2,105 research outputs found

    Innovative application of fiber optic sensors in high energy physics experiments

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    This thesis describes the innovative applications to the monitoring in harsh environment, represented by the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC), of the Fibre Bragg Grating (FBG) technology, which, although invented almost 40 years ago, is currently undergoing an explosion in variant manufacturing technologies and applications. The environment inside a large particle physic experiment like the CMS poses several challenges of monitoring spatially varying quantities in an aggressive environment, with high radiation, high magnetic field, tight electromagnetic compatibility (EMC) requirements, where particle detection priorities require monitoring sensors to have very low mass and associated service volume as well as excellent EMC compliance, conditions that can be very well satisfied by FBG-based sensors inscribed on optical fibres. The particular application described here is the monitoring of strain and temperature variation along the beryllium central beam pipe, a vacuum chamber which carries the counter-rotating proton beams in the Large Hadron Collider (LHC) to collisions within the CMS experiment

    Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

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    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