The Human Resources Strategy for Researchers

Phd contract in the field of Physics financed for three years by the University of Clermont Auvergne

    Université Clermont Auvergne
    First Stage Researcher (R1)
    23/05/2021 00:00 - Europe/Brussels
    France › Aubière


Study of CP violation in B-to D0{K0sπ+π-π0} K-decays at LHCb

The precise measurement of the γangle of the Cabibbo-Kobayashi-Maskawa Unitarity Triangle (CKM) is a central topic in flavour physics experiments. Its determination in open-charm b hadron decays is based on tree transitions and is theoretically clean. Itprovides the standard reference point for measurements sensitive to the new effects of physics potentially accessible by tests of global coherence of the KM mechanism (Nobel Prize for Physics 2008), compared to the predictions of the Standard Model of Particle Physics (SM). In addition to the results of the B factories that operated in the decade 2000-2010 (i.e. BaBar at SLAC in California and Belle in KEK in Japan), various recent measurements of the LHCb experiment at CERN can determine the value of the angle γwith an uncertainty of about 4°. While the metrology of this fundamental parameter is in itself of great interest, an accuracy well below 1 degree is highly desirable in order to provide access to the physics energy scales beyond the SM (BSM) above 20 TeV, regardless of the BSM scenario (i.e. inaccessible by direct research to the LHC by ATLAS and CMS experiments). However, at present no single measure completely dominates the global average on determining the value of this angle, as the most accurate measurements have an accuracy of about 5 to 20 degrees. The most accurate measure has just been presented this summer by LHCb at the ICHEP 2020 conference with mode B-into D0K-, where the neutral D mesons disintegrates into K0Sπ+π-. Alternative methods are therefore important to improve the accuracy of the global average. Among them, an analysis of the decay B-into D0K-, where the D disintegrates into K0sπ-π-π0, can have a significant impact. Recently, in 2019, the Belle collaboration published a γangle measurement with a sensitivity of around 12 degrees using an effective model for the disintegration of the D meson from the CLEO-c experiment. During the months of May to July 2020, I demonstrated with an M1 internship student from the Orsay Fundamental Physics Magisterium, that LHCb already has with the 2011-2018 data of a sample of beautiful mesons in this disintegration 1.5 times greater than that Belle and of which purity exceeds 80% when that of Belle does not exceed 60%. It is on these channels that we propose to work during this thesis.

Description of the thesis subject and its environment

In the LHCb group of LPC of Clermont Ferrand, under my direction, and in close collaboration with 5 colleagues from LHCb(4 of Oxford, including the former spokesperson of LHCb, Professor G. Wilkinson who is also the author of the study of CLEO-c and 1 collaborator of the Marseille LHCb group author of the analysis of Belle, mentioned above), the PhD student will initially conduct the measurement of the angle γwith disintegration B-→D0K-with D0in K0Sπ-π-π0 with all data from 2011 to 2018 from LHCb and after with dataset 2022-2023. Using companion mode B-→D0π-, with D0in K0Sπ-π-π0, more abundant, an amplitude analysis will be conducted to study the phenomenology and spectroscopy of this charmed disintegration. This analysis will accurately measure the value of the D0to K*-+branching ratio, which is a replica of the excited states of the well-known (since 1976) mode D0in K-π+ and not yet known to this day. A preliminary study conducted during a Master 1 internship in 2020 showed that the branching ratio of this disintegration is in the order of 7%, with a relative statistical accuracy of 5% (6 times better than the measurement that dates from 1992 with the Mark III experiment of Stanford in California and which was not precise enough to observe this unambiguous disintegration). This study conducted with data B-→ D0π-, with D0in K0Sπ-π-π0, will be conducted in conjunction with colleagues at Oxford who are in charge of the same study with the charmed complementary mode D*-→D0π-with D0in K0Sπ-π-π0. The PhD student will conduct both a study on the phenomenology of disintegration D0in K0Sπ-ππ0, which will lead to a joint publication with the Oxford LHCb group and that related to measuring the CP breach phase of the CKM matrix in mode B-→D0K-with D0in K0Sπ-π-π0that will lead to 1 or even 2 publications, existing and future data. The candidate will then improve these measurements by using LHC Run3 data (probably 2022-2023 data), which will allow the current statistic to be multiplied by at least 5 factors. Such a gain will be made possible by the start-up at the end of 2021 of a new "upgraded"version of the LHCb detector. Among the key factors for improving these measurements, the reconstruction efficiency of the tracker is essential, and at its heart the excellent operation of the SciFi scintillating fibers sub-detector. Mode B-→ D0h-with D0in K0Sπ-π-π0has a strong multiplicity of charged tracks in the final state of disintegration: no less than 5 tracks! The LPC group is involved in the construction of this detector. The student will participate very actively, upon arrival, at the end of construction, in the qualification and start-up and monitoring of the operation of this detector in cruising rhythm until the fall of 2024. To do this, he (she) will work in the LPC LHCb group with another doctoral student who began her thesis in October 2019 and two postdoctoral fellows, one finishing in May 2022 and the other starting his 2-year contract in September 2021 (funding awarded by CNRS IN2P3). The new postdoctoral fellow will collaborate on the analysis project and the instrumental project to commission the new SciFi tracker, which is a strong responsibility for the LPC LHCb group and brings together researchers and engineers and technicians. With the current Doctoral student and the future postdoctoral fellow, under my coordination and that of Pascal Perret, head of the LHCb group of the LPC, the new doctoral student will contribute to the qualification of the SciFi tracker and to the reconstruction of the first data collected by this detector. To do this and to ensurea good visibility of the Clermont Ferrand group within the international collaboration LHCb it would be good if the student could make one or more long stays at CERN. With this experience, the student will be able to take on the responsibility of SciFi expert in the physics analysis group of LHCb B2OC. It is within the framework of this group that the analyses related to the disintegrations B-→ D0h-with D0in K0Sπ-π-π0.

Note: Vincent Tisserand is the laureate of the 2019 Joliot Curie Grand Prize from the FrenchSociety of Physics (SFP)for work on these research topics.


More Information

Offer Requirements

    Physics: Master Degree or equivalent

Map Information

Job Work Location Personal Assistance locations
Work location(s)
1 position(s) available at
The Physics Laboratory of Clermont
Région Auvergne Rhône-Alpes
Campus Universitaire des Cézeaux, 4 Avenue Blaise Pascal, TSA 60026 CS 60026

Open, Transparent, Merit based Recruitment procedures of Researchers (OTM-R)

Know more about it at Université Clermont Auvergne

Know more about OTM-R

EURAXESS offer ID: 622980


The responsibility for the jobs published on this website, including the job description, lies entirely with the publishing institutions. The application is handled uniquely by the employer, who is also fully responsible for the recruitment and selection processes.


Please contact support@euraxess.org if you wish to download all jobs in XML.