arXiv subjects

Herbert K. Dreiner

Publications and source records attributed to Herbert K. Dreiner.

18 recordsLinked to original sources

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 decay $B\to K+ν+\barν$ at Belle II and a massless bino in R-parity-violating supersymmetry

Recently, \texttt{Belle II} announced evidence for the decay $B^+\to K^+ +ν+\barν$ at the $3.5\,σ$ significance, and measured the corresponding decay branching ratio to be $2.7\,σ$ above the Standard Model prediction. Here, we provide a theoretical explanation based on a massless bino in R-parity-violating (RPV) supersymmetry. With a single non-vanishing RPV coupling $λ'_{i23/i32}$, $λ'_{i13/i33}$, or $λ'_{i12/i22}$, where $i=1,2,3$, the decay $B^+\to K^+ +\overset{\scriptscriptstyle(-)}{ν_i}+ \tildeχ^0_1$ can be induced, which would lead to the same signature as $B^+\to K^+ +ν+\barν$. Taking into account both theoretical and experimental uncertainties, we derive the regions of the parameter space spanned by the RPV couplings and sfermion masses that could accommodate the new measurement at various significance levels and obey the existing bounds simultaneously.

hep-ph↗

arXiv2021

R-parity Violation and Light Neutralinos at ANUBIS and MAPP

In R-parity-violating supersymmetry the lightest neutralino can be very light, even massless. For masses in the range $500$ MeV$\lesssim m_{\tildeχ^0_1}\lesssim 4.5$ GeV the neutralino can be produced in hadron collisions from rare meson decays via an R-parity violating coupling, and subsequently decay to a lighter meson and a charged lepton. Due to the small neutralino mass and for small R-parity violating coupling the lightest neutralino is long-lived, leading to displaced vertices at fixed-target and collider experiments. In this work, we study such signatures at the proposed experiments ANUBIS and MAPP at the LHC. We also compare their sensitivity reach in these scenarios with that of other present and proposed experiments at the LHC such as ATLAS, CODEX-b, and MATHUSLA. We find that ANUBIS and MAPP can show complementary or superior sensitivity.

hep-ph↗

arXiv2021

Long-lived Sterile Neutrinos at the LHC in Effective Field Theory

We study the prospects of a displaced-vertex search of sterile neutrinos at the Large Hadron Collider (LHC) in the framework of the neutrino-extended Standard Model Effective Field Theory ($ν$SMEFT). The production and decay of sterile neutrinos can proceed via the standard active-sterile neutrino mixing in the weak current, as well as through higher-dimensional operators arising from decoupled new physics. If sterile neutrinos are long-lived, their decay can lead to displaced vertices which can be reconstructed. We investigate the search sensitivities for the ATLAS/CMS detector, the future far-detector experiments: AL3X, ANUBIS, CODEX-b, FASER, MATHUSLA, and MoEDAL-MAPP, and at the proposed fixed-target experiment SHiP. We study scenarios where sterile neutrinos are predominantly produced via rare charm and bottom mesons decays through minimal mixing and/or dimension-six operators in the $ν$SMEFT Lagrangian. We perform simulations to determine the potential reach of high-luminosity LHC experiments in probing the EFT operators, finding that these experiments are very competitive with other searches.

hep-ph↗

arXiv2020

Nucleon decay in the R-parity violating MSSM

We present a reanalysis of nucleon decay in the context of the R-parity violating MSSM, updating bounds on R-parity violating parameters against recent experimental and lattice results. We pay particular attention to the derivation of these constraints and specifically to the hadronic matrix elements, which usually stand as the limiting factor in order to derive reliable bounds, except for these few channels that have been studied on the lattice.

hep-ph↗

arXiv2020

R-Parity Violation and Direct Stau Pair Production at the LHC

We consider pair production of LSP staus at the LHC within R-parity violating supersymmetry. The staus decay into Standard Model leptons through the LLĒ operator. Using CheckMATE we have recast multileptonic searches to test such scenarios. We show for the first time that using these analyses the stau mass can be constrained up to 345 GeV, depending on the stau decay mode, as well as the stau mixing angle. However, there is for all scenarios a significant gap between the lower LEP limit on the stau mass and the onset of the LHC sensitivity. This approach can be used in the future to constrain the stau sector in the context of RPV lepton-number violating models.

hep-ph↗

arXiv2019

Updating Bounds on $R$-Parity Violating Supersymmetry from Meson Oscillation Data

We update the bounds on $R$-parity violating supersymmetry originating from meson oscillations in the $B^0_{d/s}$ and $K^0$ systems. To this end, we explicitly calculate all corresponding contributions from $R$-parity violating operators at the one-loop level, thereby completing and correcting existing calculations. We apply our results to the derivation of bounds on $R$-parity violating couplings, based on up-to-date experimental measurements. In addition, we consider the possibility of cancellations among flavor-changing contributions of various origins, e.g. from multiple $R$-parity violating couplings or $R$-parity conserving soft terms. Destructive interferences among new-physics contributions could then open phenomenologically allowed regions, for values of the parameters that are naively excluded when the parameters are varied individually.

hep-ph↗

arXiv2018

Long-Lived Fermions at AL3X

Recently Gligorov $\textit{et al.}$ [arXiv:1810.03636] proposed to build a cylindrical detector named '$\texttt{AL3X}$' close to the $\texttt{ALICE}$ experiment at interaction point (IP) 2 of the LHC, aiming for discovery of long-lived particles (LLPs) during Run 5 of the HL-LHC. We investigate the potential sensitivity reach of this detector in the parameter space of different new-physics models with long-lived fermions namely heavy neutral leptons (HNLs) and light supersymmetric neutralinos, which have both not previously been studied in this context. Our results show that the $\texttt{AL3X}$ reach can be complementary or superior to that of other proposed detectors such as $\texttt{CODEX-b}$, $\texttt{FASER}$, $\texttt{MATHUSLA}$ and $\texttt{SHiP}$.

hep-ph↗

arXiv2014

How alive is constrained SUSY really?

Constrained supersymmetric models like the CMSSM might look less attractive nowadays because of fine tuning arguments. They also might look less probable in terms of Bayesian statistics. The question how well the model under study describes the data, however, is answered by frequentist p-values. Thus, for the first time, we calculate a p-value for a supersymmetric model by performing dedicated global toy fits. We combine constraints from low-energy and astrophysical observables, Higgs boson mass and rate measurements as well as the non-observation of new physics in searches for supersymmetry at the LHC. Using the framework Fittino, we perform global fits of the CMSSM to the toy data and find that this model is excluded at more than 95% confidence level.

hep-ph↗

arXiv2013

Supernova Constraints on MeV Dark Sectors from e+ e- Annihilations

Theories with dark forces and dark sectors are of interest for dark matter models. In this paper we find the region in parameter space that is constrained by supernova cooling constraints when the models include dark sector particles with masses around 100 MeV or less. We include only interactions with electrons and positrons. The constraint is important for small mixing parameters.

hep-ph↗

arXiv2013

Constrained Supersymmetry after the Higgs Boson Discovery: A global analysis with Fittino

We present preliminary results from the latest global fit analysis of the constrained minimal supersymmetric standard model (CMSSM) performed within the Fittino framework. The fit includes low-energy and astrophysical observables as well as collider constraints from the non-observation of new physics in supersymmetric searches at the LHC. Furthermore, the Higgs boson mass and signal rate measurements from both the LHC and Tevatron experiments are included via the program HiggsSignals. Although the LHC exclusion limits and the Higgs mass measurements put tight constraints on the viable parameter space, we find an acceptable fit quality once the Higgs signal rates are included.

hep-ph↗

arXiv2013

White Dwarfs constrain Dark Forces

The white dwarf luminosity function, which provides information about their cooling, has been measured with high precision in the past few years. Simulations that include well known Standard Model physics give a good fit to the data. This leaves little room for new physics and makes these astrophysical objects a good laboratory for testing models beyond the Standard Model. It has already been suggested that white dwarfs might provide some evidence for the existence of axions. In this work we study the constraints that the white dwarf luminosity function puts on physics beyond the Standard Model involving new light particles (fermions or bosons) that can be pair-produced in a white dwarf and then escape to contribute to its cooling. We show, in particular, that we can severely constrain the parameter space of models with dark forces and light hidden sectors (lighter than a few tens of keV). The bounds we find are often more competitive than those from current lab searches and those expected from most future searches.

hep-ph↗

arXiv2011

Measuring a Light Neutralino Mass at the ILC: Testing the MSSM Neutralino Cold Dark Matter Model

The LEP experiments give a lower bound on the neutralino mass of about 46 GeV which, however, relies on a supersymmetric grand unification relation. Dropping this assumption, the experimental lower bound on the neutralino mass vanishes completely. Recent analyses suggest, however, that in the minimal supersymmetric standard model (MSSM), a light neutralino dark matter candidate has a lower bound on its mass of about 7 GeV. In light of this, we investigate the mass sensitivity at the ILC for very light neutralinos. We study slepton pair production, followed by the decay of the sleptons to a lepton and the lightest neutralino. We find that the mass measurement accuracy for a few-GeV neutralino is around 2 GeV, or even less if the relevant slepton is sufficiently light. We thus conclude that the ILC can help verify or falsify the MSSM neutralino cold dark matter model even for very light neutralinos.

hep-ph↗

arXiv2009

Rapidity Gap Events for Squark Pair Production at the LHC

hep-ph↗

arXiv2009

Rapidity Gap Events in Squark Pair Production at the LHC

The exchange of electroweak gauginos in the $t-$ or $u-$channel allows squark pair production at hadron colliders without color exchange between the squarks. This can give rise to events where little or no energy is deposited in the detector between the squark decay products. We discuss the potential for detection of such rapidity gap events at the Large Hadron Collider (LHC). Our numerical analysis is divided into two parts. First, we evaluate in a simplified framework the rapidity gap signal at the parton level. The second part covers an analysis with full event simulation using PYTHIA as well as Herwig++, but without detector simulation. We analyze the transverse energy deposited between the jets from squark decay, as well as the probability of finding a third jet in between the two hardest jets. For the mSUGRA benchmark point SPS1a we find statistically significant evidence for a color singlet exchange contribution. The systematical differences between current versions of PYTHIA and HERWIG++ are larger than the physical effect from color singlet exchange; however, these systematic differences could be reduced by tuning both Monte Carlo generators on normal QCD di--jet data.

hep-ph↗

arXiv2007

The Role of Beam polarization for Radiative Neutralino Production at the ILC

We analyze the impact of electron and positron beam polarization on radiative neutralino production at the International Linear Collider (ILC). We focus on three different mSUGRA scenarios in turn at the Higgs strahlung threshold, the top pair production threshold, and at $\sqrt{s} =500\GeV$. In these scenarios at the corresponding $\sqrt{s}$, radiative neutralino production is the only supersymmetric production mechanism which is kinematically allowed. The heavier neutralinos, and charginos as well as the sleptons, squarks and gluinos are too heavy to be pair produced. We calculate the signal cross section and also the Standard Model background from radiative neutrino production. For our scenarios, we obtain significances larger than 10 and signal to background ratios between 2% and 5%, if we have electron beam polarization $P_{e^-} = 0.0- 0.8$ and positron beam polarization $P_{e^+} = 0.0 - 0.3$. If we have electron beam polarization of $P_{e^-} = 0.9$, then the signal is observable with $P_{e^+} = 0.0$ but both the significance and the signal to background ratio are significantly improved for $P_{e^+} = 0.3$.

hep-ph↗

arXiv2007

Polarization aspects in radiative neutralino production

We study the impact of beam polarization on radiative neutralino production e+e- \to χ^0_1 χ^0_1 photon at the International Linear Collider. We show that longitudinal polarized beams significantly enhance the signal and simultaneously reduce the Standard Model background from radiative neutrino production e+e- \to ν\barνphoton. We point out that the radiative production of neutralinos could be the only accessible SUSY particles, if neutralinos, charginos, sleptons, as well as squarks and gluinos are too heavy to be pair-produced in the first stage of the ILC at sqrt{s} = 500 GeV.

hep-ph↗

arXiv2007

A Physics Show Performed by Students for Kids: From Mechanics to Elementary Particle Physics

We describe an initiative at the University of Bonn, where the students develop and perform a 2 hour physics show for school classes and the general public. The show is entertaining and educational and is aimed at children aged 10 and older. For the physics students this is a unique experience to apply their knowledge at an early stage and gives them the chance to develop skills in the public presentation of science, in front of 520 people per show. We have extended the activity to put on an elementary particle physics show for teenagers. Furthermore, local high schools have picked up the idea; their students put on similar shows for fellow students and parents. We would be interested in hearing about related activities elsewhere.

physics.ed-ph↗