2,666 research outputs found
Investigation of a direction sensitive sapphire detector stack at the 5 GeV electron beam at DESY-II
Extremely radiation hard sensors are needed in particle physics experiments
to instrument the region near the beam pipe. Examples are beam halo and beam
loss monitors at the Large Hadron Collider, FLASH or XFEL. Currently artificial
diamond sensors are widely used. In this paper single crystal sapphire sensors
are considered as a promising alternative. Industrially grown sapphire wafers
are available in large sizes, are of low cost and, like diamond sensors, can be
operated without cooling. Here we present results of an irradiation study done
with sapphire sensors in a high intensity low energy electron beam. Then, a
multichannel direction-sensitive sapphire detector stack is described. It
comprises 8 sapphire plates of 1 cm^2 size and 525 micro m thickness,
metallized on both sides, and apposed to form a stack. Each second metal layer
is supplied with a bias voltage, and the layers in between are connected to
charge-sensitive preamplifiers. The performance of the detector was studied in
a 5 GeV electron beam. The charge collection efficiency measured as a function
of the bias voltage rises with the voltage, reaching about 10 % at 950 V. The
signal size obtained from electrons crossing the stack at this voltage is about
22000 e, where e is the unit charge.
The signal size is measured as a function of the hit position, showing
variations of up to 20 % in the direction perpendicular to the beam and to the
electric field. The measurement of the signal size as a function of the
coordinate parallel to the electric field confirms the prediction that mainly
electrons contribute to the signal. Also evidence for the presence of a
polarisation field was observed.Comment: 13 pages, 7 figures, 3 table
Measurement of shower development and its Moli\`ere radius with a four-plane LumiCal test set-up
A prototype of a luminometer, designed for a future e+e- collider detector,
and consisting at present of a four-plane module, was tested in the CERN PS
accelerator T9 beam. The objective of this beam test was to demonstrate a
multi-plane tungsten/silicon operation, to study the development of the
electromagnetic shower and to compare it with MC simulations. The Moli\`ere
radius has been determined to be 24.0 +/- 0.6 (stat.) +/- 1.5 (syst.) mm using
a parametrization of the shower shape. Very good agreement was found between
data and a detailed Geant4 simulation.Comment: Paper published in Eur. Phys. J., includes 25 figures and 3 Table
The CMS Fast Beam Condition Monitor for HL-LHC
The high-luminosity upgrade of the LHC brings unprecedented requirements for
real-time and precision bunch-by-bunch online luminosity measurement and
beam-induced background monitoring. A key component of the CMS Beam Radiation,
Instrumentation and Luminosity system is a stand-alone luminometer, the Fast
Beam Condition Monitor (FBCM), which is fully independent from the CMS central
trigger and data acquisition services and able to operate at all times with a
triggerless readout. FBCM utilizes a dedicated front-end application-specific
integrated circuit (ASIC) to amplify the signals from CO-cooled silicon-pad
sensors with a timing resolution of a few nanoseconds, which enables the
measurement of the beam-induced background. FBCM uses a modular design with two
half-disks of twelve modules at each end of CMS, with four service modules
placed close to the outer edge to reduce radiation-induced aging. The
electronics system design adapts several components from the CMS Tracker for
power, control and read-out functionalities. The dedicated FBCM23 ASIC contains
six channels and adjustable shaping time to optimize the noise with regards to
sensor leakage current. Each ASIC channel outputs a single binary high-speed
asynchronous signal carrying time-of-arrival and time-over-threshold
information. The chip output signal is digitized, encoded and sent via a
radiation-hard gigabit transceiver and an optical link to the back-end
electronics for analysis. This paper reports on the updated design of the FBCM
detector and the ongoing testing program.Comment: 16th Topical Seminar on Innovative Particle and Radiation Detectors
(IPRD23) 2023 Sept 25-29 Siena, Ital
Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV
The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8 TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum
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