Search results for "meson"
showing 10 items of 1548 documents
Double Polarization Observables in η Electroproduction
2009
Abstract A new measurement of beam-recoil double-polarization observables in η electroproduction at the A1 collaboration at MAMI is presented. The energy region of the S 11 ( 1525 ) resonance was covered at a four-momentum transfer of Q 2 = 0.1 GeV 2 / c 2 . It turned out, that the usual interpretation of the reaction mechanism via S 11 and D 13 resonance fails to explain the relative phase between the corresponding multipole amplitudes tested by this experiment, while the new data are still in good agreement with previous measurements.
Antiproton-proton annihilation at rest into two mesons
1993
Abstract Branching ratios for antiproton-proton annihilations at rest into two mesons are given. The data were obtained at LEAR by stopping antiprotons in a liquid hydrogen target. Both charged and neutral annihilation products were detected in the Crystal Barrel detector. Representative data are presented, and their bearing on the general picture of annihilation dynamics is discussed. In addition, preliminary branching ratios for two-body radiative annihilations are given.
Meson Decays with Crystal Ball at MAMI
2012
The Crystal Ball at MAMI setup offers excellent possibilities to study decays of light mesons like η , η ′ , and ω . Here, recent results on η and ω decays are presented. Furthermore, future perspectives in this field at MAMI are described.
Formation of Slow Heavy Mesons in Nuclei
2010
Abstract We study ϕ meson production in the C 12 ( p ¯ , ϕ ) reaction at p p ¯ = 1.3 GeV/c . We also discuss the interest in and the difficulties of studying heavy meson-nucleus systems.
Measurement of the Lifetime of Neutral Charmed Mesons
1984
Abstract The lifetime of neutral charmed particles photoproduced in emulsion has been measured. The lifetime value presented here was obtained from a sample of 22D 0 mesons, 18 of which have their charmed partner seen in emulsion. The sample is essentially background-free. The result obtained is τ D 0 =(2.11 +1.21 -0.63 )×10 13 s The D 0 mass derived from 8 3C events is m D 0 = 1856 ± 36 MeV/ c 2 .
Coherent ψ(2S) photo-production in ultra-peripheral Pb Pb collisions at sNN=2.76 TeV
2015
We have performed the first measurement of the coherent ψ(2S) photo-production cross section in ultraperipheral Pb–Pb collisions at the LHC. This charmonium excited state is reconstructed via the ψ(2S) → l +l − and ψ(2S) → J/ψπ+π− decays, where the J/ψ decays into two leptons. The analysis is based on an event sample corresponding to an integrated luminosity of about 22 μb−1. The cross section for coherent ψ(2S) production in the rapidity interval −0.9 < y < 0.9 is dσcoh ψ(2S)/dy = 0.83±0.19 stat+syst mb. The ψ(2S) to J/ψ coherent cross section ratio is 0.34+0.08 −0.07(stat + syst). The obtained results are compared to predictions from theoretical models.
Measurement of the mass and width of the charmed meson D∗+ (2010)
1992
Abstract Using a high-resolution silicon vertex detector we have observed a very clean signal of 127 D∗+. After a careful study of the experimental resolution of our apparatus we have measured m( D ∗++ )−m( D 0 ) = 145.39±0.06±0.03 MeV . We have also obtained a 90% CL upper limit to γ(D∗+) of 131 keV.
Observation of the decay KL → πoγγ and of a form factor enhancement in the decay KL → e+e−γ
1991
Abstract The rare decay mode K L → o γγ has been observed in an experiment of the NA31 collaboration at CERN. From a signal of 21 events with a background of 1.5 ± 0.9 events, a branching ratio of (2.1 ± 0.6)10 −6 is calculated for decays with an invariant γγ mass above 280 MeV. This result is compared with the values estimated from theoretical models and has implications for the CP-conserving contribution to K L → π o e + e − decay. In the same experiment, 1053 decays of the type K L → e + e − γ were observed. The branching ratio is measured to be (9.2 ± 0.5 ± 0.5)10 −6 in good agreement with theoretical expectations. An enhancement is observed at high masses in the distribution of the inv…
Search for a light Higgs resonance in radiative decays of theϒ(1S)with a charm tag
2015
A search is presented for the decay Υ(1S)→ γA^0, A^0 → cc[bar], where A^0 is a candidate for the CP-odd Higgs boson of the next-to-minimal supersymmetric standard model. The search is based on data collected with the BABAR detector at the Υ(2S) resonance. A sample of Υ(1S) mesons is selected via the decay Υ(2S)→π + π − Υ(1S). The A^0 → cc[bar] decay is identified through the reconstruction of hadronic D^0, D^+, and D^∗ (2010)^+ meson decays. No significant signal is observed. The measured 90% confidence-level upper limits on the product branching fraction B(Υ(1S) → γA^0 ) × B(A^0 → cc[bar] ) range from 7.4×10^(−5) to 2.4×10^(−3) for A^0 masses from 4.00 to 8.95 GeV/c^2 and 9.10 to 9.25 Ge…
Measurement of the rate of the decay KL→e+e−γ and observation of a form factor in this decay
1990
Abstract A large sample of Dalitz decays, K L → e + e − γ , has been observed. The branching ratio is Γ(K L →e + e − γ) Γ(K L → all )=(9.2±0.5±0.5)×10 −6 in good agreement with theoretical predictions. We observe an enhancement at high masses in the distribution of the invariant electron-positron pair mass, compared to the distribution expected from QED. This excess is interpreted as being due to virtual mesons contributing to the photon propagator.