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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 ASIOP May 5, 2006

2 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, (2006) [ hep-ph/ ]; * K Cheung, CWC, N.G. Deshpande, and J. Jiang, hep-ph/ ; * CWC, N.G. Deshpande, and J. Jiang, in preparation.

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

4 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/ ]

5 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

6 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.

7 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.

8 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 ≥ % CL (particular coupling assumed). [http://www-cdf.fnal.gov/physics/exotic/r2a/ dilepton_zprime/] The initial LHC reach will be 2 TeV (with power to discriminate among models) and can go up to 5 TeV.

9 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]

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

11 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.

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

13 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) £ GeV = 18.0 ± 3.7 ps -1, and x s SM ≡ (  M s /  s ) SM = 26.3 ± 5.5.

14 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]

15 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 | = In comparison, the latest Belle results for b → d  and b → s  give a 95%CL range of ~ for the above ratio.

16 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 |.

17 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 £ In more general models,  L sb may be different. For example, if  L sb = 90 o,  L sb < 9.87 £ Note that there are regions with  L sb > 9.87 £ also allowed by the current  M s constraint. Some of these regions correspond to Z' contributions larger than the SM contributions.

18 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 £ and 2.3 £ 10 -7, respectively. [R.V. Kooten, FPCP 2006]

19 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 £ 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.

20 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 b b pairs per year, the expected branching ratio of order is observable.

21 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.

22 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.

23 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.

24 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, (2004), where no RG effects and only RH couplings were considered.]

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

26 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 |.

27 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 £ [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, (2005)] [Arhrib, Cheung, CWC, Yuan]

28 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.

29 C.W. ChiangLow-energy phenos of FCNC Z'29 Cross 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

30 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 -.

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

32 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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