Outreach activities of the LPSC LHC groups are described in details only in the French page of this site, since most of the proposed activities are at destination of local French-speaking people. Sorry !
If you want to know more about the LHC and ALICE and ATLAS experiments, you can get a lot of information there:
Outreach activities in english and possibly in other languages could be considered, please contact us at
A LPSC grid node called IN2P3-LPSC was created beginning of 2008 to meet the computing ressources requests of the LHC group (ATLAS and ALICE) of the laboratory. IN2P3-LPSC is a Tier 2 grid node of the W-LCG (WorldWide LHC Grid Computing) and is part of the LCG-France project that manage the French infrastructure.
Description
The technical description of the LPSC grid node is here.
In practice...
Practical information for LPSC grid node use may be found in this wiki page (some information only in French...)
Some links useful to get the site status:
Context
The first LHC run allowed to test the Standard Model of particle physics at an unprecedented high energy level, never reached in a particle collider. Many results were published using these LHC data among which the discovery of a Higgs boson that completes the particle content of the Standard Model. However, theoretical and experimental arguments show that this model still has limitations and needs to be extended, modified or replaced in order to give answers to the hierarchy problem, to describe the dark matter or to include the gravity in a coherent frame with the other interactions...
Theoreticians proposed several ideas to build theories beyond the standard model in order to solve some of these problems. Many of them like supersymetry, technicolor, or models with extradimensions lead to the prediction of massive particles that can be searched for in LHC data.
Signature
These new massive particles could give different signatures in the ATLAS detector. We choose to look for massive particle decaying into a top quark pair (semi-leptonic channel). Indeed the top quark, because of its properties like its high mass close to the electroweak breaking scale, plays an important role in numerous new physics models from Technicolor to extra-dimension theories. Moreover its signature at the LHC is sufficiently clear to maintain Standard Model background at a reasonable level.
Analysis
The originality of the analysis lies in the identification of the top pair final state and the reconstruction of the top pair mass. Indeed LHC collisions produce highly boosted top pairs from Standard Model processes or from new high mass particles decays. This leads to a new topology where top decay products (leptons and quarks) are quite collimated and reconstructed in one single object. New tools have thus to be developed to disentangle the different decay products and allow the identification, reconstruction and calibration of such boosted particles.
Once boosted top quark pairs are identified and their invariant mass reconstructed, the mass spectra from LHC data is compared to the one predicted by the standard model. If data and simulation are in agreement, limits can be set on the mass and the production cross-section of massive particles predicted by new models. An excess of top quark pairs with respect to the standard model would inversely sign the presence of new physics.
Results
Analysis results at 13 TeV with 36 fb-1 - run2 : 2015-2016 data - Eur. Phys. J. C 78 (2018) 565
Dark Matter model interpretation 2019 results - run2 : 2015-2016 data - ATLAS PAPER EXOT-2017-32
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Publications
- 2019, 13 TeV data, run 2 2015-16, 37 fb-1: Impact on dark matter search => publication submitted to JHEP (arXiv:1903.01400, ATLAS collaboration link : EXOT-2017-32)
- 2018, 13 TeV data, run 2 2015-16: Impact on dark matter search => note de conférence (ATLAS-CONF-2018-051)
- 2018, 13 TeV data, run 2 2015-16, 36 fb-1: publication (arXiv:1804.10823; Eur. Phys. J. C 78 (2018) 565)
- 2016, 13 TeV data, 3,2 fb-1, only boosted topology: Conference note (ATLAS-CONF-2016-014)
- 2013, 8 TeV data, 14 fb-1: Conference note ATLAS-CONF-2013-052
- 2013, 7 TeV data, 4.7 fb-1: Publication (arXiv:1305.2756, Phys. Rev. D 88, 012004 – July 2013)
- 2012, 7 TeV data, 4.66 fb-1: Conference note (ATLAS-CONF-2012-136)
Members
Members
- Sabine Crépé-Renaudin (in charge of LPSC analysis)
- Pierre-Antoine Delsart (jet substructure expert)
Previous analysis group members
At hadron colliders top quarks are predominantly produced in pairs via the flavour-conserving strong interaction, but single top-quark production can occur via charged-current electroweak processes involving a Wtb vertex. In the Standard Model of particle physics, at leading-order in QCD perturbation theory, three sub-processes contribute to single top-quark production: an exchange of a virtual W boson either in the t-channel or in the s-channel, or the associated production of a top-quark with an on-shell W boson.
In proton–proton collisions, the t-channel exchange is the dominant production process of single top-quarks. Furthermore, as a consequence of the vector–axial-vector form of the Wtb vertex in the Standard Model, the produced top-quarks are predicted to be highly polarised. Due to its short lifetime, the top quark decays before hadronisation and its spin orientation is directly accessible through the angular distributions of its decay products. Within the Standard Model the top quark decays through the electroweak interaction, and almost exclusively into a W boson and a b-quark. The W boson, which is produced as a real particle in the top-quark decay, also possesses a polarisation (or helicity state). The W boson polarisation can be accessed via angular distributions of its decay products, as well. Measuring the top-quark and W boson polarisations in t-channel single top-quark production provides a powerful and unique probe for studying the Wtb vertex in both top-quark production and decay. Physics beyond the Standard Model resulting in corrections to the Wtb vertex (anomalous couplings) would affect the measurement of the top-quark and W boson polarisations.
At the LHC run-1, the main physics analyses carried out at the LPSC to study single top-quark production in proton–proton collisions were the following:
- Cross-section and polarisation measurements in t-channel production
- Cross-section measurement in associated W+t production
- Search for s-channel production
For the LHC run-2, the physics analyses will be focused on studies of the Wtb top-quark couplings through the combination of cross-section and polarisation measurements, and their interpretation in terms of anomalous couplings and effective quantum field theory of the Standard Model.
Group members
- Annick Lleres, DR-CNRS (2008)
Past members
- Carolina Gabaldon, Post-doc Labex Enigmass (2013-2016)
- Reinhard Schwienhorst, Visitor Labex Enigmass (2014-2015)
- Arnaud Lucotte, DR-CNRS (2006-2014)
- Benoit Clément, MCF-UJF (2007-2012)
- Julien Donini, CDD-IN2P3 (2007-2011)
PhD students
- Caterina Monini (2011-2014)
- Xiaohu Sun (2010-2013)
- Thomas Delemontex (2009-2012)
- Jin Wang (2009-2012)
- Carole Weydert (2008-2011)
- Florent Chevallier (2004-2007)
Publications
- Evidence for the associated production of a W boson and a top quark in ATLAS at sqrt(s)=7 TeV, Phys. Lett. B 716 (2012) 142
- Measurement of the t-channel single top-quark production cross section in pp collisions at sqrt(s)=7 TeV with the ATLAS detector, Phys. Lett. B 717 (2012) 330
- Search for s-channel single top-quark production in proton-proton collisions at sqrt(s)=8 TeV with the ATLAS detector, Phys. Lett. B 740 (2015) 118
- Measurement of the production cross-section of a single top quark in association with a W boson at 8 TeV with the ATLAS experiment, JHEP01 (2016) 064
- Probing the Wtb vertex structure with t-channel single top-quark events in pp collisions at sqrt(s)=8 TeV with the ATLAS detector, JHEP04 (2017) 124
Theses
- Single top s-channel cross section measurement with the ATLAS detector, Caterina Monini, Université de Grenoble, 12 septembre 2014 (supervision Annick Lleres/Arnaud Lucotte), CERN-THESIS-2014-189
- Top polarization measurement in single top quark production with the ATLAS detector, Xiaohu Sun, Université de Grenoble, 1 octobre 2013 (supervision Annick Lleres), tel-00873541
- Mesure de la section efficace de production single top W+t dans le canal dilepton auprès de l'expérience ATLAS, Thomas Delemontex, Université de Grenoble, 5 octobre 2012 (supervision Arnaud Lucotte), tel-00793216
- Mesure de la section efficace de production du single top en voie-t en utilisant des arbres de décision avec ATLAS à sqrt(s)=7 TeV, Jin Wang, Université Joseph Fourier Grenoble, 29 juin 2012 (supervision Julien Donini/Annick Lleres/Cunfeng Feng), tel-00716925
- Recherche d'un boson de Higgs chargé avec le détecteur ATLAS: de la théorie à l'expérience, Carole Weydert, Université de Grenoble, 5 septembre 2011 (supervision Benoit Clément/Michael Klasen), tel-00629349
- Préparation de l'expérience ATLAS: étalonnage électronique du calorimètre électromagnétique, mesure de la polarisation des bosons W dans la décroissance des quarks top, Julien Labbé, Université Joseph Fourier de Grenoble, 1 juillet 2009 (supervision Benoit Clément/Benjamin Trocmé), tel-00420986
- Mesure de la section efficace de production de quarks top en paires dans le canal lepton+jets à D0 et à ATLAS et interprétation en terme de bosons de Higgs chargé dans ATLAS, Florent Chevallier, Université Joseph Fourier de Grenoble, 10 mai 2007 (supervision Arnaud Lucotte/Sabine Crépé), tel-00181009