Presentations topics (initial wishes)Available dates November 9,11,13,16,18,20,23Initial review dates: October 15,20,22,27Final review dates: October 28, November 3,5,10,12

chk.pt talkVaiskh Rajeev Astrophysical sources of neutrinos Oct.15 Nov. 9Jackson Slater Cosmic Microwave Background Oct.15 Nov. 9Ryne Dingler Shape of the Universe Oct.20 Nov. 11Sully Billingsley AI – efficiency in computing Oct.22 Nov. 11Abigail Hays Gravitational waves Oct.27 Nov. 23Macon Magno Neutron stars Oct.20 Nov. 13Susan Bataju ATLAS calorimetry or tracking Oct.20 Nov. 16Elijah Cruda Electronic readout in ATLAS Oct.22 Nov. 16Ryan Guess Atomic/nuclear physics Oct.15 Nov. 18Ian Perkin-Smith Fission Oct.22 Nov. 18Mohammed Saadawy Higgs boson physics Oct.22 Nov. 20Mitchell Schmenk Fusion physics Oct.27 Nov. 20Regan Thornberry Jets in High energy collisions Oct.27 Nov. 23Robert Moore Noether theorem Oct.20 Nov. 13

Name of the Speaker and subject:

Presentation Assessment Worksheet On a scale of 0 to 5, 0 being the lowest possible score, assess the following criteria that would be expected of a good presentation of scientific information. Add comments to each line in the comment box.

Criterion Score 1. Physics content: Is it presented clearly and substantively? Are physics principles applied correctly? Are main assumptions stated?

2. Mathematical/conceptual content: Is it done clearly and correctly? Are steps shown or explained? Are assumptions made clear?

3. Delivery: Is the speaker loud enough to be heard by everyone in the room? Did the speaker use slides appropriately? Was the presentation within the time allotted?

4. Organization: Did the slides include key elements: – a title slide, an introduction, a body of content, conclusions and a list of sources?

5. Slide Quality: Was the size of the fonts large enough to be visible by everyone in the audience? Was the graphical arrangement adequate?

FINAL SCORE: ____________________/25 Points

COMMENTS

To detect a signal we need to transfer the light signal through themedium to a detector that will transform light signal into an electrical pulse.

Introduction The molecular spectroscopy is the study of the interaction of electromagnetic waves and matter. The scattering of sun’s rays by raindrops to produce a rainbow and appearance of a colorful spectrum when a narrow beam of sunlight is passed through a triangular glass prism are the simple examples where white light is separated into the visible spectrum of primary colors. This visible light is merely a part of the whole spectrum of electromagnetic radiation, extending from the radio waves to cosmic rays. All these apparently different forms of electromagnetic radiations travel at the same velocity but characteristically differ from each other in terms of frequencies and wavelength (Table 1).

Table 1: The electromagnetic spectrum

Radiation type Wave length

λ , (Ǻ)

Frequency

ν = c / λ, (Hz)

Applications

radio 1014 3 x 104

Nuclear magnetic resonance 1012 3 x 106

Television 1010 3 x 108

Radar 108 3 x 1010

Spin orientation

Microwave 107 3 x 1011 Rotational

Far infrared 106 3 x 1012

Near infrared 104 3 x 1014

Vibrational

Visible 8 x 103 - 4 x 103 3.7 x 1014 -

7.5 x 1014

Ultraviolet 3 x 103 1 x 1015

X-rays 1 3 x 1018

Electronic

Gamma rays 10-2 3 x 1020

Cosmic rays 10-4 3 x 1022

Nuclear transitions

The propagation of these radiations involves both electric and magnetic forces which give rise to their common class name electromagnetic radiation. In spectroscopy, only the effects associated with electric component of electromagnetic wave are important. Therefore, the light wave traveling through space is represented by a sinusoidal trace (figure 1). In this diagram λ is the wavelength and distance A is known as the maximum amplitude of the wave. Although a wave is frequently characterized in terms of its wavelength λ, often the terms such as wavenumber ( ν ), frequency (ν), cycles per second (cps) or hertz (Hz) are also used.

2

1 angstrom = 10-10 m

Light transmission through total internal reflection is known since ~1840.Initially used mostly for illumination of fountains. First famous “jet d’eau” in Geneva was designed in 1886 and equipped with light sources. Optical quartz fibers were originally developed for signal transmission during nuclear tests. Electrical signals were unreadable due to e-m shock wave of the explosion. Such fibers were later used for the cameras in first Moon missions and spy planes. Commercial fibers made from pure silica or various plastics were developed in late 1970ties for telecommunication. Plastic optical fibers can be doped with scintillating compounds. There are also capillary tubes filled with liquid scintillator.They can be used for construction of fiber tracking devices.Since there is no “cross-talk” effect – optical fibers provide flexiblesolutions for difficult geometries of the detector.

Radiation spectra

UV

Jet d’eau, Geneve300 ft

Optical fibers as light guides

corepolystyrene

n=1.59

cladding(PMMA)n=1.49

typically <1 mm

typ. 25 µm

q

n1

n2

light transport by total internal reflectionIdealized (wrong) estimateθ ≥ arcsin n2/n1 ~ 69.6o

Light is generated mostly away from fiber axis.Light transport is mostly away from the cross-sectional plane

Wavelength shifters

p-terphenylC6H5C6H4C6H5

absorption emission

Total internal reflection in a fiber

Condition for trapping

�

sinθ 1− ρrsin(ϕ −Φ)

⎛ ⎝ ⎜

⎞ ⎠ ⎟ 2

≤ sinθ tr

Fibers doped with scintillators

Fiber tracking arrangements

a) axialb) circumferentialc) helical

Advantages: low mass, fine granularity, fast readout

Charged particle passing through a stack of scintillating fiberswith 1 mm diameter

Photo detectors

Use photoelectric effect to convert light into electrical signalsSensitivity usually expressed as quantum efficiency

QE = Nphotoelectrons/Nphotons

Photomultipliers3-step process in the photocathodes

photo ionization of moleculeelectron propagation through photocathodeescape of the electron into vacuum

Typical photocathodes are semiconductors

Photon energy has to be sufficient to bridge the band gap Eg, but also to overcome the electron affinity EA, so that the electron can be released into the vacuum.

Dynode gain ~4, so a PMT with 10 dynodes has a gain 410 ~106

Quantum efficiency of typical photo cathodes

BialkaliSbK2Cs

MultialkaliSbNa2KCs

Energy resolution of a PMT is determined by the fluctuationsof the number of secondary electrons emitted from dynodes.Poisson fluctuations

!),(

menmnPmm -

=

Relative fluctuations nnn

nn 1

==s

Dominated by the fluctuations when the numbers are smalli.e., at the first dynode.PMT’s are in general very sensitive to B-fields, even to earth field (30-60 µT) -> μ-metal shielding required.

Time resolution improvement - Multichannel plate MCP

Solid state photon detectors

PiN diodes: thin p layer to avoid light absorption by siliconhigh quantum efficiency (~80% at 700 nm)no gain – used for high light yield readouts

APD avalanche photo diodes:high reverse bias voltage ~100-200 Vhigh internal field -> avalanche multiplicationgain ~100

start stop

Time of FlightcLtb

=

)( 0bgmp =

12

22-=

Ltcpm

÷øö

çèæ ++=

LdL

tdt

pdp

mdm 2gMass resolution

( ) ( )22212

2222

2221

21 2/1/111 mm

pLcpcmpcm

cL

cLt -»+-+=÷÷

ø

öççè

æ-=Dbb

TOF difference of 2 particles at a given momentum

Performance depends n the timing resolution of the device.This year (2020) timing resolution of the LGADs (Low Gain Avalanche Devices)reached 10 ps timing resolution.

For σt = 300 psπ/K separation up to~ 1 GeV/c

L = 15 m

NA49 experiment

T rel.=

T /

T p

Cherenkov radiationSpeed of light in vacuum - cSpeed of light in a material - c/n(λ)

n - index of refraction, λ - wavelengthIf the velocity of a particle is such that β = vp/c > c/n(λ), a pulse of light is emitted around the particle direction with an opening angle (θc )

vp/c < c/n(λ)symmetricdipoles

vp/c > c/n(λ)coherent wavefront

dielectric, polarizable medium

•The threshold velocity is βc = 1/n•At velocity below βc no light is emitted•If velocity exceed phase velocity of light (rather than group velocity)there is a Cherenkov light emission

Cherenkov angle

Cherenkov photon emission – cone around particle direction•Typical intersection of cone with a photon detection plane – ring

RICH – ring imaging detector counter•Weak effect, causes no significant energy loss (<1%)•It takes place only if the track L of the particle in the radiating medium is longer than the wavelength λ of the radiated photons.

Cherenkov radiation glowing in the core of a reactor Particle physics detector

Momentum measurement + velocity threshold -> particle mass identification(at fixed momentum p=m×v particle with larger mass will have lower velocity andmay be below threshold for production of Cherenkov light)Angle + momentum measurement: cosθc = 1/(nβ) -> mass

PM

particle

mirrorradiator medium

thresholdring

SuperKamiokande, JapanSearch for proton decay and neutrino interactions

Number of emitted Cherenkov photons per unit path length and unit wavelength interval (emission spectrum)

.with 1

sin2112

2

2

2

22

2

222

22

constdxdENd

Ehcc

dxdNd

zn

zdxdNd

C

===µ

=÷÷ø

öççè

æ-=

nl

ll

qlap

blap

l dN/dl

l

Most at short wavelength – deep UVNumber of photons detected

( )dEEEc

LNi

i

E

EQep Õò= eeaq

2

1

)(sin2..!

Emission spectrumPhoto detector sensitivity

Use wavelengthshifters !