Search results for "Particle physics"
showing 10 items of 6826 documents
Photons and Lepton Pairs — The Deep Probes of Quark-Gluon Plasma
1993
Photons and lepton pairs are close to the ideal probes to study the dynamics of the dense system of strongly interacting quanta expected to be produced in ultrarelativistic nucleus-nucleus collisions1,2. Electromagnetic interactions are strong enough to lead to a detectable signal from the secondary collisions of final state particles, yet, they are weak enough to let the emitted photons and leptons to escape from the finite nuclear system without further interactions. Thus, the spectra of photons and dileptons from the dense phase of the collision can provide information on the properties of the constituents and on their momentum distributions.
Pion photoproduction on3He including final-state interaction
1991
Coherent π0 and π+ photoproduction and elastic and charge-exchange pion scattering on3He has ben calculated in a consistent model. Realistic three-body Faddeev wave functions have been used and full nonlocal DWIA results for pion photoproduction are obtained. Furthermore, two-step processes such as3He(γ, π0)3He(π0, π+)3H are included giving rise to unexpected large results. The comparison with experimental data is very good over a wide range of photon energies and nuclear momentum transfers. A long-time discrepancy between previous impulse-approximation calculations and experimental data has been removed.
Relativistic effects and spin observables in deuteron electrodisintegration
1993
The influence of relativistic effects in deuteron electrodisintegration, in particular their manifestation in spin observables, is discussed. We have used a simple phenomenological approach by adding the lowest-order relativistic corrections to the nonrelativistic one-body current and including the kinematic wave-function boost. Furthermore, final-state interaction, meson-exchange currents and isobar configurations are included in order to study kinematic regions off the quasi-free case. Sizeable relativistic effects in many observables are found even at low energies.
Heavy-mesons exchange and the backward deuteron electrodisintegration
1992
Backward electrodisintegration of the deuteron is calculated using an exchange-current operator containing π, η, ρ, ω, δ, σ, andA1 exchanges. The deuteron and1S0np wave functions are derived from the Bonn OBEPs. For completeness, we introduced theA1-meson exchange into the OBEP's as well. As a consequence, the value ofD-state probabilityPD is increased by 0.2%–0.8%. The computed cross sections are compared with new data.
A study of D*+π- production in semileptonic B decay
1995
Abstract In a sample of 1.5 million hadronic decays of the Z collected by the ALEPH detector, a search is carried out for the decays B → D 1 0 (2420)l − ν X and B → D 2 ∗0 (2460)l − ν X . The product branching ratio for D10 production is measured to be Br (b → B ) × Br( B → D 1 0 l − ν X) × Br(D 1 0 → D ∗+ π − ) = (2.04 ± 0.58 stat ± 0.34 syst ) × 10 −3 , and a 95% confidence level limit of Br(b → B ) × Br( B → D 2 ∗0 l − ν X) × Br(D 2 ∗0 → D ∗+ π − ) ≤ 0.81 × 10 −3 is obtained for D2∗0 production. A topological search sensitive to the processes above, but also to wide resonances that decay to D ∗+ π − and to non-resonant D ∗+ π − production is also carried out, yielding Br(b→ B ) ×Br( B →D…
An upper limit for the τ neutrino mass from τ → 5π(π0)ντ decays
1995
An upper limit for the tau-neutrino mass has been determined from the decay tau -> 5pi+- \nu_tau using data collected with the OPAL detector from 1991 to 1995 in e+e- collisions at \sqrt{s} ~ M_Z. A limit of 43.2 MeV at 95% CL is obtained using a two-dimensional method in the 5pi invariant mass and energy distribution from 22 selected events. Combining this result with OPAL's previously published measurement using tau+tau- -> 3h+- \bar{nu}_tau 3h-+ \nu_tau decays, a new combined limit of m_{nu_tau} < 27.6 MeV (95% CL) is obtained.
Precise Measurement of the e+e−→π+π−J/ψ Cross Section at Center-of-Mass Energies from 3.77 to 4.60 GeV
2017
The cross section for the process e(+)e(-)-> pi(+) pi(-) J/psi is measured precisely at center-of-mass energies from 3.77 to 4.60 GeV using 9 fb(-1) of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of (222.0 +/- 3.1 +/- 1.4) MeV/ c(2) and a width of (44.1 +/- 4.3 +/- 2.0)MeV, while the second one has a mass of (4320.0 +/- 10.4 +/- 7.0)MeV/c(2) and a width of (101.4(- 19.7)(+25.3) +/- 10.2) MeV, where the first errors are statistical and second ones are systematic. The first resonance agrees with the Y(4260) resonance reported by previous experiments. The precisi…
Investigation of the Dipole Response in Exotic Nuclei – Experiments at the LAND-R$^3$B Setup
2012
We present experimental results on the electromagnetic excitation of neutron-rich nickel isotopes, making use of the (RB)-B-3-LAND setup at GSI. Exotic beams were produced at approximately 500 MeV/u and their reactions were studied in inverse kinematics. Integral cross sections for Ni-58 are discussed and compared to previous data, providing a validation of our experimental method. The El excitation-energy distribution of the unstable Ni-68 is presented as well, showing an excess in cross section in the 1n decay channel when compared only with a typical Giant Dipole Resonance.
Precise Measurement of the e+e− → π+π−J/ψ Cross Section at Center-of-Mass Energies from 3.77 to 4.60 GeV
2020
The cross section for the process e(+)e(-)-> pi(+) pi(-) J/psi is measured precisely at center-of-mass energies from 3.77 to 4.60 GeV using 9 fb(-1) of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of (222.0 +/- 3.1 +/- 1.4) MeV/ c(2) and a width of (44.1 +/- 4.3 +/- 2.0)MeV, while the second one has a mass of (4320.0 +/- 10.4 +/- 7.0)MeV/c(2) and a width of (101.4(- 19.7)(+25.3) +/- 10.2) MeV, where the first errors are statistical and second ones are systematic. The first resonance agrees with the Y(4260) resonance reported by previous experiments. The precisi…
Dipole amplitude with uncertainty estimate from HERA data and applications in Color Glass Condensate phenomenology
2014
We determine the initial condition for the small-x evolution equation (BK) from the HERA deep inelastic scattering data using a new parametrization that also keeps the unintegrated gluon distribution positive. The obtained dipole amplitude and its uncertainty estimate can be used to compute single inclusive particle production in proton-proton and proton-nucleus collisions. We argue that one has to use consistently the proton transverse area measured in DIS and the total inelastic cross section when calculating the single inclusive cross section. This leads to a midrapidity nuclear modification factor RpA that approaches unity at large transverse momentum, independently of the center-of-mas…