Search results for "Particle physics"

Measurements of relativistic time dilatation for positive and negative muons in a circular orbit

1977

The lifetimes of both positive and negative relativistic (γ = 29.33) muons have been measured in the CERN Muon Storage Ring with the results τ+ = 64.419 (58) µs, τ− = 64.368 (29) µs The value for positive muons is in accordance with special relativity and the measured lifetime at rest: the Einstein time dilation factor agrees with experiment with a fractional error of 2×10−3 at 95% confidence. Assuming special relativity, the mean proper lifetime for μ− is found to be τ0− = 2.1948(10) µs the most accurate value reported to date. The agreement of this value with previously measured values of τ0+ confirms CPT invariance for the weak interaction in muon decay.

A critical analysis on deeply bound kaonic states in nuclei and the KEK experiment

2008

We critically discuss the theoretical developments that led to predictions of very deeply bound kaon states and then revise the data of the KEK experiment from where claims for evidence of deeply bound kaon atoms in nuclei were made. We conclude that the peaks seen in the experiment correspond to the absorption of kaons by a pair of nucleons leading to Σp and Λp and leaving the daughter nucleus as a spectator. These conclusions have been reconfirmed by a recent experiment at FINUDA.

Erratum to: Split-family SUSY, $$U(2)^5$$ U ( 2 ) 5 flavour symmetry and neutrino physics

2014

A reanalysis of branching fractions of charmed mesonsD 0,D + andD s +

1992

We combine highly complementary information on branching fractions of charmed mesonsD0,D+ andDs+ coming from two experiments both yielding doublecharm samples. The NA 32 experiment provided exclusive branching fractions for channels with at least two charged decay products while a recent Mark III paper provides results on inclusive charm decay properties. The knowledge of channels withK0's in the former is used to recalculate the charged multiplicity distribution in the latter. We obtain 〈nch〉=2.25±0.08 forD0, 〈nch〉=1.96±0.08 forD+ and 〈nch〉=2.41±0.38 forDs+. In turn the knowledge of the charged multiplicity improves the overall normalization of exclusive branching fractions. This reanalysi…

XYZ physics at BESIII

2014

In this talk, we present the recent study on the charmonium-like states from the BESIII Collaboration based on large data samples above DD¯$D\overline D $ threshold. The observation of X(3872) from the Y(4260) radiative transition, the study of the Y states from the e+e− → π+π−hc process, and the observation of the charged Zc states are included.

Neutrino Gas in Equilibrium with Self-Interaction

2005

We study a neutrino gas in equilibrium both at T = 0 and at finite temperature. The neutrinos are assumed to be massive Dirac particles with two generations interacting with each other via neutral currents and with a background of matter. We analyze the main properties of the neutrino eigenmodes in the medium, such as effective masses and mixing angle.

Dispersion Approach to Pion Photoproduction and GDH Sum Rule

1999

Pion photoproduction has been analyzed in the framework of dispersion relations at constant t. The results for S-wave pion production at threshold and P-wave production in the Δ (1232) resonance region are presented and compared to the data and theoretical expectations. The predictions for the GDH sum rule are shown to be very sensitive to the threshold S-wave amplitude.

$$N\bar N$$ annihilation at rest into five pions

1993

\(N\bar N\) annihilation at rest into five pions was studied in the ASTERIX spectrometer by stopping antiprotrons from LEAR in a H2 or D2 gas target. In\(\bar pp\) annihilations in H2 leading to the π+π−π+π−π0 final state, the invariant mass spectra of two, three, and four pions show no evidence for any new narrow states. In\(\bar pn \to \pi ^ + \pi ^ - \pi ^ + \pi ^ - \pi ^ - \) the difference of the four pion mass spectra recoiling against a π− and those recoiling against a π+ shows a resonance-like structure (“ζ (1480)”), confirming a previous analysis with a smaller event sample. The ζ (1480) mass is shown to depend strongly on the momentum of the spectator proton. In H2, we searched fo…

Statistical decay of hyperfragments

2011

Combining the unique features of the hypernuclear electro-production mechanism and the high precision in magnetic spectroscopy, the proposed E-08-012 experiment at Jefferson Lab, Virginia, and the scheduled hypernuclear experiment at MAMI, Germany, focus on the high-resolution spectroscopy of weak two-body decay pions from hypernuclei. These experiments will provide insight on a wide range of light hypernuclei via the production of hyperfragments from 9 Be, 6,7 Li and 12 C targets. In the present work we explore the production of Λ-hypernuclei following the micro-canonical break-up of an initially excited hypernucleus which is created by the electro/photo-production reaction. Finally the mo…

The pion electroproduction and the virtual-photon theory

1983

The double differential cross-section for pion electroproduction was measured for the processes p(e,π+n and12C(e,π+)12B. The proton-induced cross-section was evaluated by using the virtual-photon concept. The experimental data were used to test different formulae for the virtual-photon spectrum. We found significant deviations to a generally used formula (Dalitz-Yennie) and good agreement with a new formula (Tiator-Wright). In addition, we have measured pion production crosssections with real photons under equal kinematic conditions. Electro-and photoproduction measurements give the same results.