Morphology and function of Bast’s valve: additional insight in its functioning using 3D-reconstruction

The utriculo-endolymphatic valve was discovered by Bast in 1928. The function of Bast’s valve is still unclear. By means of orthogonal-plane fluorescence optical sectioning (OPFOS) microscopy 3D-reconstructions of the valve and its surrounding region are depicted. The shape of the duct at the utricular side is that of a flattened funnel. In the direction of the endolymphatic duct and sac this funnel runs into a very narrow duct. The valve itself has a rigid ‘arch-like’ configuration. The opposing thin, one cell-layer thick, utricular membrane is highly compliant. We propose that opening and closure of the valve occurs through movement of the flexible base/utricular membrane away from and toward the relatively rigid valve lip

Characterisation of Medipix3 Silicon Detectors in a Charged-Particle Beam

While designed primarily for X-ray imaging applications, the Medipix3 ASIC can also be used for charged-particle tracking. In this work, results from a beam test at the CERN SPS with irradiated and non-irradiated sensors are presented and shown to be in agreement with simulation, demonstrating the suitability of the Medipix3 ASIC as a tool for characterising pixel sensors.Comment: 16 pages, 13 figure

Hydrological regime of remote catchments with extreme gradients under accelerated change: the Baker basin in Patagonia

The Baker basin (27 000 km2) is located in one of the most pristine and remote areas of the planet. Its hydrological regime is poised to undergo dramatic changes in the near future due to hydropower development and climate change. The basin contains the second-largest lake in South America, and part of a major icefield. This study documents the natural baseline of the Baker River basin, discusses the main hydrological modes and analyses the potential for sustainable management. Annual precipitation varies several-fold from the eastern Patagonian steppes to the North Patagonian Icefield. The westernmost sub-basins are strongly governed by glacier melt with a peak discharge in the austral summer (January–March). The easternmost sub-basins have a much more seasonal response governed by quicker snowmelt in spring (November–December), while they exhibit low flows typical for semi-arid regions during summer and autumn. Topography, vegetation and wetlands may also influence streamflow. The strong spatio-temporal gradients and variability highlight the need for further monitoring, particularly in the headwaters, especially given the severe changes these basins are expected to undergo. The great diversity of hydrological controls and climate change pose significant challenges for hydrological prediction and management

First results from the NA60 experiment at CERN

Since 1986, several heavy ion experiments have studied some signatures of the formation of the quark-gluon plasma and a few exciting results have been found. However, some important questions are still unanswered and require new measurements. The NA60 experiment, with a new detector concept that vastly improves dimuon detection in proton-nucleus and heavy-ion collisions, studies several of those open questions, including the production of open charm. This paper presents the experiment and some first results from data collected in 2002.Comment: Paper presented at the XXXVIII Rencontres de Moriond, QCD and High Energy Hadronic Interactions, Les Arcs, March 22-29, 2003. 4 pages, 6 figure

Radiation damage in the LHCb vertex locator

The LHCb Vertex Locator (VELO) is a silicon strip detector designed to reconstruct charged particle trajectories and vertices produced at the LHCb interaction region. During the first two years of data collection, the 84 VELO sensors have been exposed to a range of fluences up to a maximum value of approximately 45 × 1012 1 MeV neutron equivalent (1 MeV neq). At the operational sensor temperature of approximately −7 °C, the average rate of sensor current increase is 18 μA per fb−1, in excellent agreement with predictions. The silicon effective bandgap has been determined using current versus temperature scan data after irradiation, with an average value of Eg = 1.16±0.03±0.04 eV obtained. The first observation of n+-on-n sensor type inversion at the LHC has been made, occurring at a fluence of around 15 × 1012 of 1 MeV neq. The only n+-on-p sensors in use at the LHC have also been studied. With an initial fluence of approximately 3 × 1012 1 MeV neq, a decrease in the Effective Depletion Voltage (EDV) of around 25 V is observed. Following this initial decrease, the EDV increases at a comparable rate to the type inverted n+-on-n type sensors, with rates of (1.43±0.16) × 10−12 V/ 1 MeV neq and (1.35±0.25) × 10−12 V/ 1 MeV neq measured for n+-on-p and n+-on-n type sensors, respectively. A reduction in the charge collection efficiency due to an unexpected effect involving the second metal layer readout lines is observed

First results from NA60 on low mass muon pair production in In-In collisions at 158 GeV/nucleon

The NA60 experiment at the CERN SPS studies dimuon production in proton-nucleus and nucleus-nucleus collisions. The combined information from a novel vertex telescope made of radiation-tolerant silicon pixel detectors and from the muon spectrometer previously used in NA50 allows for a precise measurement of the muon vertex and a much improved dimuon mass resolution. We report on first results from the data taken for Indium-Indium collisions at 158 AGeV/nucleon in 2003, concentrating on a subsample of about 370 000 muon pairs in the mass range $<1.2$ GeV/$c^{2}$. The light vector mesons $\omega$ and $\phi$ are completely resolved, with a mass resolution of about 23 MeV/$c^{2}$ at the $\phi$. The transverse momentum spectra of the $\phi$ are measured over the continuous range $0<p_{\rm T}<2.5$ GeV/c; the inverse slope parameter of the spectra is found to increase with centrality, with an average value of $T=252\pm3$ MeV.Comment: 9 pages, 6 figures. Plenary talk, SQM2004 conference, Cape Town, South Africa 15-20 September, 2004. To be published in Journal of Physics G: Nuclear and Particle Physic

Precision scans of the pixel cell response of double sided 3D pixel detectors to pion and x-ray beams

hree-dimensional (3D) silicon sensors offer potential advantages over standard planar sensors for radiation hardness in future high energy physics experiments and reduced charge-sharing for X-ray applications, but may introduce inefficiencies due to the columnar electrodes. These inefficiencies are probed by studying variations in response across a unit pixel cell in a 55μm pitch double-sided 3D pixel sensor bump bonded to TimePix and Medipix2 readout ASICs. Two complementary characterisation techniques are discussed: the first uses a custom built telescope and a 120GeV pion beam from the Super Proton Synchrotron (SPS) at CERN; the second employs a novel technique to illuminate the sensor with a micro-focused synchrotron X-ray beam at the Diamond Light Source, UK. For a pion beam incident perpendicular to the sensor plane an overall pixel efficiency of 93.0±0.5% is measured. After a 10o rotation of the device the effect of the columnar region becomes negligible and the overall efficiency rises to 99.8±0.5%. The double-sided 3D sensor shows significantly reduced charge sharing to neighbouring pixels compared to the planar device. The charge sharing results obtained from the X-ray beam study of the 3D sensor are shown to agree with a simple simulation in which charge diffusion is neglected. The devices tested are found to be compatible with having a region in which no charge is collected centred on the electrode columns and of radius 7.6±0.6μm. Charge collection above and below the columnar electrodes in the double-sided 3D sensor is observed

Performance of the LHCb vertex locator

The Vertex Locator (VELO) is a silicon microstrip detector that surrounds the proton-proton interaction region in the LHCb experiment. The performance of the detector during the first years of its physics operation is reviewed. The system is operated in vacuum, uses a bi-phase CO2 cooling system, and the sensors are moved to 7 mm from the LHC beam for physics data taking. The performance and stability of these characteristic features of the detector are described, and details of the material budget are given. The calibration of the timing and the data processing algorithms that are implemented in FPGAs are described. The system performance is fully characterised. The sensors have a signal to noise ratio of approximately 20 and a best hit resolution of 4 μm is achieved at the optimal track angle. The typical detector occupancy for minimum bias events in standard operating conditions in 2011 is around 0.5%, and the detector has less than 1% of faulty strips. The proximity of the detector to the beam means that the inner regions of the n+-on-n sensors have undergone space-charge sign inversion due to radiation damage. The VELO performance parameters that drive the experiment's physics sensitivity are also given. The track finding efficiency of the VELO is typically above 98% and the modules have been aligned to a precision of 1 μm for translations in the plane transverse to the beam. A primary vertex resolution of 13 μm in the transverse plane and 71 μm along the beam axis is achieved for vertices with 25 tracks. An impact parameter resolution of less than 35 μm is achieved for particles with transverse momentum greater than 1 GeV/c

Performance of the LHCb Vertex Detector Alignment Algorithm determined with Beam Test Data

LHCb is the dedicated heavy flavour experiment at the Large Hadron Collider at CERN. The partially assembled silicon vertex locator (VELO) of the LHCb experiment has been tested in a beam test. The data from this beam test have been used to determine the performance of the VELO alignment algorithm. The relative alignment of the two silicon sensors in a module and the relative alignment of the modules has been extracted. This alignment is shown to be accurate at a level of approximately 2 micron and 0.1 mrad for translations and rotations, respectively in the plane of the sensors. A single hit precision at normal track incidence of about 10 micron is obtained for the sensors. The alignment of the system is shown to be stable at better than the 10 micron level under air to vacuum pressure changes and mechanical movements of the assembled system.Comment: accepted for publication in NIM

Precision luminosity measurements at LHCb

Measuring cross-sections at the LHC requires the luminosity to be determined accurately at each centre-of-mass energy √s. In this paper results are reported from the luminosity calibrations carried out at the LHC interaction point 8 with the LHCb detector for √s = 2.76, 7 and 8 TeV (proton-proton collisions) and for √sNN = 5 TeV (proton-lead collisions). Both the "van der Meer scan" and "beam-gas imaging" luminosity calibration methods were employed. It is observed that the beam density profile cannot always be described by a function that is factorizable in the two transverse coordinates. The introduction of a two-dimensional description of the beams improves significantly the consistency of the results. For proton-proton interactions at √s = 8 TeV a relative precision of the luminosity calibration of 1.47% is obtained using van der Meer scans and 1.43% using beam-gas imaging, resulting in a combined precision of 1.12%. Applying the calibration to the full data set determines the luminosity with a precision of 1.16%. This represents the most precise luminosity measurement achieved so far at a bunched-beam hadron collider