Flavor Changing Neutral Currents involving Heavy Quarks with Four Generations

Abstract

We study various FCNC involving heavy quarks in the Standard Model (SM) with a sequential fourth generation. After imposing $B\to X_s\gamma$, $B\to X_s{l}^{+}{l}^{-}$ and $Z\to b\bar{b}$ constraints, we find $\mathcal{B}(Z\to s\bar{b}+\bar{s}b)$ can be enhanced by an order of magnitude to $10^{-7}$, while $t\to cZ,cH$ decays can reach $10^{-6}$, which are orders of magnitude higher than in SM. However,these rates are still not observable for the near future.With the era of LHC approaching, we focus on FCNC decays involving fourth generation $b^{\prime }$ and $t^{\prime }$ quarks. We calculate the rates for loop induced FCNC decays $b^{\prime }\to bZ,bH,bg,b\gamma$, as well as $t^\prime\to tZ,\tH, tg, tγ$. If $|V_{c{b}^{\prime }}|$ is of order $|V_{cb}|\simeq 0.04$, tree level $b^{\prime }\to cW$ decay would dominate, posing a challenge since $b$-tagging is less effective. For $|V_{c{b}^{\prime }}|\ll |V_{cb}|$, $b^{\prime }\to tW$ would tend to dominate, while $b^{\prime }\to t^{\prime }{W}^{\ast }$ could also open for heavier $b^{\prime }$, leading to thepossibility of quadruple-$W$ signals via $b^{\prime }{\bar{b}}^{\prime }\to b\bar{b}{W}^{+}{W}^{-}{W}^{+}{W}^{-}$. The FCNC $b^{\prime }\to bZ,bH$ decays could still dominate if $m_{b^{\prime }}$ is just above 200 GeV. For the case of $t^{\prime }$, ingeneral $t^{\prime }\to bW$ would be dominant, hence it behaves like a heavy top. For both $b^{\prime }$ and $t^{\prime }$, except for the intriguing light $b^{\prime }$ case, FCNC decays are in the $10^{-4}-10^{-2}$ range, and are quite detectable at the LHC.For a possible future ILC, we find the associated production of FCNC $e^{+}{e}^{-}\to b\bar{s}$, $t\bar{c}$ are below sensitivity, while $e^{+}{e}^{-}\to b^{\prime }\bar{b}$ and$t^{\prime }\bar{t}$ can be better probed.Tevatron Run-II can still probe the lighter $b^{\prime }$ or $t^{\prime }$ scenario. LHC would either discover the fourth generation and measure the FCNC rates, or rule out the fourth generation conclusively.

31 pages, 15 eps figures, version to appear in JHEP

References in corpus (10)

• Precision Electroweak Measurements on the Z Resonance
• Evidence for Direct CP Violation in B0 -> K+- pi-+ Decays
• See-Saw Energy Scale and the LSND Anomaly
• Corrections to sin(2 beta) from CP asymmetries in B^0 -> (pi^0,rho^0,eta,eta^',omega,phi) K_S decays
• News from FormCalc and LoopTools
• Difference in B^+ and B^0 Direct CP Asymmetry as Effect of a Fourth Generation
• Enhanced KL to pi0 nu nubar from Direct CP Violation in B to K pi with Four Generations
• Branching Fractions and CP Asymmetries in B0 -> pi0pi0, B+ -> pi+pi0 and B+ -> K+pi0 Decays and Isospin Analysis of the B -> pipi System
• Top and Higgs Flavor Changing Neutral Couplings in two Higgs Doublets Model
• eV Seesaw with Four Generations

Cited by in corpus (43)

• Four Statements about the Fourth Generation
• Less space for a new family of fermions
• How much space is left for a new family?
• SM with four generations: Selected implications for rare B and K decays
• The discovery of the fourth family at the LHC: what if?
• Search for heavy bottom-like quarks in 4.9 inverse femtobarns of pp collisions at sqrt(s) = 7 TeV
• An improved determination of the width of the top quark
• Collider aspects of flavour physics at high Q
• Search for a Vector-like Quark with Charge 2/3 in t + Z Events from pp Collisions at sqrt(s) = 7 TeV
• Experimental constraints on fourth generation quark masses
• Flavor and CP Violation with Fourth Generations Revisited
• Search for single top-quark production via flavour changing neutral currents at 8 TeV with the ATLAS detector
• A Strongly Coupled Fourth Generation at the LHC
• Rare Decay of the Top t->c l lbar and Single Top Production at International Linear Collider
• Dimension six FCNC operators and top production at the LHC
• Search for a Heavy Bottom-like Quark in pp Collisions at sqrt(s) = 7 TeV
• Direct Mass Limits for Chiral Fourth-Generation Quarks in All Mixing Scenarios
• Combined effects of strong and electroweak FCNC effective operators in top quark physics at the LHC
• Scalar Dark Matter and Standard Model with Four Generations
• Constraints on flavor-changing neutral-current $Htq$ couplings from the signal of $tH$ associated production with QCD next-to-leading order accuracy at the LHC
• Search for the Top Partner at the LHC using Multi-b-Jet Channels
• Higgs data confronts Sequential Fourth Generation Fermions in the Higgs Triplet Model
• Small violations of unitarity, the phase in Bs mixing and visible t->cZ decays at the LHC
• A fourth generation, anomalous like-sign dimuon charge asymmetry and the LHC
• CP violation and the 4th generation
• Collider signals of a composite Higgs in the Standard Model with four generations
• Leading Effect of CP Violation with Four Generations
• Extended Friedberg Lee hidden symmetries, quark masses and CP-violation with four generations
• The Fourth Generation t-prime in Extensions of the Standard Model
• Single Production of Fourth Family $t^{\prime }$ Quarks at LHeC
• A Search for the Fourth SM Family: Tevatron still has a Chance
• Fourth Generation Majorana Neutrinos
• CP Violation in Fourth Generation Quark Decays
• Top quark rare three-body decays in the littlest Higgs model with T-parity
• Fourth Generation Leptons and Muon $g-2$
• Production of Single Heavy Charged Leptons at a Linear Collider
• Detecting Fourth Generation Quarks at Hadron Colliders
• Impact of FCNC top quark interactions on BR(t -> b W)
• Heavy QQ(bar) "Fireball" Annihilation to Multiple Vector Bosons
• Higgs Phenomenology in Warped Extra-Dimensions with a 4th Generation
• Threshold Effects in the Decay of Heavy b' and t' Quarks
• The flavor-changing bottom-strange quark production in the littlest Higgs model with T parity at the ILC
• Neutron EDM in Four Generation Standard Model