The European XFEL (EuXFEL) is a 3.4-km long X-ray source, which produces femtosecond, ultrabrilliant and spatially coherent X-ray pulses at megahertz (MHz) repetition rates. This X-ray source has been designed to enable the observation of ultrafast processes with near-atomic spatial resolution. Time-resolved crystallographic investigations on biological macromolecules belong to an important class of experiments that explore fundamental and functional structural displacements in these molecules. Due to the unusual MHz X-ray pulse structure at the EuXFEL, these experiments are challenging. Here, we demonstrate how a biological reaction can be followed on ultrafast timescales at the EuXFEL. We investigate the picosecond time range in the photocycle of photoactive yellow protein (PYP) with

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The energy resolution of a highly granular 1 m 3 analogue scintillator-steel hadronic calorimeter is studied using charged pions with energies from 10 GeV to 80 GeV at the CERN SPS. The energy resolution for single hadrons is determined to be approximately 58%/ E/GeV. This resolution is improved to approximately 45%/ E/GeV with software compensation techniques. These techniques take advantage of the event-by-event information about the substructure of hadronic showers which is provided by the imaging capabilities of the calorimeter. The energy reconstruction is improved either with corrections based on the local energy density or by applying a single correction factor to the event energy sum derived from a global measure of the shower energy density. The application of the compensation algorithms to GEANT4 simulations yield resolution improvements comparable to those observed for real data.

The CALICE Semi-Digital Hadronic Calorimeter (SDHCAL) prototype, built in 2011, was exposed to beams of hadrons, electrons and muons in two short periods in 2012 on two different beam lines of the CERN SPS. The prototype with its 48 active layers, made of Glass Resistive Plate Chambers and their embedded readout electronics, was run in triggerless and power-pulsing mode. The performance of the SDHCAL during the test beam was found to be very satisfactory with an efficiency exceeding 90% for almost all of the 48 active layers. A linear response (within ± 5%) and a good energy resolution are obtained for a large range of hadronic energies (5-80 GeV) by applying appropriate calibration coefficients to the collected data for both the Digital (Binary) and the Semi-Digital (Multi-threshold) modes of the SDHCAL prototype. The Semi-Digital mode shows better performance at energies exceeding 30 GeV.

We present a description of the operation of a multi-pixel detector in the presence of non-negligible dark-count and cross-talk effects. We apply the model to devise self-consistent calibration strategies to be performed on the very light under investigation.Several concepts and technologies have been proposed that lead to the development of detectors such as visible-light photon counters (VLPC) [18], superconductive transition edge sensors (TES) [19], time-multiplexed detectors [20][21][22], hybrid photodetectors (HPD) [23,24] and Silicon photomultipliers (SiPM) [25]. Irrespective of the concept and design features, these detectors may in general be classified in terms of photon detection efficiency, spectral response, time development of the signal, dead time, and notable photon number resolving capability. As of today, the ideal detector has yet to appear and the optimal choice is application specific. This paper focuses on SiPMs, detectors featuring unique characteristics that are achieved by a rapidly evolving technology. Silicon photomultipliers consist of a high density (by now limited to ∼ 2000 cells/mm 2 ) matrix of diodes with a common output. Each diode (or cell) is operated in a limited Geiger-Mueller (GM) regime, in order to achieve gains at the level of 10 6 . Quenching mechanisms are implemented to avoid establishing self-sustaining discharges. These detectors are sensitive to single photons triggering GM avalanches and can be endowed with a dynamic range well above 100 photons/burst. The photon detection efficiency (PDE) depends on the sensor design and specification, but it may well exceed 60%. Moreover, SiPM are genuine photon-number resolving detectors in that they measure light intensity simply by the number of fired diodes. Compactness, robustness, low cost, low operating voltage, and power consumption are also added values against traditional photodetectors. On the other hand, SiPMs are affected by significant dark count rates (DCR), associated to cells fired by thermally generated charge carriers. Moreover, the GM avalanche development is known to be associated to the generation of photons [26], which may in turn trigger secondary avalanches and result in relevant cross-talk. Whether DCR and cross-talk may be directly measured, it is clear that they are folded in the detector response to any signal and need to be modelled to properly assess the statistical properties of the light field being investigated. This paper reports the experimental validation of two models, on the way to a self-consistent characterization of the SiPM response. Experimental set-upThe detector response to a weak light field is shown in Fig. 1(a), featuring the sensor output signal after a high-bandwidth amplifier with a gain of 50. The different bands in the image, obtained in persistency mode, correspond to samples with different numbers of triggered cells, i.e. different numbers of detected photons. The photon-number resolving properties are also clear in Fig. 1(b) that shows the corresponding spectrum as obtained ...