Master student Projects

Projects for Master students in the Nikhef B-physics (LHCb) group

date: May 2015

This is an overview with all available Master student projects in the Nikhef B-physics (LHCb) group.

If you have your own research proposal, need more detailed information on the (availability) of individual proposals or would like to discuss about other available projects in the group you are always welcome to contact either the contact person for the project and/or the Nikhef B-physics group leader:

Marcel Merk [e-mail: i93_at_nikhef.nl, Tel 020-5925107, Nikhef room N2xx]

For an overview of the theses written in the Nikhef B-physics group you can look at the Nikhef LHCb theses page

Master projects in the Nikhef B-physics group

J/psi phi is a flagship analysis in the LHCb experiment. However, no-one in LHCb has tested whether CPT symmetry is violated. CPT symmetry is tightly connected to the principle of Lorentz invariance. Lorentz invariantz violation would become visible if the decay rate would show any dependency to a fixed direction in space. In this project the CP violation analysis is extended to test for Lorentz Invariance violation.

For this project computer skills are needed. The ROOT programme and C++ and/or Python macros are used. This is a project that is closely related to the larger effort at Nikhef (~5 people) of measuring phi_s with Bs->J/psiPhi decays. Weekly video meetings with CERN coordinate the efforts within the LHCb collaboration.

Relevant information:

Belle Collaboration: arXiv:1203.0930v2, Search for Time-Dependent CPT Violation in Hadronic and Semileptonic B Decays

End comment Niels Nov 2014 -->

1) Bs->mumu and Bd->mumu normalization and B mesons hadronization probabilities

Supervisors: Antonio Pellegrino (physicist)

Research description:

The measurement of the Bs-> mu mu and Bd->mu mu decays is one of the flagships of the LHCb experiment, the latest result in combination with CMS has recently been published on Nature. The aim of this project is to study the yields of other decays with a J/Psi in the final state, like B+ -> J/Psi K+ and Bs-> J/Psi Phi, that can be detected triggering on the muons decay products of the J/Psi. These yields are a crucial input to obtain the Bs-> mu mu and Bd->mu mu decays branching fraction as they provide a relative normalization. Moreover, in order to use Bd decays to normalize the Bs-> mu mu yields we need to measure the relative probabilities for a b quark to hadronize into a Bs (f_s) or a Bd (f_d) meson, that can also be obtained from B+ -> J/Psi K+, Bs-> J/Psi Phi and Bd-> J/Psi K* decays. The ratio f_s/f_d is not a constant and is therefore important to measure it as a function of both the energy in the center of mass of the pp collision and the B mesons kinematics. The combination of previous data at 7 and 8 TeV and data at 13 TeV from the LHC 2015 run will provide us important new insight and is a result worth a journal publication in his own right.

For this project some programming skills are needed (PYTHON or C++). Some initial knowledge of the ROOT analysis framework is also useful. The student will perform his research in a group consisting of two seniors and two Ph.D. students engaged in the study of very rare decays of the B mesons to di-muon final states and the search for lepton-flavor violating final states (e.g. electron-muon).

Relevant information:

[1] R.Aaij et al. [LHCb Collaboration], ``Measurement of the fragmentation fraction ratio f_s/f_d and its dependence on B meson kinematics, JHEP 04 (2013) 001 [arXiv:1301.5286 [hep-ph]].

2) Measurement of BR(B0->pi-Ds+) and BR(Bs->Ds-*pi+)/BR(Bs->Ds-pi+)

Supervisors: Niels Tuning (staf), Lennaert Bel (PhD) ?, Mick Mulder (PhD) ?

Research description:

This project aims to measure the branching fraction of the decay B0->pi-Ds+. The decay B0->pi-Ds+ is quite rare, because it occurs through the transition of a b-quark to a u-quark. It has been measured at the B-factories only at modest precision (~12%). This decay is interesting, because
1) It is sensitive to the CKM-element Vub, which determination is heavily debated.
2) It can be used to determine the ratio r_pi=B0->pi-D+/B0->D-pi+ which in turn is needed for CP violation measurements.
3) It can quantify non-factorisable QCD effects in certain B-decays.

The experimental challenge is to understand the background from e.g. Bs->Ds*pi decays. The aim is to also determine the relative branching fraction of Bs->Ds*pi relative to Bs->Dspi decays. This can is useful, because
1) It helps in the measurement of B0->pi-Ds+
2) It might quantify the magnitude of the ratio of form factors F(Bs->Ds*)/F(Bs->Ds*)

The aim is that this project results in a journal publication on behalf of the LHCb collaboration. For this project computer skills are needed. The ROOT programme and C++ and/or Python macros are used. This is a project that is closely related to three important analyses in the group:
1) Measurements of fs/fd with hadronic Bs->DsPi decays,
2) Time dependent CP violation analysis of Bs->DsK decays.
Weekly video meetings with CERN coordinate the efforts with in the LHCb collaboration.

Relevant information:

[1] R.Aaij et al. [LHCb Collaboration], ``Determination of the branching fractions of B0s->DsK and B0->DsK, Submitted to JHEP [arXiv:1412.7654 [hep-ex]].

[2] R. Fleischer, N. Serra and N. Tuning, ``Tests of Factorization and SU(3) Relations in B Decays into Heavy-Light Final States, Phys. Rev. D 83, 014017 (2011) [arXiv:1012.2784 [hep-ph]].

[3] K. de Bruyn, R. Fleischer, R. Knegjens, M. Merk, M. Schiller and N. Tuning, ``Exploring Bs -> Ds(*)K Decays in the Presence of a Sizable Width Difference ??s, Nucl. Phys. B 868, 351 (2013) [arXiv:1208.6463 [hep-ph]].