Links to international meetings:
- These links are under construction!
- 1st International LC Tracking + Muon Report Conference at the Amsterdam ECFA/DESY LC Workshop, Monday 31 March 2003
- Tracking sessions at the Amsterdam workshop April 2003: Talks1st session and Talks2nd session.
- Tracking talks at ECFA LC Workshop at Montpellier 12-15 Nov. 2003
- Fetch The 6th ACFA LC Workshop at Mumbai 15-17 Dec. 2003 to click to the tracking talks there.
- Fetch The ALCPG 2004 Winter Workshop at SLAC 7-10 Jan. 2004 to click to those tracking talks.
- 2nd International LC Tracking + Muon Report Conference at that ALCPG 2004 Workshop at SLAC on 8 Jan. 2004
Tracking efforts in this webpage:
Aim of this page is to link the different activities on tracking in the framework of the World-Wide Studies of Physics and Detectors for Future Linear e+e- Colliders.
An overall description of the R&D program of the World-Wide Study can be found in the Linear Collider Detector R&D paper available as postscript or PDF version. For other activities in the International Linear Collider Detector R&D see this WWW page
All tracking-system designs under consideration include a pixelated vertex detector that closely surrounds the interaction point for accurate measurement of charged particle impact parameters. Accurate momentum measurement is provided by either a large-volume gas drift chamber (axial/stereo wires or time projection chamber) or additional silicon tracking layers (silicon drift detector or microstrips) immersed in axial magnetic fields of magnitude > 3T. Designs also include a dedicated system of forward-tracking silicon disks at low angles. For the gas chamber barrel trackers, additional special silicon, straw chamber or scintillating fiber layers are also under consideration for improving pattern recognition, momentum resolution, or timing precision. In the following R&D for each of the tracking technologies is discussed and relevant websites for tracking and other subdectors are collected below.
Excellent track reconstruction efficiency and momentum resolution are desirable over a large solid angle at the linear collider. Two distinct approaches are under consideration for the barrel tracking system, a large-volume gas drift chamber ( axial/stereo wire or time projection) with continuous tracking involving many coarse (~ 100 mu) measurements or a silicon tracker with a few precise (~ 10 mu) measurements per track. Aside from the technical tradeoffs in designing within one of these approaches, there are global tradeoffs among them, pertaining to pattern recognition, robustness against background, material budget affecting multiple scattering, bunch discrimination via timing, and interface to calorimetry. Collaborative simulation work is ongoing in the North American community to address these global issues.
The Asian detector design includes a large-volume drift chamber with axial and small-angle stereo wires. A long-term R&D program is well under way to address the following issues:
- Controlling / monitoring wire sag
- Maintaining uniform spatial resolution (85 microns) over tracking volume
- Maintaining good 2-track resolution (< 2 mm)
- Stable operation of stereo cells
- Gas gain saturation (affects dE/dx, 2-track separation)
- Lorentz angle effect on cell design
- Wire tension relaxation (Al wires)
- Gas mixture
- Coping with neutron backgrounds
Some general arguments for a TPC as main tracker are listed to illucidate the R&D issues:
- The tracks can be measured with a large number of (r-phi,z) space points, so that the tracking is essentially continuous and the efficiency remains close to 100% for high multiplicity jets and in presence of high backgrounds.
- It presents a minimum of material to particles crossing it. This is important for getting the best possible performance from the electromagnetic calorimeter, and to minimise the effects from the ~10^3 beamstrahlung photons per bunch and other backgrounds which traverse the detector. The estimated occupancy of the TPC is less than 0.3% from beam-beam backgrounds and gamma-gamma interactions and simulations have shown that the physics events can be extracted from this even if the machine background calculations are wrong by a large factor.
- The comparatively moderate point and double-hit resolution are compensated by the large volume which can be filled with fine granularity and continuous tracking. The timing is precise to 2 ns, good enough to separate events and tracks from different bunch crossings.
- It is well suited for a large magnetic field since the electrons drift parallel to the B-field, which in turn improves the two-hit resolution by compressing the transverse diffusion of the drifting electrons (FWHM_T < 2 mm for Ar-CH4 gas and a 4 T magnetic field).
- Non-pointing tracks, e.g. for V^0 detection, are an important addition to the energy flow measurement and help in the reconstruction of physics signatures in many scenarios beyond the standard model.
- The TPC gives good particle identification via the specific energy loss, dE/dx, which is also useful for the energy-flow algorithm and many physics analyses.
- A TPC is easy to maintain since, when designed properly, an endplate readout chamber can be simply exchanged if it is having problems.
The European detector design includes a large-volume time projection chamber (radius 1.7, half-length ca. 2.5 m), while the North American version has a larger radius (2 m). A collaboration of European and North American institutes have begun a comprehensive R&D program to address the following issues:
- Novel readout schemes to avoid the massive endplate required to support conventional high-tension wire planes. Frontrunners at the moment are GEMs and MicroMEGAS, which should allow for good suppression of ion feedback. Silicon and wires are also investigated.
- Readout channel reduction via optimized inductive pad shaping / ganging with attention to 2-track and dE/dx resolution.
- Optimized gas mixture (resolution vs fast clearing, quenching with hydrocarbons vs reduced neutron backgrounds), aging and implications for field cage.
- Electronics integration to cope with ~ 2 x 10^6 readout pads and higher-speed sampling (~ 20 MHz) to exploit intrinsic longitudinal granularity.
- Mechanical design to minimize material in field cages and endcaps, while providing adequate cooling for high-speed electronics.
- Distortion correction techniques for coping with space charge buildup.
- Calibration schemes (e.g., laser system, "z" chamber at outer radius).
- Detailed technical simulations of readout designs with comparison to measurement of prototype devices.
- The magnetic field has to be mapped to better than 10^-3 in order to minimise corrections for the distortion of drifting electrons.
A proposed a superlayer of straw drift chambers behind the endcap of the European TPC, mainly to improve momentum resolution at lower angles. A silicon version is also being considered (see next paragraph). Technical R&D issues include spatial resolution, material thickness, timing for bunch tagging and calorimeter splashback.
Being investigated are large silicon annular planes behind the endcap of the European TPC and a large barrel layer beyond the outer radius of the TPC, in both cases between the tracking chamber and the electromagnetic calorimeter. The endcap tracking layer significantly improves momentum resolution at forward angles. The outer barrel layer offers a calibration point for the gas chamber, a function which also may be fulfilled by the Ecal. Given the sizes of these auxiliary tracking layers, lowering cost of manufacture will be important R&D goals.
The North American study groups have considered in their simulations both a TPC and a 5-layer silicon barrel tracker of maximum outer radius 1.25 m and maximum half-length 1.67 m. Two different silicon technologies are under consideration: silicon drift detector and silicon microstrips, discussed below. A silicon drift detector design involves the following issues for an R&D program:
Simulations for a silicon microstrip detector design lead to the following an R&D issues:
- Development of thinner substrates and necessary mechanical support
- Improved spatial resolution (to better than 10 microns in both dimensions)
- Increased drift length to reduce front end electronics (FEE) in the fiducial volume
- Lower mass FEE readout
- Development of thinner substrates and necessary mechanical support
- Development of very long ladders to reduce FEE in the detector volume and exploit reduced electonic noise with longer shaping time
- Detailed comparison of tradeoffs between long & short ladders, long & short shaping times, including tolerance to accelerator backgrounds
- Development of power-switching integrated readout electronics to exploit low duty-cycle of accelerator and reduce the necessary cooling infrastructure, with attention to stability.
- Study of Lorentz angle effects in strong magnetic fields
- Alternative p-side readout for double-sided sensitivity (e.g., stereo layer)
- Pulse height measurement for time-walk compensation and coarse dE/dx determination
Both of the European and North American TPC designs also include a barrel silicon layer at a radius just short of the inner radius of the TPC. The extra layer provides improved momentum resolution and, it is hoped, provides improved pattern recognition to match tracks across the gap between the vertex detector and the gas chamber. The R&D being proposed by several groups for other silicon layers is expected to be relevant to this intermediate layer also.
Most of the tracking system designs include a set of silicon annuli providing angular coverage to cos(theta)~.99. In the European design, the first three (of seven) layers from the interaction point are active pixel sensors; the rest are silicon microstrips, as are all of the annuli in the North American designs.
In America the timing advantages of a superlayer of scintillating fibers in place or adjacent to the intermediate barrel silicon layer in the North American TPC option are being studied. R&D issues include timing precision and material thickness.
Simulations and R&D have begun on a dedicated "pair monitor", based on active pixel sensor devices at very low angles near the final beam quadrupoles. The monitor would track the passage of Bethe-Heitler pairs, as a real-time beam diagnostic and as an independent measure of luminosity.
This is a preliminary list of links and is still incomplete. Suggestions for further links to be included should please be sent to Ron Settles.
SimulationsAmerican simulation WG or
the following tracking page.
Axail/Stereo WiresStudies in Asia
TPCCollection of R&D studies in America, Asia and Europe
R&D efforts withing the framework of the DESY Physics Review Committee (PRC)
Asian CDC group, now joined with TPC work
LBNL:TPC Symposium 17 October 2003
LBNL:TPC R&D Meeting 18-19 October 2003
American simulation WG also includes Si work or
the following tracking page.
Related tracking linksSTAR TPC Electronics
TPC R&D Electronics (STAR based)
Other links of general interest
To reiterate, for world R&D related to the LC detector...
On January 2, 2003, this Tracking R&D page went public. A preliminary list of links can be found bove. The aim is to get a complete list of Tracking R&D projects. Please submit links for your specific Tracking R&D page to Ron Settles.