proposal2007_draft09.. - Henry A. Rowland Department of Physics ...

uncertainty in the measurement of the CKM angle α. This work was featured in a SLAC Today
article [299].
Events / ( 0.002 GeV/c 2 )
45
40
35
30
25
20
Events / ( 0.01 )
60
50
40
30
15
10
5
0
5.245 5.25 5.255 5.26 5.265 5.27 5.275 5.28 5.285 5.29 5.295
2
(GeV/c )
m ES
20
10
0
-0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08
DE
Figure 4: Projections of the multidimensional fit of the B 0 → ρ 0 ρ 0 decay candidates onto m ES (B
meson mass) and ∆E (energy deviation). The dashed line shows background.
2.1.3 CMS Results
2.1.3.1 Pixel Beam Tests and Modeling The JHU group has been involved in several rounds
of pixel sensor beam tests that were performed (principally) with collaborators from Zurich and
PSI at CERN in 2003, 2004, and 2005. Data from irradiated CiS and Sintef sensors at several
fluences and temperatures were obtained and have driven several (complementary) analyses. This
work has been published in a series of seven journal articles [18]-[24] and the resulting modeling of
irradiated sensors has been used in two others [25]-[26].
depleted region
Read-Out Chip
Figure 5: The grazing angle technique for determining charge collection profiles. Different pixels
sample the signal as a function of depth in the substrate.
The most interesting results of the test beam work involve the analyses of charge collection profiles
measured using the “grazing angle technique” shown in Fig. 5. These measurements demonstrate
that doubly-peaked electric fields exist in irradiated pixel sensors fabricated from diffusively
oxygenated float zone silicon and that they can be modeled using a tuned two-trap double-junction
model [22]-[24], [300]. The most recent results show that doubly-peaked fields are present even at
the modest fluence of 5 × 10 13 n eq /cm 2 . The measured and simulated charge collection profiles
at this fluence are shown for three bias voltages in Fig. 2.1.3.1(a-c). The simulated electric field
profiles are shown in Fig. 2.1.3.1(d). Since this fluence is near the famous Space Charge Sign
Inversion point, the analysis strongly suggests that the traditional model of radiation damage in
silicon involving only thermally ionized acceptors is never fully correct. The simulation also correctly
describes the measured temperature dependence of the profiles. The most recent results have
also taught us how to scale the model with fluence which is important because it is now being used
to drive the optimal pixel hit reconstruction algorithm for CMS described in Section 2.2.1.1.
2.1.3.2 Forward Pixel Wafer Testing and Assembly Barnett has been involved for many
years in the design and testing of the forward pixel detectors on a JHU HEP probe station. This
culminated in 2005-2006 via his leading a team of JHU students in the final certification of part of
6