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  1. Book ; Online: The PANDA Barrel DIRC

    Dzhygadlo, R. / Belias, A. / Gerhardt, A. / Lehmann, D. / Peters, K. / Schepers, G. / Schwarz, C. / Schwiening, J. / Traxler, M. / Wolf, Y. / Schmitt, L. / Böhm, M. / Gumbert, K. / Krauss, S. / Lehmann, A. / Miehling, D. / Düren, M. / Hayrapetyan, A. / Köseoglu, I. /
    Schmidt, M. / Wasem, T. / Sfienti, C. / Ali, A.

    2024  

    Abstract: The PANDA experiment at the international accelerator Facility for Antiproton and Ion Research in Europe (FAIR), Darmstadt, Germany, will address fundamental questions of hadron physics using $\bar{p}p$ annihilations. Excellent Particle Identification ( ... ...

    Abstract The PANDA experiment at the international accelerator Facility for Antiproton and Ion Research in Europe (FAIR), Darmstadt, Germany, will address fundamental questions of hadron physics using $\bar{p}p$ annihilations. Excellent Particle Identification (PID) over a large range of solid angles and particle momenta will be essential to meet the objectives of the rich physics program. Charged PID in the target region will be provided by a Barrel DIRC (Detection of Internally Reflected Cherenkov light) counter. The Barrel DIRC, covering the polar angle range of 22-140 degrees, will provide a $\pi/K$ separation power of at least 3 standard deviations for charged particle momenta up to 3.5 GeV/c. The design of the Barrel DIRC features narrow radiator bars made from synthetic fused silica, an innovative multi-layer spherical lens focusing system, a prism-shaped synthetic fused silica expansion volume, and an array of lifetime-enhanced Microchannel Plate PMTs (MCP-PMTs) to detect the hit location and arrival time of the Cherenkov photons. Detailed Monte-Carlo simulations were performed, and reconstruction methods were developed to study the performance of the system. All critical aspects of the design and the performance were validated with system prototypes in a mixed hadron beam at the CERN PS. In 2020 the PANDA Barrel DIRC project advanced from the design stage to component fabrication. The series production of the fused silica bars was successfully completed in 2021 and delivery of the MCP-PMTs started in May 2022.

    Comment: XI International Workshop on Ring Imaging Cherenkov Detectors
    Keywords High Energy Physics - Experiment ; Physics - Instrumentation and Detectors
    Subject code 621
    Publishing date 2024-01-12
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article ; Online: Measurement of the α-Particle Monopole Transition Form Factor Challenges Theory: A Low-Energy Puzzle for Nuclear Forces?

    Kegel, S / Achenbach, P / Bacca, S / Barnea, N / Beričič, J / Bosnar, D / Correa, L / Distler, M O / Esser, A / Fonvieille, H / Friščić, I / Heilig, M / Herrmann, P / Hoek, M / Klag, P / Kolar, T / Leidemann, W / Merkel, H / Mihovilovič, M /
    Müller, J / Müller, U / Orlandini, G / Pochodzalla, J / Schlimme, B S / Schoth, M / Schulz, F / Sfienti, C / Širca, S / Spreckels, R / Stöttinger, Y / Thiel, M / Tyukin, A / Walcher, T / Weber, A

    Physical review letters

    2023  Volume 130, Issue 15, Page(s) 152502

    Abstract: We perform a systematic study of the α-particle excitation from its ground state 0_{1}^{+} to the 0_{2}^{+} resonance. The so-called monopole transition form factor is investigated via an electron scattering experiment in a broad Q^{2} range (from 0.5 to ...

    Abstract We perform a systematic study of the α-particle excitation from its ground state 0_{1}^{+} to the 0_{2}^{+} resonance. The so-called monopole transition form factor is investigated via an electron scattering experiment in a broad Q^{2} range (from 0.5 to 5.0  fm^{-2}). The precision of the new data dramatically supersedes that of older sets of data, each covering only a portion of the Q^{2} range. The new data allow the determination of two coefficients in a low-momentum expansion, leading to a new puzzle. By confronting experiment to state-of-the-art theoretical calculations, we observe that modern nuclear forces, including those derived within chiral effective field theory that are well tested on a variety of observables, fail to reproduce the excitation of the α particle.
    Language English
    Publishing date 2023-04-28
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.130.152502
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  3. Article ; Online: Neutron skin studies of medium and heavy nuclei

    Thiel M. / Becker D. / Ferretti M. / Kumar K. / Sfienti C.

    EPJ Web of Conferences, Vol 73, p

    2014  Volume 07007

    Abstract: The recent PREX experiment at JLab has demonstrated the sensitivity of parity violating electron scattering to the neutron density, meanwhile outlining its major experimental challenges. On the other side, intermediate energy photons are an ideal probe ... ...

    Abstract The recent PREX experiment at JLab has demonstrated the sensitivity of parity violating electron scattering to the neutron density, meanwhile outlining its major experimental challenges. On the other side, intermediate energy photons are an ideal probe for studying the properties of strongly interacting matter from the nuclear scale down to the sub-nuclear components of the nucleus. Among others coherent pion photoproduction can provide information on the existence and nature of neutron skins in nuclei. The simultaneous combination of different techniques allows a systematic determination across the periodic table thus benchmarking modern calculation. Recently a systematic investigation of the latter method has been exploited at MAMI (Mainz). At MESA the same setup as in the measurement of the weak mixing angle can be used to determine the parity-violating asymmetry for polarized electrons scattered on heavy nuclei with a 1% resolution. Status and prospects of the projects are presented.
    Keywords Physics ; QC1-999 ; Science ; Q
    Language English
    Publishing date 2014-06-01T00:00:00Z
    Publisher EDP Sciences
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article ; Online: First Measurement Using Elliptically Polarized Photons of the Double-Polarization Observable E for γp→pπ^{0} and γp→nπ^{+}.

    Afzal, F / Spieker, K / Hurck, P / Abt, S / Achenbach, P / Adlarson, P / Ahmed, Z / Akondi, C S / Annand, J R M / Arends, H J / Bashkanov, M / Beck, R / Biroth, M / Borisov, N / Braghieri, A / Briscoe, W J / Cividini, F / Collicott, C / Costanza, S /
    Denig, A / Dieterle, M / Downie, E J / Drexler, P / Fegan, S / Gardner, S / Ghosal, D / Glazier, D I / Gorodnov, I / Gradl, W / Gurevich, D / Heijkenskjöld, L / Hornidge, D / Huber, G M / Kashevarov, V L / Kay, S J D / Korolija, M / Krusche, B / Lazarev, A / Livingston, K / Lutterer, S / MacGregor, I J D / Macrae, R G / Manley, D M / Martel, P P / Miskimen, R / Mocanu, M / Mornacchi, E / Mullen, C / Neganov, A / Neiser, A / Oberle, M / Ostrick, M / Otte, P B / Paudyal, D / Pedroni, P / Powell, A / Reicherz, G / Rostomyan, T / Sfienti, C / Sokhoyan, V / Steffen, O / Strakovsky, I I / Strub, T / Supek, I / Thiel, A / Thiel, M / Thomas, A / Usov, Yu A / Wagner, S / Walford, N K / Watts, D P / Werthmüller, D / Wettig, J / Witthauer, L / Wolfes, M / Zachariou, N

    Physical review letters

    2024  Volume 132, Issue 12, Page(s) 121902

    Abstract: We report the measurement of the helicity asymmetry E for the pπ^{0} and nπ^{+} final states using, for the first time, an elliptically polarized photon beam in combination with a longitudinally polarized target at the Crystal Ball experiment at MAMI. ... ...

    Abstract We report the measurement of the helicity asymmetry E for the pπ^{0} and nπ^{+} final states using, for the first time, an elliptically polarized photon beam in combination with a longitudinally polarized target at the Crystal Ball experiment at MAMI. The results agree very well with data that were taken with a circularly polarized photon beam, showing that it is possible to simultaneously measure polarization observables that require linearly (e.g., G) and circularly polarized photons (e.g., E) and a longitudinally polarized target. The new data cover a photon energy range 270-1400 MeV for the pπ^{0} final state (230-842 MeV for the nπ^{+} final state) and the full range of pion polar angles, θ, providing the most precise measurement of the observable E. A moment analysis gives a clear observation of the pη cusp in the pπ^{0} final state.
    Language English
    Publishing date 2024-04-05
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.132.121902
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Book ; Online: The percolation phase transition and statistical multifragmentation in finite systems

    Pietrzak, T. / Botvina, A. S. / Brzychczyk, J. / Buyukcizmeci, N. / Fèvree, A. Le / Łukasik, J. / Pawłowski, P. / Sfienti, C. / Trautmann, W. / Wieloch, A.

    2020  

    Abstract: The cumulant ratios up to fourth order of the $Z$ distributions of the largest fragment in spectator fragmentation following $^{107,124}$Sn+Sn and $^{124}$La+Sn collisions at 600 MeV/nucleon have been investigated. They are found to exhibit the ... ...

    Abstract The cumulant ratios up to fourth order of the $Z$ distributions of the largest fragment in spectator fragmentation following $^{107,124}$Sn+Sn and $^{124}$La+Sn collisions at 600 MeV/nucleon have been investigated. They are found to exhibit the signatures of a second-order phase transition established with cubic bond percolation and previously observed in the ALADIN experimental data for fragmentation of $^{197}$Au projectiles at similar energies. The deduced pseudocritical points are found to be only weakly dependent on the $A/Z$ ratio of the fragmenting spectator source. The same holds for the corresponding chemical freeze-out temperatures of close to 6 MeV. The experimental cumulant distributions are quantitatively reproduced with the Statistical Multifragmentation Model and parameters used to describe the experimental fragment multiplicities, isotope distributions and their correlations with impact-parameter related observables in these reactions. The characteristic coincidence of the zero transition of the skewness with the minimum of the kurtosis excess appears to be a generic property of statistical models and is found to coincide with the maximum of the heat capacity in the canonical thermodynamic fragmentation model.

    Comment: 13 pages, 5 figures
    Keywords Nuclear Experiment
    Subject code 612
    Publishing date 2020-09-02
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  6. Article: Experimental evidence of (2)He decay from (18)Ne excited states.

    Raciti, G / Cardella, G / De Napoli, M / Rapisarda, E / Amorini, F / Sfienti, C

    Physical review letters

    2008  Volume 100, Issue 19, Page(s) 192503

    Abstract: Two-proton decay from (18)Ne excited states has been studied by complete kinematical reconstruction of the decay products. The (18)Ne nucleus has been produced as a radioactive beam by (20)Ne primary projectile fragmentation at 45 AMeV incident energy on ...

    Abstract Two-proton decay from (18)Ne excited states has been studied by complete kinematical reconstruction of the decay products. The (18)Ne nucleus has been produced as a radioactive beam by (20)Ne primary projectile fragmentation at 45 AMeV incident energy on a Be target. The (18)Ne at 33 AMeV incident energy has been excited via Coulomb excitation on a (nat)Pb target. The obtained results unambiguously show that the 6.15 MeV (18)Ne state two-proton decay proceeds through a (2)He diproton resonance (31%) and democratic or virtual sequential decay (69%). The quoted branching ratio has been deduced from relative angle and momentum correlations of the emitted proton pairs.
    Language English
    Publishing date 2008-05-16
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.100.192503
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  7. Article ; Online: New Insight in the Q^{2} Dependence of Proton Generalized Polarizabilities.

    Beričič, J / Correa, L / Benali, M / Achenbach, P / Ayerbe Gayoso, C / Bernauer, J C / Blomberg, A / Böhm, R / Bosnar, D / Debenjak, L / Denig, A / Distler, M O / Downie, E J / Esser, A / Fonvieille, H / Friščić, I / Kegel, S / Kohl, Y / Makek, M /
    Merkel, H / Middleton, D G / Mihovilovič, M / Müller, U / Nungesser, L / Paolone, M / Pochodzalla, J / Sánchez Majos, S / Schlimme, B S / Schoth, M / Schulz, F / Sfienti, C / Širca, S / Sparveris, N / Štajner, S / Thiel, M / Tyukin, A / Weber, A / Weinriefer, M

    Physical review letters

    2019  Volume 123, Issue 19, Page(s) 192302

    Abstract: Virtual Compton scattering on the proton has been investigated at three yet unexplored values of the four-momentum transfer Q^{2}: 0.10, 0.20, and 0.45  GeV^{2}, at the Mainz Microtron. Fits performed using either the low-energy theorem or dispersion ... ...

    Abstract Virtual Compton scattering on the proton has been investigated at three yet unexplored values of the four-momentum transfer Q^{2}: 0.10, 0.20, and 0.45  GeV^{2}, at the Mainz Microtron. Fits performed using either the low-energy theorem or dispersion relations allowed the extraction of the structure functions P_{LL}-P_{TT}/ε and P_{LT}, as well as the electric and magnetic generalized polarizabilities α_{E1}(Q^{2}) and β_{M1}(Q^{2}). These new results show a smooth and rapid falloff of α_{E1}(Q^{2}), in contrast to previous measurements at Q^{2}=0.33  GeV^{2}, and provide for the first time a precise mapping of β_{M1}(Q^{2}) in the low-Q^{2} region.
    Language English
    Publishing date 2019-11-19
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.123.192302
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  8. Article ; Online: First Measurement of the Q^{2} Dependence of the Beam-Normal Single Spin Asymmetry for Elastic Scattering off Carbon.

    Esser, A / Thiel, M / Achenbach, P / Aulenbacher, K / Baunack, S / Beričič, J / Bosnar, D / Correa, L / Dehn, M / Distler, M O / Fonvieille, H / Friščić, I / Gorchtein, M / Heidrich, S / Herrmann, P / Hoek, M / Kegel, S / Kohl, Y / Kolar, T /
    Kreidel, H-J / Maas, F E / Merkel, H / Mihovilovič, M / Müller, J / Müller, U / Nillius, F / Palatchi, C / Paschke, K D / Pochodzalla, J / Schlimme, B S / Schoth, M / Schulz, F / Širca, S / Spruck, B / Štajner, S / Tioukine, V / Tyukin, A / Weber, A / Sfienti, C

    Physical review letters

    2018  Volume 121, Issue 2, Page(s) 22503

    Abstract: We report on the first Q^{2}-dependent measurement of the beam-normal single spin asymmetry A_{n} in the elastic scattering of 570 MeV vertically polarized electrons off ^{12}C. We cover the Q^{2} range between 0.02 and 0.05  GeV^{2}/c^{2} and determine ... ...

    Abstract We report on the first Q^{2}-dependent measurement of the beam-normal single spin asymmetry A_{n} in the elastic scattering of 570 MeV vertically polarized electrons off ^{12}C. We cover the Q^{2} range between 0.02 and 0.05  GeV^{2}/c^{2} and determine A_{n} at four different Q^{2} values. The experimental results are compared to a theoretical calculation that relates A_{n} to the imaginary part of the two-photon exchange amplitude. The result emphasizes that the Q^{2} behavior of A_{n} given by the ratio of the Compton to charge form factors cannot be treated independently of the target nucleus.
    Language English
    Publishing date 2018-07-13
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.121.022503
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  9. Article ; Online: Beam-Recoil Polarization Measurement of π^{0} Electroproduction on the Proton in the Region of the Roper Resonance.

    Štajner, S / Achenbach, P / Beranek, T / Beričič, J / Bernauer, J C / Bosnar, D / Böhm, R / Correa, L / Denig, A / Distler, M O / Esser, A / Fonvieille, H / Friedrich, J M / Friščić, I / Kegel, S / Kohl, Y / Merkel, H / Mihovilovič, M / Müller, J /
    Müller, U / Nungesser, L / Pochodzalla, J / Schlimme, B S / Schoth, M / Schulz, F / Sfienti, C / Širca, S / Thiel, M / Tiator, L / Tyukin, A / Weber, A / Yaron, I

    Physical review letters

    2017  Volume 119, Issue 2, Page(s) 22001

    Abstract: The helicity-dependent recoil proton polarizations P_{x}^{'} and P_{z}^{'} as well as the helicity-independent component P_{y} have been measured in the p(e[over →],e^{'}p[over →])π^{0} reaction at four-momentum transfer Q^{2}≃0.1  GeV^{2}, center-of- ... ...

    Abstract The helicity-dependent recoil proton polarizations P_{x}^{'} and P_{z}^{'} as well as the helicity-independent component P_{y} have been measured in the p(e[over →],e^{'}p[over →])π^{0} reaction at four-momentum transfer Q^{2}≃0.1  GeV^{2}, center-of-mass proton emission angle θ_{p}^{*}≃90°, and invariant mass W≃1440  MeV. This first precise measurement of double-polarization observables in the energy domain of the Roper resonance P_{11}(1440) by exploiting recoil polarimetry has allowed for the extraction of its scalar electroexcitation amplitude at an unprecedentedly low value of Q^{2}, establishing a powerful instrument for probing the interplay of quark and meson degrees of freedom in the nucleon.
    Language English
    Publishing date 2017-07-14
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.119.022001
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  10. Article ; Online: Signatures of the d^{*}(2380) Hexaquark in d(γ,pn[over →]).

    Bashkanov, M / Watts, D P / Kay, S J D / Abt, S / Achenbach, P / Adlarson, P / Afzal, F / Ahmed, Z / Akondi, C S / Annand, J R M / Arends, H J / Beck, R / Biroth, M / Borisov, N / Braghieri, A / Briscoe, W J / Cividini, F / Collicott, C / Costanza, S /
    Denig, A / Downie, E J / Drexler, P / Fegan, S / Fix, A / Gardner, S / Ghosal, D / Glazier, D I / Gorodnov, I / Gradl, W / Günther, M / Gurevich, D / Heijkenskjöld, L / Hornidge, D / Huber, G M / Käser, A / Kashevarov, V L / Korolija, M / Krusche, B / Lazarev, A / Livingston, K / Lutterer, S / MacGregor, I J D / Manley, D M / Martel, P P / Miskimen, R / Mornacchi, E / Mullen, C / Neganov, A / Neiser, A / Ostrick, M / Otte, P B / Paudyal, D / Pedroni, P / Powell, A / Prakhov, S N / Ron, G / Sarty, A / Sfienti, C / Sokhoyan, V / Spieker, K / Steffen, O / Strakovsky, I I / Strub, T / Supek, I / Thiel, A / Thiel, M / Thomas, A / Usov, Yu A / Wagner, S / Walford, N K / Werthmüller, D / Wettig, J / Wolfes, M / Zachariou, N / Zana, L A

    Physical review letters

    2020  Volume 124, Issue 13, Page(s) 132001

    Abstract: We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured photon energy range of 300-700 MeV provides the first ... ...

    Abstract We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured photon energy range of 300-700 MeV provides the first measurement of recoil neutron polarization at photon energies where the quark substructure of the deuteron plays a role, thereby providing important new constraints on photodisintegration mechanisms. A very high neutron polarization in a narrow structure centered around E_{γ}∼570  MeV is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition suggests this behavior could be related to the excitation of the d^{*}(2380) hexaquark.
    Language English
    Publishing date 2020-04-17
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.124.132001
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