentials, by relating them to electromagnetic couplings and/or by matching to lattice QCD calculations.

Leptophilic dark matter in gauged U(1)_{L{_e}-L_{mu }} model in light of DAMPE cosmic ray {e{^+}} + {e{^-}} excess

Motivated by the very recent cosmic-ray electron+positron excess observed by DAMPE collaboration, we investigate a Dirac fermion dark matter (DM) in the gauged {{L_e} - {L_mu }} model. DM interacts with the electron and muon via the U(1)_{e-mu } gauge boson Z^prime . The model can explain the DAMPE data well. Although a non-zero DM-nucleon cross section is only generated at one loop level and there is a partial cancellation between Z^{prime }ee and Z^{prime }mu mu couplings, we find that a large portion of Zprime mass is ruled out from direct DM detection limit leaving the allowed Z^{prime } mass to be close to two times of the DM mass. Implications for pp rightarrow Z^{prime } rightarrow 2ell and pp rightarrow 2ell + Z^{prime }, and muon g-2 anomaly are also studied.

Isotensor Axial Polarizability and Lattice QCD Input for Nuclear Double-β Decay Phenomenology.

The potential importance of short-distance nuclear effects in double-β decay is assessed using a lattice QCD calculation of the nn→pp transition and effective field theory methods. At the unphysical quark masses used in the numerical computation, these effects, encoded in the isotensor axial polarizability, are found to be of similar magnitude to the nuclear modification of the single axial current, which phenomenologically is the quenching of the axial charge used in nuclear many-body calculations. This finding suggests that nuclear models for neutrinoful and neutrinoless double-β decays should incorporate this previously neglected contribution if they are to provide reliable guidance for next-generation neutrinoless double-β decay searches. The prospects of constraining the isotensor axial polarizabilities of nuclei using lattice QCD input into nuclear many-body calculations are discussed.

Analysis of charmless two-body B decays in factorization-assisted topological-amplitude approach

We analyze charmless two-body non-leptonic B decays B rightarrow PP, PV under the framework of a factorization-assisted topological-amplitude approach, where P(V) denotes a light pseudoscalar (vector) meson. Compared with the conventional flavor diagram approach, we consider the flavor SU(3) breaking effect assisted by a factorization hypothesis for topological diagram amplitudes of different decay modes, factorizing out the corresponding decay constants and form factors. The non-perturbative parameters of topology diagram magnitudes chi and the strong phase phi are universal; they can be extracted by chi ^2 fit from current abundant experimental data of charmless Bdecays. The number of free parameters and the chi ^2 per degree of freedom are both reduced compared with previous analyses. With these best fitted parameters, we predict branching fractions and CP asymmetry parameters of nearly 100 B_{u,d} and B_s decay modes. The long-standing pi pi and pi K-CP puzzles are solved simultaneously.

Study of the polarization degree for the p ⃗ p → ppη $\overrightarrow {p}p\rightarrow pp\eta $ measurement with WASA

Understanding of the production processes of the η meson will strongly rely on the precise determination of spin observables. So far these observables have been determined only for few excess energies and with low statistics (Winter et al. Eur. Phys. J. A18, 355 2003; Czyzykiewicz et al. Phys. Rev. Lett. 98, 122003 2007; Balestra et al. Phys. Rev. C69, 064003 2004). In the year 2010 WASA detector was used for the measurement of the \(\overrightarrow {p}p\rightarrow pp\eta \) reaction with the polarized proton beam of COSY (Moskal and Hodana J. Phys. Conf. Ser 295, 012080 2011). The measurement was done for the excess energy of Q = 15 MeV and Q = 72 MeV. In total about 106 events corresponding to the \(\overrightarrow {p}p\rightarrow pp\eta \) reaction have been collected.

Baryon resonance production and dielectron decays in proton-proton collisions at 3.5 GeV

We report on baryon resonance production and decay in proton-proton collisions at a kinetic energy of $3.5$ GeV based on data measured with HADES. The exclusive channels $pp \rightarrow np\pi^{+}$ and $pp \rightarrow pp\pi^{0}$ as well as $pp \rightarrow ppe^{+}e^{-}$ are studied simultaneously for the first time. The invariant masses and angular distributions of the pion-nucleon systems were studied and compared to simulations based on a resonance model ansatz assuming saturation of the pion production by an incoherent sum of baryonic resonances (R) with masses $<2~$ GeV/$c^2$. A very good description of the one-pion production is achieved allowing for an estimate of individual baryon-resonance production-cross-sections which are used as input to calculate the dielectron yields from $R\rightarrow pe^+e^-$ decays. Two models of the resonance decays into dielectrons are examined assuming a point-like $RN \gamma^*$ coupling and the dominance of the $\rho$ meson. The results of model calculations are compared to data from the exclusive $ppe^{+}e^{-}$ channel by means of the dielectron and $pe^+e^-$ invariant mass distributions.

Di-electrons from η -meson Dalitz decay in proton-proton collisions

The reaction \(\ensuremath pp\rightarrow pp\eta\rightarrow pp\gamma e^+e^-\) is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction \(\ensuremath pp \rightarrow pp\eta\) . Our focus is on di-electrons from Dalitz decays of η -mesons, \(\ensuremath \eta\rightarrow\gamma\gamma^* \rightarrow\gamma e^+e^-\) , and the role of the corresponding transition form factor \(\ensuremath F_{\eta\gamma\gamma^*}\) . Numerical results are presented for the intermediate-energy kinematics of HADES experiments.

Study of spectator tagging in the reaction np → ppπwith a deuteron beam

The reaction \(dp \ensuremath \rightarrow ppp \pi^-\) has been studied in a kinematically complete experiment at a single beam momentum \(\ensuremath p_{d}=1.85\)GeV/c (T = 759MeV). All four ejectiles have been detected in the large-acceptance time-of-flight spectrometer COSY-TOF. We analyzed the data along the lines of the spectator model as a means to isolate the quasi-free \(\ensuremath np\rightarrow pp\pi^-\) reaction. The spectator proton was identified by its momentum and flight direction thus yielding access to the associated Fermi motion of the bound neutron. A comparison is carried out with Monte Carlo simulations based on two different parameterizations of the deuteron wave function. Up to a Fermi momentum of roughly 150MeV/c no significant deviations between experimental and simulated data of various observables were found from which we conclude that the deuteron can indeed be taken as a valid substitute for the neutron.

The study of the neutral pion production in proton-proton collisions at beam momenta 1581 and 1683 MeV/c

The detailed investigation of the reaction $pp \rightarrow pp\pi^0$ has been carried out at two incident proton momenta. Momentum, angular and effective-mass distributions were analyzed in the framework of the one-pion exchange model. Taking into account only the P 33-wave in the pole diagrams allows one to obtain a good agreement with experimental data on differential distributions. At the same time the predictions for total cross-sections are much lower than the experimental data.

Total and differential cross-sections for the $pp\rightarrow pp\eta^\prime$ reaction near threshold

The \(\eta^\prime\)-meson production in the reaction \(pp\rightarrow pp\eta^\prime\) has been studied at excess energies of Q = 26.5, 32.5 and 46.6 MeV using the internal beam facility COSY-11 at the cooler synchrotron COSY. The total cross-sections as well as one angular distribution for the highest Q-value are presented. The excitation function of the near-threshold data can be described by a pure s-wave phase space distribution with the inclusion of the proton-proton final-state interaction and Coulomb effects. The obtained angular distribution of the \(\eta^\prime\)-mesons is also consistent with pure s-wave production.

First close-to-threshold measurement of the analysing power A y in the reaction $\vec pp \rightarrow pp\eta$

At the internal facility COSY-11 a first measurement of the reaction $\vec pp \rightarrow pp\eta$ near the production threshold has been performed. Results for the analysing power will be presented and a comparison with one-meson exchange models will be discussed.

Study of baryon and search for dibaryon resonances by the $pp \rightarrow pp\pi^ + \pi^-$ reaction

Exclusive measurements of the two-pion production channel $pp \rightarrow pp\pi^ + \pi^-$ have been carried out near threshold at CELSIUS with the PROMICE/WASA detector. They reveal $pp \rightarrow pp^*(1440)\rightarrow pp\sigma \rightarrow pp(\pi^ + \pi^-)_{I = \ell = 0}$ as the dominant process at these energies, however, the data exhibit also significant contributions from $p^*(1440) \rightarrow \Delta \pi \rightarrow p(\pi^ + \pi^-)_{I = \ell = 0}$ . From the observed interference of these Roper decay routes their relative branching ratio is derived. The status on the search for NN-decoupled $NN\pi$ -resonances is reviewed with regard to recent experimental searches in the pionic double charge exchange in nuclei, the two-pion production in nucleon-nucleon collisions, the photo pion-production on the deuteron and the electro pion-production in nuclei.

Near-threshold production of $\omega$ -mesons in the $pn\rightarrow d\omega$ reaction

The first measurement of the $pn\rightarrow d\omega$ total cross-section has been achieved at mean excess energies $Q\approx 28$ and 57 MeV by using a deuterium cluster-jet target. The momentum of the fast deuteron was measured in the ANKE spectrometer at COSY-Julich and that of the slow “spectator” proton $(p_{\rm {sp}})$ from the $pd\rightarrow p_{\rm {sp}}d\omega$ reaction in a silicon telescope placed close to the target. The cross-sections lie above those measured for $pp\rightarrow pp\omega$ but seem to be below theoretical predictions.

Results of search for narrow diproton structures in the $pn\rightarrow pp\pi^{-}$ reaction at 1.98 GeV/c

Results of search for narrow diproton structures in the $pn\rightarrow pp\pi^{-}$ reaction at 1.98 GeV/c

Proton-proton bremsstrahlung below and above pion threshold: Influence of the Delta isobar.

The proton-proton bremsstrahlung is investigated within a coupled-channel model with the $\Delta$ degree of freedom. The model is consistent with the $NN$ scattering up to 1 GeV and the $\gamma N\Delta$ vertex determined in the study of pion photoproduction reactions. It is found that the $\Delta$ excitation can significantly improve the agreements with the $pp \rightarrow pp\gamma$ at $E_{lab}=280$ MeV. Predictions at $E_{lab}=550$ and $800$ MeV are presented for future experimental tests.