Central Diffraction in Proton-Proton Collisions at s=7\sqrt{s}=7\,TeV with ALICE at LHC

A double-gap topology is used for filtering central-diffractive events from a proton-proton minimum-bias data sample at a centre-of-mass energy {$\sqrt{s}=7$\,TeV}. This topology is defined by particle activity in the ALICE central barrel and absence of particle activity outside. The fraction of events satisfying the double-gap requirement $R_{DG}$ is found to be {$7.63\pm0.02(stat.)\pm0.87(syst.)\times 10^{-4}$}. The background of this double-gap fraction is estimated by studying the contributions of non-diffractive, single- and double-diffractive dissociation processes as modelled by Monte Carlo event generators, and is found to be about 10%.Comment: 4 pages, 2 figures, Proceedings Diffraction 2012 - International Workshop on Diffraction in High-Energy Physics, Puerto del Carmen, Sept. 10-15, 201

Upgrade of the ALICE Inner Tracking System

During the Long Shutdown 2 of the LHC in 2018/2019, the ALICE experiment plans the installation of a novel Inner Tracking System. It will replace the current six layer detector system with a seven layer detector using Monolithic Active Pixel Sensors. The upgraded Inner Tracking System will have significantly improved tracking and vertexing capabilities, as well as readout rate to cope with the expected increased Pb-Pb luminosity of the LHC. The choice of Monolithic Active Pixel Sensors has been driven by the specific requirements of ALICE as a heavy ion experiment dealing with rare processes at low transverse momenta. This leads to stringent requirements on the material budget of 0.3$$ per layer for the three innermost layers. Furthermore, the detector will see large hit densities of $\sim 19 \mathrm{cm}^{-2}/\mathrm{event}$ on average for minimum-bias events in the inner most layer and has to stand moderate radiation loads of 700 kRad TID and $1\times 10^{13}$ 1 MeV n$_\mathrm{eq}/\mathrm{cm}^{2}$ NIEL at maximum. The Monolithic Active Pixel Sensor detectors are manufactured using the TowerJazz 0.18 $\mu$m CMOS Imaging Sensor process on wafers with a high-resistivity epitaxial layer. This contribution summarises the recent R&D activities and focuses on results on the large-scale pixel sensor prototypes.Comment: 10 pages, 8 figures, proceedings of VERTEX 2014, 15-19 September 201

Studies for the ALICE Inner Tracking System Upgrade

The ALICE experiment at the CERN LHC identifies D0 mesons via secondary-vertex reconstruction and topological cuts to reduce the corresponding combinatorial background in heavy-ion collisions. The D0 meson is produced promptly in initial, hard scatterings via the strong interaction or as feed-down from weakly decaying B hadrons. Within this thesis, a novel method for the separation of prompt and feed-down D0 mesons using cut variations was implemented and applied to data from p–Pb collisions at sqrt(s_NN) = 5.02 TeV. The effectiveness of the secondary-vertex reconstruction strongly depends on the performance and in particular the pointing resolution of the Inner Tracking System. The upgrade of the ALICE Inner Tracking System for the Long Shutdown 2 of the LHC in 2019/2020 will significantly improve its vertex-reconstruction and tracking capabilities. It will be equipped with Monolithic Active Pixel Sensors manufactured using the TowerJazz 180nm CMOS process on wafers with a high-resistivity epitaxial layer. In another part of this thesis, several pixel-chip prototypes of the ALPIDE architecture with in-pixel amplification and discrimination as well as in-matrix data reduction were characterised. The pALPIDE-2 prototype was measured to fulfil the requirements in terms of detection efficiency, fake-hit rate, position resolution and tolerance to irradiation with non-ionising energy loss. Based on simulations modelling the tracking and vertex-reconstruction performance of the upgraded Inner Tracking System, the perspective of the feed-down separation using cut variations after the upgrade was assessed within this thesis

Digital Pixel Test Structures implemented in a 65 nm CMOS process

The ALICE ITS3 (Inner Tracking System 3) upgrade project and the CERN EP R&D on monolithic pixel sensors are investigating the feasibility of the Tower Partners Semiconductor Co. 65 nm process for use in the next generation of vertex detectors. The ITS3 aims to employ wafer-scale Monolithic Active Pixel Sensors thinned down to 20 to 40 um and bent to form truly cylindrical half barrels. Among the first critical steps towards the realisation of this detector is to validate the sensor technology through extensive characterisation both in the laboratory and with in-beam measurements. The Digital Pixel Test Structure (DPTS) is one of the prototypes produced in the first sensor submission in this technology and has undergone a systematic measurement campaign whose details are presented in this article. The results confirm the goals of detection efficiency and non-ionising and ionising radiation hardness up to the expected levels for ALICE ITS3 and also demonstrate operation at +20 C and a detection efficiency of 99% for a DPTS irradiated with a dose of $10^{15}$ 1 MeV n$_{\mathrm{eq}}/$cm$^2$. Furthermore, spatial, timing and energy resolutions were measured at various settings and irradiation levels.Comment: Updated threshold calibration method. Implemented colorblind friendly color palette in all figures. Updated reference

Characterisation of analogue Monolithic Active Pixel Sensor test structures implemented in a 65 nm CMOS imaging process

Analogue test structures were fabricated using the Tower Partners Semiconductor Co. CMOS 65 nm ISC process. The purpose was to characterise and qualify this process and to optimise the sensor for the next generation of Monolithic Active Pixels Sensors for high-energy physics. The technology was explored in several variants which differed by: doping levels, pixel geometries and pixel pitches (10-25 $\mu$m). These variants have been tested following exposure to varying levels of irradiation up to 3 MGy and $10^{16}$ 1 MeV n$_\text{eq}$ cm$^{-2}$. Here the results from prototypes that feature direct analogue output of a 4$\times$4 pixel matrix are reported, allowing the systematic and detailed study of charge collection properties. Measurements were taken both using $^{55}$Fe X-ray sources and in beam tests using minimum ionizing particles. The results not only demonstrate the feasibility of using this technology for particle detection but also serve as a reference for future applications and optimisations

Optimization of a 65 nm CMOS imaging process for monolithic CMOS sensors for high energy physics

The long term goal of the CERN Experimental Physics Department R&D on monolithic sensors is the development of sub-100nm CMOS sensors for high energy physics. The first technology selected is the TPSCo 65nm CMOS imaging technology. A first submission MLR1 included several small test chips with sensor and circuit prototypes and transistor test structures. One of the main questions to be addressed was how to optimize the sensor in the presence of significant in-pixel circuitry. In this paper this optimization is described as well as the experimental results from the MLR1 run confirming its effectiveness. A second submission investigating wafer-scale stitching has just been completed. This work has been carried out in strong synergy with the ITS3 upgrade of the ALICE experiment

Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe

Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at root(NN)-N-S=2.76 TeV

Peer reviewe

Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe