Status of the D0 fiber tracker and preshower detectors Page: 4 of 4
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Fig. 4. Scatter plots show correlation between the z position of the
hit and the time of hit arrival as measured with AFEII-t in the axial
(left) and stereo (right) layers. Note that stereo and axial layers are
read out from opposite ends.Fig. 3. (a) Charge distribution from a VLPC pixel with the peaks
corresponding to 0, 1, 2, ... converted photons (signal induced via
LED pulser). (b) Average single hit efficiency for each of the 16 dou-
blet layers. Unresponsive channels are excluded from this assessment.~ 2 5 mm) around the track projection, it is assumed that
this cluster would have been associated with the track in
the standard reconstruction. The ratio of tracks with all
16 hits to all selected tracks gives the single hit efficiency
shown in Fig. 3b for all CFT doublets, for data collected at
luminosities in the range 305 to 60 x 1030 cm-2s-1. Unre-
sponsive channels are not included in the calculation.
An added feature of the AFEII-t board is its capability
of providing information about the time of arrival of signal
generated by a charged particle in the fiber. The correlation
between the hit position and the arrival time is expected
to improve rejection of fake tracks. We observe good agree-
ment between the measured speed of light and the expected
one in the fiber (Fig. 4). Time resolution is estimated to be
3 ns for signals greater than 5 photo-electrons. This implies
a position resolution of hits along a fiber of about 50 cm.
The CPS performance was significantly improved by en-
hanced dynamic range via modified electronic gain. As the
result of this upgrade, the dynamic range increased from
13 to 54 MIPs while the measured energy remains in a
good agreement with the corresponding measurement in
the calorimeter (Fig. 5). There is an ongoing effort to im-
plement a similar improvement for the FPS detector.
Combined, the silicon and scintillating fiber trackers pro-
vide a precise measurement of impact parameter of tracks
relative to the interaction location. On average the impact
parameter resolution for high Pt (> 10 GeV) tracks reaches
values of 20 pm, whereas in the special case of single high
Pt muons the impact parameter can be determined with a
precision close to 10 pm. This allows a significant mea-
surement of the secondary vertex from a B-meson decay.
The efficiency of tagging a jet as one coming from a b quark
depends on the jet's energy. The maximum efficiency of
55% is reached in jets with energies between 40 and
100 GeV. For light-quark jets, the probability of misiden-
tification of their origin to be a b quark normally does not
exceeds 3%.Fig. 5. The energy deposited by a shower in the CPS is well correlated
with the measurement in the calorimeter over the entire active range.
7. Conclusions
The upgrade of the DO detector for Run IIb was designed
to explore a wide range of interesting problems in high en-
ergy physics at increasing peak luminosities. Many physics
analyzes depend on tracker performance, thus it is essen-
tial for the experiment to use the full potential offered by
the VLPC-based front-end electronics.
With the new CFT and PS readout electronics there is
an opportunity for DO to further improve track finding. In
particular, incorporation of the hit arrival time should help
the tracking at luminosities over 3 x 1032 cm--2s--1. Overall
the DO CFT and PS detectors are in a good shape and have
very stable performance.
References
[1] S. Abachi et al. [DO Collaboration], "The DO Detector," Nucl.
Instrum. Meth. A 338, 185 (1994).
[2] V. M. Abazov et al. [DO Collaboration], "The upgraded DO
detector," Nucl. Instrum. Meth. A 565, 463 (2006).
[3] V. M. Abazov et al. [DO Collaboration], "The muon system of the
Run II DO detector," Nucl. Instrum. Meth. A 552, 372 (2005).
[4] R. Ruchti, "Tracking with scintillating fibers," Nucl. Phys. Proc.
Suppl. 44, 308 (1995).
[5] M. G. Stapelbroek and M. D. Petroff, "Visible light photon
counters for scintillating fiber applications. II: Principles of
operation," Workshop on Scintillating Fiber Detectors (SCIFI
93), Notre Dame, IN, 24-28 Oct 1993, World Scientific (1995)
621-629.
[6] P. Baringer et al. [DO Collaboration], "Cosmic ray tests of the DO
preshower detector," Nucl. Instrum. Meth. A 469, 295 (2001).
[7] A. Bross, E. Flattum, D. Lincoln, S. Grunendahl, J. Warchol,
M. Wayne and P. Padley, "Characterization and performance
of visible light photon counters (VLPCs) for the upgraded DO
detector at the Fermilab Tevatron," Nucl. Instrum. Meth. A
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trigger," IEEE Trans. Nucl. Sci. 51, 345 (2004).4
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Smirnov, Dmitri & U., /Notre Dame. Status of the D0 fiber tracker and preshower detectors, article, January 1, 2009; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc925970/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.