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PhD position in particle physics in the Belle II experiment

IPHC Strasbourg
Strasbourg, France
Posting live until
20 May 2024

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Topic: PhD position ANR-InvISYble in the Belle II experiment @ IPHC Strasbourg

IPHC Strasbourg, France, invites applications for a joint experimental/theory PhD position to work on physics analyses within the Belle II experiment.

The Belle II group at IPHC searches for physics beyond the standard model in flavour-changing neutral-current b → s transitions, focusing on b → s nu anti-nu and b → s gamma decays. The group participates also in the operation of the silicon vertex detector (SVD) and the preparation of its upgrade.

The B → K(*) nu anti-nu decays are a formidable place to look for the new physics needed to complete the standard model of particle physics. On the one hand in the standard model their decay rate is small and well-known so that interference with new dynamics could modify its decay rate by a sizeable amount. On the other hand the two final-state neutrinos are not observed directly, thus these processes are also sensitive to new invisible particles like those that could compose dark matter.

In the foreseeable future Belle II will remain the only experiment allowing to observe B → K(*) nu anti-nu decays. In this experiment pairs of B mesons are produced in electron-positron collisions. As neutrinos from the signal are undetected, information from the other B mesons of the event (referred to as tag B) may be used to constrain their kinematic and correctly identify the signal decay. There are currently two strategies to reconstruct the tag B: the “tagged” approach where the tag-B is reconstructed via a hadronic or a semi-leptonic decay and the “untagged” approach where the signal is reconstructed first and the rest of the event is assumed to be composed of the other B only. The untagged approach affords the highest efficiency among the three approaches, at the price of a lower purity. The hadronic tag allows the best purity and the best resolution on the di-neutrino invariant mass but has a low efficiency. The semi-leptonic tag has intermediate performance in terms of efficiency and purity. The Belle II experiment recently provided the first evidence for the B+ → K+ nu anti-nu decay using the untagged approach and the tagged approach based on hadronic decays [1].

The PhD student will search for B → K(*) nu anti-nu decays using the semi-leptonic tag. They will also develop new kinematic variables inspired by supersymmetric searches that optimally exploit the topology of pair-produced heavy particles decaying semi-invisibly [2].



Practical details

The PhD position is funded for 3 years starting on the first October 2024 via the ANR InvISYble project. Review of applications will start on May 24th and continue until the position is filled.

The position is based at IPHC (Strasbourg, France) and a stay of about 6 months at LAPTh Annecy is also foreseen. Visits to KEK and participation in international conferences and workshops are also expected. The gross salary will be 2135 € per month.

Required qualifications

The candidate must hold a French master 2 degree or a comparable international master degree at the time of appointment. They should have been exposed to all standard courses in particle physics (quantum field theory and the Standard Model, experimental methods including statistical analyses). They should have analysis and software skills (ROOT, Python, C++) and should be able to communicate in English. Experience in B physics would be an advantage but is not mandatory.


The IPHC, a joint research unit under the joint supervision of CNRS and the University of Strasbourg, is a multidisciplinary laboratory where research teams from different scientific cultures (ecology, physiology and ethology, chemistry and subatomic physics) develop very high-level programs based on scientific instrumentation. The IPHC is organised in three departments and hosts 393 employees in total, amongst them 257 with permanent contacts (119 staff scientists and associated professors, 138 engineers and technicians), 46 fixed term contracts and 102 PhDs. LAPTh is a theoretical-physics laboratory located in Annecy, with a diverse expertise encompassing particle physics, astrophysics/cosmology, mathematical physics and their interfaces, as well as with the experimental aspects of the respective disciplines. The post-doctoral researcher will be welcomed into the Belle II team which includes 4 researchers, two post-doctoral researcher and two PhD students. The thesis will be in co-supervision experiment/theory. The PhD student will be supervised by Giulio Dujany and Jérôme Baudot (IPHC Strasbourg) on the experimental side and by Diego Guadagnoli (LAPTh Annecy) on the theory side.


Interested candidates are invited to send further inquiries to Giulio Dujany to be informed about the application procedure.

Preference will be given to applications received by the 24th May 2024, but the position will remain open until filled.

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