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Searches for FCP on the Earth

This article provides a non-expert's review on the search for Fractional Charge Particles (FCP) on Earth. It discusses the challenges, potential sources, experimental probes, and recent developments in the field.

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Searches for FCP on the Earth

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  1. Searches for FCP on the Earth Yusheng Wu University of Science & Technology of China Dark Photon, Monopole, FCP Workshop, May 31 – June 1 Disclaimer: a non-expert’s review, with substantial information taken from M. Perl etc. Annu. Rev. Nucl. Part. Sci. 2009.59:47-65

  2. Introduction • Charges are fundamental (in the “Standard” Theories) • Conserved quantities due to gauge symmetries • “Source” and “Strength” for particles participating in a given force Y. Wu

  3. Introduction • Electric charges are no secret • Everyday accessible • We are highly proficient in using them Semiconductor Plasma driven acceleration Conductor Y. Wu

  4. Introduction • How charge is quantized or could it be dequantized !? • Fractional charged particles? • Electric charges are still mysterious! • Everything seems to have nqe, except for confined quarks • Any unconfined particles with fractional charges (FCP)? • If yes, direct connection with • Beyond SM theories: Superstring, some GUT scenarios … • Dark matter (if mini-charged particles) • From SM: Q = T3 + (Y/2 + e) could still be possible1 • Or quantized with small extensions of the SM1, • With Dirac or GUT monopoles, or with higher dimensions 1. arXiv:hep-ph/9209259 Y. Wu

  5. Fractional Charge Particles • This is a search for unknownunknown, originated from puzzles connected with fundamental attributes within current standard theories • Similar to the monopole case: • Mass unknown (possibly large?) • Production cross-section unknown • Production mechanism unknown • But even charge range unknown (10-4, 10-2, 1/6, ½, 1/3, 2/3, 60½, …) • Requires searches in a broad scope (cosmic rays, collider, earth, moon, asteroid, comet …) • Requires precision searching (highly sensitive to charges) => push limits of experimental technologies and sensitivities Y. Wu

  6. Potential Sources of FCP FCP • From outside the earth • Produced in early universe, lightest ones likely stable, and concentrated on bulk matter • Or produced in present universe, travel to earth as cosmic rays • Or produced as cosmic rays interact with atmosphere • Produced with Accelerator • Pair production of FCPs, e.g. Drell-Yan process • Probing mass range limited by C.M.E. • Can be searched for with fix-target, e+e- and hadron colliders Y. Wu

  7. Experimental Probes Particles or bulk-matter samples to be examined via classic motion measurement (F = qE); Camera, Laser/CCD (bulk matter) Measure Charges For both cases, tricky to probe small charges via ionization energy loss in the detectors (accelerator, cosmic rays) Y. Wu

  8. Experimental Probes How about masses? Searches with bulk matter don’t depend on FCP masses, yet no sensitivity to determine it Probing mass up to 1015 GeV on the earth, due to earth gravity / coulomb force balance Experiments at Moon / space station / satellite with rocks obtained in space may probe even larger mass FCPs ??? Y. Wu

  9. Experimental Probes How about masses? Phys. Rev. D 87 (2013) 092008 Searches with collider experiments have limited mass coverage, but possible to constrain mass Phys. Rev. Lett. 90:131801 (2003) CDF High ionizing, possible to directly combined P and dE/dx to get mass Low ionizing (no direct mass calculation) Y. Wu

  10. Experimental Probes • Direct searches for FCPs require that those FCPs are isolatable for charge measurement: stableenough& separable from other particles / background environment • A broad scope of efforts have been carried out in the past • Searches using particle accelerators and fixed targets. • Searches using particle colliders. • Searches in cosmic rays. • Searches in bulk matter. • Special search methods for particles with Q very close to 0 (millicharged) Y. Wu

  11. Recent Experimental Probes Bulk Matter, Cosmic Rays, Accelerator/Fixed Target/Collider Phys. Rev. Lett. 81:1175 (1998) Phys. Rev. Lett. 99:161804 (2007) Phys. Rev. Lett. 46:967 (1981) Phys. Lett. B167:481 (2000) Phys. Rev. Lett. 113, 251801 (2014) – mini-charge Phys. Rev. Lett. 84:2576 (1983) Phys. Lett. B137:439 (1984) Phys. Rev. D 43:2843 (1991) ASR 41 (2008) 2050–2055 Phys. Rev. D 66:012002 (2002) Astropart. Phys. 2:29 (1994) Z. Phys. C 43:349 (1989) Phys. Rev. Lett. 51:731 (1983) Phys. Lett. B171:129 (1986) arXiv:hep-ex/0402006 Z. Phys C 55:549 (1992) Phys. Lett. B197:447 (1987) PRL 114, 111302 (2015) 2010 2020 2000 1980 1990 …… Fizika B 5:135 (1996) Phys. Lett. B396:315 (1997) Phys. Lett. B572:8 (2003) Phys. Rev. C 44:1672 (1991) Phys. Rev. D 87 (2013) 092008 Phys. Rev. C53 (1996) 358-361 Phys. Lett. B303:198 (1993) Phys. Rev. Lett. 90:131801 (2003) Z. Phys. C 67:203 (1995) Phys. Rev. D 46:2546 (1992) No Positive Results So Far Y. Wu

  12. Fixed Target Experiments 80’-90’: possibility that FCP could be produced in high-energy nucleus-nucleus collisions where quark confinement might not hold perfectly. Early experiments, large variety of beams and detection methods • Phys. Rev. C53 (1996) 358-361 Plaster nuclear track detectors Y. Wu

  13. Experimental Results e+e- collider Cross-section calculatable under assumptions: OPAL DELPHI OPAL ALEPH TeV hadron collider Tevatron Limitation by detector response, related to trigger efficiency and tracking reconstruction, limits Q > 1/3 e Y. Wu

  14. Experimental Results Recent results from CMS ATLAS activity seen this afternoon from Q. Li Signal Region with low Ionization No clear evidence as well Great to extend the searches to full Run-II data Y. Wu

  15. Experimental Results Cosmic Rays Results in space seen in G. Huang’s talk 80’ – 90’, cloud chambers were used to search for FCPs in cosmic rays, then: Mont Blanc Neutrino Scintillation Detector (1994) Kamiokande II (1991) MACRO (Gran Sasso) was a dedicated experiment for detecting monopoles and FCPs Final MACRO Y. Wu

  16. Experimental Results MACRO Experiment arXiv:hep-ex/0402006v1 • FCPs were searched for as lightly ionizing particles, for total run time (1989 – 2000) • Streamer tube tracker + Liquid scintillator for FCP searches Signal region, only one event, later rejected due to timing confusion Y. Wu

  17. Experimental Results More recent: CDMS-II Underground, Soudan mine in Minnesota, U.S. PRL 114, 111302 (2015) • Low-threshold solid-state detectors in an array to detect very lightly ionizing particles from cosmic rays, • Sensitive to 1/200 < q < 1/6e • No positive results • Upgrade ongoing to SuperCDMS Main focus was for WIMP Y. Wu

  18. Bulk Matter in a Nutshell 100mg • Two main classes of experiments: Liquid drop; Levitometer • Both cases need special care of samples, and need high precision system • Limitation is the sample size / throughput “One drop in the sea” Y. Wu

  19. Searches in Bulk Matter • Materials often chosen for ease of use w.r.t. experiments: • Chemical features of FCP+nuclei system unclear • Used: sea water, silicone oil, mercury, iron, niobium, meteorite • Might be interesting to do in the future: rocks from comet and Moon, plus many others to be explore ? Y. Wu

  20. Searches in Bulk Matter • Ferromagnetic Levitometer • Magnetic field to levitate the sample of O(0.1mm) diameter • Oscillating electric field with laser and photodiodes to measure charge • Sample coated with iron, or iron ball coated with sample • UV light to remove electrons one-by-one from the sample Some used diamagnetic levitation on a sample consisting of superconducting niobium ball – disadvantage of very limited sample choice; Y. Wu

  21. Searches in Bulk Matter Illustration of Levitometer experiment • Typically a day or so, to measure one sample, hours on each charge point to reduce stat. error • Taking years to reach O(1g) • Major spurious signal source could be “patch effect”: impurity in electric field plates • Extreme cares are need in these experiments Time consuming, so potential concentration level of FCP as high as possible: seawater evaporation was also tried Y. Wu

  22. Searches in Bulk Matter Liquid drop experiments Modified Version Millikan Oil experiment Traditional method need to suspend the old drop and therefore limit the throughput to <<mg Stokes’ Law Q Y. Wu

  23. Searches in Bulk Matter Liquid Drop Experiment : Important to have automated system! • Apart from data acquisition, Key is to prepare samples and produce fluid drops properly • Careful calibration and quality cleaning of drops are also necessary Y. Wu

  24. Searches in Bulk Matter Liquid Drop Experiment Laser-CCD Imaging Need to analyze multiple pictures to reconstruct the movement of each drop Y. Wu

  25. Searches in Bulk Matter For most recent experiment: Total 40M drops examined ~ 1 year ~O(g) mineral oil and meteorite rock Still no anomalies found Y. Wu

  26. Mini-charged FCP For instance • The original method to detect axion with a strong B filed can be extended to search for mini-charge FCP Phys. Rev. Lett., 81, 1175 (1998) No positive results Y. Wu

  27. Summary • Negative results so far • Experimental methodologies have improved over years • If FCP exists, we are still not sensitive to detect them • Larger sample be tested in bulk matter experiment • More “exotic” materials, such as comet or moon rocks … • LHC to utilize full data to search for FCP • Cosmic ray experiments to gain momentum again • Plus searching for mini-charged FCP, in connection with dark side searches Y. Wu

  28. Bonus Y. Wu

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