Contents

Executive Summary 5

1 Intro duction 5

2 Precision Tests of Electroweak Theory 6

3 Quantum Chromo dynamics 7

4 Heavy Flavor Physics and CP Violation 8

5 Neutrino Mass and Mixing 10

6 Electroweak Symmetry Breaking and

New Physics at the TeV Scale 11

7 Astrophysics, Cosmology, and Uni cation of Forces 12

8 Exploratory Theory 14

9 Accelerator Physics, Technology, and

Facilities 14

10 Detectors 15

11 Computing 16

12 Structural Issues in High-Energy Physics 16

13 Conclusions 17 4

Executive Summary

Roberto Peccei

University of California, Los Angeles, CA 90024

Michael E. Zeller

Yale University, New Haven, CT 06511

David G. Cassel

Cornel l University, Ithaca, NY 14853

Jonathan A. Bagger

Johns Hopkins University, Baltimore, MD 21218

Robert N. Cahn

Lawrence Berkeley Laboratory, Berkeley, CA 94720

Paul D. Grannis

State University of New York, Stony Brook, NY 11794

Frank J. Sciulli

Columbia University, Irvington-on Hudson, NY 10533

1 Intro duction arrangements of particles exist and how the forces gov-

erning them may b e more completely uni ed.

Particle physics comprises the study of the most basic

A rich program of investigations can shed lighton

comp onents of matter and the forces that govern their

these fundamental issues and the instruments available

interactions. These sub jects are the b edro ck up on which

to study them are quite varied. The Tevatron at Fermi-

the physical sciences rest, and ultimately govern such di- lab, currently the highest energy accelerator, can study

verse phenomena as the evolution of the universe from the prop erties of the newly discovered top quark and can

the moment of the Big Bang, the generation of energy in

search for new particles and phenomena in a heretofore

the stars, the prop erties of atoms and nuclei, and the un-

unexplored energy range. At the other extreme, exp er-

derstanding of the forces that bind protons and neutrons

iments attempt to determine if neutrinos have mass, an

and stimulate radioactive decays.

issue that relates intimately to our understanding of the

future of the universe. For the next decade there are fa-

Over the past two decades, substantial progress has

cilitie s under construction and in op eration in the United

b een made in identifying the basic constituents of matter,

States that will continue these studies and that o er great

their patterns and relationships, and in understanding

opp ortunity for expanding our knowledge.

and partially unifying the fundamental forces b etween

them. These advances are emb edded in the paradigm While the program that has b een set in place is di-

called the Standard Mo del of particles and forces. This verse and has great p otential, there are ma jor advances

mo del makes predictions that agree with virtually all ex- that can only b e made through accelerator-based stud-

isting exp erimental data. However, the Standard Mo del ies at energies ab out ten to twenty times those avail-

has many comp onents and parameters that are arbitrar- able at present facilities. Comp elling scienti c arguments

ily inserted to t the observations, and it o ers little p ersuaded particle physicists to try to reach these ener-

insightinto the deep est questions of why the observed gies by constructing the Sup erconducting Sup er Collider 5

SSC. The SSC will not b e built, however, and the as- present advisory structure in high-energy physics; sug-

pirations of the particle-physics community for under- gestions for p ossible additional mechanisms to more ade-

standing these fundamental issues now rest up on the re- quately plan for the future; and whether our community

cently approved Large Hadron Collider LHC at CERN should seek a structured public education role and, if so,

in Switzerland and up on accelerators, yet to b e prop osed, how broad should such an activitybe.

that might b e built in the future.

Each of the working groups was led by conveners

chosen among established leaders in the area under con-

When the survival of the SSC b ecame uncertain in

sideration. The conveners then assembled their groups

the summer of 1993, the Executive Committee of the

byinviting other activeworkers in the eld to partic-

Division of Particles and Fields DPF of the American

ipate. Most of the working groups also gathered fur-

Physical So ciety b egan serious discussions of steps that

ther input from the communityby holding various sp e-

would b est help our community face the challenges of the

cialized meetings and workshops. The working groups

future. These discussions were strongly in uenced by the

presented their preliminary ndings at a Workshop at

loss of the SSC and the subsequent app ointmentofthe

Johns Hopkins UniversityinMay 1994, and their nal

Drell Subpanel of the Department of Energy's High En-

rep orts at the DPF general meeting in Albuquerque the

ergy Physics Advisory Panel HEPAP to help provide

following August. Draft written versions of these rep orts

a vision for the future of the eld. Since the Drell Sub-

were critically discussed at a retreat of all conveners with

panel had a sp eci c charge and a relatively short time for

the memb ers of the DPF Executive Committee at the

delib eration, the DPF Executive Committee felt that the

Lawrence Berkeley Lab oratory in Octob er 1994. The

high-energy-physics community and the public on whose

corrected draft versions of the rep orts were examined one

supp ort it relies would pro t byhaving an additional

more time by an editorial b oard app ointed by the DPF

broad-based and in-depth study of the eld. This study,

Executive Committee.

called the Committee on Long-Term Planning, was initi-

The rep orts of the working groups, along with their

ated in early 1994 and its fruits are the rep orts contained

conclusions and recommendations are summarized in the

in this volume.

following sections.

This study of high-energy physics was organized on

the basis of working groups. Of the eleven working

groups in the study, seven dealt with sp eci c physics

2 Precision Tests of Electroweak Theory

topics and three with more technical areas accelerators,

particle detectors, and computers. One concentrated on

The theory of electroweak interactions unites the electro-

structural and educational issues of the eld. Broadly

magnetic and weak interactions and is the cornerstone

sp eaking, four of the physics working groups dealt with

of the Standard Mo del. In this theory, the electroweak

physics issues connected with the Standard Mo del, our

forces arise from interactions of four b osons, the pho-



present paradigm for particle physics, while the other

ton, Z , and W , with the quarks and leptons of mat-

three working groups fo cused on questions b eyond our

ter. Gauge symmetry is a fundamental ingredient of this

present knowledge, but whose answers are crucial for a

theory. The gauge symmetry of the electroweak inter-



deep er understanding of nature. The charge to eachof

actions implies that the masses of the photon, Z , W ,

the physics working groups was to articulate the broad

and the quarks and leptons all vanish. Some mechanism

range of physics questions in the group's particular area

is required to break this symmetry and provide the ob-

and to discuss the means by which these questions might

served masses of particles. In the standard electroweak

b est b e addressed, in the context of existing and future

theory, the simplest way to pro duce this symmetry break-

facilities in the United States and in the rest of the world.

ing is via interaction with an additional particle, called

Each of these working groups was asked to identify im-

the Higgs b oson.

p ortant areas of emphasis for future study.

The resulting electroweak theory dep ends on three

primary parameters, which can b e taken to b e the elec- The accelerator physics working group was charged

tromagnetic ne structure constant, , the Fermi con- to undertake a study of the current state of the art and

stantofweak interactions G , and the mass M of the of foreseeable advances in accelerator facilities for high-

F Z

Z b oson. It is then p ossible to predict many other imp or- energy physics HEP research. The particle detectors



tant quantities, such as the mass M of the W b osons, working group and the computing working group were

W

in terms of these parameters. Actually, such predictions asked, resp ectivel y, to assess the likely detector tech-

also dep end in detail on quantities like the masses of the nology and computational needs of ongoing and future

quarks and the Higgs b oson. Very extensive tests of the high-energy physics exp eriments, considering the impact

electroweak theory have b een carried out in a varietyof of existing and emerging technologies. Finally, the struc-

circumstances, most notably in the pro duction and de- tural and educational issues working group was charged

cay of the Z b oson. The agreement of these tests with with examining various issues in our community that are

the theory is remarkably go o d, often at the level of 1 of broad concern. These include the adequacy of the 6

or b etter. In addition, from the slight dep endence of pre- b osons and of the top quark and

dictions on the mass of the top quark, it is p ossible to

 to lo ok for small discrepancies b etween exp eriment

estimate its mass. This prediction of approximately 175

and theory that, if found, will p oint to new physics

GeV is in excellent agreement with recent direct measure-

beyond our present understanding.

ments of the top mass by the CDF and D collab orations

at Fermilab.

3 Quantum Chromo dynamics

Despite these notable successes, more stringent tests

of the electroweak interactions are imp ortant. There may

Quantum chromo dynamics QCD, the theory of the

well b e new interactions outside the Standard Mo del, or

strong forces b etween partons quarks and gluons, is

new particles that are to o massive to b e pro duced and

the second central ingredient of the Standard Mo del.

detected at current accelerators. These phenomena can

In QCD, the force b etween quarks is carried by b osons

cause small deviations from exp ectations for measurable

called gluons. Indeed, an imp ortant feature of QCD is

quantities and precision measurements can provide cir-

the fact that there would b e a strong force even without

cumstantial evidence for their existence. There is an ac-

the quarks b ecause gluons interact with each other. The

tive exp erimental program planned worldwide that will

strength of the interaction, called , is not a constant

S

provide signi cant improvement in precision, with a sub-

but dep ends on the energy scale at which it is measured.

stantial reduction in the errors for key electroweak pa-

At the mass of the Z b oson its value is ab out 0.12 { ab out

rameters.

a factor of 16 larger than , the corresp onding strength

Forthcoming data from LEP at CERN and from p o-

of the electromagnetic interaction.

larized Z 's at the SLC at SLAC will sharp en our knowl-

Since its formulation in the early 1970's, QCD has

edge of electroweak interactions at the Z .Further im-

develop ed into a mature theory that is well veri ed in a

provements in the accuracy with whichwe know the W

variety of exp eriments. While the evidence is comp elling

b oson's mass will provide p owerful complementary infor-

that QCD is the correct theory of the strong interac-

mation. This will come from data now b eing gathered at

tions, we cannot say that we understand all phenom-

the Fermilab Tevatron Collider and from future running

ena completely. This is not an entirely new situation:

with the Main Injector, as well as from data from LEP 2

although we b elieve that quantum mechanics and elec-

at CERN, a machine that is scheduled to b egin op era-

tromagnetism describ e completely our everydayworld,

tion in 1996. The ability to pin down the value of the

we cannot yet explain quantitatively many complex phe-

top quark mass with high precision will also b e essential

nomena. Some pro cesses in QCD can b e understo o d with

for more stringent tests of the electroweak theory. Only

p erturbation theory expansions of the interactions b e-

Fermilab will have sucient energy to explore directly

tween the partons in low orders of ; others, suchasthe

S

the prop erties of the top quark until the turn-on of the

formation of b ound states of quarks, called hadrons, can-

LHC.

not. In particular, at present in QCD there is still a very

Currentinvestigations will surely deep en our under-

incomplete understanding of how p erturbative regimes

standing of electroweak interactions and may presage

are connected with non-p erturbative regimes; of quark

new physical phenomena, whose full exploration will need

con nement the exp erimental absence of free quarks; of

higher energies. A case in p oint is the Higgs b oson,

the high temp erature and high density phases of quarks

which can b e directly detected at LEP 2 if its mass is

and gluons; and of the reason for the absence of strong

less than ab out 90 GeV. This search could p erhaps b e

CP violation.

extended if the Fermilab Collider luminosity is upgraded

There is a large and active exp erimental program

signi cantly, but ab ove this mass range the detection of

worldwide pursuing di erent asp ects of QCD. When ex-

the Higgs b oson will require the LHC or a high-energy

plored at high energies, protons are seen to contain ad-

+

electron-p ositr on e e  collider. Nevertheless , precision

ditional quark-antiquark pairs and gluons, b esides the u

electroweak measurements may help to further narrow

and d quarks of the simple quark mo del of hadron struc-

the exp ected mass range for this p ossible particle.

ture. The measurements of the distributions of these

The theory of the electroweak interactions is one of

parton densities has b een an imp ortant thrust of high-

the two pillars which underlies the Standard Mo del, the

energy physics for nearly thirtyyears and continues at

paradigm for how the fundamental constituents of mat-

b oth hadron and electron machines. Data obtained at

ter interact. Continued probing of this theory by exp eri-

the new electron-proton ep collider HERA in Hamburg

ments of increasing precision remains central to particle

show a large increase in the quark and gluon densityat

physics and has two principal goals:

small values of the Bjorken scaling variable x, and may

 to re ne our knowledge of the parameters that char- b e the rst indication of an eventual saturation of par-

acterize the Standard Mo del and the breaking of elec- ton densities a new non-p erturbative domain of QCD at

troweak symmetry, requiring improvements in the very high parton densities . Exp eriments at CERN and

accuracy with whichwe know the masses of the W SLAC are giving new information on how the proton spin 7

is shared among the constituents. Studies of jet decays tions, treating space-time as discrete, are an imp ortant

+

of the Z 's pro duced in e e collisions at LEP and SLAC to ol for probing the implications of QCD in the strong

have given very accurate understanding of the coupling coupling regime. These metho ds are just now b eginning

and underlying structure of QCD pro cesses, and provide to pro duce reliable results for low energy phenomena.

insights on the di erences b etween quark and gluon jets. With more computing p ower and further progress on the

development of algorithms, the dream of a reliable cal-

Exp eriments at hadron machines are a rich source

culation of the hadron mass sp ectrum and of low energy

of complementary information ab out QCD. Whereas in

+

hadronic matrix elements may b e close. Lattice calcula-

e e and ep collisions, one pro ceeds from a clean and

tions for are now already comp etitive with p erturba-

well understo o d initial state to a nal state involving

S

tive derivations and should eventually provide the most

parton jets, in hadron collisions one may study simple

precise determination of this fundamental quantity.

nal states  , W , and Z  free from fragmentation ef-

Even though the present exp erimental evidence for

fects but with partonic initial states that are less well

QCD is comp elling, QCD deserves further intense exp er-

understo o d. This complementarity is imp ortant b ecause

imental scrutinyindiverse circumstances to prob e areas

it allows cross checks of the e ects of proton structure

of the theory where our understanding is far from com-

and fragmentation into hadrons. The very high energy of

plete. These include:

hadron colliders enables sensitive studies of QCD and the

measurementof at short distances from high trans-

 continued studies at Fermilab of the pro duction and S

verse momentum pro duction of jets and vector b osons,

correlations of jets, W 's, Z 's, 's, and b quarks at

and their angular correlations. The increased energy,

large transverse momentum and all angles;

+

masses, and phase space available also p ermits new tests

 studies of hadronic nal states in e e collisions with

of gluon radiation calculations \resummed" to all orders.

well-de ned initial conditions;

Further insights into the transition from a p erturbativeto

 measurements aiming at elucidating the proton's

a non-p erturbative regime of QCD can come from stud-

structure at high energy and low x in ep collisions

ies of di ractive scattering and events with large kine-

at HERA;

matic gaps b etween clusters of particles in ep and hadron-

 studies of how the spin of the hadrons is carried by

hadron collisions.

the underlying partons;

Comparison of observations dep ending on the same

 exploration of di ractive phenomena in b oth ep and

underlying distributions provided by di erent measure-

hadron-hadron colliders;

ments give imp ortant cross-checks and enhance our un-

 searches for states e.g., glueballs, hybrids, and

derstanding of QCD. The high precision jet data now

strangelets allowed by QCD but not yet observed;

b eing gathered warrant re ned theoretical calculations

and

beyond those that currently exist, and an ongoing inter-

 searches for indications of a quark-gluon plasma in

action b etween theorists and exp erimenters is b oth help-

high-energy collisions b etween nuclei at RHIC.

ful and necessary for continuing progress.

Among the phenomena that may reveal surprises are

systems with a high density of quarks and gluons. Such

4 Heavy Flavor Physics and CP Violation

systems can b e created by colliding nuclei at very high

energy, which will b ecome p ossible so on at the Relativis-

Our tangible world is made of electrons and up u and

tic Heavy Ion Collider RHIC at Bro okhaven. Heavy ion

down d quarks, which are constituents of the proton

collisions o er the p ossibility of studying a new phase of

and neutron. Neutrinos  's are intangible, but also

QCD where the separate nucleons coalesce into a plasma

present. These four basic particles app ear to b e sucient

of quarks and gluons. A ma jor challenge here is to un-

to explain ordinary matter. Nonetheless, there are two

derstand how, at early times in the collision, the transi-

additional sets of four particles that follow the same pat-

tion from hadronic degrees of freedom to an equilibrated

tern: the \second generation" of charm c and strange

quark-gluon phase takes place. This is a eld where

s quarks, with the muon  and its neutrino, and the

nuclear physics and particle physics merge, and where

\third generation" of top t and b ottom b quarks, with

p erturbativephysics, non-p erturbativephysics and phe-

the tau   and its neutrino. These three generations

nomenology are essential in order to extract the desired

of quarks and leptons and the asso ciated mechanism by

information that these collisions can provide on high den-

which these particles decayinto each other are an essen-

sity and high temp erature QCD.

tial ingredient of the Standard Mo del. The reason for the

triplication is unknown, but it allows the Standard Mo del

Because of con nement, quarks and antiquarks are

to accommo date matter-antimatter asymmetry due in

b ound together by a force which increases with the dis-

part to the phenomenon known as CP violation.

tance of their separation. As a result, the prop erties of

The weak interaction can turn one kind \ avor" of hadronic b ound states cannot b e determined by straight-

quark into another. In nuclear decayadquark b ecomes forward theoretical techniques. Lattice gauge calcula- 8

a u quark while an electron and an antineutrino are emit- Tevatron collider. These studies provide direct measure-

ted. There is a general prop ensity for quarks to remain mentoftwo CKM matrix elements, V and V , and

cb ub

within one family.Thus a c quark prefers to change to an indirect measurements of some others. However, a full

s quark rather than a d quark. These prop ensities can b e understanding of the role of the CKM matrix in CP vi-

describ ed quantitatively in terms of a unitary matrix, V , olation requires intricate and dicult measurements on

called the Cabibb o-Kobayashi-Maskawa CKM matrix. many more B decays than have b een observed so far.

+

In this description, V is a factor in the amplitude for B Factories, esp ecially designed e e colliders with high

cs

a transition from a c quark to an s quark, while V is intensities and unequal b eam energies, are b eing built at

cd

the smaller factor asso ciated with a transition from a c SLAC and at KEK in Japan to facilitate these measure-

quark to a d quark. ments.

In the Standard Mo del the CKM matrix arises from

High-energy hadron machines, including the Teva-

the mismatchbetween the quarks as seen by the strong

tron Collider, which collide strongly interacting particles,

and the weak interactions. Unitarity and the fact that

are more proli c sources of B mesons. However, B 's are

only relative phases are observable imply that four in-

pro duced in only a tiny fraction of the vast number of

dep endent real parameters determine the nine complex

events that reach the detectors and the B 's are pro duced

elements of the matrix. It is p ossible to test this exp ecta-

in a much more complex environment, making the desired

tion by measuring more than four of the matrix elements

particles and correlations more dicult to observe. Full

and seeing if they are related in the anticipated way.To

exploitation of these high event rates will thus require

do this, many di erentweak decay pro cesses involving

advances in detector technology, particularly in the abil-

many di erent kinds of particles must b e measured care-

ity to \trigger" on B events selecting B events quickly

fully.

and eciently at some stage well b efore events are fully

Understanding the CKM matrix is imp ortant for two pro cessed in a computer. The high pro duction rate of

b quarks in high-energy hadron-hadron collisions has led

reasons. First, it seems likely that the CKM matrix is

many to suggest there should b e a dedicated b physics

intimately connected to the pro cess through which the

facility based on a hadron collider. The desirabilityof

quarks get their masses, that is, to the electroweak sym-

metry breaking mechanism. Second, the CKM matrix such a facility deserves careful consideration, with atten-

may also play an imp ortant role in CP violation. CP is tion to the additional reachitwould provide b eyond that

+

given by the e e B Factories. A vigorous and dedicated

short-hand for the joint application of the op erations of

b physics facility at a hadron collider may also b e able

replacing particles by their antiparticles C , and replac-

to ll the gap which will result when the LEP b program

ing right handed particles and pro cesses by left handed

ceases with the turn-on of LEP 2.

ones P . The violation of CP symmetry has b een seen

0

in the decays of K mesons, one typ e of particle contain-

It is an old adage of particle physics that everything

ing strange quarks.

that is not forbidden is compulsory. But what is ab-

+ +

CP violation is an essential element in understanding

solutely forbidden? A decay like  ! e , which

the observed dominance of matter over antimatter in the would violate conservation of angular momentum, cer-

universe. In the Big Bang, matter and antimatter should tainly seems to b e forbidden. Some decays whichhave

0 +

have b een pro duced in equal amounts. If CP were an

no such fundamental problem, like K ! e  ,have

exact symmetry, this primordial matter and antimatter

never b een observed. From the absence of such pro-

would have annihilated each other shortly after they were

cesses we infer that electron numb er and muon number

pro duced.

are separately conserved. These and similar conservation

\laws" are included in the Standard Mo del, even though

Although the CP violation that can b e describ ed by

no comp elling theoretical reason for their existence has

the CKM matrix may not b e fully resp onsible for the

b een found. Whether these conservation laws are abso-

dominance of matter in the universe, it is still imp ortant

lute, however, is an exp erimental question which can b e

to learn all we can ab out it. For thirtyyears, the decays

0

investigated esp ecially well with K b eams, as in the cur-

of K 's has b een the only source of our knowledge of CP

rent program at Bro okhaven National Lab oratory. The

violation. Crucial exp eriments at Fermilab, CERN, and

observation of violation of any of these lepton-number

Frascati in Italy, are now b eing readied to explore further

rules would have profound consequences. Because we

CP violation in this system, lo oking for tiny e ects that

are unable to predict in which sector s, c, b, t,or

should help elucidate whether its origin can b e traced to

evidence for such new physics might app ear, our studies

the CKM matrix.

need to remain as broad as p ossible. In addition, rare

The decays of B mesons, particles containing b

decays of heavy quarks provide alternative p ossibiliti es

quarks, can provide new and more complete understand-

for studying CP violation and may reveal signs of CP

ing of the CKM matrix. The decays of B mesons are al-

+

violation b eyond that predicted by the CKM matrix.

ready b eing studied very e ectively at CESR, the e e

storage ring at Cornell, as well as at LEP and at the The present U.S. exp erimental program in heavy a- 9

vor physics is healthy and extensive and includes: whether the neutrino is a Dirac particle with a distinct

antiparticle or a Ma jorana particle b eing its own an-

 CLEO at Cornell b, c, and  ,

tiparticle. In the search for physics b eyond the Stan-

 the Fermilab collider program b and t,

dard Mo del, new information in the neutrino sector may

 the Fermilab xed target program c and s, and

well play an essential role.

 rare K decay studies at Bro okhaven s.

The question of neutrino mass and mixing not only

In addition, there is substantial U.S. involvement in the

is imp ortant for particle physics, but has also enormous

LEP exp eriments at CERN b,  , and in BES in Beijing

relevance to astrophysics and cosmology.For example,

c,  .

a nonzero neutrino mass would contribute to the non-

The approved upgrades to existing U.S. facilities

baryonic dark matter, and p erhaps signi cantly to the

Phase I I I of CESR plus CLEO I I I and the Fermilab

total mass of the universe. If neutrinos are massive, it

Main Injector plus CDF and D upgrades and ap-

is likely that they mix in a manner similar to that seen

proved new facilities SLAC B Factory assure a con-

in neutral K mesons. A neutrino pro duced as a partner

tinued healthy program. However, the long-range future

ofamuon will initially p ossess muonic nature, but as

of K physics is less certain as Bro okhaven's role shifts

time passes, would evolve a comp onent of electron-typ e

with the advent of RHIC, although new opp ortunities

or tau-typ e neutrino. Suchchanges can b e observed in

may arise with the turn-on of the Main Injector at Fer-

avarietyofways by observing neutrino interactions at a

milab.

distance from the source. Several substantial indications

The mysteries of mass, avor, and CP violation,

are emerging that these neutrino oscillations might exist.

which are likely to have deep connections to each other,

One hintisprovided by the solar neutrino prob-

comp el us to continue a vigorous exp erimental and theo-

lem. The intensity of neutrinos pro duced in the inte-

retical program of studying heavy avor decay. The two

rior of the sun may b e calculated from known nuclear

most imp ortant goals of this research are:

pro cesses, which ultimately pro duce the radiant energy

 to provide enough measurements to unambiguously

visible at the solar surface. All measurements of this

overconstrain the CKM matrix and clarify its role in

electron-typ e neutrino intensity at the earth are consid-

CP violation, and

erably lower than the rates exp ected from the standard

 to search for rare and forbidden decays in order to

mo del of energy pro duction from the sun. This is hard to

exploit their sensitivitytophysics b eyond the Stan-

accommo date even by highly nonstandard astrophysical

dard Mo del, at mass scales exceeding those that can

or nuclear physics mechanisms.

b e directly prob ed at accelerators.

Another hint comes from cosmic rays; measurements

Continued progress towards these goals requires more

of neutrinos pro duced by the interaction of cosmic rays

joint exp erimental and theoretical e ort in understand-

in our atmosphere indicate that the relativenumber of

ing the interplay of the strong, weak, and electromagnetic

electron-typ e and muon-typ e neutrinos di ers from ex-

interactions in decay pro cesses.

p ectations by ab out a factor of two. Neutrino oscilla-

tions of muon-typ e neutrinos are a serious p ossibilityto

explain this discrepancy.

5 Neutrino Mass and Mixing

Finally,very recently, another indication comes from

an accelerator-based exp eriment at Los Alamos, where

The eld of neutrino physics is diverse and is carried

an anomalous signal mightbeinterpreted in terms of

out in exp eriments at university lab oratories, deep un-

neutrino oscillations.

derground sites, and accelerators. The scientists come

Although oscillations between di erent neutrino

from particle and nuclear physics, astrophysics, and cos-

sp ecies may provide an attractive explanation for some

mology and are comprised of b oth exp erimentalists and

or all of these data, a full resolution of these issues with

theorists. Exp eriments range from mass measurements

further exp eriments is essential. For the solar neutrino

of neutrinos in decays of particles and nuclei, to observa-

problem the next generation of solar-neutrino detectors,

tions of neutrinos pro duced in our sun and in sup ernovae,

the Sudbury Neutrino Observatory SNO in Canada,

to studies of neutrinos pro duced by accelerators and in

Sup erKamiokande in Japan and Borexino in Italy, should

reactors.

b e able to lo ok for signatures of solar neutrino interac-

Fortyyears after the rst direct detection of neutrino

tions and isolate e ects of electron-typ e neutrino oscilla-

interactions with matter, our knowledge of the three fam-

tions indep endently of solar mo dels.

ilies of neutrinos and their interactions has improved dra-

matically.However, crucial asp ects of our understanding Accelerator exp eriments may b e the b est waytore-

are still lacking. Many fundamental prop erties, particu- solve the hints of muon-typ e neutrino oscillation pro-

larly neutrino masses and mixing of the neutrino states, vided by the atmospheric neutrino results. Long baseline

are known only as exp erimental upp er limits. Indeed, exp eriments sensitive to oscillations bymuon-typ e neu-

the issue of neutrino mass is central to the question of trinos are b eing prop osed for the KEK, Fermilab, and 10

Bro okhaven accelerators and could b egin taking data in direction of the eld. Theory requires that electroweak

the not to o distant future. Oscillations of electron-typ e symmetry not b e broken in this way, but more subtly.



neutrinos in the same parameter range should b e visible Without the symmetry breaking, the W and Z , and all

in exp eriments b eginning shortly at the San Onofre and the quarks and leptons would b e massless. If any progress

Cho oz reactors. is to b e made in understanding these masses, the source

New information ab out the nature of neutrinos is of electroweak symmetry breaking must b e discovered.

likely to make imp ortant, p erhaps vital, contributions This is one of the core questions in high-energy physics

to our understanding of the universe and of what lies to day.

beyond the Standard Mo del. For this reason, it is im-

In one approach to electroweak symmetry breaking,

p ortant that innovative exp eriments exploring neutrino

anumb er of scalar spinless particles are intro duced.

mass, couplings, and other prop erties b e encouraged and

Some of these particles are absorb ed by the W and Z

that indications of nonzero mass and/or avor mixing b e

b osons when they acquire masses. The remaining scalars

vigorously pursued. Fortunately, an active program of

app ear as new particles. In the simplest version, there is

neutrino exp eriments is underway or planned:

just one such particle, the Higgs b oson.

 Direct mass measurements of electron-typ e neutrinos

A second p ossibility, called sup ersymmetry, predicts

in decay are probing masses of cosmological inter-

the existence of many new particles, among them a num-

est. Other exp eriments seeking evidence for double

b er of scalars like the Higgs b oson. While there is no

decay with no neutrinos may provide the rst demon-

direct evidence for sup ersymmetry, there is strong the-

stration of the Ma jorana identity of the neutrino.

oretical motivation for it. There is also some supp ort-

 Indications of neutrino oscillations from solar neu- ing circumstantial evidence from extrap olating the elec-

trinos will b e prob ed by at least three new ex- troweak and strong couplings to high energy, where the

p eriments with signi cant U.S. participation SNO, three couplings coalesce { if sup ersymmetric e ects are

included { as they should if there is a uni cation of these

Sup erKamiokande, Borexino. These exp eriments

should b e able to resolve the issue of whether the forces at high energy grand uni cation.

observed de cit of solar neutrinos has an astrophys-

A third p ossibility, referred to as strongly coupled

ical explanation or instead requires neutrino mixing.

electroweak symmetry breaking, intro duces no new scalar

particles but requires that their roles b e played by b ound

 Short baseline exp eriments presently underwayat

CERN and planned for Fermilab have the p otential pairs of new, heavy analogs of the usual quarks, dubb ed

to explore cosmologically relevant mass ranges for  techniquarks.



oscillations to  or  , with excellent mixing sen-

Which of these theories, if any, is the correct descrip-

 e

sitivity.

tion of nature can b e determined only by exp eriment.

 Full exploration of the hints of oscillations seen Finding the Higgs b oson or any of the other new particles

in atmospheric neutrino interactions awaits direct that app ear in mo dels of electroweak symmetry breaking

measurements by long baseline exp eriments using would b e a ma jor step forward. The negative results

of current exp eriments b ound the Higgs b oson mass to

accelerator-generate d neutrino b eams.

b e ab ove ab out 60 GeV. This range will b e extended to

ab out 90 GeV at LEP 2. Sup ersymmetric analogs of the

6 Electroweak Symmetry Breaking and

Higgs b oson could also b e discovered at this accelerator

New Physics at the TeV Scale

if they were light enough.

While we cannot predict the mass of the Higgs b oson

The electroweak theory is based on the realization that

wedohave con dence that whatever the source of elec-

the quantum of light, the photon, and the quanta of



troweak symmetry breaking, there must b e indications

decay, the W b osons, are intimately related. Just as

for it b elow ab out 1000 GeV 1 TeV. Therefore, it is

isospin, a symmetry of strong interactions, identi es the

crucial to explore the TeV energy scale to elucidate the

neutron and proton as partners, a new symmetry,weak

dynamics of electroweak symmetry breaking and the as-

isospin, identi es the electron or rather, its left-handed

so ciated fundamental particle sp ectrum. This program

piece and its neutrino as partners.

necessaril y will b e a primary fo cus of particle physics

The electroweak symmetry is far from exact. The W

research in the future and, at present, can only b e con-

and Z b osons are among the heaviest known elementary

templated at the LHC.

particles, while the photon is the lightest, though they

are related by this symmetry. Similarly, the neutrino An extensive study of the electroweak symmetry

and the electron can hardly b e confused, even though breaking sector will require a robust exp erimental pro-

they are partners. gram at the LHC. However, nding the source of elec-

How is the electroweak symmetry broken? The ro- troweak symmetry breaking is not the only goal of the

tational symmetry of an atom can b e broken by apply- LHC. Our current picture of particle interactions app ears

ing a magnetic eld, which explicitly distinguishes the incomplete so that there maywell b e new phenomena 11

within the LHC's range. One p ossibility is that there 7 Astrophysics, Cosmology, and Uni cation of

may b e more particles like the W and Z b osons, which Forces

transmit new forces. Moreover, due to its mass reach,

The elds of astroparticle physics, cosmology, and uni-

the LHC is in an excellent p osition to test for low-energy

cation of forces are growing areas of research that are

sup ersymmetry by lo oking for the signatures character-

at the intellectu al frontier of particle physics. Because

istic of the decays of strongly-interacting sup ersymmet-

the energy reach of theory has exceeded that of terres-

ric particles, missing transverse momentum and multi-

trial exp eriment, the pursuit of fundamental physics has

lepton nal states. Full exploitation of the p otential for

more and more come to involve astrophysics and cosmol-

these searches requires the energy and luminosity of the

ogy.Today many particle physicists, b oth theorists and

LHC, but the substantial luminosity improvements now

exp erimentalist s, are working at the interface of particle

b eing prop osed for the Fermilab collider should also p er-

physics with astrophysics and cosmology, and this trend

mit substantial progress in the next decade. For example,

is likely to increase.

the upgraded Fermilab collider with q q initial states as

opp osed to the gluon-gluon initial states predominating

The b oundaries of particle physics now touch on cos-

at the LHC could allow the observation of a Higgs b oson

mology, astrophysics and gravity. Our b est attempts to

with mass up to 130 GeV in asso ciation with a W or Z .

understand some of the most basic features of the uni-

verse { the cosmic asymmetry b etween matter and anti-

An electron p ositron linear collider with total energy

matter, the tiny primordial inhomogeneities that seed the

between 0.5 to 1.5 TeV and sucient luminosity b eam

growth of all galactic structure in the universe, the mys-

intensity would provide lower backgrounds and a b etter

terious dark matter, and the large-scale smo othness and

controlled initial state than the LHC for similar explo-

atness of the universe { involve fundamental physics.

rations. Such a machine would have greater sensitivityto

Conversely, the universe has b ecome an imp ortant lab-

weaker signals, such as Higgs b osons in sup ersymmetric

oratory for testing our b oldest ideas ab out the laws of

mo dels and low-mass weakly interacting sup ersymmetric

Nature { sup ersymmetry, grand uni cation, and sup er-

particles. An electron-p ositr on collider of appropriate en-

strings.

ergy would b e an ideal lab oratory for the detailed study

Most of the basic features of the universe can b e

of the prop erties of Higgs b osons, and a 1.5 TeV linear

explained by p ostulating a brief in ationary instant dur-

collider could prob e a strongly coupled electroweak sym-

ing which an enormous burst of expansion allows a tiny,

metry breaking sector. Thus, such a linear collider would

smo oth piece of the universe to grow and encompass all

b e in manyways complementary to the LHC.

that we can see to day. This tremendous expansion also

Physics b eyond the Standard Mo del may app ear in

allows quantum-mechanical uctuations on microscopic

other ways. Unequivo cal evidence for neutrino oscilla-

scales to evolveinto variations in the energy densityon

tions, or CP violation outside the CKM structure, or

cosmological scales, explaining the origin of the inhomo-

decay mo des that are forbidden by the Standard Mo del,

geneities needed to seed structure. In ation requires that

would have dramatic consequences. Atvery high energies

the total mass density of the universe b e equal to the crit-

wemay nd new fundamental fermions, part of a fourth

ical density, balanced b etween a universe that expands

generation, or extensions of the three known generations.

forever and one that ultimately ceases to expand and

However, this is only a sp eculation; such particles may

then collapses. However, the mass density in stars is far

or may not exist in nature. In contrast, although wedo

less than this, and the study of primordial nucleosyn-

not know precisely the origin of electroweak symmetry

thesis shows that the mass density in ordinary matter,

breaking, at least we know where and at which energy

luminous or not, is far less than the critical density, indi-

clues await us.

cating the existence of a new form of matter, called dark

Exploration of the TeV scale is essential for the long-

matter.

term vitality of particle physics. This requires a new

Even setting aside the in ationary prediction, there

generation of colliders and detectors b eyond those that

is strong evidence that much, if not most, of the mass

are currently available or those that can b e attained with

density of the universe is something other than the fa-

mo dest upgrades. This leads us to two conclusions:

miliar baryons comprising atomic nuclei. No problem

more dramatically demonstrates the con uence of parti-

 Participation of the United States in the LHC pro-

cle physics and cosmology than that of dark matter. It

gram is imp ortant and should b e vigorously sup-

app ears likely that the bulk of the dark matter exists

p orted.

in the form of elementary particles remaining from the

+

 An e e linear collider with sucient energy and

earliest moments. These particles might b e neutrinos of

luminosity could provide imp ortant opp ortunities for

mass b etween 5 and 25 eV, or something more exotic,

6

discovery at this scale, while enhancing our abilityto

like particles called axions of mass ranging from 10 to

4

interpret evidence for new physics from the LHC.

10 eV or sup ersymmetric particles of mass b etween 10 12

GeV and 1 TeV. sp ecial astrophysical interest. The solar neutrino de cit

has b een a puzzle for manyyears and new p owerful detec-

The dark matter problem provides further imp etus

tors are b eginning to address the problem. It may b e that

for the search for evidence of neutrino mass and for new,

a resolution of the solar-neutrino problem is near and will

long-lived particles. Conversely, direct searches for par-

advance our understanding of b oth neutrino physics and

ticle dark matter in our own neighb orho o d, using highly

the details of the solar interior.

innovative detectors, have the p otential to discover new

Particle physics b egan with the observation of cosmic

elementary particles.

rays. Remarkably,we still understand little ab out the

In ation and particle dark matter have led to the

origin and propagation of very-high-energy cosmic rays.

most promising explanation for how the universe evolved

Investigations high in the atmosphere, at the surface of

from a very smo oth b eginning to the abundance of struc-

the earth, and in underground detectors are addressing

ture that exists to day { galaxies, clusters of galaxies, su-

these imp ortant questions. Larger detectors, b orrowing

p ercluster s, voids, and great walls. This theory,involv-

signi cantly from technology develop ed in high-energy

ing cold or mixed dark matter, holds that most of the

physics and involving high-energy physicists, are b eing

mass in the universe exists in the form of slowly moving

designed.

elementary particles and that the density p erturbations

Because astrophysical and cosmological phenomena

that seeded all the structure arose during in ation. Cold

o ccur over such a wide range of circumstances { from

dark matter is b eing put to the test in many di erent

the cosmic rays to the early universe { they can b e ex-

ways: measurements of the temp erature variations in the

ploited to study fundamental physics in regimes b eyond

cosmic background radiation, which prob e the primeval

the reach of terrestrial lab oratories. The knowledge de-

density p erturbations; redshift surveys, which map the

rived has b een very useful: hadronic cross sections at

inhomogeneity that exists to day; deep images of the uni-

very high energies; nucleosynthesis limits to the number

verse taken by the Hubble Space Telescop e and Keck

of light neutrino sp ecies and other light particle sp ecies;

Telescop e, which reveal the recentevolution of galaxies

cosmological limits to neutrino masses and other prop er-

and clusters; x-ray studies of clusters of galaxies, which

ties; constraints on the axion based up on neutron stars,

allow a determination of the ratio of baryons to exotic

white dwarfs, and red giant stars; and a host of limits to

matter; and the search for the cold dark matter particles

neutrino prop erties based up on SN 1987A.

themselves. In addition to its obvious cosmological sig-

The uni cation of the strong, weak and electromag-

ni cance, the cold dark matter theory provides a window

netic forces seems to require the inclusion of gravity and

to physics at energies up to the uni cation scale.

to demand its quantization. There is much imp ortant

A fundamental feature of the universe is the absence

theoretical activity, ranging from the study of quantum

of antimatter and the tiny ratio of matter to radiation

asp ects of tiny black holes and to understanding the im-

ab out one baryon p er three billion photons. One of

plications of sup erstring theory for particle physics, grav-

the great triumphs of particle cosmology is baryogene-

itation, and cosmology. On the exp erimental side, a new

sis, which holds that the small net baryon numb er of the

era will dawn so on when the laser interferometric gravity-

universe evolved through interactions that do not resp ect

wave detectors b eing built in the U.S. LIGO and in

baryon-numb er conservation or CP symmetry and o c-

Europ e VIRGO are commissioned. These devices have

curred out of thermal equilibrium. The details of baryo-

the p otential to detect astrophysical sources as well as

genesis are not yet understo o d, and it is p ossible that it

sources connected with the early universe.

involved electroweak physics. Through baryogenesis the

The closely related elds of astrophysics, cosmology,

cosmic asymmetry b etween matter and antimatter and

and uni cation of forces are ourishing. Thanks to the

CP violation are intimately linked: advances made in

wealth and diversity of exp erimental and theoretical ef-

understanding CP violation in the lab oratory will fur-

fort, the eld is p oised for ma jor advances in our under-

ther our understanding of the baryon asymmetry of the

standing of:

universe and vice versa.

 solar neutrinos and the sun,

Neutrino exp eriments with astrophysical and cosmo-

 how structure formed in the universe,

logical signi cance range from table-top searches for nu-

 the earliest moments of the universe, and

clear decays with the emission of two electrons and no

 the nature of the mysterious dark matter.

neutrinos to arrays of photomultipliers monitoring vast

domains of water or ice in order to detect very-high-

Despite the rosy scienti c outlo ok, a dicult structural

energy cosmic neutrino sources. Neutrinos from the su-

problem needs to b e addressed:

p ernovae of 1987 SN 1987a in the Large Magellanic

 Because this work is intrinsicall y interdisci pli nary,it

Cloud were detected in devices intended to observe pro-

is hard to weigh prop erly quite di erent research pro-

ton decay, illustrating howintertwined astrophysics and

p osals against each other or nd appropriate fund-

particle physics have b ecome.

ing, since no agency has well-de ned resp onsibility

for the eld. Measurements of the ux of solar neutrinos are of 13

Nevertheless , string theory remains sp eculative, sep- 8 Exploratory Theory

arated from the rest of particle theory and exp eriment.

The remarkable success of the Standard Mo del is imp or-

It is imp ortant to bridge this gap and nd evidence for

tant not just for the questions it answers, but for the

or against these sp eculations. Indeed, p erhaps the most

questions it lets us ask. Are the electroweak and strong

imp ortant attribute of exploratory theory is that it de-

forces, themselves, expressions of a single, uni ed force?

mands that even the wildest sp eculations should ulti-

Is there a yet more complete uni cation, one that in-

mately b e testable exp erimentally.

cludes gravity? What determines the numb er of quarks

and leptons, their masses and the CKM quark mixing

9 Accelerator Physics, Technology, and

matrix? Sp eculating ab out these issues and exploring

Facilities

sub jects seemingly remote from exp eriment are imp or-

tantintellectual frontiers for particle physics. Further-

In the past, progress in particle physics has dep ended

more, if the past is any guide, it is likely that these deep

strongly on developments in accelerator physics and tech-

questions will b e eventually answered by the discovery of

nology.Aswe reach for higher energies and the increased

imp ortant new organizing principles.

particle uxes necessary to extend the frontier, continued

Theoretical sp eculations, no matter how attractive,

advances in accelerator physics will b ecome ever more

must ultimately b e validated by exp eriment. Thus, al-

imp ortant. This study has concentrated particularly on

though the idea of unifying the electroweak and strong

three asp ects of accelerator physics: hadron colliders,

interactions is comp elling, the absence of proton decayat

electron linear colliders, and novel technologies. It has

the predicted levels has served to rule out the simplest

led to several conclusions concerning the need for accel-

grand uni ed theories. Moreover, the predicted coales-

erator R&D in the U.S.

cence of the couplings of the electroweak and strong in-

teractions at a single high energy also did not seem to b e

Hadron Col liders

ful lled in these theories. Nevertheless the idea of uni -

cation of all forces continues to b e a theoretical b eacon.

Design considerations for luminosity and energy up-

There are attractive alternatives to the simplest grand

grades of thepp  Collider at Fermilab are imp ortantto

uni ed mo dels involving the p ossibility that nature has

the near-term prosp ects for hadron colliders. Antiproton

a symmetry, sup ersymmetry, that connects b osons with

pro duction is the key to high luminosity in the Fermilab

fermions.

Tevatron. Reviews of various options revealed no insur-

If the sp eculation that sup ersymmetry exists in na-

mountable technical barriers to achieve higher luminos-

ture is correct, then every known particle has a yet-to-b e-

ity, but the necessary trade-o s, costs, and the p otential

discovered partner with a di erent spin. While no sup er-

impact on the Main Injector program need to b e evalu-

symmetric partners haveyet b een found, there is some

ated carefully.Thus we recommend that:

indirect circumstantial evidence that these particles ex-

 Continued studies and design work on schemes to

ist, but haveTeV-scale masses. When their e ects are

increase antiproton pro duction at Fermilab should

considered, the couplings of the electroweak and strong

b e vigorously pursued.

interactions do coalesce at high energy, as required by

Sup erconducting magnets are the enabling technol-

uni cation. Furthermore, sup ersymmetric grand uni ed

ogy for the highest energy machines. If the U.S. is to

theories also lead to longer proton lifetimes. Finally, su-

remain in the forefront of accelerator physics, reassem-

p ersymmetry also helps us understand why some particle

bly of a U.S. sup erconducting magnet R&D program is

masses are much smaller than the scale set by gravity.

critical. Thus we also recommend that:

If these sp eculations are correct, sup ersymmetry should

 Supp ort for R&D in the area of sup erconducting

reveal itself directly at the energy scales which will b e

magnet technology should b e strengthened.

prob ed by the LHC, if not at lower energy accelerators.

In this resp ect, signi cant participation in the LHC

Sup ersymmetry has additional motivation. It arises

pro ject could b e a valuable and imp ortant comp onent

from the ambitious e orts to encompass all interac-

of a U.S. program for hadron collider R&D. Such par-

tions, including gravity, in a single theory. String the-

ticipation would b e most valuable if it were targeted to-

ory provides the hop e of answering many of the hard,

ward those areas which represent the greatest challenges

deep questions that face particle physics. Over the past

in moving toward the future, such as sup erconducting

decade, string theory has develop ed into a thriving disci-

magnet and b eam tub e vacuum technology.

pline, with applications b oth inside and outside particle

New ideas for overall systems design of a collider physics. In particular, string theory has suggested plausi-

facility in the 30 TeV p er b eam energy range, which ble extensions of the Standard Mo del and has motivated

could b e constructed sometime following completion of phenomenologically interesting interrelations among low

the LHC, were also explored. Although the challenges energy parameters. 14

data rates and higher precision through innovations in are enormous, some of the ideas seem feasible and should

tracking, calorimetry, electronics, and computing. b e explored further.

Innovations in detector technology have had a ma jor

impact outside particle physics. A particularly imp or-

Electron Linear Col liders

tant example is medical imaging, which b ene ts from the

The SLC has demonstrated that linear colliders can b e

high-resolution, high-sp eed, high-eciency x-ray detec-

made to work and can provide a way to reach the TeV

tion pursued at high-energy physics lab oratories around

scale in electron-p ositr on accelerators. As a result, in-

the world.

terest in this technique has grown considerably over the

Accelerators now b eing designed will demand im-

last few years and there is considerable R&D underway.

provements in many asp ects of particle detectors. In-

Snapshots of the worldwide design and prototyp e re-

creased b eam intensities will require the use of radiation-

+

search for future e e linear colliders CLIC, JLC, NLC,

hard materials and electronics. The increased data rates

SBLC, TESLA, and VLEPP are describ ed in the study

will demand higher bandwidth data acquisition systems.

and their critical issues evaluated. Although the basic

Increased particle densities from very high-energy colli-

features of these linear colliders are fairly generic, the

sions will necessitate higher density,lower cost electron-

work has led to several p ossible approaches.

ics. The tagging of particles with picosecond lifetimes

For electron linear colliders the enabling technolo-

will require improved vertex detectors and fast vertex

gies are the high gradient acceleration system, radio fre-

triggers. And the use of high precision electromagnetic

quency p ower sources and accelerator structures. The

calorimetry will call for fast, bright, radiation-hard crys-

technology required to supp ort a next generation linear

tals.

collider has made signi cant advances in the recent past

There is no question that detector research and de-

and is exp ected to reach maturity during the next few

velopment is a vital part of the U.S. HEP program. Until

years. Therefore, we recommend that:

recently, U.S. particle physicists were able to carry out

 Facilities in various parts of the glob e that test dif-

detector R&D using funding provided by the SSC Lab-

ferent technical issues and di erent technological op-

oratory. Universityphysicists also b ene ted from fund-

tions for linear colliders should b e completed as ex-

ing provided by the Texas National Research Lab ora-

p editiously as p ossible, so that a conceptual design

tory Commission. This R&D program stimulated rapid

for a next generation linear collider based on proven

progress and brought together exp erimentalists from a

technologies can b e develop ed.

variety of sub discipli nes .

Unfortunately, the cancellation of the SSC brought

these programs to an end. Much promising work was

Novel Technologies

stopp ed or signi cantly slowed. At the same time, further

Cost played a pivotal role in the cancellation of the SSC,

shortfalls have b een created by cutbacks in traditional

and is a ma jor issue in the success of the LHC. The im-

sources of detector R&D funding, such as lab oratory dis-

p ortance of cost will increase further due to the tech-

cretionary funds and university seed money. Additional

nical diculties that will b e encountered in pro ducing

pressures result from the scale of most mo dern detector

higher energies or luminosities. Thus we are challenged

pro jects, which is so large that managers are reluctantto

b oth economically and technically to nd new acceler-

risk adopting new and unproven technologies. Although

ation techniques in order to reach new frontiers. This

new technologies often enjoy some supp ort in the early

implies that:

phases of these pro jects, there is inevitably pressure to

 Continued investment in generic accelerator research

fo cus limited resources on a single technology.

is required to continue to op en new exp erimental op-

These considerations lead us to recommend that in-

p ortunities at expanding energy and luminosity fron-

dep endent supp ort b e provided for detector development

tiers.

work. Such an R&D program must b e mo dest in lightof

tremendous pressures on the HEP budget. The admin-

Wake eld, laser near- eld, inverse-Cerenkov, plasma,

istrative asp ects of this program are b est determined in and free-electron laser accelerators are among the meth-

consultation with the funding agencies. However, a few o ds considered in the rep ort. Alternate particle colliders

+

general features are desirable:

include and   colliders.

 The primary aim of the program should b e to provide

an incubation p erio d for new ideas.

10 Detectors

 Funding decisions should b e based on review bya

p eer-review committee.

Progress in particle physics requires state-of-the-art de-

 Most pro jects should b e limited to three years of tectors to exploit the increasing energy and b eam inten-

funding, after which time their supp ort should come sities at accelerators. Collider detectors at hadron and

from the detector pro jects or other sources. electron machines have met the demands of increased 15

12 Structural Issues in High-Energy Physics  The general level of funding should total ab out $3M

per year. This would allow ab out six new starts

This working group addressed three areas of concern:

of pro jects with annual budgets in the $50,000 to

Governance and Advising, Career Issues, and Education

$250,000 range.

and Outreach.

Detector development is a vital comp onent of high-

energy physics. It is essential that the eld invest in new

Governance and Advising

technologies to prepare for the challenging environments

One of the imp ortant problems for the eld to address is

of future exp erimental facilities.

that of governance, advising, and planning. At present

HEPAP plays the role of advising the government, sp ecif-

11 Computing

ically the Department of Energy, ab out issues concern-

ing high-energy physics and, to some extent, helps in the

Historically, high-energy physicists have made extensive

planning for the eld. Historically this is the only b o dy

use of state-of-the-art techniques in computer and com-

that substantively considers the eld as a whole; so far

munication technology.For example, particle physics ex-

the DPF has played only a minimal role. Concerns have

p eriments pioneered the use of real-time computer tech-

b een raised throughout the community recently ab out

niques. As collab orations grew in size and scop e, parti-

the e ectiveness, limitations, and aws of this approach

cle physicists were among the rst to make e ective use

in an era of shrinking budgets and increased demand on

of computer networks. Indeed, the p opular World-Wide

available funds. In resp onse to these concerns, it is im-

Web application was develop ed by high-energy physicists

p ortant to consider additional mechanisms which might

at CERN.

improve planning the future of the eld.

This question was discussed at two op en meetings Particle physicists have long employed advanced

held during the study as well as at town meetings held in computer analysis and simulation techniques and have

made pro ductive use of the most p owerful computers

conjunction with the work of the Drell subpanel. From

available. However, as the use of computers b ecomes in-

those gatherings, and through delib erations among the

creasingly part of the mainstream, particle physicists will

working group and with the DPF Executive Committee,

the following recommendation was formulated: need to change the way in which they use and develop

software. They must make the transition from b eing ma-

 The DPF Executive Committee should commission

jor develop ers of computer technology to b eing just one

workshops and studies on issues of great imp ortance

set of users among many areas of application.

to the eld.

 These studies, which in general should b e of short

Although this change mayintro duce some short-term

duration, would b e carried out by ad-ho c panels ap-

problems, on balance the e ect should b e p ositivebe-

p ointed by the Executive Committee in consultation

cause much of the software developmentwork that for-

with the funding agencies and the national lab orato-

merly fell to particle physicists will now b e done byspe-

ries. cialists. Ultimately, this will allow more time to b e de-

 The rep orts resulting from these studies should then

voted to science. This has already long b een the case

b e disseminated promptly to the HEP community

for computer hardware, where the HEP community has

and the public.

consistently b een able to exploit commercial pro ducts.

The main challenge for the future is to learn how

Career Issues

to make go o d use of commercial software pro ducts in a

cost-e ectiveway. The following set of recommendations

The cancellation of the SSC put more than 100 physi-

could help the community meet this challenge:

cists into the job market. That, coupled with reductions

in funding and the concomitant loss of employment op-

 The U.S. HEP community should formulate a coher-

p ortunities emphasizes the imp ortance of studying career

ent approach to the use of computing technology.

issues.

 Computing at U.S. HEP institutions universities

Reliable demographic data are a prerequisite for a

and lab oratories should b e re-capitalized in a way

meaningful study. These data are now b eing gathered by

that is compatible with current and anticipated in-

the Particle Data Group under the auspices of b oth the

dustrial developments toward op en systems.

DOE and the NSF. Obtaining accurate data, however, is

 The U.S. should provide centers of CPU p ower and

only the rst step toward understanding career opp ortu-

storage for simulation, reconstruction, and analysis,

nities op en to high-energy physicists and devising ways

that are accessible to any HEP institution.

to help improve career paths in the discipline. One early

conclusion is that it is imp ortant for high-energy physi-  Mo dest funding should b e made available to carry

cists to b e aware of all the opp ortunities op en to them out R&D in aid of this new direction. 16

Bro okhaven National Lab oratory, will provide frontier b oth within and outside the discipline. Within the pro-

capabilities in other fundamental areas of research. fession, young physicists should b e educated to the needs

The picture of the future U.S. accelerator-based pro- of employers in government and industrial lab oratories,

gram b eyond these facilities is much less in fo cus. Sp eci c as well as in universities . Conversely, it is imp ortant that

groups are considering p ossibiliti es as diverse as ro om p otential employers b e aware of how high-energy physi-

+

temp erature or sup erconducting linear e e colliders, cists can contribute to their enterprises. To foster these

substantial upgrades in the luminosity or energy of the goals, we recommend that the DPF Executive Commit-

Fermilab Tevatron, and muon colliders. Although many tee:

asp ects of these options were studied by the working

 should organize a Sub committee on Careers to ar-

groups, this e ort did not include substantial compar-

range meetings, prepare literature, and devise mech-

isons nor was there any attempt to set priorities.

anisms to educate young colleagues ab out employ-

We b elieve that now is the appropriate time to b egin

ment opp ortunities and the means of enhancing their

to develop a coherent plan for the longer term future,

prosp ects for obtaining jobs; and

based on comparison of the physics p otentials of p ossible

 should consider the appropriateness of, and p ossi-

new facilities. It is also time to movetoward a consen-

ble improvements in, the education of graduate stu-

sus for the U.S. program b eyond the LHC and current

dents, with an eyetowards enlarging the employment

upgrades to U.S. facilities, in the context of the interna-

opp ortunities for those with training in high-energy

tional program.

physics.

To accomplish this, memb ers of the U.S. HEP com-

munity should meet with individuals from other nations

Outreach and Education

to compare the capabilities, feasibilities , and relative

strengths of these initiatives with those of the LHC and

The cancellation of the SSC made it particularly clear

other facilities that will likely op erate in the LHC era.

that wemust increase our e orts to educate the public

This typ e of evaluation has traditionally taken place in

and those in government ab out the so cietal b ene ts of

DPF-sp onsored Snowmass workshops. Thus we prop ose

the pursuit of research in high-energy physics. Already

a similar workshop to b e held in the summer of 1996 to

substantial e orts are underway, b oth by individuals and

b egin to address these crucial issues.

by the lab oratories. These form a base up on whichto

build.

As a result of the study, a sub-group was formed to

examine ongoing outreach and education e orts and seek

prop osals for new directions. Named POET, for Public

Outreach and Education Team, this group has b egun to

sensitize the high-energy-physics community to its exis-

tence, and to solicit ideas ab out p ossible future activities.

To encourage these e orts we recommend that:

 The DPF Executive Committee should supp ort the

activities of the POET group as a means of enhanc-

ing the outreach and education e orts of particle

physicists.

13 Conclusions

This study has highlighted the vitality and intellectual

breadth of the U.S. program in the context of the inter-

national high-energy physics e ort. We hop e that the

study has also help ed to delineate for a wider audience

the key elements of worldwide high-energy physics re-

searchinto the rst decade of the next century.

In accord with the Drell Subpanel rep ort, we b elieve

that the LHC program will de ne the high-energy physics

frontier and that participation by U.S. physicists in this

e ort is essential. In addition, we exp ect that the Fer-

milab Main Injector, the SLAC B Factory, and Phase

I I I of CESR, as well as the RHIC accelerator at the 17