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ILC FAQ, Terminology, Acronyms, glossary, etc.

version 0.11--incomplete draft, John Yoh, 8/5/06 Please send additions, corrections, suggestions to johny@fnal.gov Note also that some basic introductory material have been included, aimed at undergraduate and high school students

We provide here useful ILC terminologies, acronyms (usually 3 letter), and other useful information.

ILC ACRONYMS--3-letter, etc.

Here's a partial list

  1. ILC (International Linear Collider) --A proposed machine colliding Electrons with Positrons at a mass of 500 Gev intending to study Higgs, Dark matter, etc. Potential upgrade to 1 TeV could be a later option. Such a collider would take about 7 years to build after funding, so will not exist before 2015.
  2. ILC GDE--Global Design Effort-- an international effort with a goal of arriving at a consensus RDR and DCR (see below) by the beginning of 2007--including detail designs of the collider and proposed detectors with costs, but NOT siting (whether it will be built in the USA, Japan, or Europe).
  3. RDR and DCR--Reference Design Report (of the ILC) and Detector Concept Report (for 4 detector types being considered for the ILC)-- note also there was also a BCD (Basic Concept Design report of 2005, a precursor to RDR).
  4. Previous or alternative version of ILC--TESLA, NLC, CLIC--Consideration for a Several Hundred GeV Linear electron-positron collider have been ongoing since 1990. Some of the previous such concepts include TESLA (Eurpoean/German), NLC (USA), and CLIC (CERN--still under consideration for research on a compact design for acceleration--so far unproven). Many Physics studies were done in these effort, and some of the results of these studies made it into the various talks for the ILC.
  5. LHC --Large Hadron Collider at CERN, Geneva, Switzerland--and European collaboration proton-protin collider at a mass of 14 Tev expected to start in November 2007 .Experiments at LHC (CMS, ATLAS, ALICE, KHCb, etc.) are expected to make major discoveries in the subsequent years--including, most likely, the discovery of the Higgs particle. However, much of the properties of the Higgs can not be determined at the LHC, due to the large backgrounds from other hadronic collisions. More detailed measurements would require a different machine, such as the much-cleaner ILC.
    LHC replaces the SSC, a previous USA-based 40 TeV Hadron Collider that was approved but cancelled in 1993. SSC would have discovered the Higgs in the late 90's.
  6. Other Previous Linear Colliders - SLC --Stanford Linear Collider --electron- positron collision at a mass of up to 100 GeV--took lots of data at the Z peak (Z mass is 90 GeV)
  7. Other previous circular colliders --LEP, Tevatron, B-factories, etc.--
    LEP (Large Electron Positron collider--CERN, Switzerland--took a lot of data at the Z peak),
    Tevatron collider --Proton-Antiproton collider at a mass of about 2 TeV (at Fermilab, with the experiments CDF and D0-- currently taking data--they discovered the top quark in 1995) and is currently looking for the Higgs (though it is very likely that they will not have the sensitivity to discover it). .
    b-factories --including BABAR at SLAC, Stanford, California, and BELLE at KEK, Japan,--both took lots of data at the Upsilon(4S), with decays into a pair of B mesons. Much of the detailed understanding of the B meson were measured there--though the experiments CDF and D0 at the Tevatron collider also did quite a few B meson measurements.
    For many ILC physics discussion of goals and physics studies, you will get references to what has already been measured elsewhere, as well as the complementary merits of measurements at ILC vs. LHC.

Terminologies of interest to ILC considerations

  1. Proposed ILC detectors --4 large collaborations of physicists have proposed detector concepts (some info of these will be part of the CDR)-- these are SiD, GLD, LDC and 4th detector--all 4 have a large solenoid magnet with tracking and (at least some) calorimetry inside. For tracking, GLD and LDC uses TPC (Time Projection Chamber).


  1. SIMULATION studies--Studies of expected performance of a detector for phsyics studies (e.g., mass resolution for a new particle and the level of backgrounds) or detector performance (e.g., energy resolution for jets in a calorimeter).
  2. PHYSICS studies--Studies to determine how well a detector will measure a particular physics process--Thes include both expected SIGNAL performance, as well as BACKGROUND estimate (and background could come from mismeasurement of Signal, as well as non-signal background processes).
  3. 4 STEPS IN PHYSICS AND SIMULATION STUDIES--in general, there are 4 steps to a physics studies--some of which also applies to simulation studies
    1. GENERATION--For a physics process, events need to be generated according to physics cross sections. In general, events are generated as un-weighted (that is, with a probablilty of one). Some studies involved weighted events (some events have a higher weight, that is, it occurs more often).
      Various programs which contains details of physics modeling are used to generate events of a particular process (such as ee into ZH). Each dataset may have additional selections (such as requiring that the Z in these events decays only into dimuons, which normally happens only 3% of the time). Thus, each dataset contains usually only selected process with selected additional requirements. Usually, signal and background datasets are generated separately --and most studies cover only certain backgrounds--not all--and thus may not be representative of what will really happen.
      These generated datasets --often using programs such as PYTHIA, VECBOS, etc.--- contains the particles properties that belong to each event.
    2. SIMULATION --These generated particles from each generated event is then simulated to go through the detector one desired--and a list of observed quantities are obtained-- these include particle tracks as measured by tracking chambers such as TPC or Si strips or pads. Observed calorimetric quantities are also derived. The level of realism depends on the level of simulation (see below)--and thus any result from such physics sutides should be taken with a grain of salt. Note that these results of the simulation are detector dependent, and hopefully, will result in an "observed event"--just as what one might get from a real detector recording events from real physics collisions.
    3. RECONSTRUCTION--Simulated events (or, for that matter, real recorded events) need to be reconstructed, to determine what the best determination of what really happen in the event. Charged tracks are reconstructed, and a list of showers (electromagnetic or hadronic) are obtained, muon track stubs are reconstructed. We then make a list of what we think is happening in the event. For example, a high Pt isolated track pointing to a EM cluster with E/P being near one is an electron candidate. A high Pt track pointing to minimum ionization deposited in the calorimetry and matching with a muon track stub is a muon candidate., etc.
    4. ANALYSIS--Reconstructed events are then analyzed--for a particular physics process under study, selection cuts are made, and event passing these cuts are analyzed to determine whether the are good candiates for the physics process one is studying. There are many more things that need to be done to convert these final cut dataset results into physics results--including studies of efficiency, biases, threshold, triggering, studies of uncertaineites, backgrounds, etc.
    5. NOTE --Some simple studies bypass one or more stages of the above--for example, a simple physics studies could just use the generated particles, and analyze them-- bypassing the simulation and reconstruction (see below--called "SIMPLE")--the results are thus potentially unreliable, since no realistic simulationa and reconstruction are considered.
  4. LEVEL OF SIMULATION --There are many levels of detector simulation-- crudely, once could seperate into FAST/ABSTRACT--MEDIUM/Parametric --DETAILED/GEANT4.
    The FAST or ABSTRACT simulation just give simple abstract response-- such as adding a generic resolution to a momentum, energy, or angle measurement.. No details of detector is usually included, such as cracks, non-gaussian responses, etc. Efficiency is usually just a rough estimate.
    MEDIUM/parametric --A real detector is simulated --but crudely-- some effort is made to provide reslistic response and some allowance for deteoctor imperfection, but often just a parameterization (e.g., response for energy resolution of a calorimeter is sometimes taken from response in a test beam, but usually just parameterized with some effort to simulate the fluctuations.
    DETAILED/GEANT4 --A realistic simulation is made, including all the elements of the detector such as cracks, material (in the beam pipe), and particles are follewed in detailed by Monte carlo (e.g., a dice is thrown to determine whether a particular photon will interact in the 1% r.l. beam pipe and produce an electron-positron pair), and detailed Monte Carlo showers (e.g., a particle is followed through a calorimeter, to determine where it will start a shower--and, in some cases, every particle of the shower remnents are followed to determine where the enegy will be deposited). These Detailed simulation often uses the latest version of the full simulation tool--GEANT4--with the details of the detector under study being put into a parameter file as input to GEANT4.
    Of course, these 3 levels indicated are just a rough sketch of simulation--there are many more gradations--and some simlation could use detailed simulation on one part of the detector--but just the medium one for another part of the detector.
    The CPU usage for these 3 levels of simulation vary widely. For example, on a typical PC, the fast simulation might take .01 sec; the medium 1 sec, and the Detailed 100 sec !!!
  5. MONTE CARLO--a tool used often in Generation, Simulation, and other studies. For example, if we do a simluation on 1000 events, each with about 100 particles, we need to detemine how many of these particles will interact in the beam pipe (with is, say 1%. r.l. --radiation length, so 1% of the photons or electrons will interact --but only .1% hadronic interaction --so, only 1 in 1000 hadrons (protons, charged pions, etc> will interact. So, for each of the 100,000 particles, we "throw a dice" (actually generated a random number--let say 4 digits from 0000 to 9999). For a photon or an electron, if the ramdom number come out as 0000 to 0099 (1%), we will simulate an interaction at the beam pipe; for hadrons, if the random number come out 0000 to 0009 (.1 %), we will make it interact in our simulation. This is "Monte Carlo" !!!!.
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