Report of the Topical Group on Environmental and Societal Impacts of Particle Physics for Snowmass 2021

We report on the work of the Topical Group on Environmental and Societal Impacts of Particle Physics for the Snowmass 2021 Community Summer Study. Topics include impacts on climate, impacts on local communities, and impacts on non-proliferation.Comment: arXiv admin note: substantial text overlap with arXiv:2203.1238

Tuning the electron energy by controlling the density perturbation position in laser plasma accelerators

A density perturbation produced in an underdense plasma was used to improve the quality of electron bunches produced in the laser-plasma wakefield acceleration scheme. Quasi-monoenergetic electrons were generated by controlled injection in the longitudinal density gradients of the density perturbation. By tuning the position of the density perturbation along the laser propagation axis, a fine control of the electron energy from a mean value of 60 MeV to 120 MeV has been demonstrated with a relative energy-spread of 15 +/- 3.6%, divergence of 4 +/- 0.8 mrad and charge of 6 +/- 1.8 pC.Comment: 7 pages, 8 figure

Probing electron acceleration and X-ray emission in laser-plasma accelerator

While laser-plasma accelerators have demonstrated a strong potential in the acceleration of electrons up to giga-electronvolt energies, few experimental tools for studying the acceleration physics have been developed. In this paper, we demonstrate a method for probing the acceleration process. A second laser beam, propagating perpendicular to the main beam is focused in the gas jet few nanosecond before the main beam creates the accelerating plasma wave. This second beam is intense enough to ionize the gas and form a density depletion which will locally inhibit the acceleration. The position of the density depletion is scanned along the interaction length to probe the electron injection and acceleration, and the betatron X-ray emission. To illustrate the potential of the method, the variation of the injection position with the plasma density is studied

Search for the Standard Model Higgs Boson in the \u3ci\u3eZH\u3c/i\u3e → νν\u3ci\u3ebb\u3c/i\u3e Channel in 5.2 fb\u3csup\u3e-1\u3c/sup\u3e of \u3ci\u3epp\u3c/i\u3e Collisions at √\u3ci\u3es\u3c/i\u3e = 1.96 TeV

A search is performed for the standard model Higgs boson in 5.2 fb-1 of pp collisions at √s = 1.96 TeV, collected with the D0 detector at the Fermilab Tevatron Collider. The final state considered is a pair of b jets and large missing transverse energy, as expected from pp → ZH → ννbb production. The search is also sensitive to the WH → ℓνbb channel when the charged lepton is not identified. For a Higgs boson mass of 115 GeV, a limit is set at the 95% C.L. on the cross section multiplied by branching fraction for [pp → (Z/W)H](H → bb) that is a factor of 3.7 larger than the standard model value, consistent with the factor of 4.6 expected

Measurement of the \u3ci\u3ett\u3c/i\u3e Production Cross Section in \u3ci\u3epp\u3c/i\u3e Collisions at √\u3ci\u3es\u3c/i\u3e = 1.96 TeV

We measure the tt production cross section in pp collisions at √s = 1.96 TeV in the lepton + jets channel. Two complementary methods discriminate between signal and background: b tagging and a kinematic likelihood discriminant. Based on 0.9 fb-1 of data collected by the D0 detector at the Fermilab Tevatron Collider, we measure σtt = 7.62 ± 0.85 pb, assuming the current world average mt = 172.6 GeV. We compare our cross section measurement with theory predictions to determine a value for the top-quark mass of 170 ± 7 GeV

Search for a Resonance Decaying into \u3ci\u3eWZ\u3c/i\u3e Boson Pairs in \u3ci\u3epp\u3c/i\u3e Collisions

We present the first search for an electrically charged resonance W’ decaying to a WZ boson pair using 4.1 fb-1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron pp collider. The WZ pairs are reconstructed through their decays into three charged leptons (ℓ = e, μ). A total of 9 data events is observed in good agreement with the background prediction. We set 95% C.L. limits on the W’WZ coupling and on the W’ production cross section multiplied by the branching fractions. We also exclude W’ masses between 188 and 520 GeV within a simple extension of the standard model and set the most restrictive limits to date on low-scale technicolor models

Evidence for production of single top quarks

We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron pp collider. The standard model predicts that the electroweak interaction can produce a top quark together with an anti-bottom quark or light quark, without the antiparticle top-quark partner that is always produced from strong-coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top-quark production has been searched for in ever larger data sets. In this analysis, we select events from a 0.9 fb-1 data set that have an electron or muon and missing transverse energy from the decay of a W boson from the top-quark decay, and two, three, or four jets, with one or two of the jets identified as originating from a b hadron decay. The selected events are mostly backgrounds such as W + jets and tt events, which we separate from the expected signals using three multivariate analysis techniques: boosted decision trees, Bayesian neural networks, and matrix-element calculations. A binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single top-quark production of σ(pp Y→ tb + X, tqb + X) = 4.7 ± 1:3 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.014%, corresponding to a 3.6 standard deviation significance. The measured cross section value is compatible at the 10% level with the standard model prediction for electroweak top-quark production. We use the cross section measurement to directly determine the Cabibbo-Kobayashi- Maskawa quark mixing matrix element that describes the Wtb coupling and find |VtbƒL1 | = 1.31-0.21+0.25 , where ƒL1 is a generic vector coupling. This model-independent measurement translates into 0.68 \u3c |Vtb| ≤ 1 at the 95% C.L. in the standard model

Measurement of the Lifetime of the \u3ci\u3eB\u3csub\u3ec\u3c/sub\u3e\u3c/i\u3e\u3csup\u3e±\u3c/sup\u3e Meson in the Semileptonic Decay Channel

Using approximately 1.3 fb-1 of data collected by the D0 detector between 2002 and 2006, we measure the lifetime of the Bc± meson in the Bc± → J/ψμ± + X final state. A simultaneous unbinned likelihood fit to the J/ψ + μ invariant mass and lifetime distributions yields a signal of 881 ± 80(stat) candidates and a lifetime measurement of τ(Bc±) = 0.448-0.036+0.038(stat) ± 0.032(syst) ps

Double parton interactions in γ = 3 jet events in \u3ci\u3epp\u3c/i\u3e collisions at √\u3ci\u3es\u3c/i\u3e = 1.96 TeV

We have used a sample of γ + 3 jets events collected by the D0 experiment with an integrated luminosity of about 1 fb-1 to determine the fraction of events with double parton scattering (fDP) in a single pp collision at √s = 1.96 TeV. The DP fraction and effective cross section (τeff ), a process-independent scale parameter related to the parton density inside the nucleon, are measured in three intervals of the second (ordered in pT) jet transverse momentum pjet2T within the range 15 ≤ pjet2T ≤ 30 GeV. In this range, fDP varies between 0.23 ≤ fDP ≤ 0.47, while σeff has the average value σave eff = 16.4 ± 0.3(stat) ± 2.3(syst) mb