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July 21- 22, 2005 Taipei Summer Institute. FCNC Z 0 Model and Effects in B Physics. Cheng-Wei Chiang National Central University & Academia Sinica. Enjoyable collaborations with: V. Barger, J. Jiang, H.-S. Lee, and P. Langacker

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fcnc z 0 model and effects in b physics

July 21- 22, 2005 Taipei Summer Institute

FCNC Z0 Model and Effects in B Physics

Cheng-Wei Chiang

National Central University & Academia Sinica

Enjoyable collaborations with:

V. Barger, J. Jiang, H.-S. Lee, and P. Langacker

PLB 580, 186(2004); 596, 229 (2004); 598, 218 (2004).

outline
Outline

-

  • Introduction to a FCNC Z0 boson
  • Collider constraints
  • Effects in low-energy effective Hamiltonian
  • Some hints of new physics in charmless |S| = 1 transitions
  • Bs mixing
  • Summary

FCNC Z' Boson (7/21/2005)

need for a z 0 boson
Need for a Z0 Boson

-

  • Extra heavy neutral Z0 gauge bosons exist in most extensions of the Standard Model and their supersymmetric versions.
  • Examples include GUT’s, extra-dimensional models, string models, little Higgs, etc.
  • The extra symmetry can forbid an elementary  term in SUSY, while allowing effective  and B terms to be generated at the U(1)0 breaking scale, providing a solution to the  problem.
  • Accompanying with the extra symmetry are some exotic fermions to cancel the anomaly and at least a Higgs singlet to break the symmetry.
  • Conclusion: for physics beyond the SM, the existence of a Z0 gauge boson is almost model-independent; only the details, such as the mass and couplings, are model specific.

FCNC Z' Boson (7/21/2005)

the fifth force
The Fifth Force

-

FCNC Z' Boson (7/21/2005)

fcnc z 0 boson
FCNC Z0 Boson

-

  • In the gauge eigenbasis, the Z0 neutral current Lagrangian is given by
  • In string models, it is possible to have family-nonuniversal Z0 couplings to fermion fields due to different constructions of the different families. [Chaudhuri et al, NPB 456, 89 (1995)]
  • After flavor mixing, one obtains FCNC Z0 interactions (non-diagonal) in the fermion mass eigenstates, which may lead to new CP-violating effects:
  • This may also imply flavor-violating Z couplings if there is Z-Z0 mixing.

FCNC Z' Boson (7/21/2005)

direct search at cdf run ii
Direct Search at CDF Run II

-

  • The mass of an extra Z0 from the non-observation of direct production (p anti-p→Z0 → l l) at CDF (√s = 1.96 TeV) is found to be ≥ 670 GeV (95% CL).[http://www-cdf.fnal.gov/physics/exotic/r2a/20040916.dilepton_zprime/]

The initial LHC reach will be 2 TeV (with power to discriminate among models) and can go up to 5 TeV.

FCNC Z' Boson (7/21/2005)

more constraints
More Constraints

-

  • Precision data also providestringent constraints.

[Erler and Langacker, Review of Particle Physics 2004]

FCNC Z' Boson (7/21/2005)

z z 0 mixing
Z-Z0 Mixing

-

  • The Z-Z0 mixing is given as

Z1 = ZSM cos + Z0 sin

Z2 = – ZSM sin + Z0 cos

  • The mixing angle  between Z and Z0 satisfies
  • LEP precision measurement of coupling constants at the Z-pole gives

| | < (a few) £ 10-3.

[Erler and Langacker, PLB 456, 68 (1999)]

  • This also implies a heavy Z0 boson.

FCNC Z' Boson (7/21/2005)

anomalies in hadronic b s q q transitions
Anomalies in Hadronicb → sq q Transitions

-

  • The sin2 measurements from various |S| = 1 B meson decays do not completely agree with the measurements from the charmonium modes.
  • These inconsistencies may have the same new physics origin.
  • Studies of the  KS mode, which has a simpler amplitude structure, indicates that it is likely to be polluted with a new EW penguin amplitude.

FCNC Z' Boson (7/21/2005)

k p anomaly
Kp Anomaly

-

  • Consider the following ratios of the BR’s of K  modes:
  • Rc and Rn should be the same in the SM. Possible explanations:
    • underestimate of p 0 detection efficiency, thus overestimating the BR’s of those corresponding modes;

[Gronau and Rosner, PLB 572, 43 (2003)]

    • Isospin-violating new physics contribution to color-allowed EW penguin amplitude.

[Buras et al, PRL 92, 101804 (2004); NPB 697, 133 (2004), hep-ph/0410407]

2.4s  1.9s

FCNC Z' Boson (7/21/2005)

low energy effective hamiltonian
Low-Energy Effective Hamiltonian

Z0

s

s

Z0

[Barger, CWC, Langacker and Lee, PLB 580, 186(2004);598, 218 (2004)]

-

  • The effective Hamiltonian of the anti-b→ anti-sq anti-q transitions mediated by the Z ' is
  • Even though the operator is suppressed by the heavy Z0 mass, they can compete with SM loop processes because of their tree-level nature.

FCNC Z' Boson (7/21/2005)

low energy effective hamiltonian1
Low-Energy Effective Hamiltonian

-

  • In general, one will receive new contributions in both QCD and EW penguin operators.
  • In view of the fact that the  K data can be explained with a new EW penguin amplitude, we assume that the Z0 mainly contributes to these operators and obtain
  • This is possible through an O(10-3) mixing angle between Z and Z0.
  • Note also that here we only include the LH coupling for the Z0-b-s coupling. The RH coupling can in principle be included, at the price of more free parameters to play with.

FCNC Z' Boson (7/21/2005)

some notations
Some Notations

-

  • To study the K  anomaly Buras et al introduce the ratio

[PRL 92, 101804 (2004)]

  • One should note that although c7,8 play a less important role compared with c9,10 in the SM, they can receive contributions from the Z ' such that we cannot neglect them.
  • In the analysis of Buras et al, it was implicitly assumed that new physics contributes dominantly to the (V-A) ­ (V-A) EW penguins.
  • As one of their conclusions under this assumption, S KS will be greater than S KS or even close to unity if one wants to explain the K  anomaly.

FCNC Z' Boson (7/21/2005)

solutions
Solutions

-

  • Using the same hadronic inputs from  modes as given by Buras et al, we get two sets of solutions: (q,) = (1.61,–84。) and (3.04,–83。), whereas they only take the small q solution.

FCNC Z' Boson (7/21/2005)

fitting with s k s too
Fitting with S KS Too

-

  • Use the following variables to parameterize our model:
  • We obtain the solutions (RH couplings included for illustration purposes only):
  • We were able to find solutions (except for (AL)) to account for both the K  and S KS data because the contributions from the O7,8 (from RH couplings at the Z0-q-qbar vertices) and O9,10 operators interfered differently in these two sets of decay modes.

FCNC Z' Boson (7/21/2005)

b s mixing
Bs Mixing

-

  • In the SM MBs is expected to be about 18 ps-1 and its mixing phase s is only a couple of degrees.
  • In contrast to the Bd system, the more than 25 times larger oscillation frequency and a factor of four lower hadronization rate from b quarks pose the primary challenges in the study of Bs oscillation and CP asymmetries.
  • Although new physics contributions may not compete with the SM processes in most of the b→c decays (s less modified), they can play an important role in Bs mixing because of its loop nature in the SM.
  • In the following, we quote the SM values:

MsSM = (1.19 ±0.24) £ 10-11 GeV = 18.0 ±3.7 ps-1, and

xsSM ≡ (Ms/s)SM = 26.3 ± 5.5.

  • Testable at Tevatron and LHC for xs up to ~75 with error at a few % level and s/s~0.15 with error ~0.02. Precision on sin(2s) depends upon xs.

FCNC Z' Boson (7/21/2005)

b s mixing with a fcnc z 0
Bs Mixing with a FCNC Z0

Barger, CWC, Jiang and Langacker, PLB 596, 229 (2004)

-

  • The mixing is induced by a tree-level Z0 exchange (LH current only):
  • In the particular case of a left-chiral (right-chiral) Z' model, one can combine the measurements of Ms (or xs) and sin 2s to determine the coupling strength L (R) and the weak phase L (R) up to discrete ambiguities.
  • Once RH currents are introduced, L-R interference dominates over purely LH or RH interactions.

FCNC Z' Boson (7/21/2005)

summary and outlook
Summary and Outlook

-

  • Extra U(1) gauge bosons are common in many extensions of the SM.
  • FCNC can be induced in models where the U(1)0 charges are non-diagonal or family-nonuniversal.
  • Such models provide new CP-violating sources that may have significant effects on low-energy physics.
  • BR’s and CPA’s of K  and  KS modes can be readily accounted for.
  • Implications in Bs mixing are analyzed.
  • Analysis of EDM, updated results of hadronic Bdecays along with analyses of semileptonic Bdecays are in progress.

FCNC Z' Boson (7/21/2005)

some notes
Some Notes

-

  • If the  H1 H2 term is missing from the superpotential ( = 0), then the theory presents an additional Peccei-Quinn symmetry. Under this symmetry, the Higgs superfield H1 undergoes a phase transition. When the bosonic component of H1 gets a non-zero vev, the PQ symmetry is broken, leading to an experimentally unacceptable Weinberg-Wilczek axion. Thus, a non-vanishing  is required to render a physically acceptable theory.
  • At least a Higgs singlet is required to break the U(1)’ symmetry. This may lead to mixing between the standard Higgs doublet and the new singlet. The LEP limit of SM-like Higgs mass (mh >= 115 GeV) does not apply and a lighter Higgs is allowed.
  • The neutralino sector is extended to have 6 components [MSSM: 4 and NMSSM: 5]. This may have significant effects on CDM.
  • Neutrinos may carry U(1)’ charges. They are Dirac fermions if they carry such charges; otherwise, they are still Majorana.

FCNC Z' Boson (7/21/2005)

some notes1
Some Notes

-

  • Accompanying with the extra symmetry are some exotic fermions to cancel the anomaly, or the anomalies are canceled by a Green-Schwarz mechanism and at least a Higgs singlet to break the symmetry.
  • In perturbative heterotic string models with supergravity mediated symmetry breaking, the U(1)’ and EW breaking are both driven by a radiative mechanism, with their scales set by the soft SUSY breaking parameters, implying that the Z’ mass should be around 1 TeV. [Cvetic et al, PRD 56, 2861 (1997)]
  • Radiative breaking of EW symmetry (SUGRA or GMSB) often yields EW/TeV-scale Z’.
  • In contrast to the Bd system, the more than 25 times larger oscillation frequency and a factor of four lower hadronization rate from b quarks pose the primary challenges in the study of Bs oscillation and CP asymmetries.
  • World average s/s = 0.24+0.28+0.03–0.38–0.04. [hep-ex/0507084]

FCNC Z' Boson (7/21/2005)

b d f k s and h 0 k s i
Bd  f Ks and h0 Ks (I)

-

1.3s / 2.7s discrepancy

CWC and Rosner, PRD 68, 014007 (2003); Barger, CWC, Langacker, and Lee, PLB 580, 186 (2004)

  • The f Ks mode is a loop-dominated process in SM (susceptible to new physics):

A(f Ks) = p ei (fSM + dp) + s ei (fSM + ds), fSM ~ arg[VcbVcs*].

  • Assume new physics contributes to one of the decay amplitudes.
  • |p| can be normalized by BR(K*0p+), consistent with SM prediction.
  • s contains EWP, assumed to be modified by new interactions.
  • The h0 Ks mode is slightly more complicated and involves color-suppressed tree amplitude.

2.2s

FCNC Z' Boson (7/21/2005)

b d f k s and h 0 k s ii
Bd  f Ks and h0 Ks (II)

-

f Ks

  • Assume new isospin-violating

4-quark interactions induced

by flavor-changing Z’

couplings.

  • Involve the parameters:

and the weak phase fL.

  • BR’s subject to hadronic

uncertainties, which are

cancelled in CPA’s.

  • CPA’s seem to favor a new

weak phase of fL' 100± and

|x| ' 10-3~10-2.

  • Z’ changes the CPA’s for both

modes in the same direction.

h0 Ks

FCNC Z' Boson (7/21/2005)

basics of b factories
Basics of B Factories

-

  • SLAC PEPII collider using BaBar detector:
    • 9.0GeV(e-) £ 3.0GeV(e+); L=6.5£1033/cm2/sec
    • s L dt = 131 fb-1; on resonance: 113 fb-1 ; 123M B anti-B pairs (2003 summer)
  • KEKB collider using Belle detector:
    • 8.0GeV(e-) £ 3.5GeV(e+); L=1.0£1034/cm2/sec
    • s L dt = 158 fb-1; on resonance: 140 fb-1; 152M B anti-B pairs (2003 summer)
    • s L dt = 219 fb-1 (3/30/2004).

FCNC Z' Boson (7/21/2005)

slide25
FCNC Z' Boson (7/21/2005)

V. Barger, J. Jiang, P. Langacker, hep-ph/0405108, submitted to PLB.