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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 @ ASIOP May 5, 2006

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C.W. ChiangLow-energy phenos of FCNC Z'2OutlineOutline [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 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, 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.

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C.W. ChiangLow-energy phenos of FCNC Z'3 Motivations for an FCNC Z 0

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C.W. ChiangLow-energy phenos of FCNC Z'4 Fifth 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]

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C.W. ChiangLow-energy phenos of FCNC Z'5 Tree-Level FCNC Z 0 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

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C.W. ChiangLow-energy phenos of FCNC Z'6 One Simple Example Take x ~ O(1), and V dL = V CKM y, then the down-sector coupling matrix Here, |B L sb | > |B L db | > |B L ds |. Same thing can be done to the up sector or even both. Such couplings may lead to observable FCNC effects.

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C.W. ChiangLow-energy phenos of FCNC Z'7 Drell-Yan Process for Z’ Discovery The production cross section of Z’ followed by the leptonic decay is given by (with the narrow width approximation) where r = M Z ' 2 /s and Z ' is the total width. The partial decay width of Z' → f f is where N f = 3(1) for quark (lepton) and = m f 2 /M Z' 2. The FCNC contributions are negligible and Z’ → W + W − is highly suppressed by the Z-Z’ mixing angle.

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C.W. ChiangLow-energy phenos of FCNC Z'8 Direct Searches at CDF Run 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.

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C.W. ChiangLow-energy phenos of FCNC Z'9 Direct Searches at CDF Run II 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]

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C.W. ChiangLow-energy phenos of FCNC Z'10 Precision Data Constraints Precision data also provide stringent 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)]

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C.W. ChiangLow-energy phenos of FCNC Z'11 Discovery 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.

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C.W. ChiangLow-energy phenos of FCNC Z'12 Neutral Meson Mixings

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C.W. ChiangLow-energy phenos of FCNC Z'13 B s Meson Mixing As in the case of B d mixing, the B s meson also provides us a good testing ground for the SM CKM mechanism. The experimental ratio M d / M s determines |V td /V ts |. In the SM, M B s 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 B s mixing because of its loop nature in the SM. SM predictions (based upon the ratio of M s / M d ): M s SM = (1.19 ± 0.24) £ 10 -11 GeV = 18.0 ± 3.7 ps -1, and x s SM ≡ ( M s / s ) SM = 26.3 ± 5.5.

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C.W. ChiangLow-energy phenos of FCNC Z'14 Results (LL Couplings Only) The LHCb will help us probe more about the production and decays of the yet-unfamiliar B S system. New physics contributions to the b → s transition induce | B| = | S| = 2 operators that affect B S mixing. [Barger, CWC, Jiang, Langacker 2004]

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C.W. ChiangLow-energy phenos of FCNC Z'15 New Results from D0 & CDF The FCNC effect in b-s sector of the SM was recently confirmed in the B s meson mixing observed by both CDF and D0: Within the SM, this implies: |V td /V ts | = 0.208 +0.008 -0.007. In comparison, the latest Belle results for b → d and b → s give a 95%CL range of 0.142 ~ 0.259 for the above ratio.

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C.W. ChiangLow-energy phenos of FCNC Z'16 New Results from DØ & CDF [Cheung, CWC, Deshpande, Jiang 2006] We re-evaluate the B s mass difference, but without reference to M d, 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 M d / M s can still be used to get |V td /V ts |.

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C.W. ChiangLow-energy phenos of FCNC Z'17 Constraint From B s Mixing Now the effect of LH FCNC induced by the Z’ boson is: For L sb =0 or 180 o, L sb < 6.20 £ 10 -4. In more general models, L sb may be different. For example, if L sb = 90 o, L sb < 9.87 £ 10 -4. Note that there are regions with L sb > 9.87 £ 10 -4 also allowed by the current M s constraint. Some of these regions correspond to Z' contributions larger than the SM contributions.

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C.W. ChiangLow-energy phenos of FCNC Z'18 Constraint From Leptonic B s Decays The branching ratio of B s → + – is given by From the Drell-Yan process, one is then able to constrain the leptonic diagonal couplings. The current upper limits on Br(B s → + – ) 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]

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C.W. ChiangLow-energy phenos of FCNC Z'19 Constraint 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.

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C.W. ChiangLow-energy phenos of FCNC Z'20 Prediction of Muonic B s Decay From the present constraints from B s mixing and Z’ production, the muonic decay of B s 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 10 12 b b pairs per year, the expected branching ratio of order 10 -9 is observable.

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C.W. ChiangLow-energy phenos of FCNC Z'21 B d Meson Mixing [CWC, Deshpande, Jiang, in progress] Since Z’ may affect the B d system too, one has to re-examine the determination of and of the unitarity triangle: We use the observed M B d and sin2 and the following inputs: This is because the Z’ contributions to the radiative B decays are both loop- and mass-suppressed.

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C.W. ChiangLow-energy phenos of FCNC Z'22ResultsResults The fitting results are as follows, with 1 and 90%CL contours, to be compared with the CKMfitter result.

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C.W. ChiangLow-energy phenos of FCNC Z'23 K Meson Mixing The general set of | S| = 2 operators relevant in this case is: With, constraints from the measured M K give The LR part is dominant due to chiral and RG enhancements in the form factor and Wilson coefficients, respectively.

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C.W. ChiangLow-energy phenos of FCNC Z'24 Constraint from K 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.]

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C.W. ChiangLow-energy phenos of FCNC Z'25 D Meson Mixing & Single-Top Production

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C.W. ChiangLow-energy phenos of FCNC Z'26 Up-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 measured D meson mixing. Here, |B L ct | > |B L ut | > |B L uc |.

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C.W. ChiangLow-energy phenos of FCNC Z'27 D Meson Mixing In D meson system, it is convenient to define: The values of x D and y D 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 M Z 0 = 1 TeV, one obtains This is very safe from the latest CLEO result: –4.5% < x D < 9.3%. [CLEO, PRD 72, 012001 (2005)] [Arhrib, Cheung, CWC, Yuan]

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C.W. ChiangLow-energy phenos of FCNC Z'28 Associated Top-Charm Production 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 fermions only) ranges from a few to a few tens of GeV, to be used in the Z 0 propagator.

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C.W. ChiangLow-energy phenos of FCNC Z'29 Cross 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, M Z’ = 1 TeV ~ O (1) fb

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C.W. ChiangLow-energy phenos of FCNC Z'30 Secondary Vertex Mass Method / Charm 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 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: D 0 → K - +, D *+ → D 0 + with D 0 → K - +, D + → K - + +, and D s + → + with → K + K -.

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C.W. ChiangLow-energy phenos of FCNC Z'31 Top-Charm Production @ ILC 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

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C.W. ChiangLow-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 B s 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.Summary

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