EXPERIMENTAL INVESTIGATIONS OF SYNCHROTRON RADIATION AT THE ONSET OF THE QUANTUM REGIME

Transcription

1 EXPERIMENTAL INVESTIGATIONS OF SYNCHROTRON RADIATION AT THE ONSET OF THE QUANTUM REGIME DEPARTMENT OF PHYSICS AND ASTRONOMY, AARHUS UNIVERSITY

2 MOTIVATION Test of quantum mechanical calculations of synchrotron radiation. Relevant for linear colliders, astrophysical objects like magnetars, heavy ion collisions and more. Magnetar SGR

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

4 SYNCHROTRON RADIATION Typical radiated energy is The strong field parameter The critical field is B photons electrons

5 dn/d SYNCHROTRON RADIATION 10 Classical synchrotron radiation Incident energy, E e =10 GeV Critical energy 0.01 Standard magnet, B = 1 T, 1m Si <110> max, B equiv = T, 0.1 mm Photon energy [MeV]

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- From the CLIC conceptual design report

9 MAGNETARS B = 10 GT > B 0 Neutron star of radius 20 km and greater mass than the sun. Gamma and X-ray emitters On the surface of quark stars 9

10 THE NA63 EXPERIMENTS Use crystalline fields to measure the quantum corrections to synchrotron radiation. 10

11 EXPERIMENTAL SETUP DC1 DC2 Krystal 11

12 GERMANIUM CRYSTAL Random orientation axis 12

13 CONTINUUM MODEL 13

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. 14

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. 15

16 THE CONSTANT FIELD APPROXIMATION Radiation emission angle: Deflection angle: Criterium for constant field approx. Magnetic bremsstrahlung 16

17 THE CONSTANT FIELD APPROXIMATION Classical synchrtron radiation The constant field approximation Two changes: Spin and recoil 17

18 THE CONSTANT FIELD APPROXIMATION Spin contribution: NIMB 119 (1996) 2 18

19 CRYSTAL RADIATION Average over positions in crystal. Strong field parameter For germanium Baier et al. 19

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

21 DEFLECTION AND DETECTION DC2 Crystal DC3 MBPL magnet LG 21

22 PILE UP AND CALOMETRIC EFFECT Lead glass detector Photon energy Multiphoton effects: Less photons at low energies A slight increase at high energies 22

23 PAIR SPECTROMETER DC5 DC6 Cu conversiontarget MDX magnet 23

24 GEOMETRIC CONSTRAINTS 2.0 m 3.2 m e - q - Drift chamber width: 15 cm MDX DC5 q + DC6 e + DC6 angle constraint: corresponding to Energy threshold: for DC6. 24

25 GEOMETRIC CONSTRAINTS 25

26 MONTE CARLO SIMULATIONS OF PS Compare the background measurements to the Bethe-Heitler formula. PRD 86, (2012) 26

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) 27

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) 28

29 RADIATION SPECTRA PRD 86, (2012) 29

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

31 ENHANCEMENT Quantum suppression of synchrotron radiation 31

32 SPIN FLIP TRANSITIONS 32

33 SPIN FLIP TRANSITIONS Polarization time For a 100 GeV electron in χ = 1 field ct becomes 10 μm or t = 32 fs PRL 87, (2001) 33

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: l f = 0.1 mm 34

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. 35

36 A SIMPLE GRAPHICAL EXPLANATION 36

37 DIRECT MEASUREMENT OF L F 45 μm target separation Small excess around 400 MeV Data has a preference for the Blankenbecler and Drell theory with the delta correction term. 37

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 38

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. 39

40 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! 40