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L'expérience CMS (du nom du détecteur Compact Muon Solenoid, en français « solénoïde compact à muons ») est une des expériences de physique des particules du Grand collisionneur de hadrons (LHC) du CERN. Le détecteur CMS est situé dans une caverne souterraine à Cessy au point 5, en France, près de la frontière avec la Suisse. Il a été construit et est exploité par environ de presque , appartenant à scientifiques. Le détecteur a une forme cylindrique de de long et de diamètre, et pèse . L'aimant solénoïde de CMS est un cylindre creux de de diamètre et de générant un champ magnétique de 4 T et pesant près de 2000 t. Contexte Un autre détecteur, ATLAS, a été bâti en un autre point du LHC et étudie la même physique que CMS par des technologies de détection différentes. Les collaborations ATLAS et CMS sont à la fois dans une situation de compétition et de coopération pour les découvertes majeures et les mesures de précision. Historiquement, ils prennent la successio

An early separation scheme for the LHC luminosity upgrade

Guido Sterbini

In this thesis we evaluate the potential of the Early Separation Scheme for the Luminosity Upgrade of the Large Hadron Collider (LHC). The main goal of the Early Separation Scheme is to reduce the crossing angle between the proton beams at the collision point in order to increase the luminosity performance of the machine and to alleviate, at the same time, the detrimental effects due to the electromagnetic interaction between the beams. The Early Separation Scheme consists of four dipoles for each of the two high luminosity Interaction Points of the LHC, corresponding to the ATLAS and CMS detectors. Two dipoles out of the four, the so-called D0 dipoles, have to be integrated in the experimental cavern. We show that, working in synergy with an increased beam current and with a stronger final focusing system, the Early Separation Scheme can provide an integrated luminosity of 3000 fb-1 over a period of 6.5 – 7 years with a leveled luminosity of 5.5 1034 cm-2 s-1. These figures are possible thanks to the luminosity leveling by using the crossing angle. We study the impact of the Early Separation Scheme from the beam dynamics point of view by evaluating its linear and non-linear effects. We show, using an analytical approach, that all induced linear effects are negligible. The non-linear effects, namely the electromagnetic interaction between the beams, are considered by means of numerical simulations and dedicated experiments. From the simulation and the experimental results, we have indications about the minimum beam crossing angle that is still compatible with the beam dynamics constraints. From these indications and by considering the different issues related to the integration of the scheme in the detectors, we propose to position the D0 dipole at 14 m from the Interaction Point. The integrated magnetic field required and the space constraints in the detectors imply the use of a superconducting D0 dipole: we optimize its aperture to reduce the power deposited on the magnet's coil by the collision debris. Due to the high power density impinging on the coil and to the 9 T magnetic field required, we propose a magnet cross-section using a Nb3Sn superconducting cable at the temperature of 4.2 K.

EPFL2010

Luminosity scans for beam diagnostics

Tatiana Pieloni

A new type of fast luminosity separation scans ("emittance scans") was introduced at the CERN Large Hadron Collider (LHC) in 2015. The scans were performed systematically in every fill with full-intensity beams in physics production conditions at the interaction point (IP) of the compact muon solenoid (CMS) experiment. They provide both transverse emittance and closed orbit measurements at a bunch-by-bunch level. The precise measurement of beam-beam closed orbit differences allowed a direct, quantitative observation of long-range beam-beam PACMAN effects, which agrees well with numerical simulations from an improved version of the TRAIN code.

AMER PHYSICAL SOC2018

Observation of the rare B-s(0)->mu(+)mu(-) decay from the combined analysis of CMS and LHCb data

Muhammad Ahmad, Liupan An, Georgios Anagnostou, Konstantin Androsov, Alexandre Aubin, Aurelio Bay, Marc-Olivier Bettler, Frédéric Blanc, Roberto Castello, Yixing Chen, Tian Cheng, Peter Clarke, Victor Coco, Giuseppe Codispoti, Greig Alan Cowan, João Miguel das Neves Duarte, Adam Davis, Michel De Cian, Alessandro Degano, Charles Dietz, Hans Dijkstra, Milos Dordevic, Mirco Dorigo, Frédéric Guillaume Dupertuis, Paolo Durante, Dipanwita Dutta, Matthias Finger, Francesco Fiori, Christoph Frei, Martin George Friedl, Sebastiana Gianì, Elena Graverini, Ruchi Gupta, Guido Haefeli, Csaba Hajdu, Xiaoxue Han, Pierre Jaton, Alexis Kalogeropoulos, Chitsanu Khurewathanakul, Joo Yeon Kim, Donghyun Kim, Ji Hyun Kim, Doohyun Kim, Ilya Komarov, Ajay Kumar, Sanjeev Kumar, Ekaterina Kuznetsova, Ho Ling Li, Yiming Li, Hao Liu, Shuai Liu, Werner Lustermann, Alessandro Mapelli, Pietro Marino, Matteo Marone, Maurizio Martinelli, Bastien Luca Muster, Tatsuya Nakada, Matthew Needham, Niko Neufeld, Ioannis Papadopoulos, Luca Pescatore, Vladimir Petrov, Cédric Potterat, Jessica Prisciandaro, Quentin Python, Barinjaka Rakotomiaramanana, Gerhard Raven, Federico Leo Redi, Andrea Rizzi, Paolo Ronchese, Julien Rouvinet, Olivier Schneider, Sourav Sen, Varun Sharma, Ashish Sharma, Lesya Shchutska, Muhammad Shoaib, Gurpreet Singh, Jan Steggemann, Liang Sun, Wei Sun, Frédéric Teubert, Mark Tobin, Minh Tâm Tran, Andromachi Tsirou, Joao Varela, Horst Vogel, Qian Wang, Rui Wang, Zheng Wang, Jian Wang, Matthias Weber, Jean Wicht, Matthias Wolf, Zhirui Xu, Yong Yang, Kai Yi, Lei Zhang, Yi Zhang

The standard model of particle physics describes the fundamental particles and their interactions via the strong, electromagnetic and weak forces. It provides precise predictions for measurable quantities that can be tested experimentally. The probabilities, or branching fractions, of the strange B meson (B-s(0)) and the B-0 meson decaying into two oppositely charged muons (mu(+) and mu(-)) are especially interesting because of their sensitivity to theories that extend the standard model. The standard model predicts that the B-s(0)->mu(+)mu(-) and B-0 ->mu(+)mu(-) decays are very rare, with about four of the former occurring for every billion B-s(0) mesons produced, and one of the latter occurring for every ten billion B-0 mesons(1). A difference in the observed branching fractions with respect to the predictions of the standard model would provide a direction in which the standard model should be extended. Before the Large Hadron Collider (LHC) at CERN2 started operating, no evidence for either decay mode had been found. Upper limits on the branching fractions were an order of magnitude above the standard model predictions. The CMS (Compact Muon Solenoid) and LHCb(Large Hadron Collider beauty) collaborations have performed a joint analysis of the data from proton-proton collisions that they collected in 2011 at a centre-of-mass energy of seven teraelectronvolts and in 2012 at eight teraelectronvolts. Here we report the first observation of the B-s(0)->mu(+)mu(-) decay, with a statistical significance exceeding six standard deviations, and the best measurement so far of its branching fraction. Furthermore, we obtained evidence for the B-0 ->mu(+)mu(-) decay with a statistical significance of three standard deviations. Both measurements are statistically compatible with standard model predictions and allow stringent constraints to be placed on theories beyond the standard model. The LHC experiments will resume taking data in 2015, recording proton-proton collisions at a centre-of-mass energy of 13 teraelectronvolts, which will approximately double the production rates of B-s(0) and B-0 mesons and lead to further improvements in the precision of these crucial tests of the standard model.

Nature Publishing Group2015

An early separation scheme for the LHC luminosity upgrade

Guido Sterbini

EPFL2010