LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of the CKM angle gamma using B-+/- -> DK +/- with D -> K-S(0)pi(+)pi(-), (KSK+K-)-K-0 decays. J. High Energy Phys., 10(10), 097–52pp.
Abstract: A binned Dalitz plot analysis of B-+/- -> DK +/- decays, with D -> K-S(0) pi(+)pi(-) and D -> K0 S K + K -, is performed to measure the C P -violating observables x(+/-) and y(+/-), which are sensitive to the Cabibbo-Kobayashi-Maskawa angle gamma. The analysis exploits a sample of proton-proton collision data corresponding to 3.0 fb(-1) collected by the LHCb experiment. Measurements from CLEO-c of the variation of the strong-interaction phase of the D decay over the Dalitz plot are used as inputs. The values of the parameters are found to be x(+) = (-7.7 +/- 2.4 +/- 1.0 +/- 0.4) x 10(-2), x(-) = (2.5 +/- 2.5 +/- 1.0 +/- 0.5) x 10(-2), y(+) = (-2.2 +/- 2.5 +/- 0.4 +/- 1.0) x 10-2, and y(-) = (7.5 +/- 2.9 +/- 0.5 +/- 1.4) x 10(-2). The first, second, and third uncertainties are the statistical, the experimental systematic, and that associated with the precision of the strong-phase parameters. These are the most precise measurements of these observables and correspond to +/- = (62(-14)(+15))degrees, with a second solution at gamma -> gamma + 180 degrees, and r(B) = 0.080(-0.021)(+0.019), where r(B) is the ratio between the suppressed and favoured B decay amplitudes.
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Ullan, M., Benitez, V., Quirion, D., Zabala, M., Pellegrini, G., Lozano, M., et al. (2014). Low-resistance strip sensors for beam-loss event protection. Nucl. Instrum. Methods Phys. Res. A, 765, 252–257.
Abstract: AC coupled silicon strip sensors can be damaged in case of a beam loss due to the possibility of a large charge accumulation in the bulk, developing very high voltages across the coupling capacitors which can destroy them. Punch-through structures are currently used to avoid this problem helping to evacuate the accumulated charge as large voltages are developing. Nevertheless, previous experiments, performed with laser pulses, have shown that these structures can become ineffective in relatively long strips. The large value of the implant resistance can effectively isolate the “far” end of the strip from the punchthrough structure leading to large voltages. We present here our developments to fabricate lowresistance strip sensors to avoid this problem. The deposition of a conducting material in contact with the implants drastically reduces the strip resistance, assuring the effectiveness of the punch-through structures. First devices have been fabricated with this new technology. Initial results with laser tests show the expected reduction in peak voltages on the low resistivity implants. Other aspects of the sensor performance, including the signal formation, are not affected by the new technology.
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Luo, X. L. et al, Agramunt, J., Egea, F. J., Gadea, A., & Huyuk, T. (2014). Test of digital neutron-gamma discrimination with four different photomultiplier tubes for the NEutron Detector Array (NEDA). Nucl. Instrum. Methods Phys. Res. A, 767, 83–91.
Abstract: A comparative study of the neutron-gamma discrimination performance of a liquid scintillator detector BC501A coupled to four different 5 in photomultiplier tubes (ET9390kb, R11833-100, XP4512 and R4144) was carried out Both the Charge Comparison method and the Integrated Rise-Time method were implemented digitally to discriminate between neutrons and gamma rays emitted by a Cf-252 source. In both methods, the neutron-gamma discrimination capabilities of the four photomultiplier tubes were quantitatively compared by evaluating their figure-of-merit values at different energy regions between 50 keVee and 1000 keVee. Additionally, the results were further verified qualitatively using time-of-flight to distinguish gamma rays and neutrons. The results consistently show that photomultiplier tubes R11833-100 and ET9390kb generally perform best regarding neutron-gamma discrimination with only slight differences in figure-of-merit values. This superiority can be explained by their relatively higher photoelectron yield, which indicates that a scintillator detector coupled to a photomultiplier tube with higher photoelectron yield tends to result in better neutron-gamma discrimination performance. The results of this work will provide reference for the choice of photomultiplier tubes for future neutron detector arrays like NEDA.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of CP asymmetry in B-s(0) -> D-s(-/+) K-/+ decays. J. High Energy Phys., 11(11), 060–30pp.
Abstract: We report on measurements of the time-dependent CP violating observables in B-s(0) -> D-s(-/+) K--/+ decays using a dataset corresponding to 1.0 fb(-1) of pp collisions recorded with the LHCb detector. We find the CP violating observables C-f = 0.53 +/- 0.25 +/- 0.04, A(f)(Delta Gamma) = 0.37 +/- 0.42 +/- 0.20, A((f) over bar)(Delta Gamma) = 0.20 +/- 0.41 +/- 0.20, S-f = -1.09 +/- 0.33 +/- 0.08, S-(f) over bar = -0.36 +/- 0.34 +/- 0.08, where the uncertainties are statistical and systematic, respectively. Using these observables together with a recent measurement of the B-s(0) mixing phase -2 beta(s) leads to the first extraction of the CKM angle gamma from B-s(0) -> D-s(-/+) K--/+ decays, finding gamma = (115(-43)(+28))degrees modulo 180 degrees at 68% CL, where the error contains both statistical and systematic uncertainties.
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NEXT Collaboration(Lorca, D. et al), Martin-Albo, J., Laing, A., Ferrario, P., Gomez-Cadenas, J. J., Alvarez, V., et al. (2014). Characterisation of NEXT-DEMO using xenon K-alpha X-rays. J. Instrum., 9, P10007–20pp.
Abstract: The NEXT experiment aims to observe the neutrinoless double beta decay of Xe-136 in a high-pressure xenon gas TPC using electroluminescence (EL) to amplify the signal from ionization. Understanding the response of the detector is imperative in achieving a consistent and well understood energy measurement. The abundance of xenon K-shell X-ray emission during data taking has been identified as a multitool for the characterisation of the fundamental parameters of the gas as well as the equalisation of the response of the detector. The NEXT-DEMO prototype is a similar to 1.5 kg volume TPC filled with natural xenon. It employs an array of 19 PMTs as an energy plane and of 256 SiPMs as a tracking plane with the TPC light tube and SiPM surfaces being coated with tetraphenyl butadiene (TPB) which acts as a wavelength shifter for the VUV scintillation light produced by xenon. This paper presents the measurement of the properties of the drift of electrons in the TPC, the effects of the EL production region, and the extraction of position dependent correction constants using K-alpha X-ray deposits. These constants were used to equalise the response of the detector to deposits left by gammas from Na-22.
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