New articles on High Energy Physics - Experiment

[1] 2105.03848

Seasonal Variation of Multiple-Muon Cosmic Ray Air Showers Observed in the NOvA Detector on the Surface

We report the rate of cosmic ray air showers with multiplicities exceeding 15 muon tracks recorded in the NOvA Far Detector between May 2016 and May 2018. The detector is located on the surface under an overburden of 3.6 meters water equivalent. We observe a seasonal dependence in the rate of multiple-muon showers, which varies in magnitude with multiplicity and zenith angle. During this period, the effective atmospheric temperature and surface pressure ranged between 210 K to 230 K and 940mbar to 990mbar, respectively; the shower rates are anti-correlated with the variation in the effective temperature. The variations are about 30% larger for the highest multiplicities than the lowest multiplicities and 20% larger for showers near the horizon than vertical showers.

[2] 2105.03977

Treatment of top-quark backgrounds in extreme phase spaces: the "top $p_{T}$ reweighting" and novel data-driven estimations in ATLAS and CMS

The top quark plays an important role in searches for physics beyond the SM, both as a dominant background and as a key signature for the signal. The most notable feature found in the top physics analyses in both ATLAS and CMS Collaborations: the disagreement between simulation and data of the top quark $p_{T}$ spectrum - is highlighted. A reweighting procedure which significantly improves the agreement between simulation and data, also known as the "top $p_{T}$ reweighting", is summarised. Commonly raised points concerning the reweighting to fixed-order predictions are discussed, and several refined approaches are mentioned. An overview of several data-driven methods developed and used to estimate the $t\bar{t}$ background in regions with large jet and b-jet multiplicities and/or high top quark $p_{T}$ is presented.

[3] 2105.04049

Generating the full SM at linear colliders

Future linear $e^+e^-$ colliders aim for extremely high precision measurements. To achieve this, not only excellent detectors and well controlled machine conditions are needed, but also the best possible estimate of backgrounds. To avoid that lacking channels and too low statistics becomes a major source of systematic errors in data-MC comparisons, all SM channels with the potential to yield at least a few events under the full lifetime of the projects need to be generated, with statistics largely exceeding that of the real data. Also machine conditions need to be accurately taken into account. This includes beam-polarisation, interactions due to the photons inevitably present in the highly focused beams, and coherent interactions of whole bunches. This endeavour has already been partly achieved in preparing design documents for both the ILC and CLIC: Comprehensive samples of fully simulated and reconstructed events are available for use. In this contribution, we present how the generation of physics events at linear colliders is categorised and organised, and the tools used. Also covered is how different aspects of machine conditions, different sources of spurious interactions (such as beam-induced backgrounds) are treated and the tools involved for these aspects.

[4] 2105.04111

Measurements of branching fractions and direct ${\it CP}$-violating asymmetries in $B^+ \to K^+ π^0~\mbox{and}~π^+ π^0$ decays using 2019 and 2020 Belle II data

We report measurements of branching fractions ($\mathcal B$) and direct ${\it CP}$-violating asymmetries ($\mathcal A_{\it CP}$) for the decays $B^+\to K^+\pi^0$ and $B^+ \to \pi^+\pi^0$ reconstructed with the Belle II detector in a sample of asymmetric-energy electron-positron collisions at the $\Upsilon(4S)$ resonance corresponding to 62.8 $\text{fb}^{-1}$ of integrated luminosity. The results are $\mathcal{B}(B^+ \to K^+\pi^0) = [11.9 ^{+1.1}_{-1.0} (\rm stat)\pm 1.6(\rm syst)]\times 10^{-6}$, $\mathcal{B}(B^+ \to \pi^+\pi^0) = [5.5 ^{+1.0}_{-0.9} (\rm stat)\pm 0.7(\rm syst)]\times 10^{-6}$, $\mathcal A_{\it CP}(B^+ \to K^+\pi^0) = -0.09 \pm 0.09 (\rm stat)\pm 0.03(\rm syst)$, and $\mathcal A_{\it CP}(B^+ \to \pi^+\pi^0) = -0.04 \pm 0.17 (\rm stat)\pm 0.06(\rm syst)$. The results are consistent with previous measurements and show a detector performance comparable with early Belle performance.

[5] 2105.04428

Muon trigger with fast Neural Networks on FPGA, a demonstrator

The online reconstruction of muon tracks in High Energy Physics experiments is a highly demanding task, typically performed with programmable logic boards, such as FPGAs. Complex analytical algorithms are executed in a quasi-real-time environment to identify, select and reconstruct local tracks in often noise-rich environments. A novel approach to the generation of local triggers based on an hybrid combination of Artificial Neural Networks and analytical methods is proposed, targeting the muon reconstruction for drift tube detectors. The proposed algorithm exploits Neural Networks to solve otherwise computationally expensive analytical tasks for the unique identification of coherent signals and the removal of the geometrical ambiguities. The proposed approach is deployed on state-of-the-art FPGA and its performances are evaluated on simulation and on data collected from cosmic rays.

[6] 2105.04507

Higgs cross-section and properties at ATLAS and CMS

Recent measurements of Higgs boson cross-section and properties are presented using up to $139~\text{fb}^{-1}$ of proton-proton collision data delivered by the Large Hadron Collider at $\sqrt{s}~=~13~\text{TeV}$ and recorded by the ATLAS and CMS detectors. Three measurements are discussed. The first is the measurement of Higgs boson production with sizeable transverse momentum decaying to a $b\bar{b}$ pair. The remaining two measurements exploit the $H \rightarrow WW^*$ decay channel in various production modes: gluon fusion, vector boson fusion, and production in association with a $W$ or $Z$ boson. The results presented are compatible with Standard Model predictions.

[7] 2105.04540

Light dark matter searches with positrons

We discuss two complementary strategies to search for light dark matter (LDM) exploiting the positron beam possibly available in the future at Jefferson Laboratory. LDM is a new compelling hypothesis that identifies dark matter with new sub-GeV "hidden sector" states, neutral under standard model interactions and interacting with our world through a new force. Accelerator-based searches at the intensity frontier are uniquely suited to explore it. Thanks to the high intensity and the high energy of the CEBAF (Continuous Electron Beam Accelerator Facility) beam, and relying on a novel LDM production mechanism via positron annihilation on target atomic electrons, the proposed strategies will allow us to explore new regions in the LDM parameters space, thoroughly probing the LDM hypothesis as well as more general hidden sector scenarios.

[8] 2105.03453

Physics reach of ${D}_{(s)}\to π(K) \ell\ell$ and other charming null test opportunities

We discuss possibilities to test physics beyond the Standard Model in $\vert\Delta c\vert=\vert\Delta u\vert= 1$ semileptonic, hadronic and missing energy decay modes. Clean null test observables such as angular observables, CP-asymmetries and lepton universality tests are presented and model-independent correlations as well as details within flavorful, anomaly-free $Z^\prime$ models are worked out.

[9] 2105.03998

Ultra-Heavy Dark Matter Search with Electron Microscopy of Geological Quartz

Self-interactions within the dark sector could clump dark matter into heavy composite states with low number density, leading to a highly suppressed event rate in existing direct detection experiments. However, the large interaction cross section between such ultra-heavy dark matter (UHDM) and standard model matter results in a distinctive and compelling signature: long, straight damage tracks as they pass through and scatter with matter. In this work, we propose using geologically old quartz samples as large-exposure detectors for UHDM. We describe a high-resolution readout method based on electron microscopy, characterize the most favorable geological samples for this approach, and study its reach in a simple model of the dark sector. The advantage of this search strategy is two-fold: the age of geological quartz compensates for the low number density of UHDMs, and the distinct geometry of the damage track serves as a high-fidelity background rejection tool.

[10] 2105.04050

On measurement of photon polarization in radiative penguin $B$ decays to baryons

A measurement of the photon polarization in radiative penguin $B$ decays provides a test of the Standard Model and a probe for New Physics, that can lead to a deviation from the Standard Model prediction of left-handed photons in $b\to s \gamma$. We propose a new method to measure the photon polarization using the baryonic decay $B^- \to \Lambda\bar{p} \gamma$. The $P$-violating $\Lambda$-hyperon decay allows a measurement of the $\Lambda$ helicity to be performed, which can be uniquely related to the photon polarization in a model-independent way. The $B^- \to \Lambda\bar{p} \gamma$ decay was recently measured to have a large branching fraction providing a possibility to get meaningful results with the data already available at LHC and B-factory experiments. An increase of the $B$-meson sample at high luminosity LHC experiments and Belle II should provide a really stringent test by using this method already in the near future.

[11] 2105.04306

Lepton family numbers and non-relativistic Majorana neutrinos

In this talk, we have reviewed the recent development on the time evolution of lepton family number carried by Majorana neutrinos \cite{Adam:2021qiq}. This article focuses on the subtle points of the derivation of the lepton family numbers and their time evolution. We also show how the time evolution is sensitive to $m_{ee}$ and $m_{e\mu}$ components of the effective Majorana mass matrix by applying the formula to the two family case. The dependence on the Majorana phase is clarified and the implication on CNB (cosmic neutrino background) is also discussed.

[12] 2105.04325

Search for dark matter annihilation in the dwarf irregular galaxy WLM with H.E.S.S

We search for an indirect signal of dark matter through very high-energy gamma rays from the Wolf-Lundmark-Melotte (WLM) dwarf irregular galaxy. The pair annihilation of dark matter particles would produce Standard Model particles in the final state such as gamma rays, which might be detected by ground-based Cherenkov telescopes. Dwarf irregular galaxies represent promising targets as they are dark matter dominated objects with well measured kinematics and small uncertainties on their dark matter distribution profiles. In 2018, the H.E.S.S. five-telescope array observed the dwarf irregular galaxy WLM for 18 hours. We present the first analysis based on data obtained from an imaging atmospheric Cherenkov telescope for this subclass of dwarf galaxy. As we do not observe any significant excess in the direction of WLM, we interpret the result in terms of constraints on the velocity-weighted cross section for dark matter pair annihilation as a function of the dark matter particle mass for various continuum channels as well as the prompt gamma-gamma emission. For the $\tau^+\tau^-$ channel the limits reach a $\langle \sigma v \rangle$ value of about $4\times 10^{-22}$ cm3s-1 for a dark matter particle mass of 1 TeV. For the prompt gamma-gamma channel, the upper limit reaches a $\langle \sigma v \rangle$ value of about $5 \times10^{-24}$ cm3s-1 for a mass of 370 GeV. These limits represent an improvement of up to a factor 200 with respect to previous results for the dwarf irregular galaxies for TeV dark matter search.

[13] 2105.04345

Prospects for diffractive dijet photoproduction at the EIC

We discuss the prospects of diffractive dijet photoproduction at the EIC to distinguish different fits of diffractive proton PDFs, different schemes of factorization breaking, to determine diffractive nuclear PDFs and pion PDFs from leading neutron production.

[14] 2105.04448

Scaffolding Simulations with Deep Learning for High-dimensional Deconvolution

A common setting for scientific inference is the ability to sample from a high-fidelity forward model (simulation) without having an explicit probability density of the data. We propose a simulation-based maximum likelihood deconvolution approach in this setting called OmniFold. Deep learning enables this approach to be naturally unbinned and (variable-, and) high-dimensional. In contrast to model parameter estimation, the goal of deconvolution is to remove detector distortions in order to enable a variety of down-stream inference tasks. Our approach is the deep learning generalization of the common Richardson-Lucy approach that is also called Iterative Bayesian Unfolding in particle physics. We show how OmniFold can not only remove detector distortions, but it can also account for noise processes and acceptance effects.

[15] 2105.04464

Single Top Quark Production with and without a Higgs Boson

One way to probe new physics beyond standard model is to check the correlation among higher dimension operators in effective field theory. We examine the strong correlation between the processes of $pp\rightarrow tHq$ and $pp\rightarrow tq$ which both depend on the same three operators. The correlation indicates that, according to the data of $pp\rightarrow tq$, $\sigma_{tHq}=\big[106.8 \pm 64.8\big]~{\rm fb}$ which is far below the current upper limit $\sigma_{tHq}\leq 900~{\rm fb}$.

[16] 2105.04530

Determining Higgs boson width at electron-positron colliders

Probing Higgs width $\Gamma_h$ is critical to test the Higgs properties. In this work we propose to measure $\Gamma_h$ at the $e^+e^-$ collider with a model-independent analysis under the Standard Model Effective Field Theory framework. We demonstrate that making use of the cross section measurements from $e^+e^-\to Zh$, $e^+e^-\to \nu_e\bar{\nu}_eh$ production and Higgs decay branching ratios $h\to WW^*/ZZ^*/\gamma\gamma$, one could determine $\Gamma_h$ at a percentage level with a center of mass energy $\sqrt{s}=250$ and 350 GeV and integrated luminosity $5~{\rm ab}^{-1}$. This conclusion would not depend on the assumption of the fermion Yukawa interactions. We further apply this result to constrain the fermion Yukawa couplings and it shows that the couplings could be well constrained.