Function Of Q2 Research Articles

Determination of short- and long-distance contributions in B0→K*0μ+μ− decays

An amplitude analysis of the B0→K*0μ+μ− decay is presented. The analysis is based on data collected by the LHCb experiment from proton-proton collisions at s=7, 8 and 13 TeV, corresponding to an integrated luminosity of 4.7 fb−1. For the first time, Wilson coefficients and nonlocal hadronic contributions are accessed directly from the unbinned data, where the latter are parametrized as a function of q2 with a polynomial expansion. Wilson coefficients and nonlocal hadronic parameters are determined under two alternative hypotheses: the first relies on experimental information alone, while the second one includes information from theoretical predictions for the nonlocal contributions. Both models obtain similar results for the parameters of interest. The overall level of compatibility with the Standard Model is evaluated to be between 1.8 and 1.9 standard deviations when looking at the C9 Wilson coefficient alone, and between 1.3 and 1.4 standard deviations when considering the full set of C9,C10,C9′ and C10′ Wilson coefficients. The ranges reflect the theoretical assumptions made in the analysis. © 2024 CERN, for the LHCb Collaboration 2024 CERN

Disentangling QCD and new physics in D \u2192 \u03c0\u2113+\u2113\u2212

In this paper we consider the decay D+ → π+ℓ+ℓ−, addressing in particular the resonance contributions as well as the relatively large contributions from the weak annihilation diagrams. For the weak annihilation diagrams we include known results from QCD factorisation at low q2 and at high q2, adapting the existing calculation for B decays in the Operator Product Expansion. The hadronic resonance contributions are obtained through a dispersion relation, modelling the spectral functions as towers of Regge-like resonances in each channel, as suggested by Shifman, imposing the partonic behaviour in the deep Euclidean. The parameters of the model are extracted using e+e− → (hadrons) and τ → (hadrons) + ντ data as well as the branching ratios for the resonant decays D+ → π+R(R → ℓ+ℓ−), with R = ρ, ω, and ϕ. We perform a thorough error analysis, and present our results for the Standard Model differential branching ratio as a function of q2. Focusing then on the observables FH and AFB, we consider the sensitivity of this channel to effects of physics beyond the Standard Model, both in a model independent way and for the case of leptoquarks.

Electroexcitation of Nucleon Resonances in a Light-Front Relativistic Quark Model

We report the predictions for the 3q core contributions to the electroexcitation of the resonances Delta(1232)3/2+, N(1440)1/2+, N(1520)3/2-, N(1535)1/2-, and N(1675)5/2- on the proton obtained in the light-front relativistic quark model (LF RQM). For these states, experimental data on the electroexcitation transition amplitudes allow us to make comparison between the experiment and LF RQM predictions in wide range of Q2 and also to quantify the expected meson-baryon contributions as a function of Q2.

Latest results on diffraction at HERA

Recent results on diffraction from the H1 and ZEUS experiments at HERA are presented. Measurement of open charm production in diffractive DIS has been performed by the H1 experiment using the event topology, given by ep → eXY, where the system X, containing at least one D*(2010) meson, is separated from a leading low-mass proton dissociative system Y by a large rapidity gap. The photoproduction of isolated photons is measured using diffractive events recorded by the ZEUS experiment. Cross sections are evaluated in the photon transverse-energy and pseudorapidity ranges 5 < EγT < 15 GeV and -0:7 < ηγ < 0:9, inclusively and with a jet with transverse-energy and pseudorapidity in the ranges 4 < EjetT < 35 GeV and -1:5 < ηjet < 1:8. The exclusive deep inelastic electroproduction and photoproduction of Ψ(2S ) and J=Ψ(1S) mesons has been also studied by ZEUS. The cross-section ratio σ(Ψ(2S))=σ(J=Ψ(1S)) has been measured as a function of Q2, W and t. The results are compared to several predictions of QCD-inspired models, providing tests of the models in a region of soft to hard diffraction.

Statistical approach to modeling relationships of composition – structure – property I: Alkaline earth phosphate glasses

This paper introduces a methodology of accurate property predictions for amorphous materials (focusing on oxide phosphate glass) based on statistical composition (C) – structure (S) – property (P) modeling. Utilizing literature reported 31P MAS NMR data (Qn, δiso, η) of binary alkaline earth phosphate glasses RO-P2O5 (R = Mg, Ca, Sr, Ba), unified relationships of RO and Qn (n = 2, 3) were firstly established. A statistical approach to modeling mathematic relationships of C-S, S-P and then C-S-P for the alkaline earth binary phosphate glasses was illustrated step by step. The C-S models of Q2 and Q3 were then used to calculate Q2 and Q3 in the mixed alkaline earth (MAE) phosphate glass, MgO-CaO-P2O5, which in turn result in S-P models accurately tracks the glass properties, density, Young's modulus, glass transition temperature, and Microhardness. The S-P models were also used to simulate non-linear relationships of the MAE phosphate glasses as a function of Q2/(Q2+Q3) from the glass network structure view point in comparison with the property responses to the change of MgO/(MgO + CaO). Within the entire composition space of the alkaline earth phosphate glasses with RO/P2O5 ≤ 1, the statistical C-S-P modeling for predicting glass properties, including glass transition temperature, Young's modulus, density, etc., requires no assumptions on glass structures or other constraints as compared with other theoretically based modeling approaches.

Electroexcitation of nucleon resonances of the [70,1−] multiplet in a light-front relativistic quark model

We utilize a light-front relativistic quark model to predict the 3q core contribution to the electroexcitation of nucleon resonances of the [70,1-] multiplet on the proton and neutron at Q2 < 5GeV2. The investigation is stimulated in large degree by expected progress in the studies of the electroexcitation of nucleon resonances in the third resonance region in the CLAS experiment. For the resonances N(1520)3/2-, N(1535)1/2-, and N(1675)5/2-, experimental data on electroexcitation amplitudes on the proton are available in a wide range of Q2. This allowed us to quantify the expected meson-baryon contributions to these amplitudes as a function of Q2.

Measurement of the cross-section ratio σψ(2S)/σJ/ψ(1S) in deep inelastic exclusive ep scattering at HERA

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range 2<Q2<80 GeV2, 30<W<210 GeV and |t|<1 GeV2, where Q2 is the photon virtuality, W is the photon–proton centre-of-mass energy and t is the squared four-momentum transfer at the proton vertex. The data for 2<Q2<5 GeV2 were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb−1. The data for 5<Q2<80 GeV2 are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb−1. The decay modes analysed were μ+μ− and J/ψ(1S)π+π− for the ψ(2S) and μ+μ− for the J/ψ(1S). The cross-section ratio σψ(2S)/σJ/ψ(1S) has been measured as a function of Q2,W and t. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.

Differential branching fraction and angular analysis of Λ0 b → Λμ+μ− decays

AbstractThe differential branching fraction of the rare decayΛb0 → Λμ+μ−is measured as a function ofq2, the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb−1, collected by the LHCb experiment. Evidence of signal is observed in theq2region below the square of theJ/ψmass. Integrating over 15&lt; q2&lt;20 GeV2/c4the differential branching fraction is measured as$$ \mathrm{d}\mathrm{\mathcal{B}}\left({\varLambda}_b^0\to \varLambda {\mu}^{+}{\mu}^{-}\right)/d{q}^2=\left({1.18}_{-0.08}^{+0.09}\pm 0.03\pm 0.27\right)\times {10}^{-7}{\left({\mathrm{GeV}}^2/{c}^4\right)}^{-1}, $$dℬΛb0→Λμ+μ−/dq2=1.18−0.08+0.09±0.03±0.27×10−7GeV2/c4−1,where the uncertainties are statistical, systematic and due to the normalisation mode,Λb0 → J/ψΛ, respectively. In theq2intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon (AFBℓ) and hadron (AFBh) systems are measured for the first time. In the range 15&lt; q2&lt;20 GeV2/c4they are found to be$$ \begin{array}{l}{A}_{\mathrm{FB}}^{\ell }=-0.05\pm 0.09\left(\mathrm{stat}\right)\pm 0.03\left(\mathrm{syst}\right)\;\mathrm{and}\hfill \\ {}{A}_{\mathrm{FB}}^h=-0.29\pm 0.07\left(\mathrm{stat}\right)\pm 0.03\left(\mathrm{syst}\right).\hfill \end{array} $$AFBℓ=−0.05±0.09stat±0.03systandAFBh=−0.29±0.07stat±0.03syst.

Spin density matrix elements in exclusive $$\omega $$ ω electroproduction on $$^1$$ 1 H and $$^2$$ 2 H targets at 27.5 GeV beam energy

Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive ρ 0 electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized hydrogen and deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted in the kinematic region 1<Q 2<7 GeV2, 3.0<W<6.3 GeV, and −t<0.4 GeV2. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic dependences of all SDMEs on Q 2 and t are presented, as well as the longitudinal-to-transverse ρ 0 electroproduction cross-section ratio as a function of Q 2. A small but statistically significant deviation from the hypothesis of s-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes; these amplitudes are naturally generated with a quark-exchange mechanism.

Measurement of beauty and charm production in deep inelastic scattering at HERA and measurement of the beauty-quark mass

Abstract: The production of beauty and charm quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q2< 1000 GeV2 using an integrated luminosity of 354 pb−1. The beauty and charm content in events with at least one jet have been extracted using the invariant mass of charged tracks associated with secondary vertices and the decay-length significance of these vertices. Differential cross sections as a function of Q2, Bjorken x, jet trans- verse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of x and Q2. The running beauty-quark mass, mb at the scale mb, was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be mb(mb) = 4.07 ± 0.14 (fit)− 0.07+ 0.01(mod.)− 0.00+ 0.05(param.)− 0.05+ 0.08(theo.) GeV.

Transverse target spin asymmetries in exclusive [formula omitted] muoproduction

Exclusive production of ρ0 mesons was studied at the COMPASS experiment by scattering 160 GeV/c muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured as a function of Q2, xBj, or pT2. The sinϕS asymmetry is found to be −0.019±0.008(stat.)±0.003(syst.). All other asymmetries are also found to be of small magnitude and consistent with zero within experimental uncertainties. Very recent calculations using a GPD-based model agree well with the present results. The data is interpreted as evidence for the existence of chiral-odd, transverse generalized parton distributions.

Exclusive neutral pion electroproduction in the deeply virtual regime

We present measurements of the ep→epπ0 cross section extracted at two values of four-momentum transfer Q2=1.9 GeV2 and Q2=2.3 GeV2 at Jefferson Lab Hall A. The kinematic range allows one to study the evolution of the extracted cross section as a function of Q2 and W. Results are confronted with Regge-inspired calculations and GPD predictions. An intepretation of our data within the framework of semi-inclusive deep inelastic scattering is also discussed.8 MoreReceived 16 March 2010DOI:https://doi.org/10.1103/PhysRevC.83.025201©2011 American Physical Society

Measurement of the neutrino neutral-current elastic differential cross section on mineral oil atEν∼1 GeV

We report a measurement of the flux-averaged neutral-current elastic differential cross section for neutrinos scattering on mineral oil (CH2) as a function of four-momentum transferred squared, Q2. It is obtained by measuring the kinematics of recoiling nucleons with kinetic energy greater than 50 MeV which are readily detected in MiniBooNE. This differential cross-section distribution is fit with fixed nucleon form factors apart from an axial mass MA that provides a best fit for MA=1.39±0.11 GeV. Using the data from the charged-current neutrino interaction sample, a ratio of neutral-current to charged-current quasielastic cross sections as a function of Q2 has been measured. Additionally, single protons with kinetic energies above 350 MeV can be distinguished from neutrons and multiple nucleon events. Using this marker, the strange quark contribution to the neutral-current axial vector form factor at Q2=0, Δs, is found to be Δs=0.08±0.26.8 MoreReceived 13 August 2010DOI:https://doi.org/10.1103/PhysRevD.82.092005© 2010 The American Physical Society

Measurement of isolated photon production in deep inelastic ep scattering

Isolated photon production in deep inelastic ep scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 320 pb−1. Measurements were made in the isolated-photon transverse-energy and pseudorapidity ranges 4<ETγ<15 GeV and −0.7<ηγ<0.9 for exchanged photon virtualities, Q2, in the range 10<Q2<350 GeV2 and for invariant masses of the hadronic system WX>5 GeV. Differential cross sections are presented for inclusive isolated photon production as functions of Q2, x, ETγ and ηγ. Leading-logarithm parton-shower Monte Carlo simulations and perturbative QCD predictions give a reasonable description of the data over most of the kinematic range.

Transverse momentum broadening of hadrons produced in semi-inclusive deep-inelastic scattering on nuclei

The first detailed measurement of the dependence on target nuclear mass of the average squared transverse momentum 〈pt2〉 of π+, π−, and K+ mesons from deep-inelastic lepton scattering is obtained as a function of several kinematic variables. The data were accumulated at the Hermes experiment at Desy, in which the Hera 27.6 GeV lepton beam was scattered off several nuclear gas targets. The average squared transverse momentum was clearly observed to increase with atomic mass number. The effect increases as a function of Q2 and x and remains constant as a function of both the virtual photon energy ν and the fractional hadron energy z, except that it vanishes as z approaches unity.

Measurement of the Differential Branching Fraction and Forward-Backward Asymmetry forB→K(*)l+l−

We study B --> K(*)l+l- decays (l = e, mu) based on a data sample of 657 x 10(6) BB pairs collected with the Belle detector at the KEKB e+e- collider. We report the differential branching fraction, isospin asymmetry, K* polarization, and the forward-backward asymmetry (A(FB)) as functions of q2 = M(ll)(2)c2. The fitted A(FB) spectrum exceeds the standard model expectation by 2.7 standard deviations. The measured branching fractions are B(B --> K*l+l-) = (10.7(-1.0)(+1.1) +/- 0.9) x 10(-7) and B(B --> Kl+l-) = (4.8(-0.4)(+0.5) +/- 0.3) x 10(-7), where the first errors are statistical and the second are systematic, with the muon to electron ratios R(K*) = 0.83 +/- 0.17 +/- 0.08 and R(K) = 1.03 +/- 0.19 +/- 0.06.

Spin density matrix elements in exclusive ρ 0 electroproduction on 1H and 2H targets at 27.5 GeV beam energy

Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive ρ0 electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized hydrogen and deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted in the kinematic region 1<Q2<7 GeV2, 3.0<W<6.3 GeV, and −t<0.4 GeV2. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic dependences of all SDMEs on Q2 and t are presented, as well as the longitudinal-to-transverse ρ0 electroproduction cross-section ratio as a function of Q2. A small but statistically significant deviation from the hypothesis of s-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes; these amplitudes are naturally generated with a quark-exchange mechanism.

Exclusive ρ0 production in deep inelastic scattering at HERA

Exclusive ρ0 electroproduction at HERA has been studied with the ZEUS detector using 120 pb−1 of integrated luminosity collected during 1996-2000. The analysis was carried out in the kinematic range of photon virtuality 2 < Q2 < 160 GeV2 and γ∗p centre-of-mass energy 32 < W < 180 GeV. The results include the Q2 and W dependence of the γ∗p → ρ0p cross section and the distribution of the squared-four-momentum transfer to the proton. The helicity analysis of the decay-matrix elements of the ρ0 was used to study the ratio of the γ∗p cross section for longitudinal and transverse photon as a function of Q2, W and t. Finally, an effective Pomeron trajectory was extracted.

S-duality action on discrete T-duality invariants

In heterotic string theory compactified on T6, the T-duality orbits of dyons of charge (Q, P) are characterized by O(6, 22; ) invariants Q2, P2 and Q ⋅ P together with a set of invariants of the discrete T-duality group O(6, 22; ). We study the action of S-duality group on the discrete T-duality invariants and study its consequence for the dyon degeneracy formula. In particular we find that for dyons with torsion r, the degeneracy formula, expressed as a function of Q2, P2 and Q ⋅ P, is required to be manifestly invariant under only a subgroup of the S-duality group. This subgroup is isomorphic to Γ0(r). Our analysis also shows that for a given torsion r, all other discrete T-duality invariants are characterized by the elements of the coset SL(2, )/Γ0(r).

Inclusive D*± meson and associated dijet production in deep-inelastic scattering at HERA

Inclusive D*± production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D*± meson is investigated. The analysis covers values of photon virtuality 2 ≤ Q2 ≤ 100 GeV2 and of inelasticity 0.05≤y≤0.7. Differential cross sections are measured as a function of Q2 and x and of various D*± meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon–gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the kT-unintegrated gluon distribution of the proton.