Accelerator Neutrinos

Abstract:

This paper presents searches for the direct pair production of charged light-flavour sleptons, each decaying into a stable neutralino and an associated Standard Model lepton. The analyses focus on the challenging “corridor” region, where the mass difference, Δ𝑚, between the slepton (𝑒˜ or 𝜇˜) and the lightest neutralino (𝜒˜ 0 1 ) is less or similar to the mass of the 𝑊 boson, 𝑚(𝑊), with the aim to close a persistent gap in sensitivity to models with Δ𝑚 ≲ 𝑚(𝑊). Events are required to contain a high-energy jet, significant missing transverse momentum, and two same-flavour opposite-sign leptons (𝑒 or 𝜇). The analysis uses 𝑝 𝑝 collision data at √ 𝑠 = 13 TeV recorded by the ATLAS detector, corresponding to an integrated luminosity of 140 fb−1 . Several kinematic selections are applied, including a set of boosted decision trees. These are each optimised for different Δ𝑚 to provide expected sensitivity for the first time across the full Δ𝑚 corridor. The results are generally consistent with the Standard Model, with the most significant deviations observed with a local significance of 2.0 𝜎 in the selectron search, and 2.4 𝜎 in the smuon search. While these deviations weaken the observed exclusion reach in some parts of the signal parameter space, the previously present sensitivity gap to this corridor is largely reduced. Constraints at the 95% confidence level are set on simplified models of selectron and smuon pair production, where selectrons (smuons) with masses up to 300 (350) GeV can be excluded for Δ𝑚 between 2 GeV and 100 GeV.

Abstract:

Measurements of the total and differential Higgs boson production cross-sections, via WH and ZH associated production using H → WW* → ℓνℓν and H → WW* → ℓνjj decays, are presented. The analysis uses proton-proton events delivered by the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector between 2015 and 2018. The data correspond to an integrated luminosity of 140 fb−1. The sum of the WH and ZH cross-sections times the H → WW* branching fraction is measured to be 0.44−0.09+0.10stat.−0.05+0.06syst. pb, in agreement with the Standard Model prediction. Higgs boson production is further characterised through measurements of the differential cross-section as a function of the transverse momentum of the vector boson and in the framework of Simplified Template Cross-Sections.

Abstract:

<jats:p>Understanding electron neutrino interactions is crucial for measurements of neutrino oscillations and searches for new physics in neutrino experiments. We present the first measurement of the flux-averaged <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mrow><a:mi>ν</a:mi></a:mrow><a:mrow><a:mi>e</a:mi></a:mrow></a:msub><a:mo>+</a:mo><a:msub><a:mrow><a:mover accent="true"><a:mrow><a:mi>ν</a:mi></a:mrow><a:mrow><a:mo stretchy="false">¯</a:mo></a:mrow></a:mover></a:mrow><a:mrow><a:mi>e</a:mi></a:mrow></a:msub></a:mrow></a:math> charged-current single charged-pion production cross section on argon using the MicroBooNE detector and data from the NuMI neutrino beam. The total cross section is measured to be <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:mo stretchy="false">[</e:mo><e:mn>0.93</e:mn><e:mo>±</e:mo><e:mn>0.13</e:mn><e:mo stretchy="false">(</e:mo><e:mi>stat</e:mi><e:mo stretchy="false">)</e:mo><e:mo>±</e:mo><e:mn>0.27</e:mn><e:mo stretchy="false">(</e:mo><e:mi>syst</e:mi><e:mo stretchy="false">)</e:mo><e:mo stretchy="false">]</e:mo><e:mo>×</e:mo><e:msup><e:mrow><e:mn>10</e:mn></e:mrow><e:mrow><e:mo>−</e:mo><e:mn>39</e:mn></e:mrow></e:msup><e:mtext> </e:mtext><e:mtext> </e:mtext><e:msup><e:mrow><e:mi>cm</e:mi></e:mrow><e:mrow><e:mn>2</e:mn></e:mrow></e:msup><e:mo>/</e:mo><e:mi>nucleon</e:mi></e:mrow></e:math> at a mean <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mrow><m:msub><m:mrow><m:mi>ν</m:mi></m:mrow><m:mrow><m:mi>e</m:mi></m:mrow></m:msub><m:mo>+</m:mo><m:msub><m:mrow><m:mover accent="true"><m:mrow><m:mi>ν</m:mi></m:mrow><m:mrow><m:mo stretchy="false">¯</m:mo></m:mrow></m:mover></m:mrow><m:mrow><m:mi>e</m:mi></m:mrow></m:msub></m:mrow></m:math> energy of 730 MeV. Differential cross sections are also reported in electron energy, electron and pion angles, and electron-pion opening angle.</jats:p>

Abstract:

A measurement is presented of elliptic ( $v_2$ ) and triangular ( $v_3$ ) azimuthal anisotropy coefficients for charged particles produced in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{{}_{\text{NN}}}}=5.02 \text{TeV}$ using a dataset corresponding to an integrated luminosity of $0.44{\text{nb}}^{-1}$ collected with the ATLAS detector at the LHC in 2018. The values of $v_2$ and $v_3$ are measured for charged particles over a wide range of transverse momentum ( $p_{\text{T}}$ ), 1–400 $\text{GeV}$ , and $\mathrm{Pb}+\mathrm{Pb}$ collision centrality, 0–60%, using the scalar-product and multiparticle cumulant methods. These methods are sensitive to event-by-event fluctuations and nonflow effects in the measurements of azimuthal anisotropies. Positive values of $v_2$ are observed up to a $p_{\text{T}}$ of approximately 100 $\text{GeV}$ from both methods across all centrality intervals. Positive values of $v_3$ are observed up to approximately 25 $\text{GeV}$ using both methods, though the application of the three-subevent technique to the multiparticle cumulant method leads to significant changes at the highest $p_{\text{T}}$ . At high $p_{\text{T}}$ ( $p_{\text{T}}⪆10 \text{GeV}$ ), charged particles are dominantly from jet fragmentation. These jets, and hence the measurements presented here, are sensitive to the path-length dependence of parton energy loss in the quark-gluon plasma produced in $\mathrm{Pb}+\mathrm{Pb}$ collisions.

Abstract:

We report the first measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasielasticlike interactions at the gadolinium-loaded Super-Kamiokande detector using the T2K neutrino beam, which has a peak energy of about 0.6 GeV. A total of 30 neutral-current quasielasticlike event candidates were selected from T2K data corresponding to an exposure of $1.76\times {10}^{20}$ protons on target. The $\gamma$ ray signals resulting from neutron captures were identified using a neural network. The flux-averaged mean neutron capture multiplicity was measured to be ${1.37\pm 0.33(\mathrm{stat}.)}_{-0.27}^{+0.17}(\mathrm{syst}.)$ , which is compatible within 2.3 sigma than predictions obtained using our nominal simulation. We discuss potential sources of systematic uncertainty in the prediction and demonstrate that a significant portion of this discrepancy arises from the modeling of hadron-nucleus interactions in the detector medium.