-
P. Achenbach,
C. Ayerbe Gayoso,
J. C. Bernauer,
R. Böhm,
D. Bosnar,
M. Bösz,
L. Debenjak,
M. O. Distler,
A. Esser,
I. Friščić, [......],
L. Nungesser,
J. Pochodzalla,
M. Potokar,
T. R. Saito, S. Sánchez Majos,
B. S. Schlimme,
S. Širca,
Th. Walcher,
M. Weinriefer,
C. J. Yoon
[show abstract]
[hide abstract]
ABSTRACT: In 2007 the Mainz Microtron MAMI has been upgraded to 1.5 GeV electron beam energy, crossing the energy threshold for open
strangeness production. The strangeness quantum number, as carried by the strange quark, provides valuable information on
the contribution of individual quark flavours to hadronic processes. Theoretically, the strange quark with its rest energy
of order 150 MeV is particularly interesting because it can neither be treated as a massless nor as a heavy quark. Experimentally,
an instrument of central importance for the charged kaon electro-production off the proton or light nuclei at MAMI is the
magnetic spectrometer Kaos that was installed recently and is now routinely operated by the A1 collaboration.
The European Physical Journal Special Topics 04/2012; 198(1):307-327. · 1.56 Impact Factor
-
J C Bernauer,
P Achenbach,
C Ayerbe Gayoso,
R Böhm,
D Bosnar,
L Debenjak,
M O Distler,
L Doria,
A Esser,
H Fonvieille, [......],
D G Middleton,
U Müller,
L Nungesser,
J Pochodzalla,
M Potokar, S Sánchez Majos,
B S Schlimme,
S Sirca,
Th Walcher,
M Weinriefer
Physical Review Letters 09/2011; 107(11):119102. · 7.37 Impact Factor
-
J. C. Bernauer,
P. Achenbach,
C. Ayerbe Gayoso,
R Böhm,
D. Bosnar,
L. Debenjak,
M. O. Distler,
L. Doria,
A. Esser,
H. Fonvieille, [......],
D. G. Middleton,
U Müller,
L. Nungesser,
J. Pochodzalla,
M. Potokar, S. Sánchez Majos,
B. S. Schlimme,
S. Širca,
Th. Walcher,
M. Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: In arXiv:1108.3058v1 [nucl-ex], Arrington criticizes the Coulomb corrections
we applied in the analysis of high precision form factor data (see
Phys.Rev.Lett.105:242001, 2010, arXiv:1007.5076v3 [nucl-ex]). We show, by
comparing different calculations cited in the Comment, that the criticism of
the Comment neglects the large uncertainty of "more modern" TPE corrections.
This uncertainty has also been seen in recent polarized measurements. We rerun
our analysis using one of these calculations. The results show that the Comment
exaggerates the quantitative effect at small Q^2.
08/2011;
-
J. C. Bernauer,
P. Achenbach,
C. Ayerbe Gayoso,
R. Böhm,
D. Bosnar,
L. Debenjak,
M. O. Distler,
L. Doria,
A. Esser,
H. Fonvieille, [......],
D. G. Middleton,
U. Müller,
L. Nungesser,
J. Pochodzalla,
M. Potokar, S. Sánchez Majos,
B. S. Schlimme,
S. Širca,
Th. Walcher,
M. Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: In arXiv:1108.3058v1 [nucl-ex], Arrington criticizes the Coulomb
corrections we applied in the analysis of high precision form factor
data (see Phys.Rev.Lett.105:242001, 2010, arXiv:1007.5076v3 [nucl-ex]).
We show, by comparing different calculations cited in the Comment, that
the criticism of the Comment neglects the large uncertainty of "more
modern" TPE corrections. This uncertainty has also been seen in recent
polarized measurements. We rerun our analysis using one of these
calculations. The results show that the Comment exaggerates the
quantitative effect at small Q^2.
07/2011;
-
H Merkel,
P Achenbach,
C Ayerbe Gayoso,
J C Bernauer,
R Böhm,
D Bosnar,
L Debenjak,
A Denig,
M O Distler,
A Esser, [......],
D G Middleton,
U Müller,
L Nungesser,
J Pochodzalla,
M Rohrbeck, S Sánchez Majos,
B S Schlimme,
M Schoth,
S Sirca,
M Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: A new exclusion limit for the electromagnetic production of a light U (1) gauge boson γ ′ decaying to e + e − was determined by the A1 Collaboration at the Mainz Microtron. Such light gauge bosons appear in several extensions of the standard model and are also discussed as candidates for the interaction of dark matter with standard model matter. In electron scattering from a heavy nucleus, the existing limits for a narrow state coupling to e + e − were reduced by nearly an order of magnitude in the range of the lepton pair mass of 210 MeV/c 2 < m e + e − < 300 MeV/c 2 . This experiment demonstrates the potential of high current and high resolution fixed target experiments for the search for physics beyond the standard model.
07/2011;
-
H Merkel,
P Achenbach,
C Ayerbe Gayoso,
J C Bernauer,
R Böhm,
D Bosnar,
L Debenjak,
A Denig,
M O Distler,
A Esser, [......],
D G Middleton,
U Müller,
L Nungesser,
J Pochodzalla,
M Rohrbeck, S Sánchez Majos,
B S Schlimme,
M Schoth,
S Sirca,
M Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: A new exclusion limit for the electromagnetic production of a light U(1) gauge boson γ' decaying to e + e- was determined by the A1 Collaboration at the Mainz Microtron. Such light gauge bosons appear in several extensions of the standard model and are also discussed as candidates for the interaction of dark matter with standard model matter. In electron scattering from a heavy nucleus, the existing limits for a narrow state coupling to e + e- were reduced by nearly an order of magnitude in the range of the lepton pair mass of 210 MeV/c2}<me +}e-<300 MeV/c2. This experiment demonstrates the potential of high current and high resolution fixed target experiments for the search for physics beyond the standard model.
Physical Review Letters 06/2011; 106(25):251802. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The technical design of the PANDA experiment at the future FAIR facility next
to GSI is progressing. At the proposed anti-proton storage ring the
spectroscopy of double Lambda hypernuclei is one of the four main topics which
will be addressed by the Collaboration. The hypernuclear experiments require
(i) a dedicated internal target, (ii) an active secondary target of alternating
silicon and absorber material layers, (iii) high purity germanium (HPGe)
detectors, and (iv) a good particle identification system for low momentum
kaons. All systems need to operate in the presence of a high magnetic field and
a large hadronic background. The status of the detector developments for this
programme is summarized.
05/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: A tracking detector based on two meters long scintillating fibers read out by
silicon photomultipliers (SiPM) is being developed for the Kaos spectrometer at
the Mainz Microtron MAMI. Results from a prototype setup using 2 mm square
fibers and large area SiPM readout are presented. The detection efficiency of
such a combination was measured to be between 83 and 100% depending on the
threshold on the SiPM amplitude. A Monte Carlo simulation based on a physical
model was employed in order to extract the photon detection efficiency of the
SiPM devices.
05/2011;
-
P. Achenbach,
C. Ayerbe Gayoso,
J. C. Bernauer,
R Böhm,
D. Bosnar,
L. Debenjak,
M. O. Distler,
A. Esser,
I. Friščić,
M. Gómez Rodríguez de la Paz, [......],
J. Pochodzalla,
M. Potokar,
I. Rusanov,
T. R. Saito, S. Sánchez Majos,
B. S. Schlimme,
S. Širca,
S. Voltz,
K. Weindel,
M. Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: The Kaos spectrometer is maintained by the A1 collaboration at the Mainz
Microtron MAMI with a focus on the study of (e,e'K^+) coincidence reactions.
For its electron-arm two vertical planes of fiber arrays, each comprising
approximately 10 000 fibers, are operated close to zero degree scattering angle
and in close proximity to the electron beam. A nearly dead-time free DAQ system
to acquire timing and tracking information has been installed for this
spectrometer arm. The signals of 144 multi-anode photomultipliers are collected
by 96-channel front-end boards, digitized by double-threshold discriminators
and the signal time is picked up by state-of-the-art F1 time-to-digital
converter chips. In order to minimize background rates a sophisticated trigger
logic was implemented in newly developed Vuprom modules. The trigger performs
noise suppression, signal cluster finding, particle tracking, and coincidence
timing, and can be expanded for kinematical matching (e'K^+) coincidences. The
full system was designed to process more than 4 000 read-out channels and to
cope with the high electron flux in the spectrometer and the high count rate
requirement of the detectors. It was successfully in-beam tested at MAMI in
2009.
05/2011;
-
P. Achenbach,
C. Ayerbe Gayoso,
J. C. Bernauer,
S. Bianchin,
R Böhm,
O. Borodina,
M. Bösz,
D. Bosnar,
V. Bozkurt,
P. Bydžovský, [......],
B. Özel-Tashenov,
J. Pochodzalla,
M. Potokar,
Ch. Rappold,
T. R. Saito, S. Sánchez Majos,
B. S. Schlimme,
S. Širca,
M. Weinriefer,
C. J. Yoon
[show abstract]
[hide abstract]
ABSTRACT: Cross section measurements of the exclusive p(e,e'K+)Lambda,Sigma^0
electroproduction reactions have been performed at the Mainz Microtron MAMI in
the A1 spectrometer facility using for the first time the Kaos spectrometer for
kaon detection. These processes were studied in a kinematical region not
covered by any previous experiment. The nucleon was probed in its third
resonance region with virtual photons of low four-momenta, Q^2= 0.030-0.055
(GeV/c)^2. The MAMI data indicate a smooth transition in Q^2 from
photoproduction to electroproduction cross sections. Comparison with
predictions of effective Lagrangian models based on the isobar approach reveal
that strong longitudinal couplings of the virtual photon to the N* resonances
can be excluded from these models.
04/2011;
-
P. Achenbach,
C. Ayerbe Gayoso,
J. C. Bernauer,
R Böhm,
D. Bosnar,
M. Bösz,
L. Debenjak,
M. O. Distler,
A. Esser,
I. Friščić, [......],
M. Makek,
H. Merkel,
U Müller,
L. Nungesser,
J. Pochodzalla,
M. Potokar, S. Sánchez Majos,
B. S. Schlimme,
S. Širca,
M. Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: Wire chambers are routinely operated as tracking detectors in magnetic
spectrometers at high-intensity continuous electron beams. Especially in
experiments studying reactions with small cross-sections the reaction yield is
limited by the background rate in the chambers. One way to determine the track
of a charged particle through a multi-wire proportional chamber (MWPC) is the
measurement of the charge distribution induced on its cathodes. In practical
applications of this read-out method, the algorithm to relate the measured
charge distribution to the avalanche position is an important factor for the
achievable position resolution and for the track reconstruction efficiency. An
algorithm was developed for operating two large-sized MWPCs in a strong
background environment with multiple-particle tracks. Resulting efficiencies
were determined as a function of the electron beam current and on the signal
amplitudes. Because of the different energy-losses of pions, kaons, and protons
in the momentum range of the spectrometer the efficiencies depend also on the
particle species.
04/2011;
-
J C Bernauer,
P Achenbach,
C Ayerbe Gayoso,
R Böhm,
D Bosnar,
L Debenjak,
M O Distler,
L Doria,
A Esser,
H Fonvieille, [......],
D G Middleton,
U Müller,
L Nungesser,
J Pochodzalla,
M Potokar, S Sánchez Majos,
B S Schlimme,
S Sirca,
Th Walcher,
M Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: New precise results of a measurement of the elastic electron-proton scattering cross section performed at the Mainz Microtron MAMI are presented. About 1400 cross sections were measured with negative four-momentum transfers squared up to Q² = 1 (GeV/c)² with statistical errors below 0.2%. The electric and magnetic form factors of the proton were extracted by fits of a large variety of form factor models directly to the cross sections. The form factors show some features at the scale of the pion cloud. The charge and magnetic radii are determined to be <r²E>½ = 0.879(5)stat(4)syst(2)model(4)group fm and <r²M>½ = 0.777(13)stat(9)syst(5)model(2)group fm.
Physical Review Letters 12/2010; 105(24):242001. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A characterisation of scintillating fibres with silicon photomultiplier
read-out was performed in view of their possible application in fibre tracking
detector systems. Such a concept is being considered for the Kaos spectrometer
at the Mainz Microtron MAMI and as a time-of-flight start detector for the
hypernuclear physics programme at the PANDA experiment of the FAIR project.
Results on particle detection effciency and time resolution are discussed. In
summary, the silicon devices are very suitable for the detection of the low
light yield from scintillating fibres insofar a trigger scheme is found to cope
with the noise rate characteristics.
06/2008;
-
P. Achenbach,
C. Ayerbe Gayoso,
J. C. Bernauer,
R Böhm,
M. O. Distler,
L. Doria,
M. Gómez Rodríguez de la Paz,
H. Merkel,
U Müller,
L. Nungesser, [......],
S Minami,
D. Nakajima,
C. Rappold,
T. R. Saito,
D Schardt,
M. Träger,
H Iwase,
S. Ajimura,
A Sakaguchi,
Y Mizoi
[show abstract]
[hide abstract]
ABSTRACT: The performance of scintillating fibre detectors was studied with electrons at the spectrometer facility of the Mainz microtron MAMI, as well as in a C-12 beam of 2 AGeV energy and in a beam of different particle species at GSI. Multi-anode photomultipliers were used to read out one or more bundles of 128 fibres each in different geometries. For electrons a time resolution of FWHM = 1 ns was measured in a single detector plane with a detection efficiency epsilon > 99%. A time resolution of 310 ps (FWHM) between two planes of fibres was achieved for carbon ions, leading to a FWHM = 220 ps for a single detector. The hit position residual was measured with a width of FWHM = 0.27 mm. The variation in the measured energy deposition was Delta E/E= 15-20% (FWHM) for carbon ions. In addition, the energy response to p/pi/d particles was studied. Based on the good detector performance fibre hodoscopes will be constructed for the KAOS/A1 spectrometer at MAMI and for the HypHI experiment at GSI.
03/2008;
-
H Merkel,
P Achenbach,
C Ayerbe Gayoso,
J C Bernauer,
R Böhm,
D Bosnar,
B Cheymol,
M O Distler,
L Doria,
H Fonvieille, [......],
U Müller,
L Nungesser,
J Pochodzalla,
M Potokar, S Sánchez Majos,
B S Schlimme,
S Sirca,
L Tiator,
Th Walcher,
M Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: The beam-recoil double polarization P(x')(h) and P(z')(h) and the recoil polarization P(y') were measured for the first time for the p(e,e'p)eta reaction at a four-momentum transfer of Q(2) = 0.1 GeV(2)/c(2) and a center of mass production angle of theta = 120 degrees at the Mainz Microtron MAMI-C. With a center of mass energy range of 1500 MeV<W<1550 MeV the region of the S11(1535) and D13(1520) resonance was covered. The results are discussed in the framework of a phenomenological isobar model (Eta-MAID). While P(x')(h) and P(z')(h) are in good agreement with the model, P(y') shows a significant deviation, consistent with existing photoproduction data on the polarized-target asymmetry.
Physical Review Letters 09/2007; 99(13):132301. · 7.37 Impact Factor
-
H. Merkel,
P. Achenbach,
C. A. Ayerbe Gayoso,
J. C. Bernauer,
R Böhm,
D. Bosnar,
B. Cheymol,
M. O. Distler,
L. Doria,
H. Fonvieille, [......],
U Müller,
L. Nungesser,
J. Pochodzalla,
M. Potokar, S. Sánchez Majos,
B. S. Schlimme,
S. Širca,
L. Tiator,
Th. Walcher,
M. Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: The beam-recoil double polarization P_{x'}^h and P_{z'}^h and the recoil polarization P_{y'} were measured for the first time for the p(\vec{e},e'\vec{p})\eta reaction at a four-momentum transfer of Q^2=0.1 GeV^2/c^2 and a center of mass production angle of \theta = 120^\circ at MAMI C. With a center of mass energy range of 1500 MeV < W < 1550 MeV the region of the S_{11}(1535) and D_{13}(1520) resonance was covered. The results are discussed in the framework of a phenomenological isobar model (Eta-MAID). While P_{x'}^h and P_{z'}^h are in good agreement with the model, P_{y'} shows a significant deviation, consistent with existing photoproduction data on the polarized-target asymmetry.
06/2007;
-
I. K. Bensafa,
P. Achenbach,
M. Ases Antelo,
C. Ayerbe,
D. Baumann,
R. Böhm,
D. Bosnar,
E. Burtin,
X. Defaÿ,
N. D'Hose, [......],
G. Rosner, S. Sánchez Majos,
M. Seimetz,
S. Širca,
T. Spitzenberg,
G. Tamas,
R. Van de Vyver,
L. Van Hoorebeke,
Th. Walcher,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: The beam-helicity asymmetry has been measured simultaneously for the reactions
e® \;\stackrel{{\rightarrow}}{{e}}\;
p→epγ and
e® \;\stackrel{{\rightarrow}}{{e}}\;
p→epπ
0 in the Δ(1232)-resonance region at Q
2 = 0.35(GeV/c)2. The experiment was performed at MAMI with a longitudinally polarized beam and an out-of-plane detection of the proton. The
results are compared with calculations based on dispersion relations for virtual Compton scattering and with the MAID model
for pion electroproduction. There is an overall good agreement between experiment and theoretical calculations. The remaining
discrepancies may be ascribed to an imperfect parametrization of some γ
(*)
N→πN multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels (γ and π
0) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization.
European Physical Journal A 03/2007; 32(1):69-75. · 2.19 Impact Factor
-
P. Achenbach,
C. Ayerbe Gayoso,
J. Bernauer,
R Böhm,
M. O. Distler,
L. Doria,
J. Friedrich,
H. Merkel,
U Müller,
L. Nungesser,
J. Pochodzalla, S. Sánchez Majos,
S. Schlimme,
Th. Walcher,
M. Weinriefer
[show abstract]
[hide abstract]
ABSTRACT: One contribution to the time resolution of a scintillation detector is the signal time spread due to path length variations of the detected photons from a point source. In an experimental study a rectangular scintillator was excited by means of a fast pulsed ultraviolet laser at different positions along its longitudinal axis. Timing measurements with a photomultiplier tube in a detection plane displaced from the scintillator end face showed a correlation between signal time and tube position indicating only a small distortion of photon angles during transmission. The data is in good agreement with a Monte Carlo simulation used to compute the average photon angle with respect to the detection plane and the average propagation time. Limitations on timing performance that arise from propagation time dispersion are expected for long and thin scintillators used in future particle identification systems.
03/2007;
-
P. Achenbach,
C. Ayerbe Gayoso,
R Böhm,
M. O. Distler,
J. Friedrich,
K. W. Krygier,
H. Merkel,
U Müller,
R. Neuhausen,
L. Nungesser, [......],
M. Palomba,
G. Raciti,
C. Sfienti,
M. Agnello,
F Ferro,
F. Iazzi,
K. Szymanska,
P. -E. Tegnér,
B. Cederwall,
L. Majling
[show abstract]
[hide abstract]
ABSTRACT: The KaoS spectrometer at the Mainz Microtron MAMI, Germany, is perceived as
the ideal candidate for a dedicated spectrometer in kaon and hypernuclei
electroproduction. KaoS will be equipped with new read-out electronics, a
completely new focal plane detector package consisting of scintillating fibres,
and a new trigger system. First prototypes of the fibre detectors and the
associated new front-end electronics are shown in this contribution. The Mainz
hypernuclei research program will complement the hypernuclear experiments at
the planned FAIR facility at GSI, Germany. At the proposed antiproton storage
ring the spectroscopy of double Lambda hypernuclei is one of the four main
topics which will be addressed by the PANDA Collaboration. The experiments
require the operation of high purity germanium (HPGe) detectors in high
magnetic fields (B= 1T) in the presence of a large hadronic background. The
performance of high resolution Ge detectors in such an environment has been
investigated.
05/2006;
-
[show abstract]
[hide abstract]
ABSTRACT: A tracking detector based on 1.5 m long scintillating fibers is being developed for the electron arm of the KAOS spectrometer at the Mainz Microtron MAMI. Measurements on light attenuation, particle detection efficiencies and accidental coincidence rates with a prototype set-up using fibers read out by silicon photomultipliers (SiPM) are presented. The highest efficiency at the lowest accidental coincidence rate was reached for high trigger thresholds at the largest SiPM bias voltages. The influence of signal attenuation and dispersion on detection efficiencies is discussed. The results are in good agreement with a Monte Carlo model that was used to predict detector characteristics for different fiber geometries.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
