V. Metag - Academia.edu (original) (raw)

Papers by V. Metag

Physical review letters, Jan 4, 2008

We present the first detailed measurement of incoherent photoproduction of neutral pions to a dis... more We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The 12C(gamma,pi(0))(12)C*(4.4 MeV) 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 pi(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. Such data are sensitive to the propagation of the Delta 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 Delta-hole model.

Physical review letters, Jan 25, 2004

The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Main... more The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI. The total inclusive cross section for the reaction gamma3He-->etaX has been measured for photon energies from threshold to 820 MeV. The total and angular differential coherent eta cross sections have been extracted up to energies of 745 MeV. A resonancelike structure just above the eta production threshold with an isotropic angular distribution suggests the existence of a resonant quasibound state. This is supported by studies of a competing decay channel of such a quasibound eta-mesic nucleus into pi(0)pX. A binding energy of (-4.4+/-4.2) MeV and a width of (25.6+/-6.1) MeV is deduced for the quasibound eta-mesic state in 3He.

Physik Journal, 1993

ABSTRACT

Physics Letters B, 1976

New fission isomers with half-lives of 10 _+ 3 ps and 40 • 15 ps are observed and assigned to 24°... more New fission isomers with half-lives of 10 _+ 3 ps and 40 • 15 ps are observed and assigned to 24°Cm and 242Cm, respectively. An upper limit of 5 ps is set on the half-life of the fission isomeric state in 244Cm.

In the 233-MeV ⁶⁴Ni + ⁹²Zr reaction the emission of two neutrons constitutes the strongest... more In the 233-MeV ⁶⁴Ni + ⁹²Zr reaction the emission of two neutrons constitutes the strongest decay channel, in contrast to statistical model calculations which predict the emission of three neutrons to be the strongest by more than one order of magnitude. Possible explanations for the apparent neutron suppression in terms of unusually large gamma-decay width, anomalously energetic neutrons or an

Coherent photoproduction ofmesons from the deuteron has been measured from threshold up to E ≈ 75... more Coherent photoproduction ofmesons from the deuteron has been measured from threshold up to E ≈ 750 MeV using the photon spectrometer TAPS at the tagged photon facility at the Mainz microtron MAMI. For the first time, differential coherent cross sections have been deduced from the coincident detection of themeson and the recoil deuteron. A missing energy analysis was used for

Physical Review D, 2008

The photoproduction of ω mesons off protons has been studied at the Bonn ELSA accelerator from th... more The photoproduction of ω mesons off protons has been studied at the Bonn ELSA accelerator from threshold to Eγ = 1700 MeV. Linearly polarized beams were produced via coherent bremsstrahlung. Large photon asymmtries in excess of 50 % were obtained, whereas the pion asymmetries from ω → π 0 γ are close to zero. The asymmetries do characteristically depend on Θcm rather than |t| and indicate s-channel resonance formation on top of t-channel exchange processes.

Many QCD based and phenomenological models predict changes of hadron properties in a strongly int... more Many QCD based and phenomenological models predict changes of hadron properties in a strongly interacting environment. The results of these models differ significantly and the experimental determination of hadron properties in nuclear matter is essential. In this paper we present a review of selected physics results obtained at GSI Helmholtzzentrum für Schwerionenforschung GmbH by HADES (High-Acceptance Di-Electron Spectrometer). The e + e − pair emission measured for proton and heavy-ion induced collisions is reported together with results on strangeness production. The future HADES activities at the planned FAIR facility are also discussed.

European Physical Journal a, 2014

Results on Λ hyperon production are reported for collisions of p (3.5 GeV) + Nb, studied with the... more Results on Λ hyperon production are reported for collisions of p (3.5 GeV) + Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. The transverse mass distributions in rapidity bins are well described by Boltzmann shapes with a maximum inverse slope parameter of about 90 MeV at a rapidity of y = 1.0, i.e. slightly below the center-of-mass rapidity for nucleonnucleon collisions, ycm = 1.12. The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The Λ phase-space distribution is compared with results of other experiments and with predictions of two transport approaches which are available publicly. None of the present versions of the employed models is able to fully reproduce the experimental distributions, i.e. in absolute yield and in shape. Presumably, this finding results from an insufficient modelling in the transport models of the elementary processes being relevant for Λ production, rescattering and absorption. The present high-statistics data allow for a genuine two-dimensional investigation as a function of phase space of the self-analyzing Λ polarization in the weak decay Λ → pπ −. Finite negative values of the polarization in the order of 5 − 20 % are observed over the entire phase space studied. The absolute value of the polarization increases almost linearly with increasing transverse momentum for pt > 300 MeV/c and increases with decreasing rapidity for y < 0.8.

Physica Scripta, 2003

The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

European Physical Journal A, 2002

The photoproduction of η-mesons from 2 H and 4 He has been studied for energies close to the prod... more The photoproduction of η-mesons from 2 H and 4 He has been studied for energies close to the production thresholds. The experiments were carried out with the tagged photon beam of the Mainz MAMI accelerator. The η-mesons were detected via their two photon decays with the electromagnetic calorimeter TAPS. Total cross sections, angular and momentum distributions of the η-mesons have been determined for both reactions. The total cross sections in the threshold region show a large enhancement over the predictions of a participant-spectator model, indicating significant final state interaction effects. The results are compared to recent model calculations taking into account nucleon-nucleon and nucleon-η final state interaction effects on different levels of sophistication.

Progress in Particle and Nuclear Physics, 2003

... The calculation has been performed by Effenberger et al. ... from the HADES and TAPS collabor... more ... The calculation has been performed by Effenberger et al. ... from the HADES and TAPS collaborations who have contributed to the physics program presented in this article, in particular, Silke Janssen, Martin Kotulla, Johan Messchendorp, Jim Ritman, and Susan Schadmand. ...

Physics Reports, 1990

Introduction 365 4.6.~qmesons 393 2. Heavy-ion reaction dynamics 365 5. Experimental data 396 2.1... more Introduction 365 4.6.~qmesons 393 2. Heavy-ion reaction dynamics 365 5. Experimental data 396 2.1. Derivation of the Vlasov-Uehling-Uhlenbeck 5.1. Experimental techniques 396 equation 366 5.2. Systematics of experimental data 399 2.2. Technical approximations 369 5.3. Prospects for experiments at higher energies 410 2.3. Numerical techniques 374 6. Comparison of theory and experiment 411 2.4. Dynamical simulations 377 6.1. Photon production 412 3. Particle production rates 380 6.2. Dilepton production 427 3.1. Motivation 380 6.3. Pion production 429 3.2. General expression for production cross sections 382 6.4. Eta production 435 4. Elementary cross sections 383 6.5. Kaon production 4.1. NN scattering cross section 383 7. Sensitivity of particle production rates to the equation of 4.2. Discussion of medium effects 384 state 4.3. Photons 385 8. Summary and outlook 4.4. Dileptons 390 References 4.5. Pions 391

Physics of Atomic Nuclei, 2012

ABSTRACT After the completion of the experimental program at SIS18 the HADES setup will migrate t... more ABSTRACT After the completion of the experimental program at SIS18 the HADES setup will migrate to FAIR, where it will deliver high-quality data for heavy-ion collisions in an unexplored energy range of up to 8 A GeV. In this contribution, we briefly present the physics case, relevant detector characteristics and discuss the recently completed upgrade of HADES.

Physics Letters B, 1971

ABSTRACT

Physics Letters B, 2010

We report measurements of electron pair production in elementary p+p and d+p reactions at 1.25 Ge... more We report measurements of electron pair production in elementary p+p and d+p reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n+p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass M e + e − > 0.15 GeV/c 2 is about an order of magnitude larger in n+p reactions as compared to p+p. A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C+C reactions are compatible with a superposition of elementary n+p and p+p collisions, leaving little room for additional electron pair sources in such light collision systems.

Physical review letters, Jan 4, 2008

We present the first detailed measurement of incoherent photoproduction of neutral pions to a dis... more We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The 12C(gamma,pi(0))(12)C*(4.4 MeV) 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 pi(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. Such data are sensitive to the propagation of the Delta 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 Delta-hole model.

Physical review letters, Jan 25, 2004

The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Main... more The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI. The total inclusive cross section for the reaction gamma3He-->etaX has been measured for photon energies from threshold to 820 MeV. The total and angular differential coherent eta cross sections have been extracted up to energies of 745 MeV. A resonancelike structure just above the eta production threshold with an isotropic angular distribution suggests the existence of a resonant quasibound state. This is supported by studies of a competing decay channel of such a quasibound eta-mesic nucleus into pi(0)pX. A binding energy of (-4.4+/-4.2) MeV and a width of (25.6+/-6.1) MeV is deduced for the quasibound eta-mesic state in 3He.

Physik Journal, 1993

ABSTRACT

Physics Letters B, 1976

New fission isomers with half-lives of 10 _+ 3 ps and 40 • 15 ps are observed and assigned to 24°... more New fission isomers with half-lives of 10 _+ 3 ps and 40 • 15 ps are observed and assigned to 24°Cm and 242Cm, respectively. An upper limit of 5 ps is set on the half-life of the fission isomeric state in 244Cm.

In the 233-MeV ⁶⁴Ni + ⁹²Zr reaction the emission of two neutrons constitutes the strongest... more In the 233-MeV ⁶⁴Ni + ⁹²Zr reaction the emission of two neutrons constitutes the strongest decay channel, in contrast to statistical model calculations which predict the emission of three neutrons to be the strongest by more than one order of magnitude. Possible explanations for the apparent neutron suppression in terms of unusually large gamma-decay width, anomalously energetic neutrons or an

Coherent photoproduction ofmesons from the deuteron has been measured from threshold up to E ≈ 75... more Coherent photoproduction ofmesons from the deuteron has been measured from threshold up to E ≈ 750 MeV using the photon spectrometer TAPS at the tagged photon facility at the Mainz microtron MAMI. For the first time, differential coherent cross sections have been deduced from the coincident detection of themeson and the recoil deuteron. A missing energy analysis was used for

Physical Review D, 2008

The photoproduction of ω mesons off protons has been studied at the Bonn ELSA accelerator from th... more The photoproduction of ω mesons off protons has been studied at the Bonn ELSA accelerator from threshold to Eγ = 1700 MeV. Linearly polarized beams were produced via coherent bremsstrahlung. Large photon asymmtries in excess of 50 % were obtained, whereas the pion asymmetries from ω → π 0 γ are close to zero. The asymmetries do characteristically depend on Θcm rather than |t| and indicate s-channel resonance formation on top of t-channel exchange processes.

Many QCD based and phenomenological models predict changes of hadron properties in a strongly int... more Many QCD based and phenomenological models predict changes of hadron properties in a strongly interacting environment. The results of these models differ significantly and the experimental determination of hadron properties in nuclear matter is essential. In this paper we present a review of selected physics results obtained at GSI Helmholtzzentrum für Schwerionenforschung GmbH by HADES (High-Acceptance Di-Electron Spectrometer). The e + e − pair emission measured for proton and heavy-ion induced collisions is reported together with results on strangeness production. The future HADES activities at the planned FAIR facility are also discussed.

European Physical Journal a, 2014

Results on Λ hyperon production are reported for collisions of p (3.5 GeV) + Nb, studied with the... more Results on Λ hyperon production are reported for collisions of p (3.5 GeV) + Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. The transverse mass distributions in rapidity bins are well described by Boltzmann shapes with a maximum inverse slope parameter of about 90 MeV at a rapidity of y = 1.0, i.e. slightly below the center-of-mass rapidity for nucleonnucleon collisions, ycm = 1.12. The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The Λ phase-space distribution is compared with results of other experiments and with predictions of two transport approaches which are available publicly. None of the present versions of the employed models is able to fully reproduce the experimental distributions, i.e. in absolute yield and in shape. Presumably, this finding results from an insufficient modelling in the transport models of the elementary processes being relevant for Λ production, rescattering and absorption. The present high-statistics data allow for a genuine two-dimensional investigation as a function of phase space of the self-analyzing Λ polarization in the weak decay Λ → pπ −. Finite negative values of the polarization in the order of 5 − 20 % are observed over the entire phase space studied. The absolute value of the polarization increases almost linearly with increasing transverse momentum for pt > 300 MeV/c and increases with decreasing rapidity for y < 0.8.

Physica Scripta, 2003

The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

European Physical Journal A, 2002

The photoproduction of η-mesons from 2 H and 4 He has been studied for energies close to the prod... more The photoproduction of η-mesons from 2 H and 4 He has been studied for energies close to the production thresholds. The experiments were carried out with the tagged photon beam of the Mainz MAMI accelerator. The η-mesons were detected via their two photon decays with the electromagnetic calorimeter TAPS. Total cross sections, angular and momentum distributions of the η-mesons have been determined for both reactions. The total cross sections in the threshold region show a large enhancement over the predictions of a participant-spectator model, indicating significant final state interaction effects. The results are compared to recent model calculations taking into account nucleon-nucleon and nucleon-η final state interaction effects on different levels of sophistication.

Progress in Particle and Nuclear Physics, 2003

... The calculation has been performed by Effenberger et al. ... from the HADES and TAPS collabor... more ... The calculation has been performed by Effenberger et al. ... from the HADES and TAPS collaborations who have contributed to the physics program presented in this article, in particular, Silke Janssen, Martin Kotulla, Johan Messchendorp, Jim Ritman, and Susan Schadmand. ...

Physics Reports, 1990

Introduction 365 4.6.~qmesons 393 2. Heavy-ion reaction dynamics 365 5. Experimental data 396 2.1... more Introduction 365 4.6.~qmesons 393 2. Heavy-ion reaction dynamics 365 5. Experimental data 396 2.1. Derivation of the Vlasov-Uehling-Uhlenbeck 5.1. Experimental techniques 396 equation 366 5.2. Systematics of experimental data 399 2.2. Technical approximations 369 5.3. Prospects for experiments at higher energies 410 2.3. Numerical techniques 374 6. Comparison of theory and experiment 411 2.4. Dynamical simulations 377 6.1. Photon production 412 3. Particle production rates 380 6.2. Dilepton production 427 3.1. Motivation 380 6.3. Pion production 429 3.2. General expression for production cross sections 382 6.4. Eta production 435 4. Elementary cross sections 383 6.5. Kaon production 4.1. NN scattering cross section 383 7. Sensitivity of particle production rates to the equation of 4.2. Discussion of medium effects 384 state 4.3. Photons 385 8. Summary and outlook 4.4. Dileptons 390 References 4.5. Pions 391

Physics of Atomic Nuclei, 2012

ABSTRACT After the completion of the experimental program at SIS18 the HADES setup will migrate t... more ABSTRACT After the completion of the experimental program at SIS18 the HADES setup will migrate to FAIR, where it will deliver high-quality data for heavy-ion collisions in an unexplored energy range of up to 8 A GeV. In this contribution, we briefly present the physics case, relevant detector characteristics and discuss the recently completed upgrade of HADES.

Physics Letters B, 1971

ABSTRACT

Physics Letters B, 2010

We report measurements of electron pair production in elementary p+p and d+p reactions at 1.25 Ge... more We report measurements of electron pair production in elementary p+p and d+p reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n+p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass M e + e − > 0.15 GeV/c 2 is about an order of magnitude larger in n+p reactions as compared to p+p. A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C+C reactions are compatible with a superposition of elementary n+p and p+p collisions, leaving little room for additional electron pair sources in such light collision systems.