L. Cassina — Page 4

arXiv2013

First observation of B0->J/ψK+K- and search for B0->J/ψϕ decays

The first observation of the B0->J/ψK+K- decay is presented with a data sample corresponding to an integrated luminosity of 1.0/fb of pp collisions at a center-of-mass energy of 7 TeV collected with the LHCb detector. The branching fraction is measured to be B(B0->J/ψK+K-) = (2.53 +/- 0.31 +/- 0.19)x10^{-6}, where the first uncertainty is statistical and the second is systematic. An amplitude analysis of the final state in the B0->J/ψK+K- decay is performed to separate resonant and nonresonant contributions in the K+K- spectrum. Evidence of the a0(980) resonance is reported with statistical significance of 3.9 standard deviations. The corresponding product branching fraction is measured to be B(B0->J/ψa0(980), a0(980)->K+K-)=(4.70 +/- 3.31 +/- 0.72)x10^{-7}, yielding an upper limit of B(B0->J/ψa0(980), a0(980)->K+K-)<9.0x10^{-7} at 90% confidence level. No evidence of the resonant decay B0->J/ψϕ\; is found, and an upper limit on its branching fraction is set to be B(B0->J/ψϕ)< 1.9x10^{-7} at 90% confidence level.

hep-ex↗

arXiv2013

GeFRO: a New Charge Sensitive Amplifier Design with a Minimal Number of Front-end Components

A new approach was developed for the design of front-end circuits for semiconductor radiation detectors. The readout scheme consists of a first stage made of only a few components located close to the detector, and of a remote second stage located far from the detector, several meters away. The second stage amplifies the signals from the first stage and closes the feedback loop to discharge the input node after each event. The circuit has two outputs: one gives a "fast" signal, with a bandwidth larger than 20 MHz, allowing to preserve the high frequency components of the detector signals, which may be useful for timing measurements, pile-up rejection or pulse shape discrimination. The second output gives a "slow" signal, whose gain depends only on the value of the feedback capacitor, as happens with a classic charge sensitive amplifier, allowing to obtain higher resolution and lower drift. The prototype was named GeFRO for Germanium front-end, and was tested with a BEGe detector from Canberra. The wide bandwidth of the "fast" signal gave a timing resolution of the order of 20 ns. The noise of the circuit at the "slow" output after a 10 us Gaussian shaping was close to 160 electrons RMS with an input capacitance of 26 pF.

physics.ins-det↗