arXiv subjects

M. Nozar

Publications and source records attributed to M. Nozar.

7 recordsLinked to original sources

arXiv2016

Measurements of the Separated Longitudinal Structure Function F_L from Hydrogen and Deuterium Targets at Low Q^2

Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the quark dynamics within the nucleon. However, it is experimentally difficult to separately determine the longitudinal and transverse structure functions, and consequently there are substantially less data available for the longitudinal structure function in particular. Here we present separated structure functions for hydrogen and deuterium at low four--momentum transfer squared, Q^2< 1 GeV^2, and compare these with parton distribution parameterizations and a k_T factorization approach. While differences are found, the parameterizations generally agree with the data even at the very low Q^2 scale of the data. The deuterium data show a smaller longitudinal structure function, and smaller ratio of longitudinal to transverse cross section R, than the proton. This suggests either an unexpected difference in R for the proton and neutron or a suppression of the gluonic distribution in nuclei.

nucl-ex↗

arXiv2008

A Precision Measurement of the Muon Decay Parameters $ρ$ and $δ$

The TWIST collaboration has performed new measurements of two of the parameters that describe muon decay: $ρ$, which governs the shape of the overall momentum spectrum, and $δ$, which governs the momentum dependence of the parity-violating decay asymmetry. This analysis gives the results $ρ=0.75014\pm 0.00017(\text{stat})\pm 0.00044(\text{syst})\pm 0.00011(η)$, where the last uncertainty arises from the correlation between $ρ$ and the decay parameter $η$, and $δ= 0.75067\pm 0.00030(\text{stat})\pm 0.00067(\text{syst})$. These are consistent with the value of 3/4 given for both parameters in the Standard Model of particle physics, and are a factor of two more precise than the measurements previously published by TWIST. A new global analysis of all available muon decay data incorporating these results is presented. Improved lower and upper limits on the decay parameter $P_μ^πξ$ of $0.99524 < P_μ^πξ\leq ξ< 1.00091$ at 90% confidence are determined, where $P_μ^π$ is the polarization of the muon when it is created during pion decay, and $ξ$ governs the muon decay asymmetry. These results set new model-independent constraints on the possible weak interactions of right-handed particles. Specific implications for left-right symmetric models are discussed.

hep-ex↗

arXiv2008

Search for the photo-excitation of exotic mesons in the pi+pi+pi- system

A search for exotic mesons in the $π^{+}π^{+}π^{-}$ system photoproduced by the charge exchange reaction $γp\to π^{+}π^{+}π^{-}(n)$ was carried out by the CLAS collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A Partial Wave Analysis (PWA) was performed on a sample of 83,000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the photoproduction of an exotic $J^{PC} = 1^{-+}$ resonant state in the 1 to 2 GeV mass range. Our PWA analysis, based on the isobar model, shows production of the $a_{2}(1320)$ and the $π_{2}(1670)$ mesons, but no evidence for the $a_{1}(1260)$, nor the $π_{1}(1600)$ exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic $π_1(1600)$ cross section, less than 2% of the $a_2(1320)$ production.

hep-ex↗

arXiv2007

Confirmation of a pi_1^0 Exotic Meson in the ηπ^0 System

The exclusive reaction $π^- p \to ηπ^0 n$, $η\to π^+ π^- π^0$ at 18 GeV$/c$ has been studied with a partial wave analysis on a sample of 23~492 $ηπ^0 n$ events from BNL experiment E852. A mass-dependent fit is consistent with a resonant hypothesis for the $P_+$ wave, thus providing evidence for a neutral exotic meson with $J^{PC} = 1^{-+}$, a mass of $1257 \pm 20 \pm 25$ MeV$/c^2$, and a width of $354 \pm 64 \pm 60$ MeV$/c^2$. New interpretations of the meson exotics in neutral $ηπ^0$ system observed in E852 and Crystal Barrel experiments are discussed.

hep-ex↗

arXiv2006

Measurement of P_{mu}xi in Polarized Muon Decay

The quantity P_{mu}^{pi}xi, where xi is one of the muon decay parameters and $P_μ^π$ is the degree of muon polarization in pion decay, has been measured. The value P_{mu}^{pi}xi = 1.0003 +- 0.0006 stat. +- 0.0038 syst. was obtained. This result agrees with previous measurements but is over a factor of two more precise. It also agrees with the Standard Model prediction for P_{mu}^{pi}xi and thus leads to restrictions on left-right symmetric models.

hep-ex↗

arXiv2005

Measurement of the Muon Decay Parameter delta

The muon decay parameter delta has been measured by the TWIST collaboration. We find delta = 0.74964 +- 0.00066(stat.) +- 0.00112(syst.), consistent with the Standard Model value of 3/4. This result implies that the product Pmuxi of the muon polarization in pion decay, Pmu, and the muon decay parameter xi falls within the 90% confidence interval 0.9960 < Pmuxi < xi < 1.0040. It also has implications for left-right-symmetric and other extensions of the Standard Model.

hep-ex↗

arXiv1995

Search for Exotic Mesons in pi- P Interactions at 18 GeV/c

The recent search for non $q \bar{q}$ mesons in $π^{-}p$ interactions at Brookhaven National Laboratory is summarized. Many final states such as $ηπ$, $η' π^{-}$, $a_{0} π$, $f_{1} π$, $a_{2} π$, $b_{1} π$, which are favored decay modes of exotics, are under investigation.

hep-ex↗