Summary of "AWAKE - creating a path for high energy particle physics"
Scientific concepts, discoveries, and nature phenomena mentioned
Particle-physics accelerator status (2021–2022 context)
- LHC shutdown and upgrades: accelerator performance and detector systems were being improved before resuming data taking (targeted around March 2022).
- Experiment upgrades:
- LHCb upgrade of a Ring Imaging Cherenkov (RICH) detector, including mirror installation and photodetectors.
- Purpose: identify charged particles using Cherenkov light patterns.
Key detector physics: Cherenkov radiation & particle ID (LHCb)
- Cherenkov effect: charged particles traveling faster than light in a medium emit a cone of radiation.
- RICH technique: detect the cone using mirrors to form a ring image.
- Particle discrimination: use the ring pattern to distinguish pions vs kaons vs protons.
- Scientific role: crucial for LHCb’s data-taking when the LHC restarts.
Higgs-boson coupling studies and limits (ATLAS)
- Higgs coupling to different fermion generations:
- Known behavior: Higgs coupling scales with mass; larger mass → larger coupling.
- Previously constrained mainly to the 3rd generation; the talk emphasizes sensitivity opening to the 2nd generation.
- Higgs coupling to charm quarks (ATLAS):
- Reported as about 26× larger than the Standard Model expectation (as a current limit/constraint).
- Goal: use more data to refine measurements and test Standard Model consistency.
Searches for new particles (ATLAS)
- “Xeno”: described as a supersymmetric particle related to the Higgs (context suggests higgs-sector SUSY searches).
- Earlier work explored one region; new exclusions cover larger phase space, leaving reduced viable parameter space.
- A nominal “chi” particle:
- Mentioned a search for a decay involving four heavy quarks (final state with 4 “b-like/top-like” heavy quarks, as described).
- Sensitivity emphasized for high masses (~2000–3000 GeV).
Neutrino physics: oscillation anomaly and the sterile-neutrino question
- MiniBooNE (since 2007):
- Reported an excess of electron-like events compared to Standard Model expectations.
- One interpretation: evidence for an additional neutrino flavor, a sterile neutrino.
- MicroBooNE:
- A liquid argon time projection chamber (LArTPC) detector.
- Better at distinguishing photons vs electrons than MiniBooNE’s earlier techniques.
- New result (stated as published at the end of October in the talk):
- No evidence of the previously observed excess.
- The excess is now explained well by Monte Carlo / background expectations.
- Implication stated: from this channel, there is currently no evidence supporting the sterile-neutrino-related interpretation.
Novel accelerator technology: Wakefield / plasma acceleration (AWAKE)
- AWAKE (Advanced Wakefield Experiment, at CERN) aims to create a new kind of particle accelerator using plasmas.
- Core motivation: probe smaller distance scales (higher energies) to continue exploring particle structure.
- Conceptual relation highlighted:
- Smaller measurable distances → higher particle momentum/energy.
- Why today’s colliders have limits:
- Circular accelerators:
- limited by synchrotron radiation (radiative energy loss) for light particles,
- limited by magnet strength for protons (maximum bending field).
- Linear accelerators:
- limited by required length given achievable RF accelerating gradients.
- Circular accelerators:
Plasma wakefield acceleration mechanism
- Plasma: ionized gas with free electrons and ions.
- Wakefield concept:
- A “driver” excites a plasma oscillation, forming a strong electric-field structure (the wake / bubble).
- A “witness” electron bunch injected later rides the wake to gain energy.
- Driver examples discussed:
- Historically: laser pulse driver (the talk cites 1979 as an early concept),
- In AWAKE: a proton bunch driver from CERN.
Self-modulation of long proton bunches (crucial AWAKE challenge)
- Problem:
- Proton bunch length (~10 cm) is much longer than the wake/bubble scale (~1 mm).
- Without correction, the long bunch would disrupt the plasma’s needed microstructure.
- Solution:
- Self-modulation instability converts the long proton bunch into a train of micro-bunches.
- Micro-bunch spacing matches the plasma wavelength, enabling coherent driving of the wake.
- Analogy used: pushing a swing at the right rhythm amplifies the motion.
AWAKE experiment details and results (as described)
- Location/setup:
- AWAKE beamline at CERN; the beam travels through a long tunnel to the experiment region (about ~1 km mentioned).
- Plasma source:
- Rubidium vapor, heated and laser-ionized to create the plasma.
- Engineering complexity: many temperature sensors (80 stated).
- Electron acceleration performance (early runs):
- First running period: 2016–2018.
- Initial beam turn-on around December 12, 2016 (described as days before shutdown).
- Reported results:
- observation of proton micro-bunch modulation,
- demonstrated electron acceleration to several GV in a few meters,
- mention of sub-picosecond time resolution for proton bunch evolution.
Future goals / Run 2 and physics applications of high-energy electrons
- Planned separation of functions:
- optimize modulation (driver → wake formation) separately from acceleration (electron trapping/energy gain).
- Run 2:
- began in July (as stated),
- goal: accelerate electron bunches suitable to begin particle-physics experiments.
- Example physics directions listed:
- Dark matter searches via “dark photons” (fixed-target style with weakly interacting photons),
- high-energy fixed-target experiments and exploration of new energy regimes,
- possible electron–proton / electron–ion colliders at higher energies than conventional proposals.
Plasma acceleration for broader (non-high-energy) applications
The talk notes plasma-accelerator techniques could also support:
- compact ion beam generation by using a laser to excite plasma,
- potential cancer therapy applications via localized energy deposition with ion beams.
Researchers or sources featured (mentioned explicitly)
People
- Professor Alan Caldwell (speaker; professor, AWAKE head at CERN)
- Christie Duffy (UKRI Future Leadership Fellow; MicroBooNE physics coordinator, Oxford)
- Giulio Villani (Dennis Wilkinson Prize; first-year performance awardee)
- Martin Tatt (Donald Perkins Prize; first-year performance awardee)
- Peter Griffin Hicks (John Adams Prize; first-year performance awardee)
- Nathan Zurich (European Physical Society young experimental physicist awardee)
- Jake Flower (poster prize mentioned)
- Sonia Zamani (poster prize mentioned)
- Chacilia Toshiri (poster/prize mention)
- Luigi Marquez (2020 ATLAS thesis award)
- Danielle (introduced the speaker; name unclear in subtitles)
Experiments / institutions / collaborations
- Oxford Particle Physics Christmas Lecture (event context)
- LHC; CERN
- ATLAS
- LHCb
- ZEUS (spokesperson noted in Caldwell’s bio)
- HERA accelerator complex (context for ZEUS)
- MiniBooNE
- MicroBooNE
- iPERk / Hyper-K (mentioned as “iper k” in Japan)
- DUNE (mentioned in the U.S.)
- SPS (used for the proton driver in AWAKE description)
- AWAKE (Advanced Wakefield Experiment)
- Isis (mentioned in a student bio; produces neutrons and muons)
- IOP and IOP meetings (award/poster contexts)
Scientific “sources” cited by context
- Rutherford (early scattering interpretation)
- Geiger and Marsden (early scattering experiments)
- McAllister and Hofstadter (proton size resolution via scattering; credited in the talk)
- Feynman lectures (educational source referenced)
- Enrico Fermi (“ultimate particle accelerator” idea)
- 1979 (historical reference for laser-driven plasma wakefield concept)
- Monte Carlo simulations (used in MicroBooNE result explanation; “Monte Carlo expectations”)
Category
Science and Nature
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