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TEVATRON: PRESENT STATUS AND FUTURE PROSPECTS
YOUNG-KEE KIM
FOR CDF AND DO/ COLLABORATION
Physics Department, University of California, Berkeley, California 94720, USA
(LBNL & Fermilab)
E-mail: [email protected]
This article describes the present status and physics prospects for Run II at the Fermilab Tevatronaccelerator. The accelerator complex and both the collider experiments, CDF and DO/, have com-pleted extensive upgrades resulting in a significant increase in luminosity and physics capability. Thesensitivity of the Tevatron Run II physics program is expected to be about 500 times that of Run I.
1 Accelerator Complex for Run II
The Tevatron accelerator at Fermilab Na-
tional Accelerator Laboratory is the highest
energy accelerator in the world, colliding pro-
tons and antiprotons at a center of mass en-
ergy of almost 2 TeV. Since the completion
of Run I in early 1996, a new 150 GeV ac-
celerator, the Main Injector, has been built
to inject the proton and anti-proton beams
into the Tevatron. The number of bunches
has been increased from 6 in Run I (with a
bunch spacing of 3.5 µsec) to 36 for the start
of Run II (with a bunch spacing of 396 nsec),
with a further upgrade to ∼100 later in the
run (with a bunch spacing of 132 nsec). In
addition the energy has been increased from
1.8 TeV to 1.96 TeV, which although appar-
ently quite modest, will nevertheless result in
a 40% increase in the production cross section
of tt̄ events and a factor of 2 increase in the
pair production of ∼300 GeV objects such as
s-quarks and gluinos.
Commissioning with the Main Injector
started with a short “engineering run” in
October 2000, and continued with the be-
ginning of Run II in March 2001. In 2001
the peak luminosity was typically about 7 ×
1030 cm−2s−1. During 2002 the luminosity
is expected to increase towards the initial de-
sign goal of 8×1031 cm−2s−1. By that time a
second new accelerator, the Recycler, will be
commissioned. The Recycler is an 8 GeV ring
of permanent magnets housed in the same
new tunnel as the Main Injector. Its role is to
collect and reuse the anti-protons remaining
at the end of each Tevatron store, providing
an additional boost to the luminosity.
Both CDF and DO/ predict that the sil-
icon trackers will suffer significant radiation
damage after about 4 fb−1, so Run II is di-
vided into two sections, IIa and IIb, with a
shutdown at the end of 2004 to allow the re-
placement of the silicon detectors. By that
time the accumulated luminosity is expected
to be about 2 fb−1 per experiment.
Figure 1 shows the instantaneous and
cumulative luminosity projected for Run II.
The goal for Run IIb is to operate at a peak
luminosity of 5 × 1032 cm−2s−1, accumulat-
ing more than 4 fb−1 per year. The Run II
total is expected to be 15 fb−1 per experi-
ment, sufficient luminosity to allow a thor-
ough search for the Higgs boson with mass
below about 180 GeV/c2, the mass range
predicted by Electroweak precision measure-
ments from LEP, Tevatron Run I, and neu-
trino experiments in the Standard Model.
2 The Upgrades to CDF and DO/
Both CDF and DO/ have undergone major up-
grades to the detectors since Run I (see their
Run II detectors in Figure 2) to accomodate
the decreased bunch spacing and higher lumi-
nosity. In addition the two experiments have
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Figure 1. Projected luminosity for Run II: peak lu-minosity in 1032 cm−2s−1 (left) and integrated lu-monisity in fb−1 (right).
Figure 2. The CDF detector with the silicon trackingbeing installed, and the end-plug calorimeter readyto close (left), and the DO/ detector after roll-in tothe collision hall, showing the extensive muon system(right).
been significantly rebuilt to qualitatively im-
prove performance.
In particular DO/ has installed a 2 Tesla
superconducting solenoid and a new track-
ing system inside the existing liquid argon
calorimeter. CDF has also completely re-
placed the tracking system for Run II. Both
CDF and DO/ have upgraded the trigger and
DAQ systems and the computing and anal-
ysis systems to accomodate the complex de-
tector systems and higher luminosity. Other
upgrades include new plug calorimeters, ex-
tended muon coverage, and a time-of-flight
system for CDF, and an improved muon sys-
tem and new pre-shower detectors for DO/.
2.1 Tracking
While the physics goals for the experiments
are similar, they have chosen quite different
solutions for the tracking detectors. Both em-
ploy silicon detectors at the inner radii (see
Figure 3. Assembly of one of the three CDF silicondetector barrels (left), and the DO/ silicon detector(right). For DO/, the six barrel-disk assemblies areinstalled as combined units.
Figure 3). The DO/ silicon tracker includes
six short four-layer barrel sections with disk
detectors between each barrel to provide for-
ward coverage. Additional disc detectors at
each end of the whole assembly provide track-
ing to |η| < 2.5. The CDF silicon tracker is
arranged entirely in a barrel geometry, with
a total of seven layers in the central region
(|η| < 1) where the outer tracking chamber,
the COT, provides coverage, and eight layers
out to |η| < 2 for stand-alone silicon tracking.
The innermost layer for CDF, L00, is sup-
ported directly on the beampipe at a radius
of only 1.5 cm. This layer employs radiation-
hard single-sided detectors connected to the
readout chips via very thin Kapton cables.
The primary role of L00 is to improve vertex
resolution for low momentum tracks from B
decays which are degraded by multiple scat-
tering.
Both experiments use double-sided sili-
con with a mix of small angle and 90-degree
stereo, with 722,000 channels for CDF and
790,000 for DO/. The readout electronics is
similar, but while DO/ uses the SVX2 ampli-
fier + ADC chip, CDF uses the SVX3 chip
which allows simultaneous digitization and
readout of a previous event while acquiring
the silicon signals for a new event. The sili-
con trackers are working well. Figure 4 shows
reconstructed J/ψ and KS signals seen in
DO/ using silicon stand-alone tracking.
Outer tracking for CDF, the COT, is per-
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Figure 4. J/ψ andKS signals seen in DO/ using siliconstand-alone tracking.
Figure 5. The COT assembly and an on-line displayof a 3-jet event in CDF.
formed by an open cell drift chamber (see
Figure 5). This chamber has 30,240 wires
arranged in 96 planes (in eight super layers),
with an outer radius of 132 cm. The position
resolution is expected to be 180 µcm. The
COT performance is well demonstrated by
the radial distribution for photon conversions
up to the innermost superlayer in the COT
as shown in Figure 6. The prominent peaks
are due to the layers and support structures
of the silicon system and the inner support
structure of the COT.
Because DO/ added a solenoid and track-
ing system inside the original calorimeter, the
tracking system is necessarily more compact
than in CDF. The outer tracking in DO/ is
provided by a scintillating fiber tracker, the
CFT, with an outer radius of 51 cm.
The CFT is read out via Visible Light
Photon Counters, VLPC, which are used for
both the tracker and the preshower coun-
ters. The VLPCs have a remarkably high
quantum efficiency of around 60% and pro-
vide excellent resolution of individual photo-
electron peaks. The downside is that they
must operate at 9-degree Kelvin, and thus
require a cryogenics system. At this time the
0 5 10 15 20 25 30 35 40 45 50
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h4
Nent = 163186
Mean = nan0x7fffffff
RMS = nan0x7fffffff
r (CTVMFT) (after sideband subtraction) h4
Nent = 163186
Mean = nan0x7fffffff
RMS = nan0x7fffffff
r (CTVMFT) after sideband subtraction
r (cm)
L00L0
L1L2
L3L4
SVX outer screen
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L7
ISL outer screen
space tube
COTinnercylinder
port cards cables
08/2001 data
h4Nent = 54021
Mean = 15.71RMS = 10.98
-11030 nbzero bin at 1460
Figure 6. The radial distribution for photon conver-sions, γ → e+e−, constructed by the COT in CDF.
CFT is partially instrumented with readout
boards. The electronics will be complete by
early 2002.
2.2 Calorimeter, Muon Systems and
Particle ID
D0 continues to use the liquid-argon
calorimeters from Run I, upgraded with new
electronics for the new bunch-spacing. CDF
has added new scintillating tile-fiber end plug
calorimeters to improve resolution in the for-
ward direction.
Both experiments use scintillator and
drift-tube layers for muon identification, and
have in particular upgraded the coverage in
the forward direction. dE/dx information
from the tracking layers is used to tag kaon
and proton tracks - particularly important in
B physics. CDF has installed a new scintilla-
tor time-of-flight system, the TOF, between
the COT and the solenoid to provide π/K
separation up to about 1.6 GeV, complemen-
tary with the dE/dx range.
2.3 Trigger, DAQ and Computing
Systems
Both CDF and DO/ have implemented new
three-level trigger systems which are very
similar in design philosophy. The initial
two levels are implemented in hardware +
firmware and the third level in a Linux pc
farm. Primitive objects such as “track”,
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Do → Κπ signal from trigger tracks
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10
20
30
40
50
60
70
80
1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2
Mass (Kπ)(GeV/c2)
CDFII, 14 nb-1
Eve
nts
per
25 M
eV/c
2
Lxy ≥ -100 µm
Lxy ≤ -100 µm
Figure 7. The mass distribution of Do→ Kπ signals
triggered by the SVT in CDF.
“muon”, “jet” or “missing-energy” and ob-
jects such as “electrons” with extrapolation
and matching between detectors are identi-
fied at Level 1, with more sophistigated clus-
tering and extrapolation and tighter match-
ing between detectors at Level 2. For CDF,
Level 2 adds the silicon tracking and impact
parameter information using the SVT pro-
cessor. The transverse impact parameter in
SVT has an r.m.s. width of 50 µm - a combi-
nation of the size of the beam spot and the sil-
icon tracking resolution. Typically a trigger
for hadronic B decays will cut at an impact
parameter of about 120 µm. Figure 7 shows
the mass distribution of Do → Kπ signals
triggered by the SVT on hadronic B decays
during summer 2001 in CDF. DO/ is develop-
ing a similar trigger scheme for implementa-
tion next year.
The Level 3 farms provide essentially full
event reconstruction and a tape logging rate
of several tens of hertz. One difference be-
tween the two experiments is in the rate ca-
pability at Level 1. DO/ will operate with a
Level 1 rate of 5-10 kHz, whereas in CDF a
fully pipelined DAQ at Levels 1 and 2 allows
Figure 8. Signals from CDF for B physics : Λ→ pπ(top left), KS → π+π− (bottom left), J/ψ → µ+µ−
(top right), and the first B signal from Run II, B+→
J/ψK+.
Figure 9. The Z → e+e− mass distribution andW → eν transverse mass distribution from CDF(left), and Z → µ+µ− candidate from DO/ showingfull efficiency of the central and forward muon track-ing.
a Level 1 rate of 40-50 kHz.
Up to summer 2001 the Tevatron deliv-
ered about 12 pb−1, and the exepriments
collected “engineering” signals for calibration
of the detectors and the reconstruction pro-
grams. KS → π+π−, J/ψ → µ+µ−, and
Λ → pπ− signals provide samples for track-
ing studies and efficiency measurements, and
are precursors to physics signals. Figure 8
shows signals from CDF for 4 pb−1 of data,
including the first B signal from Run II, and
Figure 9 shows signals from W and Z events
from CDF and DO/.
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3 Physics Prospects in Run II
The upgraded Tevatron will provide a wealth
of physics data over a very broad range of
topics – both sharpending the precision of
measurements within the framework of the
Standard Model and searching for a Standard
Model Higgs and new phenomena. A series
of workshops was held in the last two years
to focus attention on the physics of Run II 1.
3.1 Physics Prospects with 400 pb−1
Already, by the end of 2002, the deliv-
ered luminosity of 400 pb−1 will be sev-
eral times that delivered in Run I. QCD,
B physics, Top physics, Higgs searches, and
SUSY searches will be energetically pursued,
and new physics topics will be accessible with
the upgraded detectors.
The most exciting physics with this data
will be to measure the BS mixing parameter
xS . xS will be measured in CDF by trigger-
ing with SVT on hadronic B decays (see Fig-
ure 7), with the vertex resolution enhanced
by L00 and particle ID from the new TOF
system. Figure 10 shows the integrated lu-
minosity projected for the detection of xS in
CDF. With only 400 pb−1 CDF will be able
to cover the range xS < 40, thus cover the
predicted range in the Standard Model.
At this conference, both BaBar and Belle
experiments presented very beautiful and im-
pressive results on measurements of sin2β 2,
and they expect to improve these results and
to study CP violations other modes in the fu-
ture. However, the center-of-mass energies in
those two experiments are too low to produce
BS . Thus xS measurement will be unique to
the Tevatron.
3.2 Physics Prospects with 2 fb−1 and
15 fb−1
Higgs Boson
The full program of B physics at CDF
and DO/ will pin down many of the CKM pa-
0
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d lu
min
osity
(fb
-1)
5σ Observation4σ Observation3σ Observation
CDF B0s Mixing
TOF+L00, 1:1 S/B
EXCLUDED
Figure 10. The integrated luminosity projected forthe detection of xS for CDF. With 400 pb−1 CDFcovers the range xS < 40.
rameters in the Standard Model with higher
luminosity. However, as the luminosity in-
creases through Run IIa (2 fb−1 by 2004)
and into Run IIb (15 fb−1 by ∼2007), Higgs
and SUSY searches will become the major
focus. Increased precision of the top and W
masses will improve the limits on the mass
range allowed for a Standard Model Higgs
(see Figure 11 for the predicted uncertain-
ties on MW and Mtop with 2 fb−1 of data)
and with the full luminosity of Run IIb direct
searches will cover the range up to a Higgs
mass of 180 GeV.
For Higgs masses below about 140 GeV
the dominant decay mode is gg → H → bb̄.
Unfortunately this mode suffers from sig-
nificant QCD background, g → bb̄, so the
stratege is to search for Higgs produced in
association with a W or Z, which can pro-
vide a clean trigger and background rejection.
Above 140 GeV, the dominant decay mode is
H → WW ∗ and the gg → H → WW ∗ mode
extends the Higgs searches into the region be-
tween 140 and 180 GeV.
Figure 12 shows the integrated luminos-
ity projected for the detection of a Standard-
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Model Higgs boson at the Tevatron. An
integrated luminosity of 2 fb−1 per experi-
ment, expected in Run IIa, is insufficient for a
convincing observation of a Standard-Model
Higgs boson with a mass too large to be ob-
served at LEP 2. However, a 95% CL ex-
clusion is possible up to about 125 GeV with
2 fb−1. On the other hand, about 10 fb−1 per
experiment would permit detailed study of a
Standard-Model Higgs boson up to the reach
of LEP 2, MH ' 110 GeV. A 5σ discovery
will be possible up to about 125 - 130 GeV
with 30 fb−1, a factor of 2 larger than the
expected Run II luminosity. Over the range
of masses accessible in W/Z associated pro-
duction at the Tevatron, it should be possi-
ble to determine the mass of the Higgs bo-
son to ±(1 − 3) GeV. If the Higgs mass is
higher, especially around 160 GeV, the Teva-
tron has a good sensitivity for detection via
the gg → H → WW ∗ mode. An integrated
luminosity of 15 fb−1 per experiment, ex-
pected in Run II, provides a 3σ detection sen-
sitivity between 150 and 180 GeV.
Top Quark
The discovery experiments were carried
out at the Tevatron in Run I. Although the
top mass measurement from Run I was accu-
rate enough to test the Standard Model by
comparing it with the predictions from elec-
troweak observables and to predict the Higgs
mass, Run II of the Tevatron will give us
our first opportunity to use the top quark
as a tool, and not only as an object of de-
sire. With 2 fb−1 (15 fb−1), both CDF and
DO/ will have samples about 30 (200) times
greater than the Run I samples in hand due
to the top cross-section increase by nearly
40% and better detector performance in addi-
tion to the increase in integrated luminosity.
As stated earlier, the top mass measurement
will be significantly improved in Run II. In
addition Run II physics goals are to search
for tt̄ resonances, rare decays, and deviations
from the expected pattern of top decays. Ta-
80.25
80.3
80.35
80.4
80.45
80.5
80.55
80.6
160 165 170 175 180 185 190 195 200
Figure 11. Estimated errors on MW and Mtop with2 fb−1 of data.
Figure 12. Integrated luminosity projected for thedetection of a Standard-Model Higgs boson at theTevatron Collider. The curves are obtained from aparametrized simulation.
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ble 1 summarizes the expected measurements
of top quark properties and compares them
with LHC predictions.
Beyond the Standard Model
We know that the Standard Model is in-
complete – it has a non-physical high-energy
behavior, and also lacks the deep explanatory
power that we seek in a fundamental theory
of space-time, forces, and particles. There is
currently a great deal of theoretical activity
focused on new physics that would solve some
of the problems with the Standard Model and
that would also be detectable in the energy
scale accessible to the Tevatron Run II. For
example, predictions from models invoking
new phenomena at the 100-200 GeV mass
scale, the scale we will be exploring, have
been made for Supersymmetry, Technicolor,
new U(1) symmetries, Top-color, and Large
Extra-Dimension.
The cross sections for new states with
masses in the 100-200 GeV range (e.g., sys-
tems with total invariant mass in 200-400
GeV range) are typically predicted to be
in the range 10-1000 fb, so that with 2-
15 fb−1 some detailed measurements are pos-
sible. The broad-band nature of the produc-
tion process in p̄p collisions is an advantage
for searching as there is coupling to many
different production processes: for example,
in addition to Drell-Yan production, pairs of
new particles such as charginos can be pro-
duced through gluons or through top decay.
4 Conclusion
Run II has just begun and the detectors are
starting to take their first physics data. This
is an enormously challenging effort, but the
prospect for new discoveries are very excit-
ing. The luminosity will increase dramati-
cally over the next few years and we antic-
ipate significant results, maybe discoveries,
and hopefully some surprises before the LHC
takes the lead at the high energy frontier.
Acknowledgments
Many thanks to the people from CDF and
DO/ who contributed to this talk. CDF and
DO/ rely on the hard work of the technical
staff at Fermilab and the participating in-
stitutions, and the support of their funding
agencies. It is also a great pleasure to thank
our LP01 hosts and hostesses for their de-
lightful and energetic hospitality.
References
1. Physics at Run II Workshops
(http://fnth37.fnal.gov/run2.htm)
B physics at the Tevatron: Run II and
Beyond, Fermilab-Pub-01/197
Report of the Tevatron Higgs Working
Group, hep-ph/0010338
Report of the SUGRA Working Group,
hep-ph/0003154
QCD and Weak Boson Physics in Run
II, Fermilab-Pub-00/297
2. Talks in these proceedings
Jonathan Dorfan (SLAC), BaBar results
on CP violation
Stephen Olsen (University of Hawaii),
Belle results on CP violation
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Table 1. Summary of projected top quark measurements.
Top Property Run I Meas. Precision
Run I Run IIa Run IIb LHC
tt̄ Mass 174.3± 5.3 GeV 2.9% 1.2% 1.0% 1.0%
σtt̄ 6.5+1.7−1.4 pb 25% 10% 5% 5%
W helicity, Fo 0.91± 0.37± 0.13 0.4 0.09 0.04 0.01
W helicity, F+ 0.11± 0.15± 0.06 0.15 0.03 0.01 0.003
R = Br(t→Wb)Br(t→Wg) 0.94+0.31
−0.24 30% 4.5% 0.8% 0.2%
> 0.61 at 90% CL
|Vtb| 0.96+0.16−0.12 (3 gen.)
> 0.051 at 90% CL > 0.05 > 0.25 > 0.50 > 0.90
Br(t→ γq) 95%CL 0.03 0.03 2×10−3 2×10−4 2×10−5
Br(t→ Zq) 95%CL 0.30 0.30 0.02 2×10−3 2×10−4
t σt < 18.6 pb − 20% 8% 5%
Γ(t →Wb) − − 25% 10% 10%
|Vtb| − − 12% 5% 5%
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