Dielectron Events Research Articles

Measurement of the weak mixing angle using the forward\u2013backward asymmetry of Drell\u2013Yan events in mathrm {p}mathrm {p} collisions at 8,text {TeV}

A measurement is presented of the effective leptonic weak mixing angle (sin ^2theta ^{ell }_{text {eff}}) using the forward–backward asymmetry of Drell–Yan lepton pairs (mu mu and mathrm {e}mathrm {e}) produced in proton–proton collisions at sqrt{s}=8,text {TeV} at the CMS experiment of the LHC. The data correspond to integrated luminosities of 18.8 and 19.6{{,text {fb}^{-1}}} in the dimuon and dielectron channels, respectively, containing 8.2 million dimuon and 4.9 million dielectron events. With more events and new analysis techniques, including constraints obtained on the parton distribution functions from the measured forward–backward asymmetry, the statistical and systematic uncertainties are significantly reduced relative to previous CMS measurements. The extracted value of sin ^2theta ^{ell }_{text {eff}} from the combined dilepton data is sin ^2theta ^{ell }_{text {eff}} =0.23101pm 0.00036,text {(stat)} pm 0.00018,text {(syst)} pm 0.00016,text {(theo)} pm 0.00031,text {(parton distributions in proton)}=0.23101 pm 0.00053.

Search for Resonance in the Dilepton Mass at LHC Using MC Simulation

In the present work we search for Resonance in the dielectron events produced in proton-proton collisions at LHC using Monte Carlo simulation programs which may be Z'_{B-L} heavy neutral boson. To detect this resonance at LHC we used the data which are produced fro m pp collision of Pythia8 produced events at different energ ies for LHC then we use the angular d istribution for the dielectron produced fro m Z'_{B-L} decay channels to detect the Z'_{B-L}signal. B-L extension of the SM model p redicts the existence of a Z'_ {B-L}heavy neutral massive boson at high energies and fro m our results which we had simu lated for Z'_{B-L}in the B-L extension of standard model we predict that a Z'_{B-L}boson will be found at LHC and has a mass in the range fro m 1 TeV to 1.5 TeV.

Measurement of beauty photoproduction near threshold using di-electron events with the H1 detector at HERA

The cross section for ep -> e b\bar{b} X in photoproduction is measured with the H1 detector at the ep-collider HERA. The decay channel b\bar{b} -> ee X' is selected by identifying the semi-electronic decays of the b-quarks. The total production cross section is measured in the kinematic range given by the photon virtuality Q^2 <= 1 GeV^2, the inelasticity 0.05 <= y <= 0.65 and the pseudorapidity of the b-quarks |eta(b)|,|eta(\bar{b})| <= 2. The differential production cross section is measured as a function of the average transverse momentum of the beauty quarks <P_T(b)> down to the threshold. The results are compared to next-to-leading-order QCD predictions.

Search for large extra dimensions in dimuon and dielectron events in pp collisions at [formula omitted

Results are presented from a search for large, extra spatial dimensions in events with either two isolated muons or two isolated electrons. The data are from proton–proton interactions at s=7 TeV collected with the CMS detector at the LHC. The size of the data sample corresponds to an integrated luminosity of approximately 2 fb−1. The observed dimuon and dielectron mass spectra are found to be consistent with standard-model expectations. Depending on the number of extra dimensions, the 95% confidence level limits from the combined μμ and ee channels range from Ms>2.4 TeV to Ms>3.8 TeV, where Ms characterizes the scale for the onset of quantum gravity.

Heavy quark signals from radiative corrections to theZ′boson decay in 3-3-1 models

One-loop corrections to the ${Z}^{\ensuremath{'}}$ decay width are derived and analyzed in the framework of the general form of the 3-3-1 models. We identify two important sources of corrections: oblique corrections associated to the ${Z}^{\ensuremath{'}}$ propagator through vacuum polarizations induced by virtual particle-antiparticle pairs of new heavy quarks $J$, and vertex corrections to the ${Z}^{\ensuremath{'}}q\overline{q}$ vertex through virtual exchange of new ${K}^{{Q}_{1,2}}$ gauge bosons. Fixing a specific renormalization scheme, we obtain dominant oblique corrections that exhibit a quadratic dependence on the $J$ quark mass, which are absorbed into two oblique parameters: a global parameter ${\ensuremath{\rho}}_{f}^{\ensuremath{'}}$ which modify the ${Z}^{\ensuremath{'}}$ decay width, and a parameter ${\ensuremath{\kappa}}_{f}^{\ensuremath{'}}$ that define effective ${Z}^{\ensuremath{'}}$ couplings. Numerical results in an specific 3-3-1 model gives a strong contribution of the oblique corrections from about 1.3% in the $d(s)$ quark channel to 10.5% in the neutrino channel, for ${m}_{J}=2\text{ }\text{ }\mathrm{TeV}$. The vertex corrections contribute to the oblique corrections up to 1.4% for the same channel and ${m}_{J}$ value. For $pp$ collisions at the CERN LHC collider, we find that the corrections significantly modify the shape of the cross section distributions for ${e}^{+}{e}^{\ensuremath{-}}$ and $t\overline{t}$ final states, where the distributions including the radiative corrections increases up to 1.23 times the tree-level distribution for the dielectron events and to 1.07 for the top events when ${m}_{J}=3\text{ }\text{ }\mathrm{TeV}$.

Z′boson detection in the minimal quiver standard model

We undertake a phenomenological study of the extra neutral ${Z}^{\ensuremath{'}}$ boson in the minimal quiver standard model and discuss limits on the model's parameters from previous precision electroweak experiments, as well as detection prospects at the Large Hadron Collider at CERN. We find that masses lower than around 700 GeV are excluded by the $Z$-pole data from the CERN LEP collider, and below 620 GeV by experimental data from di-electron events at the Fermilab Tevatron collider. We also find that at a mass of 1 TeV the LHC cross section would show a small peak in the di-lepton and top pair channel.

Z ′ boson signal at Fermilab-Tevatron and CERN-LHC in a 331 model

We analyse the possibilities to detect a new Z ′ boson in di-electron events at Tevatron and LHC in the framework of the 331 model with right-handed neutrinos. We also study other fermions and Higgs events as final state at LHC. Using $p\bar{p}$ collision data collected by the CDF II detector at Fermilab Tevatron, we find that the 331 Z ′ boson is excluded with masses below 920 GeV. For an integrated luminosity of 100 fb−1 at LHC, and considering a central value $M_{Z^{\prime}}=1500$ GeV, we obtain the invariant-mass distribution in the process pp→Z ′→e + e −, where a huge peak, corresponding to 800 signal events/(20 GeV), is found above the SM background. The number of di-electron events vary from 50000 to 2400 in the mass range of $M_{Z^{\prime}}=800$ –2000 GeV. We also obtain branching ratios and cross sections in other fermion and Higgs channels at LHC, where a heavy top quark T exhibits the biggest ratio with m T =300 GeV.

Z' production in 331 models

We analyse the possibilities to detect a new Z' boson in di-electron events at LHC in the framework of the 331 model with right-handed neutrinos. For an integrated luminosity of 100fb-1 at LHC, and considering a central value Mz' = 1500 GeV, we obtain the invariant mass distribution in the process pp → Z' → e+e-, where a huge peak, corresponding to 800 signal events, is found above the SM background. The number of di-electron events vary from 10000 to 1 in the mass range of Mz' = 1000 - 5000 GeV.

Search forZ′→e+e−Using Dielectron Mass and Angular Distribution

We search for Z' bosons in dielectron events produced in ppbar collisions at sqrt{s}=1.96 TeV, using a 0.45 fb^(-1) dataset accumulated with the CDF II detector at the Fermilab Tevatron. To identify the Z' --> e^+e^- signal, both the dielectron invariant mass distribution and the angular distribution of the electron pair are used. No evidence of a signal is found, and 95% confidence level lower limits are set on the Z' mass for several models. Limits are also placed on the mass and gauge coupling of a generic Z', as well as on the contact interaction mass scales for different helicity structure scenarios.

Multi-electron production at high transverse momenta in ep collisions at HERA

Multi-electron production is studied at high electron transverse momentum in positron- and electron-proton collisions using the H1 detector at HERA. The data correspond to an integrated luminosity of 115 pb(-1). Di-electron and tri-electron event yields are measured. Cross sections are derived in a restricted phase space region dominated by photon-photon collisions. In general good agreement is found with the Standard Model predictions. However, for electron pair invariant masses above 100 GeV, three di-electron events and three tri-electron events are observed, compared to Standard Model expectations of 0.30 +/- 0.04 and 0.23 +/- 0.04, respectively.

Measurement of theWboson mass using large rapidity electrons

\We present a measurement of the W boson mass using data collected by the DO experiment at the Fermilab Tevatron during 1994-1995. We identify W bosons by their decays to ev final states where the electron is detected in a forward calorimeter. We extract the W boson mass M-W by fitting the transverse mass and transverse electron and neutrino momentum spectra from a sample of 11 089 W-->e nu decay candidates. We use a sample of 1687 dielectron events, mostly due to Z-->ee decays, to constrain our model of the detector response. Using the forward calorimeter data, we measure M-w=80.691+/-0.227 GeV. Combining the forward calorimeter measurements with our previously published central calorimeter results, we obtain M-W= 80.482 +/-0.091 GeV.

Measurement of theWboson mass

This paper presents a measurement of the mass of the W boson using data collected with the CDF detector during the 1992--1993 collider run at the Fermilab Tevatron. A fit to the transverse mass spectrum of a sample of 3268 W\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu} events recorded in an integrated luminosity of 19.7 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ gives ${\mathit{M}}_{\mathit{W}}^{\mathrm{\ensuremath{\mu}}}$=80.310\ifmmode\pm\else\textpm\fi{}0.205 (stat)\ifmmode\pm\else\textpm\fi{}0.130 (syst) GeV/${\mathit{c}}^{2}$. A fit to the transverse mass spectrum of a sample of 5718 W\ensuremath{\rightarrow}e\ensuremath{\nu} events recorded in 18.2 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ gives ${\mathit{M}}_{\mathit{W}}^{\mathit{e}}$=80.490\ifmmode\pm\else\textpm\fi{}0.145 (stat)\ifmmode\pm\else\textpm\fi{}0.175 (syst) GeV/${\mathit{c}}^{2}$. Combining the muon and electron results, accounting for correlated uncertainties, yields ${\mathit{M}}_{\mathit{W}}$=80.410\ifmmode\pm\else\textpm\fi{}0.180 GeV/${\mathit{c}}^{2}$.

A Measurement of theWBoson Mass at the Fermilabpp¯Collider

We report a measurement of the W boson mass based on an integrated luminosity of 82 pb −1 from pp collisions at √s = 1.8 TeV recorded in 1994-1995 by the D0 detector at the Fermilab Tevatron. We identify W bosons by their decays to e∨ V and extract the mass by fitting the transverse mass spectrum from 28 323 W boson candidates. A sample of 3563 dielectron events, mostly due to Z→ee decays, constrains models of W boson production and the detector. We measure M W = 80.44±0.10(stat)±0.07(syst) GeV. By combining this measurement with our result form the 1992-1993 data set, we obtain M W = 80.43±0.11 GeV.

Sparticle and Higgs-boson production and detection at CERN LEP II in two supergravity models.

We study the most promising signals for supersymmetry at CERN LEP II in the context of two well-motivated supergravity models: (i) the minimal SU(5) supergravity model including the stringent constraints from proton stability and a not too young universe and (ii) a recently proposed string-inspired no-scale flipped SU(5) supergravity model. Our computations span the neutralino, chargino, slepton, and Higgs sectors together with their interconnections in this class of models. We find that the number of ``mixed'' (1-lepton+2-jets+p/) events occurring in the decay of pair-produced charginos (${\mathrm{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}$) is generally significant (per scrL=100 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$) for both models and that these predictions do not overlap. That is, if ${\mathit{m}}_{\mathrm{\ensuremath{\chi}}1}^{\ifmmode\pm\else\textpm\fi{}}$100 GeV then LEP II should be able to exclude at least one of the two models. In the no-scale flipped SU(5) model we find that the number of acoplanar dielectron events from selectron pair production should allow for exploration of selectron masses up to the kinematical limit and chargino masses indirectly as high as 150 GeV. We find that the cross section ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{Z}}^{\mathrm{*}}$h deviates negligibly from the SM result in the minimal model, whereas it can be as much as 1/3 lower in the flipped model. The usually neglected invisible mode h\ensuremath{\rightarrow}${\mathrm{\ensuremath{\chi}}}_{1}^{0}$${\mathrm{\ensuremath{\chi}}}_{1}^{0}$ can erode the preferred h\ensuremath{\rightarrow}2 jets signal by as much as 40% in these models. We conclude that the charged slepton sector is a deeper probe than the chargino, neutralino, or Higgs sectors of the flipped SU(5) model at LEP II, while the opposite is true for the minimal SU(5) model where the slepton sector is no probe at all.