NON-SUPERSYMMETRIC EXTENSIONS of the STANDARD MODEL KENNETH LANE 1 Introduction the Title of My Talk Was Chosen by the Organizer

View metadata, citation and similar papers at core.ac.uk brought to you by CORE

provided by CERN Document Server

NON-SUPERSYMMETRIC EXTENSIONS OF THE STANDARD MODEL

KENNETH LANE

Department of Physics, Boston University, 590 Commonwealth Ave, Boston, MA 02215, USA

The motivations for studying dynamical scenarios of electroweak and avor symmetry breaking are reviewed and

the latest ideas, esp ecially top color-assisted technicolor, are summarized. Several technicolor signatures at the

Tevatron and Large Hadron Collider are describ ed and it is emphasized that all of them are well within the reach

of these colliders.

1 Intro duction troweak interactions have b een in place for almost

25 years. In all this time, the standard mo del has

The title of my talk was chosen by the organizers

withsto o d extremely stringent exp erimental tests,

and, while it was not their intention, they have

the latest round b eing describ ed at this conference

5 6 7

de ned my sub ject by what it is not. That leaves

by Bro ck, Tipton, and Blondel. Down to dis-

it for me to de ne what it is. So, in this talk

tances of at least 10 cm, the basic constituents

\non-sup ersymmetric extensions of the standard

of matter are known to b e spin- quarks and lep-

mo del" means Dynamical Electroweak and Flavor

tons. These interact via the exchange of spin-one

Symmetry Breaking. To be sp eci c, I will dis-

gauge b osons: the massless gluons of QCD and the

cuss asp ects of technicolor and extended techni-

massless photon and massive W and Z b osons

2 ; 3

color .

of electroweak interactions. There are six avors

I b egin in Sec. 2 by reiterating why it is still

each of quarks and leptons|identical except for

imp ortant to study scenarios in which electroweak

mass, charge and color|group ed into three gen-

and avor symmetry are broken by strong dynam-

erations.

ics at mo derate, accessible energy scales. This

The fact that the QCD gauge symmetry is ex-

is followed in Sec. 3 by a review of technicolor

act in b oth the Lagrangian and the ground state of

and extended technicolor, fo cusing on the more

the theory implies that quarks and gluons are con-

mo dern asp ects|walking technicolor, multiscale

ned at large distances into color-singlet hadrons

technicolor, and top color-assisted technicolor. In

and that they are almost noninteracting at small

Sec. 4, I will discuss several imp ortant signatures

distances. However, con nement and asymptotic

of these strong dynamics that can b e soughtover

freedom are not the only dynamical outcomes for

the next 10-15 years at the upgraded Tevatron

gauge theories. Even though gauge b osons nec-

Collider and the Large Hadron Collider. For the

essarily app ear in the Lagrangian without mass,

most part, these signatures involve the pro duc-

interactions can make them heavy. This happ ens

tion of technihadrons and ! and their de-

T T

to the W and Z b osons: electroweak gauge sym-

cay into pairs of technipions, , W and

T T L T

metry is spontaneously broken in the ground state

Z , and p ossibly dijets. I restrict myself to

L T

of the theory, a phenomenon known as the \Higgs

these hadron colliders not only b ecause they are

mechanism". Finally, fermions in the standard

the only new high-energy machines anywhere near

mo del also must start out massless. To make

the real axis, but also b ecause they have the

quarks and leptons massive, new forces beyond

greatest reach of all machines under consideration

the SU (3) SU (2) U (1) gauge interactions are

for the unknown physics of the TeV energy scale.

required. These additional interactions explicitly

break the fermions' avor symmetry and commu-

2 Why Study Strong Electroweak and Fla-

nicate electroweak symmetry breaking to them.

vor Dynamics?

Despite this great b o dy of knowledge, the in-

teractions underlying electroweak and avor sym-

The theoretical elements of the standard SU (3)

metry breakdowns remain unknown . The most

SU (2) U (1) gauge mo del of strong and elec-

imp ortant element still missing from this descrip-

Some might view mysaying this as the kiss of death. tion of particle interactions is directly connected to 1

electroweak symmetry breaking. This may mani- to search for technicolor and extended technicolor

fest itself as one or more elementary scalar \Higgs as well as the standard mo del Higgs b oson, its sim-

b osons". This happ ens in sup ersymmetry, the ple extensions, sup ersymmetry, and so on. Hadron

scenario for the physics of electroweak symme- colliders have powerful reach by virtue of their

try breaking that is by far the most p opular. high energy and luminosity, but extracting clear

Notwithstanding its p opularity, there is no ex- signals from them can b e quite demanding. Thus,

10 ; b

p erimental evidence for sup ersymmetry. We detectors should be designed to be sensitive to,

do not know the origin of electroweak symmetry and exp erimenters should be prepared to search

breaking. for, the signatures of dynamical electroweak and

avor symmetry breaking. So far, there is little

If the dynamics of the Higgs mechanism are

indication of this in the large LHC detector col-

unknown in detail, those of avor are completely

lab orations.

obscure. We don't even have a prop er name, much

less a b elievable and venerable \mechanism", for

avor symmetry breaking. Mo dels with elemen-

3 Summary of Technicolor and Extended

tary Higgs b osons, whether sup ersymmetric or

Technicolor

not, o er no explanation at all for the quark-lepton

content of the generations, the numb er of genera-

Technicolor|the strong interaction of fermions

tions, why they are identical, and why avor sym-

and gauge b osons at the scale 1TeV |

metry is broken|the bizarre pattern of quark and

describ es the breakdown of electroweak symme-

lepton masses.

try to electromagnetism without elementary scalar

Dynamical electroweak and avor symmetry

b osons. Technicolor has a great precedent in

breaking|technicolor and extended technicolor|

QCD. The chiral symmetry of massless quarks is

are plausible, attractive, natural, and nontrivial

sp ontaneously broken by strong QCD interactions,

scenarios for this physics that involve new inter-

resulting in the app earance of massless Goldstone

actions at sp eci ed, exp erimentally accessible en-

b osons, , K , . In fact, if there were no Higgs

ergy scales. Technicolor is a strong gauge inter-

b osons, this chiral symmetry breaking would itself

action mo deled after QCD. Its characteristic en-

cause the breakdown of electroweak SU (2) U (1)

ergy is 1TeV , so it may be sought in exp eri-

to electromagnetism. Furthermore, the W and Z

ments of the coming decade. Extended technicolor

2 2 2

masses would be given by M = cos M =

W Z

(ETC) emb eds technicolor, color and avor into a

2 2

g N f , where g is the weak SU (2) coupling,

larger gauge symmetry; this emb edding is neces-

N the numb er of massless quark avors, and f ,

sary to pro duce the nonzero \current-algebraic"

the pion decay constant, is only 93 MeV.

or \hard" masses of quarks and leptons. At the

In its simplest form, technicolor is a scaled

same time, ETC o ers a simple group-theoretic

up version of QCD, with massless technifermions

explanation of avor in terms of the representa-

whose chiral symmetry is sp ontaneously broken at

tion content of fermions. As we explain shortly,

. If left and right-handed technifermions are

the scale at which ETC symmetry is broken down

assigned to weak SU (2) doublets and singlets, re-

to color technicolor is O (100 TeV). Neverthe-

sp ectively, then M = cos M = gF , where

W W Z

less, the e ects of this interaction are observable

F = 246 GeV is the weak technipion decay con-

at the TeV energy scale in terms of the masses and

stant.

decay mo des of the technihadrons, and , that

T T

The principal signals in hadron collider ex-

p opulate technicolor mo dels.

p eriments of \classical" technicolor were discussed

Because we are so completely ignorant of

12 ; 13

long ago. In the minimal technicolor mo del,

electroweak and avor dynamics, exp eriments at

with just one technifermion doublet, the only

TeV energies, which for now means those planned

for the Tevatron and the LHC, must have the

The hard masses of quarks explicitly break chiral sym-

metry and give mass to , K , , which are then referred to

greatest p ossible discovery p otential. They ought

as pseudo-Goldstone b osons.

The technipions in minimal technicolor are the linear

Those who would cite the apparent uni cation of the

combinations of massless Goldstone b osons that b ecome,

SU (3) SU (2) U (1) couplings near 10 GeV as evidence

via the Higgs mechanism, the longitudinal comp onents W

now have to incorp orate the scenario of sup ersymmetry

and Z of the weak gauge b osons. breaking mediated by new gauge interactions.

L 2

prominent collider signals are the mo dest enhance- M :

ET C

ments in longitudinally-p olarized weak b oson pro-

duction. These are the s-channel color-singlet

ET C

m (M ) ' m (M ) ' hTTi ;

q ET C ` ET C ET C

technirho resonances near 1.5{2 TeV: !

ET C

T 1

0 2

(1)

W W and ! W Z . The O ( ) cross sec-

L L T 1 L

where hTT i and m (M ) are the techni-

tions of these pro cesses are quite small at such

ET C q;` ET C

fermion condensate and quark and lepton masses

masses. This and the diculty of reconstructing

renormalized at the scale M .

weak-b oson pairs with reasonable eciency make

ET C

If technicolor is like QCD, with a running cou-

observing these enhancementsachallenge.

pling rapidly b ecoming small ab ove

TC TC

Nonminimal technicolor mo dels are much

1TeV , then hTTi ' hTTi ' . To

ET C TC

more accessible b ecause they have a rich sp ec-

obtain quark masses of a few GeV thus requires

trum of lower mass technirho vector mesons and

M =g 30 TeV. This is excluded. Ex-

ET C ET C

technipion states into which they may decay.

tended technicolor b oson exchanges also generate

The often-discussed one-family mo del, contains

four-quark interactions which, generically, include

one iso doublet each of color-triplet techniquarks

jS j = 2 and jB j = 2 op erators. For these not to

(U; D ) and color-singlet technileptons (N; E ). Be-

0 0 0 0

b e in con ict with K -K and B -B mixing pa-

d d

cause the color coupling is weak ab ove 100 GeV,

rameters, M =g must exceed several hun-

ET C ET C

the technifermion chiral symmetry is approxi-

dred TeV. This implies quark and lepton masses

mately SU (8) SU (8). This symmetry and its

no larger than a few MeV, and technipion masses

breakdown to the diagonal SU (8) gives rise to

no more than a few GeV.

63 and which may be classi ed accord-

T T

Because of this con ict b etween constraints on

ing to how they transform under ordinary color

avor-changing neutral currents and the magni-

SU (3) times weak isospin SU (2). The techni-

00 0

tude of ETC-generated quark, lepton and techni-

pions are color singlets 2 (1; 1); W ;Z and

T L

pion masses, classical technicolor was sup erseded

; 2 (1; 3); color o ctets 2 (8; 1) and

a decade ago by \walking" technicolor. Here,

; 2 (8; 3); and color-triplet lepto quarks

T 8

the strong technicolor coupling runs very

; 2 (3; 3) (3; 1) (3; 3) (3; 1). The

QL LQ

slowly|walks|for a large range of momenta, p os-

b elong to the same representations.

sibly all the way up to the ETC scale of sev-

In the standard mo del and its extensions, the

eral hundred TeV. The slowly-running coupling

masses of quarks and leptons are pro duced by their

enhances hTT i =hTT i by almost a factor of

ET C TC

Yukawa couplings to the Higgs b osons|couplings

M = . This, in turn, allows quark and lep-

ET C TC

of arbitrary magnitude and phase that are put in

ton masses as large as a few GeV and M

by hand. This option is not available in techni-

100 GeV to be generated from ETC interactions

color b ecause there are no elementary scalars. In-

at M = O(100 TeV).

ET C

stead, quark and lepton chiral symmetries must

Walking technicolor requires a large number

be broken explicitly by gauge interactions alone.

of technifermions in order that runs slowly.

The most economical way to do this is to em-

These fermions may b elong to many copies of

ploy extended technicolor, a gauge group con-

the fundamental representation of the technicolor

taining avor, color and technicolor as subgroups.

gauge group, to a few higher dimensional repre-

Quarks, leptons and technifermions are combined

sentations, or to b oth. That last p ossibility in-

into the same few large representations of ETC.

spired \multiscale technicolor" mo dels containing

Then quark and lepton hard masses are generated

b oth fundamental and higher representations, and

by their coupling (with strength g ) to techni-

ET C

having a very di erent phenomenology. In mul-

fermions via ETC gauge b osons of generic mass

tiscale mo dels, there typically are two widely sep-

arated scales of electroweak symmetry breaking,

with the upp er scale set by the weak decay con-

The technipions of non-minimal technicolor include

the longitudinal weak b osons as well as additional Gold-

stant, F = 246 GeV. Technihadrons asso ciated

stone b osons asso ciated with sp ontaneous technifermion

with the lower scale may be so light that they

chiral symmetry breaking. The latter must and do acquire

are within reach of the Tevatron collider; they are

mass|from the extended technicolor interactions discussed

b elow. readily pro duced and detected at the LHC. 3

An imp ortant consequence of walking techni- masses, contribute a few GeV to m , and give

color is that the large ratio hTTi =hTT i mass to the technipions. The scale of ETC in-

ET C TC

signi cantly enhances technipion masses. Thus, teractions still must be hundreds of TeV to sup-

! decaychannels may b e closed. If this press avor-changing neutral currents and, so, the

T T T

happ ens, then ! W W or W . The pro- technicolor coupling still must walk. Early steps

T 1 L L L T

duction rates for these color singlets are 5{10 pb in the development of the TC2 scenario have b een

at the Tevatron and 25{100 pb at the LHC. If col- taken in two recent pap ers. Although the phe-

ored technifermions exist, the electrically neutral nomenology of TC2 is in its infancy, it is exp ected

color-o ctet technirho, ,mayhave its de- to share general features with multiscale techni-

T 8 T T

caychannels closed as well. In this case, it app ears color: many technihadron states, some carrying

as a relatively narrow resonance in ! dijets. ordinary color, some within range of the Tevatron,

T 8

If the , ! channels are op en, they and almost all easily pro duced and detected at the

T 1 T 8 T T

are resonantly pro duced at large rates, of order LHC at mo derate luminosities.

5 pb at the Tevatron and several nanobarns at the

I assume throughout this talk that the techni-

LHC. As we describ e in more detail b elow, techni-

color gauge group is SU (N ) and that its gauge

pions tend to decay to heavy fermions. Given

coupling walks. A minimal, one-doublet mo del

these large rates and the recent successes and com-

can havea walking only if the technifermions

ing advances in heavy avor detection, many of

b elong to a large non-fundamental representa-

these technipions should b e reconstructable in the

tion. For nonminimal mo dels, I generally con-

hadron collider environment.

sider the phenomenology of only the lighter techni-

fermions. These transform according to the funda-

Another ma jor development in technicolor

mental (N ) representation. Some of them may

was motivated by the recent discovery of the top

also be ordinary color triplets. Finally, in TC2,

quark. Theorists have concluded that ETC mo d-

there is no need for large technifermion isospin

els cannot explain the top quark's large mass

splitting asso ciated with the top-b ottom mass dif-

without running afoul of either exp erimental con-

ference. This simpli es our discussion greatly.

straints from the parameter and the Z ! bb de-

The decays of technipions are induced mainly

7 ; 17

cay rate (the ETC mass must b e ab out 1 TeV;

by ETC interactions which couple them to quarks

see Eq. (1)) or of cherished notions of naturalness

and leptons. These couplings are Higgs-like, and

(M may be higher, but the coupling g

ET C ET C

so technipions are exp ected to decay into heavy

must b e ne-tuned near to a critical value). This

fermion pairs. For the color-singlets, e.g.,

state of a airs has led to the prop osal of \top color-

assisted technicolor" (TC2).

bb if M < 2m

0 T

tt if M > 2m

In TC2, as in top-condensate mo dels of elec-

cb; cs; if M

t b

19 T

troweak symmetry breaking, almost all of the !

tb if M >m +m

t b

top quark mass arises from a new strong \top-

(2)

color" interaction. To maintain electroweak

An imp ortant exception to this rule o ccurs in TC2

symmetry b etween (left-handed) top and b ottom

mo dels. There, only a few GeV of the top mass

quarks and yet not generate m ' m , the top-

b t

arises from ETC interactions. The bb mo de of a

color gauge group under which(t; b) transform is

heavy then comp etes with tt; cb or cs comp ete

usually taken to b e SU (3) U (1). The U (1) pro-

+ +

with tb for . Note that, since the decay t ! b

T T

vides the di erence that causes only top quarks

is strongly suppressed in TC2 mo dels, the can

to condense. Then, in order that top color interac-

be much lighter than the top quark.

tions b e natural|i.e., that their energy scale not

In almost all resp ects, walking technicolor

b e far ab ove m |without intro ducing large weak

mo dels are very di erent from QCD with a few

isospin violation, it is necessary that electroweak

fundamental SU (3) representations. One exam-

symmetry breaking remain due mostly to techni-

ple of this is that integrals of weak-current sp ec-

color interactions.

Massless Goldstone \top-pions" arise from top-quark

In TC2 mo dels, ETC interactions are still

condensation. This ETC contribution to m is needed to

needed to generate the light and b ottom quark give them a mass in the range of 150{250 GeV. 4

15 ; 21

tral functions and their moments converge much pion decay constant F , is small . Conse-

more slowly than they do in QCD. Consequently, quently, it is plausible that technihadrons and

simple dominance of sp ectral integrals by a few have masses at the lower end of these ranges.

resonances cannot b e correct. This and other cal- I should not have to p oint out that suchlow-scale

culational to ols based on naive scaling from QCD technihadrons are accessible at the Tevatron.

and on large-N arguments are susp ect. Thus, Color-singlet technipions, including the lon-

it is not yet p ossible to predict with con dence gitudinal W and Z , are pair-pro duced via the

L L

the in uence of technicolor degrees of freedom Drell-Yan pro cess in hadron collisions. The O ( )

on precisely-measured electroweak quantities|the signal rates at the Tevatron and LHC are probably

S; T ; U parameters to name the most discussed ex- unobservably small compared to backgrounds un-

22 ;g

ample. less there are fairly strong color-singlet technirho

resonances, not far ab ove threshold. To pa-

T 1

rameterize the cross sections, we consider a sim-

4 Technicolor Signatures at Hadron Col-

ple mo del containing two isotriplets of technipions

liders

which are mixtures of W , Z and an isotriplet of

15 ; 24

mass-eigenstate technipions . The lighter

4.1 Color-Singlet Technipion Production

isotriplet is assumed to decay dominantly into

T 1

The ! W W and W Z signatures of

T 1

L L L

pairs of the mixed state j i = sin jW i +

T L

the minimal technicolor mo del were discussed long

cos j i, leading to the pro cesses

12 ; 13

ago. If there is to b e just one technifermion

doublet, it must b elong to a higher dimensional

W Z

0 0 0

representation of SU (N ) so that walks.

TC TC

q q ! W ! ! W ; Z

T L

T 1 L T

The main phenomenological consequence of this

is that it is questionable to use the !

T 1 T T

coupling obtained by naive scaling from QCD,

W W

L L

0 0

q q ! ; Z ! ! W

T 1

L T

=2:91 : (3)

T T

(4)

The mixing angle is sp eci ed by sin =

This coupling may be smaller than Eq. (3) indi-

F =F , where F is the decay constant and

T T T

cates, leading to a narrower . There is also the

T 1

F = 246 GeV. Although this mixing usually

p ossibility that, b ecause of its large mass (naively,

is quite small, walking technicolor enhancements

1.5{2 TeV), the has a sizable branching ratio

T 1

of technipion masses suppress or even close the

to four-weak-b oson nal states. Tomy knowledge,

! channels. Thus, the should be

T 1 T T T 1

neither of these p ossibilities has b een investigated.

quite narrow and any of the decay mo des in Eq. 4

From now on, I consider only nonminimal

may b e imp ortant. This is seen in Fig. 1 where the

mo dels which, I b elieve, are much more likely to

pro duction rates of individual channels are calcu-

lead to a satisfactory walking mo del. They havea

lated for the Tevatron as a function of M for

T 1

rich phenomenology with many diverse, relatively

. Such low mass M = 110 GeV and sin =

accessible signals. The masses of technipions in

technipions are exp ected to decayto bbor cb. Fur-

these mo dels arise from broken ETC and ordi-

thermore, some scheme such as TC2 which results

nary color interactions. In walking mo dels that

ET C

in a small coupling m =F of technipions to

have b een studied, they lie in the range 100{

the top quark is required to suppress the unseen

600 GeV; technirho vector meson masses are ex-

mo de t ! b. Heavy- avor tagging and kine-

p ected to lie between 200 and 1000 GeV. Mul-

matical selection techniques are useful to extract

tiscale and top color-assisted mo dels of technicolor

the signals. Figure 1 illustrates several imp ortant

tend to havesomany technifermions that the char-

24 ; 26

general p oints:

acteristic scale of these mo dels, set by the techni-

These comments resp ond to a question from Graham

Ross regarding the e ects of technicolor on precision elec-

troweak tests. I thank him for the opp ortunity to reiterate

them. 5

p oint dep ends to some extent on the sup-

pression factor tan , but it should not be

much di erent from this. A search for the

channel will b e rewarding, even if it is

negative.

Since the isospin of technifermions is approx-

imately conserved, the is exp ected to be

T 1

nearly degenerate with its isoscalar partner ! .

The walking technicolor enhancement of techni-

pion masses almost certainly closes o the isospin-

conserving decay ! ! . Even the

T T

triply-suppressed mo de W W Z has little or no

L L

phase space for M 300 GeV. Thus, the main

0 0

decays are exp ected to b e ! ! , Z , and

T T

. In terms of mass eigenstates, these mo des

T T

0 0 00 00

Figure 1: Total WW, W and cross sections in

T T T

are ! ! , Z , Z , ZZ ; , Z ; and

T L L

T T T T

pp collisions at 1:8TeV , as a function of M for M =

+ +

T 1

W W , W , . It is not p ossible to

L L T L T T

is 110 GeV . The mo del describ ed in the text with sin =

estimate the relative magnitudes of the decay am-

0 +

used. The curves are W Z (upp er dotted) and W W

plitudes without an explicit mo del of the ! 's con-

(lower dotted); W (upp er solid), W (lower solid),

0 0

stituent technifermions. Judging from the decays

and Z (long dashed); (upp er short dashed) and

T T T

+ 0 00

(lower short dashed).

of the ordinary ! , we exp ect ! ! Z ( ),

T T

0 00

( ) to dominate, with the latter mo de fa-

T T

vored by phase space.

Except near W threshold, the increase in

The ! is pro duced in hadron collisions just

WZ and WW pro duction is undetectably

as the is, via its vector-meson-dominance cou-

T 1

small.

pling to and Z . For M ' M , the !

! T

T T 1

pro duction cross section should b e approximately

The most imp ortant pro cesses are those with 2 0

jQ + Q j times the rate, where Q are

U D U;D

T 1

p ositive Q = [M { (sum of nal state

T 1

the electric charges of the ! 's constituent techni-

masses)] and the fewest number of longitu-

fermions. The principal signatures for ! pro duc-

dinal weak b osons. At the Tevatron, the in- +

tion, then, are ` ` (or )+bband + bb, with

clusive W rate is 5{10 pb and the Z

T T

M = M . A search for the Z mo de will use

bb T

< <

M rate is 1{3 pb for M + M

T 1 T

the same strategies as for ! Z and W .

T 1 L T L T

2M . These rates are 5{10 times larger at

The search for ! ! in hadron collider ex-

T T

the LHC. Because the is very narrow,

T 1

p eriments is under study.

the ! dijet system should have large

125 azimuthal op ening angle (jj)

4.2 Color-Octet Technirho Production and De-

and limited transverse momentum p (jj)

2 2 2 4

cay to Jets and Technipions

+ (M 2(M + M ) M (M

T T 1 T 1

2 2

Mo dels with an electroweak doublet of color-

M ) ) =2M ' 50 GeV.

T 1

triplet techniquarks (U; D )have an o ctet of I =0

technirhos, , with the same quantum numb ers

Signal events for W=Z + should exhibit a

T 8

as the gluon. The is pro duced strongly in qq

narrow p eak, consistent with resolution, cor-

T 8

and gg collisions. Assuming the one-family mo del

resp onding to the resonance. This, how-

T 1

for simplicity, the 63 technipions listed in Sec. 3

ever, may not be a good way to discriminate

signal from background b ecause kinematic

The mo des ! ! Z , ZZ were considered

T L L

cuts can \sculpt" such a p eak.

by Chivukula and Golden for a one-doublet technicolor

mo del. Our estimates of the branching ratios for the

0 0

Once M 2M + 10 GeV, the dominant

isospin-violating decays ! , Z suggest that

T 1 T

T 1

T T

they are negligible unless the mixing angle is very small. pro cess is pro duction. The crossover

T 6

Figure 2: Dijet cross sections at the Tevatron (pp collisions Figure 3: Dijet cross sections at the LHC (pp collisions at

at 1.8 TeV) including the e ect of o ctet techirho vector 14 TeV) including the e ect of o ctet techirho vector mesons

mesons at 250 and 500 GeV. The solid curve assumes p er- at 250 and 500 GeV. Resolutions and cuts are as in Fig. 2

fect jet energy resolution while the dashed curve assumes except that j j < 1:0.

(GeV ). Jet angles and ra- resolution (E )=E = 100%E

pidities were limited by cos < and j j < 2:0.

color-triplet lepto quarks decayas

c if M

also o ccur. There are two p ossibilities for de-

T 8

t if M >m

cays.

c if M

! (5)

t if M >m

In the rst, walking technicolor enhancements

! b

of the technipion masses close o the chan-

T T

! b :

nels. Then the o ctet technirho's coupling to the

gluon mediates ! qq; gg ! jets. The O ( )

T 8

The caveat regarding technipion decays to top

dijet cross sections including the enhance-

T 8

quarks in TC2 mo dels still applies. Technipion

ment are illustrated for the Tevatron and the LHC

pair pro duction rates, per channel, are exp ected

15 ; 28

in Figs. 2 and 3. For M = 250 GeV,

T 8

to lie in the range 1{10 pb at the Tevatron and 1{

the signal-to-background rates is estimated to b e

10 nb at the LHC. Detailed rate estimates dep end

0.70 nb/5.0 nb at the Tevatron and 15 nb/150 nb

on and masses and other mo del param-

T 8 T

at the LHC. For M = 500 GeV, the S=B rates

T 8

eters. The LHC rate estimates are so high that

in these gures are 10 pb/40 pb and 2.0 nb/6.0 nb,

color o ctet and triplet technipions cannot fail to

resp ectively. Searches for the dijet signal of

T 8

b e discovered there|if they exist and if they have

have b een carried out by the CDF Collab ora-

not already b een detected in Run I I of the Teva-

29 ; 30

tion. Using 103 pb of data from Teva-

tron.

tron Collider Run I, CDF has excluded the range

250 GeV

At this conference, K. Maeshima of CDF re-

rameters used in the second pap er of Ref. 15.

p orted on a search for color-triplet lepto quarks de-

caying into + jet. The limit obtained, M

The second p ossibility is that technipion decay 100 GeV assumes only pure-QCD pro duction of

channels are op en, in which case ! the lepto quark pair. A somewhat more stringent

T 8 T 8 T 8

and dominates the dijet mo des. The color (and more mo del-dep endent) limit would result if

QL LQ

o ctet technipions are exp ected to decayinto heavy it is assumed that the lepto quarks are resonantly

quark pairs, as do the color-singlets in Eq. 2. The pro duced. 7

4.3 Signatures of Topcolor-AssistedTechnicolor seems to rest on the isotriplet of top-rho vector

mesons, . It is hard to estimate M ; it may

t t

Top color and top color-assisted technicolor (TC2)

lie near 2m or closer to = O (1 TeV ). The

t t t

were reviewed at this conference by D. Kominis.

are pro duced in hadron collisions just as the corre-

The development of TC2 is still at an early stage

sp onding color-singlet technirhos discussed ab ove.

and, so, its phenomenology is not fully formed.

The conventional exp ectation is that they decay

Nevertheless, in addition to the color-singlet and

as ! , . The rates are not likely

t t t t t

nonsinglet technihadrons already discussed, there

to b e large, but the distinctive decays of top-pions

are three TC2 signatures that are likely to be

help suppress standard mo del backgrounds.

18 ; 21 ; 33 ; 28

presentinany surviving mo del:

It is also plausible that, b ecause top color is

broken near , the are not completely analo-

t t

The isotriplet of color-singlet \top-pions"

gous to the -mesons of QCD and technicolor. For

arising from sp ontaneous breakdown of the

distance scales b etween and 1 GeV , top and

top quark's SU (2) U (1) chiral symmetry.

b ottom quarks do not exp erience a growing con n-

ing force. Instead of ! , the may fall

t t t

The color-o ctet of vector b osons V , called

apart into their constituents tb, bt and tt. The

\colorons", asso ciated with breakdown of

resonance may b e visible as a signi cant increase

the top quark's strong SU (3) interaction to

in tb pro duction, but won't b e seen in tt.

ordinary color.

The V colorons of broken SU (3) top color are

The Z vector b oson asso ciated with break-

readily pro duced in hadron collisions. They are

down of the top quark's strong U (1) inter-

exp ected to have a mass of 0.5{1 TeV. Colorons

action to ordinary weak hyp ercharge.

couple with strength g cot to quarks of the

two light generations and with strength g tan

to top and b ottom quarks, where tan 1.

The three top-pions are nearly degenerate.

Their decay rate is

They couple to the top quark with strength m =F ,

t t

where m is the part of the top-quark mass induced

M 4 cot =

S V V

8 8

by top color|exp ected to b e within a few GeV of

(7)

its total mass|and F ' 70 GeV is the decay

t t

2 2 2

) ; + tan 1+ (1 m =M

constant. If the top-pion is lighter than the top

quark, then

2 2

where = 1 4m =M . Colorons may then

2 2 2

) (m M

(t ! b) ' : (6)

app ear as resonances in bb and tt pro duction.

16m F

R. Harris has studied the limits on masses and

couplings of colorons decaying to bb and tt that

The standard top-decay mo de branching ratio

+0:13 +0:13

may be set at the Tevatron in Run II ( Ldt =

B (t ! W b)=0:87 (stat.) (syst.) was

0:30 0:11

rep orted a year ago. At the 1 level, then,

2fb ) and at the high-luminosityTeV33 upgrade

M 150 GeV. At the 2 level, the lower b ound

( Ldt =30fb ). He found that nearly the en-

is 100 GeV, but such a small branching ratio for

tire interesting range, M 1:3TeV , can be

t ! W b would require (pp ! tt) at the Teva-

prob ed.

tron ab out 4 times the standard QCD value of

Colorons have little e ect on the standard di-

+0:63 +

4:75 pb . The t ! b decay mo de can

jet pro duction rate. The situation maybevery dif-

0:68

be sought in high-luminosity runs at the Teva-

ferent for the Z b oson of the broken strong U (1)

tron and with mo derate luminosity at the LHC.

interaction. In some TC2 mo dels it is natural

If M

that Z couples strongly to the fermions of the rst

t t

It is also p ossible, though unlikely, that ! ts

two generations as well as those of the third. The

through b{s mixing.

Z in these mo dels is heavier than the colorons,

36 0

roughly M = 1{3 TeV. Thus, at subpro cess If M >m, then ! tb and ! tt or

Z t

t t

energies well b elow M , the interaction of Z with cc , dep ending on whether the neutral top-pion is

all quarks is describ ed by a contact interaction, heavier or lighter than 2m . The main hop e for

just like what is exp ected for quarks with sub- discovering top-pions heavier than the top quark 8

Acknowledgments structure at a scale of a few TeV. This leads to an

37 ; 12

excess of jets at high E and invariant mass.

I thank Barry Barish and Paul Frampton for

An excess in the jet-E sp ectrum consistent with

thoughtful comments on my talk. I also thank

' 1600 GeV has b een rep orted by the CDF Col-

38 ; 5

Elizab eth Simmons for her careful reading and

lab oration. It remains to be seen whether it

comments on the manuscript. I thank the orga-

is due to top color or any other new physics. As

nizers, esp ecially Andrzej Wroblewski, for a won-

with quark substructure, the angular and rapidity

derful conference, the opp ortunity to visit Poland,

distributions of the high-E jets induced by Z

and much patience and help. I owe Chris Quigg

should be more central than predicted by QCD.

much for the opp ortunity to share my views on

The Z may also pro duce an excess of high invari-

the search for TeV scale physics. My researchwas

ant mass ` ` . It will b e interesting to compare

supp orted in part by the Department of Energy

limits on contact interactions in the Drell-Yan pro-

under Grant No. DE{FG02{91ER40676.

cess with those obtained from jet pro duction.

If the Z is strongly coupled to light fermions it

will b e pro duced directly inqq annhilation in LHC

References

exp eriments. Because it may b e strongly coupled

to so many fermions, including technifermions in

1. S. Weinb erg, Phys. Rev. D 19, 1277 (1979);

the LHC's energy range, it is likely to be very

L. Susskind, Phys. Rev. D 20, 2619 (1979).

broad. This p ossibility should be taken into ac-

2. S. Dimop oulos and L. Susskind,

count in forming strategies to lo ok for the top-

Nucl. Phys. B 155, 237 (1979).

color Z at the LHC. I reiterate, however, that it

3. E. Eichten and K. Lane, Phys. Lett. B 90,

is to o early to predict the Z couplings, width and

125 (1980).

branching fractions with con dence. I hop e for

4. S. L. Glashow, Nucl. Phys. B 22, 579 (1961);

progress on these questions in the coming year.

S. Weinb erg, Phys. Rev. Lett. 19, 1264

(1967); A. Salam, in Pro ceedings of the

8th Nob el Symp osium on Elementary Par-

5 Conclusions

ticle Theory, Relativistic Groups and Ana-

lyticity, edited by N. Svartholm (Almquist

In this talk, I have tried to emphasize the im-

and Wiksells, Sto ckholm, 1968, p. 367;

p ortance of searching for signatures of dynami-

S. L. Glashow, J. Iliop oulos and L. Maiani,

cal as well as weakly-coupled scenarios for elec-

Phys. Rev. D 2, 1285 (1970); H. Fritzsch,

troweak and avor physics. We cannot be re-

M. Gell{Mann, H. Leutwyler, Phys. Lett. B

minded to o often how unaware we remain of TeV-

47, 365 (1973); G. 't Ho oft, announce-

scale physics and that only exp eriment will remove

ment made at the Collo quium on Renor-

our ignorance. Ayoung woman in Amherst, Mass-

malization of Yang-Mills Fields, C.N.R.S.,

achusetts, said it b est over a century ago:

Marseilles, June 19-23, 1972; D. Gross and

F. Wilczek, Phys. Rev. Lett. 30, 1343

\Faith" is a ne invention

(1973); H. D. Politzer, Phys. Rev. Lett. 30,

When Gentlemen can see |

1346 (1973).

But Microscopes are prudent

5. R. Bro ck, \High-p Physics Results from

In an Emergency.

the Tevatron", Rapp orteur's talk at the 28th

International Conference on High Energy

| Emily Dickinson, 1860

Physics, Warsaw (July 1996).

6. P. Tipton, \Top quark prop erties | Exp er-

imental Asp ects", Rapp orteur's talk at the

28th International Conference on High En-

ergy Physics, Warsaw (July 1996).

7. A. Blondel, \Status of the Electroweak

Interactions|Exp erimental Asp ects", Rap-

p orteur's talk at the 28th International Con-

ference on High Energy Physics, Warsaw 9

J. Terning, Phys. Lett. B 331, 383 (1994), (July 1996).

and references therein. 8. P. W. Anderson, Phys. Rev. 110, 827

18. C. T. Hill, Phys. Lett. B 345, 483 (1995). (1958); ibid., 130, 439 (1963); Y. Nambu,

19. Y. Nambu, in New Theories in Physics, Phys. Rev. 117, 648 (1959); J. Schwinger,

Pro ceedings of the XI International Symp o- Phys. Rev. 125, 397 (1962); P. Higgs,

sium on Elementary Particle Physics, Kaz- Phys. Rev. Lett. 12, 132 (1964); F. En-

imierz, Poland, 1988, edited by Z. Ad- glert and R. Brout, Phys. Rev. Lett. 13,

juk, S. Pokorski and A. Trautmann 321 (1964); G. S. Guralnik, C. R. Hagen and

(World Scienti c, Singap ore, 1989); En- T. W. B. Kibble, Phys. Rev. Lett. 13, 585

rico Fermi Institute Rep ort EFI 89-08 (un- (1964).

published); V. A. Miransky, M. Tanabashi 9. See, e.g., Time Magazine, p66, June 17,

and K. Yamawaki, Phys. Lett. B 221, 171 1996.

(1989); Mod. Phys. Lett. A4, 1043 (1989); 10. P. Maettig, \Searches for New Particles",

W. A. Bardeen, C. T. Hill and M. Lindner, Rapp orteur's talk at the 28th International

Phys. Rev. D D41, 1647 (1990). Conference on High Energy Physics, Warsaw

20. C. T. Hill, Phys. Lett. B 266, 419 (July 1996).

(1991); S. P. Martin, Phys. Rev. D 11. For a review of technicolor up to 1993 and

45, 4283 (1992); ibid D46, 2197 (1992); a discussion of the technical meanings of

Nucl. Phys. B 398, 359 (1993); M. Lindner the terms \naturalness" and \triviality", see

and D. Ross, Nucl. Phys. B B370, 30 (1992); K. Lane, An Introduction to Technicolor,

R. Bonisch, Phys. Lett. B 268, 394 (1991); Lectures given at the 1993 Theoretical Ad-

C. T. Hill, D. Kennedy, T. Onogi, H. L. Yu, vanced Studies Institute, University of Col-

Phys. Rev. D 47, 2940 (1993). orado, Boulder, published in \The Building

21. K. Lane and E. Eichten, Phys. Lett. B 352, Blo cks of Creation", edited by S. Raby and

382 (1995); K. Lane, Phys. Rev. D 54, 2204 T. Walker, p. 381, World Scienti c (1994).

(1996). 12. E. Eichten, I. Hinchli e, K. Lane and

22. B. W. Lynn, M. E. Peskin and R. G. Stu- C. Quigg, Rev. Mod. Phys. 56, 579 (1984).

art, in Trieste Electroweak 1985, 213 13. E. Eichten, I. Hinchli e, K. Lane and

(1985); M. E. Peskin and T. Takeuchi, C. Quigg, Phys. Rev. D 34, 1547 (1986).

Phys. Rev. Lett. 65, 964 (1990); A. Longhi- 14. B. Holdom, Phys. Rev. D 24, 1441 (1981);

tano, Phys. Rev. D 22, 1166 (1980); Phys. Lett. B 150, 301 (1985); T. Ap-

Nucl. Phys. B 188, 118 (1981); R. Renken p elquist, D. Karabali and L. C. R. Wi-

and M. Peskin, Nucl. Phys. B 211, jewardhana, Phys. Rev. Lett. 57, 957

93 (1983); M. Golden and L. Randall, (1986); T. App elquist and L. C. R. Wi-

Nucl. Phys. B 361, 3 (1990); B. Holdom and jewardhana, Phys. Rev. D 36, 568 (1987);

J. Terning, Phys. Lett. B 247, 88 (1990); K. Yamawaki, M. Bando and K. Matumoto,

A. Dobado, D. Espriu and M J. Herrero, Phys. Rev. Lett. 56, 1335 (1986); T. Ak-

Phys. Lett. B 255, 405 (1990); H. Georgi, iba and T. Yanagida, Phys. Lett. B 169, 432

Nucl. Phys. B 363, 301 (1991). (1986).

23. K. Lane, Technicolor and Precision Tests of 15. K. Lane and E. Eichten, Phys. Lett. B 222,

the Electroweak Interactions, Pro ceedings of 274 (1989); K. Lane and M. V. Ramana,

the 27th International Conference on High Phys. Rev. D 44, 2678 (1991).

Energy Physics, edited byP. J. Bussey and 16. F. Ab e, et al.,

I. G. Knowles, Vol. I I, p. 543, Glasgow, June The CDF Collab oration, Phys. Rev. Lett.

20{27, 1994. 73, 225 (1994); Phys. Rev. D 50, 2966

24. E. Eichten and K. Lane, \Low-Scale Techni- (1994); Phys. Rev. Lett. 74, 2626 (1995);

color at the Tevatron", FERMILAB-PUB- S. Abachi, et al., The D Collab oration,

96/075-T, BUHEP-96-9, hep-ph/9607213; Phys. Rev. Lett. 74, 2632 (1995).

to app ear in Physics Letters B. 17. R. S. Chivukula, S. B. Selipsky, and

25. J. Incandela, Pro ceedings of the 10th Top- E. H. Simmons, Phys. Rev. Lett. 69, 575

ical Workshop on Proton-Antiproton Col- (1992); R. S. Chivukula, E. H. Simmons, and 10

Questions lider Physics, Fermilab, edited R. Ra ja and

J. Yoh, p. 256 (1995).

David J. Mil ler, University Col lege, London:

26. E. Eichten, K. Lane and J. Womersley,

SUSY has the attraction that she [sic] o ers

\Finding Low-Scale Technicolor at Hadron

us a dark matter candidate. Do es your technicolor

Colliders", in preparation.

theory?

27. R. S. Chivukula and M. Golden,

Phys. Rev. D 41, 2795 (1990).

K. Lane:

28. E. Eichten and K. Lane, \Electroweak

The top color-assisted technicolor mo dels I

and Flavor Dynamics at Hadron Colliders{

have b een investigating tend to have stable tech-

I", FERMILAB-PUB-96/297-T, BUHEP-

nibaryons. Whether or not they are electri-

96-33, hep-ph/9609297, and

cally charged and, hence, ruled out is a mo del-

II, FERMILAB-PUB-96/298-T, BUHEP-

dep endent question.

96-34, hep-ph/9609298, to app ear in the pro-

ceedings of the 1996 DPF/DPB Summer

Bernd Kniel, Max Planck Institute, Munich:

Study on New Directions for High Energy

Technifermions have gauge couplings and in-

Physics (Snowmass 96).

tro duce thresholds in the b eta functions of the

29. F. Ab e, et al., The CDF Collab oration,

gauge couplings. In addition, there is a new gauge

Phys. Rev. Lett. 74, 3538 (1995).

coupling intro duced by technicolor. Will these

30. R. M. Harris (CDF Collab oration), private

couplings meet at some grand uni cation scale as

communication.

they do in sup ersymmetry?

31. K. Maeshima, for the CDF Collab oration,

\New Particle Searches at CDF", Parallel

K. Lane:

talk at the 28th International Conference on

There already is a \p etit uni cation"|at the

High Energy Physics, Warsaw (July 1996).

extended technicolor scale of several hundred TeV

32. D. Kominis, \Top color", Parallel talk at the

where technicolor, color, and avor gauge symme-

28th International Conference on High En-

tries are rejoined. Ihave no idea whether techni-

ergy Physics, Warsaw (July 1996).

color will involve grand uni cation at some very

33. C. T. Hill and S. Parke, Phys. Rev. D 49,

high scale, although the attractiveness of that p os-

4454 (1994); K. Lane, Phys. Rev. D 52, 1546

sibility is undeniable. I remind you that the mo d-

(1995).

ern gauge-mediated scenarios of sup ersymmetry

34. S.Catani,

breaking intro duce new gauge couplings and, so,

M. Mangano, P. Nason and L. Trentadue,

also imp eril the grand uni cation claimed for the

CERN-TH/96-21, hep-ph/9602208 (1996).

SU (3) SU (2) U (1) couplings. In view of the

35. R. M. Harris, \Discovery Mass Reach for

recent developments in duality,Iwould not b e sur-

Topgluons Decaying to bb at the Teva-

prised in ten years time to nd sup ersymmetry and

tron, hep-ph/9609316, and \Discovery Mass

technicolor united into a strong-dynamical theory

Reach for Topgluons Decaying to tt at the

of electroweak and avor symmetry breaking, with

Tevatron, hep-ph/9609318, to app ear in the

quarks and leptons as comp osite entities at some

pro ceedings of the 1996 DPF/DPB Summer

scale.

Study on New Directions for High Energy

Physics (Snowmass 96).

36. For exp erimental constraints on Z masses

and couplings, see R. S. Chivukula and

J. Terning, \Precision Electroweak Con-

straints on Top color-Assisted Technicolor",

BUHEP-96-12, hep-ph/9606233.

37. E. J. Eichten, K. Lane and M. E. Peskin,

Phys. Rev. Lett. 50, 811 (1983).

38. F. Ab e, et al., The CDF Collab oration,

Phys. Rev. Lett. 77, 438 (1996). 11