Top quark is extremely sensitive to non-standard CP violating phases. General
strategies for exposing different types of phases at the NLC are outlined. SUSY
phase(s) cause PRA in $t\to Wb$. The transverse polarization of the $\tau$ in
the reaction $t\to b\tau\nu$ is extremely sensitive to a phase from the charged
Higgs sector. Phase(s) from the neutral Higgs sector cause appreciable dipole
moment effects and lead to sizable asymmetries in $e^+e^-\to t\bar tH^0$ and
$e^+e^-\to t\bar t\nu_e\bar\nu_e$.}]Comment: 4 pages, Latex, 2 figures. For the Proceedings of the 28th Int. Conf.
  on HEP, Warsaw(July 1996

Atwood, D.

Soni, A.

English

arXiv

Top quark is extremely sensitive to non-standard CP violating phases. General strategies for exposing different types of phases at the NLC are outlined. SUSY phase(s) cause PRA in t {yields} Wb. The transverse polarization of the {tau} in the reaction t {yields} b{tau}{nu} is extremely sensitive to a phase from the charged Higgs sector. Phase(s) from the neutral Higgs sector cause appreciable dipole moment effects and lead to sizable asymmetries in e{sup +}e{sup {minus}} {yields} t{anti t}H{sup 0} and e{sup +}e{sup {minus}} {yields} t{anti t}{nu}{sub e}{anti {nu}}{sub e}

UNT Digital Library

BROOKHAVEN NATIONAL LABORATORY 18 September 1996 BNL- 63458 CP VIOLATION IN TOP PHYSICS AT THE NLC* David Atwood Theory Group, National Jefferson Lab and Amarjit Soni Theory Group, Brookhaven National Laboratory, Upton, NY 11973 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. - * Invited talk presented by A. Soni at the International High Energy Physics Conference, Warsaw, Poland, 7/ 15/96--8/1/96 This manuscript has been athored under contract number DEAC02-76CH00016 with the U.S. Depart- ment of Energy. Accordingly, the U.S. Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. CP VIOLATION IN TOP PHYSICS AT THE NLC D. ATWOOD Theory Group, National Jefferson Lab, A. SONI* Theory Group, Brookhaven National Laboratory, Upton, NY 11973 Top quark is extremely sensitive to non-standard CP violating phases. General strategies for exposing different types of phases at the NLC are outlined. SUSY phase(s) cause PRA in t -+ Wb. The transverse polarization of the T in the reaction t -+ b w  is extremely sensitive to a phase from the charged Higgs sector. Phase(s) from the neutral Higgs sector cause appreciable dipole moment effects and lead to sizable asymmetries in e+ e- + t t H o  and e+e- -+ ttu,ii,. 1 Introduction The standard model (SM) with three families and the CKM phase gives a natural explanation for the size of the observed CP asymmetry in the neutral kaon complex. It also strongly suggests the pres- ence of large CP asymmetries in B-decays making B-physics very suitable for precision extraction of the CKM phase and a quantitative check of the unitarity triangle. Furthermore, the minimum SM with mt - 175 GeV >> mb,md,ms also leads to the conclusion that CP violation effects in top pro- duction and decays have to be extremely small. However, extensions of the SM, invariably lead to new CP  violating phase(s). Indeed in most exten- sions new CP violating phases appear rather natu- rally. In fact getting rid of non-standard phases in extensions of the SM may be as unnatural as it is to get rid of the CKM phase from the three gener- ation SM. Since it is widely believed that the SM cannot account for baryogenesis CP violation from new physics is very likely a necessity. Therefore, it is important for us to  seek optimal strategies to expose different types of non-standard CP vi- olating phases. Based on studies that are so far available the prominent effects of different types of phases appears to be the following: 1.  Dipole moment of the top quark could be large enough, most effectively due to phase(s) from the neutral Higgs sector, to be experimentally accessible!+ Presenter 2. 3. 4. SUSY phase(s) cause interesting partial rate asymmetry (PRA) effects in decays of the type t + Wb5* The transverse polarization of the T in the decay t + brv is very sensitive to phase(s) originating from the charged Higgs sector. CP violating phase(s) due to H o  exchanges cause large asymmetries??') in e+e- 3 tfHo and in e+e- + i f~ , t?~ , . '~~"  2 Top Polarimetry The fact that the top is so heavy has the impor- tant consequence that the top quark does not bind into hadrons. All CP violation in the top quark is therefore direct CP. Spin of the top quark be- comes a very important observable and its decays become very effective analyzers of its spin!2 The polarization of the top-quark is strongly correlated to the directions of the momentum of the charged lepton in t + blue, or to the W-momentum in t + bW, or to the direction of the most energetic jet in t + b + 2 j e t ~ ! ~ ~ ' ~  The ability to track the top spin thus plays a crucial role in CP violation tests involving the top quark. 3 Dipole Moment of the Top-Quark In many extensions of the SM the top quark can acquire dipole moment at one loop order!>2 For example, CP  violation phase from a neutral Higgs sector can cause top dipole moment of or- der 10-20e-cm i.e. about ten orders of magnitude more than in the SM wherein one needs to go to at least two loop order and i t  is expected to be X 10-30e-cm. Much attention has recently been given to detection of the dipole moment form fac- tor. ‘i3* It should be clear that  the form factor has not only a real part but there is also an imag- inary part arising at q2 2 4m:. Since the life-time of the top quark is so short form factor extraction requires simultaneous studies of production and subsequent decay. A multitude of (CP Violating) observables that are ?‘’-odd or TN-even can be constructed using beam polarization, beam mo- menta, t ,  t momenta and/or momenta of various decay products?n3* Under these circumstances it is natural to search for an optimal observable: namely, one that is the most efficient for the deter- mination of (e.g.) the real or the imaginary part of the dipole moment form factor for a fixed value of q2 .  Separating the differential cross-section into a CP conserving (EO) and a CP violating (El) piece4 4 4 )  = &(4) + XCl(4) (1) then the optimal observable, for determination of the dipole moment A is given by4 Oopt = Cl(d)/CO(dJ) (2) Studies have shown that the anticipated lu- minosity at the NLc5-I7 of 5 x cm-2s-1 l4 should be able to give limits on X to the level of - 10-lge-cm at one sigma? Thus observation of the top dipole moments that are expected in the- oretical extensions would present somewhat of a challenge but their feasibility cannot be excluded. 4 Two studies indicate that, in decays of the type 1 + W6, SUSY phase(s) can lead to  PRA up to a few %. Experimentally there are two ways to look for these effects. Firstly PRA can be searched for by comparing &b with Vr,. The expectations are that at the NLC, & can be measured to a precision of a few %b1517 So a difference between 146 and V s  less than about 10% would be rather difficult to detect. Incidentally, asecond way to search for a PRA would be to determine the BR for decays that are not accompanied by a beauty quark i.e. BR into “ugly decays” of the top quark. This would yield the effective CKM angle 14, into non-beauty PRA and the Supersymmetric Phas&‘ 2 decays. Separation into decays that contain a prompt d-quark versus a prompt s-quark is prob- ably quite unrealistic. However for the purpose of PRA this separation is not necessary. Since PRA in t -+ Wb can only arise if there are (non- standard) decays of the top, which provide the needed absorptive parts, it means that CKM uni- tarity must be violated by &, i.e. 1%12 # [I - IW21 (3) For this type of precision studies at the NLC experiments must be able to search for such “ugly decays” (i.e. top decays not accompanied by prompt beauty) with high efficiency. Of course efficiency in 6-tagging is also extremely important. 5 Transverse Polarization of the T due to a Charged Higgs Phase.7 The transverse polarization of tlic T in the de- cay t + brv is extremely scnsit.ive to the pres- ence of a CP violating phase from the charged Higgs sector. The effects are large as they orig- inate from tree level interferences and also the W -  propagator is on-shell and causes a “resonance” enhancement. There is a CP-odd, TN-odd trans- verse polarization asymmetry sensitive to the real part of the W-propogator and a CP-odd, TN- even transverse polarization asymmetry that is driven by the imaginary part of the resonant W -  propogator. The second type of asymmetry does not occur in I< -+ npu or B + D(D*).rv . .  . In top decays both types of asymmetries are quite large. For m H  - 200 GeV they can be as big as 50% and for m H  - 400 GeV they can be in the range 5-20%. At the NLC, at  6 = 500 GeV, with a luminosity of 5 x cm-2s-1 we may be able to probe asymmetries larger than about 6% with three sigma sensitivity. Clearly, the ability to measure the polarization of the T would be a very important feature in experiments at the NLC. 6 Neutral Higgs CP in e+e-  + t f H o .  CP violation phase due to a neutral Higgs sector leads to very interesting effects that occur through the interference of two tree graphs (see Fig.l)s Without using beam polarization and/or t ,  5 spin, there is only one triple correlation that is possible, i.e. (&+ - f ie - )  . (& x 6-). The resulting, TN-odd, ... 111 So -4, and A;  are T~-even requiring absorptive parts whereas A ,  is ?'N-odd requiring real Feyn- man amplitude. Therefore A, arises from interfer- ence among the t.ree level graphs in Fig. 2. Near resonance A, also arises primarily from these tree graphs; the lliggs width provides the necessary absorptive parts. /I,, though, receives additional contributions from loop graphs. In addition to CP violating polarization asym- metries there is also an interesting CP-even, TN- odd asymmetry that is quite sizable. we should be able to use it to determine the Higgs width in Figure 1: Tree-level Feynman diagrams contributing to CP violation in e+ e- --t tFHo in the two Higgs doublet model asymmetries arc in the 10-25% range. The cross section is about a few fb. Thus these asymme- tries should be observable if the projected lumi- nosity of 2 x cm-2s-1 could be reached for a 1 'TeV machine. The method is most suitable for a relatively light Higgs, m H 0  S 2mw, as then the BR(IIo -+ bb) is substantial. Gunion et a18 have extended tfrr study of this reaction. With the use of gencralizcd optimal observables they claim that at  E = 1.5 're\* the NLC would enable determi- nation of the basic couplings for Hft, Hf-yst and H Z Z  vertices and thereby clarify the nature of the Higgs boson? 7 Neutral Higgs Phase in e+e- + ui;w+ w-. This reaction is extremely interesting as it also leads to a TN-odd polarization asymmetry that arises at tree-level!' Furthermore, the resonant Higgs propagator leads to enhanced effects result- ing in the possibility of substantia1 asymmetries SM causes negligible CP violating effects in top physics whereas many types of extensions lead to large effects therein. The top can receive a large dipole moment from neutral Higgs CP. The latter can also cause significant asymmetries in e+e-  + tfHo and e+e- + tfueCe arising at tree level. SUSY phase(s) can cause PRA in t + Wb. Phase(s) from the charged Higgs sector result in large transverse polarization of T in 1 -+ b w .  There is thus the exciting possibility that the parameters needed for understanding of baryoge- nesis could be extracted or verified through CP - 10-50%. The relevant Feyninan graphs are shown in Fig. 2. Actually there are three types of polarization asymmetries that are of interest. To define these let us introduce, in the rest frame of the t ,  the ba- sis vectors: -i,a(&+ + &-); iycr(p;.V+ x p'w-) and 2, = i, xi,. Let Pj (for j = c ,  g, 2) be the po- larization of the t along i,, 2, or i,. Similarly for f. Combining the information from t , i  we define the C P  violating asymmetries: SM as well as in its extensions. The works of Ref. lO,ll, on the reaction e+e- + tfveCe, are complementary. Ref. 10 deals with interference of a neutral Higgs exchange with the other SM graphs of Fig. 2. Ref. 11 ignores that contribution to CP violation and focuses pri- marily on interference between two neutral Higgs occurring in a 2HDM. 3 w, t / \t Figure 2: The Feynrnan diagrams that participate in the subprocess W +  W- + tZ. The blob in Fig.2a represents the width of the Higgs resonance and the cut across the blob is to indicate the imaginary part. violation studies of the top quark in accelerator experiments. Acknowledgments This research was supported in part by the US- DOE contracts DC-AC05-84ER40150 (CEBAF) and DGAC-76CH00016 (BNL). References Cuypers and S.D. Rindani, Phys. Lett. B 343, 333 (1995) 4. D. Atwood and A. Soni, Phys. Reo. D 45, 2405 (1992). 5. B. Grzadkowski and W.Y. Keung, Phys. Lett. B 319, 526 (1993). 6. E. Christovaand M. Fabbrichesi, Phys. Lett. B 320, 229 (1994). 7. D. Atwood, G.  Eilarn and A .  Soni, Phys. Rev. Lett. 71, 492 (1993). 8. S .  Bar-Shalom et ai., Phys. Reo. D 53, 1162 (1996). 9. J.F. Gunion, B. Grzadkowski and X.-G. He, preprint UCD-96- 14. 10. D. Atwood and A. Soni, preprint JLAB-TH- 11. A. Pilaftsis and M. Nowakowski, Int. Jour. of Mod. Phy. A 9, 1097 (1994). 12. See e.g. C.R. Schmidt and M. Peskin, Ref. 3; G.L. Kane, G.A. Ladinsky and C.P. Yuan, PRD 45, 124 (1992); D. Atwood, A. Aeppli and A. Soni, Phys. Rev. Lett. 69, 2754 (1992). 13. B. Grzadkowski and J . F .  Gunion, Phys. Lett. B 350, 218 (1995). 14. D. Atwood and A. Soni, Phys. Rev. D 52 ,  6271 (1995). 15. Proceedings of the Workshop on Physics and Experiments with Linear e+e-  Collid- ers, Eds. F. Harris, S. Olsen, S. Pakvasa and X. Tata, World Scientific, Singapore 1996. 16. Proceedings of the Workshop on Physics and Experiments with Linear Colliders, Eds. A. Miyamoto and Y. Fuji, World Scientific, Sin- 17. H. Murayama and M. Peskin, preprint 96-14. . gapore, 1996. SLAC-PUB-7149 (hepex/9606003). 1. W. Bernreuther, T. Schrooder and T.N. Pham, Phys. Lett. B 279, 389 (1992). 2. A. Soni and R. Xu, Phys. Rev. Lett. 69, 33 (1992). 3. C.R. Schmidt and M. Peskin, Phys. Rev. Lett. 69, 410 (1992); W. Bernreuther and P. Overman, preprint hep-ph/9511256; F. 

CP violation in top physics at the NLC

Top quark is extremely sensitive to non-standard CP violating phases. General strategies for exposing different types of phases at the NLC are outlined. SUSY phase(s) cause PRA in t {r_arrow} Wb. The transverse polarization of the {tau} in the reaction t {r_arrow} b{tau}{nu} is extremely sensitive to a phase from the charged Higgs sector. Phase(s) from the neutral Higgs sector cause appreciable dipole moment effects and lead to sizable asymmetries in e{sup +}e{sup {minus}} {r_arrow} t{anti t}H{sup 0} and e{sup +}e{sup {minus}} {r_arrow} t{anti t}{nu}{sub e}anti({nu}{sub e})

hep-ph/9609418   20 Sep 1996CP VIOLATION IN TOP PHYSICS AT THE NLCD. ATWOODTheory Group, National Jeerson Lab,A. SONIaTheory Group, Brookhaven National Laboratory, Upton, NY 11973Top quark is extremely sensitive to non-standard CP violating phases. General strategies for exposing dierenttypes of phases at the NLC are outlined. SUSY phase(s) cause PRA in t! Wb. The transverse polarization ofthe  in the reaction t! b is extremely sensitive to a phase from the charged Higgs sector. Phase(s) from theneutral Higgs sector cause appreciable dipole moment eects and lead to sizable asymmetries in e+e  ! ttH0and e+e  ! ttee.1 IntroductionThe standard model (SM) with three families andthe CKM phase gives a natural explanation for thesize of the observed CP asymmetry in the neutralkaon complex. It also strongly suggests the pres-ence of large CP asymmetries in B-decays makingB-physics very suitable for precision extraction ofthe CKM phase and a quantitative check of theunitarity triangle. Furthermore, the minimumSMwith mt  175 GeV >> mb;md;ms also leads tothe conclusion that CP violation eects in top pro-duction and decays have to be extremely small.However, extensions of the SM, invariably lead tonew CP violating phase(s). Indeed in most exten-sions new CP violating phases appear rather natu-rally. In fact getting rid of non-standard phases inextensions of the SM may be as unnatural as it isto get rid of the CKM phase from the three gener-ation SM. Since it is widely believed that the SMcannot account for baryogenesis CP violation fromnew physics is very likely a necessity. Therefore,it is important for us to seek optimal strategiesto expose dierent types of non-standard CP vi-olating phases. Based on studies that are so faravailable the prominent eects of dierent typesof phases appears to be the following:1. Dipole moment of the top quark couldbe large enough, most eectively due tophase(s) from the neutral Higgs sector, tobe experimentally accessible.1{4aPresenter2. SUSY phase(s) cause interesting partial rateasymmetry (PRA) eects in decays of thetype t!Wb.5{63. The transverse polarization of the  in thedecay t ! b is very sensitive to phase(s)originating from the charged Higgs sector. 74. CP violating phase(s) due to H0 exchangescause large asymmetries8;9 in e+e  ! ttH0and in e+e  ! ttee.10;112 Top PolarimetryThe fact that the top is so heavy has the impor-tant consequence that the top quark does not bindinto hadrons. All CP violation in the top quarkis therefore direct CP. Spin of the top quark be-comes a very important observable and its decaysbecome very eective analyzers of its spin.12 Thepolarization of the top-quark is strongly correlatedto the directions of the momentum of the chargedlepton in t ! b``, or to the W -momentum int! bW , or to the direction of the most energeticjet in t ! b + 2jets.13;14 The ability to track thetop spin thus plays a crucial role in CP violationtests involving the top quark.3 Dipole Moment of the Top-QuarkIn many extensions of the SM the top quarkcan acquire dipole moment at one loop order.1;2For example, CP violation phase from a neutralHiggs sector can cause top dipole moment of or-der 10 20e cm i.e. about ten orders of magnitude1more than in the SM wherein one needs to go toat least two loop order and it is expected to be< 10 30e cm. Much attention has recently beengiven to detection of the dipole moment form fac-tor. 1;3{4 It should be clear that the form factorhas not only a real part but there is also an imag-inary part arising at q2  4m2t . Since the life-timeof the top quark is so short form factor extractionrequires simultaneous studies of production andsubsequent decay. A multitude of (CP Violating)observables that are TN -odd or TN -even can beconstructed using beam polarization, beam mo-menta, t, t momenta and/or momenta of variousdecay products.1;3{4 Under these circumstances itis natural to search for an optimal observable,3namely, one that is the most ecient for the deter-mination of (e.g.) the real or the imaginary part ofthe dipole moment form factor for a xed value ofq2. Separating the dierential cross-section into aCP conserving (0) and a CP violating (1) piece4() = 0() + 1() (1)then the optimal observable, for determination ofthe dipole moment  is given by40opt = 1()=0() (2)Studies have shown that the anticipated lu-minosity at the NLC15{17 of 5  1033 cm 2s 1 14should be able to give limits on  to the level of 10 19e-cm at one sigma.4 Thus observation ofthe top dipole moments that are expected in the-oretical extensions would present somewhat of achallenge but their feasibility cannot be excluded.4 PRA and the Supersymmetric Phase5;6Two studies indicate that, in decays of the typet ! Wb, SUSY phase(s) can lead to PRA up toa few %. Experimentally there are two ways tolook for these eects. Firstly PRA can be searchedfor by comparing Vtb with Vtb. The expectationsare that at the NLC, Vtb can be measured to aprecision of a few %.15{17 So a dierence betweenVtb and Vtb less than about 10% would be ratherdicult to detect.Incidentally, a second way to search for a PRAwould be to determine the BR for decays thatare not accompanied by a beauty quark i.e. BRinto \ugly decays" of the top quark. This wouldyield the eective CKM angle Vtx into non-beautydecays. Separation into decays that contain aprompt d-quark versus a prompt s-quark is prob-ably quite unrealistic. However for the purposeof PRA this separation is not necessary. SincePRA in t ! Wb can only arise if there are (non-standard) decays of the top, which provide theneeded absorptive parts, it means that CKM uni-tarity must be violated by Vtx i.e.jVtxj2 6= [1  jVtbj2] (3)For this type of precision studies at the NLCexperiments must be able to search for such\ugly decays" (i.e. top decays not accompaniedby prompt beauty) with high eciency. Of courseeciency in b-tagging is also extremely important.5 Transverse Polarization of the  due toa Charged Higgs Phase.7The transverse polarization of the  in the de-cay t ! b is extremely sensitive to the pres-ence of a CP violating phase from the chargedHiggs sector. The eects are large as they orig-inate from tree level interferences and also the W -propagator is on-shell and causes a \resonance"enhancement. There is a CP-odd, TN -odd trans-verse polarization asymmetry sensitive to the realpart of the W -propogator and a CP-odd, TN -even transverse polarization asymmetry that isdriven by the imaginary part of the resonant W -propogator. The second type of asymmetry doesnot occur in K !  or B ! D(D). . . . Intop decays both types of asymmetries are quitelarge. For mH  200 GeV they can be as big as50% and for mH  400 GeV they can be in therange 5{20%. At the NLC, atps = 500 GeV,with a luminosity of 5 1033 cm 2s 1 we may beable to probe asymmetries larger than about 6%with three sigma sensitivity. Clearly, the ability tomeasure the polarization of the  would be a veryimportant feature in experiments at the NLC.6 Neutral Higgs CP in e+e  ! ttH0.CP violation phase due to a neutral Higgs sectorleads to very interesting eects that occur throughthe interference of two tree graphs (see Fig.1).8Without using beam polarization and/or t, t spin,there is only one triple correlation that is possible,i.e. (~pe+   ~pe )  (~pt  ~pt). The resulting, TN -odd,2e+e-iiiqqZ, γe+e-qqZ Z, χHe+e-qqZ, γHH0000i iiFigure 1: Tree-level Feynman diagrams contributing to CPviolation in e+e  ! ttH0 in the two Higgs doublet modelasymmetries are in the 10{25% range. The crosssection is about a few fb. Thus these asymme-tries should be observable if the projected lumi-nosity of 2 1034 cm 2s 1 could be reached for a1 TeV machine. The method is most suitable fora relatively light Higgs, mH0 < 2mW , as then theBR(H0 ! bb) is substantial. Gunion et al.9 haveextended the study of this reaction. With the useof generalized optimal observables they claim thatat E = 1:5 TeV the NLC would enable determi-nation of the basic couplings for Htt, Ht5t andHZZ vertices and thereby clarify the nature of theHiggs boson.97 Neutral Higgs Phase in e+e  !W+W .This reaction is extremely interesting as it alsoleads to a TN -odd polarization asymmetry thatarises at tree-level.10 Furthermore, the resonantHiggs propagator leads to enhanced eects result-ing in the possibility of substantial asymmetries 10{50%. The relevant Feynman graphs areshown in Fig. 2.Actually there are three types of polarizationasymmetries that are of interest. To dene theselet us introduce, in the rest frame of the t, the ba-sis vectors:  êz(~pW+ + ~pW  ); êy(~pW+  ~pW  )and êx = êyêz. Let Pj (for j = x; y; z) be the po-larization of the t along êx, êy or êz . Similarly fort. Combining the information from t; t we denethe CP violating asymmetries:Ax =12(px + px); Ay =12(py   py)Az =12(pz + pz) (4)So Ax and Az are TN -even requiring absorptiveparts whereas Ay is TN -odd requiring real Feyn-man amplitude. Therefore Ay arises from interfer-ence among the tree level graphs in Fig. 2. Nearresonance Ax also arises primarily from these treegraphs; the Higgs width provides the necessaryabsorptive parts. Az, though, receives additionalcontributions from loop graphs.In addition to CP violating polarization asym-metries there is also an interesting CP-even, TN -odd asymmetry that is quite sizable. We shouldbe able to use it to determine the Higgs width inSM as well as in its extensions.The works of Ref. 10,11, on the reactione+e  ! ttee, are complementary. Ref. 10 dealswith interference of a neutral Higgs exchange withthe other SM graphs of Fig. 2. Ref. 11 ignoresthat contribution to CP violation and focuses pri-marily on interference between two neutral Higgsoccurring in a 2HDM.8 SummarySM causes negligible CP violating eects in topphysics whereas many types of extensions leadto large eects therein. The top can receive alarge dipole moment from neutral Higgs CP. Thelatter can also cause signicant asymmetries ine+e  ! ttH0 and e+e  ! ttee arising at treelevel. SUSY phase(s) can cause PRA in t ! Wb.Phase(s) from the charged Higgs sector result inlarge transverse polarization of  in t! b.There is thus the exciting possibility that theparameters needed for understanding of baryoge-nesis could be extracted or veried through CP3ttZ,WWttWWH HttbWW(c)(b)(a)Figure 2: The Feynman diagrams that participate in thesub-process W+W  ! tt. The blob in Fig.2a representsthe width of the Higgs resonance and the cut across theblob is to indicate the imaginary part.violation studies of the top quark in acceleratorexperiments.AcknowledgmentsThis research was supported in part by the US-DOE contracts DC-AC05-84ER40150 (CEBAF)and DE-AC-76CH00016 (BNL).References1. W. Bernreuther, T. Schrooder and T.N.Pham, Phys. Lett. B 279, 389 (1992).2. A. Soni and R. Xu, Phys. Rev. Lett. 69, 33(1992).3. C.R. Schmidt and M. Peskin, Phys. Rev.Lett. 69, 410 (1992); W. Bernreuther andP. Overman, preprint hep-ph/9511256; F.Cuypers and S.D. Rindani, Phys. Lett. B343, 333 (1995)4. D. Atwood and A. Soni, Phys. Rev. D 45,2405 (1992).5. B. Grzadkowski and W.Y. Keung, Phys.Lett. B 319, 526 (1993).6. E. Christova and M. Fabbrichesi, Phys. Lett.B 320, 229 (1994).7. D. Atwood, G. Eilam and A. Soni, Phys.Rev. Lett. 71, 492 (1993).8. S. Bar-Shalom et al., Phys. Rev. D 53, 1162(1996).9. J.F. Gunion, B. Grzadkowski and X.-G. He,preprint UCD-96-14.10. D. Atwood and A. Soni, preprint JLAB-TH-96-14.11. A. Pilaftsis and M. Nowakowski, Int. Jour.of Mod. Phy. A 9, 1097 (1994).12. See e.g. C.R. Schmidt and M. Peskin, Ref.3; G.L. Kane, G.A. Ladinsky and C.P. Yuan,PRD 45, 124 (1992); D. Atwood, A. Aeppliand A. Soni, Phys. Rev. Lett. 69, 2754(1992).13. B. Grzadkowski and J.F. Gunion, Phys.Lett. B 350, 218 (1995).14. D. Atwood and A. Soni, Phys. Rev. D 52,6271 (1995).15. Proceedings of the Workshop on Physicsand Experiments with Linear e+e  Collid-ers, Eds. F. Harris, S. Olsen, S. Pakvasa andX. Tata, World Scientic, Singapore 1996.16. Proceedings of the Workshop on Physics andExperiments with Linear Colliders, Eds. A.Miyamoto and Y. Fuji, World Scientic, Sin-gapore, 1996.17. H. Murayama and M. Peskin, preprintSLAC-PUB-7149 (hep-ex/9606003).4

CP Violation in Top Physics at the NLC

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