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Search Results: 1 - 10 of 329282 matches for " V. R. Zoller "
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Forward Cone in Exclusive Heavy Vector Meson Production
V. R. Zoller
Physics , 1998,
Abstract: The color dipole gBFKL phenomenology of a diffraction cone for photo- and electroproduction $\gamma^{*}N \to VN$ of heavy vector mesons (charmonium & bottonium) at HERA and in fixed target experiments is presented. A substantial shrinkage of the diffraction cone from the CERN/FNAL to the HERA range of c.m.s. energy $W$ is predicted. The $Q^{2}$-controlled selectivity to the color dipole size (scanning phenomenon) is shown to lead to a decrease of the diffraction slope with $Q^{2}$ (which is supported by the available experimental data). An approximate flavor independence of the diffraction slope in the scaling variable $Q^{2}+m_{V}^{2}$ is shown to hold.
The Running BFKL: Precocious Asymptopia for Charm and the $dF_{2}/d\log Q^2$ - Puzzle
V. R. Zoller
Physics , 1998,
Abstract: The running BFKL equation gives rise to a series of moving poles in the complex $j$-plane. The first nodes for all subleading solutions (color dipole cross sections) accumulate at $r_1\sim 0.1 fm$.Therefore the processes dominated by the dipole sizes $r\sim r_1 $ are free of subleading BFKL corrections. An example - the leptoproduction of charm. The calculated $F_2^{cc}$ is exhausted by the leading BFKL pole and gives a perfect description of the experimental data. The logarithmic slope of the subleading structure functions, $dF_2^{(n)}/d\log Q^2$, at small $Q^2$ is small compared to $dF_2^{(0)}/d\log Q^2$ due to the presence of nodes. This observation provides an explanation for the observed $x$/$Q^2$ dependence of the derivative of the proton structure function $dF_2/d\log Q^2$.
Rare processes and coherent phenomena in crystals
V. R. Zoller
Physics , 1996, DOI: 10.1134/1.567249
Abstract: We study coherent enhancement of Coulomb excitation of high energy particles in crystals. We develop multiple scattering theory description of coherent excitation which consistently incorporates both the specific resonant properties of particle-crystal interactions and the final/initial state interaction effects typical of the diffractive scattering. Possible applications to observation of induced radiative neutrino transitions are discussed.
Probing the QCD pomeron in high-energy $γ^*γ^*$ collisions
V. R. Zoller
Physics , 2000,
Abstract: Based on the color dipole representation, we investigate consequences for the $\gamma^{*}\gamma^{*},\gamma^{*}\gamma$ scattering of the finding by Fadin, Kuraev and Lipatov that incorporation of asymptotic freedom into the BFKL equation makes the QCD pomeron a series of isolated poles in the angular momentum plane. We present parameter-free predictions for the vacuum exchange contribution to the photon structure function which agree well with OPAL and L3 determinations. A good agreement is found between our predictions for the energy and photon virtuality dependence of the photon-photon cross section $\sigma^{\gamma^*\gamma^*}(W,Q^2,P^2)$ and the recent data taken by the L3 Collaboration.
Coherent Coulomb excitation of relativistic nuclei in aligned crystal targets
V. R. Zoller
Physics , 2001, DOI: 10.1134/1.1469495
Abstract: We study coherent Coulomb excitation of ultrarelativistic nuclei passing through the aligned crystal target. We develop multiple scattering theory description of this process which consistently incorporates both the specific resonant properties of particle-crystal interactions and the shadowing effect typical of the diffractive scattering. We emphasise that the effect of quantum mechanical diffraction makes the physics of ultrarelativistic nuclear excitations entirely different from the physics of non-relativistic atomic excitations experimentally studied so far. It is found that at small transverse momenta $q_{\perp}$ the shadowing effect drastically changes the dependence of coherent amplitudes on the crystal thickness $L$, from the widely discussed growth $\propto L$ typical of the Born approximation to the inverse thickness attenuation law. At relatively large $q_{\perp}$ no attenuation effect is found but the coherency condition is shown to put stringent constrain on the growth of the transition rate with growing $L$.
Coherent neutrino magnetic conversion in crystals
V. R. Zoller
Physics , 1997, DOI: 10.1016/S0370-2693(97)01177-5
Abstract: We study coherent enhancement of neutrino electro-magnetic conversion in crystals. Large coherency length which grows with the neutrino energy makes the coherent enhancement particularly effective for very small masses. We derive constraints on the conversion rate which follow from the Fresnel effects in scattering of neutrinos on atomic chains. We comment on possible applications of the crystal converter to searches for non-diagonal neutrino magnetic transitions in the CERN neutrino beam.
Diffractive beauty photoproduction as a short distance probe of QCD pomeron
V. R. Zoller
Physics , 2001, DOI: 10.1016/S0370-2693(01)00538-X
Abstract: High-energy open beauty photoproduction probes the vacuum exchange at distances $\sim 1/m_b$ and detects significant corrections to the BFKL asymptotics coming from the subleading vacuum poles. We show that the interplay of leading and subleading vacuum exchanges gives rise to the cross section $\sigma^{b\bar b}(W)$ growing much faster than it is prescribed by the exchange of the leading pomeron trajectory with intercept $\alpha_{\Pom}(0)-1=\Delta_{\Pom}=0.4$. Our calculations within the color dipole BFKL model are in agreement with the recent determination of $\sigma^{b\bar b}(W)$ by the H1 collaboration. The comparative analysis of diffractive photoproduction of beauty, charm and light quarks exhibits the hierarchy of pre-asymptotic pomeron intercepts which follows the hierarchy of corresponding hardness scales. We comment on the phenomenon of decoupling of soft and subleading BFKL singularities at the scale of elastic $\Upsilon(1S)$-photoproduction which results in precocious color dipole BFKL asymptotics of the process $\gamma p \to \Upsilon p$.
Higher twist effects in charmed-strange $\nu$DIS diffraction
Fiore, R.;Zoller, V. R.
High Energy Physics - Phenomenology , 2008, DOI: 10.1016/j.physletb.2009.09.060
Abstract: The non-conservation of charmed-strange current in the neutrino deep inelastic scattering ($\nu$DIS) strongly affects the longitudinal structure function, $F_L$, at small values of Bjorken $x$. The corresponding correction to $F_L$ is a higher twist effect enhanced at small-$x$ by the rapidly growing gluon density factor. As a result, the component of $F_L$ induced by the charmed-strange current prevails over the light-quark component and dominates $F_L=F_L^{cs}+F_L^{ud}$ at $x\lsim 0.01$ and $Q^2\sim m_c^2$. The color dipole analysis clarifies the physics behind the phenomenon and provides a quantitative estimate of the effect.
Current non-conservation effects in $\nu$DIS diffraction
Fiore, R.;Zoller, V. R.
High Energy Physics - Phenomenology , 2008, DOI: 10.1063/1.3122200
Abstract: In the neutrino DIS diffraction the charged current non-conservation gives rise to sizable corrections to the longitudinal structure function, $F_L$. These corrections is a higher twist effect enhanced at small-$x$ by the rapidly growing gluon density. The phenomenon manifests itself in abundant production of charm and strangeness by longitudinally polarized W bosons of moderate virtualities $Q^2\lsim m_c^2$.
Color dipoles, PCAC and Adler's theorem
Fiore, R.;Zoller, V. R.
High Energy Physics - Phenomenology , 2007, DOI: 10.1134/S0021364007070016
Abstract: Being reformulated in the color dipole basis of small-x QCD Adler's theorem establishes a connection between perturbative and non-perturbative descriptions of DIS and quantifies the effect of non-perturbative dynamics on would-be-perturbative observables. In particular, it provides a quantitative measure of the non-perturbative influence on the longitudinal structure function in charged current DIS and imposes stringent constraints on non-perturbative parameters of color dipole models. Our analysis calls for new experimental tests of Adler's theorem in diffractive neutrino scattering.
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