koorio.com
海量文库 文档专家
当前位置:首页 >> >>

Flavor Changing Neutral Scalar Currents at $mu^+mu^-$ Colliders


SLAC-PUB-95-6962 BNL-

arXiv:hep-ph/9507416v1 26 Jul 1995

Flavor Changing Neutral Scalar Currents at ?+ ?? Colliders David Atwooda , Laura Reinab and Amarjit Sonib

a) Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309, USA b) Department of Physics, Brookhaven National Laboratory, Upton, NY 11973, USA

Abstract: The prospect of observing the ?avor changing decay H → t? of a neutral Higgs boson produced via s-channel and its c subsequent decay into t? is considered at a ?+ ?? collider. Nuc merical estimates are given in the context of a two Higgs doublet model with ?avor changing couplings. It is found that for many values of the model parameters such tree-level ?avor changing decays will be produced at an observable level. In addition studies of the helicity of the top will allow the determination of the relative strengths of the ?avor changing Higgs couplings and these may be measured with about 103 events.

Submitted to Physical Review Letters

* This work was supported by US Department of Energy contracts DE-AC03765F00515 (SLAC) and DE-AC02-76CH0016 (BNL).

The suppression of ?avor changing neutral currents (FCNC) is an important feature of the Standard Model (SM). Thus, the measurement of such currents provides an important test which can discriminate between the SM and various models of new physics. In the SM, the relative largeness of the top mass [1, 2] leads to a measurable rate of FCNC’s in the down type quark sector through penguin processes [3]. In fact recent experiments at CLEO have observed the reaction b → sγ. At least in part due to the fact that no correspondingly heavy down type quark is thought to exist, similar FCNC processes within the up sector (e.g. t → cγ) are highly suppressed in the SM[4]. Since we do not know of a conservation law that enforces the absence of such FCNC’s their continual search is clearly warranted. These considerations have, of course, fueled the searches for ? → eγ, KL → ?e etc. for a very long time. The extraordinary mass scale of the top quark has prompted many to advocate that FCNC involving the top quark may well exist [5]. An important class of models where FCNC’s can occur among up type quarks are those where ?avor changing occurs in an extended neutral Higgs sector. In previous works [6, 7], the observation of FCNC’s (due to penguin graphs involving such a Higgs sector) was considered in the processes t → cγ or cZ and e+ e? (or indeed ?+ ?? ) → γ or Z → t? respectively. In this Letter c we suggest that the tree level coupling of such ?avor-changing neutral Higgs bosons [8] to t? may be probed by ?+ ?? → t? at suggested muon colliders c c (MUCs). Although very much in the notion stage at present, the MUC has been suggested [9]-[12] as a possible lepton collider for energies in the TeV range. The advantage of such a MUC would be that the much heavier muon su?ers appreciably less energy loss from synchrotron and beamstrahlung radiation. The obvious disadvantages include the fact that muons eventually decay as well as the new accelerator technology development needed to produce and control such beams to the necessary degree to reach high luminosities. If MUCs are eventually shown to be a practical and desirable tool for exploring physics in the TeV range, most of the applications would be very similar to electron colliders. One advantage however is that they may be able to produce Higgs bosons directly in the s channel in su?cient quantity to study their properties directly [9, 13, 14, 7]. In particular, a simple but fascinating possibility that we wish to explore here is when such a Higgs, H, has a ?avor-changing Ht? coupling then the process ?+ ?? → t? will give a c c signal which should be easy to identify, is likely to take place at an observable 1

rate and yet has a negligible SM background. Thus the properties of this important coupling can be studied in detail. The crucial point is that in spite of the fact that the ?+ ?? H coupling, being proportional to m? , is very small, if the MUC is run on the Higgs √ resonance, s = mH , Higgs bosons may be produced at an appreciable rate [9, 13, √ 7]. 14, At s = mH , the cross section for producing H, σH , normalized to σ0 = σ(?+ ?? → γ → e+ e? ), is given by: R(H) = 3 H σH = 2 B? σ0 αe (1)

H where B? is the branching ratio of H → ?+ ?? and αe is the electromagnetic coupling. If the Higgs is very narrow, the exact tuning to the resonance implied in equation (1) may not in general be possible. Let us suppose then that the energy of the beam has a ?nite spread described by δ:

where we assume that s is uniform about this range. The e?ective rate of Higgs production will thus be given by: mH δ ΓH R(H) (3) arctan mH δ ΓH We now consider an extended Higgs sector which admits FCNCs. In refs. [6, 7], for instance, a minimal FCNC Higgs model with two Higgs doublets φ1 , φ2 is considered. We assume, without loss of generality, that φ1 is aligned with the vev so that ? R(H) = < φ1 >= 0 √ v/ 2 , < φ2 >= 0 (4)

m2 (1 ? δ) < s < m2 (1 + δ) H H

(2)

√ 1 where v = ( 2GF )? 2 . There are three neutral mass eigenstates denoted by H, h, and A which are [6, 7] √ 2[(Reφ0 ? v) cos α + Reφ0 sin α] H = 1 2 √ 0 h = 2[(?Reφ1 ? v) sin α + Reφ0 cos α] 2 √ A = ? 2Imφ0 2 2

(5)

where the mixing angle α is a parameter determined by the Higgs potential. The Lagrangian for the Higgs-fermion interaction is [6, 7]: ? ? ? ? L = λU Qi φ1 Uj + λD Qi φ1 Dj + λL Li φ1 Ej ij ij ij D ? L? U ? ? + ξij Qi φ2 Uj + ξij Qi φ2 Dj + ξij Li φ2 Ej + h.c.

(6)

Here the λU,D,L couplings turn out to be proportional respectively to the ij quark and lepton mass matrices, while the ξij couplings are arbitrary and ?avor non-diagonal. For de?niteness, we will assume that the magnitude of the parameters ξij are as suggested by the ansatz of [15], √ mi mj (7) |ξij | ≈ g Mw Let us now consider that a Higgs H of mass mH is under study at a MUC. For illustrative purposes we take H = h in the above model where α = 0 (case 1) or π/4 (case 2). The main distinction between the two cases is that in case 2 the decays H → ZZ, W W are possible while in case 1 they are not. Thus case 1 is very similar to H = A. In general the coupling of h to ? f f is: Reξf f + iγ5 Imξf f g mf gmf √ sin α + χf eiγ5 λf cos α ≡ 2 mW 2mW 2

Chf f = ?

(8)

while the coupling to ZZ and W W is given by: g sin α mZ g ?ν ChW W = g sin αmW g ?ν cos θW Finally the ?avor changing Higgs ?t? coupling is given by: c √ g mt mc 1 ? (χR PR + χL PL ) Chtc = √ ξtc PR + ξct PL cos α ≡ 2mW 2 ChZZ = (9)

(10)

where χL and χR are in general complex numbers and of order unity if (7) applies. The decay rates to these modes given the above couplings can be readily calculated at tree level by using the results that exist in the literature [16]:

3

2 3gW m2 mH t ? βt βt2 + (1 ? βt2 ) sin λt χ2 Γ(H → tt) = t 32πm2 W 2 3gW m2 mH 2 b Γ(H → b? = b) χb 32πm2 W m4 g 2 m3 Z H 2 βZ (βZ + 12 4 ) sin2 α Γ(H → ZZ) = 128π m2 mH Z g 2 m3 m4 H 2 Γ(H → W W ) = βW (βW + 12 W ) sin2 α 64π m2 m4 W H

(11)

where βi = 1 ? 4m2 /m2 . i H The decay rate to t? is thus: c
2 3gW mt mc mH 32πm2 W

Γ(H → t?) = c

(m2 ? m2 )2 H t m4 H

|χR |2 + |χL |2 2

(12)

? and, Γ(H → t?) = Γ(H → ct) at the tree level that we are considering for c + ? now. The decay rate to ? ? which we require in equation (1) is Γ(H → ?+ ?? ) =
2 gW m2 mH 2 ? χ? ; 32πm2 W H B? = Γ(H → ?+ ?? )/ΓH

(13)

For the purpose of numerical estimates let us take the following sample choices of parameters: ? Case 1: α = λc = λt = 0, χ? = χb = χt = 1 and χL = χR = 1 ? Case 2: α = π/4, λc = λt = 0, χ? = χb = χt = 1 and χL = χR = 1 ? In ?gure 1 we plot R( H) with δ = 0, 10?3 and 10?2 in the two cases as well as
H H ? ? Rtc = R(H) (Bt? + Bct ) ? c

(14)

? ? Note that in case 1 if mH is below the tt threshold Rtc is about .01 ? 1 ? and in fact tc makes up a large branching ratio. Above the tt threshold Rtc drops. For case 2 the branching ratio is smaller due to the W W and ZZ threshold at about the same mass as the tc threshold and so Rtc is 4

around 10?3 . For a speci?c example if mH = 300GeV , then σ0 ≈ 1pb. For a luminosity of 1034 cm?2 s?1 , a year of 107 s (1/3 e?ciency) and for δ = 10?2 case 1 will produce about 5 × 103 (t? + tc) events and case 2 will produce c ? about 150 events. Given the distinctive nature of the ?nal state and the lack of a Standard Model background, su?cient luminosity should allow the observation of such events. If such events are observed one would like to extract the values of χL and ? χR . What is measured initially at a ?+ ?? collider is Rtc . One is required to know the total width of the H and the energy spread of the beam in order to translate this into Γ(H → t?). This then allows the determination of c 2 2 |χL | + |χR | . To get information separately on the two couplings we note that the total helicity of the top is: Ht = ?Ht = ? |χR |2 ? |χL |2 |χR |2 + |χL |2 (15)

from which one may therefore infer |χL | and |χR |. Unfortunately in the limit of small mc the helicity of the c-quark is conserved hence the relative phase of χL and χR may not be determined since the two couplings do not interfere. Of course the helicity of the t cannot be observed directly, however following the discussion of [17] one may obtain it from the decay distributions of the top. In particular if X is a particle arising in top decay let us de?ne the forward-backwards asymmetry AX = Γ(cos θX > 0) ? Γ(cos θX < 0) Γ(cos θX > 0) + Γ(cos θX < 0) (16)

where θX is the angle between PX and ?PH in the t rest frame. For each particular choice of X we de?ne ?X to be the correlation with the polarization de?ned by:
t ?X = 3 < cos θX > t where θX is the angle between X and the spin axis of a polarized top. In terms of ?X the asymmetry AX is thus given by:

(17)

1 AX = ?X Ht . 2 Let us now consider the following decays [17]: 5

(18)

? 1) for t → W b, W → l+ νl where l = e, ? then ?l = 1 and the branching fraction for this case is B1 ? 2 . 9 ? 2) For t → W b, W → hadrons then ?W = (m2 ? 2m2 )/(m2 + 2m2 ) ≈ t W t W 7 0.39 and the branching fraction for this is B2 ? 9 . The number of t? events needed to observe the top helicity with a signifc icance of 3-σ is [17]: N3σ = where Et = 36 Et2 H2 t ≈ 107 H2 t (19)

Thus at least 102 events are required to begin to measure the helicity of the top and hence the relative strengths of χL and χR . In the above numerical examples it is clear that for some combinations of parameters, particularly if the luminosity is 1034 cm?2 s?1 , su?cient events to measure the helicity may be present.

B1 ?2 + B2 ?2 ≈ .58 W l

(20)

This work was supported by US Department of Energy contracts DEAC03-765F00515 (SLAC) and DE-AC02-76CH0016 (BNL).

6

Figure Captions ? Figure 1: The value of R(H) is shown as a function of mH for scenario 1 ? (dash-dot) and for scenario 2 (dots). The value of Rtc is shown in case 1 for ?3 δ = 0 (upper solid curve); δ = 10 (middle solid curve) and δ = 10?2 (lower ? solid curve). The value of Rtc is shown in case 2 for δ = 0 (upper dashed ?2 curve) and δ = 10 (lower dashed curve).

7

References
[1] F. Abe et al., [CDF], Phys. Rev. Lett. 74, 2626 (1995); [2] S. Abachi et al., [D?], Phys. Rev. Lett. 74,2632 (1995). [3] B. Grinstein, R. Springer, and M. Wise, Phys. Lett. B202, 132 (1988); Nucl. Phys. B339, 269 (1990); R. Grigjanis, P.J. O’Donnel, M. Sutherland and H. Navelet, Phys. Lett. B213, 355 (1988); Phys. Lett. B223, 239 (1989); Phys. Lett. B237, 252 (1990); G. Cella, G. Curci, G. Ricciardi and A. Vicer?, Phys. Lett. B248, 181 (1990), Phys. Lett.B325, 227 e (1994); M. Misiak, Nuc. Phys B393, 23 (1993); A.J. Buras, M. Misiak, M. Munz, and S. Pokorski, Nuc. Phys. B424, 374 (1994); K. Adel and Y.P. Yao, Phys. Rev. D49, 4945 (1994); M. Ciuchini, E. Franco, M.Martinelli, L. Reina, L. Silvestrini, Phys. Lett. B 316, 127 (1993); Nucl. Phys. B421, 4 (1994); Phys. Lett. B 344, 137 (1994). [4] V. Ganapathi, T. Weiler, E. Laermann, I. Schmitt, and P.M. Zerwas, Phys. Rev. D27, 579 (1983); A. Axelrod, Nucl. Phys. B209 349 (1982); G. Eilam, J.L. Hewett and A. Soni, Phys. Rev. D44, 1473 (1991); B. Grzadkowski, J.F. Gunion, and P. Krawczyk, Phys. Lett. B268, 106 (1991). [5] M.J. Savage, Phys. Lett. B266,135 (1991); W.S. Hou, Phys. Lett. B296, 179 (1992); M. Luke and M. J. Savage, Phys. Lett. B307, 387 (1993); L.J. Hall and S.Weinberg, Phys. Rev. D48, R979 (1993); G.C. Branco, P.A. Parada, M.N. Rebelo, UWTHPH-1994-51, (1995); T. Han, R.D. Peccei, and X. Zhang, preprint FERMILAB-PUB-95/160-T; D. Atwood, L. Reina, and A. Soni, hep-ph/9506243. [6] M. Luke and M. J. Savage, Ref. 5. [7] D. Atwood, et al., Ref. 5. [8] In the case the Higgs is lighter than the t, one has t → cH 0 as emphasized by W.S. Hou, see Ref. 5. [9] D. Cline, Nucl. Instr. & Meth. A350, 24 (1994). [10] D.V. Neu?er, ibid, p. 27. 8

[11] W.A. Barletta and A.M. Sessler, ibid, p. 36; A.G. Ruggiero, ibid, p. 45; S. Chattopadhyay et al., ibid, p. 53. [12] R.B. Palmer, preprint, “High Frequency ?+ ?? Collider Design,” SLACAAS-Note81, 1993. [13] V. Barger, M. Berger, K. Fujii, J.F. Gunion, T. Han, C. Heusch, W. Hong, S.K. Oh, Z. Parsa, S. Rajpoot, R. Thun and B. Willis, Working group report, Proc. of the First Workshop on the Physics Potential and Development of ?+ ?? Colliders, Sausalito, CA, preprint MAD-PH-95873 (BB-9503258). [14] V. Barger, M. Berger, J. Gunion, and T. Han, hep-ph/9404330. [15] T.P. Cheng and M. Sher, Phys. Rev. D35, 3484 (1987); M. Sher and Y. Yuan, Phys. Rev. D44, 1461 (1991). [16] J. Gunion, H. Haber, G. Kane and S. Dawson, “The Higgs Hunters Guide,” published by Addison Wesley. [17] D. Atwood and A. Soni, SLAC-PUB-95-6877.

9


推荐相关:

Flavor Changing Neutral Scalar Currents at $mu^+mu^-$ ....pdf

Flavor Changing Neutral Scalar Currents at $mu^+mu^-$ Colliders_专业资料。The prospect of observing the flavor changing decay $\fH\to t\bar c$ of ...


Lepton Flavor Changing Neutral Current Processes at Lepton-....pdf

Lepton Flavor Changing Neutral Current Processes at Lepton-Hadron Colliders_...-\gamma$ couplings from the processes $ep\to\mu(\tau)X$ and $\mu p...


Higgs-photon production at mubar{mu} colliders.pdf

Higgs-photon production at mubar{mu} colliders_专业资料。We present cross sections for the reaction $\mu\bar{\mu}\to H\gamma$ over a range of $\...


...production as a probe of CP violation at a Muon Collider_....pdf

{\pm}$ boson at $\mu^+\mu^-$ colliders, in the context of the ...In the CP conserving case one ?nds two CP even neutral scalar eigenstates...


...at Lepton-Antilepton Colliders.pdf

with Photons at Lepton-Antilepton Colliders...mu^+\mu^- \to H^0 \gamma$ are considered....Flavour changing scalars and pseudoscalars may ...


Is the lepton flavour changing observable in $Z to mu^pm + ....pdf

Is the lepton flavour changing observable in $Z to mu^pm + tau^mp$ ...+ τ± which are at hand with the present colliders would give ...


Higgs-Mediated $B^0 - mu^+ mu^-$ in Minimal Supersy....pdf

Higgs-Mediated $B^0 - mu^+ mu^-$ in ...flavor-changing neutral currents within the minimal...+ ?? in Minimal Supersymmetry K.S. Babu 1 ...


...Lepton Flavor Violation at Future Colliders_免费....pdf

Lepton Flavor Violation at Future Colliders...{e}^-$ and $\tilde{\mu}^+ \tilde{\mu}^...tan β and the left-handed scalar masses. ...


Correlation of B_s - mu^+ mu^- and (g-2)_mu in Mini....pdf

Correlation of B_s - mu^+ mu^- and (g-2... the universal scalar and gaugino masses M0 and ...s are hard to detect at hadron colliders, so ...


...To $Z to b {bar{b}}$ And Flavor Changing Neutral Current ....pdf

{b}}$ And Flavor Changing Neutral Current ...the hadron and next generation linear colliders. ... and m3 correspond to mu , mc and mt for q...


...Correlations in the Decay $Hto ZZto mu^+mu^-mu^+mu^-$_图文....pdf

Energy Spectra and Energy Correlations in the Decay $Hto ZZto mu^+mu^-... a scalar 0++ particle can couple to a pair of Z’s according C to ...


$K_L ra mu^pm e^mp nu overline{nu}$ as background to $K_L ra ....pdf

$K_L ra mu^pm e^mp nu overline{nu}$ as ...? This work was supported by the U.S. ...(or perhaps a scalar) in the new physics ...


Flavor changing t - c l_1^- l_2^+ decay in the general two ....pdf

l_2=\mu at the order of magnitude of BR \...avor changing neutral currents (FCNC) in the ...2 m2 (m2 +m2 s) c c t t t l l l l ...


Charge asymmetry in $bm{gammagamma to mu^+mu^- + neutrinos}$ ....pdf

Charge asymmetry in $bm{gammagamma to mu^+mu^- + neutrinos}$ with ...The Photon Collider 1 option of the next generation linear colliders (LC)...


$dmdmu$ in the Nambu--Jona-Lasinio model.pdf

m is a mass matrix for current quarks, m = diag(mu , md , ms ). ...We can not get a reliable kaon mass in this region, and isoscalar ?S=...



Flavor-Changing Top Quark Rare Decays in the Littlest Higgs ....pdf

1 /y at the future colliders, reaching 107 tt...In the SM, the ?avor changing neutral current ...[arXiv:hep-ph/0211218]; Mu-Chun Chen and ...


Comment on $D_s^ to D_s pi^0$ Decay.pdf

(md ? mu ) 0 √πη 3 U ξR? and (3L ...pseudoscalar counterparts via single photon emission...magnitude of the neutral pion’s three-momentum....


Acceleration for the mu+ mu- Collider.pdf

Acceleration for the mu+ mu- Collider_专业


Width effects in slepton production e+ e- -- ~mu_R ~mu_R.pdf

Width effects in slepton production e+ e- -- ~mu_R ~mu_R_专业资料。...a Contribution to Workshop ‘Physics at TeV Colliders’, Les Houches, ...

网站首页 | 网站地图
All rights reserved Powered by 酷我资料网 koorio.com
copyright ©right 2014-2019。
文档资料库内容来自网络,如有侵犯请联系客服。zhit325@126.com