RICRIChhiilightslights

RICH2007 Highlights (Part III)

Stefania Ricciardi

RAL, 28 November 2007

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Piazza Unita` d’ItaliaCaffe` 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

WarNamed 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` d’Italia

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 @ RICH2007

1. Ground-based gamma-ray astonomy– @ RICH2007: MAGIC

2. Cherenkov Imaging detectors for ion identification in CR (satellite and balloon-born experiments)

– Flying spectrometers– @ RICH2007: CREAM

3. High-energy telescopes– high mass targets (≈ 109 t)

use large volumes of transparent media available in nature– @ RICH2007: Antares,

Nemo, KM3Net

(Ref to Recent seminar at RAL by Greg Hallewell)

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The experimental challenge in high energy astrophysics

INITIAL PARAMETERS NOT UNDER CONTROL AS IN HEP

ENERGY , TIME, (PATRICLE TYPE), (DIRECTION)

FLUXES ARE VERY LOW -> 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.

E.Lorenz

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GROUND-BASED ASTRONOMY Started in 1989 by discovery of s from the CRABNearly all discoveries made by Cherenkov light detectors (> 95%):Imaging Air Cherenkov Telescopes

44 SOURCES(13 As)

(NOW(FALL07) 70 SOURCES

NOT ALL SOURCES IN INNER GALACTIC PLANE SHOWN

2006)2006)

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The IACT techniquePhysics 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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

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IACT -image

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. Signal:100 photons/m2 at 1 TeVBackground: 2-5 1012 photons/(s m2 sr)High quality photomultipliers are used as photon detectors.

Image is ellipsoid pointing to centre for gammas (axis aligned with -source)

Randomly distributed for hadronsStudy of the image gives information on primary particle

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CANGAROO III(Australia & Japan)

20044 telescopes 10 meters Ø

Woomera, Australia

Komas land, Namibia

HESS(Germany & France)

20024 telescopes12 meters Ø

Roque delos Muchachos, Canary Islands

MAGICMAGIC(Germany, Italy & Spain)(Germany, Italy & Spain)

2003 20031 telescope 17 meters Ø1 telescope 17 meters Ø

Whiple obs.Base camp

Arizona

VERITAS(USA &

England)2007

4 telescopes10 meters Ø

THE NEW GENERATION OF HIGH SENSITIVITY CHERENKOV TELESCOPES

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The MAGIC Telescope• Collaboration of 22 institutes (mostly European) ~150

physicists• Installation completed 2003

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.M.Doro

Focal plane camera with 580 PMTs

Clone (Magic II) under constructionInauguration 2008

Stereoscopic MAGIC I + II will have increased performance:angular resolution

energy resolution, flux sensitivity

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MAGIC

Reflector and mirrors:– World largest dish diameter 17m

– All aluminium mirrors with sandwich structure and diamond-milled surface

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 (f=17m)

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

M.Doro

Mirror requirements

AlMgSi0.5 plate

Hexcell

Al Box

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MAGIC Summary

• 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)

M.Doro

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NEXT AIR CHERENKOV TELESCOPE PROJECTS

Aim for higher sensitivity (factor 10 increase), lower threshold (<50 GeV)a) European initiative: CTA (Cherenkov telescope array)b) US Project: AGISBoth 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..

Optimised for charge measurement (Nph Z2 sin2resolution 0.2 charge units)Has to operate a low temperature/low pressure(-10C, 5mb)

Launch expected Dec 2007

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SuperK (multiple) rings 2 electron candidates: 2 muon candidates:

PID and Pattern recognition can be a complex business – many challenges..

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 RingsApproaches to Cherenkov Ring Finding

and Reconstruction in HEP

Guy Wilkinson, Oxford UniversityRICH 2007, Trieste, October 2007

(not the speaker)

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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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LHCb: RICH 1(revolved !)

Ring without associated track

Sparselypopulatedrings

Split (orpartial)rings

Challenges in RICH Pattern Recognition

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Likelihood algorithmsLikelihood 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, π, K, p). Eg. for CLEO-c:

Ratio of likelihoods, or difference of log-likelihoods then gives a statisticallymeaningful quantity that can be cut on to distinguish between hypotheses.

,exp

,., ( | )j j j

optical joptical paths

hsignah backgrou ln

jdP PL P

backgrounddistribution

expect a certain number ofphotons, at a certain angle,with a certain resolution

there may be severalpaths by which photonhas reached detector

1 < p < 1.5 GeV/c

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Global LikelihoodVery 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 considerentire event simultaneously.

• In experiments with >1 radiator or >1 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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LHCb: K (or p) preferred hypothesisBaBar: LK > L

Kaon identification efficiency, and misid efficiency:

Performance of likelihood algorithms

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Hough transforms

Each point gives surface in HT space. Intersection of surfaces gives ring parameters. Find by peak hunting in suitably binned histogram.

xc

yc

r or θc

Detector space HT Space

Hough Transform

Hough Transform: common technique in both tracking & ring finding.Attractive features - unaffected by topological gaps in curves, splitimages, and is rather robust against noise.

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 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 cmInitial direction indicator also available.

Then perform HT: draw saturated (42 0) circles around hit tubes to look for ring centresand hence directions.

HT

Iterate, to look formultiple ring candidates

33.8 m

36.2

m 11,146 PMTs

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Conclusions on reconstruction and ID techniques

COMPASS

STAR

BABAR

DIRC

Other approaches exist, but have not yetachieved performance to displace baseline methods.

Likelihood algorithms and Hough Transforms have proven record of making sense of even the most intimidating environments. Ingeneral these make significant use of tracking information.

Will be interesting to see how methods developed on MC for high multiplicity experiments (eg. LHCb, ALICE) cope with real data!

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Lunar regolith

Salt domes

Ice

“Exotic applications of Cherenkov radiation”

This is NOT exotic nowadays!

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Radio-Cherenkov detectors

Physics: UHE Detection of EeV neutrinos(i.e. GZK neutrinos produced in interaction of UHE protons with CMB)p +CMB (→ * → n+) → n e+ e

Flux is extremely low: 10 GZK /km2/y300 Km interaction length for E=1018 eVNeed >>102 km3 volumes

(Anita Collaboration)

Active experiments:• RICE (since 1999) • Anita

Salsa

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The Askaryan effect

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Anita

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Conclusion

The three of us did appreciate

the conference and the setting!

A.P.

S.E.

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RICH 2007Stazione Marittima,Trieste, ItalyOctober 2007

Many thanks to the Organisers!