Custom ultrasonic instruments have been developed for simultaneous monitoring of binary gas mixture and flow in the ATLAS Inner Detector. Sound transit times are measured in opposite directions in ...flowing gas. Flow rate and sound velocity are respectively calculated from their difference and average. Gas composition is evaluated in real-time by comparison with a sound velocity/composition database, based on the direct dependence of sound velocity on component concentrations in a mixture at known temperature and pressure. Five devices are integrated into the ATLAS Detector Control System. Three instruments monitor coolant leaks into N2 envelopes of the silicon microstrip and Pixel detectors. Resolutions better than ±2×10−5 and ±2×10−4 are seen for C3F8 and CO2 leak concentrations in N2 respectively. A fourth instrument detects sub-percent levels of air ingress into the C3F8 condenser of the new thermosiphon coolant recirculator. Following extensive studies a fifth instrument was built as an angled sound path flowmeter to measure the high returning C3F8 vapour flux (∼1.2kgs−1). A precision of <2.3% FS for flows up to 10ms−1 was demonstrated. These instruments have many potential applications where continuous binary gas composition measurement is required, including hydrocarbon and anaesthetic gas mixtures.
Precision ultrasonic measurements in binary gas systems provide continuous real-time monitoring of mixture composition and flow. Using custom microcontroller-based electronics, we have developed ...sonar instruments, with numerous potential applications, capable of making continuous high-precision sound velocity measurements. The instrument measures sound transit times along two opposite directions aligned parallel to - or obliquely crossing - the gas flow. The difference between the two measured times yields the gas flow rate while their average gives the sound velocity, which can be compared with sound velocity vs. molar composition look-up curves to obtain the binary mixture at a given temperature and pressure. The look-up curves may be generated from prior measurements in known mixtures of the two components, from theoretical calculations, or from a combination of the two. We describe the instruments and their performance within numerous applications in the ATLAS experiment at the CERN Large Hadron Collider (LHC). The instruments can be of interest in other areas where continuous in-situ binary gas analysis and flowmetry are required.
We describe a combined ultrasonic instrument for continuous gas flow measurement and simultaneous real-time binary gas mixture analysis. In the instrument, sound bursts are transmitted in opposite ...directions, which may be aligned with the gas flow path or at an angle to it, the latter configuration being the best adapted to high flow rates. The combined flow measurement and mixture analysis algorithm exploits the phenomenon whereby the sound velocity in a binary gas mixture at known temperature and pressure is a unique function of the molar concentration of the two components. The instrument is central to a possible upgrade to the present ATLAS silicon tracker cooling system in which octafluoropropane (C F ) evaporative cooling fluid would be replaced by a blend containing up to 25% hexafluoroethane (C 2 F 6 ). The instrument has been developed in two geometries following computational fluid dynamics studies of various mechanical layouts. An instrument with 45 crossing angle has been installed for commissioning in the ATLAS silicon tracker cooling system. It can be used in gas flows up to 20 000 l.min -1 and has demonstrated a flow resolution of 2.3% of full scale for linear flow velocities up to 10 m.s in preliminary studies with air. Other instruments are currently used to detect low levels of C 2 F 8 vapor leaking into the N 2 environmental gas surrounding the ATLAS silicon tracker. A long-duration continuous study of more than a year has demonstrated a sensitivity to mixture variation of better than 5.10 -5 .
A search for the rare two-body charmless baryonic decay $B^+ \to p \bar\Lambda$ is performed with $pp$ collision data, corresponding to an integrated luminosity of $3\mbox{\,fb}^{-1}$, collected by ...the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess of $B^+ \to p \bar\Lambda$ candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the $B^+ \to K^0_{\mathrm S} \pi^+$ decay for normalisation, is \begin{eqnarray} \mathcal{B}(B^+ \to p \bar\Lambda) & = & ( 2.4 \,^{+1.0}_{-0.8} \pm 0.3 ) \times 10^{-7} \,, \nonumber \end{eqnarray} where the first uncertainty is statistical and the second systematic.
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