atlantis the event display for the atlas experiment qiang lu, juergen thomas, peter watkins particle...

ATLANTIS

The Event Display for the ATLAS Experiment

Qiang Lu, Juergen Thomas, Peter Watkins

Particle Physics Group, School of Physics and Astronomy

Atlantis Event Display, 5 Oct 05

Particle Physics explore the fundamental nature of matter and the basic forces that shape our universe.

In order to investigate ever smaller structures, ever higher energies are needed. Over the past 50 years, particle accelerators have grown from small devices to the latest and largest of today, the Large Hadron Collider (LHC), a 27 km long ring, which when completed in 2007, will collide 1011 protons 14 TeV of collision energy, 40 million times a second.

Large Hadron Collider (LHC) at CERN: 27 km ring, 100 m underground,under construction, start-up in 2007

Genevaairport (GVA)

LakeGeneva

Switzerland

France

ATLAS


Are there any extra dimensions

predicted by some theorists?

A rather simple question might also be: Is nature fully described by today's Standard Model, and nothing else ?

The new machines are huge and therefore expensive to explore the new energy regions and to enable studies of extremely rare processes ... if something was not observable in the past, we should create the chance to observe it tomorrow.LHC will accelerate particles, but to “see” them – we need appropriate detectors. One of them is ATLAS…

Why are physicists building such huge machines ?

Because there are still many unanswered questions, like:

What gives particles their

mass?

Where is the awaited Higgs

boson?

Do the predicted supersymmetry particles exist?


22 m

44 m

ATLAS: A Toroidal LHC ApparatuS


Each meeting of two bunches resultsin about 23 proton-proton collisions.The mean number of particles born in all these collisions is about 1500. The detector should record as many of them as possible.

The collision point is “watched”by surrounding detector.

Some particles just escapedfrom the collision zone, the next collision threatens.

The detector should:• have large coverage

(catch most particles)• be precise• be fast (and cheap and ...)

1011 protons in each bunchEach proton carries energy 7 TeV.

So each bunch with 1011 protons carriesenergy 1011×7×1012 eV = 7×1023 eV = 44 kJ. This is a macroscopic energy!!! In order to reach such kinetic energy on a bike, you go with a speed of more than 30 km/h!


The energetic electron radiates photons which convert to electron-positron pairs which again radiate photons, which ... This is the electromagnetic shower.

The interaction of different particles with the same high energy (here 300 GeV) in a big block of iron:

electron

muon

pion (or another hadron)

The energetic muon causes mostly just the ionization ...

The strongly interacting pion collides with an iron nucleus, creates several new particles which interact again with iron nuclei, create some new particles. This is the hadronic shower. You can also see some muons from hadronic decays.

Electrons and pionswith their “children”are almost comple-tely absorbed inthe sufficiently large iron block.

1m


Here is the general strategy of a current detector to catch almost all particles:

electron

muon

hadrons

Tracker: Not much material,finely segmented detectorsmeasure precise positions of points on tracks.

Electromagnetic calorimeter: offers a material for electro-magnetic shower and measures the deposited energy.

Hadronic calorimeter: offers a material for hadronic shower andmeasures the deposited energy.

Muon detector: does not care about muon absorption and records muon tracks.

Neutrinos escape without detection

Magnetic field bends the tracks and helps to measure the momenta of particles.


ATLAS – Being built nowWebcam picture from the ATLAS cavern, 100 m underground. The magnet coils producing the toroidal magnetic field dominate the view.

ATLAS is the largest collaborative effort ever attempted in the physical sciences. There are 1800 physicists (Including 400 students) participating from more than 150 universities and laboratories in 34 countries.

One of the many contributions of the Birmingham group is work for the Event Display,

called Atlantis


The Event Display Atlantis

http://www.cern.ch/atlantis

A tool for the visual investigation and physical understanding of all types of events inside ATLAS..

And also useful to• help develop reconstruction and analysis algorithms• facilitate debugging during commissioning• create pictures and animations for presentations, publications and exhibitions• use as online event display at the control room


How the event display Atlantis worksTry to put data from the ATLAS detector into the human brain in an intuitive way, so the human may make fast and correct conclusions.

This is largely accomplished by using data oriented projections.

Atlantis has two parts: One inside the ATLAS software framework in C++ to derive data running under Scientific Linux 3, and the actual interactive graphical tool as a standalone Java application, which can be run on any platform. Data transmission is done via XML files, IP connections or URL.

The LHC is not yet running, therefore the events shown here are simulations using Monte Carlo methods and very detailed models of the interaction with the detector’s numerous layers and materials.


Detector / Data Oriented Projections3D Cartesian coordinates x,y,z are not always optimal for colliding beam experiments.More natural and useful are the non-linear combinations which reflect the design of ATLAS:

= sqrt(x2+y2) = arctan(y/x) = arctan( /z)

Atlantis offers e.g. the following projections:

YX projection Z projection

V-Plot () in 2D Legoplot 3D.


Atlantis Graphical User Interface (GUI)

Menu bar

Window Control

Interaction Control

Parameter Groups

Parameter

Output Window


TheXY projection

…zoomed into the inner part of ATLAS. The centre of the picture is the interaction point. Dots forming curved lines are from low energy particles being bent by the magnetic field. Green lines are traces of high energy particles, being reconstructed as ‘tracks’. The electromagnetic calorimeter is shown in green, the hadronic in red, with energy depositions in yellow.


TheZ projection

…also zoomed into the inner part of ATLAS. The collision point is again at the centre, with the beam line from left to right.

The electromagnetic calorimeter in green, the hadronic in red, with energy depositions in yellow.The cylindrical geometry is visible, with ‘barrel’, ‘endcap’ and ‘forward’ parts of the calorimeters. In reality, these are very different subdetectors, both in design and materials.


Expected signature of a two-jet event:XY, Z and projection

Two-jet events are the dominant background at the LHC. Jets result from gluons or quarks. The characteristic back-to-back jets can be clearly seen in all three projections. A ‘Syncro Cursor’ can be moved around, linking the projections.


Calorimeter layersZooming option from the -projection shows the eight calorimeter layers of ATLAS, starting from the innermost electromagnetic (green), outwards to the hadronic layers (red).

Depositions are visible in yellow, the fraction of the filing of a black squares indicate the magnitude of the deposition. The black squares show the geometry. (… track …)

Green “V” represents track. Green circle represents jets. Showing all data in same

position in overlapp allows for simple visual matching of traces of same particle in different detector layers.


Expected signature of the Higgs Boson:Z projection

Simulation of the Higgs Boson decaying into two photons (’s). Clear traces (yellow) within the calorimeters (green and red) can be very well reconstructed. In reality, this process however has very large amount of background processes of very similar signature.


Simulation of the Higgs Boson decaying into two photons (’s). Clear traces (yellow) within the calorimeters (green and red) can be very well reconstructed. In reality, this process however has very large amount of ‘boring’ background processes of very similar signature.

Expected signature of the Higgs Boson:XY projection


Expected signature of a two-jet event:Legoplot projection

In this projection, the amount of energy deposited in the calorimeters is shown in 3D as tower heights, with the grid as the base.


A real event – first sign of life from ATLAS

Atlantis display of a cosmic ray recorded by the hadronic calorimeter, already installed underground.

atlantis the event display for the atlas experiment qiang lu, juergen thomas, peter watkins particle...

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