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Register a new userAre narrow unflavoured mesons a signature of new physics?
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New data of narrow low mass unflavoured mesonic structures are presented. A table of these exotic masses is obtained adding previously published data. The mass sequence shows a significant coupling of some of these clusters with stable hadrons: pion, nucleon, and deuteron. Indeed this coupling allows to reproduce rather well the masses of exotic narrow baryons and dibaryons. A discussion is presented to suggest a possible interpretation of these exotic hadronic structures.
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The recent observations of the purely leptonic decay $Ds to mu^+ u_{mu}$ and $tau^+ u_{tau}$ at CLEO-c and $B$ factory may allow a possible contribution from a charged Higgs boson. One such measurement of the decay constant $f_{D_s}$ differs from the most precise unquenched lattice QCD calculation by 4 $sigma$ level. Meanwhile, the measured ratio, ${cal BR}(Ds to mu^+ u_{mu})$ / ${cal BR}(Dp to mu^+ u_{mu})$, is larger than the standard model prediction at 2.0$sigma$ level. We discuss that the precise measurement of the ratio ${cal BR}(Ds to mu^+ u_{mu})$ / ${cal BR}(Dp to mu^+ u_{mu})$ at BES-III will shed light on the presence of new intermediate particles by comparing the theoretical predictions, especially, the predictions of high precise unquenched lattice QCD calculation.
The invariant mass spectra of e+e- pairs produced in 12-GeV proton-induced nuclear reactions are measured at the KEK Proton-Synchrotron. On the low-mass side of the omega meson peak, a significant enhancement over the known hadronic sources has been observed. The mass spectra, including the excess, are well reproduced by a model that takes into account the density dependence of the vector meson mass modification, as theoretically predicted.
We will discuss how the decays of charm mesons can be used to study light mesons spectroscopy, by presenting recent results of Dalitz plot analyses using data from Fermilab experiment E791. Emphasis will be on scalar mesons, which are found to have large contribution to the $D$ decays studied. In addition to the usual extraction of decay fractions and relative phases of the intermediate amplitudes, the Dalitz plot technique is used to measure masses and widths of scalar resonances. From the $D_s$ decay, we obtain masses and widths of $f_0(980)$ and $f_0(1370)$. We find evidence for a light and broad scalar resonance, the $sigma$ meson, in $D^+topi^-pi^+pi^+$ decay. Preliminary studies also show evidence for a light and broad resonance, the $kappa$ meson, in $D^+to K^-pi^+pi^+$ decay. These results illustrate the potential of charm decays as a laboratory for the study of light mesons.
Neutrinoless double beta decay is a hypothetical radioactive process which, if observed, would prove the neutrino to be a Majorana fermion: a particle that is its own antiparticle. In this lecture mini-series I discuss the physics of Majorana fermions and the connection between the nature of neutrino mass and neutrinoless double beta decay. We review Dirac and Majorana spinors, discuss methods of distinguishing between Majorana and Dirac fermions, and derive in outline the connection between neutrino mass and double beta decay rates. We conclude by briefly summarizing the experimental landscape and the challenges associated with searches for this elusive process.
The study of molecular systems provides exceptional opportunities for the exploration of the fundamental laws of nature and for the search for physics beyond the Standard Model of particle physics. Measurements of molecules composed of naturally occurring nuclei have provided the most stringent upper bounds to the electron electric dipole moment to date, and offer a route to investigate the violation of fundamental symmetries with unprecedented sensitivity. Radioactive molecules - where one or more of their atoms possesses a radioactive nucleus - can contain heavy and deformed nuclei, offering superior sensitivity for EDM measurements as well as for other symmetry-violating effects. Radium monofluoride, RaF, is of particular interest as it is predicted to have an appropriate electronic structure for direct laser cooling. Furthermore, some Ra isotopes are known to be octupole deformed, thereby resulting in a large enhancement of their symmetry-violating nuclear moments. Until now,however, no experimental measurements of RaF have been performed, and their study is impeded by major experimental challenges, as no stable isotopes of radium exist. Here, we present a novel experimental approach to study short-lived radioactive molecules using the highly sensitive collinear resonance ionisation method. With this technique we have measured, for the first time, the energetically low-lying electronic states for each of the isotopically pure RaF molecules at the ISOLDE-CERN. Our results provide strong evidence of the existence of a suitable laser-cooling scheme for these molecules and constitute a pivotal step towards high-precision studies in these systems. Our findings open up new opportunities in the synthesis, manipulation and study of short-lived radioactive molecules, which will have a direct impact in many-body physics, astrophysics, nuclear structure, and fundamental physics research.
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