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At least 1,801 records · Page 100

Constraints on dark matter to dark radiation conversion in the late universe with DES-Y1 and external data

We study a phenomenological class of models where dark matter converts to dark radiation in the low redshift epoch. This class of models, dubbed DMDR, characterizes the evolution of comoving dark-matter density with two extra parameters, and may be able to help alleviate the observed discrepancies between early and late-time probes of the Universe. We investigate how the conversion affects key cosmological observables such as the cosmic microwave background (CMB) temperature and matter power spectra. Combining 3x2pt data from Year 1 of the Dark Energy Survey, Planck-2018 CMB temperature and polarization data, supernovae (SN) Type Ia data from Pantheon, and baryon acoustic oscillation (BAO) data from BOSS DR12, MGS and 6dFGS, we place new constraints on the amount of dark matter that has converted to dark radiation and the rate of this conversion. The fraction of the dark matter that has converted since the beginning of the Universe in units of the current amount of dark matter, ζ, is constrained at 68% confidence level to be <0.32 for DES-Y1 3x2pt data, <0.030 for CMB+SN+BAO data, and <0.037 for the combined dataset. The probability that the DES and CMB+SN+BAO datasets are concordant increases from 4% for the ΛCDM model to 8% (less tension) for DMDR. The tension in S8=σ8Ωm/0.3 between DES-Y1 3x2pt and CMB+SN+BAO is slightly reduced from 2.3σ to 1.9σ. We find no reduction in the Hubble tension when the combined data is compared to distance-ladder measurements in the DMDR model. The maximum-posterior goodness-of-fit statistics of DMDR and ΛCDM model are comparable, indicating no preference for the DMDR cosmology over ΛCDM.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for long-lived particles using displaced jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV

An inclusive search is presented for long-lived particles using displaced jets. The search uses a data sample collected with the CMS detector at the CERN LHC in 2017 and 2018, from proton-proton collisions at a center-of-mass energy of 13 TeV. The results of this search are combined with those of a previous search using a data sample collected with the CMS detector in 2016, yielding a total integrated luminosity of 132 fb - 1 . The analysis searches for the distinctive topology of displaced tracks and displaced vertices associated with a dijet system. For a simplified model, where pair-produced long-lived neutral particles decay into quark-antiquark pairs, pair production cross sections larger than 0.07 fb are excluded at 95% confidence level (C.L.) for long-lived particle masses larger than 500 GeV and mean proper decay lengths between 2 and 250 mm. For a model where the standard model-like Higgs boson decays to two long-lived scalar particles that each decays to a quark-antiquark pair, branching fractions larger than 1% are excluded at 95% C.L. for mean proper decay lengths between 1 mm and 340 mm. A group of supersymmetric models with pair-produced long-lived gluinos or top squarks decaying into various final-state topologies containing displaced jets is also tested. Gluino masses up to 2500 GeV and top squark masses up to 1600 GeV are excluded at 95% C.L. for mean proper decay lengths between 3 and 300 mm. The highest lower bounds on mass reach 2600 GeV for long-lived gluinos and 1800 GeV for long-lived top squarks. These are the most stringent limits to date on these models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

IceCube high-energy starting event sample: Description and flux characterization with 7.5 years of data

The IceCube Neutrino Observatory has established the existence of a high-energy all-sky neutrino flux of astrophysical origin. This discovery was made using events interacting within a fiducial region of the detector surrounded by an active veto and with reconstructed energy above 60 TeV, commonly known as the high-energy starting event sample (HESE). Here, we revisit the analysis of the HESE sample with an additional 4.5 years of data, newer glacial ice models, and improved systematics treatment. This paper describes the sample in detail, reports on the latest astrophysical neutrino flux measurements, and presents a source search for astrophysical neutrinos. We give the compatibility of these observations with specific isotropic flux models proposed in the literature as well as generic power-law-like scenarios. Assuming ν e :ν μ :ν τ =1:1:1, and an equal flux of neutrinos and antineutrinos, we find that the astrophysical neutrino spectrum is compatible with an unbroken power law, with a preferred spectral index of $2.87_{-0.19}^{+0.20}$ for the 68% confidence interval.

79 ASTRONOMY AND ASTROPHYSICS↗

Search for long-lived particles decaying to jets with displaced vertices in proton-proton collisions at √ s = 13 TeV

A search is presented for long-lived particles produced in pairs in proton-proton collisions at the LHC operating at a center-of-mass energy of 13 TeV . The data were collected with the CMS detector during the period from 2015 through 2018, and correspond to a total integrated luminosity of 140 fb –1 . This search targets pairs of long-lived particles with mean proper decay lengths between 0.1 and 100 mm , each of which decays into at least two quarks that hadronize to jets, resulting in a final state with two displaced vertices. No significant excess of events with two displaced vertices is observed. In the context of R-parity violating supersymmetry models, the pair production of long-lived neutralinos, gluinos, and top squarks is excluded at 95% confidence level for cross sections larger than 0.08 fb, masses between 800 and 3000 GeV, and mean proper decay lengths between 1 and 25 mm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for charginos and neutralinos in final states with two boosted hadronically decaying bosons and missing transverse momentum in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for charginos and neutralinos at the Large Hadron Collider using fully hadronic final states and missing transverse momentum is reported. Pair-produced charginos or neutralinos are explored, each decaying into a high-p T Standard Model weak boson. Fully hadronic final states are studied to exploit the advantage of the large branching ratio, and the efficient rejection of backgrounds by identifying the high-p T bosons using large-radius jets and jet substructure information. An integrated luminosity of 139 fb -1 of proton-proton collision data collected by the ATLAS detector at a center-of-mass energy of 13 TeV is used. No significant excess is found beyond the Standard Model expectation. Exclusion limits at the 95% confidence level are set on wino or higgsino production with various assumptions about the decay branching ratios and the type of lightest supersymmetric particle. A wino (higgsino) mass up to 1060 (900) GeV is excluded when the lightest supersymmetry particle mass is below 400 (240) GeV and the mass splitting is larger than 400 (450) GeV. The sensitivity to high-mass winos and higgsinos is significantly extended relative to previous LHC searches using other final states.

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Extracting the Galactic Center excess’ source-count distribution with neural nets

The two leading hypotheses for the Galactic Center excess (GCE) in the Fermi data are an unresolved population of faint millisecond pulsars (MSPs) and dark-matter (DM) annihilation. The dichotomy between these explanations is typically reflected by modeling them as two separate emission components. However, point sources (PSs) such as MSPs become statistically degenerate with smooth Poisson emission in the ultrafaint limit (formally where each source is expected to contribute much less than one photon on average), leading to an ambiguity that can render questions such as whether the emission is PS-like or Poissonian in nature ill defined. We present a conceptually new approach that describes the PS and Poisson emission in a unified manner and only afterwards derives constraints on the Poissonian component from the so obtained results. For the implementation of this approach, we leverage deep learning techniques, centered around a neural network-based method for histogram regression that expresses uncertainties in terms of quantiles. We demonstrate that our method is robust against a number of systematics that have plagued previous approaches, in particular DM/PS misattribution. In the Fermi data, we find a faint GCE described by a median source-count distribution (SCD) peaked at a flux of ~ 4 x 10 -11 counts cm -2 s -1 (corresponding to ~ 3-4 expected counts per PS), which would require N ~ $\mathscr{O}$(10 4 ) sources to explain the entire excess (median value N = 29,300 across the sky). Although faint, this SCD allows us to derive the constraint η ρ ≤ 66% for the Poissonian fraction of the GCE flux η ρ at 95% confidence, suggesting that a substantial amount of the GCE flux is due to PSs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Search for heavy particles in the b -tagged dijet mass distribution with additional b -tagged jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV with the ATLAS experiment

A search optimized for new heavy particles decaying to two b-quarks and produced in association with additional b-quarks is reported. The sensitivity is improved by b-tagging at least one lower-p T jet in addition to the two highest-p T jets. The data used in this search correspond to an integrated luminosity of 103 fb –1 collected with a dedicated trijet trigger during the 2017 and 2018 √s = 13 TeV proton–proton collision runs with the ATLAS detector at the LHC. The search looks for resonant peaks in the b-tagged dijet invariant mass spectrum over a smoothly falling background. The background is estimated with an innovative data-driven method based on orthonormal functions. The observed b-tagged dijet invariant mass spectrum is compatible with the background-only hypothesis. Upper limits at 95% confidence level on a heavy vector-boson production cross section times branching ratio to a pair of b-quarks are derived.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for Higgs boson decays into a pair of pseudoscalar particles in the $bbμμ$ final state with the ATLAS detector in pp collisions at $\sqrt{s} =$ 13 TeV

This paper presents a search for decays of the Higgs boson with a mass of 125 GeV into a pair of new pseudoscalar particles, $H→aa$, where one a-boson decays into a b-quark pair and the other into a muon pair. The search uses 139 fb -1 of proton-proton collision data at a center-of-mass energy of $\sqrt{s} =$ 13 TeV recorded between 2015 and 2018 by the ATLAS experiment at the LHC. A narrow dimuon resonance is searched for in the invariant mass spectrum between 16 GeV and 62 GeV. The largest excess of events above the Standard Model backgrounds is observed at a dimuon invariant mass of 52 GeV and corresponds to a local (global) significance of 3.3σ (1.7σ). Upper limits at 95% confidence level are placed on the branching ratio of the Higgs boson to the $bbμμ$ final state, $B(H→aa→bbμμ)$, and are in the range 0.2-4.0×10 -4 , depending on the signal mass hypothesis.

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BICEP/ K e c k XIV: Improved constraints on axionlike polarization oscillations in the cosmic microwave background

We present an improved search for axionlike polarization oscillations in the cosmic microwave background (CMB) with observations from the Keck Array . An all-sky, temporally sinusoidal rotation of CMB polarization, equivalent to a time-variable cosmic birefringence, is an observable manifestation of a local axion field and potentially allows a CMB polarimeter to detect axionlike dark matter directly. We describe improvements to the method presented in previous work, and we demonstrate the updated method with an expanded dataset consisting of the 2012–2015 observing seasons. We set limits on the axion-photon coupling constant for mass m in the range 10 - 23 – 10 - 18 eV , which corresponds to oscillation periods on the order of hours to years. Our results are consistent with the background model. For periods between 1 and 30 d ( 1.6 × 10 - 21 ≤ m ≤ 4.8 × 10 - 20 eV ), the 95%-confidence upper limits on rotation amplitude are approximately constant with a median of 0.27°, which constrains the axion-photon coupling constant to g φ γ < ( 4.5 × 10 - 12 GeV - 1 ) m / ( 10 - 21 eV ) , if axionlike particles constitute all of the dark matter. More than half of the collected BICEP dataset has yet to be analyzed, and several current and future CMB polarimetry experiments can apply the methods presented here to achieve comparable or superior constraints. In the coming years, oscillation measurements can achieve the sensitivity to rule out unexplored regions of the axion parameter space.

79 ASTRONOMY AND ASTROPHYSICS↗

Dark Energy Survey Year 3 results: Cosmological constraints from galaxy clustering and weak lensing

We present the first cosmology results from large-scale structure using the full 5000 deg 2 of imaging data from the Dark Energy Survey (DES) Data Release 1. We perform an analysis of large-scale structure combining three two-point correlation functions ( 3 × 2 pt ): (i) cosmic shear using 100 million source galaxies, (ii) galaxy clustering, and (iii) the cross-correlation of source galaxy shear with lens galaxy positions, galaxy–galaxy lensing. To achieve the cosmological precision enabled by these measurements has required updates to nearly every part of the analysis from DES Year 1, including the use of two independent galaxy clustering samples, modeling advances, and several novel improvements in the calibration of gravitational shear and photometric redshift inference. The analysis was performed under strict conditions to mitigate confirmation or observer bias; we describe specific changes made to the lens galaxy sample following unblinding of the results and tests of the robustness of our results to this decision. We model the data within the flat Λ CDM and w CDM cosmological models, marginalizing over 25 nuisance parameters. We find consistent cosmological results between the three two-point correlation functions; their combination yields clustering amplitude S 8 = 0.77 6 - 0.017 + 0.017 and matter density Ω m = 0.33 9 - 0.031 + 0.032 in Λ CDM , mean with 68% confidence limits; S 8 = 0.77 5 - 0.024 + 0.026 , Ω m = 0.35 2 - 0.041 + 0.035 , and dark energy equation-of-state parameter w = - 0.9 8 - 0.20 + 0.32 in w CDM . These constraints correspond to an improvement in signal-to-noise of the DES Year 3 3 × 2 pt data relative to DES Year 1 by a factor of 2.1, about 20% more than expected from the increase in observing area alone. This combination of DES data is consistent with the prediction of the model favored by the Planck 2018 cosmic microwave background (CMB) primary anisotropy data, which is quantified with a probability-to-exceed p = 0.13 –0.48. We find better agreement between DES 3 × 2 pt and Planck than in DES Y1, despite the significantly improved precision of both. When combining DES 3 × 2 pt data with available baryon acoustic oscillation, redshift-space distortion, and type Ia supernovae data, we find p = 0.34 . Combining all of these datasets with Planck CMB lensing yields joint parameter constraints of S 8 = 0.81 2 - 0.008 + 0.008 , Ω m = 0.30 6 - 0.005 + 0.004 , h = 0.68 0 - 0.003 + 0.004 , and ∑ m ν < 0.13 eV (95% C.L.) in Λ CDM ; S 8 = 0.81 2 - 0.008 + 0.008 , Ω m = 0.30 2 - 0.006 + 0.006 , h = 0.68 7 - 0.007 + 0.006 , and w = - 1.03 1 - 0.027 + 0.030 in w CDM .

79 ASTRONOMY AND ASTROPHYSICS↗

Improved limits on the tensor-to-scalar ratio using BICEP and P l a n c k data

In this study, we present constraints on the tensor-to-scalar ratio r using a combination of BICEP/Keck 2018 (BK18) and Planck PR4 data allowing us to fit for r consistently with the six parameters of the Λ CDM model. We discuss the sensitivity of constraints on r to uncertainties in the Λ CDM parameters as defined by the Planck data. In particular, we are able to derive a constraint on the reionization optical depth τ and thus propagate its uncertainty into the posterior distribution for r . While Planck sensitivity to r is slightly lower than the current ground-based measurements, the combination of Planck with BK18 and baryon-acoustic-oscillation data yields results consistent with r = 0 and tightens the constraint to r < 0.032 at 95% confidence.

79 ASTRONOMY AND ASTROPHYSICS↗

Atacama Cosmology Telescope: Constraints on prerecombination early dark energy

The early dark energy (EDE) scenario aims to increase the value of the Hubble constant (H0) inferred from cosmic microwave background (CMB) data over that found in the standard cosmological model (Λ CDM ), via the introduction of a new form of energy density in the early Universe. The EDE component briefly accelerates cosmic expansion just prior to recombination, which reduces the physical size of the sound horizon imprinted in the CMB. Previous work has found that nonzero EDE is not preferred by Planck CMB power spectrum data alone, which yield a 95% confidence level (C.L.) upper limit f EDE < 0.087 on the maximal fractional contribution of the EDE field to the cosmic energy budget. In this paper, we fit the EDE model to CMB data from the Atacama Cosmology Telescope (ACT) data release 4. We find that a combination of ACT, large-scale Planck TT (similar to WMAP), Planck CMB lensing, and BAO data prefers the existence of EDE at >99.7 % C .L . : f EDE = 0.091$^{+0.020}_{-0.036}$, with H 0 = 70.9$^{+1.0}_{-2.0}$ km/s/Mpc (both 68% C.L.). From a model-selection standpoint, we find that EDE is favored over Λ CDM by these data at roughly 3 σ significance. In contrast, a joint analysis of the full Planck and ACT data yields no evidence for EDE, as previously found for Planck alone. We show that the preference for EDE in ACT alone is driven by its TE and EE power spectrum data. The tight constraint on EDE from Planck alone is driven by its high-ℓ TT power spectrum data. Understanding whether these differing constraints are physical in nature, due to systematics, or simply a rare statistical fluctuation is of high priority. Here, the best-fit EDE models to ACT and Planck exhibit coherent differences across a wide range of multipoles in TE and EE, indicating that a powerful test of this scenario is anticipated with near-future data from ACT and other ground-based experiments.

79 ASTRONOMY AND ASTROPHYSICS↗

All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO and Advanced Virgo O3 data

We present results of an all-sky search for continuous gravitational waves which can be produced by spinning neutron stars with an asymmetry around their rotation axis, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. Four different analysis methods are used to search in a gravitational-wave frequency band from 10 to 2048 Hz and a first frequency derivative from -10 -8 to 10 -9 Hz/s. No statistically significant periodic gravitational-wave signal is observed by any of the four searches. As a result, upper limits on the gravitational-wave strain amplitude ℎ 0 are calculated. The best upper limits are obtained in the frequency range of 100 to 200 Hz and they are ~1.1 ×10 -25 at 95% confidence level. The minimum upper limit of 1.10 ×10 -25 is achieved at a frequency 111.5 Hz. In conclusion, we also place constraints on the rates and abundances of nearby planetary- and asteroid-mass primordial black holes that could give rise to continuous gravitational-wave signals.

79 ASTRONOMY AND ASTROPHYSICS↗

Study of e + e - → η Φ via initial state radiation at Belle

Using 980 fb -1 of data collected on and around the (n = 1, 2, 3, 4, 5) resonances with the Belle detector at the KEKB collider, we measure the cross section of e + ⁢e - → η⁢Φ from threshold to 3.95 GeV via initial state radiation. There are clear Φ⁡(1680) and J/ψ signals but no significant Φ⁡(2170) signal in the ηΦ final state. The branching fraction $\mathscr{B}$⁡[J/ψ →η⁢Φ] is measured to be (7.2 ±0.8 ±0.5) ×10 -4 . The resonant parameters of Φ⁡(1680) are determined to be m Φ(1680) = (1696±8±10) MeV/c 2 (statistical and systematic errors, respectively), Γ Φ⁡(1680) =(175±13±16) MeV and, depending on the possible presence of predominantly constructive or destructive interference between Φ⁡(1680) and continuum production, Γ$^{e^+e^-}_{Φ⁡(1680)}$·$\mathscr{B}$⁡[Φ⁡(1680)→ηΦ] and $\mathscr{B}$⁡[Φ(1680)→η⁢Φ] are determined to be (75 ±10 ±11) eV and (25±12±2)% or (207±16±20) eV and (23 ±10 ±2)%, respectively. The upper limit for Γ$^{e^+e^-}_{Φ⁡(2170)}$·$\mathscr{B}$⁡[Φ⁡(2170) → ηΦ] is determined to be either 0.17 or 18.6 eV at the 90% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for MeV electron recoils from dark matter in EXO-200

We present a search for electron-recoil signatures from the charged-current absorption of fermionic dark matter using the EXO-200 detector. We report an average electron-recoil background rate of 6.8×10 4 ⁢cts ⁢kg −1 yr −1 keV −1 above 4 MeV and find no statistically significant excess over our background projection. Using a total 136 Xe exposure of 234.1 kg yr, we exclude new parameter space for the charged-current absorption cross section for dark matter masses between 𝑚𝜒=2.6–11.6 MeV with a minimum of 6×10 −51 cm 2 at 8.3 MeV at the 90% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Measurement of the mass and width of the Λ c ⁢(2625) + charmed baryon and the branching ratios of Λ c ⁢(2625) + → Σ$^{0}_{c}$π + and Λ c ⁢(2625) + → Σ$^{++}_{c}$π -

Using the entire data sample of 980 fb -1 collected at or near the Y⁡(4⁢S) resonance with the Belle detector operating at the KEKB asymmetric-energy e + ⁢e - collider, we report the measurement of the mass, width, and the branching ratios of the Λ c (2625) + charmed baryon. The mass difference between Λ c ⁢(2625) + and Λ$^{+}_{c}$ is measured to be M⁡(Λ c ⁢(2625) + )-M⁡(Λ$^{+}_{c}$)=341.518±0.006±0.049 MeV/c 2 . The upper limit on the width is measured to be Γ⁡(Λ c ⁢(2625) + )<0.52 MeV/c 2 at 90% confidence level. Based on a full Dalitz plot fit, branching ratios with respect to the mode Λ c⁢ (2625) + →Λ$^{+}_{c}$π + ⁢π - are measured to be $\frac{\mathscr{B}⁡(Λ_c(2625)^+ → Σ^{0}_{c}π^+)} {\mathscr{B}⁡(Λ_c(2625)^+ → ^{+}_{c}⁢π^+⁢π^-)}$ = (5.19±0.23±0.40)% and $\frac{\mathscr{B}(Λ_c (2625)^+ → Σ{_c^+}^+ π^-)}{\mathscr{B}(Λ_c (2625)^+ → Λ{_c^+} π^+π^-)}$ = (5.13±0.26±0.32)%, where the first and second uncertainties are statistical and systematic, respectively. These measurements can be used to further constrain the parameters of the underlying theoretical models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for Lorentz-invariance violation with the first KATRIN data

Some extensions of the Standard Model of particle physics allow for Lorentz invariance and charge-parity-time invariance violations. In the neutrino sector strong constraints have been set by neutrino-oscillation and time-of-flight experiments. However, some Lorentz-invariance-violating parameters are not accessible via these probes. In this work, we focus on the parameters (a$^{(3)}_{of}$)00, (a$^{(3)}_{of}$)10, and (a$^{(3)}_{of}$)11 which would manifest themselves in a nonisotropic β-decaying source as a sidereal oscillation and an overall shift of the spectral endpoint. Based on the data of the first scientific run of the KATRIN experiment, we set the first 90% confidence-level limit on (a$^{(3)}_{of}$)11| of < 0.9 × 10 –6 GeV to 3.7 × 10 –6 GeV, depending on the phase. Furthermore, we derive new constraints on (a$^{(3)}_{of}$)00 and (a$^{(3)}_{of}$)10.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for rare decays B + → D s ( * ) + η , D s ( * ) + K ¯ 0 , D + η , and D + K 0

We present a study of rare decay modes B + → D$^{+}_{s}$ℎ 0 , B + → D$^{*}_{s}$⁢ + ℎ 0 , and B + → D + ⁢ℎ 0 , where ℎ 0 denotes the neutral meson η or K 0 , using a data sample of (772 ±10) ×10 6 B$\overline{B}$ events produced at the Υ⁡(4⁢S) resonance. The data were collected by the Belle detector operating at the asymmetric-energy KEKB collider. We find no evidence for these decays, so we set upper limits at the 90% confidence level on the branching fractions of , , and D + ⁢ℎ 0 decay modes. Along with these rare decay modes, we report improved measurements of the color-suppressed decay branching fractions $\mathscr{B}$⁡($\overline{B}$ 0 →D 0 ⁢η) =(26.6 ±1.2 ±2.1) ×10 -5 and $\mathscr{B}$⁡($\overline{B}$) 0 →D 0 ⁢ $\overline{K}$ 0 ) =(5.6 ±0.5 ±0.2) ×10 -5 . The first and second quoted uncertainties are statistical and systematic, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

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