RIChilights

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RIChilights

• RICH2007 Highlights (Part III)
• Stefania Ricciardi
• RAL, 28 November 2007

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Piazza Unita dItalia

• Caffe degli Specchi (Mirrors)
• One of Trieste institutions appreciated by
  Kafka, Joyce
• and British Royal Navy which chose it as General
  Quarter at the end of second World War
• Named after large mirrors on the wall used to
  reflect inside the light from the sunset on the
  sea

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Right ingredients for a successful RICH
conference!
Piazza Unita dItalia
Mirrors
Water
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RICH2007 Sessions

• Cherenkov light imaging in particle and nuclear
  physics experiments
• Cherenkov detectors in astroparticle physics
• Novel Cherenkov Imaging Techniques
• Photon detection for Cherenkov counters
• Technological aspects of Cherenkov detectors
• Pattern recognition and data analysis
• Exotic applications of Cherenkov radiation

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RICH in AstroParticle Physics

• Cherenkov detectors are fundamental in many APP
  sectors. Discussed _at_ RICH2007
• Ground-based gamma-ray astonomy
• _at_ RICH2007 MAGIC
• Cherenkov Imaging detectors for ion
  identification in CR (satellite and balloon-born
  experiments)
• Flying spectrometers
• _at_ RICH2007 CREAM
• High-energy n telescopes
• high mass targets ( 109 t)
• ? use large volumes of transparent
• media available in nature
• _at_ RICH2007 Antares,
• Nemo, KM3Net

(Ref to Recent seminar at RAL by Greg
Hallewell)
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The experimental challenge in high energy
astrophysics
E.Lorenz

• INITIAL PARAMETERS NOT UNDER CONTROL AS IN HEP
• ENERGY , TIME, (PATRICLE TYPE), (DIRECTION)
• FLUXES ARE VERY LOW -gt NEEDS ULTRA-LARGE
  DETECTOR VOLUMES
• WATER ICE AIR
• natural media act as target and radiators
  (transparent to light) ? allow the construction
  of massive Cherenkov instruments with excellent
  performance for neutrino and astroparticle
  physics
• NEARLY ALL EXPERIMENTS IN APP RELY ON PHOTON
  DETECTION
• Need for large-active-area single-photon
• AstroParticle Physics is now a driving force for
  new photon detectors.

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GROUND-BASED g ASTRONOMY

• Started in 1989 by discovery of gs from the CRAB
• Nearly all discoveries made by Cherenkov light
  detectors (gt 95)
• Imaging Air Cherenkov Telescopes

44 SOURCES (13 As) (NOW(FALL07) 70
SOURCES
2006)
NOT ALL SOURCES IN INNER GALACTIC PLANE SHOWN
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The IACT technique

• Physics of the atmospheric showers
• Cosmic rays (protons, heavier Z, electrons,
  photons) hit the upper atmosphere
• Interactions create cascade of billions of
  particles
• Electromagnetic shower (e,e-,?)
• Hadronic shower (??, ??, e,e-,?)
• Charged particles in turn emit Cherenkov light
• Blueish flash
• 2ns duration
• 1º aperture
• Cherenkov cone reaches the ground
• Circle of 120m radius

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IACT g-image
Image is ellipsoid pointing to centre for gammas
(axis aligned with g-source) Randomly distributed
for hadrons Study of the image gives information
on primary particle
Sensitivity to single photons and the best
possible time resolution are important, because
the signal is weak, and the discrimination
against non-electromagnetic showers is helped by
determining precise arrival times. Signal100
photons/m2 at 1 TeV Background 2-5 1012
photons/(s m2 sr) High quality photomultipliers
are used as photon detectors.
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THE NEW GENERATION OF HIGH SENSITIVITY CHERENKOV
TELESCOPES
MAGIC(Germany, Italy Spain) 20031 telescope
17 meters Ø
VERITAS(USA England)20074 telescopes10
meters Ø
Whiple obs. Base camp Arizona
Roque delos Muchachos, Canary Islands
CANGAROO III(Australia Japan) 20044
telescopes 10 meters Ø
Komas land, Namibia
HESS(Germany France) 20024 telescopes 12
meters Ø
Woomera, Australia
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The MAGIC Telescope
M.Doro

• Collaboration of 22 institutes (mostly European)
  150 physicists
• Installation completed 2003

• Clone (Magic II) under construction
• Inauguration 2008
• Stereoscopic MAGIC I II will have increased
  performanceangular resolution
• energy resolution, flux sensitivity

Focal plane camera with 580 PMTs
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M.Doro

• MAGIC
• Reflector and mirrors
• World largest dish diameter 17m
• All aluminium mirrors with sandwich structure and
  diamond-milled surface

Mirror requirements
Lightweight Telescope must rotate fast and then mirrors need to be as light as possible
Mirror Shape Mirrors profile is spherical Each mirror has different radius of curvature because reflector profile is parabolic (f17m)
Rigidity Avoid oscillations due to wind Avoid bending during tracking
Insulation Sometimes strong rains and snows, high humidity, strong UV light
Optical quality Maximize reflectivity Minimize reflected spot size
AlMgSi0.5 plate
Hexcell
Al Box
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MAGIC Summary
M.Doro

• MAGIC II mirrors production is already on the
  production-line
• Technique gave excellent results in term of light
  concentration
• Insulating problems seem solved
• Price is decreased wrt to MAGIC I, nevertheless
  is still main drawback 2.8k/m2 can be a problem
  for third generation IACTs
• Scale production can decrease costs or find other
  techniques (glass)

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NEXT AIR CHERENKOV TELESCOPE PROJECTS

• Aim for higher sensitivity (factor 10 increase),
  lower threshold (lt50 GeV)
• European initiative CTA (Cherenkov telescope
  array)
• US Project AGIS
• Both in the 100-150 M price range, 50-100
  telescopes

CTA
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Y.Sallaz-Damaz
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CREAM
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CHERCAM a flying Cherenkov..
Launch expected Dec 2007
Optimised for charge measurement (Nph? Z2
sin2q, resolution 0.2 charge units) Has to
operate a low temperature/low pressure (-10C,
5mb)
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SuperK (multiple) rings
PID and Pattern recognition can be a complex
business many challenges..
2 electron candidates
2 muon candidates
The largest Cherenkov in use at an
accelerator-based experiment 50ktonnes water
viewed by 13,000 20 PMTs
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In Search of the Rings
(not the speaker)
Approaches to Cherenkov Ring Finding and
Reconstruction in HEP
Guy Wilkinson, Oxford University RICH 2007,
Trieste, October 2007
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Challenges of RICH pattern recognition in PP
LHCb RICH 1 (revolved !)
Complicated environment ! Lesson 1 main source
of background is other rings.
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Challenges in RICH Pattern Recognition
LHCb RICH 1 (revolved !)
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Likelihood algorithms
Likelihood approach is most common method of
pattern-recognition PID (note - it performs
both steps!) for experiments where tracking info
is available.
eg. LHCb, BaBar, CLEO-c, Hermes, HERA-B, DELPHI,
SLD
For a given set of photons which are candidates
to be associated with the track, formulate a
likelihood for each particle hypothesis (e, µ, p,
K, p). Eg. for CLEO-c
1 lt p lt 1.5 GeV/c
background distribution
expect a certain number of photons, at a certain
angle, with a certain resolution
there may be several paths by which photon has
reached detector
Ratio of likelihoods, or difference of
log-likelihoods then gives a statistically meaning
ful quantity that can be cut on to distinguish
between hypotheses.
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Global Likelihood
Very often it is advantageous to calculate a
single (log) likelihood for all event, being the
(sum) product of the likelihoods for all of the
tracks in all radiators.

• In high-multiplicity environments, the
  background to each signal ring
• is other signal rings!

Only way to get an unbiased estimate for each
track is to consider entire event simultaneously.

• In experiments with gt1 radiator or gt1 counters
  (eg. LHCb 3 radiators
• in 2 counters, SLD liquid and gas, HERMES
  aerogel and gas) this
• is a convenient way to make best use of all
  information.

Likelihood maximised by flipping each track
hypothesis in turn until convergence is attained.
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Performance of likelihood algorithms
Kaon identification efficiency, and ? misid
efficiency
LHCb K (or p) preferred hypothesis
BaBar LK gt L?
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Hough transforms
Hough Transform common technique in both
tracking ring finding. Attractive features -
unaffected by topological gaps in curves,
split images, and is rather robust against noise.
Each point gives surface in HT space.
Intersection of surfaces gives ring parameters.
Find by peak hunting in suitably binned
histogram.
Usual practice look for centre OR radius, ie.
reduce to 2-d or 1-d problem.
Used by several experiements in high-density
environment Alice, CERES
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Applications of Hough trasforms in n physics
SuperK
No tracking info available in SuperK standalone
ring-finding essential
Firstly find event vertex position based on
spread of hit PMT times
Find vertex to resolution of 30 cm Initial
direction indicator also available.
Then perform HT draw saturated (42 0) circles
around hit tubes to look for ring centres and
hence directions.
Iterate, to look for multiple ring candidates
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Conclusions on reconstruction and ID techniques
Likelihood algorithms and Hough Transforms have
proven record of making sense of even the most
intimidating environments. In general these make
significant use of tracking information.
Other approaches exist, but have not yet achieved
performance to displace baseline methods.
Will be interesting to see how methods developed
on MC for high multiplicity experiments (eg.
LHCb, ALICE) cope with real data!
COMPASS
STAR
BABAR DIRC
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Exotic applications of Cherenkov radiation
Ice
Salt domes
Lunar regolith
This is NOT exotic nowadays!
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Radio-Cherenkov detectors

• Active experiments
• RICE (since 1999)
• Anita

Physics UHE n Detection of EeV neutrinos (i.e.
GZK neutrinos produced in interaction of UHE
protons with CMB) p gCMB (? D ? np) ? n e ne
nm nm Flux is extremely low 10 GZK n/km2/y 300
Km interaction length for En1018 eV Need gtgt102
km3 volumes
Salsa
(Anita Collaboration)
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The Askaryan effect
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Anita
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The three of us did appreciate the conference
and the setting!
Conclusion
A.P.
S.E.
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Many thanks to the Organisers!
RICH 2007 Stazione Marittima, Trieste,
Italy October 2007