19511077
Narrow structure in the excitation function of η photoproduction off the neutron.
The photoproduction of η mesons off nucleons bound in 2H and 3He has been measured in coincidence with recoil protons and recoil neutrons for incident photon energies from threshold up to 1.4 GeV. The experiments were performed at the Mainz MAMI accelerator, using the Glasgow tagged photon facility. Decay photons from the η→2γ and η→3π0 decays and the recoil nucleons were detected with an almost 4π electromagnetic calorimeter combining the Crystal Ball and TAPS detectors. The data from both targets are of excellent statistical quality and show a narrow structure in the excitation function of γn→nη. The results from the two measurements are consistent, taking into account the expected effects from nuclear Fermi motion. The best estimates for position and intrinsic width of the structure are W=(1670±5)  MeV and Γ=(30±15)  MeV. For the first time precise results for the angular dependence of this structure have been extracted.
122280609
The calorimeter project for the Mu2e experiment
The Mu2e experiment at Fermilab aims to measure the charged lepton flavor violating neutrinoless conversion of a negative muon into an electron. The conversion results in a monochromatic electron with an energy slightly below the rest mass of the muon (104.97 MeV). We expect to set a limit of ∼ 6×10^(−17) at 90% CL in three years of running, using an intense and clean pulsed μ^− beam providing ∼10^(18) stopped muons on target in three years of running. The experiment performs a strong suppression of potential background by gating off the prompts and performing precise momentum determination in conjunction with an highly efficient cosmic veto. The calorimeter should confirm that the candidates reconstructed by the tracker system are indeed conversion electrons and provide an independent trigger (or event reduction filter) for the experiment. It should also provide standalone muon to electron rejection. Moreover, it must be able to keep functionality in a high radiation dose environment inside a 10^(−4)_(torr) vacuum enclosure and in a presence of 1 T axial magnetic field. In order to accomplish all these tasks, a LYSO crystals calorimeter has been chosen. We show the proposed design and the experimental results obtained by exposing a small size calorimeter prototype to a tagged photon beam from 40 to 300 MeV at the A2 photon facility of the Mainz Microton (MAMI), Germany.
120805738
The Bonn polarized target NMR-system
Abstract The Bonn frozen spin target is used for meson photoproduction experiments in combination with the facility PHOENICS at ELSA. The maximum polarization field of 7 T is provided by a superconducting solenoid. For electron scattering experiments a target apparatus which uses a superconducting 4 T magnet in a Helmholtz configuration is employed. For dynamic nuclear polarization of protons or deuterons various microwaves sources with frequencies of 70 GHz, 98 GHz or 140 GHz are available. Ammonia, butanol and lithium hydrids are used as target materials. The main part of the polarization detection system is the so-called Liverpool nuclear magnetic resonance module, which ensures a high flexibility for the polarization measurements of different nuclear species, e.g. 15 N at 2.5 T ( f L =10.8 MHz) and protons at 50 T ( f L =213 MHz).
94396828
Butanol in the Frozen Spin Mode
Measurements of the polarization build-up in butanol at 3.5 T are presented. Measurements of the proton relaxation times in the frozen spin mode were performed at magnetic fields of 0.5 and 0.35 Tesla, leading to the conclusion that butanol is a suitable material for the Bonn Frozen Spin Target.
126224714
Double polarized measurements with frozen spin target at MAMI
The A2 Collaboration at the Mainz Microtron MAMI measures photon absorption cross sections using circularly and linearly polarized 'Bremsstrahlung' photons up to an energy of ~1.5GeV and a polarized Frozen Spin Target. We use a 4 π detection system with the 'Crystal Ball' as central part. Our Frozen Spin Target provides both longitudinally and transversely polarized protons and deuterons. In this paper the apparatus will be described. Double polarized experiments for the investigation of the nucleons excitation spectrum via meson production and our Compton program to measure the proton polarizabilities will be briefly discussed.
121408728
Behaviour of polarized ammonia in an intense electron beam
Abstract Polarized target experiments with intense particle beams suffer from the depolarization effects due to radiation damage and beam heating. The local depolarization of the target material 14 NH 3 at the electron beam spot has been investigated by hitting it with 1.2 GeV electrons. This beam has been delivered from the electron stretcher accelerator ELSA of the Bonn University. The polarized target consists of a 4 T superconducting magnet with a Helmholtz configuration and a 4 He evaporation cryostat which operates at a temperature around 1 K. The heating of the target chips by the electron beam has been measured up to an intensity of 70 nA using a specific set-up of the nuclear magnetic resonance apparatus for the polarization measurements.
118715473
Charge symmetry violation in parton distributions
Charge symmetry is the invariance of the strong Hamiltonian under rotations of 180 degrees about the 2-axis in isospace. It implies the equality of the d-distribution in the proton, dp, and the u-distribution in the neutron, un etc. In this talk, we discuss possible charge symmetry violation in parton distributions and review a recent experimental test of charge symmetry.
120110530
Deep inelastic scattering as a probe of nucleon and nuclear structure
Abstract We briefly review recent thinking about the meaning of various phenomenologlcal models of hadronic structure in the light of modern deep-inelastic scattering data. As a particularly topical example, we argue that a widely accepted explanation of the EMC effect, in terns of a change of confinement scale, is unlikely to be correct.
46670464
Sigma terms from an SU(3) chiral extrapolation
We report a new analysis of lattice simulation results for octet baryon masses in 2+1-flavor QCD, with an emphasis on a precise determination of the strangeness nucleon sigma term. A controlled chiral extrapolation of a recent PACS-CS Collaboration data set yields baryon masses which exhibit remarkable agreement both with experimental values at the physical point and with the results of independent lattice QCD simulations at unphysical meson masses. Using the Feynman-Hellmann relation, we evaluate sigma commutators for all octet baryons. The small statistical uncertainty, and considerably smaller model-dependence, allows a signifcantly more precise determination of the pion-nucleon sigma commutator and the strangeness sigma term than hitherto possible, namely {\sigma}{\pi}N=45 \pm 6 MeV and {\sigma}s = 21 \pm 6 MeV at the physical point.
56304029
Quark Mass Variation and its effect on nuclear binding
We consider the variations of the nucleon mass and the masses of the mesons typically used in a one-boson exchange model arising from possible changes in light quark masses. These results are used to calculate the corresponding changes of the energy of the S0 anti-bound state and the binding energies of 2H, 3H, and other nuclei. The possible consequences for the standard scenario for big bang nucleosynthesis are discussed [9]. In particular the possible solution of the 7Li problem through a variation of quark masses is not supported.
124913195
Structure function in nuclear matter in the NJL model
We present a consistent description of the structure function of a free nucleon, the equation of state of nuclear matter, and the structure function of a nucleon bound in nuclear matter, in the framework of the Nambu‐Jona‐Lasinio (NJL) model. The important role of the mean vector field in the nuclear medium to explain the EMC effect is emphasized.