Search results for "MBD"
showing 10 items of 646 documents
Chiral Dynamics of the two Lambda(1405) States
2004
Using a chiral unitary approach for the meson--baryon interactions, we show that two octets of J^{\pi}=1/2^- baryon states, which are degenerate in the limit of exact SU(3) symmetry, and a singlet are generated dynamically. The SU(3) breaking produces the splitting of the two octets, resulting in the case of strangeness S=-1 in two poles of the scattering matrix close to the nominal \Lambda(1405) resonance. These poles are combinations of the singlet state and the octets. We show how actual experiments see just one effective resonance shape, but with properties which change from one reaction to another.
Charged kaon femtoscopic correlations inppcollisions ats=7 TeV
2013
Correlations of two charged identical kaons (KchKch) are measured in pp collisions at root s = 7 TeV by the ALICE experiment at the Large Hadron Collider (LHC). One-dimensional (KKch)-K-ch correlation functions are constructed in three multiplicity and four transverse momentum ranges. The (KKch)-K-ch femtoscopic source parameters R and lambda are extracted. The (KKch)-K-ch correlations show a slight increase of femtoscopic radii with increasing multiplicity and a slight decrease of radii with increasing transverse momentum. These trends are similar to the ones observed for pi pi and K-s(0) K-s(0) correlations in pp and heavy-ion collisions. However at high multiplicities, there is an indica…
Relaxing cosmological neutrino mass bounds with unstable neutrinos
2020
At present, cosmological observations set the most stringent bound on the neutrino mass scale. Within the standard cosmological model ($\Lambda$CDM), the Planck collaboration reports $\sum m_\nu < 0.12\,\text{eV}$ at 95% CL. This bound, taken at face value, excludes many neutrino mass models. However, unstable neutrinos, with lifetimes shorter than the age of the universe $\tau_\nu \lesssim t_U$, represent a particle physics avenue to relax this constraint. Motivated by this fact, we present a taxonomy of neutrino decay modes, categorizing them in terms of particle content and final decay products. Taking into account the relevant phenomenological bounds, our analysis shows that 2-body deca…
Search for exclusive decays of the Lambda_b baryon and measurement of its mass
1996
A search for fully reconstructed \lb beauty baryons is performed using about 3 million Z decays collected with the DELPHI detector at LEP. The analysis relies on the combined use of the accurate tracking and of the hadron identification capabilities of DELPHI. A total of four events has been found, three in the \lc\ppm channel and one in the \lc\a1m channel over a small background. The \lb beauty baryon mass is measured to be (~ 5668 \pm 16~ ({\rm stat.}) \pm 8~({\rm syst.})~)~ \mv.
Fermi-Dirac correlations in Lambda pairs in hadronic Z decays
2000
Two-particle correlations of Lambda Lambda and pairs have been studied in multihadronic Z decays recorded with the ALEPH detector at LEP in the years from 1992 to 1995. The correlations were measured as a function of the four-momentum difference Q of the pair. A depletion of events is observed in the region Q 2 GeV the fraction of pairs with spin one is consistent with the value of 0.75 expected for a statistical spin mixture, whilst for Q pairs, where no Fermi-Dirac correlations are expected, the spin one fraction is measured to be consistent with 0.75 over the entire analysed Q range. (C) 2000 Elsevier Science B.V. All rights reserved.
Charged lepton induced one kaon production off the nucleon
2013
We study single kaon production off the nucleon induced by electrons (positrons) i.e., e(-) (e(+)) + N -> v(e) ((v) over bar (e)) + (K) over bar (K) + N' at low energies. The possibility of observing these processes with the high luminosity beams available at TJNAF and Mainz is discussed, taking into account that the strangeness conserving electromagnetic reactions have a higher energy threshold for (K) over bar (K) production. The calculations are done using a microscopic model that starts from the SU(3) chiral Lagrangians and includes background terms and the resonant mechanisms associated to the lowest lying resonance Sigma*(1385)
Baryon Resonances
2010
10th International Conference on Hypernuclear and Strange Particle Physics. Tokai, JAPAN, SEP 14-18, 2009
Charged kaon production by coherent scattering of neutrinos and antineutrinos on nuclei
2013
With the aim of achieving a better and more complete understanding of neutrino interactions with nuclear targets, the coherent production of charged kaons induced by neutrinos and antineutrinos is investigated in the energy range of some of the current neutrino experiments. We follow a microscopic approach which, at the nucleon level, incorporates the most important mechanisms allowed by the chiral-symmetry-breaking pattern of QCD. The distortion of the outgoing K ((K) over bar) is taken into account by solving the Klein-Gordon equation with realistic optical potentials. Angular and momentum distributions, as well as the energy and nuclear dependence of the total cross section, are studied.
Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high $p_T$
2015
We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$\it c$ to 4 GeV/$\it c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$\it c$ or 200 GeV/$\it c$ impinging on polarised $\mathrm{{}^6LiD}$ or $\mathrm{NH_3}$ targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation $\Delta G$ inside the nucleon in the range of the nucleon momentum fraction carried by gluons $0.05 < x_g < 0.2$. We measured the longi…
The radiative decay of the Lambda(1405) and its two-pole structure
2007
We evaluate theoretically the radiative decay widths into $\gamma\Lambda$ and $\gamma\Sigma^0$ of the two poles of the $\Lambda(1405)$ found in chiral unitary theories and we find quite different results for each of the two poles. We show that, depending on which reaction is used to measure the $\Lambda(1405)$ radiative decays, one gives more weight to one or the other pole, resulting in quite different shapes in the $\gamma\Lambda(\Sigma^0)$ invariant mass distributions. Our results for the high-energy pole agree with those of the empirical determination of the $\gamma\Lambda$ and $\gamma\Sigma^0$ radiative widths (based on an isobar model fitting of the $K^-p$ atom data), which are someti…