# Presentation: 138347

## 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

## Slide 5

## Cables

**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 geometry

**Get 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/VmcGeometry**
- Thus 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.