scholarly journals Improving the theoretical prediction for the Bs - B̅s width difference: matrix elements of next-to-leading order ΔB = 2 operators

2018 ◽  
Vol 175 ◽  
pp. 13023 ◽  
Author(s):  
Christine Davies ◽  
Judd Harrison ◽  
G Peter Lepage ◽  
Christopher Monahan ◽  
Junko Shigemitsu ◽  
...  
Keyword(s):  
Standard Model Prediction ◽  
Bottom Quarks ◽  
Matrix Elements ◽  
Leading Order ◽  
Physical Point ◽  
Difference Matrix ◽  
Strange Quarks ◽  
Width Difference ◽  
The Standard Model ◽  
The Matrix

We present lattice QCD results for the matrix elements of R2 and other dimension-7, ΔB = 2 operators relevant for calculations of Δs, the Bs - B̅s width difference. We have computed correlation functions using 5 ensembles of the MILC Collaboration’s 2+1 + 1-flavour gauge field configurations, spanning 3 lattice spacings and light sea quarks masses down to the physical point. The HISQ action is used for the valence strange quarks, and the NRQCD action is used for the bottom quarks. Once our analysis is complete, the theoretical uncertainty in the Standard Model prediction for ΔΓs will be substantially reduced.

scholarly journals Lattice calculation of the hadronic leading order contribution to the muon g − 2

2020 ◽  
Vol 234 ◽  
pp. 01016
Author(s):  
Hartmut Wittig ◽  
Antoine Gérardin ◽  
Marco Cè ◽  
Georg von Hippel ◽  
Ben Hörz ◽  
...  
Keyword(s):  
Standard Model Prediction ◽  
Detailed Comparison ◽  
New Physics ◽  
Current Status ◽  
Leading Order ◽  
Lattice Calculation ◽  
Muon Anomalous Magnetic Moment ◽  
The Standard Model ◽  
Vacuum Polarisation

The persistent discrepancy of about 3.5 standard deviations between the experimental measurement and the Standard Model prediction for the muon anomalous magnetic moment, aµ, is one of the most promising hints for the possible existence of new physics. Here we report on our lattice QCD calculation of the hadronic vacuum polarisation contribution $ a_\mu ^{{\rm{hvp}}} $, based on gauge ensembles with Nf = 2 + 1 flavours of O(a) improved Wilson quarks. We address the conceptual and numerical challenges that one encounters along the way to a sub-percent determination of the hadronic vacuum polarisation contribution. The current status of lattice calculations of $ a_\mu ^{{\rm{hvp}}} $ is presented by performing a detailed comparison with the results from other groups.

scholarly journals Computation of parton distributions from the quasi-PDF approach at the physical point

2018 ◽  
Vol 175 ◽  
pp. 14008 ◽  
Author(s):  
Constantia Alexandrou ◽  
Simone Bacchio ◽  
Krzysztof Cichy ◽  
Martha Constantinou ◽  
Kyriakos Hadjiyiannakou ◽  
...  
Keyword(s):  
Pion Mass ◽  
Distribution Functions ◽  
Matrix Elements ◽  
Parton Distribution Functions ◽  
Physical Point ◽  
Parton Distributions ◽  
The Matrix ◽  
First Results ◽  
Perturbative Renormalization ◽  
Vector Combination

We show the first results for parton distribution functions within the proton at the physical pion mass, employing the method of quasi-distributions. In particular, we present the matrix elements for the iso-vector combination of the unpolarized, helicity and transversity quasi-distributions, obtained with Nf = 2 twisted mass cloverimproved fermions and a proton boosted with momentum [see formula in PDF] = 0.83 GeV. The momentum smearing technique has been applied to improve the overlap with the proton boosted state. Moreover, we present the renormalized helicity matrix elements in the RI’ scheme, following the non-perturbative renormalization prescription recently developed by our group.

scholarly journals A REVIEW OF THE MAGNITUDES OF THE CKM MATRIX ELEMENTS

2008 ◽  
Vol 23 (31) ◽  
pp. 4945-4958 ◽  
Author(s):  
FRANCESCA DI LODOVICO
Keyword(s):  
Standard Model ◽  
Current Status ◽  
Matrix Elements ◽  
Ckm Matrix ◽  
The Standard Model ◽  
The Matrix ◽  
The Absolute ◽  
Ckm Matrix Elements

Flavour mixing is described within the Standard Model by the Cabibbo–Kobayashi–Maskawa (CKM) matrix elements. With the increasingly higher statistics collected by many experiments, the matrix elements are measured with improved precision, allowing for more stringent tests of the Standard Model. In this paper, a review of the current status of the absolute values of the CKM matrix elements is presented, with particular attention to the latest measurements.

scholarly journals A factorisation-aware Matrix element emulator

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
D. Maître ◽  
H. Truong
Keyword(s):  
Neural Network ◽  
Phase Space ◽  
Matrix Element ◽  
Percent Level ◽  
Matrix Elements ◽  
Leading Order ◽  
Jet Production ◽  
The Neural Network ◽  
The Matrix ◽  
The One

Abstract In this article we present a neural network based model to emulate matrix elements. This model improves on existing methods by taking advantage of the known factorisation properties of matrix elements. In doing so we can control the behaviour of simulated matrix elements when extrapolating into more singular regions than the ones used for training the neural network. We apply our model to the case of leading-order jet production in e+e− collisions with up to five jets. Our results show that this model can reproduce the matrix elements with errors below the one-percent level on the phase-space covered during fitting and testing, and a robust extrapolation to the parts of the phase-space where the matrix elements are more singular than seen at the fitting stage.

scholarly journals THEORY OF THE τ LEPTON ANOMALOUS MAGNETIC MOMENT

2007 ◽  
Vol 22 (03) ◽  
pp. 159-179 ◽  
Author(s):  
S. EIDELMAN ◽  
M. PASSERA
Keyword(s):  
Standard Model ◽  
Model Prediction ◽  
Magnetic Moment ◽  
Anomalous Magnetic Moment ◽  
Standard Model Prediction ◽  
Low Energy ◽  
Leading Order ◽  
The Standard Model

This paper reviews and updates the Standard Model prediction of the τ lepton g-2. Updated QED and electroweak contributions are presented, together with new values of the leading-order hadronic term, based on the recent low energy e+ e- data from BaBar, CMD-2, KLOE and SND, and hadronic light-by-light contribution. The total prediction is confronted to the available experimental bounds on the τ lepton anomaly, and prospects for its future measurements are briefly discussed.

scholarly journals Lattice QCD Matrix Elements for the Bs0−B¯s0 Width Difference beyond Leading Order

2020 ◽  
Vol 124 (8) ◽  
Author(s):  
Christine T. H. Davies ◽  
Judd Harrison ◽  
G. Peter Lepage ◽  
Christopher J. Monahan ◽  
Junko Shigemitsu ◽  
...  
Keyword(s):  
Lattice Qcd ◽  
Matrix Elements ◽  
Leading Order ◽  
Width Difference

scholarly journals Colour?Spin Matrix Elements for Multiquark Systems

1980 ◽  
Vol 33 (6) ◽  
pp. 951 ◽  
Author(s):  
RP Bickerstaff ◽  
BG Wybourne
Keyword(s):  
Classification Scheme ◽  
Spin Operator ◽  
Tensor Operator ◽  
Matrix Elements ◽  
S Wave ◽  
Strange Quarks ◽  
Colour Singlet ◽  
Singlet States ◽  
The Matrix ◽  
Relevant Interaction

Tensor operator methods have been developed for calculating the matrix elements of the two-particle colour-spin operator that arises in the calculation of the quark-gluon interaction in the MIT bagmodel treatment of the S-wave colour singlet states of multiquark hadrons. A group classification scheme for multi quark states which distinguishes the nonstrange and strange quarks, and thus avoids the occurrence of hidden strangeness ss pairs, is constructed. This scheme has the added advantage of avoiding any need to approximate the strangeness dependence of the relevant interaction integrals. The colour-spin matrix elements for all the q4 if colour singlet states and for the strangeness - 2 states of q6 are given by way of examples. A number of checking procedures have been developed to ensure the correctness of the calculated matrix elements.

scholarly journals BSM Kaon Mixing at the Physical Point

2018 ◽  
Vol 175 ◽  
pp. 13010 ◽  
Author(s):  
Peter Boyle ◽  
Nicolas Garron ◽  
Julia Kettle ◽  
Ava Khamseh ◽  
Justus Tobias Tsang
Keyword(s):  
Domain Wall ◽  
Standard Model ◽  
Lattice Qcd ◽  
Pion Mass ◽  
Beyond The Standard Model ◽  
Matrix Elements ◽  
Physical Point ◽  
Gauge Action ◽  
The Standard Model ◽  
Mixing Matrix

We present a progress update on the RBC-UKQCD calculation of beyond the standard model (BSM) kaon mixing matrix elements at the physical point. Simulations are performed using 2+1 flavour domain wall lattice QCD with the Iwasaki gauge action at 3 lattice spacings and with pion masses ranging from 430 MeV to the physical pion mass.

scholarly journals Fully exclusive heavy quark-antiquark pair production from a colourless initial state at NNLO in QCD

2020 ◽  
Vol 2020 (11) ◽  
Author(s):  
Gábor Somogyi ◽  
Francesco Tramontano
Keyword(s):  
Bottom Quarks ◽  
Standard Model Higgs Boson ◽  
Leading Order ◽  
Initial State ◽  
Order Accuracy ◽  
Massive Quark ◽  
Subtraction Scheme ◽  
Fully Differential ◽  
The Standard Model ◽  
Analytic Expressions

Abstract We present a local subtraction scheme for computing next-to-next-to-leading order QCD corrections to the production of a massive quark-antiquark pair from a colourless initial state. The subtraction terms are built following the CoLoRFulNNLO method and refined in such a way that their integration gives rise to compact, fully analytic expressions. All ingredients necessary for a numerical implementation of our subtraction scheme are provided in detail. As an example, we calculate the fully differential decay rate of the Standard Model Higgs boson to massive bottom quarks at next-to-next-to-leading order accuracy in perturbative QCD.

scholarly journals Masses and decay constants of the η and η′ mesons from lattice QCD

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
◽  
Gunnar S. Bali ◽  
Vladimir Braun ◽  
Sara Collins ◽  
Andreas Schäfer ◽  
...  
Keyword(s):  
Quark Mass ◽  
Matrix Elements ◽  
Leading Order ◽  
Decay Constants ◽  
The Matrix ◽  
Spatial Lattice ◽  
Quark Mass Dependence ◽  
The Masses ◽  
First Time ◽  
Energy Constants

Abstract We determine the masses, the singlet and octet decay constants as well as the anomalous matrix elements of the η and η′ mesons in Nf = 2 + 1 QCD. The results are obtained using twenty-one CLS ensembles of non-perturbatively improved Wilson fermions that span four lattice spacings ranging from a ≈ 0.086 fm down to a ≈ 0.050 fm. The pion masses vary from Mπ = 420 MeV to 126 MeV and the spatial lattice extents Ls are such that LsMπ ≳ 4, avoiding significant finite volume effects. The quark mass dependence of the data is tightly constrained by employing two trajectories in the quark mass plane, enabling a thorough investigation of U(3) large-Nc chiral perturbation theory (ChPT). The continuum limit extrapolated data turn out to be reasonably well described by the next-to-leading order ChPT parametrization and the respective low energy constants are determined. The data are shown to be consistent with the singlet axial Ward identity and, for the first time, also the matrix elements with the topological charge density are computed. We also derive the corresponding next-to-leading order large-Nc ChPT formulae. We find F8 = 115.0(2.8) MeV, θ8 = −25.8(2.3)°, θ0 = −8.1(1.8)° and, in the $$ \overline{\mathrm{MS}} $$ MS ¯ scheme for Nf = 3, F0(μ = 2 GeV) = 100.1(3.0) MeV, where the decay constants read $$ {F}_{\eta}^8 $$ F η 8 = F8 cos θ8, $$ {F}_{\eta \prime}^8 $$ F η ′ 8 = F8 sin θ8, $$ {F}_{\eta}^0 $$ F η 0 = −F0 sin θ0 and $$ {F}_{\eta \prime}^0 $$ F η ′ 0 = F0 cos θ0. For the gluonic matrix elements, we obtain aη(μ = 2 GeV) = 0.0170(10) GeV3 and aη′(μ = 2 GeV) = 0.0381(84) GeV3, where statistical and all systematic errors are added in quadrature.

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