Experimental Particle Physics. Day 1 Particle identification Detectors and experiment design Day2 ATLAS detector components Physics capabilities Harold Ogren, Professor of Physics Indiana University , Bloomington, IN. Outline of lectures for today. HEP experiments Particle ID
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# authors on a typical publication
Since that is the scale
Of many inner detectors
Such as ATLAS ID
Gluckstern, NIM 24,(1963)381-389
For short flight lengths (50 cm) and dt= 3ns/sqrt(13)=0.83 ns, particle
ID is only good in the sub GeV/c momentum range.
ps timing will allow pi/K separation well above 10 GeV!
Would require Micro Channel plates, not “normal” scintillators and photomultipliers. Resistive plate tracking chambers can give resolutions as good as 50 ps. (more on this later)
Use four vector notation
P=( p, iE/c) =( gmv, igmc)
In a vacuum without interaction the radiation of
The photon is at an unphysical angle for any velocity of the incoming particle. i.e no radiation
This kinematics constraint of radiation hold for all types of interactions of a
moving charged particle.
Radiation in the optical region which is produced along the entire path-length of the charged particle in the media
Transition radiation can be
understood in this manner since it must satisfy the same angular restriction. However, TR is produced only at the boundary.
Now, since n >1, there is a range of particle velocities 1>b >1/n that allows physical radiation of photons. The angle
Is called the Cerenkov angle.
animation of the radiation from a moving particle.
In an actual detector the integration over the photon energy (E) must be done taking into account the detector efficiency and the collection efficiency.
Threshold Cerenkov counter- simple yes/no decision on whether a charged particle is above or below b = 1/n threshold. Assuming full collection efficiency and a phototube with about 25% efficiency,
The probability of seeing r photons, when the number produced is 0.15*L, is given by the Poisson distribution. The distance necessary to make 1% probability to see 0 photons,
P(0)= 0.01 -> L=30 cm ( ~4.5 photons)
( a reflecting mirror or lens will focus all parallel rays to a fixed focal point)
RICH- ring imaging Cerenkov counter.
So, an imaging counter could separate a pion from a kaon from the threshold
momentum of the pion though the momenta where the kaon is also radiating,
up to the momenta when the kaon and pion angular separation is comparable to the angular resolution of the detector ( for instance, 5 mrad).
OPAL EM calorimeter
Ne is the electron density
a is the Bohr radius
TRT end cap TR detector - tracker
n= (eRe + ieIm)1/2
between a photon created at the front edge and one created at the back edge, as viewed from infinity.
Typical medium for radiators has a value of about 20eV.
1GeV electron has g=2000
Radiation peaks near f ~ 1/g
Spectrum peaks ~ 0.3gwp=6 eV*2000
The interference is given by Sin(L/Z), We would like the
Physical size of the Radiator foil to be Comparable to Z or
Larger. Foils in TRT are about 20 microns. So we expect TR to “saturate” above 300 GeV.
Overall coherence is impossible, but it is clear that the foil thickness and the separation should be approximately the same, and that the incoherent mix might approach the sum of the individual intensities ( a photons (peak) per interface)
The summed intensity should be similar to a “multiple slit”, with the phase between emitters being from both the foil thickness and the separation of the foils.
Spectrum of TR photons
Is proportional to 1/w
We can expect that in the keV region that the absorption length
Will be about 0.001 gm/cm2. For a fiber density of 0.07gm/cm2
This will give an absorption length of 0.013cm!
Better information on the web.
2T field gives a radius of curvature
For the track of:
R=p/(0.3*2T)= 1 GeV/0.6=1.6m
( Looping tracks if R<0.5m, p<0.3 GeV.)
The deviation of the circular track from
The tangent to the circle is given by
Suppose we pick a maximum deviation
Of Y=4mm, then
x=11.4 cm sqrt(p), this is the distance
A track progresses before the TR
Produced at the beginning of the track
Becomes separated from the track itself
Even for p=0.3 GeV, x = 62mm, which is
long compared to the attenuation length of the x-rays.
30 m dia. signal wire at center
The electron drift times for
An ensemble of particle tracks
Crossing the straws, shows a
Roughly uniform distribution from
The minimum time, T0, to the
Maximum drift time from the
Spatial resolution in 3D to 60 microns can be achieved with such a TPC.
Measurement of signal size gives dE/dX information about track.
Type 1-----Type 2----------Type3
M1.32 M2.32 M3.32
Type 1 32 * 329 straws in type 1 =10528
Type 2 32* 520 straws in type2 =16640
Type 3 32* 793 straws in type 3 =25376
52544 total straws
Irradiated TRT area.
Close to the area with
maximum bent straws.
boards on front end of all modules..
Full readout backend electronics.
with Xe-CO2 gas system.
Is used for the
End Cap TRTs.
Radial straws and foil
More than 400,000
Straws in total.
DTMROC Die Size 7.7 x 9.3 mm
Active Roof Boards
Gluckstern, NIM 24(1963) 381-389, Particle Data book,sec 27.11
Consider the measurement of a circular track with N tracking layers equally spaced along the track.
The major variable in this
Equation that must be considered
Is the L dependence. Since the
improvement of the momentum
Generally increases the size of the
How small can we make L?
How small can we make
the tracking resolution in each layer?
How big can we make B?
What are the physics criteria?
Although this is correct only for
A uniform system, we can
Approximate the result as a limit
on the amount of material in the
Three layers. The result indicates
That multiple scattering will never
Limit the sign determination.
If we wanted the multiple scattering
To be less than 10% of measurement
L/x = 0.03 p2 (gm/cm2/layer)
Assume that the requirement is to discriminate the sign of a charged
Particle that is equal to the beam energy.
Assume P=7000Gev/c. (LHC)
Pick a resolution that is excellent but not impossible:
( ILC is discussing a system that has 5 micron resolution/layer)
Since we are designing a small system, a large field B=4T will
be assumed with three layers.
Assuming 1 ps resolution and 50 cm flight path
Invariant mass resolution for a
Two photon state, depends on the
Energy resolution of of each
photon E1, E2, and the angular
1.5 X0 Cubic
Full Size Samples
BaBar CsI(Tl): 16 X0
L3 BGO: 22 X0
CMS PWO(Y): 25 X0
Outside of calorimeter has a radius of about 90cm
and a length of about 2 meters!
Fe Li= 131, 16 cm
W Li = 185, 9.5 cm
Pb Li= 194,17.2 cm
Pt Li= 189, 8.8
So, the hadronic section of the “small” calorimeter would occupy >1 meter.
Typical resolution ~ 40%/Sqrt(E)
Muon system is a multilayer tracker (4), covering the radial range 2.3 meters to 2.5 meters. Barrel length is 4 meters, plus end caps.
This exercise has already been done for the International
Linear collider. We would like to make the smallest detector
With good physics capabilities.
 GLD is a tentative name of the Large/Huge detector model.
All parameters are tentative.