Fractional Charged Particle, Magnetic Monopole and Dark Photon

1. Fractional Charged Particle, Magnetic Monopole and Dark Photon Zhengguo Zhao University of Science and Technology of China (USTC) TD Lee Institute, Shanghai, 5/31/2019

2. Outline • Introduction - Key questions to the SM - Forthcoming discoveries • Fractional Charged Particle (FCP) • Magnetic MonoPole (MMP) • Dark Photon(DP) • Summary - Theoretical consideration - Sources and searches - Current results

3. Key Questions to the Standard Model • Cosmology: • Unable to explain matter anti-matter asymmetry. • Not account for the accelerating expansion of the universe (dark energy), no prediction power for dark matter candidates. • Force and unification: • Does not incorporate the full theory of gravity. • No answer to the origin of electroweak symmetry breaking. • No solution to hierarchy problem. • Particle properties: • Does not incorporate neutrino oscillation and their masses. • Does not explain electric charge quantization. Expect for new physics beyond SM

4. Forthcoming Discoveries in Particle Physics

5. Fractional Charged Particles Annu. Rev. Nucl. Part. Sci. 2009.59:4765 • 1910-1920: q = 1.602 x 10-19 coulombs •  smallest electric charge existing in nature • All observable particles have zero or integer charge in unit q •  what is the natural law for this simplicity? • FCP: Particles with Q = rq (r=fraction)

6. Standard Model of Elementary Particles FERMIONS Three Generation of Matter I II III The known elementary particles are 0, ±q, ±1/3q, ±2/3q

7. Motivation from Theory • GUTs or their extensions can have e/3, 2e/3, e/2… • Superstring can have e/5 or even smaller • QCD can have large fractional charge for heavy quark-nucleon complex • Some dark matter models, where an extra U(1) field introduces a photon analog with very small charge  mili-charged particles

8. Sources of FCP Possible Sources of CFP from Outside FCP could be produced • in the early universe and may be a stable component of the present material in the universe • in the present era through violent astrophysical processes • through the interaction between ordinary cosmic rays and the Earth’s atmosphere • in the process of particle collision

9. Search for FCP Search history: • Searches for FCP have started since the original Millikan oil experiment, ~100 years agoup to today. • After the established of quark model, the field focused for a while on searches for free quarks with 1/3e, 2/3e. • The success of QCD color confinement moved the field again to a broader scope. Noconfirmed positive results. Searches carried out: • use particle accelerator and fix targets • from outside the space • in bulk matter

10. Searches with Particle Accelerators • Fix target: hadron/lepton + N  F(Q) + X • Lepton collider (LEP): e+ + e-  F(+Q) + F(-Q) • precisely known: • Hadron collider (CDF, ATLAS, CMS): • q/gluon + anti-q/gluon  F(+Q) + X[X=F(-Q)+other particles)] • Hybrid collider (HERA): e- + p  F(+Q) + X

11. Results from Accelerator Experiments Fixed targets LEP (GeV) OPAL DELPHI OPAL ALEPH (GeV) Tevatron CDF • LHC: searches for Long-Lived Charged Massive Particles with dE/dx • CMS for fractional charges • ATLAS focused on integral charges

12. Result from Outside the Space • 1960 - 1980, many searches for FCP in cosmic rays through use of expansion cloud chambers . Only McCusker&Cairns who claimed a few events with Q = 2/3 q, which were not verified by other searches.

13. Searches from Bulk Matter • Stable FCPs can be captured in bulk matter and accumulated over the long lifetime of the earth or the moon or asteroids • Possible sources of FCPs in bulk matter: • - early universe • - cosmic ray interaction with atmosphere • Samples made of solid or liquid matter, and its total charge should be Q = ne, if there are no FCPs bounded • FCPs could bound to an ordinary nucleus that may have exceptional chemical features, which can guide the selection of materials and samples, this option is not fully explored

14. Ferromagnetic Levitometer • Magnetic field to levitating the sample O(0.1mm) • Oscillating electric field to move the sample back and forth, and the resulting motion is measured to determine the charge • Sample coated with iron, or iron ball coated with sample • UV light to remove electrons one-by-one, the resulting Q v.s. time will give hint of whether FCP exists Disadvantage: very limited sample choice

15. Liquid Drop Device • Measured terminal velocity of drops inside airflow based on Stokes’s law • Sample spread in oils • Need automated oil drop and track capture devices, and variation of electric field

16. Searches in Bulk Matter

17. Searches for Millicharged Particles • Motivated by Dark Matter Models that consider mirror particles axion, extended to other small mass exotic particle, including Millichargedparticleswith charge close to 0 or +-q. g + N  F(+Q) + F(-Q) + X The detector searched for lightly ionizing particles, but found none.

18. Prospect for FCP Searches • Need to increase the sensitivity a factor of 10. • Extend the millicharged particle search of Prinz et al. to higher energy and larger statistics. • Search for FCP at LHC and super factories of b and c . • Extend searches in bulk matter using the levitometer method with meteoritic material from asteroids.

19. A hypothetical elementary particle that is an isolated magnet with only one magnetic pole MMP: Definition and History Credit: CERN/MoEDAL • In 1894, Pierre Curie discussed the possibility of existence of MMP and could find no reason to discount its existence. • In 1931, showed that when Maxwell's equations are extended to include a MMP, electric charge can exist only in discrete values. • The existence of a MMP imply a duality between electricity and magnetism, the theory suggesting MNPs becomes exciting.

20. Maxwell's Equations + ? + ? • Unifies electric and magnetic field theory into classical electromagnetism • No magnetic charge/current • A symmetric equations allows the existence of MMP. • Electric charge is discrete

21. MMP in Theory MMP naturally from GUT theories. Mass at GUT scale ~1015GeV If isolated MMP exist, electric charge can be quantized. Mass ~GeV Hybrid between Dirac and GUT can have intermediate mass

22. Dirac’s Quantization Condition • Dirac monopole: • Why electric charge always comes in discrete values: Q = ne? • Isolated magnetic poles can lead to both the electric charge and magnetic charge quantization Unit of magnetic charge is much bigger than electric charge Strong coupling  non-perturbative MNP is difficult to predict

23. MMP of GUT • ‘t Hooft and Polyakov: • Proved that MMP arise as a result of GUT phase transition ~1015 GeV • GUT MMP are heavy and have structures • Can trigger proton decay

24. MMP and Cosmology Inflation Standard cosmology predicts many GUT MMP, which could be the critical energy density of the Universe  one of the main motivations for cosmology inflation theory Lightest MMP are stable and created in pairs magnetic charge conservation

25. Where to Find MMP • Sources of MMP • Primordial cosmic MMP • - Moving freely through outer space with relativistic speed • accelerated by galactic magnetic fields, mass 10-1014TeV • Primordial stellar MMP • - Bound in matter before star formation: earth, moon, comet, • meteorite • Secondary production • - Inside high-energy cosmic ray, or with high-energy collisions • at accelerators • Experiments to look for MMP • Cosmic rays: big detector size and long time of exposure • Bulk matter: big sample size • Accelerators: high center-of-mass energy

26. How to Detect MMP? • For direct searches: • MMP current induction (moving magnetic charge induces electric field) • A MMP passes through the ring, changes magnetic field and • induces a current. The change in the current also gives the • strength of the magnetic charge. • MMP charge ionization: • A MMP with strong magnetic charge travelling through matter • would easily strip electrons off atoms, leaving a clear track in • detector. • Look for signs of nucleon decay catalyzed by monopoles travelling through matter.

27. Search at Colliders Dirac MMP or the hybrid with GUT MMP

28. Search at Colliders

29. Searches from Cosmic Rays GUT monopoles

30. Searches from Bulk Matter Moon rocks – exposure up to 4 billion years Monopole mass [GeV]

31. Hidden Sector and Dark Photons • Dark sector has dynamics which is • not fixed by SM dynamics • A new forces and new symmetries • Multiple new states in the dark • sector, including dark matter • candidates • Interesting, distinctive • phenomenology • - Long-Lived Particles (LLPs) • - Feebly interacting particles (FIPs)

32. Dark Photon Production Mechanisms and the Mass Scale of Dark Matter A’ l+l- c1c2 (invisible)

33. Dark Portals at Accelerator e defines photon-dark photon mixing. Production rate ~ ε2 JLAB, Mainz, NA62++, e+e- collider 33

34. Dark Portals [Vector, (Pseudo)Scalar, Neutrino] at Beam Dumps (e. g. NA62++, SHiP) E. Graverini’s talk

35. Dark Photons/Scalars (SM Particles) Shoji Asai and Marcela Carena SHiP is a proposed beam dump experiment using 400 GeV protons from the SPS

36. Summary • FCP, MMP and DP are all closely related to the key science questions important to promote the researches for them. • New ideals and technologies, particularly for the super sensitivity to weak signals with super precision measurement, are needed for the searches. • FCP: none accelerator based searches done about 20 years ago. With new technologies, is it possible to improve the sensitivity a factor of 10? • MNP: too heavy to be produced via particle collision, or too few left to be detected? • DP: equally as important as dark matter.