Experimental activities in few-body physics

Understanding the few-nucleon system remains one of the challenges in modern nuclear and hadron physics. Observables in few-nucleon scattering processes are sensitive probes to study the two and many-body interactions between nucleons in nuclei. In the past decades, several facilities provided a large data base to study in detail the three-nucleon interactions below the pion-production threshold by exploiting polarized proton and deuteron beams and large-acceptance detectors. Only since recently, the four-nucleon scattering process at intermediate energies has been explored. In addition, there is a focus to collect data in the hyperon-nucleon sector, thereby providing access to understand the more general baryon-baryon interaction. In this contribution, some recent results in the few-nucleon sector are discussed together with some of the preliminary results from a pioneering and exclusive study of the four-nucleon scattering process. Furthermore, this paper discusses the experimental activities in the hyperon sector, in particular, the perspectives of the hyperon program of PANDA.Comment: 9 pages, 4 figures, proceedings of the 21st European Conference on Few Body Problems in Physics, Salamanca, Spain, 30 August - 3 September 201

Studying the ω\omega-mass in-medium in γ+A→π0γ+X\gamma + A\to \pi^0\gamma +X reactions

Simulations based on a coupled-channel transport model have been performed to analyze the feasibility to study the in-medium $\omega$ mass exploiting the process $\gamma+A\to\pi^0\gamma+X$ for C, Ca and Nb nuclei. The distortions due to final-state interactions of the $\pi^0$ and background contributions from the reaction $\gamma+A\to\pi^0\pi^0+X$ are found to be small in the mass range of interest ($0.6<M_{\pi^0\gamma}<0.8$ GeV). Furthermore, the effect of the detector resolution on the $\pi^0\gamma$-mass determination is discussed

Measurement of Proton Electromagnetic Form Factors in e(+) e(-) -&gt; p(p)over-bar in the Energy Region 2.00-3.08 GeV

The process of e+e-→pp̄ is studied at 22 center-of-mass energy points (s) from 2.00 to 3.08 GeV, exploiting 688.5 pb-1 of data collected with the BESIII detector operating at the BEPCII collider. The Born cross section (σpp̄) of e+e-→pp̄ is measured with the energy-scan technique and it is found to be consistent with previously published data, but with much improved accuracy. In addition, the electromagnetic form-factor ratio (|GE/GM|) and the value of the effective (|Geff|), electric (|GE|), and magnetic (|GM|) form factors are measured by studying the helicity angle of the proton at 16 center-of-mass energy points. |GE/GM| and |GM| are determined with high accuracy, providing uncertainties comparable to data in the spacelike region, and |GE| is measured for the first time. We reach unprecedented accuracy, and precision results in the timelike region provide information to improve our understanding of the proton inner structure and to test theoretical models which depend on nonperturbative quantum chromodynamics

Dynamically generated N∗N^{*} and Λ∗\Lambda^* resonances in the hidden charm sector around 4.3 GeV

The interactions of $\bar{D}\Sigma_{c}$-$\bar D\Lambda_c$, $\bar{D}^{*}\Sigma_{c}$-$\bar D^*\Lambda_c$, and related strangeness channels, are studied within the framework of the coupled channel unitary approach with the local hidden gauge formalism. A series of meson-baryon dynamically generated relatively narrow $N^*$ and $\Lambda^*$ resonances are predicted around 4.3 GeV in the hidden charm sector. We make estimates of production cross sections of these predicted resonances in $\bar{p} p$ collisions for PANDA at the forthcoming FAIR facility.Comment: 35 pages, 12 figure

Observation of psi (3686) -&gt; n(n)over-bar and improved measurement of psi (3686) -&gt; p(p)over-bar

We observe the decay psi (3686) -> n (n) over bar for the first time and measure psi (3686) -> p (p) over bar with improved accuracy by using 1.07 x 10(8) psi (3686) events collected with the BESIII detector. The measured branching fractions are B(psi(3686) -> n (n) over bar) = (3.06 +/- 0.06 +/- 0.14) x 10(-4) and B(psi(3686) -> p (p) over bar) = (3.05 +/- 0.02 +/- 0.12) x 10(-4). Here, the first uncertainties are statistical, and the second ones are systematic. With the hypothesis that the polar angular distributions of the neutron and proton in the center-of-mass system obey 1 + alpha cos(2) theta, we determine the a parameters to be alpha(n (n) over bar) = 0.68 +/- 0.12 +/- 0.11 and alpha(p (p) over bar) = 1.03 +/- 0.06 +/- 0.03 for psi(3686) -> n (n) over bar and psi(3686) -> p (p) over bar, respectively

Observation of the Singly Cabibbo-Suppressed Decay D+ -&gt; omega pi(+) and Evidence for D-0 -&gt; omega pi(0)

Based on 2.93 fb(-1) e(+)e(-) collision data taken at center-of-mass energy of 3.773 GeV by the BESIII detector, we report searches for the singly Cabibbo-suppressed decays D+ -> omega pi(+) and D-0 -> omega pi(0). A double tag technique is used to measure the absolute branching fractions B(D+ -> omega pi(+)) = (2.79 +/- 0.57 +/- 0.16) x 10(-4) and B(D-0 +/- omega pi(0)) = (1.17 +/- 0.34 +/- 0.07) x 10(-4), with statistical significances of 5.5 sigma and 4.1 sigma, where the first and second uncertainties are statistical and systematic, respectively

Proton-deuteron radiative capture cross sections at intermediate energies

Differential cross sections of the reaction $p(d,^3{\rm He})\gamma$ have been measured at deuteron laboratory energies of 110, 133 and 180 MeV. The data were obtained with a coincidence setup measuring both the outgoing $^3$He and the photon. The data are compared with modern calculations including all possible meson-exchange currents and two- and three- nucleon forces in the potential. The data clearly show a preference for one of the models, although the shape of the angular distribution cannot be reproduced by any of the presented models.Comment: 6 pages, 6 figures, accepted for publication in EPJ

Pluto: A Monte Carlo Simulation Tool for Hadronic Physics

Pluto is a Monte-Carlo event generator designed for hadronic interactions from Pion production threshold to intermediate energies of a few GeV per nucleon, as well as for studies of heavy ion reactions. This report gives an overview of the design of the package, the included models and the user interface.Comment: XI International Workshop on Advanced Computing and Analysis Techniques in Physics Research, April 23-27 2007, Amsterdam, the Netherland