Search results for "PARTICLE PHYSICS"
showing 10 items of 6826 documents
Search for Gluino-Mediated Bottom Squark Production inpp¯Collisions ats=1.96 TeV
2009
We report on a search for the supersymmetric partner of the bottom quark produced from gluino decays in data from 2.5 fb{sup -1} of integrated luminosity collected by the Collider Detector at Fermilab at {radical}s = 1.96 TeV. Candidate events are selected requiring two or more jets and large missing transverse energy. At least two of the jets are required to be tagged as originating from a b quark to enhance the sensitivity. The results are in good agreement with the prediction of the standard model processes, giving no evidence for gluino decay to sbottom quarks. This result constrains the gluino-pair-production cross section to be less than 40 fb at 95% credibility level for a gluino mas…
TRANSVERSE MOMENTUM-DEPENDENT PARTON DISTRIBUTIONS FROM LATTICE QCD
2012
Starting from a definition of transverse momentum-dependent parton distributions for semi-inclusive deep inelastic scattering and the Drell-Yan process, given in terms of matrix elements of a quark bilocal operator containing a staple-shaped Wilson connection, a scheme to determine such observables in lattice QCD is developed and explored. Parametrizing the aforementioned matrix elements in terms of invariant amplitudes permits a simple transformation of the problem to a Lorentz frame suited for the lattice calculation. Results for the Sivers and Boer-Mulders transverse momentum shifts are presented, focusing in particular on their dependence on the staple extent and the Collins-Soper evol…
Comment On The Lepton Mixing Matrix
1980
The problem of finding a suitable parametrization for a nontrivial lepton mixing matrix is considered in the framework of the ''sequential'' Weinberg-Salam theory. It is noted that in the case of n lepton generations there are in fact n+1 different theories, corresponding to different numbers m of right-handed neutrino fields present in the Lagrangian. These (n,m) models conserve CP for leptonic couplings naturally only for m=0 or 1 when n > or = 3. These models would seem to be useful as self-consistent approximations for reducing the number of parameters in the experimental analysis of lepton mixing matrices.
Instanton induced quark dynamics and the pentaquark
2004
We analyze the existence of the exotic $\Theta^+$ from the perspective of instanton induced quark dynamics. The 't Hooft interaction gives strong attraction in specific channels of the triquark $ud\bar s$ and diquark $ud$ configurations. In particular it leads to a light $ud\bar s$ triquark cluster, with the mass around $750 {\rm MeV}$, in the I=0, $S=1/2$ and color 3 configuration, and a light $ud$-diquark configuration, with mass $440 {\rm MeV}$, in the I=0, S=0 and color {$\bar{3}$} configuration. If we consider the pentaquark as a bound state of such triquark and diquark configurations in a relative L=1 state we obtain good agreement with the data. The small width of $\Theta^+$ has a na…
Search for New Phenomena intt¯Events with Large Missing Transverse Momentum in Proton-Proton Collisions ats=7 TeVwith the ATLAS Detector
2012
A search for new phenomena in tt events with large missing transverse momentum in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1.04 fb-1 of data collected with the ATLAS detector at the LHC. Contributions to this final state may arise from a number of standard model extensions. The results are interpreted in terms of a model where new top-quark partners are pair produced and each decay to an on-shell top (or antitop) quark and a long-lived undetected neutral particle. The data are found to be consistent with standard model expectations. A limit at 95% confidence level is set excluding a cross section times branching ratio of 1.1 pb …
Combination of the Searches for Pair-Produced Vectorlike Partners of the Third-Generation Quarks at s=13 TeV with the ATLAS Detector
2018
A combination of the searches for pair-produced vectorlike partners of the top and bottom quarks in various decay channels (T -> Zt/Wb/Ht, B -> Zb/Wt/Hb) is performed using 36.1 fb(-1) of pp ...
Search for Scalar Charm Quark Pair Production inppCollisions ats=8 TeVwith the ATLAS Detector
2015
The results of a dedicated search for pair production of scalar partners of charm quarks are reported. The search is based on an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV recorded with the ATLAS detector at the LHC. The search is performed using events with large missing transverse momentum and at least two jets, where the two leading jets are each tagged as originating from c quarks. Events containing isolated electrons or muons are vetoed. In an R-parity-conserving minimal super-symmetric scenario in which a single scalar-charm state is kinematically accessible, and where it decays exclusively into a charm quark and a neutralino, 95% confidence-level upper li…
A search for quarks in the CERN SPS neutrino beam
1978
Quarks and leptons are the only pointlike particles known so far. However, a search for a proton-breaking mechanism in high-energy neutrino-nucleon interactions had never been performed. We present here the results of the first experiment in this field.
Open-charm production measurements in pp, 1 p-Pb and Pb-Pb collisions with ALICE at the LHC
2017
ALICE (A Large Ion Collider Experiment) is designed to study the strongly in teracting matter, the Quark-Gluon Plasma (QGP), created in heavy-ion collisions at LHC energies. Charm and beauty quarks are powerful probes to study the QGP. Produced in hard partonic scattering processes on a short time scale, they are expected to traverse the QCD medium, interacting with its constituents and losing energy through radiative and collisional processes. In ALICE, open-charm production is studied through the reconstruction of the hadronic decays of D 0 , D + , D *+ and D s + mesons at mid-rapidity. High precision tracking, good vertexing capabilities and excellent particle identification offered by A…
Constraints for the nuclear sea quark distributions from the Drell–Yan process at the SPS
2000
Nuclear modifications to the Drell-Yan dilepton production cross sections in p+A and A+A collisions in the leading twist approximation are caused by nuclear effects in the parton distributions of bound nucleons. For non-isoscalar nuclei, isospin corrections must also be considered. We calculate these effects for p+A and Pb+Pb collisions at CERN SPS energies. Our goal is to place constraints on nuclear effects in sea quark distributions in the region x > 0.2. We show that the net nuclear corrections remain small for p+A collisions at E_lab=450 GeV. However, in Pb+Pb collisions at E_lab=158 AGeV, effects of > 20% are predicted at large M. The data collected by the NA50 collaboration cou…