RIC h i

lights

RICH2007 Highlights (Part III)

Stefania Ricciardi

RAL, 28 November 2007

Piazza Unita` d’Italia

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 used to reflect inside the light from the sunset on the sea on the wall 2

Piazza Unita` d’Italia

Mirrors Water

Right ingredients for a successful RICH conference!

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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

1.

2.

3.

Cherenkov detectors are fundamental in many APP sectors. Discussed @ RICH2007 – Ground-based gamma-ray astonomy @ RICH2007: MAGIC Cherenkov Imaging detectors for ion identification in CR (satellite and balloon-born experiments) – – – Flying spectrometers @ RICH2007 : CREAM High-energy n telescopes high mass targets (≈ 10 9 t)  use large volumes of transparent media available in nature – @ RICH2007: Antares, Nemo, KM3Net (Ref to Recent seminar at RAL by Greg Hallewell) 5

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 -> 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 g s from the CRAB 44 SOURCES (13 As) Nearly all discoveries made by Cherenkov light detectors (> 95%): Imaging Air Cherenkov Telescopes (NOW(FALL07) 70 SOURCES 2006) NOT ALL SOURCES IN INNER GALACTIC PLANE SHOWN 7

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 , g ) – Hadronic shower (   ,   , e + ,e , g ) • Charged particles in turn emit Cherenkov light: – Blueish flash – ~2ns duration – ~1º aperture • Cherenkov cone reaches the ground – Circle of ~120m radius QuickTime™ and a TIFF ( Uncompressed) decompressor are needed to see thi s pi ctur e.

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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. Signal:100 photons/m 2 Background: 2-5 10 12 at 1 TeV photons/(s m 2 sr) High quality photomultipliers are used as photon detectors.

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THE NEW GENERATION OF HIGH SENSITIVITY CHERENKOV TELESCOPES VERITAS

(USA & England) 2007 4 telescopes 10 meters Ø

Whiple obs.

Base camp Arizona MAGIC

(Germany, Italy & Spain) 2003 1 telescope 17 meters Ø

Roque de los Muchachos, Canary Islands HESS

2002 4 telescopes 12 meters Ø

Komas land, Namibia

(Germany & France)

CANGAROO III

(Australia & Japan) 2004 4 telescopes 10 meters Ø

Woomera, Australia

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The MAGIC Telescope

• Collaboration of 22 institutes (mostly European) ~150 physicists • Installation completed 2003 M.Doro

are needed to see thi s pi ctur e.

Clone (Magic II) under construction Inauguration 2008 Stereoscopic MAGIC I + II will have increased performance:angular resolution energy resolution, flux sensitivity Focal plane camera with 580 PMTs 11

M.Doro

MAGIC Reflector and mirrors:

–

World largest dish diameter 17m

–

All aluminium mirrors with sandwich structure and diamond-milled surface

Lightweight

AlMgSi0.5 plate Hexcell

Mirror Shape

Al Box

Rigidity Insulation Optical quality

Mirror requirements • Telescope must rotate fast and then mirrors need to be as light as possible • Mirrors profile is spherical • Each mirror has different radius of curvature because reflector profile is parabolic (f=17m) • Avoid oscillations due to wind • Avoid bending during tracking • Sometimes strong rains and snows, high humidity, strong UV light • Maximize reflectivity • Minimize reflected spot size 12

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

€/m 2 can be a problem for third generation IACTs • Scale production can decrease costs or find other techniques (glass) 13

CTA

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: AGIS Both in the 100-150 M € price range, 50-100 telescopes 14

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  Z 2 sin 2 q, resolution 0.2 charge units) Has to operate a low temperature/low pressure (-10C, 5mb) 17

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

SuperK (multiple) rings

2 electron candidates: 2 muon candidates: The largest Cherenkov in use at an accelerator-based experiment 50ktonnes water viewed by 13,000 20” PMTs 18

(not the speaker)

In Search of the Rings

Approaches to Cherenkov Ring Finding and Reconstruction in HEP Guy Wilkinson, Oxford University RICH 2007, Trieste, October 2007 19

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 !) Ring without associated track Split (or partial) rings Sparsely populated rings 21

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, π, K, p). Eg. for CLEO-c: 1 < p < 1.5 GeV/c

L h

  g   

P backgrou n d

 

optical paths

,

j P



P signa l

( |

h j

exp .

q

j

)    background distribution there may be several paths by which photon has reached detector expect a certain number of photons, at a certain angle, with a certain resolution Ratio of likelihoods, or difference of log-likelihoods then gives a statistically meaningful 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 >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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Performance of likelihood algorithms

Kaon identification efficiency, and  misid efficiency: LHCb: K (or p) preferred hypothesis BaBar: L K > L  24

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. Detector space Hough Transform HT Space r or θ c y c x c 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 25

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 11,146 PMTs 33.8 m 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.

HT Iterate, to look for multiple ring candidates 26

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 + g CMB ( → D * → n  + ) → n e + n e n m n m Flux is extremely low: 10 GZK n /km 2 /y 300 Km interaction length for E n =10 18 eV Need >>10 2 km 3 volumes Salsa (Anita Collaboration) 29

The Askaryan effect

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Anita

31

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Conclusion

A.P.

S.E.

The three of us did appreciate the conference and the setting!

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Many thanks to the Organisers!

RICH 2007 Stazione Marittima, Trieste, Italy October 2007 34