R. Klanner

The forward and rear calorimeters of the ZEUS experiment are made of 48 modules with maximum active dimensions of 4.6 m height, 0.2 m width, 7 λ depth and maximum weight of 12 t. It consists of 1 X0 uranium plates interleaved with plastic scintillator tiles read out via wavelength shifters and photomultipliers. The mechanical construction, the achieved tolerances as well as the optical and electronics readout are described. Ten of these modules have been tested with electrons, hadrons and muons in the momentum range 15–100 GeV/c. Results on resolution, uniformity and calibration are presented. Our main result is the achieved calibration accuracy of about 1% obtained by using the signal from the uranium radioactivity.

The charge collection in silicon detectors has been studied, by measuring the response to high-energy particles of a 20 μ pitch strip detector as a function of applied voltage and magnetic field. The results are well described by a simple model. The model is used to predict the spatial resolution of silicon strip detectors and to propose a detector with optimized spatial resolution.

Recent results on Limited Geiger-mode Microcell Silicon Photodiode (LGP) are described. Two new modifications of LGP have been designed and produced. Each of them consists of 104 pixels 10×10μm2 size with area of 1mm2. These pixels operate as an independent photon counters, giving the output signal as a sum of the signals from pixels fired by photons. The effective “gain” is large (≈105). The efficiency of the visible light photon detection of few percents has been measured. Low-temperature dark rate dependence has been studied. The timing by LGP at the level of 100 ps (FWHM) was found.

The design of the readout system for the high resolution ZEUS calorimeter is described. The design employs 10 MHz switched capacitor pipelines and digital signal processors, and provides linear operation over a 17-bit dynamic range. The implementation of the design is also discussed.

The European X-ray free electron laser is a new research facility currently under construction in Hamburg, Germany. Typical for XFEL machines is the high peak brilliance several orders of magnitudes above existing synchrotron facilities. With a pulse length below 100 fs and an extremely high luminosity of 30,000 flashes per second the European XFEL will have a worldwide unique time structure that enables researchers to record movies of ultrafast processes. This demands the development of new detectors tailored to the requirements imposed by the experiments while complying with the machine specific operation parameters. The adaptive gain integrating pixel detector (AGIPD) is one response to the need for large 2D detectors, able to cope with the 5 MHz repetition rate, as well as with the high dynamic range needed by XFEL experiments (from single photons to 104 12 keV photons per pixel per pulse). In addition, doses up to 1 GGy over three years are expected.

The Adaptive Gain Integrating Pixel Detector (AGIPD) is an X-ray imager, custom designed for the European X-ray Free-Electron Laser (XFEL). It is a fast, low-noise integrating detector, with an adaptive gain amplifier per pixel. This has an equivalent noise of less than 1 keV when detecting single photons and, when switched into another gain state, a dynamic range of more than 10 4 photons of 12 keV. In burst mode the system is able to store 352 images while running at up to 6.5 MHz, which is compatible with the 4.5 MHz frame rate at the European XFEL. The AGIPD system was installed and commissioned in August 2017, and successfully used for the first experiments at the Single Particles, Clusters and Biomolecules (SPB) experimental station at the European XFEL since September 2017. This paper describes the principal components and performance parameters of the system.

Silicon photomultipliers, thanks to their excellent performance, robustness and relatively simple use, are the photon-detectors of choice for many present and future applications. This paper gives an overview of methods to characterise SiPMs. The different SiPM parameters are introduced and generic setups for their determination presented. Finally, ways to extract the parameters from the measurements are discussed and the results shown. If a parameter can be obtained from different measurements, the results are compared and recommendations given, which is considered to be the most reliable. The characterisation of SiPMs, in particular for high light intensities and in high radiation fields, is presently a field of intensive research with many open questions and problems which will be discussed.

A Monte Carlo program is presented which simulates the response of SiPMs in the nonlinear regime, where the number of Geiger discharges from photons and/or from dark counts in the time interval given by the pulse shape of a single Geiger discharge, approaches or exceeds the number of SiPM pixels. The model includes the effects of after-pulses, of prompt and delayed cross-talk, and of the voltage drop over the load resistance of the readout electronics. The results of the simulation program are compared to published results from SiPMs with different number of pixels for different intensities and time distributions of photons, dark-count rates, SiPM pulse shapes, and probabilities of cross-talk and after-pulsing.

High energy photon colliders (γγ,γe) are based on e - e - linear colliders where high energy photons are produced using Compton scattering of laser light on high energy electrons just before the interaction point. This paper is a part of the Technical Design Report of the linear collider TESLA. 1 Physics program, possible parameters and some technical aspects of the photon collider at TESLA are discussed.

Progress in testing semiconductor drift detectors is reported. Generally better position and energy resolutions were obtained than resolutions published previously. The improvement is mostly due to new electronics better matched to different detectors. It is shown that semiconductor drift detectors are becoming versatile and reliable detectors for position and energy measurements.

Semiconductor drift chambers have been recently suggested and feasibility tests performed. This paper presents the first operative silicon drift detectors for position and energy measurements. Design criteria and experimental results in the laboratory and on an accelerator beam are reported.

Nearly 200 000 examples of the diffractive process K−p → K−π−π+p at 63 GeV have been obtained using a two magnet spectrometer equipped with Čerenkov counters for secondary particle identification. In addition some 2000 examples of the process K−p → ωK−p have been obtained. The Kππ data have been subjected to partial-wave analysis. The dominant JP = 1+ system couples to K∗π, in both S and D waves, ϱK, κπ and εK. The data confirm the existence of two JP = 1+ Q mesons and their masses, widths and branching ratios are given. The ifωK data show that the couplings of the Q mesons to ωK are approximately equal to the couplings to ϱ0K. The two 1+ nonets expected in the quark model are discussed in the light of this and other recent experiments. There is strong evidence for a broad JP = 0− resonance at about 1.46 GeV. At higher masses, structure in the JP = 2− partial waves establishes the existence of at least one JP = 2− L meson.

A telescope consisting of six silicon microstrip detectors achieving 5 μm spatial resolution for minimum ionizing particles has been built. The design and fabrication of the counters, electronics, and mechanical set-up is described, and first results of its performance in a 175 GeV/c beam are reported.

Elastic diffraction scattering of π−, K− and pon protons has been measured at 25 and 40 GeV/c at the Serpukhov Proton Accelerator. Differential elastic cross sections and diffraction slopes are presented in the momentum-transfer interval 0.07–0.80 (GeV/c)2 and compared with existing data at lower energies.

A sample of ∼ 70 000 fitted events of the reaction of π−p→π−π−π+p at 25 and 40 GeV/c has been obtained with the CERN-IHEP boson spectrometer at the Serpukhov accelerator. A partial-wave analysis shows that (i) A1 and A3 cannot be described by a Breit-Wigner amplitude, (ii) the A2 can be well described by a Breit-Wigner amplitude, (iii) although A1, A3 and A2 have different properties, the energy dependence of their production cross section is similar.

Diffractive production of the 3π system has been studied at 63 and 94 GeV using a two magnet spectrometer with high, uniform acceptance. The total number of events used in the analysis is ∼600 000. The A2 meson is shown to be diffractively produced. The existence of a resonant component in both the 1+ and 2− enhancements is established and resonance parameters for the corresponding A1 and A3 mesons are given. There are several indications in the data of states which would correspond to radial excitations in the quark model.

AGIPD—(Adaptive Gain Integrating Pixel Detector) is a hybrid pixel X-ray detector developed by a collaboration between Deutsches Elektronen-Synchrotron (DESY), Paul-Scherrer-Institut (PSI), University of Hamburg and the University of Bonn. The detector is designed to comply with the requirements of the European XFEL. The radiation tolerant Application Specific Integrated Circuit (ASIC) is designed with the following highlights: high dynamic range, spanning from single photon sensitivity up to 104 12.5keV photons, achieved by the use of the dynamic gain switching technique using 3 possible gains of the charge sensitive preamplifier. In order to store the image data, the ASIC incorporates 352 analog memory cells per pixel, allowing also to store 3 voltage levels corresponding to the selected gain. It is operated in random-access mode at 4.5MHz frame rate. The data acquisition is done during the 99.4ms between the bunch trains. The AGIPD has a pixel area of 200× 200 μ m2 and a 500μ m thick silicon sensor is used. The architecture principles were proven in different experiments and the ASIC characterization was done with a series of development prototypes. The mechanical concept was developed in the close contact with the XFEL beamline scientists and is now being manufactured. A first single module system was successfully tested at APS.

Measurements of open charm and beauty production cross sections in deep inelastic ep scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections are obtained in the kinematic range of negative four-momentum transfer squared of the photon $$2.5~\hbox {GeV}^2\le Q^2 \le 2000\, \hbox {GeV}^2$$ and Bjorken scaling variable $$3 \cdot 10^{-5} \le x_\mathrm{Bj} \le 5 \cdot 10^{-2}$$ . The combination method accounts for the correlations of the statistical and systematic uncertainties among the different datasets. Perturbative QCD calculations are compared to the combined data. A next-to-leading order QCD analysis is performed using these data together with the combined inclusive deep inelastic scattering cross sections from HERA. The running charm- and beauty-quark masses are determined as $$m_c(m_c) = 1.290^{+0.046}_{-0.041} \mathrm{(exp/fit)}$$ $${}^{+0.062}_{-0.014} \mathrm{(model)}$$ $${}^{+0.003}_{-0.031} \mathrm{(parameterisation)}$$ GeV and $$m_b(m_b) = 4.049^{+0.104}_{-0.109} \mathrm{(exp/fit)}$$ $${}^{+0.090}_{-0.032} \mathrm{(model)}$$ $${}^{+0.001}_{-0.031} \mathrm{(parameterisation)}~\mathrm{GeV}$$ .

Electron spin polarizations of about 8% were observed at HERA in November 1991. In runs during 1992, utilizing special orbit corrections, polarization values close to 60% have been achieved. In this paper the polarimeter, the machine conditions, the data analysis, the first results and plans for future measurements are described.

We have built a sandwich calorimeter consisting of 10 mm thick lead plates and 2.5 mm thick scintillator sheets. The thickness ratio between lead and scintillator was optimized to achieve a good energy resolution for hadrons. We have exposed this calorimeter to electrons, hadrons and muons in the energy range between 3 and 75 GeV, obtaining an average energy resolution of 23%E for electrons and 44%E for hadrons. For energies above 10 GeV and after leakage corrections, the ratio of electron response to hardron response is 1.05.

In order to extend the tracking acceptance, to improve the primary and secondary vertex reconstruction and thus enhancing the tagging capabilities for short lived particles, the ZEUS experiment at the HERA Collider at DESY installed a silicon strip vertex detector. The barrel part of the detector is a 63 cm long cylinder with silicon sensors arranged around an elliptical beampipe. The forward part consists of four circular shaped disks. In total just over 200k channels are read out using 2.9m2 of silicon. In this report a detailed overview of the design and construction of the detector is given and the performance of the completed system is reviewed.

The impact of electron hole plasmas on silicon sensor performance was studied with a multi-channel Transient Current Technique (mTCT) setup. Electron hole densities of up to 1016 cm−3 (equivalent to 105 focused 12 keV photons) were created with sub-ns lasers (660 and 1015 nm) and the time resolved current pulses of segmented sensors (4 channels simultaneously) were read out by a 2.5 GHz oscilloscope. Measurements for strip sensors of 280μm thickness and 80μm pitch as well as 450μm thickness and 50μm pitch were carried out showing an increase of the charge collection time and an increase of the charge spread (charge cloud explosion) with increased charge carrier density. These effects were studied as a function of the applied bias voltage and electron hole density. It was shown that for the current AGIPD sensor design plasma effects in p-in-n sensors of 450μm thickness are negligible if at least 500 V bias is applied.

Experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors which can withstand X-ray doses up to 1 GGy. For the investigation of X-ray radiation damage up to these high doses, MOS capacitors and gate-controlled diodes built on high resistivity n-doped silicon with crystal orientations <100> and <111> produced by two vendors, CiS and Hamamatsu, have been irradiated with 12 keV X-rays at the DESY DORIS III synchrotron light source. Using capacitance/conductance-voltage, current-voltage and thermal dielectric relaxation current measurements, the surface densities of oxide charges and interface traps at the Si-SiO2 interface, and the surface-current densities have been determined as function of dose. Results indicate that the dose dependence of the surface density of oxide charges and the surface-current density depend on the crystal orientation and producer. In addition, the influence of the voltage applied to the gates of the MOS capacitor and the gate-controlled diode during X-ray irradiation on the surface density of oxide charges and the surface-current density has been investigated at doses of 100 kGy and 100 MGy. It is found that both strongly depend on the gate voltage if the electric field in the oxide points from the surface of the SiO2 to the Si-SiO2 interface. Finally, annealing studies have been performed at 60°C and 80°C on MOS capacitors and gate-controlled diodes irradiated to 5 MGy and the annealing kinetics of oxide charges and surface current determined.

The shape of the A2 resonance has been measured in πp → pA2 at 2.6 GeV/c, i.e. near threshold, with A2 produced at minimum momentum transfer. The results confirm, with a new method and instrument, the A2 splitting found previously with the Jacobian-peak method.

The breakdown behaviour of SiPMs (Silicon PhotoMultiplier) with pixel sizes of 15$\times $15, 25$\times $25, 50$\times $50, and 100$\times $100 $\mu $m$^2$, manufactured by KETEK, has been investigated. From the current-voltage characteristics measured with and without illumination by LED light of 470 nm wavelength, the current-breakdown voltage, $V_I$, and from linear fits of the voltage dependence of the SiPM gain, measured by recording pulse-area spectra, the gain-breakdown voltage, $V_G$, have been obtained. The voltage dependence of the Geiger-breakdown probability was determined from the fraction of zero photoelectron events with LED illumination. By comparing the results to a model calculation, the photodetection-breakdown voltage, $V_{PD}$, has been determined. Within experimental uncertainties, $V_I$ and $V_{PD}$ are equal and independent of pixel size. For $V_G$, a dependence on pixel size is observed. The difference $V_I - V_G$ is about 1 V for the SiPM with 15 $\mu $m pixels, decreases with pixel size and is compatible with zero for the SiPM with 100 $\mu $m pixels.

The understanding of the weighting field of irradiated silicon sensors is essential for calculating the response of silicon detectors in the radiation environment at accelerators like at the CERN LHC.Using 1-D calculations of non-irradiated pad sensors and 1-D TCAD (Technology Computer-Aided Design) simulations of pad sensors before and after irradiation, it is shown that the time-dependence of the weighting field is related to the resistivity of low field regions with ohmic behaviour in the sensor.A simple formula is derived, which relates the time constant of the time-dependent weighting field, τ, with the resistivity and the extension of the low-field region for pad detectors.As the resistivity of irradiated silicon increases with fluence and finally reaches the intrinsic resistivity, τ becomes much larger than the charge-collection time and the weighting field becomes essentially independent of time.The TCAD simulations show that the transition from a time-dependent to a time-independent weighting field occurs at a neutron-equivalent fluence of ≈ 5×10 12 cm -2 for a 200 µm thick pad diode operated at 40 V and -20 • C. It is therefore concluded that the use of a time-independent weighting field calculated with the same method as for a fully-depleted non-irradiated sensor is also appropriate for the simulation of highly irradiated silicon sensors.

The novel type of the Silicon Photodiode — Limited Geiger-mode Photodiode (LGP) has been produced and studied. The device consists of many ≈104 mm−2 independent cells ≈10 mkm size around n+ -“pins” located between p-substrate and thin SiC layer. Very high gain more than 104 for 0.67 mkm wave length light source and up to 6·105 for single electron have been achieved. The LGP photon detection efficiency at the level of one percent has been measured.

We study the energy resolution of two compensating sandwich calorimeters using scintillators as readout material and lead and uranium as absorber, respectively. By employing the technique of the two interleaved calorimeters we extract the contribution of sampling and intrinsic fluctuations. We find that the energy resolution for hadrons is dominated by sampling fluctuations in both cases.

The reaction π−p → π−π−π+p has been measured at 25 and 40 GeV/c at the Serpukhov proton accelerator. The production cross section as a function of beam energy, momentum transfer, and 3π mass is presented, and results of the partial-wave analysis of the 3π system are discussed.

Imaging experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors with extraordinary performance specifications: doses of up to 1 GGy of 12 keV photons, up to 105 12 keV photons per 200 µm × 200 µm pixel arriving within less than 100 fs, and a time interval between XFEL pulses of 220 ns. To address these challenges, in particular the question of radiation damage, the properties of the SiO2 layer and of the Si–SiO2 interface, using MOS (metal-oxide-semiconductor) capacitors manufactured on high-resistivity n-type silicon irradiated to X-ray doses between 10 kGy and 1 GGy, have been studied. Measurements of capacitance/conductance–voltage (C/G–V) at different frequencies, as well as of thermal dielectric relaxation current (TDRC), have been performed. The data can be described by a dose-dependent oxide charge density and three dominant radiation-induced interface states with Gaussian-like energy distributions in the silicon band gap. It is found that the densities of the fixed oxide charges and of the three interface states increase up to dose values of approximately 10 MGy and then saturate or even decrease. The shapes and the frequency dependences of the C/G–V measurements can be quantitatively described by a simple model using the parameters extracted from the TDRC measurements.

A pair of spin rotators has been installed in the electron ring of HERA. Longitudinal spin polarizations up to 65% have been reached reproducibly during dedicated measurement time. This is the first time that longitudinal spin polarization has been produced in a high energy electron storage ring.

Using a high-resolution silicon vertex detector we have observed a very clean signal of 127 D∗+. After a careful study of the experimental resolution of our apparatus we have measured m(D∗++)−m(D0) = 145.39±0.06±0.03 MeV. We have also obtained a 90% CL upper limit to γ(D∗+) of 131 keV.

In partial wave analyses of the (π−π−π+) system, substantial shape changes of the 1+S (ϱπ) intensity as a function of t, and relative phase changes of ≈ 90°, provide compelling evidence for a resonant A1 of mass ≈ 1280 MeV and width ≈ 300 MeV.

Measurements of the behaviour of various high-resolution silicon strip detectors with capacitive charge division have been made in a high-energy particle beam. The results are compared with an electrostatic model which calculates the charges deposited on the strips after the passage of a minimum ionizing particle. Good agreement is found and the model is used to propose a method of improving the charge-division properties of such detectors.

The inclusive reactions h+p→φ+X, (h=π±,,K±,p±), are studied for 0⪅xF⪅0.3 and p⊥ ⩽ 1 GeV at 93 and and 63 GeV incident momentum. Differential cross sections dσ/dp⊥2 anddσ/dxF are presented and are compared with predictions of the naive parton model.

Missing-mass spectra were obtained in the reaction π−p → p X− at 25 and 40 GeV/c at the Serpukhov Accelerator. At low masses a strong peak at 1.3 and a smaller one near 1.7 GeV are observed. In the mass region above 2 GeV no structure exceeding 3μb/(geV/c2 is seen.

The production of beauty and charm quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q 2 < 1000 GeV2 using an integrated luminosity of 354 pb−1. The beauty and charm content in events with at least one jet have been extracted using the invariant mass of charged tracks associated with secondary vertices and the decay-length significance of these vertices. Differential cross sections as a function of Q 2, Bjorken x, jet trans- verse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of x and Q 2. The running beauty-quark mass, m b at the scale m b , was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be m b (m b ) = 4.07 ± 0.14 (fit) − 0.07 + 0.01 (mod.) − 0.00 + 0.05 (param.) − 0.05 + 0.08 (theo.) GeV.

Using multi-channel time-resolved current measurements (multi-TCT), the charge collection of p+n silicon strip sensors for electron–hole pairs produced close to the Si–SiO2 interface by a focussed sub-nanosecond laser with a wavelength of 660 nm has been studied. Sensors before and after irradiation with 1 MGy of X-rays have been investigated. The charge signals induced in the readout strips and the rear electrode as a function of the position of the light spot are described by a model which allows a quantitative determination of the charge losses and of the widths of the electron-accumulation and hole-inversion layers close to the Si–SiO2 interface. Depending on the applied bias voltage, biasing history and environmental conditions, like humidity, incomplete electron or hole collection and different widths of the accumulation layers are observed. In addition, the results depend on the time after biasing the sensor, with time constants which can be as long as days. The observations are qualitatively explained with the help of detailed sensor simulations. Finally, their relevance for the detection of X-ray photons and charged particles, and for the stable operation of segmented p+n silicon sensors is discussed.

The reduced cross sections for $e^{+}p$ deep inelastic scattering have been measured with the ZEUS detector at HERA at three different centre-of-mass energies, $318$, $251$ and $225$ GeV. The cross sections, measured double differentially in Bjorken $x$ and the virtuality, $Q^2$, were obtained in the region $0.13\ \leq\ y\ \leq\ 0.75$, where $y$ denotes the inelasticity and $5\ \leq\ Q^2\ \leq\ 110$ GeV$^2$. The proton structure functions $F_2$ and $F_L$ were extracted from the measured cross sections.

This paper describes the progress made in 1992 towards increasing the vertical electron beam polarization at HERA. Utilizing harmonic spin-orbit corrections and beam tuning, the vertical polarization has been increased from 15% to nearly 60% at a beam energy of 26.7 GeV. The long-term reproducibility of the polarization is excellent. Measurements of the build-up time and the energy dependence of the polarization are also described.

Four prototype modules following the same design as the ZEUS forward calorimeter (FCAL) modules have been constructed and tested with electrons, hadrons and muons in the momentum range of 1 to 100 GeV/c. The main topics under investigation were: calibration, uniformity of response, noise, light yield, energy resolution and the electron to hadron response (e/h ratio). The result of the measurements is presented and the expected performance of the FCAL is discussed in the light of these results.

The NA 32 experiment at the CERN SPS has collected 38 million hadronic interactions with incident 200 GeV/c π−,K − andp beam. Using a segmented silicon active target and a telescope of high resolution silicon microstrip counters we have selected fully reconstructedD 0→K −π+,D 0→K −π+π+π−,D +→K −π+π+,D + →K − K +π+π+ and charge conjugate decays. The integrated cross-sections forD o,D + D *+ andD + meson production and the dependence of the cross-section on longitudinal and transverse momentum of theD are presented.

As a preparation for the ZEUS high resolution calorimeter, sampling calorimeters made from 3.2 mm plates of depleted uranium read out by plastic scintillator of 3 mm and 5 mm thickness have been built. The response of hadrons, electrons and muons has been measured in the energy range between 3 and 100 GeV. In agreement with predictions, the relative response of electrons and hadrons as well as the hadronic energy resolution depend strongly on the thickness of the plastic scintillator. For 3.2 mm depleted uranium and 3 mm thick scintillator we observe over the full energy range equal response for electrons and hadrons; a hadronic energy resolution of 34.5%E[GeV] is obtained. Results are given for the spatial resolution for electrons and hadrons. Finally, results from a lead scintillator calorimeter built as a prestudy before uranium plates were available are reported.

Charge multiplication (CM) in p$^+$n epitaxial silicon pad diodes of 75, 100 and 150 $\upmu$m thickness at high voltages after proton irradiation with 1 MeV neutron equivalent fluences in the order of $10^{16}$ cm$^{-2}$ was studied as an option to overcome the strong trapping of charge carriers in the innermost tracking region of future Super-LHC detectors. Charge collection efficiency (CCE) measurements using the Transient Current Technique (TCT) with radiation of different penetration (670, 830, 1060 nm laser light and $\alpha$-particles with optional absorbers) were used to locate the CM region close to the p$^+$-implantation. The dependence of CM on material, thickness of the epitaxial layer, annealing and temperature was studied. The collected charge in the CM regime was found to be proportional to the deposited charge, uniform over the diode area and stable over a period of several days. Randomly occurring micro discharges at high voltages turned out to be the largest challenge for operation of the diodes in the CM regime. Although at high voltages an increase of the TCT baseline noise was observed, the signal-to-noise ratio was found to improve due to CM for laser light. Possible effects on the charge spectra measured with laser light due to statistical fluctuations in the CM process were not observed. In contrast, the relative width of the spectra increased in the case of $\alpha$-particles, probably due to varying charge deposited in the CM region.

Methods are developed, which use the pulse-height spectra of SiPMs measured in the dark and illuminated by pulsed light, to determine the pulse shape, the dark-count rate, the gain, the average number of photons initiating a Geiger discharge, the probabilities for prompt cross-talk and after-pulses, as well as the electronics noise and the gain fluctuations between and in pixels. The entire pulse-height spectra, including the background regions in-between the peaks corresponding to different number of Geiger discharges, are described by single functions. As a demonstration, the model is used to characterise a KETEK SiPM with 4382 pixels of 15 \mu m x 15 \mu m area for voltages between 2.5 and 8 V above the breakdown voltage at 20{\deg}C. The results are compared to other methods of characterising SiPMs. Finally, examples are given, how the complete description of the pulse-eight spectra can be used to optimise the operating voltage of SiPMs, and a method for an in-situ calibration and monitoring of SiPMs, suited for large-scale applications, is proposed.

Two-particle azimuthal correlations have been measured in neutral current deep inelastic ep scattering with virtuality Q2> 5 GeV2 at a centre-of-mass energy $$ \sqrt{s} $$ = 318 GeV recorded with the ZEUS detector at HERA. The correlations of charged particles have been measured in the range of laboratory pseudorapidity −1.5 < η < 2.0 and transverse momentum 0.1 < pT< 5.0 GeV and event multiplicities Nch up to six times larger than the average 〈Nch〉 ≈ 5. The two-particle correlations have been measured in terms of the angular observables cn{2} = 〈〈cosnΔφ〉〉, where n is between 1 and 4 and ∆φ is the relative azimuthal angle between the two particles. Comparisons with available models of deep inelastic scattering, which are tuned to reproduce inclusive particle production, suggest that the measured two-particle correlations are dominated by contributions from multijet production. The correlations observed here do not indicate the kind of collective behaviour recently observed at the highest RHIC and LHC energies in high-multiplicity hadronic collisions.

A Python program has been developed which fits a published detector-response model to SiPM charge spectra to characterise SiPMs. Spectra for SiPMs illuminated by low intensity pulsed light with Poisson-distributed number of photons and a time spread of order nanoseconds or less, and spectra without illumination can be analysed. The entire spectra, including the intervals in-between the photoelectron peaks, are fitted, which allows determining, in addition to the mean number of detected photons, gain, gain spread, prompt cross-talk, pedestal, and electronics noise, the dark-count rate as well as the probability and time constant of after-pulses. The starting values of the fit parameters are extracted from the charge spectra. The program performance has been evaluated using simulated charge spectra with the different SiPM parameters varied in a wide range. By analysing 100 simulated spectra for every parameter set, the biases and statistical uncertainties of the individual parameters have been determined. It is found that the parameters are precisely determined and that the entire spectra are well described, in most cases with a χ2/NDF close to 1. In addition, measured spectra for two types of SiPMs for a wide range of over-voltages have been analysed. The program achieves mostly a good description of the spectra, and the parameters determined agree with the values from the producers. The program can be used for detailed analyses of single spectra, but, as it is compatible with the native Python multiprocessing module, also for the automatic characterisation of large samples of SiPMs.

We have studied the hadronic production of charmed mesons in the NA 32 experiment at CERN. A special trigger together with a high resolution vertex detector consisting of charge coupled devices and silicon microstrip detectors allowed the selection of very clean samples of charmed mesons. We have collected 852 fully reconstructed decays: 60D + →K + K −π+, 543D°→K −π+ andK −π+π−π+ as well as 249D +→K −π+π+ (or charge conjugate). 147 mesons out of our $${{D^0 } \mathord{\left/ {\vphantom {{D^0 } {\bar D^0 }}} \right. \kern-\nulldelimiterspace} {\bar D^0 }}$$ sample were produced via chargedD * state. For all charmed mesons we determine the total production cross-section and study thex F andp 2 distributions.

In the CERN NA 32 experiment a high-resolution silicon vertex detector and a purely topological approach have been used to investigate various decays of charmed particles. We observe ∼620 fully reconstructed decays ofD 0 in 12 channels and determine the branching ratios. For fourD 0 decay modes involving a single (unseen) π0 the small and narrowD *+−D 0 mass difference is used to measure their branching ratios. We also observe ∼280 fully reconstructedD + decays in 10 channels, ∼90D s + decays in 11 channels as well as 160Λ s c and 18 decay channels ofD +. For theD s + , we measure the branching fractions within a subset of 16 three- and five-prong decay channels. For theΛ s c , we determine the branching fractions within a sample of 11 three- and five-prong decay channels, nearly all involving a proton.

The mobility of electrons and holes in silicon depends on many parameters. Two of them are the electric field and the temperature. It has been observed previously that the mobility in the transition region between ohmic transport and saturation velocities is a function of the orientation of the crystal lattice. This paper presents a new set of parameters for the mobility as function of temperature and electric field for 〈1 1 1〉 and 〈1 0 0〉 crystal orientation. These parameters are derived from time of flight measurements of drifting charge carriers in planar p+nn+ diodes in the temperature range between −30 °C and 50 °C and electric fields of 2 × 103 V/cm to 2 × 104 V/cm.

A K10K− mass spectrum in the A2 region has been obtained in the reaction π−p → p K10K− at 7 GeV/c. The double peak structure of the A2 meson, observed in the earlier missing mass spectra, is found to be present also in the decay channel A2− → K10K−.

Abstract The HERAPDF2.0 ensemble of parton distribution functions (PDFs) was introduced in 2015. The final stage is presented, a next-to-next-to-leading-order (NNLO) analysis of the HERA data on inclusive deep inelastic ep scattering together with jet data as published by the H1 and ZEUS collaborations. A perturbative QCD fit, simultaneously of $$\alpha _s(M_Z^2)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>α</mml:mi> <mml:mi>s</mml:mi> </mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>M</mml:mi> <mml:mi>Z</mml:mi> <mml:mn>2</mml:mn> </mml:msubsup> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> and the PDFs, was performed with the result $$\alpha _s(M_Z^2)= 0.1156 \pm 0.0011~\mathrm{(exp)}~ ^{+0.0001}_{-0.0002}~ \mathrm{(model}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>α</mml:mi> <mml:mi>s</mml:mi> </mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>M</mml:mi> <mml:mi>Z</mml:mi> <mml:mn>2</mml:mn> </mml:msubsup> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>=</mml:mo> <mml:mn>0.1156</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.0011</mml:mn> <mml:mspace /> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>exp</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> <mml:msubsup> <mml:mspace /> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>0.0002</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.0001</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace /> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>model</mml:mi> </mml:mrow> </mml:mrow> </mml:math> $$\mathrm{+ parameterisation)}~ \pm 0.0029~\mathrm{(scale)}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mi>parameterisation</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> <mml:mspace /> <mml:mo>±</mml:mo> <mml:mn>0.0029</mml:mn> <mml:mspace /> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>scale</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> . The PDF sets of HERAPDF2.0Jets NNLO were determined with separate fits using two fixed values of $$\alpha _s(M_Z^2)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>α</mml:mi> <mml:mi>s</mml:mi> </mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>M</mml:mi> <mml:mi>Z</mml:mi> <mml:mn>2</mml:mn> </mml:msubsup> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> , $$\alpha _s(M_Z^2)=0.1155$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>α</mml:mi> <mml:mi>s</mml:mi> </mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>M</mml:mi> <mml:mi>Z</mml:mi> <mml:mn>2</mml:mn> </mml:msubsup> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>=</mml:mo> <mml:mn>0.1155</mml:mn> </mml:mrow> </mml:math> and 0.118, since the latter value was already chosen for the published HERAPDF2.0 NNLO analysis based on HERA inclusive DIS data only. The different sets of PDFs are presented, evaluated and compared. The consistency of the PDFs determined with and without the jet data demonstrates the consistency of HERA inclusive and jet-production cross-section data. The inclusion of the jet data reduced the uncertainty on the gluon PDF. Predictions based on the PDFs of HERAPDF2.0Jets NNLO give an excellent description of the jet-production data used as input.

We present results from the NA32 experiment at CERN on the production characteristics of the charmed baryon Λ+c in 230 GeV π−Cu and K−Cu interactions. A high resolution vertex detector consisting of change-coupled devices and silicon microstrip detectors allowed the selection of a very clean sample of 154 Λ+c → pK−π+ (and charge conjugate) decays. Results on differential and integrated cross sections are given.

Silicon strip detectors with 5 μm spatial resolution have been used during 1982–1985 in the ACCMOR spectrometer at CERN. After a local beam flux of about 1014 minimum ionizing particles per cm2 we observe a significant increase in dark current and systematic distortions in the measured coordinates which are explained in terms of a decrease in the effective donor concentration.

We present results on a sample of Λc decays obtained in the NA32 experiment in 1985 using charge-coupled devices for vertex reconstruction and a trigger on Λc→pK−π+ (and charge conjugate). We observe a distinct peak at the Λc mass on zero background. The lifetime of the Λc is determined to be (1.4±0.30.5±0.3)x10−13 s based on a sample of 14 events.

The JPC = 2−+ partial wave intensities and their large phase changes prove the resonant nature of the A3 meson (mass ≈ 1670 MeV, width ≈ 210 MeV). The decay modes are f0π, ϱ0π, and ϵ0π. Evidence is found for a further 2− enhancement.

In silicon sensors high densities of electron-hole pairs result in a change of the current pulse shape and spatial distribution of the collected charge compared to the situation in presence of low charge carrier densities. This paper presents a detailed comparison of numerical simulations with time resolved current measurements on planar silicon sensors using 660 nm laser light to create different densities of electron hole pairs.

The European X-ray Free Electron Laser (XFEL) will deliver 27000 fully coherent, high brilliance X-ray pulses per second each with a duration below 100 fs. This will allow the recording of diffraction patterns of single molecules and the study of ultra-fast processes. One of the detector systems under development for the XFEL is the Adaptive Gain Integrating Pixel Detector (AGIPD), which consists of a pixel array with readout ASICs bump-bonded to a silicon sensor with pixels of 200 × 200 μm2. The particular requirements for the detector are a high dynamic range (0, 1 up to 105 12 keV photons/XFEL-pulse), a fast read-out and radiation tolerance up to doses of 1 GGy of 12 keV X-rays for 3 years of operation. At this X-ray energy no bulk damage in silicon is expected. However fixed oxide charges in the SiO2 layer and interface traps at the Si-SiO2 interface will build up. As function of the 12 keV X-ray dose the microscopic defects in test structures and the macroscopic electrical properties of segmented sensors have been investigated. From the test structures the oxide charge density, the density of interface traps and their properties as function of dose have been determined. It is found that both saturate (and even decrease) for doses above a few MGy. For segmented sensors surface damage introduced by the X-rays increases the full depletion voltage, the surface leakage current and the inter-pixel capacitance. In addition an electron accumulation layer forms at the Si-SiO2 interface which increases with dose and decreases with applied voltage. Using TCAD simulations with the dose dependent damage parameters obtained from the test structures the results of the measurements can be reproduced. This allows the optimization of the sensor design for the XFEL requirements.

The European X-ray Free Electron Laser (XFEL) will deliver 30,000 fully coherent, high brilliance X-ray pulses per second each with a duration below 100 fs. This will allow the recording of diffraction patterns of single complex molecules and the study of ultra-fast processes. Silicon pixel sensors will be used to record the diffraction images. In 3 years of operation the sensors will be exposed to doses of up to 1 GGy of 12 keV X-rays. At this X-ray energy no bulk damage in silicon is expected. However fixed oxide charges in the insulating layer covering the silicon and interface traps at the Si-SiO2 interface will be introduced by the irradiation and build up over time. We have investigated the microscopic defects in test structures and the macroscopic electrical properties of segmented detectors as a function of the X-ray dose. From the test structures we determine the oxide charge density and the densities of interface traps as a function of dose. We find that both saturate (and even decrease) for doses between 10 and 100 MGy. For segmented sensors the defects introduced by the X-rays increase the full depletion voltage, the surface leakage current and the inter-pixel capacitance. We observe that an electron accumulation layer forms at the Si-SiO2 interface. Its width increases with dose and decreases with applied bias voltage. Using TCAD simulations with the dose dependent parameters obtained from the test structures, we are able to reproduce the observed results. This allows us to optimize the sensor design for the XFEL requirements.

Radiation damage in silicon, caused by the creation of point and cluster defects due to energetic charged hadrons and neutrons, results in a serious degradation of silicon-sensor performance and limits their lifetime. So far not all the defects are understood. The work presented here focuses on the study of radiation damage by electrons of different kinetic energies, from 1.5 MeV to 15 MeV, in order to study the differences between point- and cluster-related defects. The introduction rate of vacancy-related point defects and of so-called clustered regions was investigated as a function of electron energy. It is shown that the ratio between cluster dominated and point defect formation increases with increasing electron energy. 1.5 MeV electrons create only point defects, and the formation of cluster defects starts already at 3.5 MeV. To study the defect kinetics, isothermal annealing at 80 °C and isochronal annealing measurements were performed.

We have investigated the effects of X-ray irradiation to doses of 0, 200 Gy, 20 kGy, 2 MGy, and 20 MGy on the Hamamatsu silicon-photomultiplier (SiPM) S10362-11-050C.The SiPMs were irradiated without applied bias voltage.From current-voltage, capacitance/conductancevoltage, capacitance/conductance-frequency, pulse-shape, and pulse-area measurements, the SiPM characteristics below and above breakdown voltage were determined.Significant changes of some SiPM parameters are observed.Up to a dose of 20 kGy the performance of the SiPMs is hardly affected by X-ray radiation damage.For doses of 2 and 20 MGy the SiPMs operate with hardly any change in gain, but with a significant increase in dark-count rate and cross-talk probability.

Within the framework of the CALICE collaboration, our group has characterized Silicon Photomultipliers (SiPMs) from various producers, in order to enhance the single cell performances of a highly granular analog hadron calorimeter, with particular emphasis on improving the linearity of the response, ensuring environmental stability, calibration portability and reducing the parameters spread among the different channels. As an outcome, new plastic scintillator tiles coupled to KETEK PM1125 SMD SiPM have been commissioned, characterized and mounted on calorimeter modules: details and results of the characterization procedure, together with the performances of the new tile and SiPM design will be discussed. The radiation tolerance to X-rays of KETEK PM1125 is also under investigation. The amount and type of damage caused by irradiation of the devices exposed to 3 kGy and 20 MGy doses will be presented.

The results of a 1-D Monte-Carlo program, which simulates the avalanche multiplication in diodes with depths of the order of 1 $\mu$m based on the method proposed in Ref.1, are presented. The aim of the study is to achieve a deeper understanding of silicon photo-multipliers. It is found that for a given over-voltage, $\mathit{OV}$, the maximum of the discharge current is reached at the breakdown voltage, $U_\mathit{bd}$, and that the avalanche stops when the voltage drops to $U_\mathit{bd} - \mathit{OV}$. This is completely different to the generally accepted understanding of SiPMs, which has already been noted in Ref.1. Simulated characteristics of the avalanche breakdown, like the time dependence of the avalanche current, over-voltage dependence of the Geiger-breakdown probability and the gain for photons and dark counts, are presented and compared to the expectations from silicon photo-multipliers.

The results of a 1-D Monte-Carlo program, which simulates the avalanche multiplication in diodes with depths of the order of 1μm based on the method proposed in Ref. Windischhofer and Riegler (2023), are presented. The aim of the study is to achieve a deeper understanding of silicon photo-multipliers. It is found that for a given over-voltage, OV, the maximum of the discharge current is reached at the breakdown voltage, Ubd, and that the avalanche stops when the voltage drops to approximately Ubd−OV. This is completely different to the generally accepted understanding of SiPMs, that the discharge stops at about Ubd. Simulated characteristics of the avalanche breakdown, like the time dependence of the avalanche current, over-voltage dependence of the Geiger-breakdown probability and the gain for photons and dark counts, are presented and compared to experimental findings.

The design, construction, installation, and performance of the small angle rear tracking detector of the ZEUS experiment are described. The results on electron position measurement, electron energy correction, and background reduction at the first-level trigger are presented. The impact on the measurement of the proton structure function is discussed.

We have exposed a sandwich calorimeter, consisting of 3.3 mm thick uranium pnterleaved with 2.6 mm thick scintillator tiles, to positive and negative electrons and pions and to protons in the momentum range of 0.5 to 10 GeV/c. We find that e/h is about 1 above 3 GeV/c, but decreases significantly for lower momenta. This ratio is the same for positive and negative pions and also for pions and protons of the same kinetic energy.

A hadron calorimeter comprising 10 mm depleted uranium plates and 5 mm plastic scintillator was exposed to electrons, hadrons and muons in the energy range 5–210 GeV. The measured ratios of sampling fractions are 0.8 for e/π and 0.6 for e/mip. The addition of a fine grained electromagnetic calorimeter with 1.6 mm depleted uranium plates and 4 mm plastic scintillator in front of the hadron calorimeter leads to a slightly worse hadronic energy resolution. Results on the longitudinal shower development and energy containment for hadron showers are given.

We have observed three unique decays of F mesons into KKπ and five unique decays of D mesons into KKπ using the NA11 spectrometer together with a telescope of high-resolution silicon microstrip detectors. The mass value obtained for the F meson is (1975 ± 4) MeV, the lifetime (3.2±1.33..0)×10−13 s.

Inclusive øø production has been studied in π−-Be interactions for 100 and 175 GeV incident momentum. An upper limit of 72 nb has been set for σ(π−Be → ηc(2980) + X) ṡBR(ηc → øø) at 175 GeV. At both momenta the number of øø events is larger than expected for uncorrelated ø pairs. A narrow width enhancement is observed at Møø≈2100 MeV with a 4 standard deviation significance.

A narrow enhancement is observed in pp states produced inclusively in proton-proton interactions at 93 GeV. The mass 1940 ± 1 MeV is consistent with that of the S(1936).

A systematic experimental study of the main challenges for silicon-pixel sensors at the European XFEL is presented. The high instantaneous density of X-rays and the high repetition rate of the XFEL pulses result in signal distortions due to the plasma effect and in severe radiation damage. The main parameters of X-ray-radiation damage have been determined and their impact on p+n sensors investigated. These studies form the basis of the optimized design of a pixel-sensor for experimentation at the European XFEL.

For experiments at the European X-Ray Free-Electron Laser (XFEL) the Adaptive Gain Integrating Pixel Detector (AGIPD) is under development. The particular requirements include a high dynamic range of 0, 1 to more than 104 photons of 12.4 keV per pixel within an XFEL pulse of less than 100 fs duration, and a radiation tolerance for doses up to 1 GGy for 3 years of operation. AGIPD is a hybrid-pixel detector system with a total of 1024 × 1024 pixels of size 200 μm × 200 μm. AGIPD will use 16 p+n-silicon sensors of 500 μm thickness. The nominal operating voltage is 500 V, however, for special applications operation close to 1000 V should be possible. Experimental data on the X-ray-dose dependence of the oxide-charge density and of the surface-current density have been implemented in the SYNOPSYS TCAD simulation program in order to optimize the design of the pixel and guard-ring layout. The methodology of the sensor design, the optimization of the most relevant parameters, and the optimized layout are described. Finally, the simulated performance, in particular the breakdown voltage, dark current and inter-pixel capacitance as function of the X-ray dose are presented.

Non-ionising energy loss of radiation produces point defects and defect clusters in silicon, which result in a significant degradation of sensor performance. In this contribution results from TSC (Thermally Stimulated Current) defect spectroscopy for silicon pad diodes irradiated by electrons to fluences of a few 1014 cm−2 and energies between 3.5 and 27 MeV for isochronal annealing between 80 and 280∘C, are presented. A method based on SRH (Shockley–Read–Hall) statistics is introduced, which assumes that the ionisation energy of the defects in a cluster depends on the fraction of occupied traps. The difference of ionisation energy of an isolated point defect and a fully occupied cluster, ΔEa, is extracted from the TSC data. For the VOi (vacancy-oxygen interstitial) defect ΔEa=0 is found, which confirms that it is a point defect, and validates the method for point defects. For clusters made of deep acceptors the ΔEa values for different defects are determined after annealing at 80∘C as a function of electron energy, and for the irradiation with 15 MeV electrons as a function of annealing temperature. For the irradiation with 3.5 MeV electrons the value ΔEa=0 is found, whereas for the electron energies of 6–27 MeV ΔEa>0. This agrees with the expected threshold of about 5 MeV for cluster formation by electrons. The ΔEa values determined as a function of annealing temperature show that the annealing rate is different for different defects. A naive diffusion model is used to estimate the temperature dependencies of the diffusion of the defects in the clusters.

The production of beauty and charm quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q 2 < 1000 GeV2 using an integrated luminosity of 354 pb−1. The beauty and charm content in events with at least one jet have been extracted using the invariant mass of charged tracks associated with secondary vertices and the decay-length significance of these vertices. Differential cross sections as a function of Q 2, Bjorken x, jet trans- verse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of x and Q 2. The running beauty-quark mass, m b at the scale m b , was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be m b (m b ) = 4.07 ± 0.14 (fit) − 0.07 + 0.01 (mod.) − 0.00 + 0.05 (param.) − 0.05 + 0.08 (theo.) GeV.

We have observed six unambiguous decays of the charmed strange baryon Ξc+ (or charge conjugate Ξc−) in the 230 GeV/c negative pions or kaons on a copper target at the CERN SPS using silicon microstrip detectors and charge-coupled devices for vertex reconstruction. Three of them have been reconstructed through the decay chain Ξc+ →Ξ−π+π+, Ξ− →Λ0π−, Λ0 →pπ− and the other three through the decay chain Ξc+ →Σ+K−π+ →pπ0. We present our measurements of the mass, lifetime and production cross-section of the Ξc+, as well as of the branching ration for the two decay modes.

The ZEUS group plans to install planes of large-area silicon diodes in depleted-uranium-scintillator calorimeters to separate electrons from hadrons in jets. This method was tested at 3, 5 and 9 GeV at CERN. Arrays of diodes were studied at depths between about 1 and 9 radiation lengths in a lead-scintillator calorimeter and in a simulated calorimeter consisting of depleted uranium and lucite. The e-h separation efficiency was measured for one and two planes of diodes as a function of depth in the calorimeter. A hadron misidentification of 2% at an electron efficiency of 90% was obtained with one plane of diodes. Addition of a second plane of diodes reduced the hadron misidentification to 0.3% with an electron efficiency of 90%. These results demonstrate that silicon diodes are excellent devices for e–h separation in a calorimeter.

We present the final result on the measurement of the lifetime of the Λc-baryon from a sample of Λc-decays obtained in the NA32 experiment at the CERN SPS using silicon microstrip detectors and charge-coupled devices for vertex reconstruction. We observe a total of 160 Λc in five different decay modes. A sample of 101 unambiguous decays of Λc→pK−π+ (and charge conjugate) above a background of 7 events is used for the Λc mass and lifetime measurement. The mean Λc lifetime is determined to be 1.96−0.20+0.23×10−13s and the Λc mass to be 2285.8±0.6±1.2 MeV/c2.

We have observed four unambiguous decays of the charmed strange baryon Ξco in the NA32 experiment at CERN. Charge- coupled devices and silicon microstrip detectors were used to reconstruct the decay mode Ξco → pK − K∗ (892)o seen in events produced by the interaction of 230 GeV/c negative poins and kaons on a copper target. We present the first measurement of the lifetime of the Ξco, together with a determination of its mass and production cross section. The resonant components of the Ξco decay are studied. We use our earlier measurement of the mass of the Ξc+ in the determination of the isospin mass splitting of the Ξc states.

Inclusive ϕ meson production has been measured for 100 GeV/c and 200 GeV/c incident π−, $$\bar p$$ andK −, and for 120 GeV/c and 200 GeV/c incident π+,p andK +, using a Be target. A total of 630,000 ϕ mesons has been recorded in the kinematic range 0<x F <0.4. Presented are the differential cross sectionsdσ/dx F anddσ/dp T 2. The longitudinal momentum distributions show that the strange valence quarks of the incidentK mesons play an important role in ϕ meson production, even at smallx F . The decay angular distribution of the ϕ meson is evaluated in the Gottfried-Jackson frame and is expressed in the elements of the density matrix. There is a small but significant cos2 θ GJ dependence for smallp T , which decreases for increasingp T .

The high intensity and high repetition rate of the European X-Ray Free-Electron Laser, presently under construction in Hamburg, will require pixel sensors which can stand X-ray doses up to 1 GGy for 3 years of operation. Within the AGIPD Collaboration the Hamburg group has systematically studied X-ray damage in silicon sensors for the dose range between 1 kGy and 1 GGy using strip sensors and test structures fabricated on high-ohmic n-type silicon from four different vendors. The densities of oxide charges, interface traps and surface current as function of dose and annealing conditions have been determined. The results have been implemented in TCAD simulations, and the radiation performance of strip sensors and guard-ring structures has been simulated and compared to experimental results. Finally, with the help of detailed TCAD simulations, the layout and technological parameters of the AGIPD pixel sensor have been optimized. It is found that the optimization for silicon sensors exposed to high X-ray doses is significantly different from that for non-irradiated sensors, and that the specifications of the AGIPD sensor can be met.

Abstract The AGIPD (adaptive gain integrating pixel detector) detector is a high frame rate (4.5 MHz) and high dynamic range (up to 10 4 ·12.4 keV photons) detector with single photon resolution (down to 4 keV taking 5 σ as limit and lowest noise settings) developed for the European XFEL (XFEL.EU). This work is focused on the characterization of AGIPD1.0, which is the first full scale version of the chip. The chip is 64×64 pixels and each pixel has a size of 200×200 μm 2 . Each pixel can store up to 352 images at a rate of 4.5 MHz (corresponding to 220 ns). A detailed characterization of the AGIPD1.0 chip has been performed in order to assess the main performance of the ASIC in terms of gain, noise, speed and dynamic range. From the measurements presented in this paper a good uniformity of the gain, a noise around 320 e − (rms) in standard mode and around 240 e − (rms) in high gain mode has been measured. Furthermore a detailed discussion about the non-linear behavior after the gain switching is presented with both experimental results and simulations.

Production of exclusive dijets in diffractive deep inelastic $$e^\pm p$$ scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb $$^{-1}$$ . The measurement was performed for $$\gamma ^{*}$$ –p centre-of-mass energies in the range $$90< W < {250}\,{\mathrm{GeV}}$$ and for photon virtualities $$Q^2 > {25}\,{\mathrm{GeV}^{2}}$$ . Energy flows around the jet axis are presented. The cross section is presented as a function of $$\beta $$ and $$\phi $$ , where $$\beta =x/x_\mathrm{I\!P}$$ , x is the Bjorken variable and $$x_\mathrm{I\!P}$$ is the proton fractional longitudinal momentum loss. The angle $$\phi $$ is defined by the $$\gamma ^{*}$$ –dijet plane and the $$\gamma ^{*}$$ – $$e^\pm $$ plane in the rest frame of the diffractive final state. The $$\phi $$ cross section is measured in bins of $$\beta $$ . The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange.

A simultaneous fit of parton distribution functions (PDFs) and electroweak parameters to HERA data on deep inelastic scattering is presented. The input data are the neutral current and charged current inclusive cross sections which were previously used in the QCD analysis leading to the HERAPDF2.0 PDFs. In addition, the polarization of the electron beam was taken into account for the ZEUS data recorded between 2004 and 2007. Results on the vector and axial-vector couplings of the $Z$ boson to $u$- and $d$-type quarks, on the value of the electroweak mixing angle and the mass of the $W$ boson are presented. The values obtained for the electroweak parameters are in agreement with Standard Model predictions.

The exclusive photoproduction reactions $\gamma p \to J/\psi(1S) p$ and $\gamma p \to \psi(2S) p$ have been measured at an $ep$ centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 373 pb$^{-1}$. The measurement was made in the kinematic range $30 < W < 180$ GeV, $Q^2 < 1$ GeV$^2$ and $|t| < 1$ GeV$^2$, where $W$ is the photon--proton centre-of-mass energy, $Q^2$ is the photon virtuality and $t$ is the squared four-momentum transfer at the proton vertex. The decay channels used were $J/\psi(1S) \to \mu^+ \mu^-$, $\psi(2S) \to \mu^+ \mu^-$ and $\psi(2S) \to J/\psi(1S) \pi^+ \pi^-$ with subsequent decay $J/\psi(1S) \to \mu^+ \mu^-$. The ratio of the production cross sections, $R = \sigma_{\psi(2S)} / \sigma_{J/\psi(1S)}$, has been measured as a function of $W$ and $|t|$ and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.

The dependence of the light yield and the transmission on magnetic fields has been measured with different methods up to 0.45 T for the plastic scintillators NE-102A, SCSN-38 and Polivar. The scintillators were excited by 25 MeV protons, 5.9 keV X-rays and UV light. When excited with ionizing radiation an increase of light yield is observed. For SCSN-38 of 2.6 mm thickness it amounts to 0.3%, 0.9%, 1.1% and 3.3% at 1, 10, 100 and 450 mT, respectively. NE-120A behaves similar, whereas an acrylic scintillator shows a stronger field dependence. The effect is independent of the direction of the field but increases for the acrylic scintillator with its thickness. No change in the decay time of the scintillator has been observed. The response of the scintillators did not change when excited by UV light in a magnetic field.

Semiconductor drift chambers for position and energy measurements have been invented, built and tested. A short 'Ccount is here given on the principles of the drift chamber and on the experimental results. Detailed reports have been written on the quoted bibliography and new reports will be published shortly.

D∗±, D±, D0, and D0 production has been observed in π −Be interactions at 120, 175, and 200 GeV. The dependence of the D cross section on transverse and longitudinal momentum is presented. The ratio of D∗ to D and charged to neutral D production is determined. Leading particle effects in D production are investigated. Relative branching ratios for several D decay modes are evaluated. A limit on D0−D0 mixing is given.

The A2 meson is studied in the decay mode ϱ0π− using partial wave analyses of 600 000 events from the reaction π−p→π−π−π+p at 63 and 94 GeV incident momentum. Common production mechanisms are indicated for this resonance and diffractive 1+ and 2− components.

The reaction K−p → K−π−π+p has been measured at 25 and 40 GeV/c at the Serpukhov Proton Accelerator. The production cross section at 25 and 40 GeV/c as a function of momentum transfer and Kππ mass is presented, and results of the partial-wave analysis of the Kππ system yielding information about Q(1300), K∗(1400) and L(1770) mesons are discussed.

The CERN boson spectrometer shows significant enhancements in the spectrum of charged non-strange bosons near 2.6 GeV and 2.8 GeV mass values.

Measurements of the drift velocities of electrons and holes as functions of electric field and temperature in high-purity n- and p-type silicon with 〈100〉 lattice orientation are presented. The measurements cover electric field values between 2.5 and 50kV/cm and temperatures between 233 and 333K. For both electrons and holes differences of more than 15% are found between our 〈100〉 results and the 〈111〉 drift velocities from literature, which are frequently also used for simulating 〈100〉 sensors. For electrons, the 〈100〉 results agree with previous 〈100〉 measurements; however, for holes differences between 5 and 15% are observed for fields above 10kV/cm. Combining our results with published data of low-field mobilities, we derive parametrizations of the drift velocities in high-ohmic 〈100〉 silicon for electrons and holes for fields up to 50kV/cm, and temperatures between 233 and 333 K. In addition, new parametrizations for the drift velocities of electrons and holes are introduced, which provide somewhat better descriptions of existing data for 〈111〉 silicon than the standard parametrization.

The photoproduction of isolated photons, both inclusive and together with a jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of 374pb−1. Differential cross sections are presented in the isolated-photon transverse-energy and pseudorapidity ranges 6<ETγ<15GeV and −0.7<ηγ<0.9, and for jet transverse-energy and pseudorapidity ranges 4<ETjet<35GeV and −1.5<ηjet<1.8, for exchanged-photon virtualities Q2<1GeV2. Differential cross sections are also presented for inclusive isolated-photon production as functions of the transverse energy and pseudorapidity of the photon. Higher-order theoretical calculations are compared to the results.

The adaptive gain integrating pixel detector (AGIPD) is a development of a collaboration between Deustsches Elektronen-Synchrotron (DESY), the Paul-Scherrer-Institute (PSI), the University of Hamburg and the University of Bonn. The detector is designed to cope with the demanding challenges of the European XFEL. Therefore it comes along with an adaptive gain stage allowing a high dynamic range, spanning from single photon sensitivity to 104 × 12.4 keV photons and 352 analogue memory cells per pixel. The aim of this report is to briefly explain the concepts of the AGIPD electronics and mechanics and then present recent experiments demonstrating the functionality of its key features.

The European X-ray Free Electron Laser (XFEL), currently being constructed in Hamburg and planning to be operational in 2017 for users, will deliver 27,000 fully coherent, high brilliance X-ray pulses per second with duration less than 100 fs. The unique features of the X-ray beam pose major challenges for detectors used at the European XFEL for imaging experiments, in particular a radiation tolerance of silicon sensors for doses up to 1 GGy for 3 years of operation at an operating voltage above 500 V. One of the detectors under development at the European XFEL is the Adaptive Gain Integrating Pixel Detector (AGIPD), which is a hybrid detector system with ASICs bump-bonded to p+n silicon pixel sensors. We have designed the silicon sensors for the AGIPD, which have been fabricated by SINTEF and delivered in the beginning of February of 2013. To demonstrate the performance of the AGIPD sensor with regard to radiation hardness, mini-sensors with the same pixel and guard-ring designs as the AGIPD together with test structures have been irradiated at the beamline P11 of PETRA III with 8 keV and 12 keV monoenergetic X-rays to dose values up to 10 MGy. The radiation hardness of the AGIPD sensor has been proven and all electrical properties are within specification before and after irradiation. In addition, the oxide-charge density and surface-current density from test structures have been characterized as function of the X-ray dose and compared to previous measurements for test structures produced by four vendors.

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range 2<Q2<80 GeV2, 30<W<210 GeV and |t|<1 GeV2, where Q2 is the photon virtuality, W is the photon–proton centre-of-mass energy and t is the squared four-momentum transfer at the proton vertex. The data for 2<Q2<5 GeV2 were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb−1. The data for 5<Q2<80 GeV2 are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb−1. The decay modes analysed were μ+μ− and J/ψ(1S)π+π− for the ψ(2S) and μ+μ− for the J/ψ(1S). The cross-section ratio σψ(2S)/σJ/ψ(1S) has been measured as a function of Q2,W and t. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.

The high-precision HERA data allows searches up to TeV scales for beyond the Standard Model contributions to electron–quark scattering. Combined measurements of the inclusive deep inelastic cross sections in neutral and charged current ep scattering corresponding to a luminosity of around 1 fb−1 have been used in this analysis. A new approach to the beyond the Standard Model analysis of the inclusive ep data is presented; simultaneous fits of parton distribution functions together with contributions of “new physics” processes were performed. Results are presented considering a finite radius of quarks within the quark form-factor model. The resulting 95% C.L. upper limit on the effective quark radius is 0.43⋅10−16cm.

A method is presented which allows to obtain the position-dependent electric field and charge density by fits to velocity profiles from edge-TCT data from silicon strip detectors. The validity and the limitations of the method are investigated by simulations of non-irradiated n+p pad sensors and by the analysis of edge-TCT data from non-irradiated n+p strip detectors. The method is then used to determine the position dependent electric field and charge density in n+p strip detectors irradiated by reactor neutrons to fluences between 1 and 10×1015 cm−2 for forward-bias voltages between 25 V and up to 550 V and for reverse-bias voltages between 50 V and 800 V. In all cases the velocity profiles are well described. The electric fields and charge densities determined provide quantitative insights into the effects of radiation damage for silicon sensors by reactor neutrons.