26/03/2020

# PhD contract in the field of Physics financed by the University Clermont Auvergne

This job offer has expired

• ORGANISATION/COMPANY
Université Clermont Auvergne
• RESEARCH FIELD
Physics
• RESEARCHER PROFILE
First Stage Researcher (R1)
21/05/2020 23:00 - Europe/Brussels
• LOCATION
France › AUBIERE
• TYPE OF CONTRACT
Other
• JOB STATUS
Other
• HOURS PER WEEK
35 H
• OFFER STARTING DATE
01/10/2020
• REFERENCE NUMBER
UCA/SF/0020
• IS THE JOB RELATED TO STAFF POSITION WITHIN A RESEARCH INFRASTRUCTURE?
Yes

Ecole Doctorale des Sciences Fondamentales

Title of the thesis: Search for rare and Lepton Flavour-violating semitauonic $b$-

hadron decays in the LHCb experiment

Supervisor : Stéphane Monteil

Laboratory : LPC

University : UCA

Email and Phone : monteil@in2p3.fr 0473407917

Co-supervisor : Régis Lefèvre

Laboratory : LPC

University : UCA

Email and Phone : lefevre@clermont.in2p3.fr 0473407917

Summary :

In the Standard Model (SM) of particle physics, electrons, muons and taus couple to gauge bosons with the same

strength. This property is known as Lepton Flavour Universality (LFU).

Recent experimental results from the LHCb experiment are currently challenging this SM prediction in

semileptonic $B$ decays. These hints of beyond SM Physics (BSM) (none of them is significant per se) can be

accounted for in models involving new gauge interactions and/or new particles such as leptoquarks. In a large

class of models, the third fermion families (quarks and leptons) own a specific status, which suggests the

possibility of significant LFU-violating effects. This is the case of the $b \to s \tau^+ \tau^-$ transitions.

Flavour-changing neutral-current semileptonic processes $b \to s \ell^+ \ell^-$ are very suppressed in the SM

(they are forbidden at tree level) and can be subjected to significant BSM Physics contributions on a general

basis. The recent hints about LFU might make this statement even stronger in the case of semitauonic final

states. As an example, the branching fraction of the decay $B^0 \to K^{*0} \tau^+ \tau^-$ could be enhanced by as

much as three orders of magnitude with respect to the SM. This decay would then be in the observable range for

LHCb.

Identifying $B^0 \to K^{*0} \tau^+ \tau^-$ decays in LHCb is very challenging since the neutrinos from the tau

decays are not detected. A novel partial reconstruction technique has been initiated within the Clermont team. It

allows to evaluate analytically the momenta of the neutrinos from the topology of the decay. Exploratory studies

both on $B^0 \to K^{*0} \tau^+ \tau^-$ Monte-Carlo samples and on large statistics control samples, such as $B^0 \to D^-D_s^+$, are promising.

The thesis subject consists in applying this topological reconstruction technique to the search for the decay $B^0 \to K^{*0} \tau^+ \tau^-$ and extending it to the searches of Lepton-Flavour violating modes such as $B^0 \to K^{*0} \tau^{\pm} \mu^{\mp}$. Improvements of the topological reconstruction technique by adding the kinematical

constraints to the LHCb tracking information and its implementation into the LHCb decay reconstruction package

are among the first year milestones of the PhD. The successful applicant will be welcome in the LHCb

collaboration.

Applicants should hold a Master of Science degree with a specialisation in Particle Physics. Software skills (C++,

Python languages in particular) will be appreciated. French language skills are not necessarily required. A good

command of the English language is welcome.

https://sf.ed.uca.fr/financement-doctoral/contrat-doctoral-allocations-ministerielles/sujets-de-these-ed-sf-2020-proposes-au-concours/

https://sf.ed.uca.fr/financement-doctoral/contrat-doctoral-allocations-m...

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#### Benefits

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#### Eligibility criteria

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#### Selection process

Interested students must send two copies of their application to the secretariat of the doctoral school before 22 May 2020, the deadline.

Audition at the doctoral school of the selected candidates:

- 4 June morning: LAMP jury

- 11th June morning: LMV jury

- 11 June afternoon: Chemistry jury

- 12 June: Physics jury

19 June: ED SF council for allocations Doctoral allocations

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#### Offer Requirements

• REQUIRED EDUCATION LEVEL
Physics: Master Degree or equivalent

#### Skills/Qualifications

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#### Specific Requirements

Speak French or very good level of English

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## Map Information

Job Work Location Personal Assistance locations
Work location(s)
1 position(s) available at
Clermont Laboratory of Physics (LPC)
France
Région Auvergne Rhône-Alpes
AUBIERE
63178
Campus Universitaire des Cézeaux TSA 60026 CS 60026 4, Avenue Blaise Pascal