Bounds on the mass of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>b</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>quark, reexamined

Oliveira, Sancho; Santos, Rui

doi:10.1103/physrevd.68.093012

Cited by 7 publications

(4 citation statements)

References 36 publications

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“…Theoretical constraints like the perturbativity of the Yukawa couplings and the perturbative unitarity of heavy fermion scattering amplitudes [17] bound the masses from above. In spite of the rather strong bounds from all the above directions, there is still parameter space available for the fourth generation that is consistent with all the data [18][19][20][21][22][23][24][25][26][27][28][29]. The fourth-generation scenario (SM4) is thus still viable even after the recent Tevatron and LHC results [30,31].…”

Section: Introductionmentioning

confidence: 90%

Large mass splittings for fourth generation fermions allowed by LHC Higgs boson exclusion

Dighe¹,

Ghosh²,

Godbole³

et al. 2012

Phys. Rev. D

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In the context of the standard model with a fourth generation, we explore the allowed mass spectra in the fourth-generation quark and lepton sectors as functions of the Higgs mass. Using the constraints from unitarity and oblique parameters, we show that a heavy Higgs allows large mass splittings in these sectors, opening up new decay channels involving W emission. Assuming that the hints for a light Higgs do not yet constitute an evidence, we work in a scenario where a heavy Higgs is viable. A Higgs heavier than ∼ 800 GeV would in fact necessitate either a heavy quark decay channel t → b W/b → t W or a heavy lepton decay channel τ → ν W as long as the mixing between the third and fourth generations is small. This mixing tends to suppress the mass splittings and hence the W -emission channels. The possibility of the W -emission channel could substantially change the search strategies of fourth-generation fermions at the LHC and impact the currently reported mass limits.

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Section: Introductionmentioning

confidence: 90%

Large mass splittings for fourth generation fermions allowed by LHC Higgs boson exclusion

Dighe¹,

Ghosh²,

Godbole³

et al. 2012

Phys. Rev. D

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“…The corresponding lower bounds are m t ′ > ∼ 220 and m b ′ > ∼ 190 GeV [30]. The above limits can be relaxed if we consider the possibility that b ′ → bH , b ′ → cW and b ′ → bZ decays can be of comparable size under certain conditions of the CKM elements [31,32]. Unless associated CKM elements are extremely small, in general the b ′ (and certainly the t ′ ) quark should not be very long-lived.…”

Section: Direct Searchmentioning

confidence: 99%

“…Searching for b ′ quark through its FCNC decays, an analysis by D0 excludes the b ′ in the mass range M Z /2 < m b ′ < M Z +m b that decays via the FCNC b ′ → bγ process [27]. CDF excludes [28] The above limits can be relaxed if we consider the possibility that b ′ → bH , b ′ → cW and b ′ → bZ decays can be of comparable size under certain conditions of the CKM elements [31,32]. Unless associated CKM elements are extremely small, in general the b ′ (and certainly the t ′ ) quark should not be very long-lived.…”

Section: Direct Searchmentioning

confidence: 99%

Flavor changing neutral currents involving heavy quarks with four generations

Arhrib¹,

Hou²

2006

J. High Energy Phys.

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We study various flavor changing neutral currents (FCNC) involving heavy quarks in the Standard Model (SM) with a sequential fourth generation. After imposing B → X s γ, B → X s l + l − and Z → bb constraints, we find B(Z → sb +sb) can be enhanced by an order of magnitude to 10 −7 , while t → cZ, cH decays can reach 10 −6 , which are orders of magnitude higher than three generation SM. However, these rates are still not observable for the near future. With the era of Large Hadron Collider approaching, we focus on FCNC decays involving fourth generation b ′ and t ′ quarks. We calculate the rates for loop induced FCNC decays b ′ → bZ, bH, bg, bγ, as well as t ′ → tZ, tH, tg, tγ. If |V cb ′ | is of order |V cb | ≃ 0.04, tree level b ′ → cW decay would dominate, posing a challenge since b-tagging is less effective. For |V cb ′ | ≪ |V cb |, b ′ → tW would tend to dominate, while b ′ → t ′ W * could also open for heavier b ′ , leading to the possibility of quadruple-W signals via b ′b′ → bbW + W − W + W − . The FCNC b ′ → bZ, bH decays could still dominate if m b ′ is just above 200 GeV. For the case of t ′ , in general t ′ → bW would be dominant, hence it behaves like a heavy top. For both b ′ and t ′ , except for the intriguing light b ′ case, FCNC decays are typically in the 10 −4 − 10 −2 range, and are quite detectable at the LHC. For a possible future International Linear Collider, we find the associated production of FCNC e + e − → bs, tc are below sensitivity, while e + e − → b ′b and t ′t can be better probed. Tevatron Run-II can still probe the lighter b ′ or t ′ scenario. LHC would either discover the fourth generation and measure the FCNC rates, or rule out the fourth generation conclusively. If discovered, the ILC can study the b ′ or t ′ decay modes in detail.

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“…If a priori assumptions on b decays are not made, limits can be found on the branching ratios of these two channels [407][408][409]. In particular, it is found that for b quarks with masses ∼100 GeV near the LEP kinematical limit there are some windows in parameter space where b could have escaped discovery.…”

Section: New Quarksmentioning

confidence: 99%

Collider aspects of flavor physics at high Q

Lari¹,

Pape²,

Porod³

et al. 2009

Flavor in the Era of the LHC

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This chapter of the "Flavor in the era of LHC" workshop report discusses flavor-related issues in the production and decays of heavy states at the LHC at high momentum transfer Q, both from the experimental and the theoretical perspective. We review top quark physics, and discuss the flavor aspects of several extensions of the standard model, such as supersymmetry, little Higgs models or models with extra dimensions. This includes discovery aspects, as well as the measurement of several properties of these heavy states. We also present publicly available computational tools related to this topic.

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Bounds on the mass of theb′quark, reexamined

Cited by 7 publications

References 36 publications

Large mass splittings for fourth generation fermions allowed by LHC Higgs boson exclusion

Large mass splittings for fourth generation fermions allowed by LHC Higgs boson exclusion

Flavor changing neutral currents involving heavy quarks with four generations

Collider aspects of flavor physics at high Q

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