FCNC Z prime - KEK

Low-Energy Phenomenologiesof FCNC Z 0

Low-Energy Phenomenologiesof FCNC Z 0

Cheng-Wei Chiang (蔣正偉)National Central University & Academia Sinica

Cheng-Wei Chiang (蔣正偉)National Central University & Academia Sinica

KEK Phenomenology Theory MeetingMarch 2-4, 2006

C.W. ChiangC.W. Chiang LowLow--energy phenomenologies of FCNC Z'energy phenomenologies of FCNC Z' 22

OutlineOutlineOutline

Motivations for a FCNC Z 0

Solutions to some puzzles in B decays

Neutral meson mixings and EDM

Single-top production

Summary

Based on:V. Barger, CWC, H.S. Lee, and P. Langacker, PLB 580, 186 (2004);V. Barger, CWC, J. Jiang, and P. Langacker, PLB 596, 229 (2004);V. Barger, CWC, H.S. Lee, and P. Langacker, PLB 598, 218 (2004);A. Arhrib, K Cheung, CWC, T.C. Yuan, hep-ph/0602175;CWC, N.G. Deshpande, J. Jiang, in preparation.


Motivations for a FCNC Motivations for a FCNC Z Z 00


Fifth ForceFifth ForceFifth ForceExtra heavy neutral Z 0 gauge bosons exist in most extensions of the SM and their SUSY versions, including GUT’s, XD models, string models, little Higgs, etc.

The extra symmetry can forbid an elementary μ term in SUSY, while allowing effective μ and Bμ terms to be generated at the U(1) 0 breaking scale, providing a solution to the μ problem.[Suematsu and Yamagishi, IJMPA 10, 4521 (1995);Cvetic and Langacker, PRD 54, 3570 (1996)]

Accompanying with the extra symmetry are some exotic fermions to cancel the anomaly and at least a Higgs singlet to break the symmetry.


Tree-Level FCNC Z 0TreeTree--Level FCNC Level FCNC Z Z 00

In the gauge eigenbasis, the Z 0 Lagrangian is given by

In string models, it is possible to have family-nonuniversal Z 0couplings to fermion fields due to different ways of constructing different families. [Chaudhuri et al, NPB 456, 89 (1995)]

After flavor mixing, one obtains FCNC Z 0 interactions in the fermion mass basis, which may lead to new CP-violating effects:

This may also induce flavor-violating Z couplings if there is a Z-Z 0 mixing.


One Simple ExampleOne Simple ExampleOne Simple ExampleTake

x ~ O(1), and VuL = VCKM†, then the up-sector coupling matrix

Here, |BtcL| > |Btu

L| > |BcuL|.

Same thing can be done to the down sector or even both.


Direct Searches at CDF Run IIDirect Searches at CDF Run IIDirect Searches at CDF Run IIThe mass of an extra Z’ from the non-observation of direct production (p anti-p → Z 0 → 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.


More ConstraintsMore ConstraintsMore Constraints

Precision data also providestringent constraints.[Erler and Langacker, Review of Particle Physics 2004]

LEP precision measurement of coupling constants at the Z-pole gives

|θ | < (a few) × 10-3.

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


Discovery Reach at LHCDiscovery Reach at LHCDiscovery Reach at LHC[Dittmar, Nicollerat, and Djouadi 2004]

The LHC can readily discover an extra neutral gauge boson with a mass of about 1 TeV from, for example, the Drell-Yan process.


Solutions to some puzzles in Solutions to some puzzles in BB decaysdecays


Anomalies in Hadronicb → s q anti-q TransitionsAnomalies in HadronicAnomalies in Hadronic

bb →→ ss q antiq anti--qq TransitionsTransitions

The sin2β measurements from various |ΔS| = 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 φ KS mode, which has a simpler amplitude structure, indicates that it is likely to be polluted with a new EWP amp.


K π Anomaly – Phase IK K ππ Anomaly Anomaly –– Phase IPhase ITwo ratios of the BR’s of K π modes (charged and neutral):

To the leading order, Rc and Rn should be the same in the SM; corrections should be ~ O([(C 0 + P 0EW) / P 0]2) ~ O(λ2).

2.42.4σ σ →→ 1.91.9σσ →→ 1.51.5σσ


K π Anomaly – Phase IIK K ππ Anomaly Anomaly –– Phase IIPhase IINow a bigger problem is in two CPA’s of the K π modes:

In the SM, T 0 and C 0 have the same weak phase (γ) and a small relative strong phase ⇒ ACP(K +π −) and ACP(K ±π 0) are expected to at least have the same sign.

3.63.6σσ !!

establishing DCPV in establishing DCPV in BB system at 5.7system at 5.7σσ levellevel


Possible ExplanationsPossible ExplanationsPossible ExplanationsFor puzzle phase-I only: underestimate of π 0 detection efficiency, thus overestimating the BR’s of those corresponding modes. [Gronau and Rosner, PLB 572, 43 (2003)]

New mechanism in SM: large color-suppressed amplitude C from NLO vertex corrections.

[Charng & Li, PRD 71, 014036 (2005); He & McKellar, hep-ph/0410098]

Beyond SM: large electroweak penguin amplitude PEW from new physics.

[Yoshikawa, JKPS 45, S479 (2004);Buras et al, PRL 92, 101804 (2004); NPB 697, 133 (2004);Baek, Hamel, London, Datta and Suprun, PRD 71, 057502 (2005);Hou, Nagashima and Soddu, PRL 95, 141601 (2005)]


Z0-Induced FCNCZZ00--Induced FCNCInduced FCNCIn view of the fact that the π K data can be explained with a new EWP amplitude, we assume that the Z 0 mainly contributes to these operators and obtain

This is possible with an O(10-3) mixing angle between Z and Z 0.

Here only the LH coupling for the Z 0-b-s coupling is shown. RH coupling can be included at the price of more free parameters.

s sZ 0

Z 0


Some NotationsSome NotationsSome NotationsTo study the K π puzzle Buras et al introduce the ratio

[Buras et al, PRL 92, 101804 (2004)]

One should note that although c7,8 play a less important role compared to c9,10 within the SM, they can receive contributions from the Z 0 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) EWPs.

As one of their conclusions under this assumption, Sφ KSwill be

greater than SΨ KSor even close to unity if one wants to explain

the K π anomaly.


SolutionsSolutionsSolutionsUsing the same hadronic inputs from π π modes as given by Buras et al, we get two sets of solutions:

(q,φ) = (1.61, –84。) and (3.04, 83。) [2 yrs ago]⇒ (0.94, –85。) and (2.37, 85。) [now],

whereas they only take the small q solution.

[Barger, CWC, Lee, Langacker 2004]


Fitting Sφ KSTooFitting Fitting SSφφ KKSSTooToo

Use the following variables to parameterize our model:

We obtain the solutions

It is possible to find solutions (except for (AL)) that account for both the K π and Sφ KS

data because the contributions from the O7,8 (from RH couplings at the Z 0-q-qbar vertices) and O9,10

operators interfered differently in these two sets of decay modes.


Neutral Meson MixingsNeutral Meson Mixingsandand

EDMEDM


Bs Meson MixingBBss Meson MixingMeson MixingIn the SM ΔMBs

is expected to be about 18 ps-1 and its mixing phase φs is only a couple of degrees.

Although new physics contributions may not compete with the SM processes in most of the b → c decays (Γs less modified), they can play an important role in Bs mixing because of its loop nature in the SM.

SM predictions:ΔMs

SM = (1.19 ± 0.24) × 10-11 GeV = 18.0 ± 3.7 ps-1, andxs

SM ≣ (ΔMs/Γs)SM = 26.3 ± 5.5.

Testable at Tevatron and LHC for xs up to ~75 with error at a few % level and ΔΓs/Γs~0.15 with error ~0.02. Precision on sin(2φs) depends upon xs.


Results (LL Couplings Only)Results (LL Couplings Only)Results (LL Couplings Only)

The LHCb will help us probe the production and decays of the yet-unfamiliar BS system.

New physics contributions to the b → s transition induce |ΔB| = |ΔS| = 2 operators that affect BS mixing.

[Barger, CWC, Jiang, Langacker 2004]


D Meson MixingD D Meson MixingMeson MixingIn D meson system, it is convenient to define:

The values of xD and yD from NLO short-distance SM physics are found to be ~ 6 × 10-7. [Golowich and Petrov,PLB 625, 53 (2005)]

Ignoring the SM contributions and considering only the LH couplings in the Z 0 model in our purely up-sector FCNC model with MZ 0 = 1 TeV, one obtains

This is very safe from the latest CLEO result:–4.5% < xD < 9.3%. [CLEO, PRD 72, 012001 (2005)]

[Arhrib, Cheung, CWC, Yuan]


K Meson MixingK K Meson MixingMeson MixingThe general set of |ΔS| = 2 operators relevant in this case is:

With , constraints from the measured ΔMK give

The LR part is dominant due to chiral and RG enhancements in the form factor and Wilson coefficients, respectively.

[CWC, Deshpande, Jiang]


Constraint from εKConstraint from Constraint from εεKK

Requiring the contribution from Z ' to be less than the theoretical error (30%) associated with the SM prediction, we have

A stronger bound is obtained by keeping only the dominant term:

[cf. He and Valencia, PRD 70, 053003 (2004), where no RG effects and only RH couplings were considered.]


Fermion EDMFermionFermion EDMEDMThe complex phases in chiral couplingsof the Z 0 can contribute to fermion EDM’s.

With the definitions a = mf

2/mZ '2,

b = (mf '2 – mf

2)/mZ ' – 1, andc = mf '

2/mZ '2

the EDM is evaluated to be


Current ConstraintsCurrent ConstraintsCurrent Constraints

Constraints on the model parameters from experimental bounds for various fermion EDM’s are

[CWC, Deshpande, Jiang]


SingleSingle--Top ProductionTop Production


Up-Sector FCNCUpUp--Sector FCNCSector FCNC[Arhrib, Cheung, CWC, and Yuan 2006]

Just in case you already forget, the following are the purely up-sector FCNC Z 0 model we are considering:


Associated Top-Charm ProductionAssociated TopAssociated Top--Charm ProductionCharm Production

As been said before, the Z 0-t-ccoupling is the largest off-diagonal term in the mixingmatrix.

Take the purely up-sector FCNC Z 0 model seriously in order to make definite predictions.

Total decay width (to fermionsonly) ranges from a few to a fewtens of GeV, to be used in theZ 0 propagator.


Cross Section @ LHCCross Section @ LHCCross Section @ LHC

The cross section of p p → (t anti-c) + (c anti-t) at LHC for some Z’ models and SM backgrounds:

with

Seq. Z, MZ’ = 1 TeV~ O (1) fb


Secondary Vertex Mass Method / Charm Tagging

Secondary Vertex Mass Method / Secondary Vertex Mass Method / Charm TaggingCharm Tagging

Since the background at LHC is still about 5 times larger than the signal, one has to rely on secondary vertex mass method or D-, D*-tagging to further separate the charmed and the bottom jets.

The bottom jet has the largest secondary vertex mass with a tailup to 4 GeV; the charmed jet has a secondary vertex mass ranging from 0 to 2 GeV with a peak around 1 GeV; and the light quark jets have the smallest secondary vertex masses.

[CDF Public Note CDF/PHYS/CDF/PUBLIC/7072]

Reconstruct prompt charmed mesons:D0 → K-π +,D*+ → D0π + with D0 → K -π +,D+ → K -π +π +, andDs

+ → φ π + with φ → K+K -.


Top-Charm Production @ ILCTopTop--Charm Production @ ILCCharm Production @ ILCAt linear colliders such as the ILC, only the s-channel diagram contributes to the process e+e-→ anti-t c or t anti-c.

Detection of such events at an e+ e-

collider is much more straight-forward because the SM single top-quark production proceeds through γ-t-q and Z-t-q FCNC couplings (q=u,c) that are GIM suppressed.[Huang, Wu, and Zhu, PLB 452, 143 (1999)]

One can measure under the Z ' peak the cross-section ratio σ(t anti-c +anti-t c)/σ(t anti-t) to determine the parameter x.

~ O (100) fb

C.W. Chiang Low-energy phenomenologies of FCNC

Z'

33

We have explored the possibility of explaining some of the puzzles in B meson decays using FCNC Z’ models.We have extracted constraints of FCNC couplings in the models using current data on neutral meson mixing.We have studied single top-quark production at both LHC and ILC in a purely top-sector FCNC Z’ model.With reasonable coupling parameters, new CPV phase, and MZ’ ~ 1 TeV, we are able to explain several puzzles existing B meson decays. Detection of single-top production at LHC can be difficult, but should be easy at ILC.We are studying constraints from the leptonic sector too, using the EDM and LFV processes.

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FCNC Z prime - KEK

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