Measurement Of Charge Asymmetry Research Articles

Discriminating between Higgs Production Mechanisms via Jet Charge at the LHC.

Discriminating between Higgs production mechanisms can play a crucial role in determining the couplings of Higgs to gauge bosons, probing the nature of electroweak symmetry breaking. We propose a novel method to distinguish the Higgs production mechanisms at the LHC by utilizing the jet charge asymmetry of the two leading forward jets in Higgs plus two jets production. This novel observable provides a way to disentangle the W fusion from the Z fusion and gluon fusion processes for the first time, due to the electric charge correlation of the two leading jets in the events. We show that the Higgs couplings to gauge bosons can be well constrained, and its conclusion does not depend on the other possible new physics effects which modify the Higgs total or partial width. We also discuss the complementary roles between the proposed jet charge asymmetry measurement and the Higgs signal strength measurements at the high luminosity LHC (HL-LHC) in determining the Higgs couplings.

Impact of a positron beam at JLab on an unbiased determination of DVCS Compton form factors

The impact of potential future measurements of beam charge asymmetries on the current knowledge of Compton form factors is evaluated. Elaborating on the results of a global neural network fit to deeply virtual Compton scattering data, a Bayesian reweighting analysis quantifies the improved determination of the real part of the Compton form factor $\mathcal{H}$. Such an improvement is particularly relevant for the experimental determination of the proton mechanical properties or for universality studies of generalized parton distributions through analyses of virtual Compton scattering in both spacelike and timelike regions.

Measurement of charge asymmetry for the decay and test of CPT symmetry with the KLOE detector

Using 1.63 fb−1 of integrated luminosity collected by the KLOE experiment about decays have been reconstructed. The measured value of the charge asymmetry for this decay is AS = (−4.9 ± 5.7stat ± 2.6 syst ) x 10−3 which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives AS = (−3.8 ± 5.0 stat ±2.6syst) x 10−3 and, together with the asymmetry of the KL semileptonic decay, provides significant tests of the CPT symmetry. The obtained results are in agreement with CPT invariance.

Test of discrete symmetries with neutral kaons at KLOE-2

The KLOE-2 experiment at the INFN Laboratori Nazionali di Frascati (LNF) completed its data-taking at the e+e− DAΦNE collider, which is implementing an innovative collision scheme based on a crab-waist configuration, and achieving the integrated luminosity goal of more than 5 fb−1. KLOE-2 represents the continuation of KLOE with an upgraded detector and an extended physics program which includes neutral kaon interferometry and test of discrete symmetries among the main topics. Entangled neutral kaon pairs produced at DAΦNE are a unique tool to test discrete symmetries and quantum coherence at the utmost sensitivity, in particular strongly motivating the experimental searches of possible CPT violating effects, which would constitute an unambiguous signal of a New Physics framework. The status of the latest ongoing analyses on KLOE/KLOE-2 data using the most refined analyses tools will be presented and discussed: (i) search for CP violating KS→3π0 decay, (ii) measurement of the KS semileptonic charge asymmetry and tests of CP and CPT symmetry, (iii) test of Time reversal and CPT in transitions in ϕ→KSKL→πν, 3π0, (2π) decays.

Combination of inclusive and differential mathrm{t}overline{mathrm{t}} charge asymmetry measurements using ATLAS and CMS data at sqrt{s}=7 and 8 TeV

This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair left(mathrm{t}overline{mathrm{t}}right) events with a lepton+jets signature by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. The data correspond to integrated luminosities of about 5 and 20 fb−1 for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are ACCHC7 = 0.005 ± 0.007 (stat) ± 0.006(syst) at 7 TeV and ACCHC8 = 0.0055 ± 0.0023 (stat) ± 0.0025 (syst) at 8 TeV. These values, as well as the combination of AC measurements as a function of the invariant mass of the mathrm{t}overline{mathrm{t}} system at 8 TeV, are consistent with the respective standard model predictions.

Light Quark Yukawa Couplings and the W±h Charge Asymmetry

I review the recent theory progress on possibly measuring the light quark couplings, emphasizing the distinction between direct and indirect measurements. I highlight the importance of the W±h charge asymmetry measurement as a direct probe of enhanced light quark Yukawa couplings. I propose the W±h→ℓ±ℓ±qq′νν final state as a promising channel for measuring the charge asymmetry. This clean, same-sign dilepton final state should reach statistical discovery sensitivity in each W±h charge mode with 300 fb-1 of Large Hadron Collider luminosity, and affords an impressive sub-percent statistical accuracy with the anticipated 3 ab-1 high luminosity upgrade. After accounting for current direct constraints on the total Higgs width, the W±h charge asymmetry could deviate from the Standard Model expectation by tens of percent. The measurement of a non-Standard Model asymmetry would hence provide strong indications of enhanced light quark Yukawa couplings.

Recent results and perspectives with KLOE-2

In this paper we summarize the recent experimental results from KLOE-2 on the dark photon search in the e+e−→Uγ, U→π+π−, measurement of Branching Ratio and Transition Form Factor of ϕ→π0e+e− decay, Dalitz plot analysis of η→π+π−π0 process and CPT symmetry and Lorentz invariance test with entangled K mesons. Additionally a discussion about ongoing test of CPT symmetry via measurement of KS charge asymmetry is included together with description of the KLOE-2 detection system.

Measurements of charge and CP asymmetries in b-hadron decays using top-quark events collected by the ATLAS detector in pp collisions at sqrt{s}=8 TeV

Same- and opposite-sign charge asymmetries are measured in lepton+jets toverline{t} events in which a b-hadron decays semileptonically to a soft muon, using data corresponding to an integrated luminosity of 20.3 fb−1 from proton-proton collisions at a centre-of-mass energy of sqrt{s}=8 TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. The charge asymmetries are based on the charge of the lepton from the top-quark decay and the charge of the soft muon from the semileptonic decay of a b-hadron and are measured in a fiducial region corresponding to the experimental acceptance. Four CP asymmetries (one mixing and three direct) are measured and are found to be compatible with zero and consistent with the Standard Model.

Measurement of the muon charge asymmetry in inclusive pp → W + X production at [formula omitted] at CMS and an improved determination of light parton distribution functions

Measurements of the muon charge asymmetry in inclusive pp→WX production at s=7 TeV are presented. The data sample corresponds to an integrated luminosity of 4.7 fb-1 recorded with the CMS detector at the LHC. With a sample of more than twenty million W→μν events, the statistical precision is greatly improved in comparison to previous measurements. These new results provide additional constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10-3 to 10-1. These measurements are used together with the cross sections for inclusive deep inelastic ep scattering at HERA in a next-to-leading-order QCD analysis.

Constraints on four-fermion interactions from the $$t\bar{t}$$ t t ¯ charge asymmetry at hadron colliders

The charge asymmetry in top quark production at hadron colliders is sensitive to beyond-the-Standard-Model four-fermion interactions. In this study we compare the sensitivity of $$t\bar{t}$$ cross-section and charge asymmetry measurements to effective operators describing four-fermion interactions and study the limits on the validity of this approach. A fit to a combination of Tevatron and LHC measurements yields stringent limits on the linear combinations $$C_1$$ and $$C_2$$ of the four-fermion effective operators.

Measurements of tt‾ charge asymmetry using dilepton final states in pp collisions at s=8TeV

The charge asymmetry in t t-bar events is measured using dilepton final states produced in pp collisions at the LHC at sqrt(s) = 8 TeV. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.5 inverse femtobarns. The measurements are performed using events with two oppositely charged leptons (electrons or muons) and two or more jets, where at least one of the jets is identified as originating from a bottom quark. The charge asymmetry is measured from differences in kinematic distributions, unfolded to the parton level, of positively and negatively charged top quarks and leptons. The t t-bar and leptonic charge asymmetries are found to be 0.011 +/- 0.011 (stat) +/- 0.007 (syst) and 0.003 +/- 0.006 (stat) +/- 0.003 (syst), respectively. These results, as well as charge asymmetry measurements made as a function of the invariant mass, rapidity, and transverse momentum of the t t-bar system, are in agreement with predictions of the standard model.

Measurement of the electron charge asymmetry inpp¯→W+X→eν+Xdecays inpp¯collisions ats=1.96 TeV

We present a measurement of the electron charge asymmetry in $p\bar{p}\rightarrow W+X \rightarrow e\nu +X$ events at a center-of-mass energy of 1.96 TeV, using data corresponding to 9.7~fb$^{-1}$ of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron pseudorapidity and is presented in five kinematic bins based on the electron transverse energy and the missing transverse energy in the event. The measured asymmetry is compared with next-to-leading-order predictions in perturbative quantum chromodynamics and provides accurate information for the determination of parton distribution functions of the proton. This is the most precise lepton charge asymmetry measurement to date.

Impact of CMS measurements on PDFs

Recently 2 analyses have been published by the CMS collaboration that study the effect of a specific CMS measurement on PDFs. A review of these studies is given here.The first analysis consists of a double differential inclusive jet cross-section measurement, performed on 4.7 fb−1 of data at √s = 7 TeV. Using the HERAFITTER code, the effect of adding this measurement in the PDF fit procedure together with DIS data from HERA-I is studied. The CMS data is able to significantly reduce the uncertainties on the gluon PDF, especially for gluons with large momenta relative to the proton (x > 0:01). A moderate reduction in the uncertainty of the u and d valence quark PDFs is also observed for x > 0:01. The quark PDFs are more directly probed by gauge boson production. Therefore the second analysis studies the effect of W-boson production measurements on PFDs. This consists of a W-boson charge asymmetry measurement and a study of W-boson production in association with a c-(anti-)quark, both performed on 5.0 fb−1 of data at √s = 7 TeV. A clear reduction in the uncertainty on the u and d valence quark PDFs is seen for x < 0:1. Furthermore the W-boson + c-quark production measurements allow for the determination of an independent s quark PDF, which is not possible on DIS data alone.

Measurement of the muon charge asymmetry in inclusivepp→W+Xproduction ats=7 TeVand an improved determination of light parton distribution functions

Measurements of the muon charge asymmetry in inclusive pp to WX production at sqrt(s) = 7 TeV are presented. The data sample corresponds to an integrated luminosity of 4.7 inverse femtobarns recorded with the CMS detector at the LHC. With a sample of more than twenty million W to mu nu events, the statistical precision is greatly improved in comparison to previous measurements. These new results provide additional constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10E-3 to 10E-1. These measurements and the recent CMS measurement of associated W + charm production are used together with the cross sections for inclusive deep inelastic ep scattering at HERA in a next-to-leading-order QCD analysis. The determination of the valence quark distributions is improved, and the strange-quark distribution is probed directly through the leading-order process g + s to W + c in proton-proton collisions at the LHC.

Measurement of the muon charge asymmetry in inclusive pp to WX production at sqrt(s) = 7 TeV

Measurement of the muon charge asymmetry in inclusive pp to WX production at sqrt(s) = 7 TeV

Measurement of the DirectCP-violating Charge Asymmetry inDs±→ϕπ±Decays

We present a measurement of the direct CP-violating charge asymmetry in Ds+→ϕπ± decays where the ϕ meson decays to K+K−, using the full Run II data set with an integrated luminosity of 10.4 fb−1 of proton-antiproton collisions collected using the D0 detector at the Fermilab Tevatron Collider. The normalized difference ACP in the yield of Ds+ and Ds− mesons in these decays is measured by fitting the difference between their reconstructed invariant mass distributions. This results in an asymmetry of ACP=[−0.38±0.27]%, which is the most precise measurement of this quantity to date. The result is consistent with the standard model prediction of zero CP asymmetry in this decay.Received 4 December 2013DOI:https://doi.org/10.1103/PhysRevLett.112.111804© 2014 American Physical Society

Measurement of the muon charge asymmetry inpp¯→W+X→μν+Xevents ats=1.96 TeV

We present a measurement of the muon charge asymmetry from the decay of the W boson via W→μν using 7.3 fb−1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider at s=1.96 TeV. The muon charge asymmetry is presented in two kinematic regions in muon transverse momentum and event missing transverse energy: (pTμ>25 GeV, E̸T>25 GeV) and (pTμ>35 GeV, E̸T>35 GeV). The measured asymmetries are compared with theory predictions made using three parton distribution function sets. The data at pTμ>35 GeV, E̸T>35 GeV, and larger values of |ημ| favor an increased d(x)/u(x) ratio at higher values of x than is predicted.Received 11 September 2013DOI:https://doi.org/10.1103/PhysRevD.88.091102© 2013 American Physical Society

Compilation and analysis of charge asymmetry measurements from electron and positron scattering on nucleon and nuclei

World data on the lepton-charge asymmetry in the elastic and inelastic lepton scattering off the proton and nuclei are compiled and discussed. After reviewing the published results, we compare the elastic data to a model calculation of the two-photon exchange mechanism. We show that the existing data do not provide any evidence for the two-photon contribution. At significance level 0.05 the data allow to exclude the two-photon exchange as an explanation for the difference between Rosenbluth and polarization measurements of proton electromagnetic form factors.

Top Quark Charge Asymmetry Measurement with ATLAS at the LHC

In the Standard Model top-antitop pair production is foreseen to be charge asymmetric in quark-antiquark annihilation at NLO. Although the dominant tt̄ production mechanism in pp collisions at the LHC is gluon-gluon fusion, QCD predicts a small excess of top quarks produced at higher absolute rapidities than antitops. The measurement of the top quark charge asymmetry is therefore an important test of QCD and is also sensitive to new physics. We present measurements of this asymmetry using data corresponding to an integrated luminosity of 1.04 fb−1 and 4.70 fb−1 of pp collisions at = 7 TeV collected by the ATLAS detector in the single lepton and dilepton channels respectively.

Measurement of direct CP violation parameters in B± → J/ψK± and B± → J/ψπ± decays with 10.4 fb-1 of Tevatron data.

We present a measurement of the direct CP-violating charge asymmetry in B(±) mesons decaying to J/ψK(±) and J/ψπ(±) where J/ψ decays to μ(+) μ(-), using the full run II data set of 10.4 fb(-1) of proton-antiproton collisions collected using the D0 detector at the Fermilab Tevatron Collider. A difference in the yield of B(-) and B(+) mesons in these decays is found by fitting to the difference between their reconstructed invariant mass distributions resulting in asymmetries of A(J/ψK) = [0.59 ± 0.37]%, which is the most precise measurement to date, and A(J/ψπ) = [-4.2 ± 4.5]%. Both measurements are consistent with standard model predictions.