C. Ayerbe Gayoso

High-precision determination of the electric and magnetic form factors of the proton.

New precise results of a measurement of the elastic electron-proton scattering cross section performed at the Mainz Microtron MAMI are presented. About 1400 cross sections were measured with negative four-momentum transfers squared up to Q{sup 2}=1 (GeV/c){sup 2} with statistical errors below 0.2%. The electric and magnetic form factors of the proton were extracted by fits of a large variety of form factor models directly to the cross sections. The form factors show some features at the scale of the pion cloud. The charge and magnetic radii are determined to be {sup 1/2}=0.879(5){sub stat}(4){sub syst}(2){sub model}(4){sub group} fm and {sup 1/2}=0.777(13){sub stat}(9){sub syst}(5){sub model}(2){sub group} fm.

Electric and magnetic form factors of the proton

New precise results of a measurement of the elastic electron-proton scattering cross section performed at the Mainz Microtron MAMI are presented. About 1400 cross sections were measured with negative four-momentum transfers squared up to Q² = 1 (GeV/c)² with statistical errors below 0.2%. The electric and magnetic form factors of the proton were extracted by fits of a large variety of form factor models directly to the cross sections. The form factors show some features at the scale of the pion cloud. The charge and magnetic radii are determined to be ½ = 0.879(5)stat(4)syst(2)model(4)group fm and ½ = 0.777(13)stat(9)syst(5)model(2)group fm.

Search at the Mainz Microtron for light massive gauge bosons relevant for the muon g-2 anomaly.

H. Merkel,1, ∗ P. Achenbach,1 C. Ayerbe Gayoso,1 T. Beranek,1 J. Beričič,2 J. C. Bernauer,1, † R. Böhm,1 D. Bosnar,3 L. Correa,1 L. Debenjak,2 A. Denig,1 M. O. Distler,1 A. Esser,1 H. Fonvieille,4 I. Friščić,3 M. Gómez Rodrı́guez de la Paz,1 M. Hoek,1 S. Kegel,1 Y. Kohl,1 D. G. Middleton,1 M. Mihovilovič,1 U. Müller,1 L. Nungesser,1 J. Pochodzalla,1 M. Rohrbeck,1 G. Ron,5 S. Sánchez Majos,1 B. S. Schlimme,1 M. Schoth,1 F. Schulz,1 C. Sfienti,1 S. Širca,2, 6 M. Thiel,1 A. Tyukin,1 A. Weber,1 and M. Weinriefer1 (A1 Collaboration) Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, D-55099 Mainz, Germany‡ Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia Department of Physics, University of Zagreb, HR-10002 Zagreb, Croatia Clermont Université, Université Blaise Pascal, CNRS/IN2P3, LPC, BP 10448, F-63000 Clermont-Ferrand, France Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel Department of Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia (Dated: April 22, 2014)

Hypernuclear spectroscopy of products from Li-6 projectiles on a carbon target at 2 A GeV

Abstract A novel experiment, aiming at demonstrating the feasibility of hypernuclear spectroscopy with heavy ion beams, was conducted. Using the invariant mass method, the spectroscopy of hypernuclear products of 6Li projectiles on a carbon target at 2 A GeV was performed. Signals of the Λ-hyperon and H Λ 3 and H Λ 4 hypernuclei were observed for final states of p + π − , He 3 + π − and He 4 + π − , respectively, with significance values of 6.7, 4.7 and 4.9σ. By analyzing the proper decay time from secondary vertex distribution with the unbinned maximum likelihood fitting method, their lifetime values were deduced to be 262 − 43 + 56 ± 45 ps for Λ, 183 − 32 + 42 ± 37 ps for H Λ 3 , and 140 − 33 + 48 ± 35 ps for H Λ 4 .

Observation of H Λ 4 Hyperhydrogen by Decay-Pion Spectroscopy in Electron Scattering

At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a (9)Be target in order to study the Λ binding energy of light hypernuclei. Positively charged kaons were detected by a short-orbit spectrometer with a broad momentum acceptance at 0° forward angles with respect to the beam, efficiently tagging the production of strangeness in the target nucleus. Coincidentally, negatively charged decay pions were detected by two independent high-resolution spectrometers. About 10(3) pionic weak decays of hyperfragments and hyperons were observed. The pion momentum distribution shows a monochromatic peak at pπ≈133  MeV/c, corresponding to the unique signature for the two-body decay of hyperhydrogen Λ(4)H→(4)He+π(-), stopped inside the target. Its Λ binding energy was determined to be BΛ=2.12±0.01  (stat)±0.09  (syst)MeV with respect to the (3)H+Λ mass.

Exclusive electroproduction of K+Λ and K+Σ0 final states at Q2 = 0.030–0.055 (GeV/c)2

Cross-section measurements of the exclusive p(e, e′K+)Λ, Σ0electroproduction reactions have been performed at the Mainz Microtron MAMI in the A1 spectrometer facility using for the first time the KAOS spectrometer for kaon detection. These processes were studied in a kinematical region not covered by any previous experiment. The nucleon was probed in its third-resonance region with virtual photons of low four-momenta, Q2 = 0.030–0.055 (GeV/c)2. The MAMI data indicate a smooth transition in Q2 from photoproduction to electroproduction cross-sections. Comparison with predictions of effective Lagrangian models based on the isobar approach reveal that strong longitudinal couplings of the virtual photon to the N* resonances can be excluded from these models. Modern isobar and Regge-plus-resonance models are in agreement with the data.

Determination of quadrupole strengths in the gamma*p-->Delta(1232) transition at Q2= 0.20 (GeV/c)2

We report new precise p

Determination of quadrupole strengths in the γ∗p→Δ(1232) transition at Q2=0.20(GeV/c)2

(\vec{e},e^\prime p)\pi^0

A new measurement of the structure functions PLL - PTT/ε and PLT in virtual Compton scattering at Q2 = 0.33 (GeV/c)2

measurements at the peak of the

Measurement of propagation time dispersion in a scintillator

\Delta^{+}(1232)