MuPix and ATLASPix -- Architectures and Results

High Voltage Monolithic Active Pixel Sensors (HV-MAPS) are based on a commercial High Voltage CMOS process and collect charge by drift inside a reversely biased diode. HV-MAPS represent a promising technology for future pixel tracking detectors. Two recent developments are presented. The MuPix has a continuous readout and is being developed for the Mu3e experiment whereas the ATLASPix is being developed for LHC applications with a triggered readout. Both variants have a fully monolithic design including state machines, clock circuitries and serial drivers. Several prototypes and design variants were characterised in the lab and in testbeam campaigns to measure efficiencies, noise, time resolution and radiation tolerance. Results from recent MuPix and ATLASPix prototypes are presented and prospects for future improvements are discussed.Comment: 10 pages, proceedings, The 28th International Workshop on Vertex Detectors (VERTEX 2019), 13 - 18 Oct 2019, Lopud Island, Croati

Technical design of the phase I Mu3e experiment

The Mu3e experiment aims to find or exclude the lepton flavour violating decay $\mu \rightarrow eee$ at branching fractions above $10^{-16}$. A first phase of the experiment using an existing beamline at the Paul Scherrer Institute (PSI) is designed to reach a single event sensitivity of $2\cdot 10^{-15}$. We present an overview of all aspects of the technical design and expected performance of the phase~I Mu3e detector. The high rate of up to $10^{8}$ muon decays per second and the low momenta of the decay electrons and positrons pose a unique set of challenges, which we tackle using an ultra thin tracking detector based on high-voltage monolithic active pixel sensors combined with scintillating fibres and tiles for precise timing measurements.Comment: 114 pages, 185 figures. Submitted to Nuclear Instruments and Methods A. Edited by Frank Meier Aeschbacher This version has many enhancements for better readability and more detail

Technical design of the phase I Mu3e experiment

The Mu3e experiment aims to find or exclude the lepton flavour violating decay μ→eee at branching fractions above 10−16. A first phase of the experiment using an existing beamline at the Paul Scherrer Institute (PSI) is designed to reach a single event sensitivity of 2⋅10−15. We present an overview of all aspects of the technical design and expected performance of the phase I Mu3e detector. The high rate of up to 108 muon decays per second and the low momenta of the decay electrons and positrons pose a unique set of challenges, which we tackle using an ultra thin tracking detector based on high-voltage monolithic active pixel sensors combined with scintillating fibres and tiles for precise timing measurements

AUGER RECOMBINATION DYNAMICS IN ISOLATED MERCURY CLUSTER ANIONS Hgn−_n^- (n=9−22n=9 - 22) FOLLOWING S→PS \rightarrow P INTERBAND EXCITATION AT 4.65 eV

B. v. Issendorff, and O. Cheshnovsky, Annu. Rev. Phys. Chem.R. Busani, R. Giniger, T. Hippler, and O. Cheshnovsky, Phys. Rev. Lett.G. B. Griffin, A. Kammrath, O. T. Ehrler, R. M. Young, O. Cheshnovsky, and D. M. Neumark Chem. Phys.Author Institution: Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720, United States; School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, IsraelThe electronic structure of mercury clusters follows the Bloch-Wilson model over a wide size range. As the number of atoms increases, the $s/p$-hybridisation is enhanced, accompanied by a widening of the filled valence $s$ band and the empty $p$-band. This leads to a reduction of the gap between those bands, which will eventually merge. The band-gap can be readily observed by photoelectron spectroscopy of mercury cluster anions Hg$_n^-$, and its closure was extrapolated to occur at $n \approx 400$ atoms.} \textbf{56}, 549 (2005).} At sufficiently high photon energies, absorption competes the photodetachment promoting a second electron into the $p$-band and leaving a hole of $s$-character. The excitation can interact both with nuclear and electronic degrees of freedom before recombining and emitting the remaining electron from the $p$-band. This leads to characterstic tails in the photoelectron spectra as a fingerprint of the preceeding relaxation dynamics.} \textbf{90}, 083401 (2003).} \vspace{.5em} We have directly measured the dynamics of electronic relaxation following \textit{s} to \textit{p} interband excitation of mass selected mercury cluster anions Hg$_n^-$ (with $n=9-22$) using ultrafast time-resolved pump/probe photoelectron spectroscopy.} (2007) \\ \textbf{doi:}10.1016/j.chemphys.2007.12.005.} Auger decay of the excited clusters was found to occur on a timescale of $300-500$~fs, changing abruptly between $n=12$ and 13. These dynamics also define an upper limit of the non-adiabatic coupling and are an order of magnitude faster than results previously reported on such electronic relaxation in Hg$_n$. This difference is interpreted as the result of correlated electron dynamics, and mechanisms are posited for relaxation of both the excited electrons in the \textit{p}-band and the hole in the \textit{s}-band