GEM Foil Quality Assurance For The ALICE TPC Upgrade

The ALICE (A Large Ion Collider Experiment) experiment at the Large Hadron Collider (LHC) at CERN is dedicated to heavy ion physics to explore the structure of strongly interacting matter. The Time Projection Chamber (TPC) of ALICE is a tracking detector located in the central region of the experiment. It offers excellent tracking capabilities as well as particle identification. After the second long shutdown (LS2) the LHC will run at substantially higher luminosities. To be able to increase the data acquisition rate by a factor of 100, the ALICE TPC experiment has to replace the Multi-Wire Proportional Chamber (MWPC) –based readout chambers. The MWPC are operated with gating grid that limits the rate to O(kHz). The new ReadOut Chamber (ROC) design is based on Gas Electron Multiplier (GEM) technology operating in continuous mode. The current GEM productions scheme foresees the production of more than 800 GEM foils of different types. To fulfill the requirements on the performance of the GEM TPC readout, necessitates thorough Quality Assurance (QA) measures. The QA scheme, developed by the ALICE collaboration, will be presented in detail.Peer reviewe

Observation of Central Exclusive Diphoton Production at the Tevatron

We have observed exclusive γγ production in proton-antiproton collisions at the Tevatron at sqrt(s) = 1.96 TeV. We use data corresponding to 1.11 ± 0.07 fb^{−1} integrated luminosity taken by the Run II Collider Detector at Fermilab, with a trigger requiring two electromagnetic showers, each with transverse energy ET > 2 GeV, and vetoing on hits in the forward beam shower counters. We select events with two electromagnetic showers, each with transverse energy ET > 2.5 GeV and pseudorapidity |η| 2.5 GeV) = 2.48 +0.40 -0.35 (stat) +0.40 -0.51 (syst) pb and in agreement with the theoretical predictions. This process is closely related to exclusive Higgs boson production pp → p + H + p at the Large Hadron Collider. The observation of the exclusive production of diphotons shows that exclusive Higgs production can happen and could be observed with a proper experimental setup.Not availabl

The GEM QA protocol of the ALICE TPC upgrade project

The ALICE experiment at the Large Hadron Collider at CERN is upgrading its central tracking detector, the Time Projection Chamber (TPC). The installation is foreseen during the second long shutdown of the Large Hadron Collider. The upgrade includes the complete exchange of the present MWPC readout chambers (ROC) with new ones based on Gas Electron Multiplier detectors. This is necessary due to the higher LHC luminosity and thus higher interaction rate. The new ROCs allow for continuous readout at 50 kHz compared to 500 Hz of the gated MWPC readout, while maintaining the particle identification capability of the present system. A thorough quality assurance scheme was developed to build a strict QA protocol. The QA consists of two stages. The first stage, the basic QA is done close to the GEM production workshop at CERN and later at the framing and assembly centers. The second stage, the advanced QA is done at dedicated QA centers. Full traceability of detector components will be maintained throughout the process. A detailed description of the protocol will be given with emphasis on the high definition optical scanning and gain measurements of individual GEM foils. The production of the new ALICE TPC ROCs has finally started. First QA experience under production conditions and workload will be presented.Peer reviewe

Hole misalignment and gain performance of Gaseous Electron Multipliers

It is well known and has been shown that the gain performance of Gaseous Electron Multipliers (GEM) depends on the size of the holes. With an optical scanner it is possible to measure the dimensions of the holes, and to predict the performance of GEMs. However, the gain prediction of GEMs that are manufactured with a double mask etching technique is not straightforward. With the hole size information alone, it is not possible to make precise prediction of the gain. We show that the alignment of the photo-masks between the two sides of the GEM foils plays a crucial role. A misalignment of a few microns can lower the gain substantially. The study is performed by using the Helsinki high definition optical scanner for quality control of GEM foils, and this will show its true potential.Peer reviewe

High-precision measurement of the W boson mass with the CDF II detector

The mass of the W boson, a mediator of the weak force between elementary particles, is tightly constrained by the symmetries of the standard model of particle physics. The Higgs boson was the last missing component of the model. After observation of the Higgs boson, a measurement of the W boson mass provides a stringent test of the model. We measure the W boson mass, M-W, using data corresponding to 8.8 inverse femtobarns of integrated luminosity collected in proton-antiproton collisions at a 1.96 tera-electron volt center-of-mass energy with the CDF II detector at the Fermilab Tevatron collider. A sample of approximately 4 million W boson candidates is used to obtain M-W = 80,433.5 +/- 6.4(stat) +/- 6.9(syst) = 80,433.5 +/- 9.4MeV/c(2), the precision of which exceeds that of all previous measurements combined (stat, statistical uncertainty; syst, systematic uncertainty; MeV, mega-electron volts; c, speed of light in a vacuum). This measurement is in significant tension with the standard model expectation.Peer reviewe

Study of interpad-gap of HPK 3.1 production LGADs with Transient Current Technique

The Phase-2 upgrade of the Large Hadron Collider (LHC) to High-Luminosity LHC (HL-LHC) allows an increase in the operational luminosity value by a factor of 5-7 that will result in delivering 3000 fb(-1) or more integrated luminosity. Due to high luminosity, the number of interactions per bunch crossings (pileup) will increase up to a value of 140-200. To cope with high pileup rates, a precision minimum ionising particles (MIPs) timing detector (MTD) with a time resolution of similar to 30-40 ps and hermetic coverage up to a pseudo-rapidity of vertical bar eta vertical bar = 3 is proposed by the Compact Muon Solenoid (CMS) experiment. An endcap part (1.6 <vertical bar eta vertical bar <3) of the MTD, called the endcap timing layer, will be based on low-gain avalanche detector (LGAD) technology. LGADs provide a good timing resolution due to a combination of a fast signal rise time and high signal-to-noise ratio. The performance of the ETL depends on optimising the crucial features of the sensors, namely; gain, signal homogeneity, fill factor, leakage current, uniformity of multiple-pad sensors and long term stability. The paper mainly focuses on the study of the fill factor of LGADs with varying temperature and irradiation at varying proton fluences as these sensors will be operated at low temperatures and are subjected to a high radiation environment. The 3.1 production of LGADs from Hamamatsu Photonics K.K. (HPK) includes 2x2 sensors with different structures, in particular, different values of narrower inactive region widths between the pads, called the no-gain region. In this paper, the term interpad-gap is used instead of no-gain region in order to follow the conventional terminology. These sensors have been designed to study their fill factor, which is the ratio of the area within the active region (gain region) to the total sensor area. A comparative study on the dependence of breakdown voltage with the interpad-gap width for the sensors has been carried out. Using infrared light (as the electron-hole pair creation by IR laser mimics closely to the traversing of MIPs) from the Scanning-Transient Current Technique (Scanning-TCT) set-up shows that the fill factor does not vary significantly with a variation in temperature and irradiation at high proton fluences.Peer reviewe

Characterization of Heavily Irradiated Dielectrics for Pixel Sensors Coupling Insulator Applications

An increase in the radiation levels during the high-luminosity operation of the Large Hadron Collider calls for the development of silicon-based pixel detectors that are used for particle tracking and vertex reconstruction. Unlike the conventionally used conductively coupled (DC-coupled) detectors that are prone to an increment in leakage currents due to radiation, capacitively coupled (AC-coupled) detectors are anticipated to be in operation in future collider experiments suitable for tracking purposes. The implementation of AC-coupling to micro-scale pixel sensor areas enables one to provide an enhanced isolation of radiation-induced leakage currents. The motivation of this study is the development of new generation capacitively coupled (AC-coupled) pixel sensors with coupling insulators having good dielectric strength and radiation hardness simultaneously. The AC-coupling insulator thin films were aluminum oxide (Al2O3) and hafnium oxide (HfO2) grown by the atomic layer deposition (ALD) method. A comparison study was performed based on the dielectric material used in MOS, MOSFET, and AC-coupled pixel prototypes processed on high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates. Post-irradiation studies with 10 MeV protons up to a fluence of 10(15) protons/cm(2) suggest HfO2 to be a better candidate as it provides higher sensitivity with negative charge accumulation on irradiation. Furthermore, even though the nature of the dielectric does not affect the electric field within the AC-coupled pixel sensor, samples with HfO2 are comparatively less susceptible to undergo an early breakdown due to irradiation. Edge-transient current technique (e-TCT) measurements show a prominent double-junction effect as expected in heavily irradiated p-type detectors, in accordance with the simulation studies.Peer reviewe

TOTEM Physics

This article discusses the physics programme of the TOTEM experiment at the LHC. A new special beam optics with beta* = 90 m, enabling the measurements of the total cross-section, elastic pp scattering and diffractive phenomena already at early LHC runs, is explained. For this and the various other TOTEM running scenarios, the acceptances of the leading proton detectors and of the forward tracking stations for some physics processes are described.Peer reviewe