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Choong Sun Kim (C.S. Kim)

Forward-Backward Asymmetry of Top quark In Unparticle Physics. Choong Sun Kim (C.S. Kim). Department of Physics, Yonsei University, Korea. ICPP-Istanbul II. 2 nd International Conference on Particle Physics. Outline. Motivation  Observation at Tevatron

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Choong Sun Kim (C.S. Kim)

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  1. Forward-Backward Asymmetry of Top quark In Unparticle Physics Choong Sun Kim (C.S. Kim) Department of Physics, YonseiUniversity, Korea ICPP-Istanbul II 2nd International Conference on Particle Physics

  2. Outline • Motivation  Observation at Tevatron • Phenomenon & History over Q-FBA • Possible Models & Mechanisms • Our results in Unparticle Physics • Summary

  3. 1. Observations at TevatronD PRL100, 142002 (2008) • Process: p pbar→ t tbar + X; the first measurement of the integrated forward-backward (FB) charge asymmetry • D Observable: • Nf(b): number of events with a positive (negative) Δy y = yt– ytbar, y: rapidity

  4. Observations at TevatronCDF: PRL101, 202001 (2008) • CDF observable: • With 1.9 fb−1 • With 3.2 fb-1

  5. 2. Phenomenon • If CP is invariant, Asymmetry • Integral charge asymmetry Ni (j): # of particle i observed in the direction of particle j • Forward-backward asymmetry

  6. History over Heavy Quark FBA Brown et al, PRL43(1979)1069; FBA of c-quak production in analogy to QED. [1] F. Halzen, P. Hoyer, C.S. Kim, PLB195(1987)74; FBA of b,t-quark in QCD from (i) radiative corrections to q-qbar annihilation, (ii) interference between different contributions to qg t+tbar+q, (and its CP conj.) ~~~ no more progress about 10 years [2] J.H. Kuhn, G. Rodrigo, PRL81(1998)49; detailed QCD calculation [3] O. Antunano, J.H. Kuhn, G. Rodrigo, PRD77(2008)014003;  FBA of t-quak within the SM = 0.050 +- 0.015 D0 and CDF measured FBA ~ 20%  Now so many works beyond the SM

  7. SM prediction Kuhn& Rodrigo PRD59(99); Antunanoetal PRD77(08); • Leading order (d): charge asymmetry vanishes • Next-to-leading order: nonzero AC will be induced by the interference between (a) and (b) and the interference between (c) and (d) • Since the measurements of D and CDF have 2 deviation from the SM, the observed large FBA strongly indicate the new Physics

  8. 3. Models by s-channelFerrario & Rodrigo PRD80(09); Frampton etal, arXiv:0911.2955 • Axigluon: Color-octet gauge bosons (AGs) that couple to quarks with a nonvanishing axial-vector couplings • It could be generated by symmetry breaking from SU(3)RSU(3)L to SU(3)C • AG could be as heavy as TeV

  9. Models by s-channelDjouadiMoreau, Richard,Singh, arXiv:0906.0604 • KK excitations of gluons in warped extra dimensional models • The couplings of KK to quarks have the axial-vector component • AtFB|RS~ few %

  10. Models by t-channelJung, Murayama, Pierce, Wells, arXiv:0907.4112 • New Z’ gauge boson • Nonuniversal Z’ model

  11. Models by t-channelCheung,Keung, Yuan PLB682(09); Barger, Keung, Yu: arXiv:1002.1048

  12. Model-independent approachD.W. Jung, P. Ko, J.S. Lee, S.H. Nam, arXiv:0912.1105 • Effective interactions

  13. SUSY R-parity violationby J. Chao, Z. Heng, L. Wu and J.M. Yang, arXiv:0912.1447

  14. Diquark modelsShu,Tait, Wang :0911.3237, Arhrib, Benbrik,Chen:0911.4875, Dorsneretal :0912.0972 • Diquark is the particle that couples to quarks by qaT C qbHab , where a, b are the color indices • The possible representations under SU(3)CSU(2)LU(1)Y : (6, 3)1/3 , (6,1) 4/3,1/3,-2/3 , (3, 3)-1/3 ,, (3,1)2/3,-1/3,-4/3 • We would like to pay attention to (3,1,-4/3) and (6,1,4/3) • The relevant interactions • The corresponding Feynman diagram

  15. 4. Unparticle Physics, s-channelC.H. Chen, Gorazd Cvetic, C.S Kim, PLB694(2011)393 Phys.Rev.Lett.98:221601,2007 Phys.Lett.B650:275-278,2007 Cacciapaglia, Marandella, Terning, JHEP0801:070,2008 A stuff dictated by scale invariance, proposed by Georgi Here, we considered colored unparticle, in which the effective interactions to quarks are proposed to be Due to nonintegral scale dimension and no mass scale in the propagator, it will be interesting to see the unparticle effects on the top-quark FBA

  16. with Then, Scattering amplitude combined with the SM becomes

  17. Spinand color averaged amplitude-square is

  18. 3 physical observables are: 3 independent parameters: ( , ) first we set 2 remaining dimensionless parameters are from assuming flavor blind (colored) unparticle and finally the scale dimension  i.e. the flavor-blind and chirality-independent couplings Experimental numerical constraints: M. Cacciari et al., JHEP 0809, 127 (2008); N. Kidonakis and R. Vogt, Phys. Rev. D 78, 074005 (2008); S. Moch and P. Uwer, Phys. Rev. D 78, 034003 (2008)

  19.  d_U=1.28+-0.22, lambda=2.05+-0.45

  20. Phys.Rev.Lett.102:222003,2009 (CDF).

  21. For detailed analysis, cosiderMtt-restricted FBA,

  22. 5. Summary • An unexpected large FBA of top-quark is observed by D and CDF: strongly indicate the new physics effects (NLO effects). • Various possible solutions to the “anomaly” are proposed, like axigluon, KK excitations of gluon, Z’, W’, colored scalars, etc • We investigated whether colored flavor-conserving unparticle • can explain the measured FBA of ttbar production at Tevatron. • With a natural assumption of quark flavor-blind and chirality- • independent unparticle, UP contribution can explain the • deviation.

  23. Thank you for your attention

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