Periodic Reporting for period 4 - PRECISION (Precision measurements to discover new scalar and vector particles)
Okres sprawozdawczy: 2021-06-01 do 2022-11-30
The Standard Model of particle physics successfully describes all known particles and their interactions. However,
questions like the nature of dark matter or the hierarchy of masses and couplings of quarks and leptons remain to be
understood. Hence, one searches for new phenomena that will lead to a superior theory that can explain these questions.
All such theories introduce additional quantum corrections. Decay rates of processes which are strongly suppressed in the
Standard Model are highly sensitive to these corrections.
The ERC project PRECISION aims to discover new scalar or vector particles in precision measurements of leptonic and semi-leptonic
beauty decays. These new particles are not predicted by the Standard Model of particle physics, a potential discovery
would mark the most important finding in High Energy Physics of the last decades. Some existing anomalies in flavour data
can be interpreted as hints for the particles searched for in this proposal. Two classes of measurements are planned within
this project: a scan of purely leptonic beauty decays which include flavour changing neutral current as well as
lepton flavour violating modes. Lepton flavour universality is tested in loop decays through a novel inclusive strategy.
Concerning leptonic decays, B-meson decays to two muons, two electron and four muons have been published. These have
advanced the knowledge significantly. On lepton flavour universality, recently the by far most stringent test
of the SM has been published, in agreement to the SM. This last measurement especially marks a breakthrough as
it contradicts earlier evidence for New Physics and hence constitutes a crucial insight.
questions like the nature of dark matter or the hierarchy of masses and couplings of quarks and leptons remain to be
understood. Hence, one searches for new phenomena that will lead to a superior theory that can explain these questions.
All such theories introduce additional quantum corrections. Decay rates of processes which are strongly suppressed in the
Standard Model are highly sensitive to these corrections.
The ERC project PRECISION aims to discover new scalar or vector particles in precision measurements of leptonic and semi-leptonic
beauty decays. These new particles are not predicted by the Standard Model of particle physics, a potential discovery
would mark the most important finding in High Energy Physics of the last decades. Some existing anomalies in flavour data
can be interpreted as hints for the particles searched for in this proposal. Two classes of measurements are planned within
this project: a scan of purely leptonic beauty decays which include flavour changing neutral current as well as
lepton flavour violating modes. Lepton flavour universality is tested in loop decays through a novel inclusive strategy.
Concerning leptonic decays, B-meson decays to two muons, two electron and four muons have been published. These have
advanced the knowledge significantly. On lepton flavour universality, recently the by far most stringent test
of the SM has been published, in agreement to the SM. This last measurement especially marks a breakthrough as
it contradicts earlier evidence for New Physics and hence constitutes a crucial insight.
The project PRECISION has two main work areas: the scan of purely leptonic beauty decays including the search for lepton flavour violation and the test of lepton flavour universality. The team members of the ERC grant PRECISION have made significant contributions to the publication of beauty decays to two muons [Phys. Rev. Lett. 118 (2017) 191801] and have guided LHCb's researchers for a search for B -> e mu [JHEP 03 (2018) 078]. The not so sensitive decays to tau leptons have been published by the LHCb collaboration independently of PRECISION [Phys. Rev. Lett. 118 (2017) 251802]. The researchers of PRECISION have then focussed on a search for Lepton Flavour Violation in B-> Kemu decays, one of the most interesting modes of this kind. The analysis is finished and has been presented by the PRECISION researcher Titus Mombächer on the MIAPP workshop in May 2018 [Phys. Rev. Lett.123 (2019) 241802]. The second focus in this area is the search for purely electronic B decays, the search for B and Bs -> e+e- [Phys. Rev. Lett. 124 (2020) 211802]. This measurement improved the former bounds by more than a factor of 30. Recently, B meson decays to four muons has been searched for [JHEP 03 (2022) 109], no signal was seen. This imposes strong constraints on proposed new light scalar particles. The measurement of B decays to two muons has also been published with the full LHCb dataset [Phys. Rev. Lett. 128, (2022) 041801, Phys. Rev. D105 (2022) 012010], one of the roadmap measurements of LHCb. Concerning lepton flavour universality, the tests have been extended to the baryon sector with Lb -> pK ll decays [JHEP 05 (2020) 040], and recently, the last measurement of the program of PRECISION has been published: an test of lepton flavour uiniversality inclusively measured in several bins of the decays B+ -> K+ ll and B0 -> K*0 ll [arXiv:2212.09152 (submitted to PRL), arXiv:2212.09153 (submitted to PRD)]. Especially this last measurement sparked a lot of interest, as it reduces the tension to teh SM compared to the previously published evidence for New Physics.
The project PRECISION also had another component, the developemnt and implementation of a novel trigger system for the LHCb experiment. The system has been proposed [Computing and Software for Big Science volume 4, Article number: 7 (2020)] and later validated for performance [Computing and Software for Big Science volume 6, Article number: 1 (2022)]. The novel system, with a triggerless readout and a full software trigger implemented in GPU's at the first stage now runs as trigger system of LHCb for Run 3.
The project PRECISION also had another component, the developemnt and implementation of a novel trigger system for the LHCb experiment. The system has been proposed [Computing and Software for Big Science volume 4, Article number: 7 (2020)] and later validated for performance [Computing and Software for Big Science volume 6, Article number: 1 (2022)]. The novel system, with a triggerless readout and a full software trigger implemented in GPU's at the first stage now runs as trigger system of LHCb for Run 3.
The project PRECISION has already produced several world leading results, see above. The worlds knowledge in flavour physics, specially
in the area of indirect tests for New Physics has been advanced dramatically. Additionally to the analyses published, the code-base
developed for the LFU analysis sets a new scale for state-of-the-art analysis code in LHCb and is already been used by several following
analyses.
The documentation of the landmark analyses of B->mumu [Phys. Rev. Lett. 128, (2022) 041801, Phys. Rev. D105 (2022) 012010] and of
lepton flavour universality [arXiv:2212.09152 (submitted to PRL), arXiv:2212.09153 (submitted to PRD)] is extraordinary, with a short letter
summarizing the most visible results and a very detailed description of the methodology and analysis details.
Beyond the physics analyses, the project was an important part in the realization of LHCb's full software trigger - a novelty in HEP
real time event selection that will be followed by many future experiments.
in the area of indirect tests for New Physics has been advanced dramatically. Additionally to the analyses published, the code-base
developed for the LFU analysis sets a new scale for state-of-the-art analysis code in LHCb and is already been used by several following
analyses.
The documentation of the landmark analyses of B->mumu [Phys. Rev. Lett. 128, (2022) 041801, Phys. Rev. D105 (2022) 012010] and of
lepton flavour universality [arXiv:2212.09152 (submitted to PRL), arXiv:2212.09153 (submitted to PRD)] is extraordinary, with a short letter
summarizing the most visible results and a very detailed description of the methodology and analysis details.
Beyond the physics analyses, the project was an important part in the realization of LHCb's full software trigger - a novelty in HEP
real time event selection that will be followed by many future experiments.