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Particle Physics

Probing CP-violating Higgs contributions in γγ → ff

Profile image of Rohini M GodboleRohini M Godbole

2007, Pramana

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Abstract

We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct polarization asymmetries which can isolate the contribution of a Higgs boson φ in γγ → ff , f = τ /t, from that of the QED continuum. This can help in getting information on the γγφ coupling in case φ is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case φ has indeterminate CP. Furthermore, we take the MSSM with CP violation as an example to demonstrate the potential of these asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well as its CP properties over a wide range of MSSM parameters. In particular, the method suggested can cover the region where a light Higgs boson may have been missed by LEP due to CP violation in the Higgs sector, and may be missed as well at the LHC.

Figures (17)
FIG. 1: Feynman diagrams contributing to yy — ff produc- tion. to the CP-even and CP-odd parts. At both colliders, the LHC and the ILC, the determination of the CP quantum number of the Higgs boson seems feasible, while deter- mination of CP mixing seems difficult; the best chance for the latter being offered by the exploitation of the f f¢ coupling [15].
FIG. 1: Feynman diagrams contributing to yy — ff produc- tion. to the CP-even and CP-odd parts. At both colliders, the LHC and the ILC, the determination of the CP quantum number of the Higgs boson seems feasible, while deter- mination of CP mixing seems difficult; the best chance for the latter being offered by the exploitation of the f f¢ coupling [15].
TABLE I: Combinations of form factors vy, af, Ay and By that occur in the helicity amplitudes of Eqs. (4) and (5). The form factors A, and B, are complex whereas vf, ar can be taken to be real without loss of generality. The non-standard vertices given by Eqs. (1) and (3) involve four independent form factors: vy, af, Ay, B,. In the MSSM with CPV, these form factors are functions of var- ious model parameters: tan 8; myz+; (||, ®,,); (|Azl, ® 7); (|Mi|,®:), i = 1,2,3; mg7; ete., where (|z|,®z) denotes x = |ale’?=
TABLE I: Combinations of form factors vy, af, Ay and By that occur in the helicity amplitudes of Eqs. (4) and (5). The form factors A, and B, are complex whereas vf, ar can be taken to be real without loss of generality. The non-standard vertices given by Eqs. (1) and (3) involve four independent form factors: vy, af, Ay, B,. In the MSSM with CPV, these form factors are functions of var- ious model parameters: tan 8; myz+; (||, ®,,); (|Azl, ® 7); (|Mi|,®:), i = 1,2,3; mg7; ete., where (|z|,®z) denotes x = |ale’?=
FIG. 2: Luminosity distribution plotted against z (which is related to the yy invariant mass W = 2,/oiw2 via z = W/(2Ev)) for e- = 4.8. The solid line corresponds to AeAr = —1, the short-dashed line is for A.A; = 1, and the long-dashed one for AeA; = 0. The conversion distance is taken to be zero. The grey patch highlights the region 0.75 < z < 0.83.
FIG. 2: Luminosity distribution plotted against z (which is related to the yy invariant mass W = 2,/oiw2 via z = W/(2Ev)) for e- = 4.8. The solid line corresponds to AeAr = —1, the short-dashed line is for A.A; = 1, and the long-dashed one for AeA; = 0. The conversion distance is taken to be zero. The grey patch highlights the region 0.75 < z < 0.83.
TABLE II: Polarization observables and interactions and combinations that they can probe. the presence of a CP-conserving Higgs Py is zero. This is because the left chiral and the right chiral components of fermions couple to the Higgs boson with equal strength. Thus the net polarization of the fermions, if any, will sig- nal CP violation in the Higgs sector. In general it is a signal of P violation, but in the process under consider- ation f couples only to self-conjugate neutral particles, 7y and ¢. Hence Pr # 0 is also a signal of CP violation. We note that PY is a pure but a poor probe of CPV.
TABLE II: Polarization observables and interactions and combinations that they can probe. the presence of a CP-conserving Higgs Py is zero. This is because the left chiral and the right chiral components of fermions couple to the Higgs boson with equal strength. Thus the net polarization of the fermions, if any, will sig- nal CP violation in the Higgs sector. In general it is a signal of P violation, but in the process under consider- ation f couples only to self-conjugate neutral particles, 7y and ¢. Hence Pr # 0 is also a signal of CP violation. We note that PY is a pure but a poor probe of CPV.
FIG. 3: Variation of 6Pt, 56P~ and 6P© asa function of E» for a Higgs boson of mass 54 GeV. For a value of Ey in the grey patch, the mass of the Higgs boson matches with the yy invariant mass in the grey band shown in Fig. 2.
FIG. 3: Variation of 6Pt, 56P~ and 6P© asa function of E» for a Higgs boson of mass 54 GeV. For a value of Ey in the grey patch, the mass of the Higgs boson matches with the yy invariant mass in the grey band shown in Fig. 2.
TABLE III: List of MSSM parameters for the CPX scenario used as input for the programs CPsuperH and FeynHiggs. and to probe the CP properties of its couplings. In the CP-conserving MSSM, there exist three neutral Higgs bosons: the CP-even h,H and the CP-odd A. CP- viola gsino and viola ting phases of the MSSM parameters such as the hig- mass parameter ju, gaugino masses M; (i = 1, 2,3) trilinear couplings Ay (f = t,b,7), can induce CP tion in the Higgs sector via loops. This allows Higgs states with different CP to mix; the three mass eigen- states hence do not have definite CP. These states are deno ted by 61, ¢2 and ¢3 with their masses in increasing order. For the numerical analysis, we choose the so-called CPX [28] scenario with parameters as listed in Table TI. In this scenario, one can have large CP-violating effects in the Higgs sector depending upon the size of the phases of the trilinear couplings A; »,-. Due to this large CP vi- olation, the coupling of the lightest state ¢, to vector
TABLE III: List of MSSM parameters for the CPX scenario used as input for the programs CPsuperH and FeynHiggs. and to probe the CP properties of its couplings. In the CP-conserving MSSM, there exist three neutral Higgs bosons: the CP-even h,H and the CP-odd A. CP- viola gsino and viola ting phases of the MSSM parameters such as the hig- mass parameter ju, gaugino masses M; (i = 1, 2,3) trilinear couplings Ay (f = t,b,7), can induce CP tion in the Higgs sector via loops. This allows Higgs states with different CP to mix; the three mass eigen- states hence do not have definite CP. These states are deno ted by 61, ¢2 and ¢3 with their masses in increasing order. For the numerical analysis, we choose the so-called CPX [28] scenario with parameters as listed in Table TI. In this scenario, one can have large CP-violating effects in the Higgs sector depending upon the size of the phases of the trilinear couplings A; »,-. Due to this large CP vi- olation, the coupling of the lightest state ¢, to vector
FIG. 4: CPX scenario: contours of (a) Ay (see Eq.(2)) for V=W,Z, (b) me, and (c) (Mo ~ m¢,)/(T 1 + P49) com- puted with CPsuperH as well as FeynHiggs.
FIG. 4: CPX scenario: contours of (a) Ay (see Eq.(2)) for V=W,Z, (b) me, and (c) (Mo ~ m¢,)/(T 1 + P49) com- puted with CPsuperH as well as FeynHiggs.
FIG. 5: Contours of constant 5P> in units of 10~? in the (tan G-mj;+) plane for the CPX scenario with ©:,,- = 0° (top panels) and ©; »,, = 90° (bottom panels) for the “peak Ey,” choice with dE = 1 GeV. The left panels show the results obtained with CPsuperH, the rights panels those obtained with FeynHiggs.
FIG. 5: Contours of constant 5P> in units of 10~? in the (tan G-mj;+) plane for the CPX scenario with ©:,,- = 0° (top panels) and ©; »,, = 90° (bottom panels) for the “peak Ey,” choice with dE = 1 GeV. The left panels show the results obtained with CPsuperH, the rights panels those obtained with FeynHiggs.
FIG. 6: Contours of constant 6P;* in units of 107? in the (tan@-m y+) plane for the CPX scenario with ®;»,, = 0° (to panels) and ®,»,, = 90° (bottom panels) for the “peak Ey” choice. The left panels show the results for dP, obtained wit! CPsuperH and the rights panels those for 6P;" obtained with FeynHiggs, see text.
FIG. 6: Contours of constant 6P;* in units of 107? in the (tan@-m y+) plane for the CPX scenario with ®;»,, = 0° (to panels) and ®,»,, = 90° (bottom panels) for the “peak Ey” choice. The left panels show the results for dP, obtained wit! CPsuperH and the rights panels those for 6P;" obtained with FeynHiggs, see text.
FIG. 7: Contours of constant 6PCP in units of 107? in the (tan@—-m,,+) plane for the CPX scenario with ©;,, = 90° and “peak Ey” choice. The left panel shows the results obtained with CPsuperH, the right panel those obtained with FeynHiggs.
FIG. 7: Contours of constant 6PCP in units of 107? in the (tan@—-m,,+) plane for the CPX scenario with ©;,, = 90° and “peak Ey” choice. The left panel shows the results obtained with CPsuperH, the right panel those obtained with FeynHiggs.
FIG. 8: Contours of constant 6P> in units of 107? for fixed E, and ®1,b,. = 0° and 90° using CPsuperH (left panels) and FeynHiggs (right panels) to compute the Higgs masses, couplings and widths. E, = 77 GeV, except for the lower-right plot where Ey = 82 GeV, see text.
FIG. 8: Contours of constant 6P> in units of 107? for fixed E, and ®1,b,. = 0° and 90° using CPsuperH (left panels) and FeynHiggs (right panels) to compute the Higgs masses, couplings and widths. E, = 77 GeV, except for the lower-right plot where Ey = 82 GeV, see text.
FIG. 9: Contours of constant 6P> in units of 10~? in the (®t,0,7 — m+) plane for tan @ = 30 and E, = 77 GeV with CPsuperH (left panel) and FeynHiggs (right panel).
FIG. 9: Contours of constant 6P> in units of 10~? in the (®t,0,7 — m+) plane for tan @ = 30 and E, = 77 GeV with CPsuperH (left panel) and FeynHiggs (right panel).
“IG. 10: Contours of constant 6P* in units of 10~? for fixed Ey» = 300 GeV and ;»,, = 0° (top) and 90° (bottom) using ‘PsuperH (left) and FeynHiggs (right) to compute the Higgs masses, couplings and widths.
“IG. 10: Contours of constant 6P* in units of 10~? for fixed Ey» = 300 GeV and ;»,, = 0° (top) and 90° (bottom) using ‘PsuperH (left) and FeynHiggs (right) to compute the Higgs masses, couplings and widths.
FIG. 11: Contours of constant 5PLP in units of 107? in the (®t,07 —m,+) plane for tan 3 = 4 and Ey = 300 GeV with CPsuperH (left panel) and FeynHiggs (right panel).
FIG. 11: Contours of constant 5PLP in units of 107? in the (®t,07 —m,+) plane for tan 3 = 4 and Ey = 300 GeV with CPsuperH (left panel) and FeynHiggs (right panel).
FIG. 12: Contours of constant 5PLP in units of 107? in the (®;,, — tan 3) plane for my+ = 475 GeV and E, = 300 GeV with CPsuperH (left panel) and FeynHiggs (right panel).
FIG. 12: Contours of constant 5PLP in units of 107? in the (®;,, — tan 3) plane for my+ = 475 GeV and E, = 300 GeV with CPsuperH (left panel) and FeynHiggs (right panel).
FIG. 13: Contours of constant 3 in units of 107? for “peak E,” and ®15,, = 30° and 90°; Higgs masses, couplings and widths computed with CPsuperH.
FIG. 13: Contours of constant 3 in units of 107? for “peak E,” and ®15,, = 30° and 90°; Higgs masses, couplings and widths computed with CPsuperH.
FIG. 14: Contours of constant A3 in units of 107? for fixed EF, = 300 GeV and 15,7 = 30° and 90°; Higgs masses, couplings and widths computed with CPsuperH.
FIG. 14: Contours of constant A3 in units of 107? for fixed EF, = 300 GeV and 15,7 = 30° and 90°; Higgs masses, couplings and widths computed with CPsuperH.

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Publisher’s Note: Probing CP-violating Higgs contributions in γγ→ff¯ through fermion polarization [Phys. Rev. D 74, 095006 (2006)]
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