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Z explicitly 0 bosons 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 model Higgs boson, its sim- bosons”. This happens in supersymmetry, the ple extensions, supersymmetry, 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 popular. 9 high energy and luminosity, but extracting clear Notwithstanding its popularity, there is no ex- signals from them can be quite demanding. Thus, perimental evidence for supersymmetry. 10, b We detectors should be designed to be sensitive to, do not know the origin of electroweak symmetry and experimenters should be prepared to search breaking. for, the signatures of dynamical electroweak and If the dynamics of the Higgs mechanism are flavor symmetry breaking. So far, there is little unknown in detail, those of flavor are completely indication of this in the large LHC detector col- obscure. We don’t even have a proper name, much laborations. less a believable and venerable “mechanism”, for flavor symmetry breaking. Models with elemen- 3 Summary of Technicolor and Extended tary Higgs bosons, whether supersymmetric or Technicolor not, offer no explanation at all for the quark-lepton content of the generations, the number of genera- Technicolor—the strong interaction of fermions tions, why they are identical, and why flavor sym- and gauge bosons at the scale Λ ∼ 1 TeV— metry is broken—the bizarre pattern of quark and TC describes the breakdown of electroweak symme- lepton masses. try to electromagnetism without elementary scalar Dynamical electroweak and flavor symmetry 1 bosons. 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 spontaneously broken by strong QCD interactions, scenarios for this physics that involve new inter- resulting in the appearance of massless Goldstone actions at specified, experimentally accessible en- c 11 bosons, π, K, η. In fact, if there were no Higgs ergy scales. Technicolor is a strong gauge inter- bosons, this chiral symmetry breaking would itself action modeled after QCD. Its characteristic en- < cause the breakdown of electroweak SU(2) ⊗ U(1) ergy is ∼ 1 TeV, so it may be sought in experi- to electromagnetism. Furthermore, the W and Z ments of the coming decade. Extended technicolor 2 2 2 masses would be given by MW = cos θW MZ = (ETC) embeds technicolor, color and flavor into a 1 2 2 g NF f , where g is the weak SU(2) coupling, larger gauge symmetry; this embedding is neces- 8 π NF the number of massless quark flavors, and fπ, sary to produce 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 offers a simple group-theoretic up version of QCD, with massless technifermions explanation of flavor in terms of the representa- whose chiral symmetry is spontaneously broken at tion content of fermions. As we explain shortly, Λ . If left and right-handed technifermions are the scale at which ETC symmetry is broken down TC assigned to weak SU(2) doublets and singlets, re- to color ⊗ technicolor is O(100 TeV). Neverthe- spectively, then M = cos θ M = 1 gF , where less, the effects of this interaction are observable W W Z 2 π F = 246GeV is the weak technipion decay con- at the TeV energy scale in terms of the masses and π stant. d decay modes of the technihadrons, ρ and π , that T T The principal signals in hadron collider ex- populate technicolor models. periments of “classical” technicolor were discussed Because we are so completely ignorant of long ago. 12,13 In the minimal technicolor model, electroweak and flavor dynamics, experiments 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 cThe hard masses of quarks explicitly break chiral sym- greatest possible discovery potential. They ought metry and give mass to π, K, η, which are then referred to as pseudo-Goldstone bosons. bThose who would cite the apparent unification of the dThe technipions in minimal technicolor are the linear SU(3)⊗SU(2)⊗U(1) couplings near 1016 GeV as evidence combinations of massless Goldstone bosons that become, ± now have to incorporate the scenario of supersymmetry via the Higgs mechanism, the longitudinal components WL 0 breaking mediated by new gauge interactions. and ZL of the weak gauge bosons.
2 prominent collider signals are the modest enhance- METC: ments in longitudinally-polarized weak boson pro- 2 duction. These are the s-channel color-singlet gETC ¯ 0 mq(METC) ≃ mℓ(METC ) ≃ 2 hTT iETC , technirho resonances near 1.5–2 TeV: ρT 1 → METC + − ± ± 0 2 WL WL and ρT 1 → WL ZL. The O(α ) cross sec- (1) tions of these processes are quite small at such where hTT¯ iETC and mq,ℓ(METC ) are the techni- masses. This and the difficulty of reconstructing fermion condensate and quark and lepton masses weak-boson pairs with reasonable efficiency make renormalized at the scale METC . observing these enhancements a challenge. If technicolor is like QCD, with a running cou- Nonminimal technicolor models are much pling αTC rapidly becoming small above ΛTC ∼ ¯ ¯ 3 more accessible because they have a rich spec- 1 TeV, then hTT iETC ≃ hTT iTC ≃ ΛTC . To trum of lower mass technirho vector mesons and obtain quark masses of a few GeV thus requires < technipion states into which they may decay. e METC/gETC ∼ 30 TeV. This is excluded. Ex- The often-discussed one-family model, contains tended technicolor boson exchanges also generate one isodoublet each of color-triplet techniquarks four-quark interactions which, generically, include (U,D) and color-singlet technileptons (N, E). Be- |∆S| = 2 and |∆B| = 2 operators. For these not to 0 ¯ 0 0 ¯0 cause the color coupling is weak above 100 GeV, be in conflict with K -K and Bd-Bd mixing pa- rameters, METC/gETC must exceed several hun- the technifermion chiral symmetry is approxi- 3 mately SU(8) ⊗ SU(8). This symmetry and its dred TeV. This implies quark and lepton masses breakdown to the diagonal SU(8) gives rise to no larger than a few MeV, and technipion masses no more than a few GeV. 63 ρT and πT which may be classified accord- ing to how they transform under ordinary color Because of this conflict between constraints on SU(3) times weak isospin SU(2). The techni- flavor-changing neutral currents and the magni- 0′ ± 0 tude of ETC-generated quark, lepton and techni- pions are color singlets πT ∈ (1, 1); WL ,ZL and ± 0 pion masses, classical technicolor was superseded πT , πT ∈ (1, 3); color octets ηT ∈ (8, 1) and 14 ± 0 a decade ago by “walking” technicolor. Here, πT 8, πT 8 ∈ (8, 3); and color-triplet leptoquarks ¯ ¯ the strong technicolor coupling αTC runs very πQL¯ , πLQ¯ ∈ (3, 3) ⊕ (3, 1) ⊕ (3, 3) ⊕ (3, 1). The slowly—walks—for a large range of momenta, pos- ρT belong to the same representations. sibly all the way up to the ETC scale of sev- In the standard model and its extensions, the eral hundred TeV. The slowly-running coupling masses of quarks and leptons are produced by their enhances hTT¯ iETC /hTT¯ iTC by almost a factor of Yukawa couplings to the Higgs bosons—couplings METC/ΛTC . This, in turn, allows quark and lep- of arbitrary magnitude and phase that are put in > ton masses as large as a few GeV and MπT ∼ by hand. This option is not available in techni- 100GeV to be generated from ETC interactions color because there are no elementary scalars. In- at METC = O(100 TeV). 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 α runs slowly. The most economical way to do this is to em- TC These fermions may belong to many copies of ploy extended technicolor, a gauge group con- the fundamental representation of the technicolor taining flavor, color and technicolor as subgroups. gauge group, to a few higher dimensional repre- Quarks, leptons and technifermions are combined sentations, or to both. That last possibility in- into the same few large representations of ETC. spired “multiscale technicolor” models containing Then quark and lepton hard masses are generated both fundamental and higher representations, and by their coupling (with strength g ) to techni- ETC having a very different phenomenology. 15 In mul- fermions via ETC gauge bosons of generic mass tiscale models, there typically are two widely sep- arated scales of electroweak symmetry breaking, eThe technipions of non-minimal technicolor include with the upper scale set by the weak decay con- the longitudinal weak bosons as well as additional Gold- stant, Fπ = 246 GeV. Technihadrons associated stone bosons associated with spontaneous technifermion with the lower scale may be so light that they chiral symmetry breaking. The latter must and do acquire mass—from the extended technicolor interactions discussed are within reach of the Tevatron collider; they are below. readily produced and detected at the LHC.
3 f An important consequence of walking techni- masses, contribute a few GeV to mt, and give color is that the large ratio hTT¯ iETC/hTT¯ iTC mass to the technipions. The scale of ETC in- significantly enhances technipion masses. Thus, teractions still must be hundreds of TeV to sup- ρT → πT πT decay channels may be closed. If this press flavor-changing neutral currents and, so, the happens, then ρT 1 → WLWL or WLπT . The pro- technicolor coupling still must walk. Early steps duction rates for these color singlets are 5–10 pb in the development of the TC2 scenario have been at the Tevatron and 25–100 pb at the LHC. If col- taken in two recent papers. 21 Although the phe- ored technifermions exist, the electrically neutral nomenology of TC2 is in its infancy, it is expected color-octet technirho, ρT 8, may have its πT πT de- to share general features with multiscale techni- cay channels closed as well. In this case, it appears color: many technihadron states, some carrying as a relatively narrow resonance in ρT 8 → dijets. ordinary color, some within range of the Tevatron, If the ρT 1, ρT 8 → πT πT channels are open, they and almost all easily produced and detected at the are resonantly produced at large rates, of order LHC at moderate luminosities. 5 pb at the Tevatron and several nanobarns at the I assume throughout this talk that the techni- LHC. As we describe in more detail below, techni- color gauge group is SU(NTC ) and that its gauge pions tend to decay to heavy fermions. Given coupling walks. A minimal, one-doublet model these large rates and the recent successes and com- can have a walking αTC only if the technifermions ing advances in heavy flavor detection, many of belong to a large non-fundamental representa- these technipions should be reconstructable in the tion. For nonminimal models, I generally con- hadron collider environment. sider the phenomenology of only the lighter techni- fermions. These transform according to the funda- Another major development in technicolor mental (NTC ) representation. Some of them may was motivated by the recent discovery of the top 16 also be ordinary color triplets. Finally, in TC2, quark. Theorists have concluded that ETC mod- there is no need for large technifermion isospin els cannot explain the top quark’s large mass splitting associated with the top-bottom mass dif- without running afoul of either experimental con- ference. This simplifies our discussion greatly. straints from the ρ parameter and the Z → ¯bb de- 7,17 The decays of technipions are induced mainly cay rate (the ETC mass must be about 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 (METC may be higher, but the coupling gETC so technipions are expected to decay into heavy must be fine-tuned near to a critical value). This fermion pairs. For the color-singlets, e.g., state of affairs has led to the proposal of “topcolor- assisted technicolor” (TC2). 18 ¯ 0 bb if MπT < 2mt πT → ¯ tt if MπT > 2mt In TC2, as in top-condensate models of elec- + 19 c¯b, cs,¯ τ ν if M
4 15,21 tral functions and their moments converge much pion decay constant FT , is small . Conse- more slowly than they do in QCD. Consequently, quently, it is plausible that technihadrons πT and simple dominance of spectral integrals by a few ρT have masses at the lower end of these ranges. resonances cannot be correct. This and other cal- I should not have to point out that such low-scale culational tools based on naive scaling from QCD technihadrons are accessible at the Tevatron. and on large-NTC arguments are suspect. Thus, Color-singlet technipions, including the lon- it is not yet possible to predict with confidence gitudinal WL and ZL, are pair-produced via the the influence of technicolor degrees of freedom Drell-Yan process in hadron collisions. The O(α2) 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- ample. 22, g less there are fairly strong color-singlet technirho ±,0 resonances, ρT 1 not far above threshold. To pa- 4 Technicolor Signatures at Hadron Col- rameterize the cross sections, we consider a sim- liders ple model containing two isotriplets of technipions ± 0 which are mixtures of WL , ZL and an isotriplet of 15,24 4.1 Color-Singlet Technipion Production mass-eigenstate technipions πT . The lighter + − ± 0 isotriplet ρT 1 is assumed to decay dominantly into The ρT 1 → W W and W Z signatures of L L L L pairs of the mixed state |ΠT i = sin χ |WLi + the minimal technicolor model were discussed long cos χ |πT i, leading to the processes ago. 12,13 If there is to be just one technifermion doublet, it must belong to a higher dimensional ± 0 WL ZL representation of SU(NTC ) so that αTC walks. ′ ± ± ± 0 ± 0 qq¯ → W → ρT 1 → WL πT , πT ZL The main phenomenological consequence of this ± 0 πT πT is that it is questionable to use the ρ 1 → π π T T T coupling αρ obtained by naive scaling from QCD, + − T WL WL 0 0 ± ∓ qq¯ → γ,Z → ρT 1 → WL πT 3 + − αρT =2.91 . (3) πT πT NTC (4) The mixing angle χ is specified by sin χ = This coupling may be smaller than Eq. (3) indi- FT /Fπ, where FT is the ΠT decay constant and cates, leading to a narrower ρT 1. There is also the F = 246 GeV. Although this mixing usually possibility that, because of its large mass (naively, π is quite small, walking technicolor enhancements 1.5–2 TeV), the ρT 1 has a sizable branching ratio of technipion masses suppress or even close the to four-weak-boson final states. To my knowledge, ρ 1 → π π channels. Thus, the ρ 1 should be neither of these possibilities has been investigated. T T T T quite narrow and any of the decay modes in Eq. 4 From now on, I consider only nonminimal may be important. This is seen in Fig. 1 where the models which, I believe, are much more likely to production rates of individual channels are calcu- lead to a satisfactory walking model. They have a lated for the Tevatron as a function of M for rich phenomenology with many diverse, relatively ρT 1 M = 110GeV and sin χ = 1 . Such low mass accessible signals. The masses of technipions in πT 3 technipions are expected to decay to b¯b or c¯b. Fur- these models arise from broken ETC and ordi- thermore, some scheme such as TC2 which results nary color interactions. In walking models that ETC 15 in a small coupling m /F of technipions to have been studied, they lie in the range 100– t T the top quark is required to suppress the unseen 600 GeV; technirho vector meson masses are ex- mode t → π+b. 25 Heavy-flavor tagging and kine- pected to lie between 200 and 1000 GeV. Mul- T matical selection techniques are useful to extract tiscale and topcolor-assisted models of technicolor the signals. Figure 1 illustrates several important tend to have so many technifermions that the char- general points: 24,26 acteristic scale of these models, set by the techni- gThese comments respond to a question from Graham Ross regarding the effects of technicolor on precision elec- troweak tests. I thank him for the opportunity to reiterate them. 23
5 point depends to some extent on the sup- pression factor tan χ, but it should not be much different from this. A search for the ± 0 πT πT channel will be rewarding, even if it is negative.
Since the isospin of technifermions is approx- imately conserved, the ρT 1 is expected to be nearly degenerate with its isoscalar partner ωT . The walking technicolor enhancement of techni- pion masses almost certainly closes off the isospin- + − 0 conserving decay ωT → ΠT ΠT ΠT . Even the + − triply-suppressed mode WL WL ZL has little or no < phase space for MωT ∼ 300 GeV. Thus, the main 0 0 decays are expected to be ωT → γΠT , ZΠT , and + − ΠT ΠT . In terms of mass eigenstates, these modes Figure 1: Total WW , WπT and πT πT cross sections in 0 0 0′ 0′ are ωT → γπT , γZL, ZπT , ZZL; γπT , ZπT ; and pp¯ collisions at 1.8 TeV, as a function of MρT 1 for MπT = + − ± ∓ + − h 1 WL WL , πT WL , πT πT . It is not possible to 110 GeV. The model described in the text with sin χ = 3 is used. The curves are W ±Z0 (upper dotted) and W +W − estimate the relative magnitudes of the decay am- ± 0 ± ∓ (lower dotted); W πT (upper solid), W πT (lower solid), plitudes without an explicit model of the ωT ’s con- 0 ± ± 0 and Z πT (long dashed); πT πT (upper short dashed) and stituent technifermions. Judging from the decays + − 0 0′ πT πT (lower short dashed). of the ordinary ω, we expect ωT → ZπT (πT ), 0 0′ γπT (πT ) to dominate, with the latter mode fa- vored by phase space. • Except near W πT threshold, the increase in The ωT is produced in hadron collisions just WZ and W W production is undetectably 0 as the ρT 1 is, via its vector-meson-dominance cou- small. 0 pling to γ and Z . For MωT ≃ MρT 1 , the ωT production cross section should be approximately • The most important processes are those with 2 0 |QU + QD| times the ρT 1 rate, where QU,D are positive Q = [Mρ 1 – (sum of final state T the electric charges of the ωT ’s constituent techni- masses)] and the fewest number of longitu- fermions. The principal signatures for ωT produc- dinal weak bosons. At the Tevatron, the in- tion, then, are ℓ+ℓ− (or νν¯) +b¯b and γ + ¯bb, with clusive W π rate is 5–10pb and the Zπ T T M¯ = M . A search for the Zπ mode will use < < bb πT T rate is 1–3pb for Mπ + MW Mρ 1 T ∼ T ∼ the same strategies as for ρT 1 → ZLπT and WLπT . 2Mπ . These rates are 5–10 times larger at T The search for ωT → γπT in hadron collider ex- the LHC. Because the ρT 1 is very narrow, periments is under study. 26 the πT → dijet system should have large ◦ azimuthal opening angle ∆φ(jj) ∼> 125 < 4.2 Color-Octet Technirho Production and De- and limited transverse momentum pT (jj) ∼ 4 2 2 2 cay to Jets and Technipions (MρT 1 − 2(MπT + MW ) MρT 1 + (MπT − 1 2 2 2 MW ) ) /2MρT1 ≃ 50 GeV. Models with an electroweak doublet of color- triplet techniquarks (U,D) have an octet of I =0 • Signal events for W/Z + πT should exhibit a technirhos, ρT 8, with the same quantum numbers narrow peak, consistent with resolution, cor- as the gluon. The ρT 8 is produced strongly inqq ¯ responding to the ρT 1 resonance. This, how- and gg collisions. Assuming the one-family model ever, may not be a good way to discriminate for simplicity, the 63 technipions listed in Sec. 3 signal from background because kinematic h cuts can “sculpt” such a peak. The modes ωT → γZL, ZZL were considered by Chivukula and Golden for a one-doublet technicolor model. 27 Our estimates of the branching ratios for the 0 0 • Once MρT 1 ≥ 2MπT +10 GeV, the dominant isospin-violating decays ρT 1 → γπ , Zπ suggest that ± 0 T T process is πT πT production. The crossover they are negligible unless the mixing angle χ is very small. 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 effect of octet techirho vector 14 TeV) including the effect of octet techirho vector mesons mesons at 250 and 500 GeV. The solid curve assumes per- at 250 and 500 GeV. Resolutions and cuts are as in Fig. 2 fect jet energy resolution while the dashed curve assumes except that |ηj | < 1.0. 1 resolution σ(E)/E = 100%E 2 (GeV). Jet angles and ra- ∗ 2 pidities were limited by cos θ < 3 and |ηj | < 2.0. color-triplet leptoquarks decay as
cν¯τ if MπT
7 4.3 Signatures of Topcolor-Assisted Technicolor seems to rest on the isotriplet of top-rho vector mesons, ρ±,0. It is hard to estimate M ; it may Topcolor and topcolor-assisted technicolor (TC2) t ρt lie near 2m or closer to Λ = O(1 TeV). The ρ were reviewed at this conference by D. Kominis. 32 t t t are produced in hadron collisions just as the corre- The development of TC2 is still at an early stage sponding color-singlet technirhos discussed above. and, so, its phenomenology is not fully formed. The conventional expectation is that they decay Nevertheless, in addition to the color-singlet and ±,0 ± 0 + − as ρ → π π , π π . The rates are not likely nonsinglet technihadrons already discussed, there t t t t t to be large, but the distinctive decays of top-pions are three TC2 signatures that are likely to be help suppress standard model backgrounds. present in any surviving model: 18,21 ,33,28 It is also plausible that, because topcolor is broken near Λ , the ρ are not completely analo- • The isotriplet of color-singlet “top-pions” π t t t gous to the ρ-mesons of QCD and technicolor. For arising from spontaneous breakdown of the distance scales between Λ−1 and 1 GeV−1, top and top quark’s SU(2) ⊗ U(1) chiral symmetry. t bottom quarks do not experience a growing confin- ±,0 • The color-octet of vector bosons V8, called ing force. Instead of ρt → πtπt, the ρt may fall ¯ ¯ ¯ ± “colorons”, associated with breakdown of apart into their constituents tb, bt and tt. The ρt the top quark’s strong SU(3) interaction to resonance may be visible as a significant increase ¯ 0 ¯ ordinary color. in tb production, but ρt won’t be seen in tt. The V8 colorons of broken SU(3) topcolor are • The Z′ vector boson associated with break- readily produced in hadron collisions. They are down of the top quark’s strong U(1) inter- expected to have a mass of 0.5–1 TeV. Colorons action to ordinary weak hypercharge. couple with strength −gS cot ξ to quarks of the two light generations and with strength gS tan ξ 33 The three top-pions are nearly degenerate. to top and bottom quarks, where tan ξ ≫ 1. Their decay rate is They couple to the top quark with strength mt/Ft, where mt is the part of the top-quark mass induced 1 2 by topcolor—expected to be within a few GeV of ΓV8 = 6 αSMV8 4cot ξ 18 its total mass—and Ft ≃ 70 GeV is the πt decay (7) 2 2 2 + tan ξ 1+ βt(1 − m /M ) , constant. If the top-pion is lighter than the top t V8 quark, then where β = 1 − 4m2/M 2 . Colorons may then (m2 − M 2 )2 t t V8 + t πt q Γ(t → πt b) ≃ 2 . (6) appear as resonances in b¯b and tt¯ production. 16πmtFt R. Harris has studied the limits on masses and The standard top-decay mode branching ratio couplings of colorons decaying to ¯bb and tt¯ that + +0.13 +0.13 B(t → W b)=0.87−0.30 (stat.) −0.11 (syst.) was may be set at the Tevatron in Run II ( Ldt = reported a year ago. 25 At the 1σ level, then, 2 fb−1) and at the high-luminosity TeV33R upgrade > −1 Mπt ∼ 150 GeV. At the 2σ level, the lower bound ( Ldt = 30 fb ). He found that nearly the en- < is 100 GeV, but such a small branching ratio for tireR interesting range, MV8 ∼ 1.3TeV, can be t → W +b would require σ(pp¯ → tt¯) at the Teva- probed. 35 tron about 4 times the standard QCD value of Colorons have little effect on the standard di- +0.63 34 + 4.75−0.68 pb. The t → πt b decay mode can jet production rate. The situation may be very dif- be sought in high-luminosity runs at the Teva- ferent for the Z′ boson of the broken strong U(1) tron and with moderate luminosity at the LHC. interaction. In some TC2 models 21 it is natural + ¯ ′ If Mπt < mt, then πt → cb through t–c mixing. that Z couples strongly to the fermions of the first + It is also possible, though unlikely, that πT → ts¯ two generations as well as those of the third. The through b–s mixing. Z′ in these models is heavier than the colorons, + 0 36 ¯ ¯ ′ If Mπt > mt, then πt → tb and πt → tt or roughly MZ = 1–3 TeV. Thus, at subprocess ′ cc¯ , depending on whether the neutral top-pion is energies well below MZ′ , the interaction of Z with heavier or lighter than 2mt. The main hope for all quarks is described by a contact interaction, discovering top-pions heavier than the top quark just like what is expected for quarks with sub-
8 structure at a scale of a few TeV. This leads to an Acknowledgments 37,12 excess of jets at high ET and invariant mass. An excess in the jet-ET spectrum consistent with I thank Barry Barish and Paul Frampton for Λ ≃ 1600GeV has been reported by the CDF Col- thoughtful comments on my talk. I also thank laboration. 38,5 It remains to be seen whether it Elizabeth Simmons for her careful reading and is due to topcolor or any other new physics. As comments on the manuscript. I thank the orga- with quark substructure, the angular and rapidity nizers, especially Andrzej Wroblewski, for a won- ′ distributions of the high-ET jets induced by Z derful conference, the opportunity to visit Poland, should be more central than predicted by QCD. and much patience and help. I owe Chris Quigg The Z′ may also produce an excess of high invari- much for the opportunity to share my views on ant mass ℓ+ℓ−. It will be interesting to compare the search for TeV scale physics. My research was limits on contact interactions in the Drell-Yan pro- supported in part by the Department of Energy cess with those obtained from jet production. under Grant No. DE–FG02–91ER40676. If the Z′ is strongly coupled to light fermions it will be produced directly inqq ¯ annhilation in LHC References experiments. Because it may be strongly coupled to so many fermions, including technifermions in 1. S. Weinberg, 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 possibility should be taken into ac- 2. S. Dimopoulos and L. Susskind, count in forming strategies to look 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 too early to predict the Z′ couplings, width and 125 (1980). branching fractions with confidence. I hope for 4. S. L. Glashow, Nucl. Phys. B 22, 579 (1961); progress on these questions in the coming year. S. Weinberg, Phys. Rev. Lett. 19, 1264 (1967); A. Salam, in Proceedings of the 5 Conclusions 8th Nobel Symposium on Elementary Par- ticle Theory, Relativistic Groups and Ana- In this talk, I have tried to emphasize the im- lyticity, edited by N. Svartholm (Almquist portance of searching for signatures of dynami- and Wiksells, Stockholm, 1968, p. 367; cal as well as weakly-coupled scenarios for elec- S. L. Glashow, J. Iliopoulos and L. Maiani, troweak and flavor physics. We cannot be re- Phys. Rev. D 2, 1285 (1970); H. Fritzsch, minded too often how unaware we remain of TeV- M. Gell–Mann, H. Leutwyler, Phys. Lett. B scale physics and that only experiment will remove 47, 365 (1973); G. ’t Hooft, announce- our ignorance. A young woman in Amherst, Mass- ment made at the Colloquium on Renor- achusetts, said it best over a century ago: malization of Yang-Mills Fields, C.N.R.S., Marseilles, June 19-23, 1972; D. Gross and “Faith” is a fine invention F. Wilczek, Phys. Rev. Lett. 30, 1343 When Gentlemen can see — (1973); H. D. Politzer, Phys. Rev. Lett. 30, 1346 (1973). But Microscopes are prudent 5. R. Brock, “High-pT Physics Results from In an Emergency. the Tevatron”, Rapporteur’s talk at the 28th International Conference on High Energy — Emily Dickinson, 1860 Physics, Warsaw (July 1996). 6. P. Tipton, “Top quark properties — Exper- imental Aspects”, Rapporteur’s talk at the 28th International Conference on High En- ergy Physics, Warsaw (July 1996). 7. A. Blondel, “Status of the Electroweak Interactions—Experimental Aspects”, Rap- porteur’s talk at the 28th International Con- ference on High Energy Physics, Warsaw
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10 lider Physics, Fermilab, edited R. Raja and Questions J. Yoh, p. 256 (1995). 26. E. Eichten, K. Lane and J. Womersley, David J. Miller, University College, London: “Finding Low-Scale Technicolor at Hadron SUSY has the attraction that she [sic] offers Colliders”, in preparation. us a dark matter candidate. Does your technicolor 27. R. S. Chivukula and M. Golden, theory? Phys. Rev. D 41, 2795 (1990). 28. E. Eichten and K. Lane, “Electroweak K. Lane: and Flavor Dynamics at Hadron Colliders– The topcolor-assisted technicolor models I I”, FERMILAB-PUB-96/297-T, BUHEP- have been investigating tend to have stable tech- 96-33, hep-ph/9609297, and nibaryons. Whether or not they are electri- II, FERMILAB-PUB-96/298-T, BUHEP- cally charged and, hence, ruled out is a model- 96-34, hep-ph/9609298, to appear in the pro- dependent question. ceedings of the 1996 DPF/DPB Summer Study on New Directions for High Energy Bernd Kniel, Max Planck Institute, Munich: Physics (Snowmass 96). Technifermions have gauge couplings and in- 29. F. Abe, et al., The CDF Collaboration, troduce thresholds in the beta functions of the Phys. Rev. Lett. 74, 3538 (1995). gauge couplings. In addition, there is a new gauge 30. R. M. Harris (CDF Collaboration), private coupling introduced by technicolor. Will these communication. couplings meet at some grand unification scale as 31. K. Maeshima, for the CDF Collaboration, they do in supersymmetry? “New Particle Searches at CDF”, Parallel talk at the 28th International Conference on K. Lane: High Energy Physics, Warsaw (July 1996). There already is a “petit unification”—at the 32. D. Kominis, “Topcolor”, Parallel talk at the extended technicolor scale of several hundred TeV 28th International Conference on High En- where technicolor, color, and flavor gauge symme- ergy Physics, Warsaw (July 1996). tries are rejoined. I have no idea whether techni- 33. C. T. Hill and S. Parke, Phys. Rev. D 49, color will involve grand unification at some very 4454 (1994); K. Lane, Phys. Rev. D 52, 1546 high scale, although the attractiveness of that pos- (1995). sibility is undeniable. I remind you that the mod- 34. S.Catani, ern gauge-mediated scenarios of supersymmetry M. Mangano, P. Nason and L. Trentadue, breaking introduce new gauge couplings and, so, CERN-TH/96-21, hep-ph/9602208 (1996). also imperil the grand unification claimed for the 35. R. M. Harris, “Discovery Mass Reach for SU(3) ⊗ SU(2) ⊗ U(1) couplings. In view of the Topgluons Decaying to ¯bb at the Teva- recent developments in duality, I would not be sur- tron, hep-ph/9609316, and “Discovery Mass prised in ten years time to find supersymmetry and Reach for Topgluons Decaying to tt¯ at the technicolor united into a strong-dynamical theory Tevatron, hep-ph/9609318, to appear in the of electroweak and flavor symmetry breaking, with proceedings of the 1996 DPF/DPB Summer quarks and leptons as composite entities at some Study on New Directions for High Energy scale. Physics (Snowmass 96). 36. For experimental constraints on Z′ masses and couplings, see R. S. Chivukula and J. Terning, “Precision Electroweak Con- straints on Topcolor-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. Abe, et al., The CDF Collaboration, Phys. Rev. Lett. 77, 438 (1996).
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