1. Experimental investigations of synchrotron radiation at the onset of the quantum regime

2. motivation
Test of quantum mechanical calculations of synchrotron radiation.
Relevant for linear colliders, astrophysical objects like magnetars, heavy ion collisions and more.
Nævn experiment og tydeligt formål
Magnetar SGR

3. Beamstrahlung
Electric field from one bunch boosted by 2g2-1 as seen by particles in the other bunch
The electric field of the oncoming bunch is seen as a magnetic and electric field in the rest frame of the first bunch.
Small beams, high Lorentz factors =>
Strong electromagnetic fields =>
Beam focusing
Increase of luminosity
Beamstrahlung

4. Synchrotron radiation
Typical radiated energy is
The strong field parameter
The critical field is B
photons
electrons

5. Synchrotron radiation
Obvious problems when the field is very high

6. Beamstrahlung parameters
For colliders the strong field parameter is given by
And the luminosity is without disruption.
separates the classical from the quantum regime.

7. Clic parameter For CLIC we get
However due to disruption of the beam the averaged parameter is
From the CLIC conceptual design report
For ILC this is

8. Clic luminosity
Large reduction due to beamstrahlung but even worse if the quantum suppression was not present-
It worse by approx a factor 2
From the CLIC conceptual design report

9. magnetars
B = 10 GT > B0
Neutron star of radius 20 km and greater mass than the sun.
Gamma and X-ray emitters
On the surface of quark stars

10. the na63 experiments
Use crystalline fields to measure the quantum corrections to synchrotron radiation.

11. Experimental setup
DC1
DC2
Krystal

12. Germanium crystal
Random orientation
axis

13. Continuum model

14. Crystal potential and field
Strong field parameter
Remark the figure shows the potential energy for a positron along the crystal axis
The potential is taken from Baier et al.

15. Accessible phase space
The potential energy at a given
distance from the axis
The transverse kinetic energy
The particle is free to move
between different axes.
Well channelled particles have extremely small entrance angles.

16. The constant field approximation
Radiation emission angle:
Deflection angle:
Criterium for constant field approx.
Magnetic bremsstrahlung

17. The constant field approximation
Classical synchrtron radiation
The constant field approximation
Two changes: Spin and recoil

18. The constant field approximation
Spin contribution:
You do not get a polarized beam since the field is in all directions
NIMB 119 (1996) 2

19. Crystal radiation Average over positions in crystal.
Strong field parameter
For germanium
Baier et al.

20. Radiation enhancement
Radiation emission is enhanced compared to bremsstrahlung.
Bethe-Heitler
formula:

21. Deflection and detection
DC2
DC3
Crystal
MBPL magnet LG

22. Pile up and calometric effect
Lead glass detector
Photon energy
Less photons at low energies
A slight increase at high energies
Multiphoton effects:

23. Pair spectrometer
DC5
DC6
Cu conver-
siontarget
MDX magnet

24. Geometric constraintsq-
Drift chamber width: 15 cm q+
MDX e+
DC5
DC6
DC6 angle constraint:
corresponding to
Energy threshold:
for DC6.

25. Geometric constraints

26. Monte carlo simulations of ps
Compare the background measurements to the Bethe-Heitler formula.
PRD 86, (2012)

27. Monte carlo simulations of ps
The goal is to verify measurements of Bethe-Heitler radiation and determine the efficiency of the pair spectrometer.
PRD 86, (2012)

28. Pair spectrometer efficiency
From the Monte Carlo simulations we deduce the efficiency of the pair spectrometer from the incident photons and the measured spectrum.
Depends on:
Detector geometry
Conversion probability
Internal structure of detector
Drift chamber efficiency
PRD 86, (2012)

29. Radiation spectra
PRD 86, (2012)

30. Radiation spectra Full theoretical calculation
100 GeV data
Full theoretical calculation
Single field CFA fit with and without the spin correction.
Classical synchrotron radiation
PRD 86, (2012)

31. Enhancement
Quantum suppression of synchrotron radiation

32. Spin flip transitions

33. Spin flip transitions
’Polarization time’
For a 100 GeV electron in χ = 1 field ct becomes 10 μm or t = 32 fs
2 eksempler:
For a 100 GeV electron in a χ = 1 field cτs f becomes 10 μm or τs f = 32 fs. For
the more usual situation of a 1 GeV electron in a 1 T field, cτs f is 7.3 AU and τs f
is 61 minutes - a typical polarization time in an accelerator.
PRL 87, (2001)

34. The concept of formation length
The distances the emitted photon travels before it is separated by a Compton wavelength from the emitting electron.
High particle energy, low photon energy:
Long formation length
250 GeV e-, 1 GeV γ: lf = 0.1 mm

35. The concept of formation length
For synchrotron radiation one can relate the magnetic field to the formation length.
For a 100 GeV electron in a 1 kT field this corresponds to a 9 GeV photon.

36. A simple graphical explanation
Red is only to highlight one field line

37. Direct measurement of lf
45 μm target separation
Small excess around 400 MeV
Data has a preference for the Blankenbecler and Drell theory with the delta correction term.

38. Crystalline undulators
Periodically bent crystals consisting of silicon and germanium and made by molecular beam epitaxy.
Amplitude a > d
Stable channelling
Many periods
Low radiative loss

39. Crystalline undulators
Measured at MAMI
270 MeV electrons in planar channelling for a flat crystal (blue) and crystal undulator (red).
The excess is seen around the 1st harmonic at 70 keV.

40. And thanks for your attention!
Thanks to
the CERN NA63 collaboration in which this work was done.
Aarhus University:
Group of Ulrik Uggerhøj;
Helge Knudsen
Heine Thomsen
Jakob Esberg
Søren Andersen
Other members of NA63
Pietro Sona
Alessio Mangiarotti
Sergio Ballestrero
Tjeerd Ketel
Aarhus University:
Technical staff:
Per Christensen
Poul Aggerholm
And thanks for your attention!