New articles on High Energy Physics - Experiment

[1] 2312.00915

Inclusive and differential results of top quark pair production from the ATLAS and CMS experiments

This report summarizes recent results of inclusive and differential $\mathrm{t\bar{t}}$ cross section measurements from the ATLAS and CMS Collaborations at the LHC. Measurements at $\sqrt{s}=7,\ 8,\ 13$, and $13.6\,$TeV are compared to state-of-the-art theory predictions, using different PDF sets, matrix element calculations, or parton shower models. No significant disagreement of a single inclusive measurement is found, with an overall trend towards lower values. For the differential measurements, no theory model is able to describe the data across all bins.

[2] 2312.00920

The Targets of Opportunity Source Catalog for the EUSO-SPB2 Mission

The Extreme Universe Space Observatory on a Super Pressure Balloon 2, EUSO SPB2, mission was designed to take optical measurements of extensive air showers, EASs, from suborbital space. The EUSO SPB2 payload includes an optical Cherenkov Telescope, CT, which searches above and below the Earth's limb. Above the limb, the CT measures Cherenkov light from PeV scale EASs induced by cosmic rays. Below the limb, the CT searches for upwards going Cherenkov emission from PeV scale EASs induced by tau neutrinos, to follow up on astrophysical Targets of Opportunity, ToO. Target candidates include gamma ray bursts, tidal disruption events, and, after the start of the O4 obervation run from Ligo, Virgo, Kagra, binary neutron star mergers. Reported here is the selection and prioritization of relevant ToOs from alert networks such as the General Coordinates Network, Transient Name Server, and Astronomer Telegrams, and the translation to a viewing schedule for EUSO SPB2. EUSO SPB2 launched on a NASA super pressure balloon in May of 2023 from Wanaka, NZ.

[3] 2312.01463

Development of a Monte Carlo tool for simulating electron transport in noble liquids

This study presents a Monte Carlo simulation tool for modeling the transportation processes of thermal electrons in noble liquids, specifically focusing on liquid argon and liquid xenon. The study aims to elucidate the microscopical mechanisms governing the drift and diffusion of electrons within the context of time projection chambers (TPCs), with detailed considerations of coherent electron-atom scattering and electric field force. The simulation tool is implemented in the Geant4 framework, allowing for the exploration of electron transport parameters, including drift velocity, longitudinal diffusion coefficient, and transverse diffusion coefficient. The simulation is validated by comparing its results for drift velocity and diffusion coefficients with experimental measurements, revealing good agreement in the low to moderate electric field ranges. Discrepancies in high electric field regions are discussed, highlighting the impact of impurities and the need for improved cross-section calculations. Despite some limitations, the simulation tool provides valuable insights into electron transport in noble liquids, offering a foundation for future enhancements and applications in diverse research areas.

[4] 2312.01485

Strangeness production in double gap events in ALICE

The ALICE detector at the LHC was upgraded in the long shutdown of 2019-2021 in order to take data at much-increased Run 3 and 4 rates. The various challenges of this upgrade are presented, and the first results of strangeness production in double gap events collected in 2022 are shown by presenting distributions of kaon pairs.

[5] 2312.01772

Momentum scale calibration of the LHCb spectrometer

For accurate determination of particle masses accurate knowledge of the momentum scale of the detectors is crucial. The procedure used to calibrate the momentum scale of the LHCb spectrometer is described and illustrated using the performance obtained with an integrated luminosity of $1.6~ fb^{-1}$ collected during 2016 in $pp$ running. The procedure uses large samples of $J/\psi \rightarrow \mu^+ \mu^-$ and $B^+ \rightarrow J/\psi K^+$ decays and leads to a relative accuracy of $3 \times 10^{-4}$ on the momentum scale.

[6] 2312.01942

Search for the decay of the Higgs boson to a $Z$ boson and a light pseudoscalar particle decaying to two photons

A search for the decay of the Higgs boson to a $Z$ boson and a light, pseudoscalar particle, $a$, decaying respectively to two leptons and to two photons is reported. The search uses the full LHC Run 2 proton-proton collision data at $\sqrt{s}=13$ TeV, corresponding to 139 fb$^{-1}$ collected by the ATLAS detector. This is one of the first searches for this specific decay mode of the Higgs boson, and it probes unexplored parameter space in models with axion-like particles (ALPs) and extended scalar sectors. The mass of the $a$ particle is assumed to be in the range 0.1-33 GeV. The data are analysed in two categories: a merged category where the photons from the $a$ decay are reconstructed in the ATLAS calorimeter as a single cluster, and a resolved category in which two separate photons are detected. The main background processes are from Standard Model $Z$ boson production in association with photons or jets. The data are in agreement with the background predictions, and upper limits on the branching ratio of the Higgs boson decay to $Za$ times the branching ratio $a\to\gamma\gamma$ are derived at the 95% confidence level and they range from 0.08% to 2% depending on the mass of the $a$ particle. The results are also interpreted in the context of ALP models.

[7] 2312.02030

First Constraints on WIMP-Nucleon Effective Field Theory Couplings in an Extended Energy Region From LUX-ZEPLIN

Following the first science results of the LUX-ZEPLIN (LZ) experiment, a dual-phase xenon time projection chamber operating from the Sanford Underground Research Facility in Lead, South Dakota, USA, we report the initial limits on a model-independent non-relativistic effective field theory describing the complete set of possible interactions of a weakly interacting massive particle (WIMP) with a nucleon. These results utilize the same 5.5 t fiducial mass and 60 live days of exposure collected for the LZ spin-independent and spin-dependent analyses while extending the upper limit of the energy region of interest by a factor of 7.5 to 270~keV$_\text{nr}$. No significant excess in this high energy region is observed. Using a profile-likelihood ratio analysis, we report 90% confidence level exclusion limits on the coupling of each individual non-relativistic WIMP-nucleon operators for both elastic and inelastic interactions in the isoscalar and isovector bases.

[8] 2312.00806

Accessing CKM suppressed top decays at the LHC

We present an strategy for measuring the off-diagonal elements of the third row of CKM matrix $|V_{tq}|$ through the branching fractions of top quark decays $t\to q W$, where $q$ is a light quark jet. This strategy is an extension of existing measurements, with the improvement rooted in the use of orthogonal $b$- and $q$-taggers that add a new observable, the number of light-quark-tagged jets, to the already commonly used observable, the fraction of $b$-tagged jets in an event. Careful inclusion of the additional complementary observable significantly increases the expected statistical power of the analysis, with the possibility of excluding a null $|V_{td}|^2+|V_{ts}|^2$ at $95\%$ C.L. at the HL-LHC.

[9] 2312.00872

Precise tests of the axion coupling to tops

We present an in-depth analysis of axions and axion-like particles in top-pair production at the LHC. Our main goal is to probe the axion coupling to top quarks at high energies. To this end, we calculate the top-antitop cross section and differential distributions including ALP effects up to one-loop level. By comparing these predictions with LHC precision measurements, we constrain the top coupling of axion-like particles with masses below the top-antitop threshold. Our results apply to all UV completions of the ALP effective theory with dominant couplings to top quarks, in particular to DFSZ-like axion models.

[10] 2312.00982

Higgs Portal Interpretation of the Belle II $B^+ \to K^+ νν$ Measurement

The Belle II experiment recently observed the decay $B^+ \to K^+ \nu \nu$ for the first time, with a measured value for the branching ratio of $ (2.3 \pm 0.7) \times 10^{-5}$. This result exhibits a $\sim 3\sigma$ deviation from the Standard Model (SM) prediction. The observed enhancement with respect to the Standard Model could indicate the presence of invisible light new physics. In this paper, we investigate whether this result can be accommodated in a minimal Higgs portal model, where the SM is extended by a singlet Higgs scalar that decays invisibly to dark sector states. We find that current and future bounds on invisible decays of the 125 GeV Higgs boson completely exclude a new scalar with a mass $\gtrsim 10$ GeV. On the other hand, the Belle II results can be successfully accommodated if the new scalar is lighter than $B$ mesons but heavier than kaons. We also investigate the cosmological implications of the new states and explore the possibility that they are part of an abelian Higgs extension of the SM. Future Higgs factories are expected to place stringent bounds on the invisible branching ratio of the 125 GeV Higgs boson, and will be able to definitively test the region of parameter space favored by the Belle II results.

[11] 2312.01008

Explore the Nucleon Tomography through Di-hadron Correlation in Opposite Hemisphere in Deep Inelastic Scattering

We investigate the correlation of di-hadron productions between the current fragmentation region (CFR) and target fragmentation region (TFR) in deep inelastic scattering as a probe of the nucleon tomography. The QCD factorization and powering counting method are applied to compute the relevant diffractive parton distribution functions in the valence region. In particular, we show that the final state interaction effects lead to a nonzero longitudinal polarized quark distribution associated with the unpolarized nucleon target. This explains the observed beam single spin asymmetry (BSA) from a recent Jefferson Lab experiment. We further show that the BSA in the single diffractive hadron productions in the TFR, although kinematically suppressed, also exists because of the final state interaction effects.

[12] 2312.01293

A novel design for 100 meter-scale water attenuation length measurement and monitoring

Water Cherenov detector is a vital part in most of neutrino or cosmic ray research. As detectors grow in size, the water attenuation length (WAL) becomes increasingly essential for detector performance. It is essential to measure or monitor the WAL. While many experiments have measured WAL in the lab or detector, only the Super-Kamiokande experiment has achieved values exceeding 50 meters in the detector with a moving light source. However, it is impractical for many experiments to place a moving light source inside the detector, necessitating an alternative method for investigating long WAL. A novel system has been proposed to address the challenge of investigating long WAL. This system focuses on ample water Cherenkov detectors and features a fixed light source and photomultiplier tubes (PMTs) at varying distances, eliminating the need for moving parts. The static setup demands high precision for accurate measurement of long WAL. Each component, including LED, diffuse ball, PMTs, and fibers, is introduced to explain uncertainty control. Based on lab tests, the system's uncertainty has been controlled within 5\%. Additionally, camera technology is also used during the evaluation of the system uncertainty, which has the potential to replace PMTs in the future for this measurement. Monte Carlo simulations have shown that the system can achieve a 5\% measurement uncertainty at WAL of 80 meters and 8\% at WAL of 100 meters. This system can be used in experiments with large Cherenkov detectors such as JUNO water veto and Hyper-K.

[13] 2312.01470

ee$\in$MC: Low Energy Mesons and the Residual QCD Potential

The Flux-Tube Breaking Model in ee$\in$MC is expanded to include the residual QCD potential between the Final-State mesons, within the non-relativistic limit. These residual QCD potentials have been predicted in the context of the Flux-Tube Breaking Models to generate meson-meson molecular states for the $f_{0}(500)$, $f_{0}(980)$, $a_{0}(980)$, through the colour hyper-fine spin-spin interaction. These residual potentials are also found to have an important impact on the $S_{1}$ decay of the $a_{1}$ and $K_{1}$ axial-vector mesons due to the colour hyper-fine spin-spin interaction. It is found that in the low mass regions, the $\rho(770)$ and $K^{*}(892)$ are sensitive to the linear-confining potential and colour-Coulomb potential suggesting that with the high statistics at the B-Factories, it may be possible to probe the linear-confining potential and colour-Coulomb potential through a model dependent description of the resonance shape or by exploiting multiple production process.

[14] 2312.01525

$Z_3$ symmetry of the CKM and PMNS matrices

We develop for the CKM and PMNS matrices a new representation with special properties. It is obtained by splitting each of these matrices into two rotations by the angle ${\sim}2\pi/3$ and a universal diagonal matrix with elements, which are cubic roots of~1. Such a representation of the CKM and PMNS matrices may indicate the $Z_{3}$ symmetry to be present in the Yukawa sector of the~SM. Identical mathematical structure of the CKM and PMNS matrices is also an extension of the quark-lepton universality. In this approach the CP violation is a natural consequence of the structure of the Yukawa couplings. The CP violating phase is not a fitted parameter and its value is governed by the parameters of two rotations. The parameters of the diagonalizing matrices of the bi-unitary transformation do not exhibit a hierarchy, which means that the origins of the hierarchy of quark masses and of the CKM matrix elements are not the same.

[15] 2312.01851

Radiation effects on scientific CMOS sensors for X-ray astronomy: I. proton irradiation

Complementary metal-oxide-semiconductor (CMOS) sensors are a competitive choice for future X-ray astronomy missions. Typically, CMOS sensors on space astronomical telescopes are exposed to a high dose of irradiation. We investigate the impact of irradiation on the performance of two scientific CMOS (sCMOS) sensors between -30 to 20 degree at high gain mode (7.5 times), including the bias map, readout noise, dark current, conversion gain, and energy resolution. The two sensors are irradiated with 50 MeV protons with a total dose of 5.3*10^10 p/cm^2. After the exposure, the bias map, readout noise and conversion gain at various temperatures are not significantly degraded, nor is the energy resolution at -30 degree. However, after the exposure the dark current has increased by hundreds of times, and for every 20 degree increase in temperature, the dark current also increases by an order of magnitude. Therefore, at room temperature, the fluctuations of the dark currents dominate the noise and lead to a serious degradation of the energy resolution. Moreover, among the 4k * 4k pixels, there are about 100 pixels whose bias at 50 ms has changed by more than 10 DN (~18 e-), and about 10 pixels whose readout noise has increased by over 15 e- at -30 degree. Fortunately, the influence of the dark current can be reduced by decreasing the integration time, and the degraded pixels can be masked by regular analysis of the dark images. Some future X-ray missions will likely operate at -30 degree, under which the dark current is too small to significantly affect the X-ray performance. Our investigations show the high tolerance of the sCMOS sensors for proton radiation and prove their suitability for X-ray astronomy applications.

[16] 2312.01989

Strange hidden-charm pentaquark poles from $B^-\to J/ψΛ\bar{p}$

Recent LHCb data for $B^-\to J/\psi\Lambda\bar{p}$ show a clear peak structure at the $\Xi_c\bar{D}$ threshold in the $J/\psi\Lambda$ invariant mass ($M_{J/\psi\Lambda}$) distribution. The LHCb's amplitude analysis identified the peak with the first hidden-charm pentaquark with strangeness $P_{\psi s}^\Lambda(4338)$. We conduct a coupled-channel amplitude analysis of the LHCb data by simultaneously fitting the $M_{J/\psi\Lambda}$, $M_{J/\psi\bar{p}}$, $M_{\Lambda\bar{p}}$, and $\cos\theta_{K^*}$ distributions. Rather than the Breit-Wigner fit employed in the LHCb analysis, we consider relevant threshold effects and a unitary $\Xi_c\bar{D}$-$\Lambda_c\bar{D}_s$ coupled-channel scattering amplitude from which $P_{\psi s}^\Lambda$ poles are extracted for the first time. In our default fit, the $P_{\psi s}^\Lambda(4338)$ pole is almost a $\Xi_c \bar{D}$ bound state at $( 4338.2\pm 1.4)-( 1.9\pm 0.5 )\,i$ MeV. Our default model also fits a large fluctuation at the $\Lambda_c\bar{D}_s$ threshold, giving a $\Lambda_c\bar{D}_s$ virtual state, $P_{\psi s}^\Lambda(4255)$, at $4254.7\pm 0.4$ MeV. We also found that the $P_{\psi s}^\Lambda(4338)$ peak cannot solely be a kinematical effect, and a nearby pole is needed.

[17] 2312.02045

Fast Posterior Probability Sampling with Normalizing Flows and Its Applicability in Bayesian analysis in Particle Physics

In this study, we use Rational-Quadratic Neural Spline Flows, a sophisticated parametrization of Normalizing Flows, for inferring posterior probability distributions in scenarios where direct evaluation of the likelihood is challenging at inference time. We exemplify this approach using the T2K near detector as a working example, focusing on learning the posterior probability distribution of neutrino flux binned in neutrino energy. The predictions of the trained model are conditioned at inference time by the momentum and angle of the outgoing muons released after neutrino-nuclei interaction. This conditioning allows for the generation of personalized posterior distributions, tailored to the muon observables, all without necessitating a full retraining of the model for each new dataset. The performances of the model are studied for different shapes of the posterior distributions.

[18] 2312.02053

Tensions in $e^+e^-\toπ^+π^-(γ)$ measurements: the new landscape of data-driven hadronic vacuum polarization predictions for the muon $g-2$

The situation of the experimental data used in the dispersive evaluation of the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is assessed in view of two recent measurements: $e^+e^- \to \pi^+\pi^-$ cross sections in the $\rho$ resonance region by CMD-3 and a study of higher-order radiative effects in the initial-state-radiation processes $e^+e^- \to \mu^+\mu^-\gamma$ and $e^+e^- \to \pi^+\pi^-\gamma$ by BABAR. The impact of the latter study on the KLOE and BESIII cross-section measurements is evaluated and found to be indicative of larger systematic effects than uncertainties assigned. The new situation also warrants a reappraisal of the independent information provided by hadronic $\tau$ decays, including state-of-the-art isospin-breaking corrections. The findings cast a new light on the longstanding deviation between the muon $g-2$ measurement and the Standard Model prediction using the data-driven dispersive approach, and the comparison with lattice QCD calculations.