Transcript Lego Plot Changelog - Nevis Laboratories

Visualizing Data from the LHC
with the Atlantis Event Display
Program
Joshua Auriemma
Advisor: Andy Haas
Part I: Everything You Always
Wanted to Know About ATLAS,
Only Wrong
A general overview of detector components.
A Toroidal LHC Apparatus
Inner Detector
• Is mainly a “tracking detector”, required in
order to determine the momentum,
position, and impact parameter (λ )
INT
• The inner detector consists of three main
sections: the pixel detector, the semiconductor tracker, and the
transition radiation tracker.
The Pixel Detector
• Provides tracking information for pattern recognition near the
collision point and largely determines the Inner Detector’s ability to
find secondary vertices.
• Three measurements over the full acceptance are performed in
order to find the impact parameter resolution, and the detector’s
ability to find short-lived particles such as B hardrons and t leptons.
Semi-Conductor Tracker
• A charged particle passing through this detector liberates charge
carriers, electrons, and "holes". When separated by the E-field, the
"holes" drift to the back-plane, and the electrons to the readout strip.
This creates a potential difference which can be measured.
Transition Radiation Detector
• Why Have a TRD? Many high-energy particles “look” very similar to
each other due to similar momentum. The TRD measures E/m – a
value which differs greatly depending on the particle.
• How Does it Work? As high-energy electrons transverse the
detector, X-Rays are produced which ionize a gasseous Xe and CO2
compound.
• All particles will create a signal!
Calorimeter Detectors
• The calorimeter detectors are designed to stop
basically every particle except neurtinos and
muons.
• The inner-most calorimeter detector is known as
the electromagnetic detector.
• The outer-most calorimeter detector is the
hadronic calorimeter detector.
Electromagnetic Calorimeter
• Responsible for stopping electrons, positrons, and photons.
• Detector material causes bremsstrahlung.
• The energy lost is found by:
• Insufficient technique for photons (photoelectric, Rayleigh,
Compton, pair production…).
Hadronic Calorimeter
• Hadrons have most likely already interacted with the EM
Calorimeter.
• Generally in the first interaction jets of particles are produced.
• Charged particles will interact with scintillator.
Muon Chambers
• Because muons are so massive, they generally pass
straight through the inner detector, and both calorimeters
without losing very much energy.
• Extremely massive muon detectors must therefore be
constructed in order to detect these particles.
• The detection system is based on the deflection of
muons by the large barrel toroid.
• The muons are measured in three layers of chambers
around the beam axis using Monitored Drift Tubes and a
Cathode Strip Chambers. Detection will occur inside the
Resistive Plate Chambers and the Thin Gap Chambers.
Monitored Drift Tubes
• Aluminum tubes pictured above act as beam pipes for the muons.
• Each tube has a wire within it with a potential difference.
• Changes in the muon’s course due to the E-field provided by the
toroid will cause induction in the wire and can be measured.
• Knowledge of the drift-speed allows for tracking.
Cathode Strip Chambers
• The CSCs are multi-wire proportional chambers with cathode strip
read-outs.
• The precision coordinate is obtained by measuring the charge
induced on the segmented cathode by the avalanche formed by the
anode wire.
• Relatively good special resolutions can be obtained through charge
interpolations (resolution of ~60 mm).
• Absence of hydrogen in the gas mixture, combined with a small gap
width, allows for a low sensitivity to neutron background.
• Less sensitive to variations in gas parameters than the MDTs
Resistive Plate Chambers
• The RPS is a gaseous detector (C2H2$F4).
• There is a narrow gap formed by two parallel plates made from
bakelite of 2 mm thickness which is separated by insulating spacers.
• Avelanches are generated by high field of 4.5 kV/mm.
• The signal is measured through a capacitive coupling by metal strips
on both sides of the detector.
Thin Gap Chambers
• In the TGCs, however, the wire distances are small enough to
guarantee short drift times, and therefore, good timing resolution.
• The anode plane is sandwiched between two cathode planes made
of 1.6 mm G-10 plates on which the graphite cathode is deposited.
• On the backside of the cathode plates facing the center plane of the
chamber, etched copper strips provide the readout of the azimuthal
coordinate.
• On the outside, the gas pressure is sustained by 5 mm thick paper
honeycomb panels.
Part II: Neat Physics with Atlantis
About Atlantis
•
The Atlantis project is a java-based event
display program that represents over 40 years
of work.
• The Atlantis collaboration currently consists of
14 members at 8 different institutions.
• Atlantis subscribes to the following 3
principles:
1. Atlantis is fast
2. Atlantis is used intuitively.
3. Atlas is used for complete ATLAS events.
Reasons for Atlantis
• The Atlantis program has two main objectives.
1. To serve as a means of examining and
verifying pre-flagged “interesting physics”.
2. To obtain a physics understanding of
algorithms related to the detector.
Confirming New Physics
While Atlantis will likely never be the first program to find new
physics, it certainly serves as a useful verification of physics. For
example, one may note an obvious B hadron due to the track
reconstruction near the point of interaction. That same person may
note that two very prominent electrons were absorbed in the
calorimeter detector. Theoretically, it would seem logical that the
missing ET of this event would be low, since it is likely that a top
quark decayed into a W-boson and a b-quark, and that b-quark then
decayed into an electron and an electron neutrino.
Algorithm Construction
While algorithm construction is loosely tired to the first goal, many
of Atlantis' contributors actually consider this reason the number one
reason for the existence of a graphical display program. One may be
programming something which uses vertices in order to b-tag. While
out of context, the algorithm may make very little sense, applying it in
the context of an event display such as Atlantis, the code can become
much more intuitive.
Understanding the Coordinate System
The ATLAS coordinate system (x,y,z) is defined as:
z = beam axis = cylinder axis
x = horizontal axis
y = vertical axis
Additionally, the coordinate system (f,h,r) is defined as:
r = sqrt(x2 + y2)
f = arctan(y/x)
h = arctan(r/Z)
Revisiting the Detector
•
The resolution of the detector is fine
enough such that it is possible to make
out the structure of the detector through
hits.
The Pixel Detector
Inner Detector
Impact Parameter
Examining Simulated Events
•
Having simulated data for specific types
of events, Atlantis can be used in order
to verify that these algorithms are
working properly.
Electron (XY)
Electron (rZ)
Electron (Lego plot)
Muon (XY)
Muon (rZ)
Jet (XY)
Jet (rZ)
Jet (Lego Plot)
In Conclusion
•
•
•
Although it is not meant to replace
triggering systems, Atlantis is a great
way of visualizing events.
Extremely complicated events can be
very easily examined through the use of
a graphical display program.
Atlantis is great!