Dead material in IT

Why ?

• Proper accounting of (dead) material is critical aspect of Kalman filter technique, mainly due to multiple Coulomb scattering. Only this way allows to trust chi2 obtained in the fit.

• To understand systematical shifts of fit parameters. An example, “fudge” factor in conversion curvature to pT of 0.25% has been used in IT.

• Comparison simulation and reconstruction gives ~ 3 MeV reduction in reconstructed energy

=> 2 g/cm**2 of dead material (see next slide).

Shift reconstructed energy with respect to simulation

dE (GeV)

q/pT (GeV/c)

Primary tracks

dE=3MeV

Weight of SVT

• Total weight of SVT + SSD + cables = 166 kg (David Lynn)

• Stasim geometry y2005x:– Weight of SVTT : 299.2 kg– Weight of FTPC : 99.2 kg (included in SVTT

mother volume)– Weight of SVTT - 2*FPTC = 100.8 kg

(we hope that difference between Lynn’s weight and starsim one is due to cables on support cone which have not been accounted yet)

• Weight of SVT in IT (wafer + hybrid) = 4.4 kg

Cables

water

Priority material list obtained by shooting particles from x=y=z=0

Material nent aver.track length x0 length/x0 SVTT_COPPER#12 90637 0.032639 1.430000 2.068742% SVTT_WATER#74 87375 0.459519 35.70000 1.124663%

SVTT_SENSITIVE#77 87994 0.115131 9.360000 1.082354%

SVTT_AIR#16 100000 247.7500 30400.000 0.814967% SVTT_AGPD#81 75417 0.007018 0.807000 0.655857% SVTT_BEO#79 75745 0.117219 14.400000 0.616580% SVTT_CARBON#7 10915 0.998387 18.800000 0.579649% SVTT_G10#72 13962 0.491031 18.200000 0.376691% SVTT_GLASS#80 75489 0.035105 12.200000 0.217217% SVTT_SILICON#18 39662 0.047361 9.360000 0.200687% SVTT_ALKAP#73 99582 0.035264 18.50000 0.189819%

SVTT_CH2#75 9682 0.523975 47.200000 0.107481% SVTT_ROHA#78 73035 0.083653 1450.0000 0.004214% SVTT_PYREX#76 30 0.301281 12.600000 0.000717%

List of SVT volumes • GEANT names: • SOUM: Outer shielding structure• SXR[L,1,2]: Circular water feeds• SCBM: Mother of All Cables• SALM: aluminum shield mesh• SOSH: SVT outer shield "• SISH: SVT inner shield "• SLY[D,1,2,3,4,5]: layer mother• SROD: Support rod• SBSP: Beam pipe support mother• SCON: Support cone mother• SBWC: water manifold to support cone bracket mother• SWMM: water manifold mother• SBRG: Bracket joining the end rungs• SOER: outer end ring• SIRT: inner end ring tube piece • SIRP: inner end ring polygon piece

Virtual Monte Carlo (VMC) Geometry

The proper way to account material is to use GEANE approach i.e. to use full geometry description of the detector in simulation for reconstruction.

To do this we can use starsim geometry converted (g2root) to VMC.

This tools exists, it has been checked.Only problem is CPU which can affect IT

performance.

Access to VMC geometryGet VMC geometry via

starsim -> Mortran geometry description (g-files) -> rz-files -> g2root -> TGeo (VMC) geometry;

Keep as Geometry.version.root

with version = (year2000,year2001,year2002,year2003,y2003a,y2003b,

y2003x,y2004a,y2004b,y2004,y2004x,y2005x,…).Under $STAR/StarDb/VmcGeometryThus these geometries can be accessible via St_db_Maker standard way with time stamp set.

Once again to use VMC directly might cause CPU performance degradation (it should be checked). For the moment I suggest to extend IT geometry to account dead material.

Limitation of present IT geometry

• In IT there are only two type of detector elements:– Infinite planes parallel to Z-axis, and– Cylinders with Z-axis at X = Y = 0

Modification to IT geometry

To account dead material in IT is needed:• at least to add disks i.e. plane perpendicular to

Z limited by circles with limited thickness in Z. – It is needed to be done.

• procedure which will create “averaging” over dead material volumes with “mixed” material from VMC geometry. – It has been done. It is needed to check created

“mixed” geometry for overlaps.