alignment for z-direction

Alignment
and
beam position study
contents
- primary vertex distribution
- alignment in Z direction
- beam position study
Hidemitsu Asano
primary yvtx vs zvtx
yvtx
zvtx
primary xvtx vs zvtx
xvtx
zvtx
tangent-like structure
case 1
entire rotation of barrel
case 2
misalignment in x direction
xoffset?
x
x
z(=beam axis)
y
z
y
Shimomura-sanのnDST
• The East center is -190 micron shifted.
x
v
t
x
zvtx
yvtx
zvtx
次のexternal alignmentで治ると期待
alignment in Z direction
•
- change central arm geometry
- vtx measurement supposedly more accurate and precise than
central arm measurement
- therefore this is the cleanest way
- however: this requires touching legacy code
と,いうことをanalysis meetingでは議論されたらしい。
- alignment of VTX in Z direction
1.先にVTX west –VTX east offsetを合わせる
2.pixel はsurvey dataが入ってる。pixel基準で1のwest east offsetを決めてしまい。
stripをpixel layerに合うように調整する。
3. ladder by ladder alignment ( ただし細かい方法については要検討)
VTX west east offset
(SvxPriVertexSeedFinderを改造)
measurement of …..
-seedz by pixel
-seedz by strip
-seedz by pixel west
-seedz by pixe east
analysis setup
-run 349369
-seedz by strip west
-|bbcz|<15cm
-no bbc charge cut
-seedz by strip east
-applied hot dead map
seedpixel_west – seedpixel_east
seedpixel_west – seedpixel_east
(rebin)
seedpixel_west – seedpixel_east
vs
BBCZ
seedpixel_west - seedpixel
pixelseed_east - pixelseed
stripseed_west – pixel seed_west
stripseed_east – pixel seed_east
で、どうするか
-とりあえず、測ったmeanをz_offsetとして採用
-strip layerもpixelに合うように動かす。
-もう一度external alignment (primary_zの位置
が変わるから)
-segmentのクラスターを使ってladder by ladder
にzvtxを組んで、zvtx_meanに合わせて見る
（思いつき）
beam position study
start of fill
run 349160 – 0000,0001（prdf segment #)
start 2011-06-16 18:20:26 Fill:16075
end of fill
run 349168 – 0070,0071
start 2011-06-16 21:21:54 Fill:16075
beam center
• run 349160
run 349160
(x,y)=(0.0594,-0.0591) (cm)
run 349168
(x,y)=(0.0590,-0.0583) (cm)
mean,sigmaともに数μm程度の違い
back up
variables
・(central arm west – central arm east) Z offset
・(central arm west - svx west )Z offset
・(svx west – svx east )Z offset
・ladder by ladder z position in svx coordinate.
(written in svxPISA.par ,should not be changed
by access)
Z
21
• ところで VTX のアライメントどうしよう？
(1mm以下のスケールで)
Lei さんのスライドより
vtx west east gap
今CNTを使うとカオスに
なりはしまいか？
秋元君から(seed –seed )
east
west
bbcz – svx primary (Z)
RUN# 349369
Au+Au 200 GeV
date : Jun,18th 2011
This is a difference btw
bbcz and primary z_vertex
position calculated by VTX.
bbcz mean is in good
agreement with VTX_Z
after Jun. 7th
unit:cm
padvtx[2]-svx primary z
but,in the same run,
Z_vertex calculated
from pad chamber
is off from VTX_Z
(~1 cm)
There is a discrepancy
between pad chamber
coordinate and VTX
coordinate in z-direction.
unit:cm
padvtx is obtained from vtxout
PC3
PC1
search window from bbcz
padvtx
padvtx_west
bbcz
1.select pc1,3 clusters associated with
CNT track
2. straight line projection to (x,y)=(0,0)
3. cut z_vertex far from bbcz (>4cm)
4. calculate mean of zvtx from 3. on east
and west arm individually event by event.
pc3dz
PC3
PC1
CNT track
bbcz
There is also a
discrepancy btw
EAST arm and WEST
arm.
This plot is pc3dz for
west arm only(blue)
and pc3dz for east arm
only (red).
(bbc charge <200 cut is
applied.)
The difference is ~1cm.
2.4m
2.5m
pc3dz=
(cluster position – CNT projected point)
blue:west pc3dz
red:east pc3dz
unit:cm
EMCal cluster
PC1
CNT track
bbcz
There is another evidence
of EAST-WEST discrepancy.
This plot is emcdz for west
arm only(blue) and emcdz
for east arm only (red).
The difference is ~2,3cm.
blue:west emcdz
red:east emcdz
Summary and outlook
- Our original plan is to align VTX ladders in the central arm coordinate. In
x-y plane, all ladders are aligned in DCH coordinate.
- In z direction, there is a large (~1cm) discrepancy between VTX
coordinate and central arm coordinate , and between west arm and east
arm also.
- We don’t think actual location of VTX is off around 1cm from the center
of central magnet.
- We need to match central arm coordinate system and VTX coordinate
system for the alignment and global tracking .
- We will discuss with central arm detector experts about this coordinate
problem.

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