Fixing%20the%20Spacepoints

1
Fixing the Spacepoints
2
Step 1 Fix f

• Lines along the strips do not intersect on the
  z-axis.
• Result can be modeled by a small rotation around
  the center of the module (MC).
• Fix Create SP as usual. Then find the 2D local
  vector connecting MC to SP. Rotate that vector by
  the rotation angle. Revert back to global
  coordinates.
• double xsp rspcos(phisp), ysp
  rspsin(phisp)
  
  
  xsp - posPhi.x() ysp - posPhi.y()
• double tlsp atan2(ysp,xsp)
• double rlsp sqrt(xspxspyspysp)
• xsp rlspcos(tlsprotAng)
• ysp rlspsin(tlsprotAng)
• xsp posPhi.x() ysp posPhi.y()
• sp-gtphi(atan2(ysp,xsp))

MC
3
Step 2 Fix r

• r coordinate of SP calculated with
• Here a is the stereo angle, obtained from
• sina uv_element-gtsinStereo()
• alphaasin(sina)
• Unfortunately, when there is misalignment, this
  is incorrect! Fix
• const Hep3Vector dirT phi_element-gtphiAxis()
  
• const Hep3Vector dirT2 uv_element-gtphiAxis()
• double rotAng -asin((dirT.getX()posPhi.x()
• dirT.getY()posPhi.y())/posPhi.perp())
• double rotAng2 -asin((dirT2.getX()posPhi.x()
• dirT2.getY()posPhi.y())/posPhi.perp())
• alpha rotAng-rotAng2

10-20 effect in a causes r to be miscalculated
by centimeters!
4
Step 3 Find missing SPs

• Disc 8 Inner ring is missing and middle ring is
  populated with short-middle modules!
• SiDetectorElementcenter() returns center of
  active area, not the point around which the
  stereo rotation is done.
• Fix (temporary) Reduce rF (r of MC)

MCF
MCS
?correction?
rspRphiB if (maxLocLlt35 Rphigt400) //
short-mid strips double posDiff
sqrt(pow(posPhi.x()-posStereo.x(),2) pow(posPhi.
y()-posStereo.y(),2)) rsp(Rphi-posDiff/2./sin(
fabs(alpha)/2.))B
Crot
5
Conclusion

• Worked on five example events where IDScan
  failed.
• After corrections, all tracks are successfully
  reconstructed.
• Was using offline clusters gt Now investigate
  cluster issue.
• Will run on hundreds of events to make sure the
  fixes do not have unexpected side effects.