1. Low energy g - g Collider for QED measurements
Luca Serafini – INFN Milano
Why a Photon-Photon elastic/inelastic scattering experiment? Fundamental test for QED never observed so far (elastic scattering with real photons, pure light-to-light interaction)
Why now? Future availability of tunable/polarized/mono-chromatic/high-phase-space-density MeV-class photon beams mutuated from Nuclear Photonics (ELI-NP-GBS, HiGS, etc)
The Challenge: run a high luminosity collider at 1 MeV center of mass energy to sample photon-photon total cross section spanning from atto-barns to hundreds of milli-barns
Fundamental HEP research with a Light Source!
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

2. Feymann tree-level diagrams, all imply interaction e. m. field - el
Feymann tree-level diagrams, all imply interaction e.m. field - el. charge
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015
Courtesy Oliver Pike

3. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

4. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015
Courtesy Oliver Pike

5. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015
Courtesy Oliver Pike

6. Photon-photon scattering is a probe into
the structure of the vacuum of QFT
The QFT vacuum holds the key to the understanding of renormalization in QFTs.
Different vacua are possible, and the observation of photon-photon scattering would provide important clues on the actual structure of the QFT vacuum.
Feymann fermion loop diagram
Photon-photon scattering at low energy is very difficult to observe, the total cross-section is extremely small. The total unpolarized scattering cross section predicted by QED is
Where
This evaluates to a very small number with low energy (≈ 1 eV) photons, however it increases as the sixth power of photon energy.
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

7. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

8. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

9. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

10. Tunability! Narrow bdw! optical transparency of the Universe
Thomson cross sect. = 670 mbarn
peak cross-section, ≈1.6 µbarn at
cross-section for unpolarized initial state
(average over initial polarizations)
Tunability!
Narrow bdw!
optical transparency
of the Universe
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

11. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

12. threshold of the
Breit-Wheeler
process
1 nb-1
10 pb-1
integrated luminosity corresponding to a bare minimum of about 100 scattering events (total).
ECM ≈
630 keV
880 keV
13 MeV
140 MeV
Bethe-Heitler
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

13. Gamma ray beam polarization is a must!
Unpolarized and (circularly) polarized initial photons.
The scattering of polarized photons yields additional information
CM energy (MeV)
+ + and - -
+ - and - +
Gamma ray beam polarization is a must!
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

14. Differential Cross Section is larger
at large scattering angles for lower
photon energies – easier detection
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

15. Differential Cross Section is smaller at
large scattering angles for higher photon
energies – more difficult detection
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

16. We evaluated the event production rate of several schemes for photon-photon scattering, based on ultra-intense lasers, brehmstralhung machines, Nuclear Photonics gamma-ray machines, etc, in all possible combinations: collision of 0.5 MeV photon beams is the only viable solution to achieve 1 nbarn-1 in a reasonable measurement time.
Colliding 2 ELI-NP 10 PW lasers under construction (ready in 2018), hn=1.2 eV, f=1/60 Hz, we achieve (Ecm=3 eV): LSC=6.1045, cross section= , events/sec=10-19
Colliding 1 ELI-NP 10 PW laser with the 20 MeV gamma-ray beam of ELI-NP-GBS we achieve (Ecm=5.5 keV): LSC=6.1033, cross section=10-41, events/sec = 10-8
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

17. Colliding a high power Brehmstralhung 50 keV X-ray beam (unpolarized, 100 kW on a mm spot size) with ELI-NP-GBS 20 MeV gamma-ray beam (Ecm=2 MeV) we achieve: LSC=6.1022, cross section=1 mbarn, events/s = 10-8
4) Colliding 2 gamma-ray 0.5 MeV beams, carrying photons per pulse at 100 Hz rep rate, with focal spot size at the collision point of about 2 mm, we achieve: LSC=2.1026, cross section = 1 mbarn, events/s=2.10-4, events/day=18, 1 nanobarn-1 accumulated after 3.2 months of 5/24 machine running.
Colliding 2 LCLS-2 10 keV 1013 photons at 1 MHz we would achieve: LSC=8.1038, cross section=1 atto-barn, events/s =
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

18. A Photon-Photon Scattering Machine based on twin Photo-Injectors and Compton Sources
Mono-chromatic High Brilliance micron-spot psec Gamma Ray beams are needed for pursuing Photon-Photon scattering experiments at high luminosity ⇒ scaling laws
Similar to those generated by Compton (back-scattering) Sources for Nuclear Physics/Photonics
(mini) Colliders similar to g-g colliders, but at low energy (in the MeV range): issue with photon beam diffraction!
Best option: twin system of X-band 200 MeV photo-injectors with Compton converters and amplified J-class ps lasers (ELI-NP-GBS/STAR) – single bunch no laser re-circulation
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

19. Pointing stability at 2 Compton Sources
Strawman Design of Photon-Photon Scattering machine based on X-Band SLAC RF Photo-Injector + SLAC new X-band (Tantawi-Dolgashev) RF cavities + J-class Yb:Yag 100 Hz collision laser (Amplitude/ELI-NP-GBS&EuroGammaS)
Electron beam operation in single bunch – focusability to 3 micron spot size at Compton Interaction Point
Pointing stability at 2 Compton Sources
Control Moeller scattering of counter-propagating electrons
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

20. Formulas for photon scattering Luminosity
extensively tested vs. ELI-NP-GBS simulations
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

21. Formula for Lsc is valid if distance between 2
Compton conversion IP’s is smaller than b*
Example g=300 sS=3 mm b*=1 mm
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

22. and X-band RF structures
A.Bacci – first attempt,
SLAC X-band RF gun
and X-band RF structures
250 pC, 3 mm spot size
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

23. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

24. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

25. E. Milotti et al.
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

26. 1 nanobarn-1 accumulated after 3.2 months of
we can achieve: LSC=2.1026, cross section = 1 mbarn, events/s=2.10-4, events/day=18,
1 nanobarn-1 accumulated after 3.2 months of
5/24 machine running.
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

27. Clear Scientific Case on Fundamental QED and QFT
CONCLUSIONS
Clear Scientific Case on Fundamental QED and QFT
Technical Solution for the Machine (challenging)
Uniqueness: a HEP experiment performed with a Light Source
Many Thanks to: E. Milotti, D. Babusci, A. Bacci, C. Curceanu,
M. Iliescu, I. Drebot, D. Palmer, B. Spataro, E. Tassi, D. Micieli
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

28. Recent references on possible photon-photon scattering schemes
Recent references on low-energy light-magnetic field scattering (photon-photon scattering between real infrared photons and virtual magnetic field photons)
F. Della Valle, E. Milotti, A. Ejlli, G. Messineo, L. Piemontese, G. Zavattini, U. Gastaldi, R. Pengo, G. Ruoso: "First results from the new PVLAS apparatus: A new limit on vacuum magnetic birefringence", accepted for publication in Physical Review D
F. Della Valle, U. Gastaldi, G. Messineo, E. Milotti, R. Pengo, L. Piemontese, G. Ruoso, G. Zavattini: "Measurements of vacuum magnetic birefringence using permanent dipole magnets: the PVLAS experiment", New J. Phys. 15 (2013)
Recent references on possible photon-photon scattering schemes
A. Torre, G. Dattoli, I. Spassovsky, V. Surrenti, M. Ferrario, and E. Milotti: "A double FEL oscillator for photon-photon collisions", Journal of the Optical Society of America B 30 (2013)
E. Milotti, F. Della Valle, G. Zavattini, G. Messineo, U. Gastaldi, R. Pengo, G. Ruoso, D. Babusci, C .Curceanu, M. Iliescu, C. Milardi: "Exploring quantum vacuum with low-energy photons", Int. J. of Quantum Information 10 (2012)
Historical reference on photon-photon scattering opportunities
Paul L. Csonka, “Are photon-photon scattering experiments feasible?”, Phys. Lett. 24B (1967) 625
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

29. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

30. K. Homma and K. Nakajima
conf-extreme-light-s-new-horizons-paris-france/slides/slides kjsp?RF=
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

31. Envelopes of the laser beam (dotted line), first electron beam (for Compton back-scattering, dashed) deflected after collision with laser to clear the second electron beam (solid line).
laser envelope
envelope of first
electron beam deflected
x [mm]
Laser intensity distribution
and first electron bunch at
Compton back-scattering
Collision point
collision
point
second electron beam
envelope to collision
incoming gamma
photon beam envelope
z [mm]
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

32. Enlarged view (zoomed out over 1 cm in z and microns in x) to show laser envelope clearance and deflecting dipole poles (0.3 T B field applied).
laser envelope
x [mm]
envelope of first
electron beam deflected
collision
point
second electron beam
envelope to collision
incoming gamma
photon beam envelope
z [mm]
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

33. Illya Drebot with CAIN – single bunch mode 100 Hz no laser re-circul.
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

34. Multiphoton Breit-Wheeler scattering was observed at SLAC.
However, as clearly stated also in the paper, “The multiphoton
Breit􏰊-Wheeler reaction becomes accessible for n > 3 laser photons
of wavelength 527 nm colliding with a 29.2 GeV photon􏰁“.
Indeed, the straghtforward two-photon Breit-Wheeler reaction
has never been observed. The difference may appear minor,
however it isn’t. Multi photon scattering has a considerably
more complex kinematics, and the dynamical calculation clearly
requires more than one internal propagator in the Feynman diagram.
But more than that, Breit-Wheeler scattering — be it multi photon
or not — is described by a simple tree-level diagram at the lowest
perturbative order, while photon+photon —> photon+photon,
needs a fermion loop at the lowest level, and thus is a true probe
of the quantal nature of field theory.
Edoardo Milotti - INFN-Trieste
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

35. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

36. STAR X-Ray Imaging STAR Nuclear Photonics X (keV) hn=2.4 eV hn=1.2 eV
g (MeV)
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

37. c) 1 J Yb:Yag 100 Hz collision laser (0.8 J expected at ELI-NP-GBS)
a) 200 MeV/m peak cathode field of X-Band SLAC RF Photo-Injector (recently proven)
b) 100 MeV/m SLAC (Tantawi/Dolgashev/Spataro) new X-band RF cavities (recently demonstrated)
c) 1 J Yb:Yag 100 Hz collision laser (0.8 J expected at ELI-NP-GBS)
PH2SC
Electron beam operation in single bunch – focusability to 3 micron spot size at Compton Interaction Point
Pointing stability at 2 Compton Sources
Deflection of counter-propagating electron bunches to avoid
e-/e- interactions
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

38. EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

39. Luminosity in collision
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

40. Formulas for energy of Compton scattered photons, Luminosity, # scattered photons, rms bandwidth, angle, etc
(1)
(2)
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

41. (3)
(4)
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

42. (10)
(11)
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

43. (12)
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

44. Definitions of Quantities
UL = Laser pulse energy
Q = electron bunch charge
fRF = RF rep rate
nRF = #bunches per RF pulse
f = collision angle (<<1)
f = 0 for head-on collision
st = laser pulse length
w0 = laser focal spot size
hn = laser photon energy [eV]
sx = electron bunch spot size at collision point
N.B. all sigma’s and angles are intended as rms,
all distributions are assumed as gaussians in (phase) space and time
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

45. FEL resonance condition
(magnetostatic undulator )
Example : for lR=1A, lw=2cm, E=7 GeV
(electromagnetic undulator )
Example : for lR=1A, l=0.8mm, E=25MeV
laser power
laser spot size
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

46. Courtesy V. Petrillo – Univ. of Milan
The Physics of Compton Inverse Scattering is quite straightforward
3 regimes: a) Elastic, Thomson b) Quasi-Elastic, Compton with Thomson cross-section c) Inelastic, Compton, recoil dominated
Courtesy V. Petrillo – Univ. of Milan
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

47. FELs (pure g2) X/g [MeV] D Te [MeV] g-g Colliders Polarized Positrons
Nuclear
Photonics D
Thomson
X-rays
1 GeV
1 TeV
Te [MeV]
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

48. Brilliance of Lasers and X-ray sources
ELI
12.4
1.24
0.124
l (nm)
BELLA
FLASH
Thomson/Compton Sources
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

49. Courtesy V. Zamfir – ELI-NP
ELI-NP γ beam: the quest for narrow bandwidths (from 10-2 down to 10-3)
Courtesy V. Zamfir – ELI-NP
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

50. Extreme Light Infrastructure
ELI on ESFRI list
ELI-PP
December 2009 (EC)
3 Pillars
(Structural Funds):
CZECH Rep: Beamlines
HUNGARY: Short Pulses
ROMANIA: Nuclear Physics
Courtesy of Victor Zamfir
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

51. ELI – RO Nuclear Physics Courtesy Victor Zamfir
“Extreme Light”
two 10 PW APOLLON-type lasers,
output energy higher than 200 J, fs,
intensity higher than 1023W/cm2
the most brilliant γ beam, <19.5 MeV, BW:10-3
produced by Compton scattering on a 600 MeV
electron beam (LINAC)
Courtesy Victor Zamfir
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

52. Courtesy Victor Zamfir
Two Apollon 10 PW Lasers
280 Meuro
80 Mil. Lasers and beam trans.
60 Mil. γ beam
60 Mil. Construction
24 Mil. Experiments
23 Mil. Personnel
ELI-NP
Building
Map view
700 MeV
RF Linac +
Compton-Source
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015
Courtesy Victor Zamfir

53. ELI-NP-GammaBeamSystem designed by EuroGammaS
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015

54. 108 Authors, 327 pages Published on ArXiv
EAAC-2015, WG4, Elba (Italy), Sept. 15th 2015