# High Energy Physics - Experiment

## New submissions

[ total of 8 entries: 1-8 ]
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### New submissions for Mon, 19 Feb 18

[1]
Title: Light isovector resonances in $π^- p \to π^-π^-π^+ p$ at 190 GeV/${\it c}$
Subjects: High Energy Physics - Experiment (hep-ex); High Energy Physics - Phenomenology (hep-ph)

We have performed the most comprehensive resonance-model fit of $\pi^-\pi^-\pi^+$ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction $\pi^- + p \to \pi^-\pi^-\pi^+ + p_{recoil}$ with a 190 GeV/${\it c}$ pion beam. The PWA results, which were obtained in 100~bins of three-pion mass, 0.5 < $m_{3\pi}$ < 2.5 GeV/${\it c}^2$, and simultaneously in 11 bins of the reduced four-momentum transfer squared, 0.1 < $t'$ < 1.0 (GeV/${\it c})^2$, are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with $J^{PC} = 0^{-+}$, $1^{++}$, $2^{++}$, $2^{-+}$, $4^{++}$, and spin-exotic $1^{-+}$ quantum numbers. The model contains the well-known resonances $\pi$(1800), $a_1$(1260), $a_2$(1320), $\pi_2$(1670), $\pi_2$(1880), and $a_4$(2040). In addition, it includes the disputed $\pi_1$(1600), the excited states $a_1$(1640), $a_2$(1700), and $\pi_2$(2005), as well as the resonance-like $a_1$(1420). We measure the resonance parameters mass and width of these objects by combining the information from the PWA results obtained in the 11 $t'$ bins. We extract the relative branching fractions of the $\rho$(770)$\pi$ and $f_2$(1270)$\pi$ decays of $a_2$(1320) and $a_4$(2040), where the former one is measured for the first time. In a novel approach, we extract the $t'$ dependence of the intensity of the resonances and of their phases. The $t'$ dependence of the intensities of most resonances differs distinctly from the $t'$ dependence of the nonresonant components.

[2]
Title: Measurement of the $t\bar{t}Z$ Production Cross Section in the Final State with Three Charged Leptons using 36.1 fb$^{-1}$ of $pp$ Collisions at 13 TeV at the ATLAS Detector
Authors: Nils-Arne Rosien
Comments: 214 pages, originally published by Georg-August-Universit\"at G\"ottingen: this https URL CERN Document Server: this https URL
Subjects: High Energy Physics - Experiment (hep-ex)

A measurement of the production cross section for a top quark pair in association with a $Z$ boson ($t\bar{t}Z$) is presented in this PhD thesis. Final states with exactly three charged leptons (electrons or muons) are used, taking into account the decay of the top quark pair in the lepton+jets channel and the decay of the $Z$ boson into two charged leptons. The dataset used for this analysis corresponds to 36.1 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of 13 TeV, recorded during 2015 and 2016 by the ATLAS detector at the Large Hadron Collider. The result of a profile likelihood fit to the event yields in four signal enriched regions and two background enriched regions is $\sigma_{t\bar{t}Z}=966^{+114}_{-102}(\text{stat.})^{+115}_{-114}(\text{syst.})$ fb. The observed (expected) significance is $7.2$ ($6.4$) standard deviations from the background-only hypothesis. Within the experimental uncertainties, the result is in good agreement with the Standard Model prediction. This result is compared with two other $t\bar{t}Z$ analysis channels, using the same dataset but different lepton multiplicities. The analysis presented here is found to be the most sensitive one in terms of observed significance. The result of a combined fit of all three analysis channels is discussed. Two feasibility studies of possible future $t\bar{t}Z$ analysis techniques are demonstrated.

### Cross-lists for Mon, 19 Feb 18

[3]  arXiv:1802.05721 (cross-list from hep-ph) [pdf, ps, other]
Title: Single lepton charge asymmetries in $t \bar t$ and $t \bar t γ$ production at the LHC
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)

We discuss lepton charge asymmetries in $t \bar t$ and $t \bar t \gamma$ production at the LHC, which can be measured in the semileptonic decay channel $t \bar t \to W^+ b \, W^- \bar b \to \ell^+ \nu b \, q \bar q' \bar b$ (or the charge conjugate). Considering several new physics scenarios, it is seen that for $t \bar t$ these asymmetries may have a sensitivity competitive with the dilepton asymmetry already measured. For $t \bar t \gamma$ the new leptonic asymmetries, as well as the $t \bar t$ charge asymmetry, will reach their full potential with the high luminosity LHC upgrade. These asymmetries can pinpoint deviations at the $3\sigma-4\sigma$ level for new physics scenarios where the charge asymmetries already measured in $t \bar t$ production agree within $1\sigma$.

[4]  arXiv:1802.05987 (cross-list from physics.ins-det) [pdf, other]
Title: The CMS High-Granularity Calorimeter for Operation at the High-Luminosity LHC
Authors: Florian Pitters (On behalf of the CMS collaboration)
Subjects: Instrumentation and Detectors (physics.ins-det); High Energy Physics - Experiment (hep-ex)

The High Luminosity LHC (HL-LHC) will integrate 10 times more luminosity than the LHC, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry, and hallmarks the issue for future colliders. As part of its HL-LHC upgrade program, the CMS collaboration is designing a High Granularity Calorimeter to replace the existing endcap calorimeters. It features unprecedented transverse and longitudinal segmentation for both electromagnetic (ECAL) and hadronic (HCAL) compartments. This will facilitate particle-flow calorimetry, where the fine structure of showers can be measured and used to enhance pileup rejection and particle identification, whilst still achieving good energy resolution. The ECAL and a large fraction of HCAL will be based on hexagonal silicon sensors of 0.5 to 1 cm$^2$ cell size, with the remainder of the HCAL based on highly-segmented scintillators with SiPM readout. The intrinsic high-precision timing capabilities of the silicon sensors will add an extra dimension to event reconstruction, especially in terms of pileup rejection. An overview of the HGCAL project is presented, covering motivation, engineering design, readout and trigger concepts, and expected performance.

[5]  arXiv:1802.06008 (cross-list from physics.ins-det) [pdf, other]
Title: The CLIC Detector Concept
Authors: Florian Pitters
Subjects: Instrumentation and Detectors (physics.ins-det); High Energy Physics - Experiment (hep-ex)

The Compact Linear Collider (CLIC) is a concept for a future linear collider that would provide e$^+$e$^-$ collisions at up to 3 TeV. The physics aims require a detector system with excellent jet energy and track momentum resolution, highly efficient flavour tagging and lepton identification capabilities, full geometrical coverage extending to low polar angles, and timing information of the order of nanoseconds to reject beam-induced background. To deal with these requirements, an extensive R&D programme is in place to overcome current technological limits. The CLIC detector concept includes a low-mass all-silicon vertex and tracking detector system and fine-grained calorimeters designed for particle flow analysis techniques, surrounded by a 4 T solenoid magnet. An overview of the requirements and design optimisations for the CLIC detector concept is presented.

[6]  arXiv:1802.06039 (cross-list from astro-ph.IM) [pdf, other]
Title: Projected WIMP sensitivity of the LUX-ZEPLIN (LZ) dark matter experiment
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Experiment (hep-ex); Instrumentation and Detectors (physics.ins-det)

LUX-ZEPLIN (LZ) is a next generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with Weakly Interacting Massive Particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6 tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections above $1.6 \times 10^{-48}$ cm$^{2}$ for a 40 $\mathrm{GeV}/c^{2}$ mass WIMP. Additionally, a $5\sigma$ discovery potential is projected reaching cross sections below the existing and projected exclusion limits of similar experiments that are currently operating. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of $2.7 \times 10^{-43}$ cm$^{2}$ ($8.1 \times 10^{-42}$ cm$^{2}$) for a 40 $\mathrm{GeV}/c^{2}$ mass WIMP is expected. With construction well underway, LZ is on track for underground installation at SURF in 2019 and will start collecting data in 2020.

### Replacements for Mon, 19 Feb 18

[7]  arXiv:1711.10493 (replaced) [pdf, other]
Title: Flavoured Dark Matter Moving Left
Title: Constraints on the double-parton scattering cross section from same-sign W boson pair production in proton-proton collisions at $\sqrt{s} =$ 8 TeV