# Scalar-mediated \( t\bar{t} \) forward-backward asymmetry

## Abstract

A large forward-backward asymmetry in \( t\bar{t} \) production, for largeinvariant mass of the \( t\bar{t} \) system, has been recently observed by the CDF collaboration. Among the scalar mediated mechanisms that can explain such a large asymmetry, all colored representations are inconsistent by more than 2*σ* with at least one other top-related measurement. In contrast, the *t*-channel exchange of a color-singlet weak-doublet scalar is consistent with the differential and with the integrated \( t\bar{t} \) cross section measurements. Constraints from flavor changing processes dictate a very specific structure for the Yukawa couplings of such a new scalar. No sizable deviation in the differential or integrated \( t\bar{t} \) production cross section is expected at the LHC.

## Keywords

Phenomenological Models## References

- [1]CDF collaboration, T. Aaltonen et al.,
*Evidence for a mass dependent forward-backward asymmetry in top quark pair production*,*Phys. Rev.***D 83**(2011) 112003 [arXiv:1101.0034] [INSPIRE].ADSGoogle Scholar - [2]L.G. Almeida, G.F. Sterman and W. Vogelsang,
*Threshold resummation for the top quark charge asymmetry*,*Phys. Rev.***D 78**(2008) 014008 [arXiv:0805.1885] [INSPIRE].ADSGoogle Scholar - [3]M. Bowen, S. Ellis and D. Rainwater,
*Standard model top quark asymmetry at the Fermilab Tevatron*,*Phys. Rev.***D 73**(2006) 014008 [hep-ph/0509267] [INSPIRE].ADSGoogle Scholar - [4]O. Antunano, J.H. Kuhn and G. Rodrigo,
*Top quarks, axigluons and charge asymmetries at hadron colliders*,*Phys. Rev.***D 77**(2008) 014003 [arXiv:0709.1652] [INSPIRE].ADSGoogle Scholar - [5]D0 collaboration, V. Abazov et al.,
*First measurement of the forward-backward charge asymmetry in top quark pair production*,*Phys. Rev. Lett.***100**(2008) 142002 [arXiv:0712.0851] [INSPIRE].ADSCrossRefGoogle Scholar - [6]CDF collaboration, T. Aaltonen et al.,
*Forward-backward asymmetry in top quark production in*\( p\bar{p} \)*collisions at*\( \sqrt {s} = 1.96 \)*TeV*,*Phys. Rev. Lett.***101**(2008) 202001 [arXiv:0806.2472] [INSPIRE].ADSCrossRefGoogle Scholar - [7]B. Grinstein, A.L. Kagan, M. Trott and J. Zupan,
*Forward-backward asymmetry in*\( t\bar{t}t\bar{t} \)*production from flavour symmetries*,*Phys. Rev. Lett.***107**(2011) 012002 [arXiv:1102.3374] [INSPIRE].ADSCrossRefGoogle Scholar - [8]K.M. Patel and P. Sharma,
*Forward-backward asymmetry in top quark production from light colored scalars in*SO(10)*model*,*JHEP***04**(2011) 085 [arXiv:1102.4736] [INSPIRE].ADSCrossRefGoogle Scholar - [9]Z. Ligeti, G.M. Tavares and M. Schmaltz,
*Explaining the*\( t\bar{t} \)*forward-backward asymmetry without dijet or flavor anomalies*,*JHEP***06**(2011) 109 [arXiv:1103.2757] [INSPIRE].ADSCrossRefGoogle Scholar - [10]J. Aguilar-Saavedra and M. Pérez-Victoria,
*Probing the Tevatron*\( t\bar{t} \)*asymmetry at LHC*,*JHEP***05**(2011) 034 [arXiv:1103.2765] [INSPIRE].ADSCrossRefGoogle Scholar - [11]M.I. Gresham, I.-W. Kim and K.M. Zurek,
*On models of new physics for the Tevatron top A*_{FB},*Phys. Rev.***D 83**(2011) 114027 [arXiv:1103.3501] [INSPIRE].ADSGoogle Scholar - [12]J. Shu, K. Wang and G. Zhu,
*A revisit to top quark forward-backward asymmetry*, arXiv:1104.0083 [INSPIRE]. - [13]J. Aguilar-Saavedra and M. Pérez-Victoria,
*No like-sign tops at Tevatron: constraints on extended models and implications for the*\( t\bar{t} \)*asymmetry*,*Phys. Lett.***B 701**(2011) 93 [arXiv:1104.1385] [INSPIRE].ADSGoogle Scholar - [14]A.E. Nelson, T. Okui and T.S. Roy,
*A unified, flavor symmetric explanation for the*\( t\bar{t} \)*asymmetry and Wjj excess at CDF*, arXiv:1104.2030 [INSPIRE]. - [15]G. Zhu,
*B physics constraints on a flavor symmetric scalar model to account for the*\( t\bar{t} \)*asymmetry and W*_{jj}*excess at CDF*,*Phys. Lett.***B 703**(2011) 142 [arXiv:1104.3227] [INSPIRE].ADSGoogle Scholar - [16]K. Babu, M. Frank and S.K. Rai,
*Top quark asymmetry and Wjj excess at CDF from gauged flavor symmetry*,*Phys. Rev. Lett.***107**(2011) 061802 [arXiv:1104.4782] [INSPIRE].ADSCrossRefGoogle Scholar - [17]Y. Cui, Z. Han and M.D. Schwartz,
*Top condensation as a motivated explanation of the top forward-backward asymmetry*,*JHEP***07**(2011) 127 [arXiv:1106.3086] [INSPIRE].ADSCrossRefGoogle Scholar - [18]J. Aguilar-Saavedra and M. Pérez-Victoria,
*Simple models for the top asymmetry: constraints and predictions*, arXiv:1107.0841 [INSPIRE]. - [19]L. Vecchi,
*Color & weak triplet scalars, the dimuon asymmetry in B*_{s}*decay, the top forward-backward asymmetry and the CDF dijet excess*,*JHEP***10**(2011) 003 [arXiv:1107.2933] [INSPIRE].ADSCrossRefGoogle Scholar - [20]J. Shu, T.M. Tait and K. Wang,
*Explorations of the top quark forward-backward asymmetry at the Tevatron*,*Phys. Rev.***D 81**(2010) 034012 [arXiv:0911.3237] [INSPIRE].ADSGoogle Scholar - [21]A. Arhrib, R. Benbrik and C.-H. Chen,
*Forward-backward asymmetry of top quark in diquark models*,*Phys. Rev.***D 82**(2010) 034034 [arXiv:0911.4875] [INSPIRE].ADSGoogle Scholar - [22]I. Dorsner, S. Fajfer, J.F. Kamenik and N. Kosnik,
*Light colored scalars from grand unification and the forward-backward asymmetry in*\( t\bar{t} \)*production*,*Phys. Rev.***D 81**(2010) 055009 [arXiv:0912.0972] [INSPIRE].ADSGoogle Scholar - [23]D.-W. Jung, P. Ko, J.S. Lee and S.-h. Nam,
*Model independent analysis of the forward-backward asymmetry of top quark production at the Tevatron*,*Phys. Lett.***B 691**(2010) 238 [arXiv:0912.1105] [INSPIRE].ADSGoogle Scholar - [24]J. Cao, Z. Heng, L. Wu and J.M. Yang,
*Top quark forward-backward asymmetry at the Tevatron: a comparative study in different new physics models*,*Phys. Rev.***D 81**(2010) 014016 [arXiv:0912.1447] [INSPIRE].ADSGoogle Scholar - [25]Q.-H. Cao, D. McKeen, J.L. Rosner, G. Shaughnessy and C.E. Wagner,
*Forward-backward asymmetry of top quark pair production*,*Phys. Rev.***D 81**(2010) 114004 [arXiv:1003.3461] [INSPIRE].ADSGoogle Scholar - [26]CDF collaboration, T. Aaltonen et al.,
*First measurement of the*\( t\bar{t} \)*differential cross section*\( {{{d\sigma }} \left/ {{dM\left( {t\bar{t}} \right)}} \right.} \)*in*\( p\bar{p} \)*Collisions at*\( \sqrt {s} = 1.96 \)*TeV*,*Phys. Rev. Lett.***102**(2009) 222003 [arXiv:0903.2850] [INSPIRE].ADSCrossRefGoogle Scholar - [27]V. Ahrens, A. Ferroglia, M. Neubert, B.D. Pecjak and L.L. Yang,
*Renormalization-group improved predictions for top-quark pair production at hadron colliders*,*JHEP***09**(2010) 097 [arXiv:1003.5827] [INSPIRE].ADSCrossRefGoogle Scholar - [28]CDF collaboration,
*Combination of CDF top quark pair production cross section measurements with up to*4*.*6*fb*^{−1}, CDF note 9913 (2009).Google Scholar - [29]CDF and D0 collaboration, C. Schwanenberger,
*Top quark production at the Tevatron*, arXiv:1012.2319 [INSPIRE]. - [30]D0 Collaboration,
*Measurements of the*\( t\bar{t} \)*corss section in the lepton + jets chammel with*4*.*3*fb*^{−1}, D0 note 6037 (2010).Google Scholar - [31]N. Kidonakis,
*Next-to-next-to-leading soft-gluon corrections for the top quark cross section and transverse momentum distribution*,*Phys. Rev.***D 82**(2010) 114030 [arXiv:1009.4935] [INSPIRE].ADSGoogle Scholar - [32]U. Langenfeld, S. Moch and P. Uwer,
*Measuring the running top-quark mass*,*Phys. Rev.***D 80**(2009) 054009 [arXiv:0906.5273] [INSPIRE].ADSGoogle Scholar - [33]M. Cacciari, S. Frixione, M.L. Mangano, P. Nason and G. Ridolfi,
*Updated predictions for the total production cross sections of top and of heavier quark pairs at the Tevatron and at the LHC*,*JHEP***09**(2008) 127 [arXiv:0804.2800] [INSPIRE].ADSCrossRefGoogle Scholar - [34]A. Martin, W. Stirling, R. Thorne and G. Watt,
*Parton distributions for the LHC*,*Eur. Phys. J.***C 63**(2009) 189 [arXiv:0901.0002] [INSPIRE].ADSCrossRefGoogle Scholar - [35]CTEQ collaboration, H. Lai et al.,
*Global QCD analysis of parton structure of the nucleon: CTEQ5 parton distributions*,*Eur. Phys. J.***C 12**(2000) 375 [hep-ph/9903282] [INSPIRE].ADSCrossRefGoogle Scholar - [36]K. Blum et al.,
*Implications of the CDF*\( t\bar{t} \)*forward-backward asymmetry for boosted top physics*,*Phys. Lett.***B 702**(2011) 364 [arXiv:1102.3133] [INSPIRE].ADSGoogle Scholar - [37]S. Jung, A. Pierce and J.D. Wells,
*Top quark asymmetry from a non-Abelian horizontal symmetry*,*Phys. Rev.***D 83**(2011) 114039 [arXiv:1103.4835] [INSPIRE].ADSGoogle Scholar - [38]K. Blum, Y. Grossman, Y. Nir and G. Perez,
*Combining*\( {K^0} - {\bar{K}^0} \)*mixing and*\( {D^0} - {\bar{D}^0} \)*mixing to constrain the flavor structure of new physics*,*Phys. Rev. Lett.***102**(2009) 211802 [arXiv:0903.2118] [INSPIRE].ADSCrossRefGoogle Scholar - [39]B. Grinstein, A. L. Kagan, M. Trott and J. Zupan, work in progress.Google Scholar
- [40]G. Isidori, Y. Nir and G. Perez,
*Flavor physics constraints for physics beyond the standard model*,*Ann. Rev. Nucl. Part. Sci.***60**(2010) 355 [arXiv:1002.0900] [INSPIRE].ADSCrossRefGoogle Scholar - [41]M. Beneke, G. Buchalla, M. Neubert and C.T. Sachrajda,
*QCD factorization in B*→*πK, ππ decays and extraction of Wolfenstein parameters*,*Nucl. Phys.***B 606**(2001) 245 [hep-ph/0104110] [INSPIRE].ADSCrossRefGoogle Scholar - [42]G. Buchalla, A.J. Buras and M.E. Lautenbacher,
*Weak decays beyond leading logarithms*,*Rev. Mod. Phys.***68**(1996) 1125 [hep-ph/9512380] [INSPIRE].ADSCrossRefGoogle Scholar - [43]M. Beneke, G. Buchalla, M. Neubert and C.T. Sachrajda,
*QCD factorization for B*→*ππ decays: strong phases and CP-violation in the heavy quark limit*,*Phys. Rev. Lett.***83**(1999) 1914 [hep-ph/9905312] [INSPIRE].ADSCrossRefGoogle Scholar - [44]Particle Data Group collaboration, K. Nakamura et al.,
*Review of particle physics*,*J. Phys.***G 37**(2010) 075021 [INSPIRE].ADSGoogle Scholar - [45]Belle collaboration, A. Das et al.,
*Measurements of branching fractions for B*^{0}→*D*_{s}^{+}*π*^{−}*and*\( {\bar{B}^0} \to D_s^{+} {K^{-} } \),*Phys. Rev.***D 82**(2010) 051103 [arXiv:1007.4619] [INSPIRE].ADSGoogle Scholar - [46]Belle collaboration, M. Iwabuchi et al.,
*Search for B*^{+}→*D*^{∗+}*π*_{0}*decay*,*Phys. Rev. Lett.***101**(2008) 041601 [arXiv:0804.0831] [INSPIRE].ADSCrossRefGoogle Scholar - [47]BELLE collaboration, F. Ronga et al.,
*Measurements of CP-violation in B*_{0}→*D*^{∗−}*π*^{+}*and B*_{0}→*D*^{−}*π*^{+}*decays*,*Phys. Rev.***D 73**(2006) 092003 [hep-ex/0604013] [INSPIRE].ADSGoogle Scholar - [48]
- [49]Q.-H. Cao et al.,
*W plus two jets from a quasi-inert Higgs doublet*,*JHEP***08**(2011) 002 [arXiv:1104.4776] [INSPIRE].ADSCrossRefGoogle Scholar - [50]D0 collaboration, V.M. Abazov et al.,
*Model-independent measurement of t-channel single top quark production in*\( p\bar{p} \)*collisions at*\( \sqrt {s} = 1.96 \)*TeV*, arXiv:1105.2788 [INSPIRE]. - [51]N. Kidonakis,
*Single top production at the Tevatron: threshold resummation and finite-order soft gluon corrections*,*Phys.*Rev*.***D**7**4**(2006) 114012 [hep-ph/0609287] [INSPIRE].ADSGoogle Scholar - [52]CMS collaboration, S. Chatrchyan et al.,
*Measurement of the t-channel single top quark production cross section in pp collisions at*\( \sqrt {s} = 7 \)*TeV*,*Phys. Rev. Lett.***107**(2011) 091802 [arXiv:1106.3052] [INSPIRE].ADSCrossRefGoogle Scholar - [53]N. Kidonakis,
*Next-to-next-to-leading-order collinear and soft gluon corrections for t-channel single top quark production*,*Phys. Rev.***D 83**(2011) 091503 [arXiv:1103.2792] [INSPIRE].ADSGoogle Scholar - [54]CDF collaboration, T. Aaltonen et al.,
*Direct top-quark width measurement CDF*,*Phys. Rev. Lett.***105**(2010) 232003 [arXiv:1008.3891] [INSPIRE].ADSCrossRefGoogle Scholar - [55]D0 collaboration, V.M. Abazov et al.,
*Determination of the width of the top quark*,*Phys. Rev. Lett.***106**(2011) 022001 [arXiv:1009.5686] [INSPIRE].ADSCrossRefGoogle Scholar - [56]CDF collaboration, T. Aaltonen et al.,
*Search for sign-like top quark pair production af CDF with*6*.*1*fb*^{−1}, CDF note 10466 (2011).Google Scholar - [57]CDF collaboration, T. Aaltonen et al.,
*Search for new particles decaying into dijets in proton-antiproton collisions at*\( \sqrt {s} = 1.96 \)*TeV*,*Phys. Rev.***D 79**(2009) 112002 [arXiv:0812.4036] [INSPIRE].ADSGoogle Scholar - [58]UA2 collaboration, J. Alitti et al.,
*A Search for new intermediate vector mesons and excited quarks decaying to two jets at the CERN*\( \bar{p}p \)*collider*,*Nucl. Phys.***B 400**(1993) 3 [INSPIRE].ADSCrossRefGoogle Scholar - [59]CMS collaboration, V. Khachatryan et al.,
*Measurement of dijet angular distributions and search for quark compositeness in pp collisions at*\( \sqrt {s} = 7 \)*TeV*,*Phys. Rev. Lett.***106**(2011) 201804 [arXiv:1102.2020] [INSPIRE].ADSCrossRefGoogle Scholar - [60]ATLAS collaboration, G. Aad et al.,
*Search for new physics in dijet mass and angular distributions in pp collisions at*\( \sqrt {s} = 7 \)*TeV measured with the ATLAS detector*,*New J. Phys.***13**(2011) 053044 [arXiv:1103.3864] [INSPIRE].ADSCrossRefGoogle Scholar - [61]M.E. Peskin and D.V. Schroeder,
*An introduction to quantum field theory*, Addison-Wesley, U.S.A. (1995), p. 842.Google Scholar