Low-Energy Phenomenologies of FCNC Z 0 Cheng-Wei Chiang ( 蔣正偉 ) National Central University & Academia Sinica Cheng-Wei Chiang ( 蔣正偉 ) National Central

Low-Energy Phenomenologies of FCNC Z 0

Low-Energy Phenomenologies of 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

Seminar @ ASIOPMay 5, 2006

C.W. ChiangC.W. Chiang Low-energy phenos of FCNC Z'Low-energy phenos of FCNC Z' 22

OutlineOutlineOutlineOutline

[You will hear this talk again on 5/20.]

Motivations for an FCNC Z 0

Constraints from neutral meson mixings in the down sector

D meson mixing and single-top production

SummaryBased 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, PRD 73, 075015 (2006)

[hep-ph/0602175];* K Cheung, CWC, N.G. Deshpande, and J. Jiang, hep-ph/0604223;* CWC, N.G. Deshpande, and J. Jiang, in preparation.


Motivations for an FCNC Motivations for an FCNC Z Z 00


Fifth ForceFifth ForceFifth ForceFifth Force

Extra 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 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.[Suematsu and Yamagishi, IJMPA 10, 4521 (1995);Cvetic and Langacker, PRD 54, 3570 (1996)]

Accompanying with the extra symmetry are some extra fermions to cancel the anomaly and at least a Higgs singlet to break the symmetry. [e.g. Batra et al, hep-ph/0510181]


Tree-Level FCNC Tree-Level FCNC Z Z 00Tree-Level FCNC Tree-Level FCNC Z Z 00

In the flavor eigenbasis, the Z 0 NC Lagrangian is given by

In string models, it is possible to have family-nonuniversal Z 0 couplings 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 mass basis, which may even lead to new CP-violating effects:

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

cf. Z


One Simple ExampleOne Simple ExampleOne Simple ExampleOne Simple Example

Take

x ~ O(1), and VdL = VCKMy, then the down-sector coupling matrix

Here, |BLsb| > |BL

db| > |BLds|.

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

Such couplings may lead to observable FCNC effects.


Drell-Yan Process for Drell-Yan Process for Z’Z’ DiscoveryDiscovery

Drell-Yan Process for Drell-Yan Process for Z’Z’ DiscoveryDiscovery

The production cross section of Z’ followed by the leptonic decay is given by (with the narrow width approximation)

where r = MZ '2/s and Z ' is the total width.

The partial decay width of Z' → f f is

where Nf = 3(1) for quark (lepton) and = mf2/MZ'

2.

The FCNC contributions are negligible and Z’ → W +W − is highly suppressed by the Z-Z’ mixing angle.


Direct Searches at CDF Run Direct Searches at CDF Run II (2004)II (2004)

Direct Searches at CDF Run Direct Searches at CDF Run II (2004)II (2004)

The 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 (particular coupling assumed).[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.


Direct Searches at CDF Run Direct Searches at CDF Run IIII

Direct Searches at CDF Run Direct Searches at CDF Run IIII

More recent data based on the integrated luminosity of 819 pb-1 of the Drell-Yan process at CDF (√s = 1.96 TeV ):[http://www-cdf.fnal.gov/harper/diEleAna.html]


Precision Data ConstraintsPrecision Data ConstraintsPrecision Data ConstraintsPrecision Data 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

| | < (a few) 10-3.

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


Discovery Reach at LHCDiscovery 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.


Neutral Meson MixingsNeutral Meson Mixings


BBss Meson Mixing Meson MixingBBss Meson Mixing Meson MixingAs in the case of Bd mixing, the Bs meson also provides us a good testing ground for the SM CKM mechanism.

The experimental ratio Md/Ms determines |Vtd/Vts|.

In the SM, MBs is expected to be about 18 ps-1, and its mixing

phase s is only a couple of degrees.

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

SM predictions (based upon the ratio of Ms/Md):

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

xsSM ≡ (Ms/s)SM = 26.3 ± 5.5.


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

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

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

[Barger, CWC, Jiang, Langacker 2004]


New Results from D0 & CDFNew Results from D0 & CDFNew Results from D0 & CDFNew Results from D0 & CDF

The FCNC effect in b-s sector of the SM was recently confirmed in the Bs meson mixing observed by both CDF and D0:

Within the SM, this implies:

|Vtd/Vts| = 0.208+0.008-0.007.

In comparison, the latest Belle results forb → d and b → s give a 95%CL rangeof 0.142 ~ 0.259 for the above ratio.


New Results from DØ & CDFNew Results from DØ & CDFNew Results from DØ & CDFNew Results from DØ & CDF[Cheung, CWC, Deshpande, Jiang 2006]

We re-evaluate the Bs mass difference, but without reference to Md, at the price of a larger hadronic uncertainty:

This is consistent with the experimental result. One therefore can use it to constrain new physics parameters.

Moreover, in the string-inspired model mentioned above, the ratio Md/Ms can still be used to get |Vtd/Vts|.


Constraint From Constraint From BBss Mixing MixingConstraint From Constraint From BBss Mixing Mixing

Now the effect of LH FCNC induced by the Z’ boson is:

For Lsb=0 or 180o, L

sb < 6.20 £ 10-4.

In more general models, Lsb may

be different. For example, if L

sb = 90o, Lsb < 9.87 £ 10-4.

Note that there are regions with L

sb > 9.87 £ 10-4 also allowed by the current Ms constraint. Some of these regions correspond to Z' contributions larger than the SM contributions.


Constraint From Leptonic Constraint From Leptonic BBss DecaysDecays

Constraint From Leptonic Constraint From Leptonic BBss DecaysDecays

The branching ratio of Bs → +– is given by

From the Drell-Yan process, one is then able to constrain the leptonic diagonal couplings.

The current upper limits on Br(Bs → + –) from CDF and DØ based on 780 and 700 pb-1 data are 1.0£10-7 and 2.3£10-7, respectively.[R.V. Kooten, talk @ FPCP 2006]


Constraint From Drell-YanConstraint From Drell-YanConstraint From Drell-YanConstraint From Drell-Yan

In the particular model with only FCNC in the down sector,

one can translate the upper limit L

sb < 6.20 £ 10-4 to bounds on the flavor-diagonal Z’-q-q couplings.

From the Drell-Yan process, one is then able to constrain the diagonal leptonic couplings as a function of the Z’ mass and the model parameter x.


Prediction of Muonic Prediction of Muonic BBss DecayDecay

Prediction of Muonic Prediction of Muonic BBss DecayDecay

From the present constraints from Bs mixing and Z’ production, the muonic decay of Bs may not be observed at the Tevatron if the projected integrated luminosity is less than O(5-10) fb.

At LHCb, with anticipated production of 1012 b b pairs per year, the expected branching ratio of order 10-9 is observable.


BBdd Meson MixingMeson MixingBBdd Meson MixingMeson Mixing[CWC, Deshpande, Jiang, in progress]

Since Z’ may affect the Bd system too, one has to re-examine the determination of and of the unitarity triangle:

We use the observed MBd and sin2 and the following inputs:

This is because the Z’ contributions to the radiative B decays are both loop- and mass-suppressed.


ResultsResultsResultsResultsThe fitting results are as follows, with 1 and 90%CL contours, to be compared with the CKMfitter result.


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

With , constraints from the measured MK give

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


Constraint from Constraint from KKConstraint from Constraint from KK

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.]


D Meson MixingD Meson Mixing&&

Single-Top ProductionSingle-Top Production


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

As said before, the FCNC can occur to the up sector too:

In order to make definite predictions in our analysis, we take the above mixing matrix seriously. But we need to check the constraints from measuredD meson mixing.

Here, |BLct| > |BL

ut| > |BLuc|.


D D Meson MixingMeson MixingD D Meson MixingMeson Mixing

In 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]


Associated Top-Charm Associated Top-Charm ProductionProduction

Associated Top-Charm Associated Top-Charm ProductionProduction

Production of single-top events at hadron colliders can provide a means to study new physics interactions. [Tait, Yuan 2001]

As seen from the mixing matrix, the Z 0-t-c coupling is the largest off-diagonal term.

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 @ 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 Secondary Vertex Mass Method / Method /

Charm TaggingCharm Tagging

Secondary Vertex Mass Secondary Vertex Mass Method / Method /

Charm TaggingCharm TaggingSince 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 tail up 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-+,D*+ → D0+ with D0 → K -+,D+ → K -++, andDs

+ → + with → K+K -.


Top-Charm Production @ Top-Charm Production @ ILCILC

Top-Charm Production @ Top-Charm Production @ ILCILC

At 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 -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 (t anti-c +anti-t c)/(t anti-t) to determine the parameter x.

~ O (100) fb

C.W. Chiang Low-energy phenos of FCNC Z' 32

We have extracted constraints of FCNC couplings in the models using current data on neutral meson mixing.

In particular, we studied the b-s sector using latest Bs mixing data and its implication in a particular type of models.

We have studied single top-quark production at both LHC and ILC in a purely top-sector FCNC Z’ model.

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 lepton EDM and LFV processes.

SummarySummary

Documents

Low-Energy Phenomenologies of FCNC Z 0 Cheng-Wei Chiang ( 蔣正偉 ) National Central University & Academia Sinica Cheng-Wei Chiang ( 蔣正偉 ) National Central