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

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

Supervisors: Antonio Pellegrino (staff), Maarten van Veghel (PhD)

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 one of the main uncertainties in the measurements of the branching fractions by measuring 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 fractions 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(Lb->p Ds+)

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

Research description:

This project aims to measure the branching fraction of the decay Lb->p Ds+. The decay Lb->p Ds+ is quite rare, because it occurs through the transition of a b-quark to a u-quark. It has not been measured yet (although some LHCXb colleagues claim to have seen it in the past).

This decay is interesting, because
1) It is sensitive to the CKM-element Vub, which determination is heavily debated.
2) It can quantify non-factorisable QCD effects in b-baryon decays.

The decay is closely related to B0->pi-Ds+, which proceeds through a similar Feynman diagram. Also the final state of B0->pi-Ds+ is almost identical to Lb->p Ds+. The aim is to determine the relative branching fraction of Lb->pDs+ with respect to B0->D+pi- decays, in close collaboration with the PhD (who will study BR(B0->pi-Ds+)/BR(B0->D+pi-) ).

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 previous analyses in the group. Weekly video meetings with CERN coordinate the efforts with in the LHCb collaboration.

Relevant information:

[1] R.Aaij et al. [LHCb Collaboration], ``Study of the kinematic dependences of Lambda_b production in pp collisions and a measurement of the Lambda_b->Lambda_c pi branching fraction, JHEP 08 (2014) 143 [arXiv:1405.6842 [hep-ex]].

[2] R.Aaij et al. [LHCb Collaboration], ``Determination of the branching fractions of B0s->DsK and B0->DsK, JHEP 05 (2015) 019 [arXiv:1412.7654 [hep-ex]].

[3] 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]].

[4] 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 Delta Gamma_s, Nucl. Phys. B 868, 351 (2013) [arXiv:1208.6463 [hep-ph]].

3) B meson Production Asymmetries

Supervisors: Jeroen van Tilburg (Vidi Laureate), Jacco de Vries (PhD)

Research description: At the LHC, B0 mesons and anti-B0 mesons are not produced in equal quantities (about 0.5% more B0 mesons than anti-B0 mesons). This production asymmetry can be measured with semileptonic decays of the type B0 -> D-(*) mu+ nu (and its charge conjugate decay). The goal of this measurement is to measure the asymmetry as function of the transverse momentum and (pseudo)-rapidity of the B0 (or anti-B0). This requires to unfold of the observed kinematic distributions.

4) A search for heavy neutrinos in the decay of W at LHCb

Supervisors: Wouter Hulsbergen (staff), Elena Dall'Occo (PhD) Research description: Neutrinos are arguably the most mysterious of all known fundamental fermions as they are both much lighter than all others and only weakly interacting. It is thought that the tiny mass of neutrinos can be explained by their mixing with so-far unknown, much heavier, neutrino-like particles. In this research proposal we look for these new neutrinos in the decay of the SM W-boson using data with the LHCb experiment at CERN. The W boson is assumed to decay to a heavy neutrino and a muon. The heavy neutrino subsequently decays to a muon and a pair of quarks. Both like-sign and opposite-sign muon pairs will be studied. The result of the analysis will either be a limit on the production of the new neutrinos or the discovery of something entirely new.

5) Quantum Decoherence

Supervisors: Jeroen can Tilburg (Vidi Laureate)

Research description: When two particles are created in an anti-symmetric wave function, the two particles are entangled, even though they may be separated by large distances. If one of the particles is forced into one state (projection), this determines the other state instantaneously. Several theoretical models, motivated by quantum gravity effects, predict the existance of a decoherence parameter. Using decays of phi->K_S K_L, it is possible to measure this decoherence parameter by counting the number of phi decays where both neutral kaons are measured as K_S-> pi+ pi-. If this parameter is measured to be non-zero, it would mean that our current understanding of quantum mechanics is not complete.