Flip Amplitudes Research Articles

Deeply Virtual Compton Scattering Cross Section at High Bjorken xB

We report high-precision measurements of the deeply virtual Compton scattering (DVCS) cross section at high values of the Bjorken variable x_{B}. DVCS is sensitive to the generalized parton distributions of the nucleon, which provide a three-dimensional description of its internal constituents. Using the exact analytic expression of the DVCS cross section for all possible polarization states of the initial and final electron and nucleon, and final state photon, we present the first experimental extraction of all four helicity-conserving Compton form factors (CFFs) of the nucleon as a function of x_{B}, while systematically including helicity flip amplitudes. In particular, the high accuracy of the present data demonstrates sensitivity to some very poorly known CFFs.

Nucleon Structure and Spin Effects in Elastic Hadron Scattering

Soft diffraction phenomena in elastic nucleon scattering are considered from the viewpoint of the spin dependence of the interaction potential. Spin-dependent pomeron effects are analyzed for elastic pp scattering, and spin-dependent differential cross sections and spin correlation parameters are calculated. The spin correlation parameter AN is examined on the basis of experimental data from s=4.9 GeV up to 23.4GeV in the framework of the extended High Energy Generalized Structure (HEGS) model. It is shown that the existing experimental data of proton-proton and proton-antiproton elastic scattering at high energy in the region of the diffraction minimum and at large momentum transfer give the support of the existence of the energy-independent part of the hadron spin flip amplitude.

Gluon helicity flip in a plane wave background

We compute the leading probability for a gluon to flip helicity state upon traversing a background plane wave gauge field in pure Yang-Mills theory and QCD, with an arbitrary number of colours and flavours. This is a one-loop calculation in perturbative gauge theory around the gluonic plane wave background, which is treated without approximation (i.e., to all orders in the coupling). We introduce a background-dressed version of the spinor helicity formalism and use it to obtain simple formulae for the flip amplitude with pure external gluon polarizations. We also give in-depth examples for gauge group SU(2), and evaluate both the high- and low-energy limits. Throughout, we compare and contrast with the calculation of photon helicity flip in strong-field QED.

The First Asymmetry Measurements in High-Energy Polarized Proton-Nucleus Collision at PHENIX-RHIC

The single spin asymmetries in very forward neutron production had been first observed about a decade ago at RHIC in transversely polarized proton + proton collision at √s = 200 GeV. Although neutron production near zero degrees is well described by the one-pion exchange (OPE) framework, the OPE appeared to be not satisfactory to describe the observed analyzing power A N . The absorptive correction to the OPE generates the asymmetry as a consequence of a phase shift between the spin flip and non-spin flip amplitudes. However the amplitude predicted by the OPE is too small to explain the large observed asymmetries. Only the model which introduces interference between major pion and small a 1 -Reggeon exchange amplitudes has been successful in reproducing the experimental data. During RHIC Run-15, RHIC delivered polarized proton collisions with Au and Al for the first time, enabling the exploration of the mechanism of transverse single-spin asymmetries with nuclear collisions. A very striking A-dependence was discovered in very forward neutron production at PHENIX in transversely polarized proton + nucleus collision at √s = 200 GeV. Such a dependence has not been predicted from the existing framework which has been succesful in proton + proton collision. In this report, experimental and theoretical efforts are discussed to disentangle the mysterious A-dependence in the very forward neutron asymmetry.

Relativistic effects in double ionization of helium via Compton scattering

In this article we present the relativistic calculations, based on the QED theory, for double ionization of helium by the Compton scattering. In particular, we calculate the contribution of the spin–flip amplitude to the total cross section. Due to this amplitude the final triplet spin state of the ejected electrons is possible. In the calculations based on the non–relativistic A2 term of the electron–photon interaction only the singlet spin state for the final electrons is allowed. We further assume the shake-off mechanism for process of double ionization. For the ground state of helium we use both the non–correlated and highly correlated wave function. We also discuss a degree of the scattered photon polarization in correlation with the formation of spin triplet state. Our calculations cover the photon impact energy range from 150 to 1000keV.

The First Transverse Single Spin Measurement in High Energy Polarized Proton-Nucleus Collision at the PHENIX experiment at RHIC

Large single spin asymmetries in very forward neutron production seen using the PHENIX zero-degree calorimeters are a long established feature of transversely polarized proton-proton collisions at RHIC. Neutron production near zero degrees is well described by the one-pion exchange framework. The absorptive correction to the OPE generates the asymmetry as a consequence of a phase shift between the spin flip and non-spin flip amplitudes. However, the amplitude predicted by the OPE is too small to explain the large observed asymmetries. A model introducing interference of pion and a1-Reggeon exchanges has been successful in reproducing the experimental data. During the RHIC experiment in year 2015, RHIC delivered polarized proton collisions with Au and Al nuclei for the first time, enabling the exploration of the mechanism of transverse single-spin asymmetries with nuclear collisions. The observed asymmetries showed surprisingly strong A-dependence in the inclusive forward neutron production, while the existing framework which was successfull in p+p only predicts moderate A- dependence. Thus the observed data are absolutely unexpected and unpredicted. In this report, experimental and theoretical efforts are discussed to disentangle the observed A-dependence using somewhat semi-inclusive type measurements and Monte-Carlo study, respectively.

High energy hadron spin flip amplitude

The high energy part of the hadron spin flip amplitude is examined in the framework of the new high energy general structure (HEGS) model of the elastic hadron scattering at high energies. The different forms of the hadron spin flip amplitude are compared in the impact parameters representation. It is shown that the existing experimental data of the proton-proton and proton-antiproton elastic scattering at high energy in the region of the diffraction minimum and at large momentum transfer give support in the presence of the energy-independent part of the hadron spin flip amplitude with the momentum dependence proposed in the works by Galynskii-Kuraev.

Ellipticity Induced in Vacuum Birefringence

We consider signals of photon-photon scattering in laser-based, low energy experiments. In particular, we consider the ellipticity induced on a probe beam by a strong background field, and compare it with a recent worldline expression for the photon polarisation flip amplitude. When the probe and the background are plane waves, the ellipticity is equal to the flip amplitude. Here we investigate the ellipticity-amplitude relation for more physical fields.

Vacuum refractive indices and helicity flip in strong-field QED

Vacuum birefringence is governed by the amplitude for a photon to flip helicity or polarisation state in an external field. Here we calculate the flip and non-flip amplitudes in arbitrary plane wave backgrounds, along with the induced spacetime-dependent refractive indices of the vacuum. We compare the behaviour of the amplitudes in the low energy and high energy regimes, and analyse the impact of pulse shape and energy. We also provide the first lightfront-QED derivation of the coefficients in the Heisenberg-Euler effective action.

Measurements of the energy dependence of the analyzing power in pp elastic scattering in the CNI region

We present new measurements of the analyzing power AN in proton-proton elastic scattering in the Coulomb-Nuclear Interference region at √s = 7.7 and 21.7 GeV obtained with the polarized atomic hydrogen jet target at RHIC. These measurements complement our earlier results at √s = 6.8 and 13.7 GeV confirming the presence of a hadronic helicity flip amplitude contribution in proton-proton elastic scattering at lower energies (√s <8 GeV) while higher energy data (√s >13 GeV) are consistent with no hadronic helicity flip contribution.

Forward pion-nucleon charge exchange reaction and Regge constraints

We present our recent study of pion-nucleon charge exchange amplitudes above 2 GeV. We analyze the forward pion-nucleon charge exchange reaction data in a Regge model and compare the resulting amplitudes with those from the Karlsruhe–Helsinki and George-Washington-University partial-wave analyses. We explore possible high-energy constraints for theoretical baryon resonance analyses in the energy region above 2 GeV. Our results show that for the pion-nucleon charge exchange reaction, the appropriate energy region for matching meson-nucleon dynamics to diffractive scattering should be around 3 GeV for the helicity flip amplitude.

Molecular Motions and Ion Diffusions of the Room-Temperature Ionic Liquid 1,2-Dimethyl-3-propylimidazolium Bis(trifluoromethylsulfonyl)amide (DMPImTFSA) Studied by 1H, 13C, and 19F NMR

The diffusive properties of an imidazolium room-temperature ionic liquid (RTIL), 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide (DMPImTFSA), are studied from the ionic conductivity and the ion diffusion coefficients measured by pulsed field gradient spin echo NMR. The temperature-dependent (1)H, (19)F, and (13)C NMR spin-lattice relaxation time T(1) values were observed, and the (1)H T(1) for DMPIm showed T(1) minima for various protons. According to the Bloemberger-Purcell-Pound (BPP) equation, the correlation time tau(c) values were directly calculated from (1)H NMR. By using the (1)H tau(c) values, an evaluation of the (13)C T(1) was attempted for the carbons having protons. The tau(c) estimated for molecular motions of DMPIm changes from 1.3 ns at 253 K to 72 ps at 353 K. The Stokes-Einstein-Debye (SED) model suggests that the tau(c) is too short for the overall molecular reorientation near room temperature. Consequently, the possibility of small-angle molecular rotation is proposed and tentative flip angles are calculated by using the translational diffusion coefficient, the bulk viscosity measured in this study, and the tau(c) obtained from (1)H T(1) data in the temperature range between 283 and 353 K. The flip amplitude increases with the temperature. DMPIm has isotropic reorientational motions with temperature-dependent amplitude, in addition to fast intramolecular motions such as methylene segmental motions, methyl rotational motion, and conformational exchange of the imidazolium ring. The existence of fast motions of TFSA is also shown. The translational diffusion of the ions is the slowest dynamic process in the present RTIL. Ab initio molecular orbital calculations are performed to understand the geometries of stable complexes of DMPIm(+) and TFSA(-), and the formation energies from the isolated ions are evaluated. The computed results are important for interpreting the (1)H T(1) behaviors observed for the imidazolium ring protons.

Engineering exotic phases for topologically protected quantum computation by emulating quantum dimer models

We use a nonperturbative extended contractor renormalization (ENCORE) method for engineering quantum devices for the implementation of topologically protected quantum bits described by an effective quantum dimer model on the triangular lattice. By tuning the couplings of the device, topological protection might be achieved if the ratio between effective two-dimer interactions and flip amplitudes lies in the liquid phase of the phase diagram of the quantum dimer model. For a proposal based on a quantum Josephson junction array [L. B. Ioffe , Nature (London) 415, 503 (2002)] our results show that optimal operational temperatures below 1 mK can only be obtained if extra interactions and dimer flips, which are not present in the standard quantum dimer model and involve three or four dimers, are included. It is unclear if these extra terms in the quantum dimer Hamiltonian destroy the liquid phase needed for quantum computation. Minimizing the effects of multidimer terms would require energy scales in the nano-Kelvin regime. An alternative implementation based on cold atomic or molecular gases loaded into optical lattices is also discussed, and it is shown that the small energy scales involved-implying long operational times-make such a device impractical. Given the many orders of magnitude between bare couplings in devices, and the topological gap, the realization of topological phases in quantum devices requires careful engineering and large bare interaction scales.

Single transverse-spin asymmetry in very forward and very backward neutral particle production for polarized proton collisions at [formula omitted

In the 2001–2002 running period of the Relativistic Heavy Ion Collider (RHIC), transversely polarized protons were accelerated to 100 GeV for the first time, with collisions at s=200 GeV. We present results from this run for single transverse-spin asymmetries for inclusive production of neutral pions, photons and neutrons of the energy region 20–100 GeV for forward and backward production for angles between 0.3 mrad and 2.2 mrad with respect to the polarized proton direction. An asymmetry of AN=(−0.090±0.006±0.009)×(1.0−0.24+0.47) was observed for forward neutron production, where the errors are statistical and systematic, and the scale error is from the beam polarization uncertainty. The forward photon and π0, and backward neutron, photon, and π0 asymmetries were consistent with zero. The large neutron asymmetry indicates a strong interference between a spin–flip amplitude, such as one pion exchange which dominates lower energy neutron production, and remaining spin–non-flip amplitudes such as reggeon exchange.

Beam normal spin asymmetry in the quasireal Compton scattering approximation

he two-photon exchange contribution to the single spin asymmetries with the spin orientation normal to the reaction plane is discussed for elastic electron-proton scattering in the equivalent photon approximation. In this case, the hadronic part of the two-photon exchange amplitude describes real Compton scattering (RCS). We show that in the case of the beam normal spin asymmetry this approximation selects only the photon helicity flip amplitudes of RCS. At low energies, we make use of unitarity and estimate the contribution of the piN multipoles to the photon helicity flip amplitudes. In the Regge regime, the quasi-RCS (QRCS) approximation allows for a contribution from two-pion exchange, and we provide an estimate of such contributions.

Perturbative and non-perturbative QCD corrections to wide-angle Compton scattering

We investigate corrections to the handbag approach for wide-angle Compton scattering off protons at moderately large momentum transfer: the photon-parton subprocess is calculated to next-to-leading order QCD and contributions from the generalized parton distribution E} are taken into account. Photon and proton helicity flip amplitudes are non-zero due to these corrections which leads to a wealth of polarization phenomena in Compton scattering. Thus, for instance, the incoming photon asymmetry or the transverse polarization of the proton are non-zero although small.

Hard electroproduction of mesons: Helicity flip amplitudes with tensor gluon contributions

We consider hard electroproduction of mesons at twist-3 level and focus our attention on helicity flip amplitudes corresponding to the production of transversely polarized mesons by transverse photons. We demonstrate that helicity-flip amplitude for the transversely polarized particles are closely related to the contributions of the matrix elements of the tensor gluon operator which can serve as pure gluonic probe of the hadrons. Using standard factorisation approach and Wanzura-Wilczek approximation for the twist-3 matrix elements we find that such amplitudes do not have divergencies from the endpoint regions which appear in the other twist-3 amplitudes.

Helicity in diffractive vector-meson production

We study the helicity amplitudes describing the quasielastic production of vector mesons in deep inelastic scattering within the context of the model which we previously introduced to describe the ratio of longitudinal to transverse cross sections. We calculate here a full set of spin flip (and non-flip) amplitudes and naturally find a significant violation of s-channel helicity conservation. We present predictions for the 15 spin-density matrix elements which completely define the angular distributions and the helicity properties of the produced meson.

Elastic electroproduction of

The elastic electroproduction of $\rho$ mesons is studied at HERA with the H1 detector for a photon virtuality in the range $1 < Q^2 < 60 {\rm GeV^2}$ and for a hadronic centre of mass energy in the range $30 < W < 140$ GeV. The shape of the ( $\pi \pi$ ) mass distribution in the $\rho$ resonance region is measured as a function of $Q^2$ . The full set of $\rho$ spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of $8 \pm 3\%$ of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on $Q^2$ , W and t (the four-momentum transfer squared to the proton). They suggest that, especially at large $Q^2$ , the $\gamma^*p$ cross section develops a stronger W dependence than that expected from the behaviour of elastic and total hadron–hadron cross sections.

Elastic electroproduction of $\rho$ mesons at HERA

The elastic electroproduction of rho mesons is studied at HERA with the H1 detector for a photon virtuality in the range 1 Q^2 60 GeV^2 and for a hadronic centre of mass energy in the range 30 W 140 GeV. The shape of the pipi mass distribution in the rho resonance region is measured as a function of Q^2. The full set of rho spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of 8 +- 3 % of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on Q^2, W and t (the four-momentum transfer squared to the proton). They suggest that, especially at large Q^2, the gamma^*p cross section develops a stronger W dependence than that expected from the behaviour of elastic and total hadron-hadron cross sections.