Missions

We invite applications for a highly motivated post-doctoral researcher for a 2-year duration to work on data analysis of light and heavy flavour particles with LHCb in fixed target mode. The candidate will work on the data analysis of the PbAr data already collected and to be collected until the end of Run 3, with primary focus on the analysis of light vector meson photoproduction in ultra-peripheral collisions (UPC). The candidate will also participate in the preparation for the 2025 Pb-gas data taking and will develop the trigger lines and software selections for UPC physics. He/She will conduct feasibility studies for quarkonium photoproduction measurements. Depending on the candidate profile, light or heavy flavour particle elliptic flow measurements in PbAr collisions could also be envisioned.

The researcher will be based in the LHCb group of the IJCLab (CNRS/IN2P3), Orsay, France, located on the Paris Saclay University campus. Frequent travels to CERN are expected. The candidate is expected to take shifts during the data taking and is encouraged to participate in service tasks for the ion and fixed target WG of LHCb. The position is funded for two years and can be filled as soon as June 2025 and no later than Sept. 2025.

Activités

The LHCb detector, thanks to its System For measuring Overlap with Gas (SMOG2) [1], offers a unique capability at the LHC to perform fixed target pH, pA and AA collisions at c.o.m energies ranging from 69 to 115 GeV. The physics motivations to perform fixed target collisions at the LHC are reviewed in Ref [2]. The project concerns the analysis of LHCb fixed target data with primary focus on PbAr collisions. Thanks to the boost between the colliding nucleon centre-of-mass frame and the laboratory frame, the far backward rapidity region is accessible by the LHCb detector, allowing for the study of nuclear structure at large Bjorken-x, in a complementary region to the one probed at colliders. In addition, the usage of asymmetric collision systems enables studies as a function of the system size and nuclear structure. A clean experimental tool for such studies is the production of vector mesons in ultraperipheral heavy ion collisions [3]. In such collisions, nuclei are separated by impact parameters larger than the sum of their radii and therefore hadronic interactions are strongly suppressed. In this project we propose to conduct the first exploratory vector meson measurement in UPC PbAr fixed target data at LHCb, with the data collected so far and starting with the abundantly produced 𝞀0 vector meson. The project will then focus on the developments of trigger and software selection lines dedicated to UPC physics for the PbA data to be collected in 2025. The feasibility of quarkonium photoproduction measurements will also then be explored.
Furthermore, PbA collisions in fixed target mode at a center-of-mass energy of about 70 GeV, provide a complementary coverage to the RHIC- and SPS-based experiments, in a region of high temperature and low baryonic chemical potential where the Quark Gluon Plasma (QGP) is expected to be produced. Identified particle azimuthal anisotropy coefficients (vn) measured at large rapidities are powerful tools to study the QGP medium properties, in particular they provide information on the medium shear viscosity to density entropy ratio and its temperature dependence [4]. In the quarkonium sector, the elliptic flow permits to investigate the fate of quarkonium in medium, in particular if recombination mechanisms take place [5]. The LHCb IJCLab group has also interest in light and heavy flavours flow measurements in fixed target mode.

[1] P. Di Nezza et al., The SMOG2 project, CERN-PBC-Notes-2018-007
[2] C. Hadjidakis et al., A fixed target programme at the LHC : physics case and projected performances for heavy-ion, hadron, spin and astro-particle studies, Phys. Rep. 911 (2021) 1-83
[3] A. J. Baltz et al., The physics of Ultraperipheral collisions at the LHC, Phys. Rep. 458 (2008) 1-171
[4] G. Denicol et al., Moving forward to constrain shear viscosity of QCD matter, Phys. Rev. Lett. 116 (2016) 212301
[5] R. Rapp et al., Charmonium and bottomonium production in heavy-ion collisions, Prog. Part. Nucl. Phys 65 (2010) 209-266

Compétences

Applicants are expected to hold a PhD degree in subatomic physics or in a related field. Good programming and computational skills are required. In particular, experience in data analysis and simulation, in a large experimental collaboration, will be considered a plus. The eligible candidate should be able to communicate at a scientific level in English. The CNRS is an equal opportunity/affirmative action employer.

Contexte de travail

The Irène Joliot-Curie Physics Laboratory of 2 Infinities (IJCLab) is an UMR under the supervision of the CNRS (IN2P3), the University of Paris-Saclay and the University of Paris. It is located on the campus of the University of Paris-Saclay in Orsay. The campus is located 20 km south of Paris and easily accessible by RER in 35 minutes. IJCLab was born in 2020 from the merger of five units (CSNSM, IMNC, IPN, LAL, LPT). The staff is made up of nearly 560 permanent (340 engineers, technicians and administrators and 220 researchers and teacher-researchers) and approximately 200 non-permanent including 120 doctoral students. The research themes of the laboratory are nuclear physics, high energy physics, theoretical physics, astroparticles, astrophysics and cosmology, particle accelerators, energy and environment, and health. IJCLab has very significant technical capacities in all the major fields required to design, develop / implement the experimental devices necessary for its scientific activity, as well as the design, development and use of instruments.

The LHCb IJCLab group is composed of 6 permanent researchers, 1 emeritus, 3 postdocs and 6 PhD students. The team is involved in CP violation studies in B decays, in indirect searches for effects beyond the standard model, and in heavy flavor production studies in proton-proton and proton-lead collisions for QCD precision tests. The group was in charge of the design and production of the Front-End boards and Control boards for the Electromagnetic and hadronic calorimeters of the LHCb Upgrade 1 Phase. The group had also the responsibility to build, install, commission and now operate the PLUME detector installed in 2021. The LHCb IJCLab group has played a leading role in the development of the LHCb heavy ion programme since 2015.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

Frequent travels to CERN in Switzerland are expected. The postdoctoral researcher will also travel frequently abroad to present his/her work in international conferences. Work during nights and week-end is expected during data taking shift periods (2 to 3 weeks per year).