Nuclear Theory·nucl-th

Tuesday·September 15, 2015

14 papers—7 primary·7 cross-listed

08
Scaling properties of inclusive W $^{\pm}$ production at hadron colliders
François Arleo🇫🇷 · Émilien Chapon🇫🇷 · Hannu Paukkunen🇫🇮
We consider the hadroproduction of W gauge bosons in their leptonic decay mode. Starting from the leading-order expressions, we show that by defining a suitable scaling variable the centre-of-mass dependence of the cross sections at the LHC energies can be essentially described by a simple power law. The scaling exponent is directly linked to the small- $x$ behaviour of parton distribution functions (PDF) which, at the high virtualities involved in W production, is largely dictated by QCD evolution equations. This entails a particularly simple scaling law for the lepton charge asymmetry and also predicts that measurements in different collision systems (p-p, p- $p ˉ$ , p-Pb Pb-Pb) are straightforwardly related. The expectations are compared with the existing data and a very good overall agreement is observed. It is shown that the PDF uncertainty in certain cross-section ratios between nearby centre-of-mass energies can be significantly reduced by taking the ratios at fixed value of scaling variable instead of fixed rapidity.
↳ hep-phhep-exnucl-exnucl-thEPJC(2016)·12 citations
09
Symmetry violations in nuclear and neutron $β$ decay
K.K. Vos🇳🇱 · H.W. Wilschut🇳🇱 · R.G.E. Timmermans🇳🇱
The role of $β$ decay as a low-energy probe of physics beyond the Standard Model is reviewed. Traditional searches for deviations from the Standard Model structure of the weak interaction in $β$ decay are discussed in the light of constraints from the LHC and the neutrino mass. Limits on the violation of time-reversal symmetry in $β$ decay are compared to the strong constraints from electric dipole moments. Novel searches for Lorentz symmetry breaking in the weak interaction in $β$ decay are also included, where we discuss the unique sensitivity of $β$ decay to test Lorentz invariance. We end with a roadmap for future $β$ -decay experiments.
↳ hep-phhep-exnucl-exnucl-thRMP(2015)·71 citations
10
Pentaquarks and Tetraquarks at LHCb
Sheldon Stone🇺🇸
Exotic resonant structures found in $Λ_{b}^{0}$ and $B^{0}$ decays into charmonium in the LHCb experiment are discussed. Examination of the $J / ψ p$ system in $Λ_{b}^{0} \to J / ψ K^{-} p$ decays shows two states each of which must be composed of $uu d c c$ quarks, and thus are called charmonium pentaquarks. Their masses are $4380 \pm 8 \pm 29$ ~MeV and $4449.8 \pm 1.7 \pm 2.5$ ~MeV, and their corresponding widths ( $Γ$ ) are $205 \pm 18 \pm 86$ MeV, and $39 \pm 5 \pm 19$ MeV. The preferred $J^{P}$ assignments are of opposite parity, with one state having spin 3/2 and the other 5/2. Models of internal binding of the pentaquark states are discussed. Finally, another mesonic state is discussed, the $Z (4430)^{-}$ that decays into $ψ^{'} π^{-}$ and was first observed by the Belle collaboration in $B^{0} \to ψ^{'} K^{+} π^{-}$ decays. Using a sample of approximately 25,000 signal events, LHCb determines the $J^{P}$ to be $1^{+}$ .
↳ hep-exhep-phnucl-exnucl-thPoS(2015)·13 citations
11
Heavy flavor in nucleus-nucleus and proton-nucleus: quenching, flow and correlations
M. Nardi🇮🇹 · A. Beraudo🇮🇹 · A. De Pace🇮🇹 · M. Monteno🇮🇹 · F. Prino (INFN Torino)🇮🇹
We present recent results for heavy-flavor observables in nucleus-nucleus collisions at LHC energies, obtained with the POWLANG transport setup. The initial creation of c-cbar and b-bbar pairs is simulated with a perturbative QCD approach (POWHEG+PYTHIA); their propagation in the medium (created in the nucleus-nucleus or in proton-nucleus collision) is studied with the relativistic Langevin equation, here solved using weak-coupling transport coefficients. Successively, the heavy quarks hadronize in the medium. We compute the nuclear modification factor and the elliptic flow parameter of the final D mesons both in nucleus-nucleus and in (for the first time, in the POWLANG setup) proton-nucleus collisions and compare our results to experimental data.
↳ hep-phnucl-thNucl.Part.Phys.Proc.(2016)·7 citations
12
Transition form factors $γ^{*} \to γ f_{2} (1270)$ and $γ^{*} \to γ a_{2} (1320)$ in the $e^{+} e^{-}$ collisions
N.N. Achasov🇷🇺 · A.V. Kiselev🇷🇺
The predictions for transition form factors $γ^{*} \to γ f_{2} (1270)$ and $γ^{*} \to γ a_{2} (1320)$ and corresponding $e^{+} e^{-} \to γ^{*} \to f_{2} γ$ and $e^{+} e^{-} \to γ^{*} \to a_{2} γ$ cross sections are obtained for the energy region up to $2$ GeV. These predictions are coordinated with the recent Belle data on the $γ^{*} (Q^{2}) γ \to f_{2}$ transition. It is shown that the QCD asymptotics of the amplitudes of the reactions $e^{+} e^{-} \to γ^{*} \to f_{2} γ$ and $e^{+} e^{-} \to γ^{*} \to a_{2} γ$ can be reached only by taking into account a compensation of contributions of $ρ (770)$ , $ω (782)$ with contributions of their radial excitations. The relation $σ (e^{+} e^{-} \to γ^{*} \to f_{2} γ) / σ (e^{+} e^{-} \to γ^{*} \to a_{2} γ) \approx 25/9$ , obtained with the help of the $q q ˉ$ model of $a_{2}$ and $f_{2}$ and QCD, is used to determine the $σ (e^{+} e^{-} \to γ^{*} \to a_{2} γ)$ at high energies. Recent BABAR measurement of the $e^{+} e^{-} \to f_{2} γ \to π^{+} π^{-} γ$ cross section at $10.58$ GeV gives hope for detailed investigation of the $γ^{*} (s) \to f_{2} γ$ and $γ^{*} (s) \to a_{2} γ$ transition form factors at high energy region.
↳ hep-phhep-exnucl-thEPJ Web Conf.(2016)·2 citations
13
Proton-lambda correlation functions at the LHC with account for residual correlations
V. M. Shapoval🇺🇦 · Yu. M. Sinyukov🇺🇦 · V. Yu. Naboka🇺🇦
The theoretical analysis of $p ˉ - Λ \oplus p - Λ ˉ$ correlation function in 10% most central Au+Au collisions at RHIC energy $s_{N N} = 200$ GeV shows that the contribution of residual correlations is the necessary factor to obtain a satisfactory description of the experimental data. A neglecting of the residual correlation effect, leads to unrealistically low source radius, about 2 times smaller than the corresponding value for $p - Λ \oplus p ˉ - Λ ˉ$ case, when one fits the experimental correlation function within Lednicky-Lyuboshitz analytical model. Recently an approach accounting effectively for residual correlations for the baryon-antibaryon correlation function was proposed, and a good RHIC data description was reached with the source radius extracted from the hydrokinetic model (HKM). The $p ˉ - Λ$ scattering length, as well as the parameters characterizing the residual correlation effect --- annihilation dip amplitude and its inverse width --- were extracted from the corresponding fit. In this paper we use these extracted values and simulated in HKM source functions for Pb+Pb collisions at the LHC energy $s_{N N} = 2.76$ TeV to predict the corresponding $p Λ$ and $p Λ ˉ$ correlation functions.
↳ hep-phhep-exnucl-exnucl-thPRC(2015)·2 citations
14
Photon and dilepton production from a non-equilibrium quark-gluon plasma
Lusaka Bhattacharya🇺🇸 · Radoslaw Ryblewski🇵🇱 · Michael Strickland🇺🇸
We calculate leading-order medium photon and dilepton yields from a quark-gluon plasma using (3+1)-dimensional anisotropic hydrodynamics. In the case of dileptons, at leading-order it is sufficient to take into account non-equilibrium corrections to the rate through the use of anisotropic distribution functions. In the case of photons, non-equilibrium corrections to the rate are taken into account using a self-consistent modification of the distribution functions and the corresponding anisotropic hard-loop quark self-energies. We present predictions for the high-energy photon and dilepton spectrum and the photon elliptic flow as a function of invariant mass, transverse momentum, shear viscosity, and initial momentum-space anisotropy. Our findings indicate that both high-energy photon and dilepton production are sensitive to the assumed level of initial momentum-space anisotropy of the quark-gluon plasma. In addition, we find that the photon elliptic flow depends on the initial momentum-space anisotropy.
↳ hep-phnucl-thNucl.Part.Phys.Proc.(2016)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE

Scaling properties of inclusive W± production at hadron colliders

Symmetry violations in nuclear and neutron β decay

Pentaquarks and Tetraquarks at LHCb

Heavy flavor in nucleus-nucleus and proton-nucleus: quenching, flow and correlations

Transition form factors γ∗→γf2​(1270) and γ∗→γa2​(1320) in the e+e− collisions

Proton-lambda correlation functions at the LHC with account for residual correlations

Photon and dilepton production from a non-equilibrium quark-gluon plasma

Affiliations

Scaling properties of inclusive W $^{\pm}$ production at hadron colliders

Symmetry violations in nuclear and neutron $β$ decay

Transition form factors $γ^{} \to γ f_{2} (1270)$ and $γ^{} \to γ a_{2} (1320)$ in the $e^{+} e^{-}$ collisions