Palaiseau, 13/1/ 2005 P. Colas - Optimising tracking 1 Optimising a Detector from the Tracking Point-of-View P.Colas, CEA Saclay constraints role Optimisation : trade-off between constraints to help the detector to fulfill its role best

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking2 THE ROLE OF THE TRACKING  Reconstruct vertices  Enough accuracy to separate b from c  Determine vertex charge  Reconstruct most of V°s  Measure charged tracks  High efficiency down to low angles and momenta, even for close tracks, for particle flow  High accuracy to tell the charge at highest momenta  If possible, identify particle (e, , ,K,free quark,…)

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking3 Linear Collider Specificity  Physics requirements  Flavour tagging by vertex finding  Higgs recoil mass (ZH->     anything)  Multijet final states : two-track separation  Missing energy measurement : hermeticity  Processes peaked at low angle : good coverage  Environment  Backgrounds: muons, photons, neutrons : go 3D, go high segmentation

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking4 PHYSICS

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking5 Magnetic field  Roles:  Curve tracks for p measurmnt  p T /p T =8  /0.3Bl 2  Curve tracks to separate charged from neutrals (particle flow)  Background confinement  Parameters  Radius (transportation, cost), length  Field intensity  Homogeneity Mask B field (See talk by F. Kircher)

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking6 Backgrounds  Effect of the beam crossing angle (K.Bü  er, SLAC MDI meeting, 5 jan 2005)  Head-on ? 2mrad? 20 mrad? Small/large hole?  Input from the detector to the machine design! TPC VxDet

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking7 Backgrounds : neutrons  Impacts the aging of the silicon  Causes occupation in the TPC, especially if the gas contains Hydrogen

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking8 TECHNOLOGY  See talks by S. Aplin and T. Greenshaw  Digital TPC?  Could be used at an intermediate radius between the vertex detector and a standard TPC STANDARD TPC DIGITAL TPC Vx Det

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking9 GEOMETRY  What must be the radius of the TPC? Trading size (R 2 ) against sagitta accuracy / B has a limit : V 0 s must be contained.  Up to which R do we need Silicon? Where from do we start gas?  Limit on the number of silicon layers fixed by the multiple scattering. About 5 for 300 micron wafers, more if layers are thinner.

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking10 LOW ANGLE COVERAGE  L has to be finite. A special device is needed to cover low angles (K. Moenig)  (deg.) A extended silicon envelope would allow TPC syst. to be corrected (A. Savoy-Navarro). But would not a few % of the surface be enough? Would the first layer of the calorimeter play this role?

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking11 An example : pad size in the TPC, momentum resol°  Depends on details of the design: gas, technology, electronics  What is acceptable? Twice the cost for half the resolution?  BON COURAGE TESLA TDR Goal D. Karlen Pad dimensions (mm x mm)

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking12 COST ISSUES  trade-off running time / resolution (  /  N), N ~ time ~ money)  trade-off reliability / price of components  trade-off multi-technology / scale effect

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking13 BENCHMARKS Process Tested item A FB  +  - Charge separation ZH ->  +  - X Recoil mass resolution Bhabha acolinearity, WW with W->  Low-angle coverage H branching ratios Vertex finding, b/c discrimination (see M. Battaglia’s talk)

Palaiseau, 13/1/ 2005P. Colas - Optimising tracking14 CONCLUSIONS A lot has been done already to optimize the tracking, but: x Technology evolution might lead us to revise some choices x Need to be realistic in supports / cables / services Benchmarks with realistic simulation and various options are strongly needed.