A large Time Projection Chamber is the main device for tracking and charged-particle identification in the ALICE experiment at the CERN LHC. After the second long shutdown in 2019/20, the LHC will ...deliver Pb beams colliding at an interaction rate of about 50 kHz, which is about a factor of 50 above the present readout rate of the TPC. This will result in a significant improvement on the sensitivity to rare probes that are considered key observables to characterize the QCD matter created in such collisions. In order to make full use of this luminosity, the currently used gated Multi-Wire Proportional Chambers will be replaced. The upgrade relies on continuously operated readout detectors employing Gas Electron Multiplier technology to retain the performance in terms of particle identification via the measurement of the specific energy loss by ionization d\(E\)/d\(x\). A full-size readout chamber prototype was assembled in 2014 featuring a stack of four GEM foils as an amplification stage. The performance of the prototype was evaluated in a test beam campaign at the CERN PS. The d\(E\)/d\(x\) resolution complies with both the performance of the currently operated MWPC-based readout chambers and the challenging requirements of the ALICE TPC upgrade program. Detailed simulations of the readout system are able to reproduce the data.
Due to their large active volume and low energy threshold for particle detection Time Projection Chambers (TPCs) are promising candidates to characterise neutrino beams at the next generation long ...baseline neutrino oscillation experiments such as DUNE and Hyper-K. The higher target density for the incoming neutrino beam of a TPC filled with gas at High Pressure (HPTPC) will potentially allow a better neutrino-nucleus interaction measurements as compared with TPCs at atmospheric pressure.
The HPTPC we built has an active volume of about 0.5m3 which is embedded into a pressure vessel rated up to 6bar absolute pressure. A cascade of three meshes amplifies the primary ionisations. The induced charge on each mesh is read out. In addition the photons emitted during the gas amplification are read out by four CCD cameras focused on the readout plane, which thus image the 2D projection of a particle’s tracks on the transverse plane. The third coordinate is reconstructed from the charge signal.
We tested the HPTPC’s performance during a four week beam test at the CERN PS, measuring low momentum proton (≤0.5GeV) interactions with the counting gas. Several mixtures with Argon predominance have been tested for their light yield and gas gain. The aim is to calculate the proton-Ar cross-section from the data sample, which will enter the calculations of final state interactions in neutrino Ar scattering.
We explore the use of Fourier series to describe the kinematics of human running. From a database of 285 trials of treadmill running, we drive a musculoskeletal model with 104 anatomical joint angles ...to obtain kinematics. Using FFT analysis, we determine a fundamental frequency for all independent joint angles and compute average step kinematics. Finally, we represent the average step kinematics using Fourier series with numbers of coefficient pairs ranging from one through ten. We find that five or fewer Fourier coefficient pairs provide an accurate (Pearson’s correlation > 0.99 and root mean square difference < 0.5 degrees) representation for most joint angles. In conclusion, Fourier series appear to provide a compact and valid representation of running kinematics, thus enabling researchers to confidently use Fourier series in research of human running.
The main objective was to investigate whether the cumulative load of the lower limbs, defined as the product of external load and step rate, could be predicted using spatiotemporal variables gathered ...with a commercially available wearable device in running. Therefore, thirty‐nine runners performed two running tests at 10 and 12 km/h, respectively. Spatiotemporal variables (step rate, ground contact time, and vertical oscillation) were collected using a commercially available wearable device. Kinetic variables, measured with gold standard equipment (motion capture system and instrumented treadmill) and used for the calculation of a set of variables representing cumulative load, were peak vertical ground reaction force (peak vGRF), vertical instantaneous loading rate (VILR), vertical impulse, braking impulse, as well as peak extension moments and angular impulses of the ankle, knee and hip joints. Separate linear mixed‐effects models were built to investigate the prediction performance of the spatiotemporal variables for each measure of cumulative load. BMI, speed, and sex were included as covariates. Predictive precision of the models ranged from .11 to .66 (R2m) and .22 to .98 (R2c), respectively. Greatest predictive performance was obtained for the cumulative peak vGRF (R2m = .66, R2c = .97), VILR (R2m = .43, R2c = .97), braking impulse (R2m = .52, R2c = .98), and peak hip extension moment (R2m = .54, R2c = .90). In conclusion, certain variables representing cumulative load of the lower limbs in running can be predicted using spatiotemporal variables gathered with a commercially available wearable device.
After the Long Shutdown 2 (LS2) the LHC will provide lead–lead collisions at interaction rates as high as 50 kHz. In order to cope with such conditions the ALICE Time Projection Chamber (TPC) needs ...to be upgraded.
After the upgrade the TPC will run in a continuous mode, without any degradation of the momentum and d
E
/d
x
resolution compared to the performance of the present TPC. Since readout by multi-wire proportional chambers is no longer feasible with these requirements, new technologies have to be employed. In the new readout chambers the electron amplification is provided by a stack of four Gas ElectronMultiplier (GEM) foils. Here foils with a standard hole pitch of 140 μm as well as large pitch foils (280 μm) are used. Their high voltage settings and orientation have been optimised to provide an energy resolution of
σ
E
/
E
≤ 12% at the photopeak of
55
Fe. At the same settings the Ion BackFlow into the drift volume is less than 1% of the effective number of ions produced during gas amplification and the primary ionisations. This is necessary to prevent the accumulation of space charge, which eventually will distort the field in the drift volume. To ensure stable operation at the high loads during LHC run 3 the chambers have to be robust against discharges, too. With the selected configuration in a quadruple GEMstack the discharge probability is kept at the level of 10
-12
discharges per incoming hadron. An overview of the ALICE TPC upgrade activities will be given in these proceedings and the optimised settings foreseen for the GEM stacks of the future readout chambers are introduced. Furthermore the outcome of two beam time campaigns at SPS and PS (at CERN) in the end of 2014 is shown. At this campaigns the stability against discharges and the d
E
/d
x
performance of a full size readout chamber prototype was tested. In addition it is reported on charging-up studies of 4GEM stacks and on tests of electromagnetic sagging of large GEM foils.
A detector has been constructed for measuring ion mobilities of gas mixtures at atmospheric pressure and room temperature. The detector consists of a standard triple GEM amplification region and a ...drift region where ions drift. A method has been developed to measure the ions’ arrival time at a cathode wire-grid by differentiating the recorded signals on this electrode. Simulations prove that this method is accurate and robust. The ion mobility in different gas mixtures is measured while applying different drift field values ranging from 200Vcm−1 to 1100Vcm−1. From an extrapolation of a Blanc’s law fit to measurements in Ar-CO2 mixtures we find the reduced mobility of the drifting (cluster) ion species in pure argon to be 1.94±0.01 cm2V−1s−1 and in pure carbon-dioxide to be 1.10±0.01 cm2V−1s−1. Applying the same procedure to our measurements in Ne-CO2 yields 4.06±0.07 cm2V−1s−1 and 1.09±0.01 cm2V−1s−1 for the reduced mobilities in pure neon and carbon-dioxide, respectively. Admixtures of N2 to Ne-CO2 (90-10) reduce somewhat the mobility. For the baseline gas mixture of the future ALICE Time Projection Chamber, Ne-CO2-N2 (90-10-5), the measured reduced mobility of the drifting ions is 2.92±0.04 cm2V−1s−1. Ion mobilities are examined for different water content ranging from 70ppm to about 2000ppm in the gas using Ar-CO2 (90-10) and Ne-CO2 (90-10). A slight decrease of ion mobility is observed for the addition of several hundred ppm of water.
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