New Physics search via WW-fusion at the ILC

New Physics search via WW-fusion at the ILC

Koji TSUMURA (Osaka Univ. → KEK after April)in collaboration with S. Kanemura & K. Matsuda

KEK Theory Meeting on Particle Physics Phenomenology 2007 Mar. 1-3

KEK-PH 07 Mar. 1-3 Koji TSUMURA 2/15

Introduction

• 4-fermi interaction has been tested in collision & decays.• ee -> WW has been well examined @ LEP by using helicity an

alysis.

• For Higgs boson & heavy fermions, we would like to study vector boson fusion (WW-fusion) process.– Higgs boson strongly couples to heavy particles.

Kanemura, Nomura, Tsumura, PRD74:076007,2006Larios et.al. hep-ph/9709316Asakawa, Hagiwara, Eur.Phys.J.C31:351,2003Grzadkowski et.al. JHEP 0511:029,2005Cho, Hagiwara et.al. PRD73:054002,2006

Gaemews et.al. Z.Phys.C1:259,1979 Hagiwara et.al. Nucl.Phys.B282:253,1987 Hagiwara et.al. NPB496,66,1996


New Physics search via top-Higgs interaction

– For lighter Higgs boson (SUSY like scenario)• ee -> ttH associate production

– For heavier or intermediate Higgs boson masses

• If theory has (relatively) heavy Higgs, WW-fusion can be an useful probe.

(Effective theory approach, extra Higgs, Little Higgs, Extra-D, Top Color, etc.)

T. Han, et. al. PRD61, 015006 (2000)


Effective theory approach

– Below the new physics scale , the non-SM int. is characterized by higher dimension operators.

– The coupling strength can be calculated in each model.– ex. MSSM Feng, Li, Maalampi PRD69,115007

– ex. Extra Higgs


– Complete set of gauge invariant dim.6 ops. Has been discussed.

Buchmuller et. al in NPB268, 621 (1986)

• 4-fermi operators • Scalar only (6 scalar, 4 scalar + 2 derivative)• Scalar & vector operators• 2-fermi operators (Yukawa + 2 scalar)• 2-fermi operators (Yukawa + 2 derivative [2 vector] )… so many operators !!

– We introduce these dim.6 ops. for 3rd generation quarks. • Bottom quark operators are strongly constrained by Z→bb.

Dimension-six operators


Experimental limits

– Direct search• No experimental bound for .• There are no stringent bounds for

by vector boson exchange processes at LEP and Tevatron.

ex. for

– Precision data• can give oblique corrections.

Hikasa et. al. PRD58, 114003 (1998)

Gounaris et. al. PRD52, 451 (1995)

has no linear contribution.

Ot1 : no experimental boundOt3 : weaker bound from oblique correctionODt : smaller ⊿ρ compare to t2, tWΦ, tBΦ

In this talk, we concentrate on three dim.6 operators Ot1: direct correction for top-Yukawa

ODt: correction for top-Yukawa including derivativesOt3: right-handed vector interaction


Unitarity bounds– Tree level unitarity for dim.6 ops. Has been discussed. Gounaris et. al. in Z. Phys. C76, 333

(1997).

• Imposing unitarity @ • Considering 2-body scattering channels (hh, WLWL, ZLZL,

hZL and t anti-t), then we obtained


Effects of dimension-six coupling– Effective top-Yukawa

– Decay width for Higgs boson Kanemura Nomura Tsumura PRD74, 076007 (2006) • For , non-SM effect (only 　 ) can be observed i

n the top-pair production .• For lighter Higgs mass, loop induced decays

can be enhanced.• For , we can not reach non-SM effect.

(main ) FIG. 1: The top pair production via W boson fusion

Ci Set A Set B Set C Set D Set E

C t1 0 ¡ 16¼3p

2¤v + 16¼

3p

2¤v 0 0

CDt 0 0 0 +10:2 ¡ 6:2

TABLE I : Sets of the dimension-six couplings we used for the analyses.

dimension-six operators Oi can beconstrained theoretically by using theidea of partial wave

unitarity[15]. Due to thestructureof a dimension-six operator, the two-body elastic scatter-

ing amplitudes is proportional to the square of thescattering energy, so that the coe±cient

becomes strong at someenergy scale, and violate tree-level unitarity. T he unitarity bounds

for thecoe±cients Ci=¤2 areobtained by setting the scaleof unitarity violation to beabove

¤. T he bounds for Ct1 and CD t are evaluated as

jCt1j ·16¼

3p

2

µ¤v

¶; (8)

¡ 6:2 · CD t · 10:2: (9)

These results are almost the same as those in Ref. [13].

The value of the anomalous coupling Ct1 is free from the constraint from current exper-

imental data[16, 24], because it only a®ects the genuine interaction between the top quark

and the Higgs boson which has not been measured yet. T herefore, only the theoretical

consideration such as perturbativeunitarity is important to constrain this operator. On the

other hand, CD t turns out to receive strong experimental limits from the electroweak rho

parameter result[16, 25, 26], since theoperator OD t changes the interaction of the top quark

6


– Solid , dotted – The non-SM (t1,Dt) effect can be

significant under the unitarity bounds.

WW-fusion @ ILC Kanemura Nomura Tsumura PRD 74, 076007 (2006)

SMSM

The non-SM (t1,Dt) effect can be significant under the unitarity bounds.

How to extract more information ?

Smaller dim.6 coupling ?Smaller Higgs mass ?

Much operators ?Separate each operator ?


Helicity amplitude for WW-fusion

– Amplitudes are calculated which respect to W-boson helicity and t-quark spin.

• To obtain further information, we consider top-quark spin correlations.

• By using W-boson helicity, each amp. can be checked by BRS sym.

• In this talk, we concentrate on the WW-fusion sub-process.FIG. 4: Feynman diagrams for the subprocess W ¡ W + ! t¹t in the SM.

FIG. 5: T he helicity cross sections for W ¡¸ W +

¹ ! t¹t as a function of the collision energyp

s in

the SM, where ¸ (¹ ) is the helicity of the incoming W ¡ (W +) boson. T he mass mH of the Higgs

boson is set to be 500 GeV.

OD t. The results for the decay branching ratios are shown in Fig. 3 for Set A, Set B, ¢¢¢,

and Set E. We note that in Set E a cancellation of the branching ratio of H ! t¹t can be

seen between theSM contribution and that from OD t around mH » 600 GeV. T his happens

since the ¯rst term and the third term in the right-hand side of Eq. (11) cancel each other

when m2H = ¡ q2 ' (600GeV)2.

I I I . SU B P ROC E SS

Weherestudy thecross section for thesubprocess W ¡ W + ! t¹t[27]. By using the results

in this section, we evaluate the cross section of the full process e¡ e+ ! W ¡ W +º ¹º ! t¹tº ¹º

in thethee®ectiveW approximation (EWA)[28] in Sec. IV , and compareit to thenumerical

results of calculation of the full matrix elements by the full useof thepackages CalcHEP[29]

and LanHEP[30].

In theSM, Feynman diagrams for thesubprocess areshown in Fig. 4. Cross sections ¾SM¸ ¹

for thehelicity amplitudes of W ¡¸ W+

¹ ! t¹t with helicity sets (¸, ¹ ) areshown as a function

9


WW-fusion in the SM

LL polarized WW is dominant.

Effect of top-Yukawa

Other polarization sets


WW-fusion with Ot1

Higgs width become wide

Not changed !!

Enhanced by the effect of effective top-Yukawa


WW-fusion with ODt

Enhanced by the effect of effective top-Yukawa

Enhancement from the t-channel process Direct effect of Dt

Energy dependence differ from t1


WW-fusion with Ot3

little enhancement through t-channel

Strongly modified vector int. in right-handed vector current


Summary

– New Physics effect can be seen in WW-fusion.– dim.6 operators can be distinguished by using helicity metho

d (top-spin correlation)• We concentrate on the WW-fusion sub-process.• We should calculate spin correlation for the full-process.

• We should estimate detectable

size of dim.6 coupling.

– Issues• Smaller values of dim.6 coupling.

(not only t1,Dt,t3 but also t2, tWΦ,tBΦ)• Lighter Higgs


WW-fusion @ ILC Kanemura Nomura Tsumura PRD 74, 076007 (2006)

– Dotted curves are calculated by using the package CalcHEP.• The EWA results agree with those of CalcHEP in about

20-30 % error for heavier Higgs boson.

SM

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New Physics search via WW-fusion at the ILC