Physics opportunities for a fixed-target programme in the ALICE experiment

A fixed-target programme in the ALICE experiment using the LHC proton and lead beams offers many physics opportunities related to the parton content of the nucleon and nucleus at high-$x$, the nucleon spin and the Quark-Gluon Plasma. We investigate two solutions that would allow ALICE to run in a fixed-target mode: the internal solid target coupled to a bent crystal and the internal gas target. The feasibility of these solutions are being studied for a possible installation at the LHC interaction point IP2 during the Long Shutdown 3

A single photoelectron calibration system for the NectarCAM camera of the Cherenkov Telescope Array Medium-Sized Telescopes

International audienceThis contribution aims to introduce the single photo-electron system designed to calibrate the camera of the Medium-Sized Telescopes of the Cherenkov Telescope Array (CTA). This system will allow us to measure accurately the gain of the camera’s photodetection chain and to constrain the systematic uncertainties on the energy reconstruction of gamma rays detected by CTA. The system consists of a white painted screen, a fishtail light guide, a flasher and an XY motorization to allow movement. The flashes guided by the fishtail mimic the Cherenkov radiation and illuminate the focal plane under the screen homogeneously. Then, through the XY motorisation, the screen is moved across the entire focal plane of the NectarCAM camera, which consists of 1855 photo-multiplier tubes. In this contribution, we present the calibration system and the study on its optimum scan positions required to cover the full camera effectively. Finally, we illustrate the results of the calibration data analysis and discuss the performance of the system

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Design and characterization of a single photoelectron calibration system for the NectarCAM camera of the medium-sized telescopes of the Cherenkov Telescope Array

International audienceIn this work, we describe the optical properties of the single photoelectron (SPE) calibration system designed for NectarCAM, a camera proposed for the Medium Sized Telescopes (MST) of the Cherenkov Telescope Array (CTA). One of the goals of the SPE system, as integral part of the NectarCAM camera, consists in measuring with high accuracy the gain of its photo-detection chain. The SPE system is based on a white painted screen where light pulses are injected through a fishtail light guide from a dedicated flasher. The screen – placed 15 mm away from the focal plane – is mounted on an XY motorization that allows movements over all the camera plane. This allows in-situ measurements of the SPE spectra via a complete scan of the 1855 photo-multiplier tubes (PMTs) of NectarCAM. This calibration process will enable the reduction of the systematic uncertainties on the energy reconstruction of γ -rays coming from distant astronomical sources and detected by CTA.We discuss the design of the screen used in the calibration system and we present its optical performances in terms of light homogeneity and timing of the signal

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

International audienceIn this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

LHC fixed target experiments: Report from the LHC Fixed Target Working Group of the CERN Physics Beyond Colliders Forum

Several fixed-target experiments at the LHC are being proposed and actively studied. Splitting of beam halo from the core by means of a bent crystal combined with a second bent crystal after the target has been suggested in order to study magnetic and electric dipole moments of short-lived particles. A similar scheme without the second crystal or other schemes with more conventional solid or gas target have been proposed to study the hadronic matter and the quark-gluon plasma, as well as to provide inputs to cosmic ray physics. Most notably, an upgrade of the existing and already productive LHCb gas target (SMOG), which would make use of a storage cell, has been proposed, designed, and extensively reviewed. The implementation in LHCb of a polarised gas target, based on the storage cell technique, was also discussed, motivated by the nucleon-spin study. The status of these proposals, their technical feasibility and impacts on the LHC machine have been studied in the LHC fixed-target working group of the Physics Beyond Collider forum at CERN. The status and outcome of these studies are presented here