arXiv subjects

Martin Schürmann

Publications and source records attributed to Martin Schürmann.

5 recordsLinked to original sources

arXiv2026

The ABC of RPV III: Classification of R-parity Violating Signatures from LQD Couplings and their Coverage at the LHC

We consider the R-parity violating Minimal Supersymmetric Standard Model (RPV-MSSM) with its wide range of signatures as a test model for the coverage of beyond the Standard Model searches at the LHC. Here we present a systematic study of the phenomenological and experimental status of specifically the R-parity violating $LQ\bar D$ operators, as the third study in the ABC of RPV series, following our previous analyses of the $LL\bar E$ and $\bar U\bar D\bar D$ operators. We classify the distinct collider signatures for all possible LSPs and for eight representative $LQ\bar D$ couplings, considering both direct LSP production and production through gauge cascades. Assuming one non-zero $LQ\bar D$ coupling at a time, we assess the current LHC coverage using ATLAS and CMS searches implemented in $\texttt{CheckMATE 2}$, and identify recent searches relevant for future recasting. We find substantial sensitivity to the colored sector, while gaps remain for wino- and higgsino-like LSPs for couplings involving $τ$ leptons, when the LSP is the only sparticle within the LHC kinematic limit. Slepton LSPs remain unconstrained in their direct production at the LHC, although some sensitivity is found for slepton NLSPs with a bino-like LSP. These results highlight gaps in the $\texttt{CheckMATE 2}$ search database, as well as the need for targeted LHC searches for specific $LQ\bar D$ signatures.

hep-ph↗

arXiv2026

Theory Calculations for LDMX and LOHENGRIN beyond Coherent Bethe-Heitler Scattering

The Light Dark Matter eXperiment (LDMX), DarkSHINE, and LOHENGRIN are proposed new experiments. They aim to search for missing momentum signals sourced by the direct production of dark photons with masses in the MeV-GeV range in bremsstrahlung processes, in which an electron beam of a few GeV scatters off a fixed target. So far, the signal characteristics, i.e. the behavior of the recoiling electron, have mostly been studied in coherent Bethe-Heitler electron-nucleus scattering with a dark photon that couples only to the Standard Model charged leptons. In this work, we present the calculations of the differential cross sections of all contributing real emission processes up to third order in the electromagnetic fine structure constant and fourth order in the kinetic mixing parameter associated with the dark photon. We consider a dark photon coupling to both the beam electron and the hadronic target and we take into account the scattering off both the target nucleus and its nuclear constituents. Besides real emission processes, we also discuss virtual dark photon contributions and their relevance for the signal prediction. After discussing the different phase space regions and constraints emerging from the experimental setups, we show numerical results of the cross sections and differential distributions, including the signal and dominant background. Within our framework, we find that the LOHENGRIN experiment will require an extension of its HCAL to effectively veto background processes originating from diffractive scattering. Apart from that, the contributions beyond coherent Bethe-Heitler scattering, in the presence of realistic experimental selections, have only a limited effect on the predicted signal and background in the relevant dark photon mass range.

hep-ph↗

arXiv2025

The ABC of RPV II: Classification of R-parity Violating Signatures from UDD Couplings and their Coverage at the LHC

We perform a detailed study of the current phenomenological status of baryon number violating operators within the framework of the $R$-parity violating Minimal Supersymmetric Standard Model (RPV-MSSM). This study aims to identify any gaps in the experimental coverage of the RPV landscape. We identify the unique final states for all possible LSPs decaying via four different benchmark UDD operators. Both the direct production of the LSP and its production via gauge-cascades are considered. For each LSP, we assume that only one UDD coupling is non-zero at a time and confront the signals with existing ATLAS and CMS searches implemented in the recasting framework \texttt{CheckMATE\;2}. We find that the UDD colored LSP sector is well covered with the mass bounds on the gluino LSP being the strongest, and with possible improvements for some of the right-handed squark LSPs. We also point out that there is limited coverage for electroweakino and slepton LSPs with UDD decays. This limitation may be due to the lack of targeted experimental searches for these specific final states or the appropriate recasting of existing searches.

hep-ph↗

arXiv2025

A Proposal for the Lohengrin Experiment to Search for Dark Sector Particles at the ELSA Accelerator

We present a proposal for a future light dark matter search experiment at the Electron Stretcher Accelerator ELSA in Bonn: Lohengrin. It employs the fixed-target missing momentum based technique for searching for dark-sector particles. The Lohengrin experiment uses a high intensity electron beam that is shot onto a thin target to produce mainly SM bremsstrahlung and - in rare occasions - possibly new particles coupling feebly to the electron. A well motivated candidate for such a new particle is the dark photon, a new massive gauge boson arising from a new gauge interaction in a dark sector and mixing kinetically with the standard model photon. The Lohengrin experiment is estimated to reach sensitivity to couplings small enough to explain the relic abundance of dark matter in various models for dark photon masses between approximately 1 MeV and approximately 100 MeV.

hep-ex↗

arXiv2023

Recasting Bounds on Long-lived Heavy Neutral Leptons in Terms of a Light Supersymmetric R-parity Violating Neutralino

In R-parity-violating (RPV) supersymmetric models, light neutralinos with masses from the GeV-scale down to even zero are still allowed by all laboratory constraints. They are further consistent with dark matter observations, as they decay via RPV couplings. These RPV couplings are in general constrained to be small. Hence, such light neutralinos, if produced, e.g., at a beam-dump or collider experiment, appear as displaced vertices or missing energy at the detector level. The same signatures have been extensively searched for at various experiments in the theoretical context of sterile neutrinos which mix with active neutrinos. In this work, we recast the sensitivity of both past and present experiments to sterile neutrinos to obtain new bounds on RPV couplings associated with a light neutralino. We find experiments such as T2K, BEBC, FASER, DUNE, and MoEDAL-MAPP can improve the current bounds on RPV couplings by up to $3-4$ orders of magnitude in several benchmark scenarios.

hep-ph↗