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Electroweak and Flavor Dynamics at Hadron Colliders–II

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Electroweak and Flavor Dynamics at Hadron Colliders–II Electroweak and Flavor Dynamics at Hadron Colliders±II b y Estia Eichtena and Kenneth Lane a Fermi National Accelerator Laboratory, P.O. Box 500 Batavia, IL 60510 b Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, MA 02215 ABSTRACT II. SIGNATURES OF TOPCOLOR-ASSISTED This is the second of two reports cataloging the principal sig- TECHNICOLOR pp pp natures of electroweak and ¯avor dynamics at and collid- The development of topcolor-assisted technicolor is still at an ers. Here, we complete our overview of technicolor with a dis- early stage and, so, its phenomenology is not fully formed. Nev- cussion of signatures speci®c to topcolor-assisted technicolor. ertheless, in addition to the color-singlet and nonsinglet techni- We also review signatures of ¯avor dynamics associated with hadrons already discussed, there are three TC2 signatures that quark and lepton substructure. These occur in excess produc- are likely to be present in any surviving model; see Refs. [1, 2, E tion rates for dijets and dileptons with high T and high invari- 3, 4, 5]: ant mass. An important feature of these processes is that they exhibit fairly central angular and rapidity distributions. The isotriplet of color-singlet ªtop-pionsº t arising from (2) U (1) spontaneous breakdown of the top quark's SU chiral symmetry; I. INTRODUCTION V The color-octet of vector bosons 8 , called ªcoloronsº, as- This and the preceding report summarize the major signals for (3) sociated with breakdown of the top quark's strong SU dynamical electroweak and ¯avor symmetry breaking in exper- interaction to ordinary color; iments at the Tevatron Collider and the Large Hadron Collider. 0 Z In the preceding report (referred to below as I), we reviewed The vector boson associated with breakdown of the top (1) the technicolor and extended technicolor scenarios of dynamical quark's strong U interaction to ordinary weak hyper- electroweak and ¯avor symmetry breaking. We also discussed charge. signals for color-singlet and nonsinglet technipions, resonantly produced via technirho and techni-omega vector mesons. In this The three top-pions are nearly degenerate. They couple to the m =F m t t report, we complete this discussion with a summary of the main top quark with strength t ,where is the part of the top- quark mass induced by topcolorÐexpected to be within a few signatures of tocolor-assisted technicolor: top-pions t and the 0 F ' 70 GeV t GeV of its total massÐand t [3] is the decay V Z color-octet 8 and singlet of broken topcolor gauge symme- 1 tries. These are presented in section 2. This arbitrary division constant. If the top-pion is lighter than the top quark, then has been necessitated by the length requirements of submissions 2 2 2 ) (m M t + t : (t ! ) ' to the Snowmass '96 proceedings. In section 3 we motivate and b (1) t 2 32m F t discuss the main ªlow-energyº signatures of quark and lepton t E substructure: excess productionof high- T jets and high invari- +0:13 +0:13 + (t ! W b)=0:87 It is known that B (stat.) 0:11 0:30 ant mass dileptons. Cross sections are presented for a simple > 1 M 150 GeV 2 (syst.)[6]. At the level, then, .Atthe form of the contact interaction induced by substructure. We re- t level, the lower bound is 100 GeV, but such a small branching emphasize that the shapes of angular distributions are an impor- + ! W b (pp ! tt) ratio for t would require at the Teva- tant test for new physics as the origin of such excesses. We also +0:63 :75 pb tron about 4 times the standard QCD value of 4 [7]. 0:68 stress the need to study the effect of other forms for the contact + ! b The t decay mode can be sought in high-luminosity interactions. At the end of this report, we have provided a table t which summarizes for the Tevatron and LHC the main processes runs at the Tevatron and with moderate luminosity at the LHC. + M <m ! cb t c t If ,then through ± mixing. It is also pos- t and sample cross sections that we discussed in these two reports. t + ! ts b s sible, though unlikely, that through ± mixing. These reports are not intended to constitute a complete sur- T + 0 M >m ! tb ! tt cc t If ,then and or ,de- t t vey of electroweak and ¯avor dynamics signatures accessible at t 2m hadron colliders. We have limited our discussion to processes pending on whether the top-pion is heavier or lighter than t . with the largest production cross sections and most promising The main hope for discovering top-pions heavier than the top signal-to-background ratios. Even for the processes we list, we quark seems to rest on the isotriplet of top-rho vector mesons, ;0 M 2m t .Itishardtoestimate ; it may lie near or closer to t have not provided detailed cross sections for signals and back- t = O (1 TeV) grounds. Signal rates depend on masses and model parame- t . They are produced in hadron collisions just as ters; they and their backgrounds also depend strongly on de- the corresponding color-singlet technirhos (Eq. (3.1) of I). The ;0 0 ! conventional expectation is that they decay as , t t tector capabilities. Experimenters in the detector collaborations t will have to carry out these studies. 1As far as we know, the rest of the discussion in this and the next paragraph has not appeared in print before. It certainly deserves more thought than has [email protected] gone into it here. One possible starting place is the paper by Hill, Kennedy, y [email protected] Onogi and Yu in Ref. [2]. 1006 + 0 Z . Then, the top-pion production rates may be estimated QCD. The may also produce an excess of high invariant mass t t + C =1 ` ` =2:91 AB from Eqs. (3.2) and (3.5) of I with and .. It will be interesting to compare limits on contact interac- T The rates are not large, but the distinctive decays of top-pions tions in the Drell-Yan process with those obtained from jet pro- help suppress standard model backgrounds. duction. 0 Z qq Life may not be so simple, however. The t are not completely The topcolor will be produced directly in annhilation 0 analogous to the -mesons of QCD and technicolor because top- in LHC experiments. Because Z may be strongly coupled to 1 color is broken near t . Thus, for distance scales between t so many fermions, including technifermions in the LHC's en- 1 and 1 GeV , top and bottom quarks do not experience a grow- ergy range, it is likely to be very broad. The development of 0 ! Z t t ing con®ning force. Instead of t , it is also possible that TC2 models is at such an early stage that the couplings, its ;0 tb bt tt fall apart into their constituents , and .The t reso- t width and branching fractions, cannot be predicted with con®- b nance may be visible as a signi®cant increase in t production, dence. These studies are underway and we hope for progress on 2 t but it won't be in t . these questions in the coming year. V SU (3) The 8 colorons of broken topcolor are readily pro- duced in hadron collisions. They are expected to have a mass of III. SIGNATURES FOR QUARK AND LEPTON g cot 1/2±1 TeV.Colorons couple with strength S to quarks of SUBSTRUCTURE g tan the two light generations and with strength S to top and 1 bottom quarks, where tan [5]. Their decay rate is The presence of three generations of quarks and leptons, ap- parently identical except for mass, strongly suggests that they M S V 8 2 2 2 2 4 cot + tan 1+ (1 m =M ) = t V are composed of still more fundamental fermions, often called t V 8 8 6 ªpreonsº. It is clear that, if preons exist, their strong interaction (2) q energy scale must be much greater than the quark and lepton 2 2 = 1 4m =M where t . Coloronsmay then appear as res- t V 8 masses. Long ago, 't Hooft ®gured out how interactions at high bb tt O ( ) onances in and production. For example, the S cross energy could produce essentially massless composite fermions: qq ! tt section for becomes the answer lies in unbroken chiral symmetries of the preons and p con®nement by their strong ªprecolorº interactions[12]. There 2 2 2 s^ M i d^ (qq ! tt) V t 8 V S 2 2 2 8 followed a great deal of theoretical effort to construct a realis- p = : 2 + z t t 2 dz 9^s s M + i s^ ^ tic model of composite quarks and leptons (see, e.g., Ref. [13]) V 8 V 8 (3) which, while leading to valuable insights on chiral gauge theo- ! tt For completeness, the gg rate is ries, fell far short of its main goal. In the midst of this activity, it was pointed out that the exis- 2 2 2 d^ (gg ! tt) 1+ z t t 2 2 S 9 tence of quark and lepton substructure will be signalled at en- = (1 + z )[ t 2 16 2 dz 6^s 1 z t ergies well below by the appearance of four-fermion ªcon- 2 2 2 ) 1 (1 tactº interactions which differ from those arising in the standard t t 2 2 2 1 9 + ]+ (1 z ) : + (4) t t 2 2 8 8 2 2 2 model[9, 10].
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