Masses, Forces, Higgs and Gluons Elton S. Smith, Jefferson Lab Constituents and forces Electromagnetic + weak interaction Color forces between quarks Why is the glue interesting

All the mass is contained in the small nucleus Components of an atom Atom contains negative electrons positive protons neutral neutrons All the mass is contained in the small nucleus

Elementary constituents charge p The Standard Model +1 u d +2/3 −1/3 charge e- −1 n electron neutrino d u +2/3 −1/3 n And all their anti-particles Quarks are confined inside the proton and neutron

Forces and force carriers p e The electrons are bound to atoms by the electromagnetic force g p e But there are two other forces at play in the atomic nucleus the “color force” keeps the quarks bound inside nucleons (more later) “Weak” -decays change neutron into a proton and emit an electron d n u d u e g W± u d

Differences: electromagnetic and weak forces p e Electromagnetic force One carrier Charge = 0 Mass = 0 Weak force n p e W± Two carriers Charge = +1 and -1 Mass = heavy

Similarities: electromagnetic and weak forces p e Electromagnetic n p e W± Weak interactions The weak force behaves just like the electromagnetic force at high energies The connection is found in a symmetry of nature

Symmetries and conservation laws Symmetry Conservation translation momentum time invariance energy rotations angular momentum Gauge symmetry charge The E&M force obeys a U(1) Gauge symmetry

“Massive” gauge symmetry Gauge symmetry and the conservation of charge is intimately related to the fact that the mass of the photon is zero. Theory of massless particles satisfying Gauge Symmetry + New particle (Higgs Particle) = Interactions of massive particles Portrait of Peter Higgs by Ken Currie

Unification: gauge symmetry for weak forces To put the electromagnetic and weak forces on the same footing, we assume the weak force has SU(2) Gauge symmetry, This symmetry requires a neutral force carrier (or gauge boson), call it the Z0 CM energy (GeV) s (nb) ~ 1990 But to make the force carriers massive, the Higgs boson was still missing until...

Discovery of Higgs Particle Higgs particle decays to two jets and e+ e- pair (and many other particles) On July 4, 2012, CMS and ATLAS experiments at CERN announce evidence for the Higgs boson at a mass of 126 GeV Mechanism for generation of quark masses is confirmed

Carriers of the force between quarks d g Color force Quantum Chromodynamics (QCD) Gluons are massless, so why is the interaction short range?

Asymptotic Freedom The 2004 Nobel Prize was awarded for work that lead to our understanding of the theory of one of Nature's fundamental forces, the force that ties together the smallest pieces of matter – the quarks.

Strong coupling constant as vs energy Confinement Asymptotic Freedom Large distance small distance Coupling constant Energy (GeV)

Electromagnetic and color forces +/- charges g 3 “color” charges

Mass without mass Mass of u quark ~ 0.003 GeV Mass of d quark ~ 0.005 GeV Mass of the proton ~ 1 GeV p u d +2/3 −1/3 d u +2/3 −1/3 Most of the mass of the proton and neutron comes from the energy stored in the gluon fields that bind the quarks inside. n Note that 99% of the mass of ordinary matter is in the form of protons and neutrons

But... signs of gluons are hard to find Puzzle Essentially all properties of protons, neutrons and mesons are described by quarks alone. q mesons Passive gluons Our investigations aim and understanding the nature of gluonic fields inside these particles glueball meson hybrid meson q Search for states that must exist Active gluons

JPC quantum numbers for normal mesons Families of particles with definite JPC are generated by taking combinations of the 3 lightest quarks (u,d,s and u,d,s) K+ p− K− p+ p0 h’ h K0 L q q JPC = 0– + 0++ 1– – 1+ – 2++ … Allowed combinations JPC = 0– – 0+ – 1– + 2+ – … Not-allowed: exotic

QCD calculations on the lattice Calculations in QED are perturbative expansions in the (small) coupling constant a At high energies, QCD calculations be performed by expanding in the (small) coupling constant as At low energies, calculations in QCD are extremely challenging and are computed at discrete points on a space-time grid (lattice) to avoid singularities. The coupling constant as as can be arbitrarily large.

Meson Spectroscopy from LQCD exotics normal mesons Isovector mesons, mp~700 MeV Dudek PRD 83 (2011) 111502 Dudek PRD 84 (2011) 074023

Search for QCD exotics 1 1 ’1 b2 h2 h’2 b0 h0 h’0 1−+ 2+− 0+− Mass scale ~ 2 GeV h1 → a+1p- → (o+)(-) → +-+- h0 → bo1po → (o)gg → +-gggggg h’2 → K+1K− → o K+ K− → +−K+K− all charged many photons strange particles The GlueX Detector Design has been driven by the need to carry out Amplitude analysis.  p X ,K,g n,p

Areal view of accelerator

Photon beam and experimental area Tagger area Hall D North linac Electron Beam dump Top View 75 m Tagger Area Experimental Hall D Electron beam Coherent Bremsstrahlung photon beam Solenoid- Based detector Collimator Photon Beam dump Counting House Radiator East arc

Pb-glass detector (Fcal) Superconducting 2 T solenoid Hall D – GlueX detector Pb-glass detector (Fcal) Time- of-flight (tof) Hermetic detection of charged and neutral particles in solenoid magnet Barrel Calorimeter (Bcal) Target (LH2) Initial Flux 107 g/s 18,000 FADCs 4,000 pipeline TDCs 20 KHz L1 trigger 300 MB/s to tape Tagger Spectrometer (Upstream) Tracking Cathode strips Drift chambers Straw tubes Superconducting 2 T solenoid

“typical” gp 2p+2p- p

Detector status

Summary The symmetry of electro-weak interactions is responsible for the masses of quarks through their coupling to the Higgs particle. But most of the mass of protons and neutrons comes from gluonic fields, not quarks The gluonic fields are poorly understood The GlueX experiment at Jefferson Lab is being built in the new Hall D to search for new particle states that have clear signatures of gluonic excitations.