118 research outputs found
A method to polarise antiprotons in storage rings and create polarised antineutrons
An intense circularely polarised photon beam interacts with a cooled
antiproton beam in a storage ring. Due to spin dependent absorption cross
sections for the reaction gamma+antiproton > pi- + antineutron a built-up of
polarisation of the stored antiprotons takes place. Figures-of-merit around 0.1
can be reached in principle over a wide range of antiproton energies. In this
process antineutrons with Polarisation > 70% emerge. The method is presented
for the case of 300 MeV/c cooled antiproton beam
Bunch Compressor Performances at the CLIC Test Facility
The Test Facility of the "Compact Linear Collider" (CLIC) at CERN (CTF), has to prove the feasibility of transporting high charge beams through decelerating structures at 30 GHz to create RF power. This RF power is used to supply, in the final scheme, the cavities of the main linac. To optimise this power generation, a bunch compressor has been installed in the test line. This compressor shortens the electron bunches after creation and acceleration in the RF gun. The compressed bunches are then accelerated by a high gradient cavity (50 MV/m) and transported to a 30 GHz cavity. Compressed bunch length mesurements showed that lengths of 0.6 mm (rms) were obtained at the entrance of 30 GHz cavity for a 10 nC beam. Compression of electron bunches of charges between 2 and 17 nC have also been measured. Emittance measurements were done to study the transverse effects of the bunch compressor on the beam. The use of the code PARMELA allowed the design and optimisation of the chicane. The simulations results have been compared to the experimental measurements
First attempt of the measurement of the beam polarization at an accelerator with the optical electron polarimeter POLO
The conventional methods for measuring the polarization of electron beams are either time consuming, invasive or accurate only to a few percent. We developed a method to measure electron beam polarization by observing the light emitted by argon atoms following their excitation by the impact of polarized electrons. The degree of circular polarization of the emitted fluorescence is directly related to the electron polarization. We tested the polarimeter on a test GaAs source available at the MAMI electron accelerator in Mainz, Germany. The polarimeter determines the polarization of a 50 keV electron beam decelerated to a few eV and interacting with an effusive argon gas jet. The resulting decay of the excited states produces the emission of a circularly polarized radiation line at 811.5 nm which is observed and analyzed
Beam-Normal Single Spin Asymmetry in Elastic Electron Scattering off Si and Zr
We report on a new measurement of the beam-normal single spin asymmetry
in the elastic scattering of 570 MeV transversely polarized
electrons off Si and Zr at . The
studied kinematics allow for a comprehensive comparison with former results on
C. No significant mass dependence of the beam-normal single spin
asymmetry is observed in the mass regime from C to Zr.Comment: Submitted for publication to Physics Letters
Evidence for Strange Quark Contributions to the Nucleon's Form Factors at = 0.108 (GeV/c)
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 = \Qsquare
(GeV/c) and at a forward electron scattering angle of 30. The measured asymmetry is = (\Aphys
\Deltastat \Deltasyst) 10. The
expectation from the Standard Model assuming no strangeness contribution to the
vector current is A = (\Azero \DeltaAzero) 10. We
have improved the statistical accuracy by a factor of 3 as compared to our
previous measurements at a higher . We have extracted the strangeness
contribution to the electromagnetic form factors from our data to be +
\FakGMs = \GEsGMs \DeltaGEsGMs at = \Qsquare (GeV/c).
As in our previous measurement at higher momentum transfer for + 0.230
, we again find the value for + \FakGMs to be positive,
this time at an improved significance level of 2 .Comment: 4 pages, 3 figure
The helicity amplitudes A and A for the D resonance obtained from the reaction}
The helicity dependence of the reaction
has been measured for the first time in the photon energy range from 550 to 790
MeV. The experiment, performed at the Mainz microtron MAMI, used a
4-detector system, a circularly polarized, tagged photon beam, and a
longitudinally polarized frozen-spin target. These data are predominantly
sensitive to the resonance and are used to determine its
parameters.Comment: 5 pages, 4 figure
Measurement of the Transverse Beam Spin Asymmetry in Elastic Electron Proton Scattering and the Inelastic Contribution to the Imaginary Part of the Two-Photon Exchange Amplitude
We report on a measurement of the asymmetry in the scattering of transversely
polarized electrons off unpolarized protons, A, at two Q values of
\qsquaredaveragedlow (GeV/c) and \qsquaredaveragedhighII (GeV/c) and a
scattering angle of . The measured transverse
asymmetries are A(Q = \qsquaredaveragedlow (GeV/c)) =
(\experimentalasymmetry alulowcorr \statisticalerrorlow
\combinedsyspolerrorlowalucor) 10 and
A(Q = \qsquaredaveragedhighII (GeV/c)) = (\experimentalasymme
tryaluhighcorr \statisticalerrorhigh
\combinedsyspolerrorhighalucor) 10. The first
errors denotes the statistical error and the second the systematic
uncertainties. A arises from the imaginary part of the two-photon
exchange amplitude and is zero in the one-photon exchange approximation. From
comparison with theoretical estimates of A we conclude that
N-intermediate states give a substantial contribution to the imaginary
part of the two-photon amplitude. The contribution from the ground state proton
to the imaginary part of the two-photon exchange can be neglected. 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.Comment: 4 figures, submitted to PRL on Oct.
First measurement of the Gerasimov-Drell-Hearn integral for Hydrogen from 200 to 800 MeV
A direct measurement of the helicity dependence of the total photoabsorption
cross section on the proton was carried out at MAMI (Mainz) in the energy range
200 < E_gamma < 800 MeV. The experiment used a 4 detection system, a
circularly polarized tagged photon beam and a frozen spin target.
The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward
spin polarizability determined from the data are 226 \pm 5 (stat)\pm
12(sys) \mu b and -187 \pm 8 (stat)\pm 10(sys)10^{-6} fm^4, respectively, for
200 < E_\gamma < 800 MeV.Comment: 6 pages, 3 figures, 3 table
Measurement of Strange Quark Contributions to the Nucleon's Form Factors at Q^2=0.230 (GeV/c)^2
We report on a measurement of the parity-violating asymmetry in the
scattering of longitudinally polarized electrons on unpolarized protons at a
of 0.230 (GeV/c)^2 and a scattering angle of \theta_e = 30^o - 40^o.
Using a large acceptance fast PbF_2 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} +- 0.27_{\rm sys}) 10^{-6}. The Standard Model
expectation assuming no strangeness contributions to the vector form factors is
. 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 + 0.225 G^s_M = 0.039 +- 0.034 or F^s_1 + 0.130 F^s_2
= 0.032 +- 0.028.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Letters on Dec 11, 200
Results from the CLIC Test Facility
In order to study the principle of the Compact Linear Collider (CLIC) based on the Two Beam Acceleration (TBA) scheme at high frequency, a CLIC Test Facility (CTF) has been set-up at CERN. After four years of successful running, the experimental programme is now fully completed and all its objectives reached, particularly the generation of a high intensity drive beam with short bunches by a photo-injector, the production of 30 GHz RF power and the acceleration of a probe beam by 30 GHz structures. A summary of the CTF results and their impact on linear collider design is given. This covers 30 GHz high power testing, study of intense, short single bunches; as well as RF-Gun, photocathode and beam diagnostic developments. A second phase of the test facility (CTF2) is presently being installed to demonstrate the feasibility of the TBA scheme by constructing a fully engineered, 10 m long, test section very similar to the CLIC drive and main linacs, producing up to 480 MW of peak RF power at 30 GHz and accelerating the beam up to 320 MeV. The present status of CTF2 is reported
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