Kabi Bantawa - Academia.edu (original) (raw)

Papers by Kabi Bantawa

Physical Review C, 2009

The dynamics of the η → 3π 0 decay have been studied with the Crystal Ball multiphoton spectromet... more The dynamics of the η → 3π 0 decay have been studied with the Crystal Ball multiphoton spectrometer and the TAPS calorimeter. Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz microtron MAMI-C and tagged by the Glasgow photon spectrometer were used for η-meson production. The analysis of 3 × 10 6 γp → ηp → 3π 0 p → 6γp events yields the value α = −0.032 ± 0.003 for the η → 3π 0 slope parameter, which agrees with the majority of recent experimental results and has the smallest uncertainty. The π 0 π 0 invariant-mass spectrum was investigated for the occurrence of a cusplike structure in the vicinity of the π + π − threshold. The observed effect is small and does not affect our measured value for the slope parameter.

Physical Review Letters, 2013

The photoproduction of η mesons off nucleons bound in 2H and 3He has been measured in coincidence... more 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.

ABSTRACT The gamman ->K^0 lambda reaction on a liquid deuterium target was measured in the... more ABSTRACT The gamman ->K^0 lambda reaction on a liquid deuterium target was measured in the A2 Hall of the MAMI-C electron accelerator facility at the Institut f"ur Kernphysik in Mainz, Germany. An incident electron beam of energy 1.5 GeV was directed on a 10-mum copper radiator to produce a bremsstrahlung photon beam that was tagged using the Glasgow Photon Tagger. The final-state K^0 and lambda were identified by their decays K^0 ->20ˆ and lambda->0ˆn, respectively. These three 0ˆs were reconstructed by detecting and analyzing the six photons resulting from the 0ˆ decays using the Crystal Ball multiphoton spectrometer and the TAPS detector as a forward wall. This combined detector system covered nearly 4pi in solid angle. Kinematic fitting was used to select good events. This reaction is expected to shine light on isospin-1/2 nucleon resonances in the 1.7-GeV mass range. An experimental overview and preliminary results for differential and integrated cross sections will be presented.

The gamman ->K^0 lambda reaction on a liquid deuterium target was measured in the A2 Hall of t... more The gamman ->K^0 lambda reaction on a liquid deuterium target was measured in the A2 Hall of the MAMI-C electron accelerator facility at the Institut f"ur Kernphysik in Mainz, Germany. An incident electron beam of energy 1.5 GeV was directed on a 10-mum copper radiator to produce a bremsstrahlung photon beam that was tagged using the Glasgow Photon Tagger. The final-state K^0 and lambda were identified by their decays K^0 ->20ˆ and lambda->0ˆn, respectively. These three 0ˆs were reconstructed by detecting and analyzing the six photons resulting from the 0ˆ decays using the Crystal Ball multiphoton spectrometer and the TAPS detector as a forward wall. This combined detector system covered nearly 4pi in solid angle. Kinematic fitting was used to select good events. This reaction is expected to shine light on isospin-1/2 nucleon resonances in the 1.7-GeV mass range. An experimental overview and preliminary results for differential and integrated cross sections will be pre...

Photoproduction of pieta\pi\etapieta-pairs from nucleons has been investigated from threshold up to incid... more Photoproduction of pieta\pi\etapieta-pairs from nucleons has been investigated from threshold up to incident photon energies of approx\approxapprox~1.4~GeV. The quasi-free reactions gammaprightarrowppi0eta\gamma p\rightarrow p\pi^0\etagammaprightarrowppi0eta, gammanrightarrownpi0eta\gamma n\rightarrow n\pi^0\etagammanrightarrownpi0eta, gammaprightarrownpi+eta\gamma p\rightarrow n\pi^+\etagammaprightarrownpi+eta, and gammanrightarrowppi−eta\gamma n\rightarrow p\pi^-\etagammanrightarrowppi−eta were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the gammaprightarrownpi+eta\gamma p\rightarrow n\pi^+\etagammaprightarrownpi+eta reaction was measured for the first time). For the pi0eta\pi^0\etapi0eta final state coherent production via the gammadrightarrowdpi0eta\gamma d\rightarrow d\pi^0\etagammadrightarrowdpi0eta reaction was also investigated. The experiments were performed at the tagged photon beam of the Mainz MAMI accelerator using an almost 4pi4\pi4pi coverage electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The total cross s...

Journal of Nepal Physical Society, 2016

Since 20 years, a very successful experimental program with real photons has been achieved at the... more Since 20 years, a very successful experimental program with real photons has been achieved at the Mainz Microtron (MAMI) facility.The A2 Collaboration at MAINZ is a unique place for the experimental facility of photoproduction reaction. The combination of highly sensitive photo spectrometers Crystal Ball and TAPS as forward wall detector along with particle identification detector and Multiwire proportional chambers as inner wall detectors provide the high precision of the measurement. MAMI-C, which consists of there Race Track Microtrons (RTMs) with the Harmonic Double-Sided Microtron (HDSM) is an intense, stable and continuous-wave accelerator to accelerate electron to 1.5 GeV. This electron beam is responsible to produce real photons via bremsstrahlung process at Glasgow Photon Tagger. A major part of the ongoing and future programme at MAMI will exploit polarised nucleon targets.

The European Physical Journal A, 2016

Quasi-free photoproduction of πη-pairs has been investigated from threshold up to incident photon... more Quasi-free photoproduction of πη-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the πη and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions γp → pπ 0 η, γn → nπ 0 η, γp → nπ + η, and γn → pπ − η from nucleons bound inside the deuteron. For the γp initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of π 0 η pairs from nucleons bound in 3 He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost 4π covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential ∆ ⋆ 3/2 − → η∆(1232) → πηN decay chain, mainly with ∆(1700)3/2 − and ∆(1940)3/2 −. The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data.

The European Physical Journal A, 2015

Total cross sections, angular distributions, and invariant-mass distributions have been measured ... more Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of π 0 π 0 pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557 MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400 MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final state invariant masses up to ≈1550 MeV), where both reactions are dominated by the N (1520)3/2 − → ∆(1232)3/2 + π decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an N ⋆ → N σ decay for the proton, while the reaction is dominated by a sequential decay via a ∆π intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled channel analysis.

The European Physical Journal A, 2013

Physical Review C, 2015

An experimental study of ω photoproduction on the proton was conducted by using the Crystal Ball ... more An experimental study of ω photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The γp → ωp differential cross sections are measured from threshold to the incident-photon energy Eγ = 1.40 GeV (W = 1.87 GeV for the center-of-mass energy) with 15-MeV binning in Eγ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the ωN scattering length αωp is provided.

Physical Review C, 2014

Differential and total cross sections for the quasifree reactions γp → ηp and γn → ηn have been d... more Differential and total cross sections for the quasifree reactions γp → ηp and γn → ηn have been determined at the MAMI-C electron accelerator using a liquid deuterium target. Photons were produced via bremsstrahlung from the 1.5 GeV incident electron beam and energy-tagged with the Glasgow photon tagger. Decay photons of the neutral decay modes η → 2γ and η → 3π 0 → 6γ and coincident recoil nucleons were detected in a combined setup of the Crystal Ball and the TAPS calorimeters. The η-production cross sections were measured in coincidence with recoil protons, recoil neutrons, and in an inclusive mode without a condition on recoil nucleons, which allowed a check of the internal consistency of the data. The effects from nuclear Fermi motion were removed by a kinematic reconstruction of the final-state invariant mass and possible nuclear effects on the quasifree cross section were investigated by a comparison of free and quasifree proton data. The results, which represent a significant improvement in statistical quality compared to previous measurements, agree with the known neutron-to-proton cross-section ratio in the peak of the S11(1535) resonance and confirm a peak in the neutron cross section, which is absent for the proton, at a center-of-mass energy W = (1670 ± 5) MeV with an intrinsic width of Γ ≈ 30 MeV.

Physical review letters, Jan 11, 2014

Precise angular distributions have been measured for the first time for the photoproduction of π0... more Precise angular distributions have been measured for the first time for the photoproduction of π0 mesons off neutrons bound in the deuteron. The effects from nuclear Fermi motion have been eliminated by a complete kinematic reconstruction of the final state. The influence of final-state-interaction effects has been estimated by a comparison of the reaction cross section for quasifree protons bound in the deuteron to the results for free protons and then applied as a correction to the quasifree neutron data. The experiment was performed at the tagged photon facility of the Mainz Microtron MAMI with the Crystal Ball and TAPS detector setup for incident photon energies between 0.45 and 1.4 GeV. The results are compared to the predictions from reaction models and partial-wave analyses based on data from other isospin channels. The model predictions show large discrepancies among each other and the present data will provide much tighter constraints. This is demonstrated by the results of...

Physical Review C, 2014

A new measurement of the rare, doubly radiative decay η → π 0 γγ was conducted with the Crystal B... more A new measurement of the rare, doubly radiative decay η → π 0 γγ was conducted with the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. New data on the dependence of the partial decay width, Γ(η → π 0 γγ), on the two-photon invariant mass squared, m 2 (γγ), as well as a new, more precise value for the decay width, Γ(η → π 0 γγ) = (0.33 ± 0.03tot) eV, are based on analysis of 1.2 × 10 3 η → π 0 γγ decays from a total of 6 × 10 7 η mesons produced in the γp → ηp reaction. The present results for dΓ(η → π 0 γγ)/dm 2 (γγ) are in good agreement with previous measurements and recent theoretical calculations for this dependence.

Measurements of γp → K + Λ and γp → K + Σ 0 cross-sections have been obtained with the photon tag... more Measurements of γp → K + Λ and γp → K + Σ 0 cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel K + meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy (W) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. The new analyses disfavor a strong role for quark-diquark dynamics in the nucleon.

Physics Letters B, 2010

The circular photon asymmetry for π 0 η photoproduction on the proton was measured for the first ... more The circular photon asymmetry for π 0 η photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the ∆(1700)D 33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D 33 amplitude.

Physical Review C, 2009

The dynamics of the η → 3π 0 decay have been studied with the Crystal Ball multiphoton spectromet... more The dynamics of the η → 3π 0 decay have been studied with the Crystal Ball multiphoton spectrometer and the TAPS calorimeter. Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz microtron MAMI-C and tagged by the Glasgow photon spectrometer were used for η-meson production. The analysis of 3 × 10 6 γp → ηp → 3π 0 p → 6γp events yields the value α = −0.032 ± 0.003 for the η → 3π 0 slope parameter, which agrees with the majority of recent experimental results and has the smallest uncertainty. The π 0 π 0 invariant-mass spectrum was investigated for the occurrence of a cusplike structure in the vicinity of the π + π − threshold. The observed effect is small and does not affect our measured value for the slope parameter.

Physical Review Letters, 2013

The photoproduction of η mesons off nucleons bound in 2H and 3He has been measured in coincidence... more 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.

ABSTRACT The gamman ->K^0 lambda reaction on a liquid deuterium target was measured in the... more ABSTRACT The gamman ->K^0 lambda reaction on a liquid deuterium target was measured in the A2 Hall of the MAMI-C electron accelerator facility at the Institut f"ur Kernphysik in Mainz, Germany. An incident electron beam of energy 1.5 GeV was directed on a 10-mum copper radiator to produce a bremsstrahlung photon beam that was tagged using the Glasgow Photon Tagger. The final-state K^0 and lambda were identified by their decays K^0 ->20ˆ and lambda->0ˆn, respectively. These three 0ˆs were reconstructed by detecting and analyzing the six photons resulting from the 0ˆ decays using the Crystal Ball multiphoton spectrometer and the TAPS detector as a forward wall. This combined detector system covered nearly 4pi in solid angle. Kinematic fitting was used to select good events. This reaction is expected to shine light on isospin-1/2 nucleon resonances in the 1.7-GeV mass range. An experimental overview and preliminary results for differential and integrated cross sections will be presented.

The gamman ->K^0 lambda reaction on a liquid deuterium target was measured in the A2 Hall of t... more The gamman ->K^0 lambda reaction on a liquid deuterium target was measured in the A2 Hall of the MAMI-C electron accelerator facility at the Institut f"ur Kernphysik in Mainz, Germany. An incident electron beam of energy 1.5 GeV was directed on a 10-mum copper radiator to produce a bremsstrahlung photon beam that was tagged using the Glasgow Photon Tagger. The final-state K^0 and lambda were identified by their decays K^0 ->20ˆ and lambda->0ˆn, respectively. These three 0ˆs were reconstructed by detecting and analyzing the six photons resulting from the 0ˆ decays using the Crystal Ball multiphoton spectrometer and the TAPS detector as a forward wall. This combined detector system covered nearly 4pi in solid angle. Kinematic fitting was used to select good events. This reaction is expected to shine light on isospin-1/2 nucleon resonances in the 1.7-GeV mass range. An experimental overview and preliminary results for differential and integrated cross sections will be pre...

Photoproduction of pieta\pi\etapieta-pairs from nucleons has been investigated from threshold up to incid... more Photoproduction of pieta\pi\etapieta-pairs from nucleons has been investigated from threshold up to incident photon energies of approx\approxapprox~1.4~GeV. The quasi-free reactions gammaprightarrowppi0eta\gamma p\rightarrow p\pi^0\etagammaprightarrowppi0eta, gammanrightarrownpi0eta\gamma n\rightarrow n\pi^0\etagammanrightarrownpi0eta, gammaprightarrownpi+eta\gamma p\rightarrow n\pi^+\etagammaprightarrownpi+eta, and gammanrightarrowppi−eta\gamma n\rightarrow p\pi^-\etagammanrightarrowppi−eta were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the gammaprightarrownpi+eta\gamma p\rightarrow n\pi^+\etagammaprightarrownpi+eta reaction was measured for the first time). For the pi0eta\pi^0\etapi0eta final state coherent production via the gammadrightarrowdpi0eta\gamma d\rightarrow d\pi^0\etagammadrightarrowdpi0eta reaction was also investigated. The experiments were performed at the tagged photon beam of the Mainz MAMI accelerator using an almost 4pi4\pi4pi coverage electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The total cross s...

Journal of Nepal Physical Society, 2016

Since 20 years, a very successful experimental program with real photons has been achieved at the... more Since 20 years, a very successful experimental program with real photons has been achieved at the Mainz Microtron (MAMI) facility.The A2 Collaboration at MAINZ is a unique place for the experimental facility of photoproduction reaction. The combination of highly sensitive photo spectrometers Crystal Ball and TAPS as forward wall detector along with particle identification detector and Multiwire proportional chambers as inner wall detectors provide the high precision of the measurement. MAMI-C, which consists of there Race Track Microtrons (RTMs) with the Harmonic Double-Sided Microtron (HDSM) is an intense, stable and continuous-wave accelerator to accelerate electron to 1.5 GeV. This electron beam is responsible to produce real photons via bremsstrahlung process at Glasgow Photon Tagger. A major part of the ongoing and future programme at MAMI will exploit polarised nucleon targets.

The European Physical Journal A, 2016

Quasi-free photoproduction of πη-pairs has been investigated from threshold up to incident photon... more Quasi-free photoproduction of πη-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the πη and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions γp → pπ 0 η, γn → nπ 0 η, γp → nπ + η, and γn → pπ − η from nucleons bound inside the deuteron. For the γp initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of π 0 η pairs from nucleons bound in 3 He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost 4π covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential ∆ ⋆ 3/2 − → η∆(1232) → πηN decay chain, mainly with ∆(1700)3/2 − and ∆(1940)3/2 −. The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data.

The European Physical Journal A, 2015

Total cross sections, angular distributions, and invariant-mass distributions have been measured ... more Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of π 0 π 0 pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557 MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400 MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final state invariant masses up to ≈1550 MeV), where both reactions are dominated by the N (1520)3/2 − → ∆(1232)3/2 + π decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an N ⋆ → N σ decay for the proton, while the reaction is dominated by a sequential decay via a ∆π intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled channel analysis.

The European Physical Journal A, 2013

Physical Review C, 2015

An experimental study of ω photoproduction on the proton was conducted by using the Crystal Ball ... more An experimental study of ω photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The γp → ωp differential cross sections are measured from threshold to the incident-photon energy Eγ = 1.40 GeV (W = 1.87 GeV for the center-of-mass energy) with 15-MeV binning in Eγ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the ωN scattering length αωp is provided.

Physical Review C, 2014

Differential and total cross sections for the quasifree reactions γp → ηp and γn → ηn have been d... more Differential and total cross sections for the quasifree reactions γp → ηp and γn → ηn have been determined at the MAMI-C electron accelerator using a liquid deuterium target. Photons were produced via bremsstrahlung from the 1.5 GeV incident electron beam and energy-tagged with the Glasgow photon tagger. Decay photons of the neutral decay modes η → 2γ and η → 3π 0 → 6γ and coincident recoil nucleons were detected in a combined setup of the Crystal Ball and the TAPS calorimeters. The η-production cross sections were measured in coincidence with recoil protons, recoil neutrons, and in an inclusive mode without a condition on recoil nucleons, which allowed a check of the internal consistency of the data. The effects from nuclear Fermi motion were removed by a kinematic reconstruction of the final-state invariant mass and possible nuclear effects on the quasifree cross section were investigated by a comparison of free and quasifree proton data. The results, which represent a significant improvement in statistical quality compared to previous measurements, agree with the known neutron-to-proton cross-section ratio in the peak of the S11(1535) resonance and confirm a peak in the neutron cross section, which is absent for the proton, at a center-of-mass energy W = (1670 ± 5) MeV with an intrinsic width of Γ ≈ 30 MeV.

Physical review letters, Jan 11, 2014

Precise angular distributions have been measured for the first time for the photoproduction of π0... more Precise angular distributions have been measured for the first time for the photoproduction of π0 mesons off neutrons bound in the deuteron. The effects from nuclear Fermi motion have been eliminated by a complete kinematic reconstruction of the final state. The influence of final-state-interaction effects has been estimated by a comparison of the reaction cross section for quasifree protons bound in the deuteron to the results for free protons and then applied as a correction to the quasifree neutron data. The experiment was performed at the tagged photon facility of the Mainz Microtron MAMI with the Crystal Ball and TAPS detector setup for incident photon energies between 0.45 and 1.4 GeV. The results are compared to the predictions from reaction models and partial-wave analyses based on data from other isospin channels. The model predictions show large discrepancies among each other and the present data will provide much tighter constraints. This is demonstrated by the results of...

Physical Review C, 2014

A new measurement of the rare, doubly radiative decay η → π 0 γγ was conducted with the Crystal B... more A new measurement of the rare, doubly radiative decay η → π 0 γγ was conducted with the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. New data on the dependence of the partial decay width, Γ(η → π 0 γγ), on the two-photon invariant mass squared, m 2 (γγ), as well as a new, more precise value for the decay width, Γ(η → π 0 γγ) = (0.33 ± 0.03tot) eV, are based on analysis of 1.2 × 10 3 η → π 0 γγ decays from a total of 6 × 10 7 η mesons produced in the γp → ηp reaction. The present results for dΓ(η → π 0 γγ)/dm 2 (γγ) are in good agreement with previous measurements and recent theoretical calculations for this dependence.

Measurements of γp → K + Λ and γp → K + Σ 0 cross-sections have been obtained with the photon tag... more Measurements of γp → K + Λ and γp → K + Σ 0 cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel K + meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy (W) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. The new analyses disfavor a strong role for quark-diquark dynamics in the nucleon.

Physics Letters B, 2010

The circular photon asymmetry for π 0 η photoproduction on the proton was measured for the first ... more The circular photon asymmetry for π 0 η photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the ∆(1700)D 33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D 33 amplitude.