We improve the theoretical predictions for the production of extra neutral gauge bosons at hadron colliders by implementing the
Z
′
-bosons in the MC@NLO generator and by computing their differential ...and total cross sections in joint
p
T
and threshold resummation. The two improved predictions are found to be in excellent agreement with each other for mass spectra,
p
T
spectra, and total cross sections, while the PYTHIA parton and “power” shower predictions usually employed for experimental analyses show significant shortcomings both in normalization and shape. The theoretical uncertainties from scale and parton density variations and non-perturbative effects are found to be
+
6
/
−
3
%
,
+
/
−
5
%
, and less than
+
3
/
−
6
%
, respectively, and thus under good control. The implementation of our improved predictions in terms of the new MC@NLO generator or resummed
K factors in the analysis chains of the Tevatron and LHC experiments should be straightforward and lead to more precise determinations or limits of the
Z
′
-boson masses and/or couplings.
A module of the ATLAS electromagnetic barrel liquid argon calorimeter was exposed to the CERN electron test-beam at the H8 beam line upgraded for precision momentum measurement. The available ...energies of the electron beam ranged from 10 to 245
GeV. The electron beam impinged at one point corresponding to a pseudo-rapidity of
η
=
0.687
and an azimuthal angle of
φ
=
0.28
in the ATLAS coordinate system. A detailed study of several effects biasing the electron energy measurement allowed an energy reconstruction procedure to be developed that ensures a good linearity and a good resolution. Use is made of detailed Monte Carlo simulations based on GEANT4 which describe the longitudinal and transverse shower profiles as well as the energy distributions. For electron energies between 15 and 180
GeV the deviation of the measured incident electron energy over the beam energy is within 0.1%. The systematic uncertainty of the measurement is about 0.1% at low energies and negligible at high energies. The energy resolution is found to be about 10%
·
E
for the sampling term and about 0.2% for the local constant term.
The DELPHI pixels Becks, K.H.; Borghi, P.; Brunet, J.M. ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
02/1997, Letnik:
386, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
To improve tracking in the very forward direction for running at LEP200, the angular acceptance of the DELPHI Vertex detector has been extended from 45° to 11° with respect to the beam axis. Pixel ...detector crowns cover the region between 25° and 13°. Due to very tight space and material thickness constraints it was necessary to develop new techniques (integrated busses in the detector substrate, high density layout on Kapton, etc.). About 1000 cm
2 of pixels are already installed and working in DELPHI. Techniques, tests and production of these detectors will be described, as well as the main problems encountered during this work.
A measurement of the $ZZ$ production in the $\ell^{-}\ell^{+}\ell^{\prime -}\ell^{\prime +}$ and $\ell^{-}\ell^{+}\nu\bar{\nu}$ channels $(\ell = e, \mu)$ in proton--proton collisions at $\sqrt{s} = ...8$ TeV at the Large Hadron Collider at CERN, using data corresponding to an integrated luminosity of 20.3 fb$^{-1}$ collected by the ATLAS experiment in 2012 is presented. The fiducial cross sections for $ZZ\to\ell^{-}\ell^{+}\ell^{\prime -}\ell^{\prime +}$ and $ZZ\to \ell^{-}\ell^{+}\nu\bar{\nu}$ are measured in selected phase-space regions. The total cross section for $ZZ$ events produced with both $Z$ bosons in the mass range 66 to 116 GeV is measured from the combination of the two channels to be $7.3\pm0.4\textrm{(stat)}\pm0.3\textrm{(syst)}\pm0.2\textrm{(lumi)}$ pb, which is consistent with the Standard Model prediction of $6.6^{+0.7}_{-0.6}$ pb. The differential cross sections in bins of various kinematic variables are presented. The differential event yield as a function of the transverse momentum of the leading $Z$ boson is used to set limits on anomalous neutral triple gauge boson couplings in $ZZ$ production.
Commissioning of the DELPHI Pixel Detector Becks, K.H; Brunet, J.M; Caccia, M ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
1998, Letnik:
418, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
The DELPHI Vertex Detector has been upgraded for LEP200 with 2 layers of pixel detectors and 2 layers of ministrips as endcaps, thus covering the polar angular range between 10° and 21° and allowing ...for standalone pattern recognition. During the 1995/96 shutdown the first 95 modules were installed and the installation was completed in May 97 with all 152 modules. Production yields and failures during the assembly will be presented. The detector operated at a threshold of around 9000 electrons resulting in a number of noisy pixels at the 10
−3 level. After masking these hot pixels in the readout, the remaining number of random hits per event is at the 10
−6 level. The observed resolution of about 100
μm is close to the expectation for binary readout. The track reconstruction efficiency increased by more than 100% in the central part of the forward tracker.
Two searches for new phenomena in final states containing a same-flavour opposite-lepton (electron or muon) pair, jets, and large missing transverse momentum are presented. These searches make use of ...proton--proton collision data, collected during 2015 and 2016 at a centre-of-mass energy $\sqrt{s}=13$ TeV by the ATLAS detector at the Large Hadron Collider, which correspond to an integrated luminosity of 14.7 fb$^{-1}$. Both searches target the pair production of supersymmetric particles, squarks or gluinos, which decay to final states containing a same-flavour opposite-sign lepton pair via one of two mechanisms: a leptonically decaying Z boson in the final state, leading to a peak in the dilepton invariant-mass distribution around the Z boson mass; and decays of neutralinos (e.g. $\tilde{\chi}_2^0 \rightarrow \ell^+\ell^- \tilde{\chi}_1^0$), yielding a kinematic endpoint in the dilepton invariant-mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted in simplified models of gluino-pair (squark-pair) production, and provide sensitivity to gluinos (squarks) with masses as large as 1.70 TeV (980 GeV).
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