THGEM-based detectors for sampling elements in DHCAL: laboratory and beam evaluation

We report on the results of an extensive R&D program aimed at the evaluation of Thick-Gas Electron Multipliers (THGEM) as potential active elements for Digital Hadron Calorimetry (DHCAL). Results are presented on efficiency, pad multiplicity and discharge probability of a 10x10 cm2 prototype detector with 1 cm2 readout pads. The detector is comprised of single- or double-THGEM multipliers coupled to the pad electrode either directly or via a resistive anode. Investigations employing standard discrete electronics and the KPiX readout system have been carried out both under laboratory conditions and with muons and pions at the CERN RD51 test beam. For detectors having a charge-induction gap, it has been shown that even a ~6 mm thick single-THGEM detector reached detection efficiencies above 95%, with pad-hit multiplicity of 1.1-1.2 per event; discharge probabilities were of the order of 1e-6 - 1e-5 sparks/trigger, depending on the detector structure and gain. Preliminary beam tests with a WELL hole-structure, closed by a resistive anode, yielded discharge probabilities of <2e-6 for an efficiency of ~95%. Methods are presented to reduce charge-spread and pad multiplicity with resistive anodes. The new method showed good prospects for further evaluation of very thin THGEM-based detectors as potential active elements for DHCAL, with competitive performances, simplicity and robustness. Further developments are in course.Comment: 15 pages, 11 figures, MPGD2011 conference proceedin

Characterization of microbulk detectors in argon- and neon-based mixtures

A recent Micromegas manufacturing technique, so called Microbulk, has been developed, improving the uniformity and stability of this kind of detectors. Excellent energy resolutions have been obtained, reaching values as low as 11% FWHM at 5.9 keV in Ar+5%iC4H10. This detector has other advantages like its flexible structure, low material budget and high radio-purity. Two microbulk detectors with gaps of 50 and 25 um have been characterized in argon- and neon-based mixtures with ethane, isobutane and cyclohexane. The results will be presented and discussed. The gain curves have been fitted to the Rose-Korff gain model and dependences of the electron mean free path and the threshold energy for ionization have been obtained. The possible relation between these two parameters and the energy resolution will be also discussed.Comment: Submitted to the Journal of Instrumentatio

MICROMEGAS chambers for hadronic calorimetry at a future linear collider

Prototypes of MICROMEGAS chambers, using bulk technology and analog readout, with 1x1cm2 readout segmentation have been built and tested. Measurements in Ar/iC4H10 (95/5) and Ar/CO2 (80/20) are reported. The dependency of the prototypes gas gain versus pressure, gas temperature and amplification gap thickness variations has been measured with an 55Fe source and a method for temperature and pressure correction of data is presented. A stack of four chambers has been tested in 200GeV/c and 7GeV/c muon and pion beams respectively. Measurements of response uniformity, detection efficiency and hit multiplicity are reported. A bulk MICROMEGAS prototype with embedded digital readout electronics has been assembled and tested. The chamber layout and first results are presented

Shower development of particles with momenta from 15 GeV to 150 GeV in the CALICE scintillator-tungsten hadronic calorimeter

We present a study of showers initiated by electrons, pions, kaons, and protons with momenta from 15 GeV to 150 GeV in the highly granular CALICE scintillator-tungsten analogue hadronic calorimeter. The data were recorded at the CERN Super Proton Synchrotron in 2011. The analysis includes measurements of the calorimeter response to each particle type as well as measurements of the energy resolution and studies of the longitudinal and radial shower development for selected particles. The results are compared to Geant4 simulations (version 9.6.p02). In the study of the energy resolution we include previously published data with beam momenta from 1 GeV to 10 GeV recorded at the CERN Proton Synchrotron in 2010.Comment: 35 pages, 21 figures, 8 table

Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes

We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re

Construction and test of a 1×1 m2 Micromegas chamber for sampling hadron calorimetry at future lepton colliders

Equipe MicromegasSampling calorimeters can be finely segmented and used to detect showers with high spatial resolution. This imaging power can be exploited at future linear collider experiments where the measurement of jet energy by a Particle flow method requires optimal use of tracking and calorimeter information. Gaseous detectors can achieve high granularity and a hadron sampling calorimeter using Micromegas chambers as active elements is considered in this paper. Compared to traditional detectors using wires or resistive plates, Micromegas is free of space charge effects and could therefore show superior calorimetric performance. To test this concept, a prototype of 1×1 m2 equipped with 9216 readout pads of 1×1 cm2 has been built. Its technical and basic operational characteristics are reported

Observation of two new Ξb−\Xi_b^- baryon resonances

Two structures are observed close to the kinematic threshold in the $\Xi_b^0 \pi^-$ mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content $bds$ are expected in this mass region: the spin-parity $J^P = \frac{1}{2}^+$ and $J^P=\frac{3}{2}^+$ states, denoted $\Xi_b^{\prime -}$ and $\Xi_b^{*-}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(\Xi_b^{\prime -}) - m(\Xi_b^0) - m(\pi^{-}) = 3.653 \pm 0.018 \pm 0.006$ MeV$/c^2$, $m(\Xi_b^{*-}) - m(\Xi_b^0) - m(\pi^{-}) = 23.96 \pm 0.12 \pm 0.06$ MeV$/c^2$, $\Gamma(\Xi_b^{*-}) = 1.65 \pm 0.31 \pm 0.10$ MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of $\Gamma(\Xi_b^{\prime -}) < 0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.Comment: 17 pages, 2 figure

Observation of an Excited Bc+ State

Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date

The Time Structure of Hadronic Showers in highly granular Calorimeters with Tungsten and Steel Absorbers

The intrinsic time structure of hadronic showers influences the timing capability and the required integration time of hadronic calorimeters in particle physics experiments, and depends on the active medium and on the absorber of the calorimeter. With the CALICE T3B experiment, a setup of 15 small plastic scintillator tiles read out with Silicon Photomultipliers, the time structure of showers is measured on a statistical basis with high spatial and temporal resolution in sampling calorimeters with tungsten and steel absorbers. The results are compared to GEANT4 (version 9.4 patch 03) simulations with different hadronic physics models. These comparisons demonstrate the importance of using high precision treatment of low-energy neutrons for tungsten absorbers, while an overall good agreement between data and simulations for all considered models is observed for steel.Comment: 24 pages including author list, 9 figures, published in JINS

Study of WW boson production in association with beauty and charm

The associated production of a $W$ boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data corresponding to integrated luminosities of 1.0 and $2.0\,{\rm fb}^{-1}$ collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The $W$ bosons are reconstructed using the $W\to\mu\nu$ decay and muons with a transverse momentum, $p_{\rm T}$, larger than 20 GeV in the pseudorapidity range $2.0 20$ GeV and $2.2 < \eta < 4.2$. The sum of the muon and jet momenta must satisfy $p_{\rm T} > 20$ GeV. The fraction of $W+$jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the $W\!+\!b$ and $W\!+\!c$ production cross-sections. The ratio of the $W+$jet to $Z+$jet production cross-sections is also measured using the $Z\to\mu\mu$ decay. All results are in agreement with Standard Model predictions