-
S. Baunack,
D. Balaguer Ríos,
L. Capozza,
J. Diefenbach,
R. Frascaria,
B. Gläser,
D. v. Harrach,
Y. Imai, R. Kothe,
R. Kunne,
J. H. Lee,
F. E. Maas,
M. C. Mora Espí,
M. Morlet,
S. Ong,
E. Schilling,
J. van de Wiele,
C. Weinrich
[show abstract]
[hide abstract]
ABSTRACT: Sufficient energy resolution is the key issue for the calorimetry in particle
and nuclear physics. The calorimeter of the A4 parity violation experiment at
MAMI is a segmented calorimeter where the energy of an event is determined by
summing the signals of neighbouring channels. In this case the precise matching
of the individual modules is crucial to obtain a good energy resolution. We
have developped a calibration procedure for our total absorbing electromagnetic
calorimeter which consists of 1022 lead fluoride (PbF_2) crystals. This
procedure reconstructs the the single-module contributions to the events by
solving a linear system of equations, involving the inversion of a 1022 x
1022-matrix. The system has shown its functionality at beam energies between
300 and 1500 MeV and represents a new and fast method to keep the calorimeter
permanently in a well-calibrated state.
02/2011;
-
S Baunack,
K Aulenbacher,
D Balaguer Ríos,
L Capozza,
J Diefenbach,
B Gläser,
D von Harrach,
Y Imai,
E-M Kabuss, R Kothe, [......],
M A El-Yakoubi,
R Frascaria,
R Kunne,
F E Maas,
M Morlet,
S Ong,
J van de Wiele,
S Kowalski,
Y Prok,
S Taylor
[show abstract]
[hide abstract]
ABSTRACT: A new measurement of the parity violating asymmetry in elastic electron scattering on hydrogen at backward angles and at a four momentum transfer of Q;{2} = 0.22 (Ge V / c);{2} is reported here. The measured asymmetry is A_{LR} = (-17.23 +/- 0.82_{stat} +/- 0.89_{syst}) x 10;{-6}. The standard model prediction assuming no strangeness is A_{0} = (-15.87 +/- 1.22) x 10;{-6}. In combination with previous results from measurements at forward angles, it is possible to disentangle for the first time the strange form factors at this momentum transfer, G_{E};{s} = 0.050 +/- 0.038 +/- 0.019 and G_{M};{s} = -0.14 +/- 0.11 +/- 0.11.
Physical Review Letters 05/2009; 102(15):151803. · 7.37 Impact Factor
-
S. Baunack,
K. Aulenbacher,
D. Balaguer Ríos,
L. Capozza,
J. Diefenbach,
B. Gläser,
D. v. Harrach,
Y. Imai,
E. -M. Kabu\ss, R. Kothe, [......],
J. Arvieux,
M. A. El-Yakoubi,
R. Kunne,
F. E. Maas,
M. Morlet,
S. Ong,
J. Van de Wiele,
S. Kowalski,
Y Prok,
S Taylor
[show abstract]
[hide abstract]
ABSTRACT: A new measurement of the parity violating asymmetry in elastic electron scattering on hydrogen at backward angles and at a four momentum transfer of Q^2=0.22 (GeV/c)^2 is reported here. The measured asymmetry is A_LR=(-17.23 +- 0.82_stat +-0.89_syst) ppm. The Standard Model prediction assuming no strangeness is A_0=(-15.87 +- 1.22) ppm. In combination with previous results from measurements at forward angles, it it possible to disentangle for the first time the strange electric and magnetic form factors at this momentum transfer, G_E^s(0.22)=0.050 +- 0.038 +- 0.019 and G_M^s(0.22)=-0.14 +- 0.11 +- 0.11. Comment: Submitted to Physical Review Letters
03/2009;
-
I. Altarev,
E. Schilling,
S. Baunack,
L. Capozza,
J. Diefenbach,
K. Grimm,
Th. Hammel,
D. vonHarrach,
Y. Imai,
E M Kabuss, R. Kothe,
J H Lee,
A. LopesGinja,
F. E. Maas,
A. SanchezLorente,
G. Stephan,
C. Weinrich
[show abstract]
[hide abstract]
ABSTRACT: We present a new powerful liquid hydrogen target developed for the precise study of parity violating electron scattering on hydrogen and deuterium. This target has been designed to have minimal target density fluctuations under the heat load of a 20$\mu$A CW 854.3 MeV electron beam without rastering the electron beam. The target cell has a wide aperture for scattered electrons and is axially symmetric around the beam axis. The construction is optimized to intensify heat exchange by a transverse turbulent mixing in the hydrogen stream, which is directed along the electron beam. The target is constructed as a closed loop circulating system cooled by a helium refrigerator. It is operated by a tangential mechanical pump with an optional natural convection mode. The cooling system supports up to 250 watts of the beam heating removal. Deeply subcooled liquid hydrogen is used for keeping the in-beam temperature below the boiling point. The target density fluctuations are found to be at the level 10$^{-3}$ at a beam current of 20 $\mu$A. Comment: 24 pages, 14 figures, submitted to NIM A
04/2005;
-
T. Hammel,
P. Achenbach,
S. Baunack,
L. Capozza,
J. Diefenbach,
K. Grimm,
D. von Harrach,
Y. Imai,
E. Kabuß, R. Kothe,
J.H. Lee,
A. Lopes Ginja,
F.E. Maas,
A. Sanchez Lorente,
E. Schilling,
G. Stephan,
C. Weinrich,
I. Altarev
[show abstract]
[hide abstract]
ABSTRACT: A water Cherenkov luminosity monitor system with associated electronics has been developed for the A4 parity violation experiment at MAMI. The detector system measures the luminosity of the hydrogen target hit by the MAMI electron beam and monitors the stability of the liquid hydrogen target. Both are required for the precise study of the count rate asymmetries in the scattering of longitudinally polarized electrons on unpolarized protons. Any helicity correlated fluctuation of the target density leads to false asymmetries. The performance of the luminosity monitor, investigated in about 2000 h with electron beam, and the results of its application in the A4 experiment are presented.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 04/2005;
-
F E Maas,
K Aulenbacher,
S Baunack,
L Capozza,
J Diefenbach,
B Gläser,
T Hammel,
D von Harrach,
Y Imai,
E-M Kabuss, [......],
M El-Yakoubi,
R Frascaria,
R Kunne,
M Morlet,
S Ong,
J van de Wiele,
S Kowalski,
B Plaster,
R Suleiman,
S Taylor
[show abstract]
[hide abstract]
ABSTRACT: We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of Q(2)=0.108 (GeV/c)(2) and at a forward electron scattering angle of 30 degrees <theta(e)<40 degrees . The measured asymmetry is A(LR)(e-->p)=[-1.36+/-0.29(stat)+/-0.13(syst)]x10(-6). The expectation from the standard model assuming no strangeness contribution to the vector current is A(0)=(-2.06+/-0.14)x10(-6). We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher Q2. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be G(s)(E)+0.106G(s)(M)=0.071+/-0.036 at Q(2)=0.108 (GeV/c)(2). We again find the value for G(s)(E)+0.106G(s)(M) to be positive, this time at an improved significance level of two sigma.
Physical Review Letters 04/2005; 94(15):152001. · 7.37 Impact Factor
-
F E Maas,
K Aulenbacher,
S Baunack,
L Capozza,
J Diefenbach,
B Gläser,
Y Imai,
T Hammel,
D von Harrach,
E-M Kabuss, [......],
J Arvieux,
M Elyakoubi,
R Frascaria,
R Kunne,
M Morlet,
S Ong,
J Vandewiele,
S Kowalski,
R Suleiman,
S Taylor
[show abstract]
[hide abstract]
ABSTRACT: We report on a measurement of the asymmetry in the scattering of transversely polarized electrons off unpolarized protons, A( perpendicular), at two Q2 values of 0.106 and 0.230 (GeV/c)(2) and a scattering angle of 30 degrees <theta(e)<40 degrees . The measured transverse asymmetries are A( perpendicular)(Q(2)=0.106 (GeV/c)(2))=(-8.59+/-0.89(stat)+/-0.75(syst))x10(-6) and A( perpendicular)(Q(2)=0.230 (GeV/c)(2))=(-8.52+/-2.31(stat)+/-0.87(syst))x10(-6). The first errors denote the statistical error and the second the systematic uncertainties. From comparison with theoretical estimates of A( perpendicular) we conclude that piN-intermediate states give a substantial contribution to the imaginary part of the two-photon amplitude. There is no obvious reason why this should be different for the real part of the two-photon amplitude, which enters into the radiative corrections for the Rosenbluth separation measurements of the electric form factor of the proton.
Physical Review Letters 03/2005; 94(8):082001. · 7.37 Impact Factor
-
F. E. Maas,
K. Aulenbacher,
S. Baunack,
L. Capozza,
J. Diefenbach,
B. Gläser,
T. Hammel,
D Von Harrach,
Y. Imai,
E. -M. Kabu\ss, [......],
M. El-Yakoubi,
R. Frascaria,
R. Kunne,
M. Morlet,
S. Ong,
J. Van de Wiele,
S. Kowalski,
B. Plaster,
R Suleiman,
S Taylor
[show abstract]
[hide abstract]
ABSTRACT: We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of $Q^2$ = \Qsquare (GeV/c)$^2$ and at a forward electron scattering angle of 30$^\circ < \theta_e < 40^\circ$. The measured asymmetry is $A_{LR}(\vec{e}p)$ = (\Aphys $\pm$ \Deltastat$_{stat}$ $\pm$ \Deltasyst$_{syst}$) $\times$ 10$^{-6}$. The expectation from the Standard Model assuming no strangeness contribution to the vector current is A$_0$ = (\Azero $\pm$ \DeltaAzero) $\times$ 10$^{-6}$. We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher $Q^2$. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be $G_E^s$ + \FakGMs $G_M^s$ = \GEsGMs $\pm $ \DeltaGEsGMs at $Q^2$ = \Qsquare (GeV/c)$^2$. As in our previous measurement at higher momentum transfer for $G_E^s$ + 0.230 $G_M^s$, we again find the value for $G_E^s$ + \FakGMs $G_M^s$ to be positive, this time at an improved significance level of 2 $\sigma$.
01/2005;
-
F E Maas,
P Achenbach,
K Aulenbacher,
S Baunack,
L Capozza,
J Diefenbach,
K Grimm,
Y Imai,
T Hammel,
D von Harrach, [......],
M Guidal,
R Kunne,
D Marchand,
M Morlet,
S Ong,
J van de Wiele,
S Kowalski,
B Plaster,
R Suleiman,
S Taylor
[show abstract]
[hide abstract]
ABSTRACT: We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta (e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028.
Physical Review Letters 08/2004; 93(2):022002. · 7.37 Impact Factor
-
S. Baunack,
K. Aulenbacher,
D. Balaguer Rios,
L. Capozza,
J. Diefenbach,
B. Glaser,
D Von Harrach,
Y. Imai,
E. -M. Kabub, R. Kothe, [......],
M. A. El-Yakoubi,
R. Frascaria,
R. Kunne,
F. E. Maas,
M. Morlet,
S. Ong,
J. Van de Wiele,
Stanley B. Kowalski,
Y Prok,
S Taylor
[show abstract]
[hide abstract]
ABSTRACT: A new measurement of the parity violating asymmetry in elastic electron scattering on hydrogen at backward angles and at a four momentum transfer of Q[superscript 2]=0.22 (GeV/c)[superscript 2] is reported here. The measured asymmetry is A[subscript LR]=(-17.23±0.82stat±0.89syst)×10-6. The standard model prediction assuming no strangeness is A[subscript 0]=(-15.87±1.22)×10[superscript -6]. In combination with previous results from measurements at forward angles, it is possible to disentangle for the first time the strange form factors at this momentum transfer, GE[superscript s]=0.050±0.038±0.019 and GM[superscript s]=-0.14±0.11±0.11.
APS.
-
I. Altarev,
E. Schilling,
S. Baunack,
L. Capozza,
J. Diefenbach,
K. Grimm,
T. Hammel,
D. von Harrach,
Y. Imai,
E.M. Kabuß, R. Kothe,
J.H. Lee,
A. Lopes Ginja,
F.E. Maas,
A. Sanchez Lorente,
G. Stephan,
C. Weinrich
[show abstract]
[hide abstract]
ABSTRACT: We present a new powerful liquid hydrogen target developed for the precise study of parity violating electron scattering on hydrogen and deuterium. This target has been designed to have minimal target density fluctuations under the heat load of a CW 854.3 MeV electron beam without rastering the electron beam. The target cell has a wide aperture for scattered electrons and is axially symmetric around the beam axis. The construction is optimized to intensify heat exchange by a transverse turbulent mixing in the hydrogen stream, which is directed along the electron beam. The target is constructed as a closed loop circulating system cooled by a helium refrigerator. It is operated by a tangential mechanical pump with an optional natural convection mode. The cooling system supports removal of up to 250 W of beam heating removal. Deeply subcooled liquid hydrogen is used to keep the in-beam temperature below the boiling point. The target density fluctuations are found to be at the level of 10-3 at a beam current of .
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
