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Search Results: 1 - 10 of 208479 matches for " L. Witthauer "
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Comment on "Evidence for narrow resonant structures at $W\approx$ 1.68 GeV and $W\approx$ 1.72 GeV in real Compton scattering off the proton"
D. Werthmüller,L. Witthauer,D. I. Glazier,B. Krusche
Physics , 2015, DOI: 10.1103/PhysRevC.92.069801
Abstract: We comment on the statement by Kuznetsov et al. that the structure around W=1.72 GeV seen in the beam asymmetry in Compton scattering off the proton is not observed in the total cross section of $\eta$ photoproduction on the neutron.
Photoproduction of eta-Mesons off 3He
Lilian Witthauer
Physics , 2011,
Abstract: Photoproduction of eta-mesons off 3He has been studied at the MAMI accelerator using the Crystal Ball/TAPS detector setup. The total cross section for the coherent eta-photoproduction was measured with improved statistical quality. Both, the total and differential cross sections show evidence for dominant final state interaction. Additionally, the photoproduction of eta- mesons off quasi-free protons and neutrons was studied. The preliminary cross section on the neutron confirms the narrow bump-like structure at W \simeq 1.7 GeV, which was already seen in different experiments on the deuterium target
Accurate Test of Chiral Dynamics in the \boldmath$\vecγ p \rightarrow π^0p$ Reaction
D. Hornidge,P. Aguar Bartolome,J. R. M. Annand,H. J. Arends,R. Beck,V. Bekrenev,H. Berghaeuser,A. M. Bernstein,A. Braghieri,W. J. Briscoe,S. Cherepnya,M. Dieterle,E. J. Downie,P. Drexler,C. Fernandez-Ramirez,L. V. Filkov,D. I. Glazier,P. Hall Barrientos,E. Heid,M. Hilt,I. Jaegle,O. Jahn,T. C. Jude,V. L. Kashevarov,I. Keshelashvili,R. Kondratiev,M. Korolija,A. Koulbardis,D. Krambrich,S. Kruglov,B. Krusche,A. T. Laffoley,V. Lisin,K. Livingston,I. J. D. MacGregor,J. Mancell,D. M. Manley,E. F. McNicoll,D. Mekterovic,V. Metag,S. Micanovic,D. G. Middleton,K. W. Moores,A. Mushkarenkov,B. M. K. Nefkens,M. Oberle,M. Ostrick,P. B. Otte,B. Oussena,P. Pedroni,F. Pheron,A. Polonski,S. Prakhov,J. Robinson,T. Rostomyan,S. Scherer,S. Schumann,M. H. Sikora,A. Starostin,I. Supek,M. Thiel,A. Thomas,L. Tiator,M. Unverzagt,D. P. Watts,D. Werthmueller,L. Witthauer
Physics , 2012, DOI: 10.1103/PhysRevLett.111.062004
Abstract: A precision measurement of the differential cross sections $d\sigma/d\Omega$ and the linearly polarized photon asymmetry $\Sigma \equiv (d\sigma_\perp - d\sigma_\parallel) \slash (d\sigma_\perp + d\sigma_\parallel)$ for the $\vec{\gamma} p \rightarrow \pi^0p$ reaction in the near-threshold region has been performed with a tagged photon beam and almost $4\pi$ detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multi-photon detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the $S$- and all three $P$-wave amplitudes for the first time and provide the most stringent test to date of the predictions of Chiral Perturbation Theory and its energy region of agreement with experiment.
First measurement of target and beam-target asymmetries in the $γ p\to π^0ηp$ reaction
J. R. M. Annand,H. J. Arends,R. Beck,N. Borisov,A. Braghieri,W. J. Briscoe,S. Cherepnya,C. Collicott,S. Costanza,E. J. Downie,M. Dieterle,A. Fix,L. V. Fil'kov,S. Garni,D. I. Glazier,W. Gradl,G. Gurevich,P. H. Barrientos,D. Hamilton,D. Hornidge,D. Howdle,G. M. Huber,V. L. Kashevarov,I. Keshelashvili,R. Kondratiev,M. Korolija,B. Krusche,A. Lazarev,V. Lisin,K. Livingston,I. J. D. MacGregor,J. Mancel,D. M. Manley,P. Martel,E. F. McNicoll,W. Meyer,D. Middleton,R. Miskimen,A. Mushkarenkov,A. Neganov,A. Nikolaev,M. Oberle,H. Ortega,M. Ostrick,P. Ott,P. B. Otte,B. Oussena,P. Pedroni,A. Polonski,V. V. Polyanski,S. Prakhov,G. Reicherz,T. Rostomyan,A. Sarty,S. Schumann,O. Steffen,I. I. Strakovsky,T. Strub,I. Supek,L. Tiator,A. Thomas,M. Unverzagt,Y. A. Usov,D. P. Watts,D. Werthmüller,L. Witthauer,M. Wolfes
Physics , 2015, DOI: 10.1103/PhysRevC.91.055208
Abstract: The first data on target and beam-target asymmetries for the $\gamma p\to\pi^0\eta p$ reaction at photon energies from 1050 up to 1450 MeV are presented. The measurements were performed using the Crystal Ball and TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The general assumption that the reaction is dominated by the $\Delta 3/2^-$ amplitude is confirmed. The data are in particular sensitive to small contributions from other partial waves.
Measurement of 3pi^0 photoproduction on the proton from threshold to 1.4 GeV
A. Starostin,I. M. Suarez,B. M. K. Nefkens,J. Ahrens,J. R. M. Annand,H. J. Arends,K. Bantawa,P. A. Bartolome,R. Beck,V. Bekrenev,A. Braghieri,D. Branford,W. J. Briscoe,J. Brudvik,S. Cherepnya,M. Dieterle,E. J. Downie,L. V. Fil'kov,D. I. Glazier,R. Gregor,E. Heid,D. Hornidge,I. Jaegle,O. Jahn,T. C. Jude,V. L. Kashevarov,I. Keshelashvili,R. Kondratiev,M. Korolija,A. Koulbardis,S. Kruglov,B. Krusche,V. Lisin,K. Livingston,I. J. D. MacGregor,D. M. Manley,M. Martinez,J. C. McGeorge,E. F. McNicoll,V. Metag,A. Mushkarenkov,M. Oberle,M. Ostrick,P. Pedroni,A. Polonski,S. Prakhov,J. Robinson,G. Rosner,T. Rostomyan,S. Schumann,M. H. Sikora,D. Sober,I. Supek,M. Thiel,A. Thomas,M. Unverzagt,D. P. Watts,D. Wertmueller,L. Witthauer
Physics , 2011,
Abstract: The total cross section for gamma p -> 3pi0 p has been measured for the first time from threshold to 1.4 GeV using the tagged photon beam of the Mainz Microtron. The equipment utilized the Crystal Ball multiphoton spectrometer, the TAPS forward detector and a particle identification detector. The gamma p -> 3pi0 p total cross section has two broad enhancements at sqrt{s}~1.5 GeV and 1.7 GeV. We obtained the ratio of the total cross sections gamma p -> 3pi0 p to gamma p -> eta p equal to 0.014 \pm 0.001 at sqrt{s}~1.5 GeV.
Quasi-free photoproduction of eta-mesons off the deuteron
I. Jaegle,B. Krusche,A. V. Anisovich,J. C. S. Bacelar,B. Bantes,O. Bartholomy,D. E. Bayadilov,R. Beck,Y. A. Beloglazov,R. Castelijns,V. Crede,M. Dieterle,H. Dutz,D. Elsner,R. Ewald,F. Frommberger,C. Funke,R. Gothe,R. Gregor,A. B. Gridnev,E. Gutz,W. Hillert,S. Hoeffgen,P. Hoffmeister,I. Horn,J. Junkersfeld,H. Kalinowsky,S. Kammer,I. Keshelashvili,V. Kleber,Frank Klein,Friedrich Klein,E. Klempt,M. Konrad,M. Kotulla,M. Lang,H. Loehner,I. V. Lopatin,S. Lugert,Y. Maghrbi,D. Menze,T. Mertens,J. G. Messchendorp,V. Metag,V. A. Nikonov,M. Nanova,D. V. Novinski,R. Novotny,M. Oberle,M. Ostrick,L. M. Pant,H. van Pee,M. Pfeiffer,F. Pheron,A. Roy,A. V. Sarantsev,S. Schadmand,C. Schmidt,H. Schmieden,B. Schoch,S. V. Shende,V. Sokhoyan,A. Suele,V. V. Sumachev,T. Szczepanek,U. Thoma,D. Trnka,R. Varma,D. Walther,C. Wendel,D. Werthmueller,L. Witthauer
Physics , 2011, DOI: 10.1140/epja/i2011-11089-0
Abstract: Precise data for quasi-free photoproduction of $\eta$ mesons off the deuteron have been measured at the Bonn ELSA accelerator with the combined Crystal Barrel/TAPS detector for incident photon energies up to 2.5 GeV. The $\eta$-mesons have been detected in coincidence with recoil protons and neutrons. Possible nuclear effects like Fermi motion and re-scattering can be studied via a comparison of the quasi-free reaction off the bound proton to $\eta$-production off the free proton. No significant effects beyond the folding of the free cross section with the momentum distribution of the bound protons have been found. These Fermi motion effects can be removed by an analysis using the invariant mass of the $\eta$-nucleon pairs reconstructed from the final state four-momenta of the particles. The total cross section for quasi-free $\eta$-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around 1 GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant mass spectrum of the $\eta$-neutron pairs. Position and width of the peak in the invariant mass spectrum are $W\approx 1665$ MeV and FWHM $\Gamma\approx 25$ MeV. The data are compared to the results of different models.
Measurement of pi^0 photoproduction on the proton at MAMI C
P. Adlarson,F. Afzal,C. S. Akondi,J. R. M. Annand,H. J. Arends,Ya. I. Azimov,R. Beck,N. Borisov,A. Braghieri,W. J. Briscoe,S. Cherepnya,F. Cividini,C. Collicott,S. Costanza,A. Denig,E. J. Downie,M. Dieterle,M. I. Ferretti Bondy,L. V. Fil'kov,A. Fix,S. Gardner,S. Garni,D. I. Glazier,D. Glowa,W. Gradl,G. Gurevich,D. J. Hamilton,D. Hornidge,G. M. Huber,A. K?ser,V. L. Kashevarov,S. Kay,I. Keshelashvili,R. Kondratiev,M. Korolija,B. Krusche,V. V. Kulikov,A. Lazarev,J. Linturi,V. Lisin,K. Livingston,I. J. D. MacGregor,D. M. Manley,P. P. Martel,M. Martemianov,J. C. McGeorge,W. Meyer,D. G. Middleton,R. Miskimen,A. Mushkarenkov,A. Neganov,A. Neiser,M. Oberle,M. Ostrick,P. Ott,P. B. Otte,B. Oussena,D. Paudyal,P. Pedroni,A. Polonski,V. V. Polyanski,S. Prakhov,A. Rajabi,G. Reicherz,G. Ron,T. Rostomyan,A. Sarty,D. M. Schott,S. Schumann,C. Sfienti,V. Sokhoyan,K. Spieker,O. Steffen,I. I. Strakovsky,Th. Strub,I. Supek,M. F. Taragin,A. Thiel,M. Thiel,L. Tiator,A. Thomas,M. Unverzagt,Yu. A. Usov,S. Wagner,D. P. Watts,D. Werthmüller,J. Wettig,L. Witthauer,M. Wolfes,R. L. Workman,L. A. Zana
Physics , 2015, DOI: 10.1103/PhysRevC.92.024617
Abstract: Differential cross sections for the gamma p -> pi^0 p reaction have been measured with the A2 tagged-photon facilities at the Mainz Microtron, MAMI C, up to the center-of-mass energy W=1.9 GeV. The new results, obtained with a fine energy and angular binning, increase the existing quantity of pi^0 photoproduction data by ~47%. Owing to the unprecedented statistical accuracy and the full angular coverage, the results are sensitive to high partial-wave amplitudes. This is demonstrated by the decomposition of the differential cross sections in terms of Legendre polynomials and by further comparison to model predictions. A new solution of the SAID partial-wave analysis obtained after adding the new data into the fit is presented.
Measurement of the g p -> K^0 Sigma^+ reaction with the Crystal Ball/TAPS detectors at the Mainz Microtron
P. Aguar-Bartolomé,J. R. M. Annand,H. J. Arends,K. Bantawa,R. Beck,V. Bekrenev,H. Bergh?user,A. Braghieri,W. J. Briscoe,J. Brudvik,S. Cherepnya,R. F. B. Codling,C. Collicott,B. Demissie,M. Dieterle,E. J. Downie,P. Drexler,L. V. Fil'kov,A. Fix,D. I. Glazier,R. Gregor,D. Hamilton,E. Heid,D. Hornidge,D. Howdle,L. Isaksson,I. Jaegle,O. Jahn,T. C. Jude,V. L. Kashevarov,I. Keshelashvili,R. Kondratiev,M. Korolija,M. Kotulla,A. Koulbardis,S. Kruglov,B. Krusche,V. Lisin,K. Livingston,I. J. D. MacGregor,Y. Maghrbi,J. Mancel,D. M. Manley,E. F. McNicoll,D. Mekterovic,V. Metag,A. Mushkarenkov,B. M. K. Nefkens,A. Nikolaev,R. Novotny,M. Oberle,H. Ortega,M. Ostrick,P. Ott,P. B. Otte,B. Oussena,P. Pedroni,F. Pheron,A. Polonski,S. Prakhov,J. Robinson,G. Rosner,T. Rostomyan,S. Schumann,M. H. Sikora,D. I. Sober,A. Starostin,I. I. Strakovsky,I. M. Suarez,I. Supek,C. M. Tarbert,M. Thiel,A. Thomas,M. Unverzagt,D. P. Watts,D. Werthmüller,L. Witthauer,F. Zehr.
Physics , 2013, DOI: 10.1103/PhysRevC.88.044601
Abstract: The g p -> K^0 Sigma^+ reaction has been measured from threshold to Eg=1.45 GeV (W_cm=1.9 GeV) using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. In the present experiment, this reaction was searched for in the 3pi^0 p final state, by assuming K^0_S -> pi^0 pi^0 and Sigma^+ -> pi^0 p. The experimental results include total and differential cross sections as well as the polarization of the recoil hyperon. The new data significantly improve empirical knowledge about the g p -> K^0 Sigma^+ reaction in the measured energy range. The results are compared to previous measurements and model predictions. It is demonstrated that adding the present g p -> K^0 Sigma^+ results to existing data allowed a better description of this reaction with various models.
Measurement of the transverse target and beam-target asymmetries in $η$ meson photoproduction at MAMI
C. S. Akondi,J. R. M. Annand,H. J. Arends,R. Beck,A. Bernstein,N. Borisov,A. Braghieri,W. J. Briscoe,S. Cherepnya,C. Collicott,S. Costanza,E. J. Downie,M. Dieterle,A. Fix,L. V. Fil'kov,S. Garni,D. I. Glazier,W. Gradl,G. Gurevich,P. Hall Barrientos,D. Hamilton,D. Hornidge,D. Howdle,G. M. Huber,V. L. Kashevarov,I. Keshelashvili,R. Kondratiev,M. Korolija,B. Krusche,A. Lazarev,V. Lisin,K. Livingston,I. J. D. MacGregor,J. Mancel,D. M. Manley,P. Martel,E. F. McNicoll,W. Meyer,D. Middleton,R. Miskimen,A. Mushkarenkov,B. M. K. Nefkens,A. Neganov,A. Nikolaev,M. Oberle,M. Ostrick,H. Ortega,P. Ott,P. B. Otte,B. Oussena,P. Pedroni,A. Polonski,V. V. Polyanski,S. Prakhov,G. Reicherz,T. Rostomyan,A. Sarty,S. Schumann,O. Steffen,I. I. Strakovsky,Th. Strub,I. Supek,L. Tiator,A. Thomas,M. Unverzagt,Yu. A. Usov,D. P. Watts,D. Werthmüller,L. Witthauer,M. Wolfes
Physics , 2014, DOI: 10.1103/PhysRevLett.113.102001
Abstract: We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $\vec \gamma \vec p\to\eta p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $\eta$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed.
Measurements of Double-Polarized Compton Scattering Asymmetries and Extraction of the Proton Spin Polarizabilities
P. P. Martel,R. Miskimen,P. Aguar-Bartolome,J. Ahrens,C. S. Akondi,J. R. M. Annand,H. J. Arends,W. Barnes,R. Beck,A. Bernstein,N. Borisov,A. Braghieri,W. J. Briscoe,S. Cherepnya,C. Collicott,S. Costanza,A. Denig,M. Dieterle,E. J. Downie,L. V. Fil'kov,S. Garni,D. I. Glazier,W. Gradl,G. Gurevich,P. Hall Barrientos,D. Hamilton,D. Hornidge,D. Howdle,G. M. Huber,T. C. Jude,A. Kaeser,V. L. Kashevarov,I. Keshelashvili,R. Kondratiev,M. Korolija,B. Krusche,A. Lazarev,V. Lisin,K. Livingston,I. J. D. MacGregor,J. Mancell,D. M. Manley,W. Meyer,D. G. Middleton,A. Mushkarenkov,B. M. K. Nefkens,A. Neganov,A. Nikolaev,M. Oberle,H. Ortega Spina,M. Ostrick,P. Ott,P. B. Otte,B. Oussena,P. Pedroni,A. Polonski,V. Polyansky,S. Prakhov,A. Rajabi,G. Reicherz,T. Rostomyan,A. Sarty,S. Schrauf,S. Schumann,M. H. Sikora,A. Starostin,O. Steffen,I. I. Strakovsky,T. Strub,I. Supek,M. Thiel,L. Tiator,A. Thomas,M. Unverzagt,Y. Usov,D. P. Watts,L. Witthauer,D. Werthmüller,M. Wolfes
Physics , 2014, DOI: 10.1103/PhysRevLett.114.112501
Abstract: The spin polarizabilities of the nucleon describe how the spin of the nucleon responds to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is through polarized Compton scattering. Double-polarized Compton scattering asymmetries on the proton were measured in the $\Delta(1232)$ region using circularly polarized incident photons and a transversely polarized proton target at the Mainz Microtron. Fits to asymmetry data were performed using a dispersion model calculation and a baryon chiral perturbation theory calculation, and a separation of all four proton spin polarizabilities in the multipole basis was achieved. The analysis based on a dispersion model calculation yields $\gamma_{E1E1} = -3.5 \pm 1.2$, $\gamma_{M1M1}= 3.16 \pm 0.85$, $\gamma_{E1M2} = -0.7 \pm 1.2$, and $\gamma_{M1E2} = 1.99 \pm 0.29$, in units of $10^{-4}$ fm$^4$.
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