Download Any Light Particle Search - (ALPS) experiment

Any Light Particle Search – ALPS II
Natali Kuzkova
Ph.D. student, DESY
PIER PhD seminar
20th January, 2015
Fundamental questions: physics beyond the Standard Model
> Standard Model (SM) of particle physics
describes basic properties of known matter
and forces.
> SM not a complete and fundamental theory:
 No satisfactory explanation for values of its many
parameters. Why is the neutron dipole moment so
tiny? → charge parity (CP) conservation in
quantum chromodynamics (QCD);
 No quantum theory of gravity;
 No explanation of the origin of the dark sector of
the universe. What constitutes dark matter and
dark energy?
> Astrophysical riddles:
 Why is the universe transparent to TeV photons?
 Why do white dwarfs cool so fast?
 Why is there a soft X-ray excess from galaxy
clusters?
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[NASA]
Fundamental questions: physics beyond the Standard Model
Well-motivated SM extensions provide
dark matter candidates:
 Neutralinos and other Weakly Interacting
Massive Particles (WIMPs);
 Axions and other very Weakly Interacting
Slim (ultra-light) Particles (WISPs).
Axion like particles (ALPs), light spin
particles
called
"hidden
sector
photons" or light minicharged particles.
 The axion provides the most elegant
solution to the strong CP problem;
 ALPs are embedded in string theory
inspired Standard Model extensions;
 ALPs, axions (and other WISPs) could
explain dark matter;
 They would be a good explanation for
several astrophysical phenomena
(TeV transparency, white dwarf cooling).
[Kim, Carosi 10]
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TeV Transparency
 One astrophysical hint pertains to the
propagation of cosmic gamma rays with
TeV energies.
 Even if no absorbing matter blocks the way
of these high energy photons, absorption
must be expected as the gamma rays
deplete through electron-positron pair
production
through
interaction
with
extragalactic background light.
 The anomalous transparency can be
explained if photons convert into ALPs
in astrophysical magnetic fields. The
ALPs then travel unhindered due to their
weak coupling to normal matter.
 Close to the solar neighborhood, ALPs
could then be reconverted to highenergy photons.
[Manuel Meyer, PATRAS Workshop 2011]
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Light-Shining-Through-a-Wall experiment
> How to detect ALPs:
 Light from a strong laser is shone into a
magnetic field;
 Laser photons can be converted into a
ALPs (WISPs) in front of a light-blocking
barrier (generation region) in a magnetic field
and pass the wall;
 Behind the wall, the ALPs reconverted into
photons back in a magnetic field;
 Light is detected by a detector.
WISPs produced by laser light as well
as reconverted photons originating
from these WISPs have laser-like
properties. This allows to:
 Guide them through long and narrow
tubes inside accelerator dipole
magnets;
 To exploit resonance effects by
setting up optical resonators.
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Present and future of the ALPS
> The ALPS Collaboration started its first
Light-Shining-Through-a-Wall experiment to
search for photon oscillations into WISPs in
2007. Results were published in 2009 and
2010. The ALPS I experiment at DESY set the
world-wide best laboratory limits for WISPs in
2010, improving previous results by a factor of
10.
> After its completion the ALPS collaboration
decided to continue looking for WISPs by
designing the ALPS II experiment for probing
further into regions where there are strong
astrophysical hints for their existence.
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Stages of the experiment
ALPS I
Parameters of the long
cavity of ALPS-IIa:
• 20 m length;
• Two 750 ppm curved
mirrors (250 m ROC);
• Finesse 4100.
ALPS-IIa
Advantages of the long
cavity:
• More stable: G-factor
0,85 (for 10 m flat/curved:
G-factor 0,96);
• Two mirrors from the
same coating run;
• Impedance
matched
cavity.
ALPS-IIc
 ALPS-IIa: with two 10m long production and regeneration
cavities, without HERA superconducting dipole magnets;
 ALPS-IIc: with two 100m long cavities using magnets.
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Conceptual design
> A major challenge of the ALPS II optical design is the stabilization of both optical
cavities to ensure a decent overlap between the optical modes.
> To avoid disturbance of the single photon detector with spurious photons from optical
readout of the regeneration cavity mode, an auxiliary green beam obtained via second
harmonic generation from the infrared production field is fed into the regeneration
cavity. The green light is then separated from the infrared signal field prior to detection. A
production probability for 1064 nm from 532 nm photons of less than 10-21 photons is to
be achieved.
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Production and regeneration cavities
> Schematic of the ALPS-II injection stage including the production cavity (PC):
> Schematic of the ALPS-II regeneration cavity (RC) including control loop:
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Optical setup of the ALPS II
The resonant enhancement of the production and regeneration process is a key feature of the
experiment. WISP flux from the production region is increased by a factor equal to the power
buildup of the production cavity (PB PC = 5 000) and likewise is the reconversion probability
on the right-hand side of the wall enhanced by the power buildup of the regeneration cavity
(PB RC = 40 000) when both cavities resonate on the same optical mode.
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Laser system
An end-pumped laser design was chosen to
achieve a well defined Gaussian mode and an
efficient amplification with excellent beam quality.
> 35 W, 1064 nm laser power;
> Single mode;
> Single frequency;
> High intrinsic frequency
stability;
> Frequency modulation with
PZT.
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Present status of the experiment
> Using a 532 nm green laser which was aligned inside the beam pipe a central position of
a laser beam which will go through the PC and RC mirrors was set. The results proved
that it will be possible to achieve a power buildup 40000 with 0,025 m (2,5 cm)
available effective mirror diameter. Behind the wall, the regeneration cavity increases
the production probability with which photons are created from the axion field by a factor
of 40000.
> Calculated dependence of the power buildup vs effective mirror diameter to achieve a RC
buildup 40000:
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ALPS II in the HERA tunnel
Straightening magnets
> To increase the sensitivity for the
detection of axion-like particles, the
ALPS-II collaboration plans to set up
optical cavities both on the production
and the regeneration side of the
experiment and magnet strings of
superconducting HERA dipoles as
long as possible, as the sensitivity for the
detection of axion-like particles scales
with the product of magnetic field
strength B and magnetic length L.
> The maximal length is determined by the
aperture of the beam tube, because ALPS II schedule
clipping losses of the laser light are to be
avoided. Such an aperture would limit
ALPS II to 8 magnets.
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