m. deveaux, cbm collaboration meeting, 14.-17. oct. 2008, dubna, russia a revision of the concept of...
TRANSCRIPT
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
A revision of the concept of the CBM – MVDOr: Do we need an intermediate pixel detector?
• Why a revision of the concept?• Strategies to improve detector resolution• Occupancy and consequences• Summary and conclusion
M. Deveaux, Goethe University Frankfurt/Main
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
Why a revision?
Conclusion:“To measure c
+ CBM needs thin (less 200m !) MAPS detectors.”
Harder impact parameter-cut
Sufficient S/B
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
Why a revisionM
. De
vea
ux e
t al.: “R
&D
activitie
s for th
e C
BM
Micro
Ve
rtex D
ete
ctor (M
VD
)”C
BM
colla
bo
ratio
n m
ee
ting
, 25
. – 2
8. F
eb
20
08
, GS
I, Da
rmsta
dt
z = 10 cm
Requirement
Our running conditions
Optimistic estimate of the material budget of the first MVD-station
There is an obvious misfit between required and possible material budgetRevise global MVD concept
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
Standard detector layout (reminder)
MVD 1z=10cm MVD 2
z=20cmStrip 1z=30cm
Target
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
Detector resolution?
1) A good detector resolution.
Detector needs to be better than a standard MVD with a first station at 10 cm and 200 µm silicon.
What does this means in terms of resolution?
Primary VertexSecondary Vertex
z(Secondary Vtx)Impa
ct-p
aram
eter
Let’s calculate the impact parameter resolution of the MVD
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
What do we need?
Primary Vertex
Impa
ct-p
aram
eter
z1
z2
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
Impact parameter resolution
We are multiple scattering dominated.We have to reach an IP-resolution of ~ 45 µm (Easy if first station at z=5 cm).Open: Can one put the first station to 5 cm?
0.002 0.004 0.006 0.008 0.01
20
40
60
80
100
120
z1 = 5 cm
Material budget [X0]
IP-r
esol
utio
n [µ
m]
Required
Iouri’s “thin detector”
Probable material budget
Iouri’s “thick detector”
z1 = 10 cm
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
A vertex detector at z = 5cm?
Detector lifetime? @10 cm => 12.0 x 1011 min. bias collisions@ 5 cm => 4.4 x 1011 min. bias collisions (46 days at 105 coll/s) Open iss
ue
Occupancy?
C. Trageser, Bachelor Thesis (together with S.Seddiki)
Hit
s / c
oll.
/ mm
²
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
Cluster merging?
Assume: We want a < 1% probability for cluster merging. How to estimate max. occupancy?
Cluster
Detector
Free detectorsurface
Occupied detectorsurface
!
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
Cluster merging?
Free detectorsurface
Occupied detectorsurface
Cluster, 3x3 pixelpixel pitch = 15µm
10 µs time resolution => maximum collision rate ~ 2 x 105/s
Station at 5cm => ~ 3.5 tracks / (106 µm²) => Pileup = 2
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
Track matching probability
MVD 1z = 5 cm MVD 2
z= ???Strip 1z=30cm
Target
Wrong charm signature
To avoid this scenario, pointing resolutionof station 2 to station 1 must be sufficiently good.Assume: Search cone = cluster size (~ 20 µm) => PAmb < 1%
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
What about track matching?
Mat
eria
l bud
get [
% X
0]
Detector – Position [cm]
6 8 10 12 14 16 18 20
0.5
1
1.5
2
2.5
The minimum material budget of detector stations depends on theirposition.
6 8 10 12 14
20406080
100120140160
Accounting for this, we estimate thepointing precision from Station 2 => Station 1
Station 2 has to be placed atz = ~ 8 cm=> Hit density ~1.5 / mm² / coll
Pos (station 2) [cm]
Poin
ting
res
olut
ion
Station 3 has to be placed at z = ~ 11.5 cm, mat. budget = 700 µm Si equivalentHit density: ~1.2 / mm² / coll.
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
MVD – STS – Track matching
MVDTarget
z =
7.5
cm
z =
5 c
m
z =
11.
5 cm
STS
1, z
= 3
0 cm
500 µm Si
Old Geometrie (with Deltas):Old Geometrie (no Deltas):
Track matching from STS to MVD turns into a crucial issue.Probably: Intermediate detectors are needed (Hybrid pixels?)
M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia
Summary and conclusion
Higher, realistic material budget reduces the selectivity of the MVDTo remain sensitive for open charm, the MVD must be placed closer to the target
Close distance to target + delta electrons generate very high occupancyHit finding and track matching become crucial already at ~ 105 coll. /s
A “compact MVD” design is seems required for reasonable track matching in MVDIntermediate pixel detectors might be needed for STS=> MVD track matching.
Assumptions made are conservative:
• Hot spot occupancy is assumed• Option to detect/reject bad clusters or ambiguous tracks is ignored
Might clever algorithms allow for > 105 col/s operation? Needs to be simulated.
Neglect the occupancy from delta electrons in simulation is not justified.