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The high design luminosity of the SuperKEKB electron-positron collider will result in challenging levels of beam-induced backgro\ unds in the interaction region. Understanding and mitigating these backgrounds is critical to the success of the Belle~II experi\ ment. We report on the first background measurements performed after roll-in of the Belle II detector, a period known as SuperKE\ KB Phase 2, utilizing both the BEAST II system of dedicated background detectors and the Belle II detector itself. We also repor\ t on first revisions to the background simulation made in response to our findings. Backgrounds measured include contributions f\ rom synchrotron radiation, beam-gas, Touschek, and injection backgrounds. At the end of Phase 2, single-beam backgrounds origina\ ting from the 4 GeV positron Low Energy Ring (LER) agree reasonably well with simulation, while backgrounds from the 7 GeV elect\ ron High Energy Ring (HER) are approximately one order of magnitude higher than simulation. We extrapolate these backgrounds for\ ward and conclude it is safe to install the Belle II vertex detector., Comment: 22 Pages, 33 figures

International audience; The PiXeL detector (PXL) for the Heavy Flavor Tracker (HFT) of the STAR experiment at RHIC is the first application of the state-of-the-art thin Monolithic Active Pixel Sensors (MAPS) technology in a collider environment. Custom built pixel sensors, their readout electronics and the detector mechanical structure are described in detail. Selected detector design aspects and production steps are presented. The detector operations during the three years of data taking (2014–2016) and the overall performance exceeding the design specifications are discussed in the conclusive sections of this paper.

For the 2014 heavy ion run of RHIC a new micro-vertex detector called the Heavy Flavor Tracker (HFT) was installed in the STAR experiment. The HFT consists of three detector subsystems with various silicon technologies arranged in 4 approximately concentric cylinders close to the STAR interaction point designed to improve the STAR detector's vertex resolution and extend its measurement capabilities in the heavy flavor domain. The two innermost HFT layers are placed at radii of 2.8 cm and 8 cm from the beam line. These layers are constructed with 400 high resolution sensors based on CMOS Monolithic Active Pixel Sensor (MAPS) technology arranged in 10-sensor ladders mounted on 10 thin carbon fiber sectors to cover a total silicon area of 0.16 m 2 . Each sensor of this PiXeL (“PXL”) sub-detector combines a pixel array of 928 rows and 960 columns with a 20.7 μm pixel pitch together with front-end electronics and zero-suppression circuitry in one silicon die providing a sensitive area of ∼3.8 cm 2 . This sensor architecture features 185.6 μs readout time and 170 mW/cm 2 power dissipation. This low power dissipation allows the PXL detector to be air-cooled, and with the sensors thinned down to 50 μm results in a global material budget of only 0.4% radiation length per layer. A novel mechanical approach to detector insertion allows us to effectively install and integrate the PXL sub-detector within a 12 hour period during an on-going multi-month data taking period. The detector requirements, architecture and design, as well as the performance after installation, are presented in this paper.

The “Heavy Flavor Tracker” (HFT) is an approved micro-vertex detector upgrade to the STAR experiment at RHIC, consisting of three subsystems with various technologies of silicon sensors arranged in 4 concentric cylinders, to be installed in STAR by 2014. This new vertex detector will improve the track-pointing resolution in STAR to a distance of closest approach (DCA) of ~ 30 μm in order to allow for a direct and full topological reconstruction of heavy quark meson decays and a better determination of the heavy quark meson spectra. The two innermost layers of the HFT close to the beam pipe, the Pixel (“PXL”) subsystem, employ CMOS monolithic active pixel sensor (MAPS) technology that integrates the sensor, front-end electronics, and zero-suppression circuitry in one silicon wafer. The PXL layers of the HFT will consist of 400 MAPS sensors arranged in 40 ladders (10 ladders at a radius of 2.5 cm and 30 ladders at 8 cm from the beam), each containing 10 of these sensors. This paper will present selected design characteristics of the PXL detector part of the HFT and the hardware and firmware architecture of the proposed readout system for this detector, as well as its integration into the existing STAR framework. A prototype of this readout system has recently been used at CERN to take data from a telescope consisting of 7 sensors arranged in parallel planes and shown to be fully functional.

The heavy quark hadrons are suggested as a clean probe for studying the early dynamic evolution of the dense and hot medium created in high-energy nuclear collisions. The Heavy Flavor Tracker (HFT) of the STAR experiment, designed to improve the vertex resolution and extend the measurement capabilities in the heavy flavor domain, was installed for the 2014 heavy ion run of RHIC. It is composed of three different silicon detectors arranged in four concentric cylinders close to the STAR interaction point. The two inner-most layers are based on CMOS monolithic active pixels (MAPS), featured for the first time in a collider experiment, while the two outer layers are based on pads and strips. The two innermost HFT layers are placed at a radius of 2.7 and 8 cm from the beam line and accommodate 400 ultra-thin (50 μm) high resolution MAPS sensors arranged in 10-sensor ladders to cover a total silicon area of 0.16 m2. Each sensor includes a pixel array of 928 rows and 960 columns with a 20.7 μm pixel pitch, providing a sensitive area of ∼ 3.8 cm2. The sensor features 185.6 μs readout time and 170 mW/cm2 power dissipation. The detector is air-cooled, allowing a global material budget as low as 0.39% X/X0 on the inner layer. A novel mechanical approach to detector insertion enables effective installation and integration of the pixel layers within an 8 hour shift during the on-going STAR run. After a detailed description of the design specifications and the technology implementation, the detector status and operations during the current 200 GeV Au+Au run will be presented in this paper, with a particular focus on calibration and general system operations aimed at stabilizing the running conditions. A preliminary estimation of the detector performance meeting the design requirements will be reported.

The Heavy Flavor Tracker (HFT) is a recently installed micro-vertex detector upgrade to the STAR experiment at RHIC, consisting of three subsystems with various technologies of silicon sensors arranged in 4 concentric cylinders. The two innermost layers of the HFT close to the beam pipe, the Pixel ("PXL") subsystem, employ CMOS Monolithic Active Pixel Sensor (MAPS) technology that integrate the sensor, front-end electronics, and zero-suppression circuitry in one silicon die. This paper presents selected characteristics of the PXL detector part of the HFT and the hardware, firmware and software associated with the readout system for this detector.

CMOS Monolithic Active Pixel Sensors (MAPS) provide an attractive solution for high precision tracking of minimum ionizing particles. In these devices, a thin, moderately doped, undepleted silicon layer is used as the active detector volume with the readout electronics implemented on top of it. Recently, a new MAPS prototype was fabricated using the AMS 0.35 $mu$m OPTO process, featuring a thick epitaxial layer. A systematic study of tracking performance of that prototype using high-energy particle beam is presented in this work. Noise performance, signal amplitude from minimum ionizing particles, detection efficiency, spurious hit suppression and spatial resolution are shown as a function of the readout pitch and the charge collecting diode size. A test array with a novel readout circuitry was also fabricated and tested. Each pixel circuit consists of a front-end voltage amplifier, capacitively coupled to the charge collecting diode, followed by two analog memory cells. This architecture implements an on-pixel correlated double sampling method, allowing for optimization of integration independently of full frame readout time and strongly reduces the pixel-to-pixel output signal dispersion. First measurements using this structure are also presented.

The Heavy Flavor Tracker (HFT) was installed in the STAR experiment for the 2014 heavy ion run of RHIC. Designed to improve the vertex resolution and extend the measurement capabilities in the heavy flavor domain, the HFT is composed of three different silicon detectors based on CMOS monolithic active pixels (MAPS), pads and strips respectively, arranged in four concentric cylinders close to the STAR interaction point. The two innermost HFT layers are placed at a radius of 2.7 and 8 cm from the beam line, respectively, and accommodate 400 ultra-thin (50 μ m) high resolution MAPS sensors arranged in 10-sensor ladders to cover a total silicon area of 0.16 m2. Each sensor includes a pixel array of 928 rows and 960 columns with a 20.7 μ m pixel pitch, providing a sensitive area of ~ 3.8 cm2. The architecture is based on a column parallel readout with amplification and correlated double sampling inside each pixel. Each column is terminated with a high precision discriminator, is read out in a rolling shutter mode and the output is processed through an integrated zero suppression logic. The results are stored in two SRAM with ping-pong arrangement for a continuous readout. The sensor features 185.6 μ s readout time and 170 mW/cm2 power dissipation. The detector is air-cooled, allowing a global material budget as low as 0.39% on the inner layer. A novel mechanical approach to detector insertion enables effective installation and integration of the pixel layers within an 8 hour shift during the on-going STAR run.In addition to a detailed description of the detector characteristics, the experience of the first months of data taking will be presented in this paper, with a particular focus on sensor threshold calibration, latch-up protection procedures and general system operations aimed at stabilizing the running conditions. Issues faced during the 2014 run will be discussed together with the implemented solutions. A preliminary analysis of the detector performance meeting the design requirements will be reported.

A new silicon based vertex detector called the Heavy Flavor Tracker (HFT) was installed at the Soleniodal Tracker At RHIC (STAR) experiment for the Relativistic Heavy Ion Collider (RHIC) 2014 heavy ion run to improve the vertex resolution and extend the measurement capabilities of STAR in the heavy flavor domain. The HFT consists of four concentric cylinders around the STAR interaction point composed of three different silicon detector technologies based on strips, pads and for the first time in an accelerator experiment CMOS monolithic active pixels (MAPS) . The two innermost layers at a radius of 2.8 cm and 8 cm from the beam line are constructed with 400 high resolution MAPS sensors arranged in 10-sensor ladders mounted on 10 thin carbon fiber sectors giving a total silicon area of 0.16 m(2). Each sensor consists of a pixel array of nearly 1 million pixels with a pitch of 20.7 μm with column-level discriminators, zero-suppression circuitry and output buffer memory integrated into one silicon die with a sensitive area of ~ 3.8 cm(2). The pixel (PXL) detector has a low power dissipation of 170 mW/cm(2), which allows air cooling. This results in a global material budget of 0.5% radiation length per layer for detector used in this run. A novel mechanical approach to detector insertion allows for the installation and integration of the pixel sub detector within a 12 hour period during an on-going STAR run. The detector specifications, experience from the construction and operation, lessons learned and initial measurements of the PXL performance in the 200 GeV Au-Au run will be presented.

This paper describes a monolithic silicon pixel detector for ionizing radiation manufactured using the Silicon On Insulator (SOI) technology. In this novel device, the sensor is implemented in a high resistive SOI bottom wafer while the associated CMOS read-out circuits are built in a SOI device layer. Preliminary measurements of simple test detectors are presented. They prove that the detector is working properly showing the typical sensitivity of a fully depleted Silicon detector.

A detector, equipped with 50 um thin CMOS Pixel Sensors (CPS), is being designed for the upgrade of the Inner Tracking System (ITS) of the ALICE experiment at LHC. Two CPS flavours, MISTRAL and ASTRAL, are being developed at IPHC aiming to meet the requirements of the ITS upgrade. The first is derived from the MIMOSA28 sensor designed for the STAR-PXL detector. The second, which integrates a discriminator in each pixel, improves the readout speed and power consumption. This paper will describe in details the sensor development and show some preliminary test results.

We present development and prototyping efforts directed towards construction of a new vertex detector for the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) accelerator at BNL. The new detector system will extend the physics range of STAR by providing capability for precision measurements of yields and spectra of particles containing heavy quarks. The most precise and central part of the new detector system is a high resolution pixel-type detector (PIXEL) based on the Monolithic Active Pixel Sensor (MAPS) technology. We describe basic PIXEL requirements and selected progress on sensor prototypes dedicated to the PIXEL detector and the detector readout system architecture that has been validated in recent tests of hardware prototypes.

We propose to construct a Heavy Flavor Tracker (HFT) for the STAR experiment at RHIC. The HFT will bring new physics capabilities to STAR and it will significantly enhance the physics capabilities of the STAR detector at central rapidities. The HFT will ensure that STAR will be able to take heavy flavor data at all luminosities attainable throughout the proposed RHIC II era.

The paper discusses basic characterization of Monolithic Active Pixel Sensors (MAPS) carried out at the X12A beam-line at National Synchrotron Light Source (NSLS), Upton, NY, USA. The tested device was a MIMOSA V (MV) chip, back-thinned down to the epitaxial layer. This 1M pixels device features a pixel size of 17 × 17 μ m 2 and was designed in a 0.6 μ m CMOS process. The X-ray beam energies used range from 5 to 12 keV. Examples of direct X-ray imaging capabilities are presented.

International audience; Monolithic Active Pixel Sensors (MAPS) have been proposed as sensing devices for the vertex detectors at the International Linear Collider (ILC), of the STAR upgrade and of the Compressed Baryonic Matter (CBM) experiment. These applications require substantial tolerance to non-ionising doses, which range up to $\sim10^{13}n_{eq}/cm^2$. Intense studies were undertaken in order to measure the, so far widely unknown, radiation hardness of MAPS optimised for charged particle tracking and to identify the dominating effects of non-ionising radiation on these devices. This paper focuses on the recombination of signal electrons in the sensitive volume, which is the dominating problem provoked by bulk damage in MAPS. The dependence of this effect on some aspects of the pixel architecture is discussed, aiming to optimise the latter with respect to radiation tolerance.

International audience; Fast Monolithic Active Pixel Sensors (MAPS) are now being studied for the high-spatial resolution and high readout speed vertex detector which will be required for the future International Linear Collider (ILC). A 32×128 pixels prototype chip has been developed on the 0.25 μm CMOS TSMC digital process. Combined with in-pixel amplification, in-pixel correlated double sampling (CDS) operation is realized. An auto-zero discriminator is implemented at the end of each column. The power consumption of each column is about 430 μW (pixel+discriminator). The chip is optimized to operate with a readout speed of 20 μs/frame. Beam tests with high energy electrons show that detection efficiency is around 98%

We report on the performance of the MIMOSA8 chip. The chip is a 128/spl times/32 pixels array where 8 columns have analog direct outputs and 24 have discriminated outputs. The array is divided in four blocks of pixels with different conversion factors and is controlled by a serially programmable sequencer. MIMOSA8 is a representative of the CMOS sensors development option considered as a promising candidate for the vertex detector of the future International Linear Collider (ILC). The readout technique, implemented on the chip, combines high spatial resolution capabilities with high processing readout speed. Data acquisition, providing control of the chip and signal buffering and linked to a VME system, was made on the 8 analog outputs. Analog data, without and with a /sup 55/Fe X-ray source, were acquired and processed using off-line analysis software. From the reconstruction of pixel clusters, built around a central pixel, we deduce that the charge spread is limited to the closest 25 pixels and almost all the available charge is collected. The position of the total charge collection peak (and subsequently the charge-to-voltage conversion factor) stays unaffected when the clocking frequency is increased even up to 150 MHz (13.6 /spl mu/s readout time per frame). The discriminators, placed in the readout chain, have proved to be fully functional. Beam tests have been made with high energy electrons at DESY (Germany) to study detection efficiency.

We report on the performance of the MIMOSA8 (HiMAPS1) chip. The chip is a 128$, times ,$32 pixels array where 24 columns have discriminated binary outputs and eight columns analog test outputs. Offset correction techniques are used extensively in this chip to overcome process related mismatches. The array is divided in four blocks of pixels with different conversion factors and is controlled by a serially programmable sequencer. MIMOSA8 is a representative of the CMOS sensors development option considered as a promising candidate for the Vertex Detector of the future International Linear Collider (ILC). The readout technique, implemented on the chip, combines high spatial resolution capabilities with high processing readout speed. Data acquisition, providing control of the chip and signal buffering and linked to a VME system, was made on the eight analog outputs. Analog data, without and with a $^{55}$Fe X-ray source, were acquired and processed using off-line analysis software. From the reconstruction of pixel clusters, built around a central pixel, we deduce that the charge spread is limited to the closest 25 pixels and almost all the available charge is collected. The position of the total charge collection peak (and subsequently the charge-to-voltage conversion factor) stays unaffected when the clock frequency is increased even up to 150 MHz (13.6 $mu$s readout time per frame). The discriminators, placed in the readout chain, have proved to be fully functional. Beam tests have been made with high energy electrons at DESY (Germany) to study detection efficiency. The results prove that MIMOSA8 is the first and fastest successful monolithic active pixel sensor with on-chip signal discrimination for detection of MIPs.

LEPSI; The SUCIMA collaboration has been developing instruments and methods for real-time, high granularity imaging of extended electron sources. In particular, dosimetry of intravascular brachytherapy β sources has been intensively studied, together with monitoring of hadrontherapy beams by imaging of secondary electrons emitted by a non-disruptive target. The paper reports the latest results on absolute dosimetry with a large-area silicon strip detectors and on beam monitoring with a hybrid pad sensor.

In order to develop precision vertex detectors for the future linear collider, fast monolithic active pixel sensors are studied. A standard CMOS 0.25$mu$m digital process is used to design a test chip which includes different pixel types, column-level discriminators, and a fully programmable digital sequencer. In-pixel amplification is implemented together with double sampling. Different charge-to-voltage conversion factors were obtained using amplifiers with different gains or diode sizes. Pixel architectures with dc and ac coupling to charge sensing element were proposed. Hits from conversion of $^55$Fe photons were recorded for the dc-coupled and ac-coupled pixel versions. Double sampling is functional and allows almost a complete cancellation of fixed pattern noise.

Future high energy physics experiments require high luminosities and efficient and pure bottom and charm tagging. Monolithic Active Pixel Sensors (MAPS) promise to be particularly well suited for these tasks. In contrast to other technologies, MAPS are fabricated using standard CMOS processes, which allows to implement on-chip data processing (system-on-chip). The paper concentrates on two aspects of the current R&D programme: the prototype for the upgrade of the vertex detector of the STAR experiment at the Brookhaven National Laboratory; architectures to handle the event rates expected at the International Linear Collider (ILC). The STAR experiment requires a sensor which operates at ambient temperatures. For this application, CMOS processes optimised for low leakage currents may be best suited. First results are presented which are obtained with a prototype (MIMOSA-9) build in such a process. Two concepts are presented for a vertex detector at the ILC: fast parallel readout and in situ storage.

LEPSI; SUCIMA (Silicon Ultra fast Cameras for electron and γ sources In Medical Applications) is a project approved by the European Commission within the Fifth Framework Programme, with the primary goal of developing a real time dosimeter based on direct detection of ionising particles in a position sensitive Silicon sensor. The main applications of this device are imaging of intravascular brachytherapy radioactive sources with activities up to 3 GBq and real time monitoring of hadrontherapy beams. In order to perform a feasibility study, during the first two years a real time dosimeter has been engineered using Silicon microstrip detectors read out by an integrating dead-timeless front-end electronics. The prototypes have been qualified as relative dosimeter with respect to certified secondary standards; moreover, further measurements are on going in order to investigate the possibility to use the sensors as absolute dosimeters. Since the final device is supposed to provide a two dimensional image, two different Monolithic Active Pixel dosimeters have been designed and produced by the collaboration based on CMOS and Silicon On Insulator technologies. The main features of the two sensors are presented in this paper.

A detector, equipped with 50 μm thin CMOS Pixel Sensors (CPS), is being designed for the upgrade of the Inner Tracking System (ITS) of the ALICE experiment at LHC. Two CPS flavours, MISTRAL and ASTRAL, are being developed at IPHC aiming to meet the requirements of the ITS upgrade. The first is derived from the MIMOSA28 sensor designed for the STAR-PXL detector. The second integrates a discriminator in each pixel to improve the readout speed and power consumption. This paper will describe in details the sensor development and show some preliminary test results.