arXiv subjects

Michal Kreps

Publications and source records attributed to Michal Kreps.

18 recordsLinked to original sources

arXiv2025

Constraints on new physics from decays of polarized $\Lambda_b^0$ baryons at the FCC-ee

The $Z^0$ bosons produced in electron-positron collisions at the potential Future Circular Collider (FCC-ee) provide unique opportunities for flavour physics. The non-zero polarization of \Lb baryons produced in $Z^0$ decays enables access to a much larger set of observables than at the LHC, where the $\Lambda_b^0$ baryons are produced unpolarized. This paper presents a toy angular analysis of $\Lambda_b^0\to \Lambda(\to p\pi^-)\mu^+\mu^-$ decays using simulation samples of collisions at the FCC-ee reconstructed using the IDEA detector concept and assuming a dataset of $6\times 10^{12}$ $Z^0$ bosons. While the statistical sensitivity achieved for individual angular observables is not expected to significantly exceed that from the LHCb Upgrade II experiment, the addition of the polarized observables leads to a significant improvement of the knowledge on the Wilson coefficients $C_{9^{(\prime)}}$ and $C_{10^{(\prime)}}$.

hep-ex↗

arXiv2025

Kaon Physics: A Cornerstone for Future Discoveries

The kaon physics programme, long heralded as a cutting-edge frontier by the European Strategy for Particle Physics, continues to stand at the intersection of discovery and innovation in high-energy physics (HEP). With its unparalleled capacity to explore new physics at the multi-TeV scale, kaon research is poised to unveil phenomena that could reshape our understanding of the Universe. This document highlights the compelling physics case, with emphasis on exciting new opportunities for advancing kaon physics not only in Europe but also on a global stage. As an important player in the future of HEP, the kaon programme promises to drive transformative breakthroughs, inviting exploration at the forefront of scientific discovery.

hep-ph↗

arXiv2025

Proposal of the KOTO II experiment

The KOTO II experiment is proposed to measure the branching ratio of the decay $K_L\toπ^0ν\barν$ at J-PARC. With a beamline to extract long-lived neutral kaons at 5 degrees from a production target, the single event sensitivity of the decay is $8.5\times 10^{-13}$, which is much smaller than the Standard Model prediction $3\times 10^{-11}$. This allows searches for new physics beyond the Standard Model and the first discovery of the decay with a significance exceeding $5σ$. As the only experiment proposed in the world dedicated to rare kaon decays, KOTO II will be indispensable in the quest for a complete understanding of flavor dynamics in the quark sector. Moreover, by combining efforts from the kaon community worldwide, we plan to develop the KOTO II detector further and expand the physics reach of the experiment to include measurements of the branching ratio of the $K_L\toπ^0\ell^+\ell^-$ decays, studies of other $K_L$ decays, and searches for dark photons, axions, and axion-like particles. KOTO II will therefore obtain a comprehensive understanding of $K_L$ decays, providing further constraints on new physics scenarios with existing $K^+$ results.

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arXiv2023

Performance of a prototype TORCH time-of-flight detector

TORCH is a novel time-of-flight detector, designed to provide charged particle identification of pions, kaons and protons in the momentum range 2-20 GeV/c over a 9.5 m flight path. A detector module, comprising a 10mm thick quartz plate, provides a source of Cherenkov photons which propagate via total internal reflection to one end of the plate. Here, the photons are focused onto an array of custom-designed Micro-Channel Plate Photo-Multiplier Tubes (MCP-PMTs) which measure their positions and arrival times. The target time resolution per photon is 70 ps which, for 30 detected photons per charged particle, results in a 10-15 ps time-of-flight resolution. A 1.25 m length TORCH prototype module employing two MCP-PMTs has been developed, and tested at the CERN PS using a charged hadron beam of 8 GeV/c momentum. The construction of the module, the properties of the MCP-PMTs and the readout electronics are described. Measurements of the collected photon yields and single-photon time resolutions have been performed as a function of particle entry points on the plate and compared to expectations. These studies show that the performance of the TORCH prototype approaches the design goals for the full-scale detector.

physics.ins-det↗

arXiv2023

Angular distribution of $Λ_b^0\to pK^-\ell^+\ell^-$ decays comprising $Λ$ resonances with spin up to $\leq5/2$

This paper describes the angular distribution of $Λ_b^0\to Λ(\to pK^-)\ell^+\ell^-$ decays. A full expression is given for the case of multiple interfering spin-states with spin $\leq \tfrac{5}{2}$. This distribution is relevant for future measurements of $Λ_b^0\to pK^-\ell^+\ell^-$ decays, where different states cannot easily be separated based on their mass alone. New observables arise when considering spin-$\tfrac{5}{2}$ states as well as interference between states. An exploration of their behaviour for a variety of beyond the Standard Model scenarios shows that some of these observables exhibit interesting sensitivity to the Wilson coefficients involved in $b\to s\ell^+\ell^-$ transitions. Others are insensitive to the Wilson coefficients and can be used to verify the description of $Λ_b^0\to Λ$ form-factors. A basis of weighting functions that can be used to determine all of the angular observables described in this paper in a moment analysis of the experimental data is also provided.

hep-ph↗

arXiv2022

Picosecond timing of charged particles using the TORCH detector

TORCH is a large-area, high-precision time-of-flight (ToF) detector designed to provide charged-particle identification in the 2-20 GeV$/c$ momentum range. Prompt Cherenkov photons emitted by charged hadrons as they traverse a 10mm quartz radiator are propagated to the periphery of the detector, where they are focused onto an array of micro-channel plate photomultiplier tubes (MCP-PMTs). The position and arrival times of the photons are used to infer the particles' time of entry in the radiator, to identify hadrons based on their ToF. The MCP-PMTs were developed with an industrial partner to satisfy the stringent requirements of the TORCH detector. The requirements include a finely segmented anode, excellent time resolution, and a long lifetime. Over an approximately 10m flight distance, the difference in ToF between a kaon and a pion with 10GeV$/c$ momentum is 35ps, leading to a 10-15ps per track timing resolution requirement. On average 30 photons per hadron are detected, which translates to a single-photon time resolution of 70ps. The TORCH research and development program aims to demonstrate the validity of the detector concept through laboratory and beam tests, results from which are presented. A timing resolution of 70-100ps was reached in beam tests, approaching the TORCH design goal. Laboratory timing tests consist of operating the MCP-PMTs coupled to the TORCH readout electronics. A time resolution of about 50ps was measured, meeting the TORCH target timing resolution.

physics.ins-det↗

arXiv2021

HL-LHC Computing Review Stage-2, Common Software Projects: Event Generators

This paper has been prepared by the HEP Software Foundation (HSF) Physics Event Generator Working Group (WG), as an input to the second phase of the LHCC review of High-Luminosity LHC (HL-LHC) computing, which is due to take place in November 2021. It complements previous documents prepared by the WG in the context of the first phase of the LHCC review in 2020, including in particular the WG paper on the specific challenges in Monte Carlo event generator software for HL-LHC, which has since been updated and published, and which we are also submitting to the November 2021 review as an integral part of our contribution.

hep-ph↗

arXiv2017

Angular distribution of polarised $Λ_b$ baryons decaying to $Λ\ell^+\ell^-$

Rare $b \to s\ell^+\ell^-$ flavour-changing-neutral-current processes provide important tests of the Standard Model of particle physics. Angular observables in exclusive $b \to s\ell^+\ell^-$ processes can be particularly powerful as they allow hadronic uncertainties to be controlled. Amongst the exclusive processes that have been studied by experiments, the decay $Λ_b\to Λ\ell^+\ell^-$ is unique in that the $Λ_b$ baryon can be produced polarised. In this paper, we derive an expression for the angular distribution of the $Λ_b\to Λ\ell^+\ell^-$ decay for the case where the $Λ_b$ baryon is produced polarised. This extends the number of angular observables in this decay from 10 to 34. Standard Model expectations for the new observables are provided and the sensitivity of the observables is explored under a variety of new physics models. At low-hadronic recoil, four of the new observables have a new short distance dependence that is absent in the unpolarised case. The remaining observables depend on the same short distance contributions as the unpolarised observables, but with different dependence on hadronic form-factors. These relations provide possibilities for novel tests of the SM that could be carried out with the data that will become available at the LHC or a future $e^+e^-$ collider.

hep-ph↗

arXiv2011

A Hierarchical NeuroBayes-based Algorithm for Full Reconstruction of B Mesons at B Factories

We describe a new B-meson full reconstruction algorithm designed for the Belle experiment at the B-factory KEKB, an asymmetric e+e- collider that collected a data sample of 771.6 x 10^6 BBbar pairs during its running time. To maximize the number of reconstructed B decay channels, it utilizes a hierarchical reconstruction procedure and probabilistic calculus instead of classical selection cuts. The multivariate analysis package NeuroBayes was used extensively to hold the balance between highest possible efficiency, robustness and acceptable consumption of CPU time. In total, 1104 exclusive decay channels were reconstructed, employing 71 neural networks altogether. Overall, we correctly reconstruct one B+/- or B0 candidate in 0.28% or 0.18% of the BBbar events, respectively. Compared to the cut-based classical reconstruction algorithm used at the Belle experiment, this is an improvement in efficiency by roughly a factor of 2, depending on the analysis considered. The new framework also features the ability to choose the desired purity or efficiency of the fully reconstructed sample freely. If the same purity as for the classical full reconstruction code is desired ~25%, the efficiency is still larger by nearly a factor of 2. If, on the other hand, the efficiency is chosen at a similar level as the classical full reconstruction, the purity rises from ~25% to nearly 90%.

hep-ex↗

arXiv2011

Measurement of CP violation in Bs --> J/psi phi decay

We briefly discuss measurements of CP violation in Bs --> J/psi phi decay. Both the phenomenology of Bs mixing and the importance of the measurement to searches for new physics, as well as technical details and issues with the analysis are included. While current results are consistent with the standard model, even large contributions from new physics cannot be excluded.

hep-ex↗

arXiv2011

Summary of WG4: "Lifetime, mixing and weak mixing phase in charm and beauty, including direct determination of V_{tx}

We present the summary of the Working Group on lifetimes, mixing and weak mixing phases in charm and beauty mesons at the CKM 2010 workshop. In the past year or so good progress was achieved on both experimental and theoretical sides. While this yields improvement in our understanding of neutral meson mixing, further work is necessary to achieve the highest possible precision in order to investigate current hints for deviations between experiment and standard model predictions. With the recent LHC startup we see bright prospects for the near term future for huge improvements.

hep-ph↗

arXiv2010

Measurement of B_s mixing phase at CDF

We present improved bounds on the CP-violating phase β_s^{\Jpsiϕ} and on the decay-width difference ΔΓof the neutral B_s^0 meson system obtained by the CDF experiment at the Tevatron collider . We use 6500 B_s^0 --> J/psi phi decays collected by the dimuon trigger and reconstructed in a sample corresponding to integrated luminosity of 5.2 fb-1. Besides exploiting a two-fold increase in statistics with respect to the previous measurement, several improvements have been introduced in the analysis including a fully data-driven flavour-tagging calibration and proper treatment of possible S-wave contributions.

hep-ex↗

arXiv2010

B Physics (Experiment)

In past few years the flavor physics made important transition from the work on confirmation the standard model of particle physics to the phase of search for effects of a new physics beyond standard model. In this paper we review current state of the physics of b-hadrons with emphasis on results with a sensitivity to new physics.

hep-ex↗

arXiv2009

Tevatron Experimental Issues at High Luminosities

In this paper we describe the detector components, triggers and analysis techniques for flavor physics at the Tevatron experiments CDF and DO. As Tevatron performs very well and runs at higher luminosities regularly we also touch issues related to it and efforts to improve detectors and triggers for such running.

hep-ex↗

arXiv2009

Charmonium Spectroscopy (X,Y,Z) at the B Factories

Since 2003 several states in the charmonium mass region were discovered. While in the conventional c c-bar spectrum some states are missing, the number of states observed up to now is larger than empty spaces in the c c-bar spectrum. This, together with other difficulties to explain observed states as a c c-bar mesons triggered discussions on a possible exotic interpretations. In this proceedings we present current experimental status from B-factories of the so called X, Y and Z states.

hep-ex↗

arXiv2007

D and B meson spectroscopy, new states, baryons at the Tevatron

We review recent results in heavy quark hadron spectroscopy at the Tevatron. With increasing data samples the Tevatron experiments start to uncover information on the b-hadrons. Most important are the first observations of the narrow Bs** as well as Sigma_b, Sigma_b* and Xi_b- baryons. In addition we present updated results on the narrow B** and Bc mesons.

hep-ex↗

arXiv2007

Branching Fractions and Direct CP Asymmetries of Charmless B Decay Modes at CDF

We present new CDF results on the branching fractions and time-integrated direct CP asymmetries for $B^0$ and $B^0_s$ decay modes into pairs of charmless charged hadrons (pions or kaons). The data-set for this update amounts to 1 $\mathrm{fb}^{-1}$ of $p\bar p$ collisions at a center of mass energy 1.96 $\mathrm{TeV}$. We report the first observation of the $B_s \to K^- π^+$ mode and a measurement of its branching fraction and direct CP asymmetry. We also observe for the first time two charmless decays of the $Λ_b^0$-baryon: $Λ_b^0 \to pπ^-$ and $Λ_b^0 \to pK^-$.

hep-ex↗

arXiv2007

New Heavy Quark Baryons

During the past year many interesting results were published in heavy quark baryon spectroscopy. In addition to several refined measurements, new states were directly observed both in the charm and the bottom sector. In this paper we review recent results on heavy quark baryons from B-factories and Tevatron experiments.

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