Engineering topics

Riordan, Seamus

Publications and source records attributed to Riordan, Seamus.

6 records

DOE OSTI2018

The P2 experiment: A future high-precision measurement of the weak mixing angle at low momentum transfer

Here we describe the research and development work for the P 2 experiment which aims for a high precision determination of the weak mixing angle sin 2 θ W to a precision of 0.15% at a four-momentum transfer of 4.5×10 –3 GeV 2 . This accuracy, comparable to existing measurements at the Z pole, allows for a sensitive test of the Standard Model up to a mass scale of 50 TeV, extendable to 60 TeV. The weak mixing angle is connected to the weak charge of the proton which will be extracted from a measurement of the parity violating cross section asymmetry –39.94×10 –9 in elastic electron-proton scattering. A total accuracy of 0.57×10 –9 is achievable in a measurement time of 11000 h using a 150μA polarized electron beam impinging on a 60 cm liquid hydrogen target. The P 2 asymmetry is smaller than any asymmetry measured so far in electron scattering with an unprecedented goal for the accuracy. The use of a solenoid spectrometer with 100% Φ-acceptance as well as an atomic hydrogen trap polarimeter are new features, which have never before been used in parity-violation experiments. In order to collect the enormous statistics required for this measurement, the new Mainz Energy-Recovering Superconducting Accelerator (MESA) is under construction. Plans for the associated beam control system and the polarimetry are described in this article as well. A liquid hydrogen high-power target with an extremely low noise level of 10 ppm needs to be designed and constructed. We report in addition on the conceptual design of the P 2 spectrometer, its Cherenkov detectors, the integrating read-out electronics as well as the ultra-thin, fast tracking detectors. The physics program of the MESA facility comprises indirect, high precision search for physics beyond the Standard Model, measurement of the neutron distribution in nuclear physics, single-spin asymmetries, and a possible future extension to the measurement of hadronic parity violation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Weak Neutral Current Studies with Positrons

Weak neutral current interactions with charged leptons have offered unique opportunities to study novel aspects of hadronic structure and search for physics beyond the standard model. These studies in the medium energy community have been primarily through parity-violating processes with electron beams, but with the possibility of polarized positron beams, new and complementary observables can be considered in experiments analogous to their electron counterparts. Such studies include elastic proton, deep inelastic, and electron target scattering. Potential positron neutral current experiments along with their potential physics reach, requirements, and feasibility are presented.

Riordan, Seamus↗

DOE OSTI2014

Precision Measurement of the Neutron Twist-3 Matrix Element dn2: Probing Color Forces

Double-spin asymmetries and absolute cross sections were measured at large Bjorken x (0.25 lte x lte 0.90), in both the deep-inelastic and resonance regions, by scattering longitudinally polarized electrons at beam energies of 4.7 and 5.9 GeV from a transversely and longitudinally polarized 3He target. In this dedicated experiment, the spin structure function g2 on 3He was determined with precision at large x, and the neutron twist-three matrix element dn2 was measured at ?Q2? of 3.21 and 4.32 GeV2/c2, with an absolute precision of about 10?5. Our results are found to be in agreement with lattice QCD calculations and resolve the disagreement found with previous data at ?Q2?= 5 GeV2/c2. Combining dn2 and a newly extracted twist-four matrix element, fn2, the average neutron color electric and magnetic forces were extracted and found to be of opposite sign and about 60 MeV/fm in magnitude.

Posik, Matthew↗

DOE OSTI2014

Probing the Repulsive Core of the Nucleon-Nucleon Interaction via the 4 He(e,e`pN) Triple-Coincidence Reaction

We studied simultaneously the 4 He(e,e'p), 4 He(e,e'pp), and 4 He(e,e'pn) reactions at Q 2 =2 [GeV/c] 2 and x B >1, for a (e,e'p) missing-momentum range of 400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A=2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum in a region where the nucleon-nucleon force is expected to change from predominantly tensor to repulsive. Neutron-proton pairs dominate the high-momentum tail of the nucleon momentum distributions, but their abundance is reduced as the nucleon momentum increases beyond ~500 MeV/c. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum in the range we studied. Our data are compared with ab-initio calculations of two-nucleon momentum distributions in 4 He.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2012

Parity-violating deep inelastic scattering with SoLID at Jefferson Lab

Deep inelastic electron scattering has been an invaluable tool in understanding the internal structure of the nucleon and has provided motivation for the standard model of quarks and the concept of asymptotic freedom. When coupled with parity-violating measurements through the interference of a virtual photon and weakly interacting Z boson, new linear combinations of quarks are probed which can provide information which is complementary to the standard electromagnetic interactions. Precision measurements on deuterium allows for novel tests of the standard model, possible observations of quark-level charge symmetry violation, and the study of specific higher-twist effects. Additionally, measurements on a proton target can provide a precise extraction of the parton ratio $d/u$ as the Bjorken scaling variable $x \rightarrow 1$. Presented will be an approved experimental program at Thomas Jefferson National Accelerator Facility using the Solenoidal Large Intensity Device (SoLID) to study parity-violating deep inelastic scattering.

Riordan, Seamus↗

DOE OSTI2012

Measurement of the Neutron Radius of 208 Pb Through Parity-Violation in Electron Scattering

We report the first measurement of the parity-violating asymmetry A PV in the elastic scattering of polarized electrons from 208 Pb. A PV is sensitive to the radius of the neutron distribution (R n ). The result A PV = 0.656 ± 0.060 (stat) ± 0.013 (syst) corresponds to a difference between the radii of the neutron and proton distributions R n -R p = 0.33 -0.18 +0.16 fm and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗