For Publisher’s use - INFN · For Publisher’s use Figure 1. Projected luminosity for Run II: peak lu-minosity in 1032 cm 2s 1 (left) and integrated lu-monisity in fb 1 (right)

For Publisher’s use

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

kim: submitted to World Scientific on January 30, 2002 1


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-



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

100

200

300

400

500

600

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

L6F/BL6C

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”,



Do → Κπ signal from trigger tracks

0

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/.



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

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 5 10 15 20 25 30 35 40xs

Req

uire

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-



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.



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



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%


Documents

For Publisher’s use - INFN · For Publisher’s use Figure 1. Projected luminosity for Run II: peak lu-minosity in 1032 cm 2s 1 (left) and integrated lu-monisity in fb 1 (right)