Multiple volume reflection by different planes in a bent silicon crystal with its 〈111〉 axis orientation close to the beam direction was observed for the first time for 400 GeV/c protons at the CERN ...SPS. The proton beam was deflected to the side opposite to the crystal bend by an angle of about 67 μrad, which is five times larger than in a single volume reflection by the (110) bent planes. The registered efficiency of one side deflection was about 84%. It was shown that multiple volume reflection transforms to a single volume reflection when the orientation angle of the 〈111〉 axis relative to the beam direction is increased.
Probability of inelastic nuclear interactions in a short bent silicon crystal for its orientations optimal for channeling and volume reflection was investigated using 400
GeV/c protons of the CERN ...SPS. The contribution of nuclear interactions from channeled protons was observed to be about 3–4% of the probability for the amorphous orientation. For the crystal orientation optimal for volume reflection the nuclear interaction probability of protons was a few percents larger than in the amorphous case. It was shown that in the limiting case of a quasi parallel beam realizing for the collider beam halo the inelastic nuclear losses should decrease by more than five times, which is an additional advantage of a crystal as a primary collimator for the LHC collimation system.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).Exclusive electroproduction of ... mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region ...of ... GeV..., 3.0 GeV ... 6.3 GeV, and ... GeV... Results on the angular distribution of the ... meson, including its decay products, are presented. The data were accumulated with the HERMES forward spectrometer during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio reveals that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are presented in projections of ... or ... Violation of ...-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse ... production by longitudinal and transverse virtual photons, ... and ..., is determined for the first time. A hierarchy of helicity amplitudes is established, which mainly means that the unnatural-parity-exchange amplitude describing the ... transition dominates over the two natural-parity-exchange amplitudes describing the ... and ... transitions, with the latter two being of similar magnitude. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions, which are of unnatural parity.
Different kinds of deflection in a silicon crystal bent along the 〈111〉 axis was observed for 150 GeV/c negative particles, mainly π− mesons, at one of the secondary beams of the CERN SPS. The whole ...beam was deflected to one side in quasi-bound states of doughnut scattering (DSB) by atomic strings with the efficiency (95.4±0.2)% and with the peak position close to the bend crystal angle, α=185 μrad. It was observed volume capture of π− mesons into the DSB states with a probability higher than 7%. A beam deflection opposite to the crystal bend was observed for some orientations of the crystal axis due to doughnut scattering and subsequent multiple volume reflections of π− mesons by different bent planes crossing the axis.
Multiple volume reflections of the 400 GeV/c proton beam by the sequence of fourteen bent silicon strips has been studied at the CERN SPS. The sequence is close to be parallel that is the spread of ...the strip orientation angles is much smaller than their bend angle and eleven strips working coherently in the regime of volume reflections deflected the beam by 110 μrad with the efficiency 88%, which is significantly larger than the estimation based on independent reflections. The mechanism giving the efficiency increase has been studied by simulation. It appears that many particles volume captured in one of the strips take part in volume reflections in the subsequent ones. Such a crystal multi reflector can be successfully used as a primary collimator for the beam halo collimation of high-energy accelerators.
Bent silicon crystals in channeling mode are already used for beam extraction and collimation in particle accelerators. Volume reflection of beam particles is more efficient than beam channeling; ...however, the mean deflection angle is rather small. An experiment on the deflection of a 400 GeV/
c
proton beam and a 150 GeV/
c
π
−
beam at CERN using a multi-strip silicon deflector in reflection mode is described. The mean deflection angle of beam particles has been considerably increased due to sequential volume reflections realized in the deflector. This gives possibility for a successful usage of the multi-strip deflectors for beam collimation in high-energy accelerators.
Fermilab experiment E835 has measured the cross section for the reaction p̄p→e+e− at s=11.63, 12.43, 14.40 and 18.22 GeV2. From the analysis of the 66 observed events new high-precision measurements ...of the proton magnetic form factor are obtained.
Design of a Test Bench for MgB2 and HTS Wires STATERA, M; CIULLO, G; LENISA, P ...
IEEE transactions on applied superconductivity,
06/2013, Volume:
23, Issue:
3
Conference Proceeding
The article presents the results on the investigation of the channeling and volume reflection effects in a bent silicon crystal with 13GeV/c positive and negative hadrons (mainly pi +, p and pi -) at ...the CERN PS T9 line. In particular, this is the first study carried out on volume reflection at this energy providing a deflection angle of 69.4 plus or minus 4.7 mu rad and an efficiency of 92.7 plus or minus 3.3%, with positive particles. The measurements have been carried out on a bent silicon strip crystal, using a high precision tracking system based on microstrip silicon detectors; this setup is allowed to trigger on the desired beam portion and to select the incoming particle angular range. The article presents a brief introduction on the bent crystal phenomena, the experimental setup and the results of the measurements.
PDF
