Bounds on vector leptoquarks

Leurer, Miriam

doi:10.1103/physrevd.50.536

Cited by 68 publications

(72 citation statements)

References 43 publications

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“…Other LQ couplings involving the light fermions of the first and second generations are constrained by the existing experimental data to be much smaller than the limits (5.20) and (5.21) [69]. However, if we have to learn a lesson from the hierarchy in the fermion Yukawa couplings, then it seems natural to expect a large hierarchy in the LQ couplings to the different generations as well.…”

Section: Light Leptoquarksmentioning

confidence: 99%

First limit on inclusive decay and constraints on new physics

1996

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In a recent article [1] we presented the derivation of the first limit on the inclusive B → X s νν decay rate. Our work stemmed from the observation that a published ALEPH bound on BR(B → τν) [2], inferred from the absence of large missing energy events in B decays, implies also a limit on BR(B → X s νν). We estimated this limit by comparing the missing energy spectra in the two decay modes. Theoretically, B → X s νν is a very clean process, which is also sensitive to several possible sources of new physics [1]. Therefore, a dedicated experimental search is important. The result of such an analysis by the ALEPH Collaboration, using the full LEP-I data sample, is to appear soon [3].As a result of discussions with members of the ALEPH Collaboration [4], we found two errors in our numerical results. The corrected analysis yields a limit weaker than our original result [1] by about a factor of three. The corrections included here are formally beyond the free quark decay result at tree level (of order α s , Λ QCD /m b , and higher). However, they affect the final limit significantly, due to the specific details of the experimental analysis.First, due to a mistake in our Monte Carlo code, the energy of the X s hadronic final state in the B rest frame was evaluated as a fraction of the b quark mass, rather than as a fraction of the B meson mass. This resulted in a harder missing energy spectrum than the true one. Correcting for this weakens the limit by about 35%.Second, we neglected the effects of the invariant mass distribution of the final hadrons, 1 which we (implicitly) assumed not to extend to high mass states. However, the invariant mass of the X s system can be well above 1 GeV [5]. Because of the large boost into the LEP laboratory frame and the high missing energy range (> 35 GeV) used in the analysis[2] (which is large compared to the average B meson energy at LEP), neglecting this effect yielded a missing energy spectrum in the laboratory frame considerably harder than the correct one.It is not straightforward to include properly this second effect into the analysis. However, an estimate can be obtained by approximating the invariant mass spectrum of the X s system with a Gaussian distribution with mean (µ) and variance (σ) fitted to the averages M 2 X and M 4 X , as given in [5]. Such a fit yields µ ≃ 1.35 GeV and σ ≃ 0.6 GeV. There is about a 10% uncertainty in these values, due to their dependences on the heavy quark effective theory parameterΛ (≃ m B − m b ). Treating the X s mass distribution as independent of the energy spectrum, and including a theoretical uncertainty of about 15% related to the fitted values of µ and σ, we find that the original limit given in [1] is weakened by about a factor of three. While small values of E X favor small values of M X (beyond the trivial kinematic constraint E X > M X ), the correlation between E X and M X only slightly improve the bound.In conclusion, the bound on BR(B → X s νν) given in the Abstract and in Eqs. (1.2) and (6.1) of [1] is weaker by about a facto...

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Section: Light Leptoquarksmentioning

confidence: 99%

First limit on inclusive decay and constraints on new physics

1996

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“…The states S 0 , S 1/2 and V 0 , V 1/2 couple to both left-and right-handed quarks. Here, only g L or g R is assumed to be non-zero since low energy processes and rare decays of π and K constrain the product g L g R [26]. Upper limits on the allowed values for |g| are presented in Figure 3 for scalar leptoquarks and in Figure 4 for vector leptoquarks.…”

Section: Leptoquarksmentioning

confidence: 99%

Search for manifestations of new physics in fermion-pair production at LEP

Acciarri¹,

Achard²,

Adriani³

et al. 2000

Physics Letters B

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The measurements of hadron and lepton-pair production cross sections and leptonic forward-backward asymmetries performed with the L3 detector at centre-of-mass energies between 130 GeV and 189 GeV are used to search for new physics phenomena such as: contact interactions, exchange of virtual leptoquarks, scalar quarks and scalar neutrinos, effects of TeV strings in models of quantum gravity with large extra dimensions and non-zero sizes of the fermions. No evidence for these phenomena is found and new limits on their parameters are set.

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“…The strongest bounds for leptoquarks coupling to the first lepton and quark generations arise from atomic parity violation experiments and from universality in leptonic π decays. Davidson et al [12] give M LQ /λ limits in the range of 1.6 to 2.2 TeV for scalar leptoquarks and 2.2 to 3.1 TeV for vector leptoquarks, while Leurer [13] arrives at values up to a factor of ∼ 1.5 either lower or higher, and generally gets larger values for scalar than for vector leptoquarks. Despite of these uncertainties, our most stringent limits for vector leptoquarks are within a factor of two close to the ones extracted from the very low energy experiments.…”

Section: Leptoquarksmentioning

confidence: 99%

Leptoquarks and compositeness scales from a contact interaction analysis of deep inelastic e±p scattering at HERA

Aïd¹,

Andreev²,

Andrieu

et al. 1995

Physics Letters B

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Abstract.A contact interaction analysis is presented to search for new phenomena beyond the Standard Model in deep inelastic e ± p → e ± hadrons scattering. The data are collected with the H1 detector at HERA and correspond to integrated luminosities of 0.909 pb −1 and 2.947 pb −1 for electron and positron beams, respectively. The differential cross sections dσ/dQ 2 are measured in the Q 2 range between 160 GeV 2 and 20, 000 GeV 2 . The absence of any significant deviation from the Standard Model prediction is used to constrain the couplings and masses of new leptoquarks and to set limits on electron-quark compositeness scales and on the radius of light quarks.

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Bounds on vector leptoquarks

Cited by 68 publications

References 43 publications

First limit on inclusive decay and constraints on new physics

First limit on inclusive decay and constraints on new physics

Search for manifestations of new physics in fermion-pair production at LEP

Leptoquarks and compositeness scales from a contact interaction analysis of deep inelastic e±p scattering at HERA

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