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LTP: Laboratory for Particle Physics

The Laboratory of Particle Physics (LTP) at the Paul Scherrer Institute pursues fundamental research, addressing the most up to date questions in modern physics. read more



Latest Scientific Highlights

20 September 2017

Commissioning and first performance studies of the new CMS pixel detector



In the previous months the new CMS pixel detector was brought into operation. The detector was moved from PSI to CERN and installed in February, followed by an intensive period of commissioning and calibration. This process mostly involved the adjustment of many operational parameters which influence the detector performance, e.g. the individual pixel thresholds had to be optimized for each pixel in order to achieve the best possible detector resolution – a challenging task, as there are 80 million pixels which operate at a readout speed of 40 MHz and have to cope with rates of up to 500 MHz/cm2 in the inner part of the detector. The detector consists of 4 cylindrical barrel layers located at radii between 3 cm and 16 cm around the LHC collision point. The inner most layer is equipped with a newly developed readout chip (PROC600) which has a very different readout architecture compared to the readout chip used in the other layers. As the inner layer has to deal with the highest rates it took a considerable time to understand and learn how to efficiently operate this part of the detector.

After this intense phase of commissioning and calibration the pixel detector has been included in the CMS data acquisition and first performance studies were done. The two most important performance parameters are the hit efficiency and the position resolution.

The efficiency is higher than in the previous pixel detector: It is above 99%, except for the inner layer, where high-rate related data losses limit the efficiency to 97% at the highest LHC collision rates. The achieved position resolutions are very good, too, and illustrated in the two plots: The detector can measure the position of charged particles with an accuracy of ~12 μm in the r-phi direction and ~22 μm in the z-direction.
Facility: Particle Physics

19 June 2017

Comparison of ultracold neutron sources for fundamental physics measurements



Ultracold neutrons (UCNs) are key for precision studies of fundamental parameters of the neutron and in searches for new charge-parity-violating processes or exotic interactions beyond the Standard Model of particle physics. The most prominent example is the search for a permanent electric-dipole moment of the neutron (nEDM). We have performed an experimental comparison of the leading UCN sources currently operating. We have used a “standard” UCN storage bottle with a volume of 32 liters, comparable in size to nEDM experiments, which allows us to compare the UCN density available at a given beam port.
Facility: Particle Physics

Reference: Bison, G., Daum, M., Kirch K., et al, Phys. Rev. C 95 (2017), 045503-1

Read full article: here

16 March 2017

High-resolution non-destructive three-dimensional imaging of integrated circuits

Modern nanoelectronics has advanced to a point at which it is impossible to image entire devices and their interconnections non- destructively because of their small feature sizes and the complex three-dimensional structures resulting from their integration on a chip. This metrology gap implies a lack of direct feedback between design and manufacturing processes, and hampers quality control during production, shipment and use. Here we demonstrate that X-ray ptychography - a high-resolution coherent diffractive imaging technique - can create three-dimensional images of integrated circuits of known and unknown designs with a lateral resolution in all directions down to 14.6 nanometres. We obtained detailed device geometries and corresponding elemental maps, and show how the devices are integrated with each other to form the chip. Our experiments represent a major advance in chip inspection and reverse engineering over the traditional destructive electron microscopy and ion milling techniques. Foreseeable developments in X-ray sources, optics and detectors, as well as adoption of an instrument geometry optimized for planar rather than cylindrical samples, could lead to a thousand-fold increase in efficiency, with concomitant reductions in scan times and voxel sizes.
Facility: SLS

Reference: M. Holler et al, Nature 543, 402 (2017)

Read full article: here

1 March 2017

Silicon pixel barrel detector successfully installed in the CMS experiment

Middle of February the upgraded CMS silicon pixel barrel detector has been moved from PSI to CERN and was successfully installed in the CMS experiment. The new pixel detector is part of the so-called phase1-upgrade of the CMS detector, located at a distance of only a few centimetres away from the interaction point and able to cope with the harsh particle environment expected due to the increased luminosity of the LHC collider.
The installation of the upgraded pixel detector so far crowns the work of approximately 15 year of a collaborative R&D effort led by the High Energy Group of the Laboratory for Particle Physics. After the installation of the previous pixel detector in 2008 the work concentrated on the design of a series of radiation tolerant pixel readout chips with low pixel thresholds, low noise behaviour and high pixel hit rate capabilities of up to 600 MHz/cm2 and the development and construction of a very light, low material budget detector mechanics.
The performance of the chips and related readout electronics was regularly tested at the πE1 beamline which offers with its high momentum and high rate pion beam similar conditions as the hadronic particle environment close to the interaction point of the CMS experiment. The silicon pixel technology developed at PSI for the first CMS silicon vertex detector was successfully transferred to industry and led in 2007 to the foundation of the spin-off company DECTRIS which fabricates and sells x-ray counting pixel detectors all over the world.
Facility: Particle Physics