Introduction Glasgow’s NPE research Group uses high precision electromagnetic probes to study the...
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Transcript of Introduction Glasgow’s NPE research Group uses high precision electromagnetic probes to study the...
Introduction
Glasgow’s NPE research Group uses high precision electromagnetic probes to study the subatomic structure of matter. Alongside this we are involved in the preparation of future experiments with electron, photon and antiproton beams.
Our work is best classified into four interdependent and overlapping physics themes (see Fig. 1). Within each of these themes, we make optimum use of the available experimental facilities throughout Europe and the USA by selecting the facility which best matches the physics requirements of each experiment. Each theme utilises multiple facilities to provide complementary data sets which combine to provide the maximum physics output.
Hadron Physics Highlights
Nucleon Resonance Spectroscopy
At the energy and distance scales typical of the nucleon, QCD is extremely challenging due to its non-perturbative nature. Nucleon resonance spectroscopy provides a key to unlocking this challenge. To disentangle the many overlapping resonances (Fig. 3) we measure differential cross sections and polarisation observables (Fig. 4) of π, η and K mesons. To achieve this we employ the JLab CLAS and MAMI A2 (Fig. 2) facilities, which are ideally suited to our requirements for large acceptance detector systems and polarised beams and targets.
New Forms of Hadronic Matter
We commonly observe baryons, such as the nucleon, with three valence quarks and mesons, such as the pion, which contain a quark-antiquark pair. However, the theory of Quantum ChromoDynamics (QCD) allows any state that is colour neutral. To test this theory, we should search for other colour-neutral states which are predicted to exist but remain unobserved e.g. Glueballs and hybrids.
The photon is an ideal source of energy for the excitation of exotic waves due to it’s spin and parity. This technique will be exploited to produce hybrids at:
Short Range Nuclear Structure
Concentration of strongly interacting matter inside the nucleus may lead to changes in the properties of hadronic matter. We will study variation in:
The structure of the nucleon still poses significant questions:
What is the origin of its mass? The current quark mass accounts for approximately 2% of the nucleon mass, the remaining 98% is generated dynamically via strong interactions described by QCD.
What is the origin of the spin of the nucleon? In most accurate measurement to date, HERMES found that the quark spins contribute only 33% of the spin of the nucleon. What is the origin of the remaining 67%?
Figure 1: Themes, Laboratories and Collaborations
Figure 3: Meson photo-production from the proton
Figure 7: Diagrams of known and new forms of hadronic matter.
JLab HyCLAS JLab GlueX
To produce Glueballs, it is necessary to provide a gluon rich environment and this is ideally provided by proton-antiproton annihilation at PANDA
MAMI Highlights
Electromagnetic moments of baryon resonances
Elusive basic parameters of the P11(1440) resonance
First complete measurement of pseudoscalar meson photoproduction giving unambiguous decomposition of the resonance spectrum in π and η photoproduction
Figure 2: CB@MAMI detector setup in MAMI A2
JLab CLAS Highlights
Access to new resonances via polarisation observables in strangeness photoproduction
First complete measurements of strangeness photoproduction allowing unambiguous determination of the resonance spectrum in KΛ and K channels Figure 4: Strangeness polarisation
observables from JLab CLAS
Nucleon Structure
Crystal Ball, 672 NaI elements
TAPS, 512 BaF2 elements Glasgow PhotonTagging Spectrometer
5x106 γ/secGPDs
Nucleon elastic form factorPioneering measurements in MAMI A1, double polarisation JLab Hall A results challenge
nucleon structure models
Generalised Parton Distributions describe
the 3D structure of the nucleon
Hard exclusive meson productionAnalysis experience from HERMES
will be used in new CLAS experiments
Deeply Virtual Compton Scattering (DVCS)Production of real photon in electron scattering
from an individual quark in the nucleon. Pioneering HERMES expertise transferred to
measurements at CLAS 12 & PANDA
Parton Distribution Functions (PDF)PDFs measured at HERMES form
input for GPDs
Wide Angle Compton ScatteringPolarised Compton Scattering in
JLab Hall A provide first high precision measurements in the
few GeV range.
Figure 6: Recent DVCS results showing limits on
the total angular momentum of the up (Ju)
and down (Jd) quark. Neutron data from Hall A,
proton data from HERMES.
Charge distribution within the proton (JLab Hall A)
Nucleon polarisibilities (JLab Hall A)
Mass of the pion-pion (σ) system (MAMI A2)
Mass of the Ω meson
within the nuclear medium.
Meson exchange models do not describe the nucleon-nucleon interaction at short range properly. Two-nucleon- knockout reactions at MAMI A1, A2 and JLab Hall A provide input for nucleon-nucleon correlation based approaches.
Figure 5: Short range nucleon interaction