Studies on $R_K$ with Large Dilepton Invariant-Mass, $\\$ Scalable Pythonic Fitting,$\\$ and Online Event Interpretation with GNNs at LHCb

Eschle, Jonas

doi:10.5167/uzh-257886

Studies on $R_K$ with Large Dilepton Invariant-Mass, $\\$ Scalable Pythonic Fitting, $\\$ and Online Event Interpretation with GNNs at LHCb

Jonas Eschle
(
- Zurich U.
)

Jan 24, 2024

269 pages

Supervisors:

Thesis: PhD

Zurich U.

(defense: 2024)

Published: Mar 1, 2024
and
Published: Jan 24, 2024

e-Print:

2402.12622 [hep-ex]

DOI:

10.5167/uzh-257886

Report number:

CERN-THESIS-2024-036,
arXiv:2402.12622

View in:

reference search0 citations

Citations per year

0 Citations

Abstract: (Zurich U.)

The Standard Model of particle physics is the established theory describing nature's phenomena involving the most fundamental particles. However, the model has inherent shortcomings, and recent measurements indicate tensions with its predictions, suggesting the existence of a more fundamental theory. Experimental particle physics aims to test the Standard Model predictions with increasing precision in order to constrain or confirm physics beyond the Standard Model.A large part of this thesis is dedicated to the first measurement of the ratio of branching fractions of the decays

B^+ \rightarrow K^+ \mu^+ \mu^-

and

B^+ \rightarrow K^+ e^+ e^-

, referred to as

R_K

, in the high dilepton invariant mass region. The presented analysis uses the full dataset of proton-proton collisions collected by the LHCb experiment in the years 2011-2018, corresponding to an integrated luminosity of 9~

\mathrm{fb}^{-1}

. The final result for

R_K

is still blinded.The sensitivity of the developed analysis is estimated to be

\sigma^{(\mathrm{stat})}_{R_K} = 0.073

and

\sigma^{(\mathrm{syst})}_{R_K} = 0.031

. Applying all analysis steps to a control channel, where the value of

R_K

is known, successfully recovers the correct value.In addition to the precision measurement of

R_K

at a high dilepton invariant mass, this thesis contains two more technical topics. First, an algorithm that selects particles in an event in the LHCb detector by performing a full event interpretation, referred to as \textsc{DFEI}. This tool is based on multiple Graph Neural Networks and aims to cope with the increase in luminosity in current and future upgrades of the LHCb detector. Comparisons with the current approach show at least similar, sometimes better, performance with respect to decay reconstruction and selection using charged particles. The efficiency is mostly independent of the luminosity, which is crucial for future upgrades.Second, a \textsc{Python} package for likelihood model fitting called \textsc{zfit}. The increasing popularity of the \textsc{Python} programming language in High Energy Physics creates a need for a flexible, modular, and performant fitting library. The \textsc{zfit} package is well integrated into the \textsc{Python} ecosystem, highly customizable and fast thanks to its computational backend \textsc{TensorFlow}.

Note:

PhD thesis, 269 pages, 130 figures, contains parts of arxiv:1910.13429 and arxiv:2304.08610, future publication on RK coming

p p: colliding beams
branching ratio: ratio
LHC-B: upgrade
p p: scattering
B+: semileptonic decay
electron: pair production
muon: pair production
dilepton: mass spectrum
mass spectrum: (electron positron)
mass spectrum: (muon+ muon-)

References(142)

Figures(0)

[1]

Nasfarley88

MissMJ

[2]

Yvette Kosmann-Schwarzbach. The Noether theorems. Invariance and conservation laws in the twentieth century. Transl. from the French

by Bertram E.

•
DOI:
- 10.1007/978-0-387-87868-3

[3]

Introduction to elementary particles

David J. Griffiths

[4]

QUARKS AND LEPTONS: AN INTRODUCTORY COURSE IN MODERN PARTICLE PHYSICS

[5]

An Introduction to Quantum Field Theory. 1st. Westview Press,. isbn: 978-0-201-50397-5

Michael E. Peskin
,
Daniel V. Schroeder

[6]

Michela D’Onofrio and Kari Rummukainen. Standard model cross-over on the lattice. Phys

Rev. D

[6]

Standard model cross-over on the lattice

Michela D'Onofrio
(
- U. Bern, AEC and
- Helsinki Inst. of Phys. and
- Helsinki U.
)
,
Kari Rummukainen
(
- Helsinki U. and
- Helsinki Inst. of Phys.
)

- Phys.Rev.D 93 (2016) 2, 025003
•
e-Print:
- 1508.07161
•
DOI:
- 10.1103/PhysRevD.93.025003

[7]

Review of Particle Physics

R.L. Workman
(
- George Washington U.
)
,
V.D. Burkert
(
- Jefferson Lab
)
,
V. Crede
(
- Florida State U.
)
,
E. Klempt
(
- Bonn U., HISKP
)
,
U. Thoma
(
- Bonn U., HISKP
)

et al.

- PTEP 2022 (2022) 083C01
•
DOI:
- 10.1093/ptep/ptac097

[8]

2 (7 Oct.), pp. 1285-1292

S.L. Glashow
,
J. Iliopoulos
,
L. Maiani

[8]

Weak Interactions with Lepton-Hadron Symmetry

- Phys.Rev.D 2 (1970) 1285-1292,
- Also in *Lai, C. H. (ed.): Gauge Theory Of Weak and Electromagnetic Interactions*, 203-210,
- In *Rosner, J.L. (ed.): New Particles*, 18-25,
- In *Lichtenberg, D. B. (Ed.), Rosen, S. P. (Ed.): Developments In The Quark Theory Of Hadrons, Vol. 1*, 193-200.,
- In *Bologna 1984, Proceedings, Fifty Years of Weak-Interaction Physics* 687-694
•
DOI:
- 10.1103/PhysRevD.2.1285

[9]

Yasaman Farzan and Mariam Tórtola. Neutrino Oscillations and Non-standard Interactions. Frontiers in Physics 6 . issn: 2296-424x

[9]

00010

•
DOI:
- 10.3389/fphy

[10]

Neutrino oscillations: The rise of the PMNS paradigm

Claudio Giganti
(
- Paris U., VI-VII
)
,
Stéphane Lavignac
(
- IPhT, Saclay
)
,
Marco Zito
(
- IRFU, Saclay
)

- Prog.Part.Nucl.Phys. 98 (2018) 1-54
•
e-Print:
- 1710.00715
•
DOI:
- 10.1016/j.ppnp.2017.10.001

[11]

Planck 2018 results. VI. Cosmological parameters

Planck

Collaboration

•

N. Aghanim
(
- Orsay, IAS
)

et al.

- Astron.Astrophys. 641 (2020) A6,
- Astron.Astrophys. 652 (2021) C4 (erratum)
•
e-Print:
- 1807.06209
•
DOI:
- 10.1051/0004-6361/201833910

[11]

Planck 2018 results. VI. Cosmological parameters

Planck

Collaboration

•

N. Aghanim
(
- Orsay, IAS
)

et al.

- Astron.Astrophys. 641 (2020) A6,
- Astron.Astrophys. 652 (2021) C4 (erratum)
•
e-Print:
- 1807.06209
•
DOI:
- 10.1051/0004-6361/201833910

[12]

Violation of CP Invariance, C asymmetry, and baryon asymmetry of the universe

A.D. Sakharov
(
- Lebedev Inst.
)

- Pisma Zh.Eksp.Teor.Fiz. 5 (1967) 32-35,
- JETP Lett. 5 (1967) 24-27,
- Sov.Phys.Usp. 34 (1991) 5, 392-393,
- Usp.Fiz.Nauk 161 (1991) 5, 61-64
•
DOI:
- 10.1070/PU1991v034n05ABEH002497

[13]

Evidence for the $2\pi$ Decay of the $K_2^0$ Meson

- Phys.Rev.Lett. 13 (1964) 138-140,
- Also in *Wolfenstein, L. (ed.): CP violation* 14-16. (see Book Index),
- In *Lichtenberg, D. B. (Ed.), Rosen, S. P. (Ed.): Developments In The Quark Theory Of Hadrons, Vol. 1*, 224-226.
•
DOI:
- 10.1103/PhysRevLett.13.138

[13]

Evidence for the $2\pi$ Decay of the $K_2^0$ Meson

- Phys.Rev.Lett. 13 (1964) 138-140,
- Also in *Wolfenstein, L. (ed.): CP violation* 14-16. (see Book Index),
- In *Lichtenberg, D. B. (Ed.), Rosen, S. P. (Ed.): Developments In The Quark Theory Of Hadrons, Vol. 1*, 224-226.
•
DOI:
- 10.1103/PhysRevLett.13.138