Abstract We present results for SCET and bHQET matching coefficients and jet functions in the large-β 0 limit. Our computations exactly predict all terms of the form α s n + 1 n f n $$ ...{\alpha}_s^{n+1}{n}_f^n $$ for any n ≥ 0, and we find full agreement with the coefficients computed in the full theory up to O α s 4 $$ \mathcal{O}\left({\alpha}_s^4\right) $$ . We obtain all-order closed expressions for the cusp and non-cusp anomalous dimensions (which turn out to be unambiguous) as well as matrix elements (with ambiguities) in this limit, which can be easily expanded to arbitrarily high powers of α s using recursive algorithms to obtain the corresponding fixed-order coefficients. Examining the poles laying on the positive real axis of the Borel-transform variable u we quantify the perturbative convergence of a series and estimate the size of non-perturbative corrections. We find a so far unknown u = 1/2 renormalon in the bHQET hard factor H m that affects the normalization of the peak differential cross section for boosted top quark pair production. For ambiguous series the so-called Borel sum is defined with the principal value prescription. Furthermore, one can assign an ambiguity based on the arbitrariness of avoiding the poles by contour deformation into the positive or negative imaginary half-plane. Finally, we compute the relation between the pole mass and four low-scale short distance masses in the large-β 0 approximation (MSR, RS and two versions of the jet mass), work out their μ- and R-evolution in this limit, and study how their implementation improves the convergence of the position-space bHQET jet function, whose three-loop coefficient in full QCD is numerically estimated.
A
bstract
We present results for SCET and bHQET matching coefficients and jet functions in the large-
β
0
limit. Our computations exactly predict all terms of the form
α
s
n
+
1
n
f
n
for any
n
≥ 0, ...and we find full agreement with the coefficients computed in the full theory up to
O
α
s
4
. We obtain all-order closed expressions for the cusp and non-cusp anomalous dimensions (which turn out to be unambiguous) as well as matrix elements (with ambiguities) in this limit, which can be easily expanded to arbitrarily high powers of
α
s
using recursive algorithms to obtain the corresponding fixed-order coefficients. Examining the poles laying on the positive real axis of the Borel-transform variable
u
we quantify the perturbative convergence of a series and estimate the size of non-perturbative corrections. We find a so far unknown
u
= 1
/
2 renormalon in the bHQET hard factor
H
m
that affects the normalization of the peak differential cross section for boosted top quark pair production. For ambiguous series the so-called Borel sum is defined with the principal value prescription. Furthermore, one can assign an ambiguity based on the arbitrariness of avoiding the poles by contour deformation into the positive or negative imaginary half-plane. Finally, we compute the relation between the pole mass and four low-scale short distance masses in the large-
β
0
approximation (MSR, RS and two versions of the jet mass), work out their
μ
- and R-evolution in this limit, and study how their implementation improves the convergence of the position-space bHQET jet function, whose three-loop coefficient in full QCD is numerically estimated.
In this letter, we evaluate the potential of linear e+e− colliders to measure the top quark mass in radiative events and in a suitable short-distance scheme. We present a calculation of the ...differential cross section for production of a top quark pair in association with an energetic photon from initial state radiation, as a function of the invariant mass of the tt¯ system. This matched calculation includes the QCD enhancement of the cross section around the tt¯ production threshold and remains valid in the continuum well above the threshold. The uncertainty in the top mass determination is evaluated in realistic operating scenarios for the Compact Linear Collider (CLIC) and the International Linear Collider (ILC), including the statistical uncertainty and the theoretical and experimental systematic uncertainties. With this method, the top quark mass can be determined with a precision of 110 MeV in the initial stage of CLIC, with 1 ab−1 at s=380 GeV, and with a precision of approximately 150 MeV at the ILC, with L=4 ab−1 at s=500 GeV. Radiative events allow measurements of the top quark mass at different renormalization scales, and we demonstrate that such a measurement can yield a statistically significant test of the evolution of the MSR mass mtMSR(R) for scales R<mt.
A
bstract
The Compact Linear Collider (CLIC) is a proposed future high-luminosity linear electron-positron collider operating at three energy stages, with nominal centre-of-mass energies
s
= 380 GeV, ...1
.
5 TeV, and 3 TeV. Its aim is to explore the energy frontier, providing sensitivity to physics beyond the Standard Model (BSM) and precision measurements of Standard Model processes with an emphasis on Higgs boson and top-quark physics. The opportunities for top-quark physics at CLIC are discussed in this paper. The initial stage of operation focuses on top-quark pair production measurements, as well as the search for rare flavour-changing neutral current (FCNC) top-quark decays. It also includes a top-quark pair production threshold scan around 350 GeV which provides a precise measurement of the top-quark mass in a well-defined theoretical framework. At the higher-energy stages, studies are made of top-quark pairs produced in association with other particles. A study of t
̄
tH production including the extraction of the top Yukawa coupling is presented as well as a study of vector boson fusion (VBF) production, which gives direct access to high-energy electroweak interactions. Operation above 1 TeV leads to more highly collimated jet environments where dedicated methods are used to analyse the jet constituents. These techniques enable studies of the top-quark pair production, and hence the sensitivity to BSM physics, to be extended to higher energies. This paper also includes phenomenological interpretations that may be performed using the results from the extensive top-quark physics programme at CLIC.
Form factors in the radiative pion decay Mateu, V.; Portolés, J.
European physical journal. C, Particles and fields,
10/2007, Letnik:
52, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We perform an analysis of the form factors that rule the structure-dependent amplitude in radiative pion decay. The resonance contributions to π→eνeγ decays are computed through the proper ...construction of the vector and axial-vector form factors by setting the QCD driven asymptotic properties of the three-point Green functions 〈VVP〉 and 〈VAP〉, and by demanding the smoothening of the form factors at high transfer of momentum. A comparison between theoretical and experimental determination of the form factors is also carried out. We also consider and evaluate the role played by a non-standard tensor form factor. We conclude that, at present and due to the hadronic uncertainties, the search for new physics in this process is not feasible.
In this work we take a revised look at the charm quark mass determination from QCD sum rules analyses. On the theoretical side we use the most up to date calculations (amounting to up
expressions) ...and on the experimental side, to our knowledge, the most complete data set (maximum coverage of the energy spectrum). We reconsider the estimate of perturbative uncertainties (due to truncation of the series in
α
s
) proposing four alternative methods (equivalent in perturbation theory) to determine the
charm quark mass. We also use a very robust method to combine data from different experiments when systematic correlated errors are mainly due to normalization. This allows to use experimental data up to 10.5GeV, and to quantify statistic and systematic experimental errors in a meaningful way.
This report of the BOOST2012 workshop presents the results of four working groups that studied key aspects of jet substructure. We discuss the potential of first-principle QCD calculations to yield a ...precise description of the substructure of jets and study the accuracy of state-of-the-art Monte Carlo tools. Limitations of the experiments’ ability to resolve substructure are evaluated, with a focus on the impact of additional (pile-up) proton proton collisions on jet substructure performance in future LHC operating scenarios. A final section summarizes the lessons learnt from jet substructure analyses in searches for new physics in the production of boosted top quarks.
Allergic rhinitis is the most frequent chronic allergic disease in children, and may be an important risk factor for the subsequent development of asthma.
To describe the characteristics of patients ...younger than 14 years of age presenting with rhinitis and the possible association with asthma.
We carried out a prospective, observational, descriptive, cross-sectional epidemiologic study (Alergológica 2005) of 917 patients under the age of 14 consulting for the first time in allergy departments in Spain.
Rhinitis was diagnosed in 42.5% of the children. The association between asthma and rhinitis was significantly higher in children than in adults (44.9% vs 35.5%; P<.05). Time from onset of rhinitis was significantly associated with the development of asthma (2.97 vs 2.06 years; P<.0001). Allergy was the most frequent cause of rhinitis in children with and without asthma. Allergy to epithelia and fungi was more frequent in children with rhinitis and asthma than in children with rhinitis alone. We found no differences in the frequency of treatment with immunotherapy between children with and without asthma.
Rhinitis was frequently associated with asthma in children consulting for the first time at allergy departments. Time since onset of rhinitis and sensitivity to epithelia and fungi were associated with the development of asthma.
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