Search results for "Muon"

2017

Abstract Exclusive production of ω mesons was studied at the COMPASS experiment by scattering 160 GeV / c muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured in the range of photon virtuality 1 ( GeV / c ) 2 Q 2 10 ( GeV / c ) 2 , Bjorken scaling variable 0.003 x Bj 0.3 and transverse momentum squared of the ω meson 0.05 ( GeV / c ) 2 p T 2 0.5 ( GeV / c ) 2 . The measured asymmetries are sensitive to the nucleon helicity-flip Generalised Parton Distributions (GPD) E that are related to the orbital angular momentum of quarks, the chiral-odd GPDs H T that are related to the transversity Parton Distribution Functions, and the si…

Search for single production of scalar leptoquarks in pp¯ collisions decaying into muons and quarks with the D0 detector

2007

We report on a search for second generation leptoquarks LQ_2 which decay into a muon plus quark in p\bar{p} collisions at a center-of-mass energy of sqrt{s} = 1.96 TeV in the D0 detector using an integrated luminosity of about 300 pb-1. No evidence for a leptoquark signal is observed and an upper bound on the product of the cross section for single leptoquark production times branching fraction beta into a quark and a muon was determined for second generation scalar leptoquarks as a function of the leptoquark mass. This result has been combined with a previously published D0 search for leptoquark pair production to obtain leptoquark mass limits as a function of the leptoquark-muon-quark cou…

Elliptic flow of muons from heavy-flavour hadron decays at forward rapidity in Pb–Pb collisions at sNN=2.76 TeV

2016

The elliptic flow, $v_{2}$, of muons from heavy-flavour hadron decays at forward rapidity ($2.5 < y < 4$) is measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}}$~=~2.76 TeV with the ALICE detector at the LHC. The scalar product, two- and four-particle $Q$ cumulants and Lee-Yang zeros methods are used. The dependence of the $v_2$ of muons from heavy-flavour hadron decays on the collision centrality, in the range 0--40\%, and on transverse momentum, $p_{\rm T}$, is studied in the interval $3 < p_{\rm T} < 10$~GeV/$c$. A positive $v_2$ is observed with the scalar product and two-particle $Q$ cumulants in semi-central collisions (10--20\% and 20--40\% centrality classes) for the $p_{\rm T}$ int…

Search for pair production of the scalar top quark in the electron-muon final state

2010

We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ($\tilde{t}_1$) in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The scalar top quarks are assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tilde{\nu}$), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected, and improved exclusion limits at the 95% C.L. are set in the the ($M_{\tilde{t}_1}$,$M_{\tilde{\nu}}$) mass plane.

Exclusive ω meson production at COMPASS

2016

Exclusive ω meson production is studied by the COMPASS Collaboration using the CERN 160 GeV/ c muon beam and a transversely polarised proton target. Single-spin and double-spin asymmetries are measured, some of which are sensitive to the Generalised Parton Distributions E that are related to quark orbital angular momenta. The results, which are sensitive also to the pion-pole contribution to the production mechanism, are compared to the predictions of a phenomenological model.

A dynamical mechanism for quark mixing and neutrino oscillations

1999

We show that assuming fermion generations to be given by a gauge symmetry plus a certain Higgs mechanism for its breaking, the known empirical features of quark and lepton mixing can be largely explained, including in particular the fact that the mixing (CKM) matrix element $U_{\mu3}$ responsible for the muon anomaly in atmospheric neutrinos is near maximal and much larger than their quark counterparts $V_{cb}$ and $ V_{ts}$, while the corner elements for both quarks ($V_{ub}, V_{td}$) and leptons ($U_{e3}$) are all very small. The mechanism also gives automatically a hierarchical fermion mass spectrum which is intimately related to the mixing pattern.

A Measurement of the Bbbar Forward-backward Asymmetry Using the Semileptonic Decay Into Muons

1992

Nuclear structure with radioactive muonic atoms

2018

Muonic atoms have been used to extract the most accurate nuclear charge radii based on the detection of X-rays from the muonic cascades. Most stable and a few unstable isotopes have been investigated with muonic atom spectroscopy techniques. A new research project recently started at the Paul Scherrer Institut aims to extend the highresolution muonic atom spectroscopy for the precise determination of nuclear charge radii and other nuclear structure properties of radioactive isotopes. The challenge to combine the high-energy muon beam with small quantity of stopping mass is being addressed by developing the concept of stopping the muon in a high-density, a high-pressure hydrogen cell and sub…

Precision measurement of structure function ratios for $^{6}$Li, $^{12}$C and $^{40}$Ca

1992

The structure function ratiosF2C/F2Li,F2Ca/F2Li andF2Ca/F2C were measured in deep inelastic muonnucleus scattering at an incident muon energy of 90 GeV, covering the kinematic range 0.0085<x<0.6 and 0.8<Q2<17GeV2. The sensitivity of the nuclear structure functions to the size and mean density of the target nucleus is discussed.

Laser spectroscopy of light muonic atoms and the nuclear charge radii

2021

The energy levels of hydrogen-like atomic systems are shifted slightly by the complex structure of the nucleus, in particular by the finite size of the nucleus. These energy shifts are vastly magnified in muonic atoms and ions, i.e. the hydrogen-like systems formed by a negative muon and a nucleus. By measuring the 2S-2P energy splitting in muonic hydrogen, muonic deuterium and muonic helium, we have been able to deduce the p, d, ^33He and ^44He nuclear charge radii to an unprecedented accuracy. These radii provide benchmarks for hadron and nuclear theories, lead to precision tests of bound-state QED in regular atoms and to a better determination of the Rydberg constant.