arXiv subjects

K. Foehl

Publications and source records attributed to K. Foehl.

12 recordsLinked to original sources

arXiv2019

Particle Identification with DIRCs at PANDA

The DIRC technology (Detection of Internally Reflected Cherenkov light) offers an excellent possibility to minimize the form factor of Cherenkov detectors in hermetic high energy detectors. The PANDA experiment at FAIR in Germany will combine a barrel-shaped DIRC with a disc-shaped DIRC to cover an angular range of 5 to 140 degrees. Particle identification for pions and kaons with a separation power of 3 standard deviations or more will be provided for momenta between 0.5 GeV/c and 3.5 GeV/c in the barrel region and up to 4 GeV/c in the forward region. Even though the concept is simple, the design and construction of a DIRC is challenging. High precision optics and mechanics are required to maintain the angular information of the Cherenkov photons during multiple internal reflections and to focus the individual photons onto position sensitive photon detectors. These sensors must combine high efficiencies for single photons with low dark count rates and good timing resolution at high rates. The choice of radiation hard fused silica for the optical material and of MCP-PMT photon sensors is essential for DIRC detectors to survive in an environment of radiation and strong magnetic field. The two DIRC detectors differ in the focusing optics, in the treatment of chromatic dispersion and in the electronic readout systems. The technical design of the two DIRC detectors and their validation by testing prototypes in a mixed particle beam at CERN are presented.

physics.ins-det↗

arXiv2017

The PANDA DIRC Detectors at FAIR

The PANDA detector at the international accelerator Facility for Antiproton and Ion Research in Europe (FAIR) addresses fundamental questions of hadron physics. An excellent hadronic particle identification (PID) will be accomplished by two DIRC (Detection of Internally Reflected Cherenkov light) counters in the target spectrometer. The design for the barrel region covering polar angles between 22 deg. to 140 deg. is based on the successful BABAR DIRC with several key improvements, such as fast photon timing and a compact imaging region. The novel Endcap Disc DIRC will cover the smaller forward angles between 5 deg. (10 deg.) to 22 deg. in the vertical (horizontal) direction. Both DIRC counters will use lifetime-enhanced microchannel plate PMTs for photon detection in combination with fast readout electronics. Geant4 simulations and tests with several prototypes at various beam facilities have been used to evaluate the designs and validate the expected PID performance of both PANDA DIRC counters.

physics.ins-det↗

arXiv2016

Search for eta-mesic 4He in the dd->3He n pi0 and dd->3He p pi- reactions with the WASA-at-COSY facility

The search for 4He-eta bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd->3He n pi0 and dd->3He p pi- processes. The beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd->4He eta reaction ranging from Q=-70 MeV to Q=30 MeV. The luminosity was determined based on the dd->3He n reaction and quasi-free proton-proton scattering via dd->pp n_spectator n_spectator reactions. The excitation functions determined independently for the measured reactions do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in dd->(4He-eta)_bound->3He n pi0 and dd->(4He-eta)_bound->3He p pi- processes were determined taking into account the isospin relation between both the channels considered. The results of the analysis depend on the assumptions of the N* momentum distribution in the anticipated mesic-4He. Assuming as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in 4He, we determined that (for the mesic bound state width in the range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for npi0 and ppi- channels, respectively. However, based on the recent theoretical findings of the N*(1535) momentum distribution in the N*-3He nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for npi0 and ppi- channels respectively.

nucl-ex↗

arXiv2016

Search for an Isospin I =3 Dibaryon

Various theoretical calculations based on QCD or hadronic interactions predict that in addition to the recently observed dibaryon resonance $d^*(2380)$ with $I(J^P) = 0(3^+)$ there should also exist a dibaryon resonance with mirrored quantum numbers $I(J^P) = 3(0^+)$. We report here on a search for such a $NN$-decoupled state in data on the $pp \to ppπ^+π^+π^-π^-$ reaction. Since no clear-cut evidence has been found, we give upper limits for the production cross section of such a resonance in the mass range 2280 - 2500 MeV.

nucl-ex↗

arXiv2014

Neutron skin of $^{208}$Pb from Coherent Pion Photoproduction

Information on the size and shape of the neutron skin on $^{208}$Pb has been extracted from coherent pion photoproduction cross sections measured using the Crystal Ball together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections the half-height radius and diffuseness of the neutron distribution are found to be 6.70$\pm 0.03(stat)$ fm and 0.55$\pm 0.01(stat)$$^{+0.02}_{-0.03}(sys)$ fm respectively, corresponding to a neutron skin thickness $Δr_{np}$=0.15$\pm 0.03(stat)$$^{+0.01}_{-0.03}(sys)$ fm. The results give the first successful extraction of a neutron skin with an electromagnetic probe and indicate the skin of $^{208}$Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.

nucl-ex↗

arXiv2014

Evidence for a New Resonance from Polarized Neutron-Proton Scattering

Exclusive and kinematically complete high-statistics measurements of quasifree polarized $\vec{n}p$ scattering have been performed in the energy region of the narrow resonance structure $d^*$ with $I(J^P) = 0(3^+)$, $M \approx$ 2380 MeV/$c^2$ and $Γ\approx$ 70 MeV observed recently in the double-pionic fusion channels $pn \to dπ^0π^0$ and $pn \to dπ^+π^-$. The experiment was carried out with the WASA detector setup at COSY having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process $\vec{d}p \to np + p_{spectator}$. That way the $np$ analyzing power $A_y$ was measured over a large angular range. The obtained $A_y$ angular distributions deviate systematically from the current SAID SP07 NN partial-wave solution. Incorporating the new $A_y$ data into the SAID analysis produces a pole in the $^3D_3 - ^3G_3$ waves as expected from the $d^*$ resonance hypothesis.

nucl-ex↗

arXiv2013

Search for the eta-mesic 4He with WASA-at-COSY detector

An exclusive measurement of the excitation function for the dd->3Heppi- reaction was performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 GeV/c to 2.400 GeV/c crossing the kinematic threshold for the eta meson production in the dd->4He-eta reaction at 2.336 GeV/c. The corresponding excess energy with respect to the 4He-eta system varied from -51.4MeV to 22MeV. The integrated luminosity in the experiment was determined using the dd->3Hen reaction. The shape of the excitation function for the dd->3Heppi- was examined. No signal of the 4He-eta bound state was observed. An upper limit for the cross-section for the bound state formation and decay in the process dd->(4He-eta)bound->3Heppi- was determined on the 90% confidence level and it varies from 20nb to 27nb for the bound state width ranging from 5MeV to 35MeV, respectively.

nucl-ex↗

arXiv2012

ABC Resonance Structure in the Double-Pionic Fusion to 4He

Exclusive and kinematically complete high-statistics measurements of the double pionic fusion reaction $dd \to ^4$He$π^0π^0$ have been performed in the energy range 0.8 - 1.4 GeV covering thus the region of the ABC effect, which denotes a pronounced low-mass enhancement in the $ππ$-invariant mass spectrum. The experiments were carried out with the WASA detector setup at COSY. Similar to the observation in the basic $pn \to d π^0π^0$ reaction, the data reveal a correlation between the ABC effect and a resonance-like energy dependence in the total cross section. The maximum occurs at m=2.37 GeV + 2$m_N$, i.e. at the same position as in the basic reaction. The observed resonance width $Γ\approx$ 160 MeV can be understood from broadening due to Fermi motion of the nucleons in initial and final nuclei together with collision damping. Differential cross sections are described equally well by the hypothesis of a $pn$ resonance formation during the reaction process.

nucl-ex↗

arXiv2011

ABC Effect in Basic Double-Pionic Fusion --- Observation of a new resonance?

We report on a high-statistics measurement of the basic double pionic fusion reaction $pn \to dπ^0π^0$ over the energy region of the so-called ABC effect, a pronounced low-mass enhancement in the $ππ$-invariant mass spectrum. The measurements were performed with the WASA detector setup at COSY. The data reveal the ABC effect to be associated with a Lorentzian shaped energy dependence in the integral cross section. The observables are consistent with a resonance with $I(J^P) =0(3^+)$ in both $pn$ and $ΔΔ$ systems. Necessary further tests of the resonance interpretation are discussed.

nucl-ex↗

arXiv2007

Incoherent pion photoproduction on $^{12}$C

We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The $^{12}$C$(γ,π^{0})^{12}$C$^{*}_{4.4MeV}$ reaction has been studied with the Glasgow photon tagger at MAMI employing a new technique which uses the large solid angle Crystal Ball detector both as a $π^{0}$ spectrometer and to detect decay photons from the excited residual nucleus. The technique has potential applications to a broad range of future nuclear measurements with the Crystal Ball and similar detector systems elsewhere. The data are sensitive to the propagation of the $Δ$ in the nuclear medium and will give the first information on matter transition form factors from measurements with an electromagnetic probe. The incoherent cross sections are compared to two theoretical predictions including a $Δ$-hole model.

nucl-ex↗

arXiv1998

Search for Exotic Muon Decays

Recently, it has been proposed that the observed anomaly in the time distribution of neutrino induced reactions, reported by the KARMEN collaboration, can be interpreted as a signal from an exotic muon decay branch mu+ to e+ X. It has been shown that this hypothesis gives an acceptable fit to the KARMEN data if the boson X has a mass of m_X=103.9MeV/c^2, close to the kinematical limit. We have performed a search for the X particle by studying for the first time the very low energy part of the Michel spectrum in mu+ decays. Using a HPGe detector setup at the muE4 beamline at PSI we find branching ratios BR(mu+ to e+ X)<5.7e-4 (90% C.L.) for most of the region 103MeV/c^2<m_X<105MeV/c^2.

hep-ph↗

arXiv1998

The Reaction 7Li(pi+,pi-)7B and its Implications for 7B

The reaction 7Li(pi+,pi-)7B has been measured at incident pion energies of 30-90 MeV. 7Li constitutes the lightest target nucleus, where the pionic charge exchange may proceed as a binary reaction to a discrete final state. Like in the Delta-resonance region the observed cross sections are much smaller than expected from the systematics found for heavier nuclei. In analogy to the neutron halo case of 11Li this cross section suppression is interpreted as evidence for a proton halo in the particle-unstable nucleus 7B.

nucl-ex↗