1. ALPS II @ DESY Axel Lindner DESY
Any Light Particle Search II
ALPS DESY Axel Lindner DESY
IAXO workshop, Frascati, 18 April 2016

2. ALPS II motivation: a bibliometric look
Key words “axion”, “relaxion”, “axion-like particle”, “WISP” try to restrict analysis to “physics”
WoS, Scopus
Significant increase in WISP-related publications!

3. ALPS II physics motivation: theory
Axion cosmology: arXiv: [hep-lat] lattice QCD calculations are used to determine the amount of axion Dark Matter today via the temperature dependence of the axion mass.
Baryon genesis from the axion: Phys.Rev.Lett. 113 (2014) 17, this cold genesis requires a coupling of the Higgs to a new scalar with O(100 GeV) mass (to be tested at LHC!).
A naturally small electroweak scale: arXiv: [hep-ph] could be explained by a cosmological Higgs-axion interplay. The symmetry breaking scale fa may be at the same time the see-saw scale explaining the active neutrino masses, mA ~ mν ~ 1/fa , JHEP 1406 (2014) 037
There are viable theoretical models addressing fundamental problems in cosmology and particle physics based on axion-like particles or other WISPS.

4. TeV photons may “hide” as axions.
ALPs in the sky (1)
Axion-like particles might explain the apparent transparency of the universe for TeV photons:
TeV photons may “hide” as axions.
M. Meyer, 7th Patras Workshop on Axions, WIMPs and WISPs, 2011

5. ALPs in the sky (1)
New FERMI limits on ALPS from search for irregularities in the spectrum of NGC1275 ( Do we start to zoom into the properties of the axion-like particle explaining the TeV transparency hint?

6. ALPs in the sky (2)
Hints for ALPS from developments of stars (M. Giannotti, I. Irastorza, J. Redondo, A. Ringwald, Indications for “BSM energy losses” of different kinds of stars could be consistently explained by one axion-like particle coupling to photons and electrons. It could be the same ALP as the one explaining the “TeV transparency”.
electron coupling

7. Purely laboratory experiments

8. ALPS I 2007-2010: our starting point
(PLB Vol. 689 (2010), 149, or
Unfortunately, no light was shining through the wall!
The most sensitive WISP search experiment in the laboratory (up to 2014).
laser hut
HERA dipole
detector
3.5·1021 1/s
< /s

9. The ALPS II challenge
Improve on the ALPS-photon-photon coupling strength g by > 1,000.
The experiment measures a rate ~ g4:
The experimental sensitivity is to increased by a factor 1012!

10. Prospects for ALPS II @ DESY
laser hut
HERA dipole
detector
Laser with optical cavity to recycle laser power, switch from 532 nm to 1064 nm, increase effective power from 1 to 150 kW.
Magnet: upgrade to straightened HERA dipoles instead of ½+½ used for ALPS I.
Regeneration cavity to increase WISP-photon conversions, single photon counter (superconducting transition edge sensor).
All set up in a clean environment!

11. ALPS II is realized in stages (JINST 8 (2013) T09001)
ALPS I: basis of success was the optical resonator in front of the wall.
ALPS IIa
Optical resonator to increase effective light flux by recycling the laser power
Optical resonator to increase the conversion probability WISP→

12. ALPS II is realized in stages (JINST 8 (2013) T09001)
ALPS I: basis of success was the optical resonator in front of the wall.
ALPS IIa
The optics concept was invented three times independently:
Hoogeveen F, Ziegenhagen T. Nucl. Phys. B358:3 (1991)
Fukuda Y, Kohmoto T, Nakajima Si, Kunitomo M. Prog. Cryst. Growth Charact.Mater. 33:363 (1996)
Sikivie P., Tanner D.B., van Bibber K. Phys.Rev.Lett. 98 (2007)
Optical resonator to increase effective light flux by recycling the laser power
Optical resonator to increase the conversion probability WISP→

13. ALPS II is realized in stages (JINST 8 (2013) T09001)
ALPS IIa
ALPS IIc
20 HERA dipoles, 200 m long

14. The ALPS II challenge Photon regeneration probability: ALPS II:
FPC = 5000, FRC = (power build-up in the optical resonators)
B = 5.3 T, l = 88 m (two times)
P = 6·10-23 , 30 photons per hour
P = 6·10-27 , 2 photons per month

15. ALPS II: main experimental challenges
HERA dipole magnets: straighten the cold mass cheap and reliably to increase the 35 mm aperture to 50 mm.
Optics: construct and operate two 100 m long optical resonators of high quality which are mode matched and aligned to better than 10 µrad.
Detector: characterize and operate a superconducting Transition Edge Sensor (25µm·25µm·20nm) at 80 mK to count single 1064 nm photons.
DESY expertise, but mostly retired experts only.
Adapt LIGO techniques, AEI Hanover, U. of Florida, DESY
DESY, HH, Mainz, in close collaboration with NIST (Boulder) and PTB Berlin

16. ALPS II optics Production cavity, infrared Wall
Regeneraton cavity, locked with green light.

17. ALPS II optics Production cavity, infrared Wall
Regeneraton cavity, locked with green light.

18. ALPS II optics Production cavity, infrared Wall
Regeneraton cavity, locked with green light.

19. ALPS II optics
Pound-Drever hall “locking“ to compensate for seismic noise fluctuations. ok
Differential wavefront sensing for auto-aligning the optical axis of the cavity. ok

20. ALPS II optics
Generate and adapt 532 nm light to control the regeneration cavity behind the wall (ok)

21. ALPS II optics
Feed 532 nm light into the regeneration cavity with “perfect” filtering out 1064 nm light. (ok)

22. ALPS II optics
Pound-Drever hall “locking“ to compensate for seismic noise fluctuations. (ok)
Differential wavefront sensing for auto-aligning the optical axis of the cavity. (ok)

23. ALPS II optics
Design and build central breadboard with two flat mirrors fixed and aligned to an accuracy better than 10 µrad (ok)

24. ALPS II optics
Guide 1064 nm signal photons into the detector with “perfect” filtering out 532 nm light (ok)

25. The photon source
The laser has been developed for LIGO: 35 W, 1064 nm, M2<1.1 based on 2 W NPRO by Innolight/Mephisto (Nd:YAG (neodymium-doped yttrium aluminium garnet)

26. The central optics
0,0006 mm

27. Status of optics (1)
Before late 2015 faulty cavity mirrors exceeding the roughness specification prevented a stable cavity operation. New mirrors were ordered to test the 20 m setup ALPS IIa with a confocal cavity:
Goals:
Understand properties of the cavity.
Be able to lock the cavity for “infinity”.
Get the auto-alignment system into operation.

28.  Status of optics (2) Understand properties of the cavity.
Be able to lock the cavity for “infinity”.
Get the auto-alignment system into operation. 
There are 200 ppm unexplained losses which will probably vanish once we operate the cavity in vacuum.

29.   Status of optics (3) Understand properties of the cavity.
Be able to lock the cavity for “infinity”.
Get the auto-alignment system into operation. 
The seismic noise in the ALPS IIa lab can be handled by the control system.

30.    Status of optics (4) Understand properties of the cavity.
Be able to lock the cavity for “infinity”.
Get the auto-alignment system into operation.  

31. Optics: next steps
Implement the a simplified version of the central breadboard.
Operate 10 m production cavity.
Operate production cavity in vacuum.
High power tests in vacuum.
Implement prototype of central breadboard.
Test the (simultaneous) operation of both cavities.

32. Control loops for the ALPS II PC at work
control signal
error signal

33. Control loops for the ALPS II PC at work

34. ALPS II detector
Transition Edge Sensor (TES)

35. ALPS II detector
Transition Edge Sensor (TES)
ΔT  100 µK

36. ALPS II detector
Transition Edge Sensor (TES)
ΔT  100 µK
ΔR  1 Ω

37. ALPS II detector Transition Edge Sensor (TES) ΔT  100 µK ΔR  1 Ω
ΔI  70 nA

38. ALPS II detector Transition Edge Sensor (TES)
ΔT  100 µK
ΔR  1 Ω
ΔI  70 nA
Expectation: very high quantum efficiency, also at 1064 nm, very low noise.

39. ALPS II: Transition Edge Sensor (TES)
25 x 25 µm2
8 µm

40. ALPS II: Transition Edge Sensor (TES)
Tungsten film kept at the transition to superconductivity at 80 mK.
Sensor size 25µm x 25µm x 20nm.
Single 1066 nm photon pulses!
Energy resolution 8%.
Dark background 10-4 counts/second.
Ongoing: background studies, optimize fibers, minimize background from ambient thermal photons.

41. ALPS II: heterodyne detection under study in Florida
Mix signal with a local oscillator and look for beat-signal.
Strong requirements on phase stabilities.
Courtesy Guido Mueller

42. ALPS II schedule (rough)
2015
2016
2017
2018
2019
ALPS IIa
(without magnets)
Install.
risk assessments
Runs
ALPS IIc
Closure of the LINAC tunnel of the European XFEL under construction at DESY.
ALPS IIa today
ALPS IIc in in the HERA tunnel

43. ALPS II schedule (rough)
Latest input from QED VMB studies on the ALPS IIc design!
2015
2016
2017
2018
2019
ALPS IIa
(without magnets)
Install.
risk assessments
Runs
ALPS IIc
Closure of the LINAC tunnel of the European XFEL under construction at DESY.
ALPS IIa today
ALPS IIc in in the HERA tunnel

44. The axion-like particle landscape

45. ALPS II ALPS II sensitivity Well beyond current limits.
Aim for data taking in 2019.
QCD axions not in reach.
Able to probe hints from astrophysics.
ALPS II

46. Beyond ALPS II Rough estimation with some crucial parameters:
QCD axions not in reach.
Able to probe hints from astrophysics.
Exp.
Photon flux (1/s)
Photon E (eV)
B (T)
L (m)
B·L (Tm)
PB reg.cav.
Sens. (rel.)
Mass reach (eV)
ALPS I
3.5·1021
2.3
5.0
4.4 22 1
0.0003
0.001
ALPS II
1·1024
1.2
5.3
106
468
40,000
0.0002
“ALPS III”
1·1025 15
400
6000
100,000
25-30
0.0001

47. ALPS III Beyond ALPS II QCD axions not in reach.
Could measure properties of a lightweight ALPs discovered by IAXO!
ALPS III

48. Summary
In addition to axions, also axion-like particles (ALPs) are going strong.
ALPs are expected in extensions of the Standard Model.
Astrophysics phenomena might point at the existence of ALPs.
ALPs might also constitute the dark matter.
ALPS II has a sufficient sensitivity to discover axion-like particles or other WISPs, especially in the region hinted at by astrophysics.
ALPS II will conduct a first hidden photon search in 2017.
The full experiment could be ready in 2019.
On the longer run, options for an “ALPS III” should be explored.
In WISP physics, haloscopes like IAXO and purely laboratory based experiments like ALPS II nicely complement each other!

49. Lessons learned from ALPS II
It is fascinating physics nicely complementing other particle physics enterprises:
New ideas are realized by combining different expertise.
Particle physics (DESY) and optics (LIGO) join forces.
Young people have fun taking responsibilities at ALPS II.
Four Ph.D. theses and two postdoc careers since the start in 2011.
At present eight Ph.D. and six postdocs are at work.
Funding works out!
Once ALPS II preparation had started seriously, external contributions got approved!

50. ALPS II and IAXO: a likely case
ALPS II discovery an axion-like particle.
The coupling strength to photons will be determined.
The mass might be measured or limited.
IAXO will see such axion-like particles produced in the sun.
Other couplings (electron, nucleon) could be probed.
Solar physics cold be probed.
With ALPS II and IAXO data we could narrow down the many opportunities of beyond-the-standard-model theories.

51. ALPS II and IAXO:

52. ALPS II and IAXO: an equally likely case
ALPS II does not see an axion-like particle.
IAXO is baldy required to solve the astroparticle physics riddles hinting at axion-like particles.
With IAXO and ALPS III data we could narrow down the many opportunities of beyond-the-standard-model theories.
Thank your for your attention!