A
bstract
The production of Υ mesons in pp collisions at
s
=
7
and 8 TeV is studied with the LHCb detector using data samples corresponding to an integrated luminosity of 1 fb
−1
and 2 fb
−1
...respectively. The production cross-sections and ratios of cross-sections are measured as functions of the meson transverse momentum
p
and rapidity
y
, for
p <
30 GeV
/c
and 2
.
0
< y <
4
.
5.
An upgrade of the near detector of the T2K long baseline neutrino oscillation experiment is currently being conducted. This upgrade will include two new Time Projection Chambers, each equipped with ...16 charge readout resistive Micromegas modules.
A procedure to validate the performance of the detectors at different stages of production has been developed and implemented to ensure a proper and reliable operation of the detectors once installed. A dedicated X-ray test bench is used to characterize the detectors by scanning each pad individually and to precisely measure the uniformity of the gain and the deposited energy resolution over the pad plane. An energy resolution of about 10% is obtained.
A detailed physical model has been developed to describe the charge dispersion phenomena in the resistive Micromegas anode. The detailed physical description includes initial ionization, electron drift, diffusion effects and the readout electronics effects. The model provides an excellent characterization of the charge spreading of the experimental measurements and allowed the simultaneous extraction of gain and charge spreading information of the modules.
A search for the decays Bc+→J/ψD(*)0K+ and Bc+→J/ψD(*)+K*0 is performed with data collected at the LHCb experiment corresponding to an integrated luminosity of 3 fb−1. The decays Bc+→J/ψD0K+ and ...Bc+→J/ψD*0K+ are observed for the first time, while first evidence is reported for the Bc+→J/ψD*+K*0 and Bc+→J/ψD+K*0 decays. The branching fractions of these decays are determined relative to the Bc+→J/ψπ+ decay. The Bc+ mass is measured, using the J/ψD0K+ final state, to be 6274.28±1.40(stat)±0.32(syst) MeV/c2. This is the most precise single measurement of the Bc+ mass to date.
Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of the cosmic rays with the highest-energies, which are correlated with the positions of ...relatively nearby active galactic nuclei (AGN) Pierre Auger Collaboration, Science 318 (2007) 938. The correlation has maximum significance for cosmic rays with energy greater than ∼6
×
10
19
eV and AGN at a distance less than ∼75
Mpc. We have confirmed the anisotropy at a confidence level of more than 99% through a test with parameters specified a priori, using an independent data set. The observed correlation is compatible with the hypothesis that cosmic rays with the highest-energies originate from extra-galactic sources close enough so that their flux is not significantly attenuated by interaction with the cosmic background radiation (the Greisen–Zatsepin–Kuz’min effect). The angular scale of the correlation observed is a few degrees, which suggests a predominantly light composition unless the magnetic fields are very weak outside the thin disk of our galaxy. Our present data do not identify AGN as the sources of cosmic rays unambiguously, and other candidate sources which are distributed as nearby AGN are not ruled out. We discuss the prospect of unequivocal identification of individual sources of the highest-energy cosmic rays within a few years of continued operation of the Pierre Auger Observatory.
The first study is presented of CP violation with an amplitude analysis of the Dalitz plot of B0 → DK+π– decays, with D → K+π–, K+K–, and π+π–. The analysis is based on a data sample corresponding to ...3.0 fb–1 of pp collisions collected with the LHCb detector. No significant CP violation effect is seen, and constraints are placed on the angle γ of the unitarity triangle formed from elements of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. Hadronic parameters associated with the B0 → DK*(892)0 decay are determined for the first time. These measurements can be used to improve the sensitivity to γ of existing and future studies of the B0 → DK*(892)0 decay.
In this paper we describe the performance of a prototype of the High Angle Time Projection Chambers (HA-TPCs) that are being produced for the Near Detector (ND280) upgrade of the T2K experiment. The ...two HA-TPCs of ND280 will be instrumented with eight Encapsulated Resistive Anode Micromegas (ERAM) on each endplate, for a total of 32 ERAMs. This innovative technique allows the detection of the charge emitted by ionization electrons over several pads, improving the determination of the track position.
The TPC prototype has been equipped with the first ERAM module produced for T2K and with the HA-TPC readout electronics chain and it has been exposed to an electron beam at DESY in order to measure spatial and dE/dx resolution. In this paper we characterize the performances of the ERAM and, for the first time, we compare them with a newly developed simulation of the detector response.
Spatial resolution better than 800 μm and dE/dx resolution better than 10% are observed for all the incident angles and for all the drift distances of interest. All the main features of the data are correctly reproduced by the simulation and these performances fully fulfill the requirements for the HA-TPCs of T2K.
Using a pp collision data sample corresponding to an integrated luminosity of 3.0 fb–1, collected by the LHCb detector, we present the first search for the strangeness-changing weak decay Ξb– → ...Λ0bπ–. No b hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported.
We present a search for ultrarelativistic magnetic monopoles with the Pierre Auger observatory. Such particles, possibly a relic of phase transitions in the early Universe, would deposit a large ...amount of energy along their path through the atmosphere, comparable to that of ultrahigh-energy cosmic rays (UHECRs). The air-shower profile of a magnetic monopole can be effectively distinguished by the fluorescence detector from that of standard UHECRs. No candidate was found in the data collected between 2004 and 2012, with an expected background of less than 0.1 event from UHECRs. The corresponding 90% confidence level (C.L.) upper limits on the flux of ultrarelativistic magnetic monopoles range from 10−19(cm2 sr s)−1 for a Lorentz factor γ=109 to 2.5×10−21(cm2 sr s)−1 for γ=1012. These results-the first obtained with a UHECR detector-improve previously published limits by up to an order of magnitude.
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