Polarized top decay into polarized W t(↑)→W(↑)+b at O(αs)

Fischer, M.; Groote, S.; Körner, Jürgen; Mauser, M. C.; Lampe, Bodo

doi:10.1016/s0370-2693(99)00194-x

Cited by 61 publications

(100 citation statements)

References 22 publications

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“…Note that both the production and decay density matrices are gauge invariant. The one-loop QCD corrections to the semileptonic decays of polarised top quarks and to t → W + b can be extracted from the results of [16] and [17,18], respectively. In the following we describe our computation of the density matrices for tt production by qq annihilation.…”

Section: Pacs Number(s)mentioning

confidence: 99%

Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions

Bernreuther

Brandenburg²,

2000

Physics Letters B

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Abstract:Future hadron collider experiments are expected to record large to huge samples of tt events. The analysis of these data with respect to tt spin-spin correlations requires precise predictions of the production of these quark pairs in a general spin configuration. Therefore we have computed, at next-to-leading order (NLO) in the QCD coupling, the spin density matrices describing tt production by quark antiquark annihilation, which is the dominant production process at the Tevatron. Moreover we have computed the strength of the tt spin correlation at NLO, using various spin quantization axes. Pairs of top and antitop quarks will be produced copiously with the upgraded Fermilab Tevatron collider and in even larger numbers with the Large Hadron Collider (LHC) at CERN, allowing for detailed investigations of the properties of these quarks in the future. For this aim the study of top spin phenomena will play an important role. This is because the top quark, as compared with lighter quarks, is unique in that it is sufficiently short-lived to prevent hadronization effects from diluting the spin-polarisations and spin-spin correlations that were imprinted upon the t andt quarks by their production mechanism. Hence spin-polarization and spin-correlation phenomena will provide valuable information about the interactions of top quarks. An attempt to detect these spin correlations in a small tt dilepton sample collected at the Tevatron was recently reported by the D0 collaboration [1]. Needless to say, in order to interpret future data, the predictions of these spin phenomena should be as precise as possible. Within the Standard Model (SM) top antitop pair production at hadron colliders is determined by QCD. So far the nextto-leading order (NLO) QCD corrections are known for the spin-averaged differential tt cross section [2,3,4,5], while spin correlations were analysed only to leadingorder [6,7,8,9,10,11] in α s . In this letter we report on progress in providing a complete description of these spin effects within QCD at NLO: We have computed, as a first step in this direction, the tt spin density matrices for the parton reactions qq → tt, ttg to order α 3 s . We have also calculated, for these reactions, the degree of the tt spin correlation at NLO for different t andt spin quantization axes. PACS number(s):At the Tevatron qq annihilation is the dominant process for producing top quark pairs while at the LHC tt production is mainly due to gluon gluon fusion. The tt spin correlations and spin polarisations can be inferred from appropriate angular correlations and distributions of the t andt decay products. In the SM the main top decay modes are t → bW → bqq ′ , bℓν ℓ . Among these final states the charged leptons, or the jets from quarks of weak isospin -1/2 originating from W decay, are most sensitive to the polarisation of the top quarks. Hence to leading order in the QCD coupling one has to treat the two parton reactionswhere f = q, ℓ, ν ℓ . The amplitudes for these two-to six-body processes, with intermediate t...

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Section: Pacs Number(s)mentioning

confidence: 99%

Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions

Bernreuther

Brandenburg²,

2000

Physics Letters B

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“…The results are taken from Ref. [3]. We divide out the total m b = 0 Born term rate and denote the scaled…”

Section: O(α S ) Radiative Correctionsmentioning

confidence: 99%

“…The two transverse helicity rates i = +, − are obtained from the i = U, F rates given in [3] by taking the linear combinations Γ ± = 1 2 (Γ U ± Γ F ) as discussed before. One haŝ…”

Section: O(α S ) Radiative Correctionsmentioning

confidence: 99%

“…Optimistically the measurement errors can eventually be reduced to the (1−2)% level [2]. If such a level of accuracy can in fact be reached it is important to discuss the radiative corrections to the different helicity rates [3,4] considering the fact that the O(α s ) radiative corrections to the total width Γ are rather large (≈ −9.4%) [5,6,7,8,9]. The transverse-plus rate Γ + is particularly interesting in this regard.…”

Section: Introductionmentioning

confidence: 99%

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$O(\alpha _{s})$ radiative corrections to spin observables in polarized $t$ and $b$ decays

Koerner¹

2000

Proceedings of Third Latin American Symposium on High Energy Physics — PoS(silafae-III)

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In this talk we consider the O(α s ) radiative corrections to the decay of an unpolarized top quark into a bottom quark and a W gauge boson where the helicities of the W are specified as transverse-plus, transverse-minus and longitudinal. The O(α s ) radiative corrections lower the normalized longitudinal rate Γ L /Γ by 0.8%. We find that the normalized transverse-plus rate Γ + /Γ, which vanishes at the Born term level for m b → 0, receives radiative correction contributions at the sub-percent level. Our results are discussed in the light of recent measurements of the helicity content of the W in top quark decays by the CDF Collaboration.

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“…The fraction of longitudinally polarized W bosons is defined by [3], gives F 0 = 0.697 ± 0.007, where the given uncertainty is only due to the uncertainty in the top quark mass. Next-toleading-order corrections to the total decay width and the partial decay width into longitudinal W bosons amount to about -10% [10,11,12,13,14,15,16,17,18,19]. However, the fraction of longitudinal W bosons is only negligibly changed.…”

Section: Introductionmentioning

confidence: 98%

Measurement of the helicity fractions ofWbosons from top quark decays using fully reconstructedtt¯events with CDF II

Abulencia¹,

Adelman²,

Affolder³

et al. 2007

Phys. Rev. D

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We present a measurement of the fractions F0 and F+ of longitudinally polarized and right-handed W bosons in top quark decays using data collected with the CDF II detector. The data set used in the analysis corresponds to an integrated luminosity of approximately 318 pb −1 . We select tt candidate events with one lepton, at least four jets, and missing transverse energy. Our helicity measurement uses the decay angle θ * , which is defined as the angle between the momentum of the charged lepton in the W boson rest frame and the W momentum in the top quark rest frame. The cos θ * distribution in the data is determined by full kinematic reconstruction of the tt candidates. We find F0 = 0.85 +0.15 −0.22 (stat) ± 0.06 (syst) and F+ = 0.05−0.05 (stat) ± 0.03 (syst), which is consistent with the standard model prediction. We set an upper limit on the fraction of right-handed W bosons of F+ < 0.26 at the 95% confidence level.

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Polarized top decay into polarized W t(↑)→W(↑)+b at O(αs)

Cited by 61 publications

References 22 publications

Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions

Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions

$O(\alpha _{s})$ radiative corrections to spin observables in polarized $t$ and $b$ decays

Measurement of the helicity fractions ofWbosons from top quark decays using fully reconstructedtt¯events with CDF II

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