Opportunities and challenges for strong interaction physics with the - - PowerPoint PPT Presentation

Opportunities and challenges for strong interaction physics with the future CERN pre-accelerator complex after the HL-LHC (or after LS3?)

Daniël Boer, University of Groningen, The Netherlands

Scope

Charge: review the opportunities (and challenges) for strong interaction physics with the (potential) future CERN pre-accelerator complex in the era of HE-LHC, FCC, LHeC, CLIC, AWAKE, etc (Q: possibly include AMBER-II, RF-separated beams? eSPS?)

Possible future high-energy physics colliders

• HL-LHC run4 & run5 after LS3: mid-2026-2038 [5-7x nominal luminosity @ 14 TeV,

expected integrated luminosity 3000 fb-1]

• U.S.-based EIC (possible construction after FRIB completion ~ FY20), completion at the

earliest in the period 2025-2030, c.o.m. energies between 22-141 GeV

• LHeC: can be in operation at the earliest around 2030, c.o.m. energy 1.3 TeV
• HE-LHC after HL-LHC: 2040+, c.o.m. energy 27 TeV
• FCC: mid 2040s, FCC-hh c.o.m. energy 100 TeV
• CLIC (Compact Linear Collider, e+e− collisions at 350 GeV-3 TeV): construction could start

as early as 2026 with first beams by 2035

• AWAKE: SPS proton bunches as drivers yield electron energies of 50−100 GeV, whereas

LHC proton bunches yield TeV-scale electrons. SPS option: PEPIC A very high energy (9 TeV) electron–proton collider, VHEeP, with modest luminosity can then be realized.

Potential future pre-accelerator complex

• LHeC: SPS, LHC and PERLE (Energy Recovery Linac)

[Id159, Id147, PERLE CDR]

• HE-LHC: SPS, LHC [no specific input?]
• FCC: SPS, LHC [no specific input?]
• CLIC: SPS, LHC [no specific input?]
• AWAKE: SPS, LHC [Id50, Id58]

AWAKE++

• Proton-driven plasma wakefield acceleration allows the

transfer of energy from a proton bunch to a trailing bunch

• f particles, the ‘witness’ particles, via plasma electrons.
• Because of their high energy and mass, proton bunches

can drive wakefields over much longer plasma lengths than other drivers.

• Using SPS proton bunches as drivers, electron energies

in the range 50−100 GeV are expected to be possible, whereas TeV-scale electrons should be possible using LHC proton bunches as drivers

AWAKE++: SPS-driven fixed target option

• With the AWAKE acceleration scheme electron energies

up to 70 GeV can be achieved and the rates can be significantly higher and therefore provide the highest energy, high charge electron bunches in the world.

• Fixed target experiments are the first applications of these

electrons from the AWAKE scheme and could be realized already during LS3

• c.o.m. energy: 12 GeV, like JLab12
• Interesting for beam dump experiments: dark photons

AWAKE++: SPS-driven ep collider (PEPIC)

• Electrons accelerated in a wakefield driven by the SPS proton beam collide

with LHC protons and ions, this collider is called ’PEPIC’ (Plasma Electron- Proton/Ion Collider).

• The experiment would focus on studies of the structure of matter and QCD

in a new kinematic domain, in particular at low value of Bjorken x where the event rate is high.

• c.o.m. energy: 1.4 TeV, like LHeC
• The PEPIC luminosity is 1.46×1027 cm−2 s−1. Assuming a running period of

about 107 s per year this would give an integrated luminosity of about 10 nb−1. So although PEPIC would have the same energy reach as the LHeC project, but with luminosities several orders of magnitude lower, this collider could be an interesting option for CERN should the LHeC not be realized.

PEPIC

By widening the extraction line tunnel TI2 from the SPS to the LHC, the SPS proton beam can be used to drive wakefields in a ∼130 m long plasma cell in TI2 in order to accelerate electrons that collide with LHC protons.

AWAKE++: LHC-driven fixed target option

• TeV-scale electrons should be possible using LHC proton bunches as drivers
• 3 TeV electron beams on FT
• c.o.m. energy: 75 GeV, similar in energy to U.S.-based EIC (15 − 140 GeV)
• Using a thick liquid hydrogen target of the kind developed for COMPASS

would yield of order 107 events in the range x > 0.6 and Q2 > 20 GeV2, per year of running, allowing for high precision structure function measurements in a crucial kinematic range which currently has large uncertainties.

• Initial studies indicate that under the right conditions, electron polarization can

be maintained during the acceleration process. Using a polarized target would allow for a spin physics program, albeit at much smaller integrated luminosities than planned for the EIC.

AWAKE++: LHC-driven ep collider (VHEeP)

• VHEeP

, with ep center-of-mass energy of about 9 TeV, a factor of six higher than proposed for the LHeC and a factor

• f 30 higher than HERA. The luminosity will presumably be

relatively modest with a target of 10 pb−1 over the lifetime of the collider

• c.o.m. energy: 9 TeV, surpassing even the FCC-eh (60 GeV e-

beam with the 50 TeV p-beam of the planned FCC (Future Circular Collider), with a cms energy of 3.5 TeV)

• mention eA?
• Mention timeline mid 2040s?

LHC as part of the pre-accelerator complex

• Fixed-target experiments like AFTER@LHC or

LHCspin@LHCb (if they don’t happen during HL-LHC run)

• VHEeP

PERLE: ep collider LHeC

• A 60 GeV high current electron beam to operate e-p at √s =

1.3 TeV concurrently with p-p of HL-LHC

• Uses a novel, energy recovery LINAC (PERLE) to reach high

luminosity, exceeding HERA’s by nearly 3 orders of magnitude

• Integrated luminosity projected to be O(100) fb−1, a factor of

100 more than HERA over its lifetime of 15 years

• “the cleanest, high resolution microscope accessible to the

world” aka “CERN Hubble Telescope for the Micro-Universe” 😁

From LHeC document

LHeC kinematic reach

From C. Gwenlan, DIS2018 From talk by M. Klein

High precision pdfs

PERLE: fixed target options

• A 60 GeV high current electron beam on a fixed target: √s = 11 GeV,

again similar to JLab, but higher luminosity than SPS-AWAKE++ on FT

• Possibilities for new precision measurements of the proton form

factors, pion production

• Possible structures below Q2min and their influence on the proton radius

could be studied with a single, low beam energy and forward scattering experiment, similar to the PRad experiment. At lower energies and higher beam currents than planned for PRad, an ERL beam with a point-like target (e.g. a gas jet) could provide higher rates and smaller systematic uncertainties. An alternative approach is to exploit initial state radiation, measuring deep into the radiative tail to probe Q2- values that are orders of magnitude smaller than directly accessible.

PERLE: fixed target options

• The uncertainties in the proton form factors need to be strongly reduced. This can be

achieved in a first phase of experiments measuring the scattering distributions, at both forward and backward angles, with an unpolarized beam. These measurements can reduce the uncertainties in form factors by an order or magnitude compared to present knowledge, and provide adequate precision for the measurement of sin2 θW.

• The low-Q2 structure in GM could be studied by performing an angular scan of the cross

section and multiple energies up to 300 MeV. It would produce an electric radius with similar uncertainties, and a magnetic radius with substantially improved precision compared to current results. Additionally, with a polarised beam and target, an asymmetry measurement, sensitive to the ratio GE/GM , could be performed. Such a measurement would help to disentangle GE and GM from the cross-section measurement and would make it possible to study whether the structure is related to imperfect radiative corrections.

• The high-Q2 structure could be studied with high precision using beam energies of 1 GeV

and up, possibly with just one angular scan of the cross section at a fixed energy around 1.3 GeV

PERLE: fixed target options

• In elastic ep scattering, the proton radius can be accessed through the slope of

the electric form factor at Q2 = 0. At PERLE, with a beam energy of 500 MeV or below, detecting scattered electrons down to 4◦ would allow to reach Q2 ∼ 10−4 GeV2, an order of magnitude below the limit of existing data. New data from PERLE would strongly reduce the uncertainty in the extrapolation to Q2 = 0, and provide an excellent opportunity to consolidate the electron results.

• Pion electroproduction 


Using virtual photon tagging, it is possible to study confinement-scale QCD. At forward angles, the virtual photons are almost real, so that a forward scattering electron tagger can be used as a highly efficient substitute. Because of the high efficiency and high beam currents, it is possible to use pure, thin targets and detect low energy recoil particles which would not escape traditional, thick

• targets. It is thus possible to measure the reactions like γp→π0p. Such an

experiment requires beam energies of 300 MeV or more.

• Photon-nuclear physics can be very interesting as well
• Potential for fundamental research with γ-ray beams that the

PERLE facility will be capable of producing by laser-Compton back- scattering off the intense cw electron beam.

• 1000 times intensity of European Extreme Light Infrastructure
• Nuclear Physics (ELI-NP)
• Many uses e.g. nuclear structure physics, nuclear matrix

elements for 0νββ-decay

• See for more details in PERLE CDR

PERLE: fixed target options

• PERLE will also be operated as an intense source of quasi-

monochromatic, energy-tunable, fully-polarised γ radiation. The γ-ray beams will be produced by the process of Laser-Compton back- scattering on the intense relativistic electron beams of PERLE’s third recirculation beam line providing γ-beam energies between 0.2 and 5 MeV. PERLE’s γ-ray beams can reach a significantly narrower bandwidth and simultaneously a much higher repetition rate than the Gamma Beam System at the Extreme Light Infrastructure - Nuclear Physics (ELI-NP), the new-generation facility currently under construction at Magurele, Romania.

• Photonuclear reactions will significantly contribute to progress in the

fields of nuclear structure physics, particle-physics metrology, nuclear astrophysics

PERLE: fixed target options