arXiv subjects
Publications and source records attributed to Ivan Schmidt.
Using global fits of valence u and d quark parton distributions and data on quark and nucleon form factors in the Euclidean region, we derive a light-front quark model for the nucleon structure consistent with quark counting rules.
In this paper we study nuclear effects in the neutrinoproduction of pions. We found that in a Bjorken kinematics, for moderate $x_{B}$ accessible in ongoing and forthcoming neutrino experiments the cross-section is dominated by the incoherent contribution; the coherent contribution becomes visible only for small $|t|\lesssim1/R_{A}^{2}$, which requires $x_{B}\lesssim0.1$. Our results could be relevant to the kinematics of the ongoing MINERvA experiment in ME configuration. We provide a code which could be used for evaluation of the $ν$DVMP observables using different parametrizations of GPDs and different models of nuclear structure.
We investigate the double spin asymmetries of pion production in semi-inclusive deep inelastic scattering with a longitudinal polarized beam off a transversely polarized proton target. Particularly, we consider the $\cosϕ_S$ and $\cos(2ϕ_h -ϕ_S)$ modulations, which can be interpreted by the convolution of the twist-3 transverse momentum dependent distributions and twist-2 fragmentation functions. Three different origins are taken into account simultaneously for each asymmetry: the $g_T D_1$ term, the $e_T H_1^\perp$ term, and the $e_T^\perp H_1^\perp$ term in the $\cosϕ_S$ asymmetry; and the $g_T^\perp D_1$ term, the $e_T H_1^\perp$ term, and the $e_T^\perp H_1^\perp$ term in the $\cos(2ϕ_h -ϕ_S)$ asymmetry. We calculate the four twist-3 distributions $g_T(x,\boldsymbol{k}_T^2)$, $g_T^\perp(x,\boldsymbol{k}_T^2)$, $e_T(x,\boldsymbol{k}_T^2)$, and $e_T^\perp(x,\boldsymbol{k}_T^2)$ in a spectator-diquark model including vector diquarks. Then we predict the two corresponding asymmetries for charged and neutral pions at the kinematics of HERMES, JLab, and COMPASS for the first time. The numerical estimates indicate that the two different angular-dependence asymmetries are sizable by several percent at HERMES and JLab, and the $\cosϕ_S$ asymmetry has a strong dependence on the Bjorken $x$. Our predictions also show that the dominant contribution to the $\cosϕ_S$ asymmetry comes from the $g_T D_1$ term, while the $g_T^\perp D_1$ term gives the main contribution to the $\cos(2ϕ_h -ϕ_S)$ asymmetry; the other two $T$-odd terms almost give negligible contributions. In particular, the $\cos(2ϕ_h -ϕ_S)$ asymmetry provides a unique opportunity to probe the distribution $g_T^\perp$.
The zero-degree calorimeters (ZDC) installed in the ALICE, ATLAS and CMS experiments at the LHC, make possible simultaneous detection of forward-backward leading neutrons, pp=>nXn. Such data with sufficiently high statistics could be a source of information about the pion-pion total cross section at high energies, provided that the absorption corrections, which are expected to be strong, are well understood. Otherwise, making a plausible assumption about the magnitude of the pion-pion cross section, one can consider such measurements as a way to study the absorption effects, which is the main focus of the present paper. These effects introduced at the amplitude level, are found to be different for the pion fluxes, which either conserve or flip the nucleon helicity. The pion fluxes from both colliding protons are essentially reduced by absorption, moreover, there is a common absorption suppression factor, which breaks down the factorized form of the cross section. We also evaluate the feed-down corrections related to the initial/final state inelastic processes possessing a rapidity gap, and found them to be small in the kinematic range under consideration. The contribution of other iso-vector Reggeons, spin-flip natural parity rho and a2, and spin non-flip unnatural parity a1 are also evaluated and found to be rather small.
In this paper we study the relation between the light-front (infinite momentum) and rest-frame descriptions of quarkonia. While the former is more convenient for high-energy production, the latter is usually used for the evaluation of charmonium properties. In particular, we discuss the dynamics of a relativistically moving system with nonrelativistic internal motion and give relations between rest frame and light-front potentials used for the description of quarkonium states. We consider two approximations, first the small coupling regime, and next the nonperturbative small binding energy approximation. In both cases we get consistent results. Our results could be relevant for the description of final state interactions in a wide class of processes, including quarkonium production on nuclei and plasma. Moreover, they can be extended to the description of final state interactions in the production of weakly bound systems, such as for example the deuteron.
A colorless c-cbar dipole emerging from a heavy ion collision and developing the charmonium wave function can be broken-up by final state interactions (FSI) propagating through the hot medium created in the collision. We single out two mechanisms of charmonium attenuation: (i) Debye color screening, called melting; and (ii) color-exchange interaction with the medium, called absorption. The former problem has been treated so far only for charmonia at rest embedded in the medium, while in practice their transverse momenta at the LHC are quite high, =7-10 GeV^2. We demonstrate that a c-cbar dipole may have a large survival probability even at infinitely high temperature. We develop a procedure of Lorentz boosting of the Schroedinger equation to a moving reference frame and perform the first realistic calculations of the charmonium survival probability employing the path-integral technique, incorporating both melting and absorption. These effects are found to have comparable magnitudes. We also calculated the FSI suppression factor for the radial excitation psi(2S) and found it to be stronger than for J/psi, except large p_T, where psi(2S) is relatively enhanced. The azimuthal asymmetry parameter v_2 is also calculated.
We derive a light-front Schrodinger-type equation of motion for the quark-antiquark wave function of heavy quarkonia imposing constraints from the holographic soft-wall model.
A charmonium produced in heavy ion collisions at RHIC and LHC propagates through a dense co-moving matter with a rather high relative momentum, =4-10GeV^2. In spite of Debye screening of the binding potential, the charmonium survives with a substantial probability, even if the c-cbar potential is completely screened in the hot environment. In addition, the color-exchange interaction with the medium is another important source of charmonium suppression. Attenuation in a hot medium caused by both effects is evaluated by means of the path integral technique, which requires ability of boosting the binding potential to a moving reference frame. This problem is solved in the approximation of small intrinsic velocities of the charmed quarks.
We study gravity with torsion in extra dimensions and derive an effective four-dimensional theory containing four-fermion contact operators at the fundamental scale of quantum gravity in the TeV range. These operators may have an impact on the low-energy observables and can manifest themselves or can be constrained in precision measurements. We calculate possible contributions of these operators to some observables at the one-loop level. We show that the existing precision data on the lepton decay mode of Z boson set limits on the fundamental scale of the gravity and compactification radius, which are more stringent than the limits previously derived in the literature.
It is well known that inclusion of torsion in the gravitational formalism, leads to four-fermion interactions. Although the coupling constant of this interaction is strongly suppressed in four dimensions, its value is enhanced in models with $n$ extra dimensions. In this context, we reinterpret the recent limits established by LHC experiments to four-fermion contact interactions, to set bounds on the size of the extra dimensions. For $n=2$, the limits are comparable to those in the literature, while for $n\ge 3$ the volume of the extra dimensions is strongly constrained.
A parton produced with a high transverse momentum in a hard collision is regenerating its color field, intensively radiating gluons and losing energy. This process cannot last long, if it ends up with production of a leading hadron carrying the main fraction z_h of the initial parton momentum. So energy conservation imposes severe constraints on the length scale of production of a single hadron with high pT. As a result, the main reason for hadron quenching observed in heavy ion collisions, is not energy loss, but attenuation of the produced colorless dipole in the created dense medium. The latter mechanism, calculated with the path-integral method, explains well the observed suppression of light hadrons and the elliptic flow in a wide range of energies, from the lowest energy of RHIC up to LHC, and in a wide range of transverse momenta. The values of the transport coefficient extracted from data range within 1-2 GeV^2/fm, dependent on energy, and agree well with the theoretical expectations.
We study the twist-3 corrections to the neutrino induced deeply virtual meson production due to the chiral odd transversity Generalized Parton Distribution (GPD). We found that in contrast to pion electroproduction, in neutrino-induced processes these corrections are small. This occurs due to large contribution of unpolarized GPDs $H,\, E$ to the twist-2 amplitude in neutrinoproduction. Our results are important for analyses of the pion and kaon production in the Minerva experiment at FERMILAB.
In this paper we estimate the size of twist-3 corrections to the deeply virtual meson production in neutrino interactions due to the chiral odd transversity Generalized Parton Distribution (GPD). We conclude that in contrast to pion electroproduction, in neutrino-induced reactions these corrections are small. This happens due to large contribution of unpolarized GPDs H, E to the leading-twist amplitude in neutrinoproduction. We provide a computational code, which can be used for evaluation of the cross-sections accounting for these twist-3 corrections with various GPD models. Our results are particularly relevant for analyses of the pion and kaon production in the Minerva experiment at FERMILAB.
The Impact-Parameter dependent Color Glass Condensate (b-CGC) dipole model is based on the Balitsky-Kovchegov non-linear evolution equation and improves the Iancu-Itakura-Munier dipole model by incorporating the impact-parameter dependence of the saturation scale. Here we confront the model to the recently released high precision combined HERA data and obtain its parameters. The b-CGC results are then compared to data at small-x for the structure function, the longitudinal structure function, the charm structure function, exclusive vector meson (J/ψ, ϕ, ρ) production and Deeply Virtual Compton Scattering (DVCS). We also compare our results with the Impact-Parameter dependent Saturation model (IP-Sat). We show that most features of inclusive DIS and exclusive diffractive data, including the Q^2, W, |t| and x dependence are correctly reproduced in both models. Nevertheless, the b-CGC and the IP-Sat models give different predictions beyond the current HERA kinematics, namely for the structure functions at very low x and high virtualities Q^2, and for the exclusive diffractive vector meson and DVCS production at high t. This can be traced back to the different power-law behavior of the saturation scale in x, and to a different impact-parameter b dependence of the saturation scale in these models. Nevertheless, both models give approximately similar saturation scale Q_S<1 GeV for the proton in HERA kinematics, and also both models lead to the same conclusion that the typical impact-parameter probed in the total γ^{*}p cross-section is about b\approx 2÷3 GeV^{-1}. Our results provide a benchmark for further investigation of QCD at small-x in heavy ion collisions at RHIC and the LHC and also at future experiments such as an Electron-Ion Collider and the LHeC.
We study the contribution of massive dominantly sterile neutrinos, $N$, to the Lepton Number and Lepton Flavor Violating semileptonic decays of $τ$ and $B, D, K$-mesons. We focus on special domains of sterile neutrino masses $m_{N}$ where it is close to its mass-shell. This leads to an enormous resonant enhancement of the decay rates of these processes. This allows us to derive stringent limits on the sterile neutrino mass $m_{N}$ and its mixing $U_{αN}$ with active flavors. We apply a joint analysis of the existing experimental bounds on the decay rates of the studied processes. In contrast to other approaches in the literature our limits are free from ad hoc assumptions on the relative size of the sterile neutrino mixing parameters. We analyze the impact of this sort of assumptions on the extraction of the limits on $m_{N}$ and $U_{αN}$, and discuss the effect of finite detector size. Special attention was paid to the limits on meson decays with $e^{\pm}e^{\pm}$ in final state, derived from non-observation of $0νββ$-decay. We point out that observation of these decays may, in particular, shed light on the Majorana phases of the neutrino mixing matrix.
Gluons at small x in high-energy nuclei overlap in the longitudinal direction, so the nucleus acts as a single source of gluons, like higher Fock components in a single nucleon, which contribute to inelastic collisions with a high multiplicity of produced hadrons. This similarity helps to make a link between nuclear effects in pA and high-multiplicity pp collisions. Such a relation is well confirmed by data for the J/Psi production rate in high-multiplicity pp events measured recently in the ALICE experiment. Broadening of J/Psi transverse momentum is predicted for high-multiplicity pp collisions.
The analysis of deeply virtual meson production is extended to neutrino-production of the pseudo-Goldstone mesons (pions, kaons, eta-mesons) on nucleons, with the flavor content of the recoil baryon either preserved, or changed to a hyperon from the same SU(3) octet. We rely on the SU(3) relations and express all the cross-sections in terms of the proton generalized parton distributions (GPDs). The corresponding amplitudes are calculated at the leading twist level and in the leading order in α_{s}, using a phenomenological parametrization of GPDs. We also included in the analysis the electromagnetic O(alpha_{em})-corrections to neutrino-induced deeply virtual meson production (\nuDVMP). We found that such electromagnetic corrections decrease with Q^2 in the Bjorken regime less than the standard \nuDVMP handbag contribution, so the electromagnetic mechanism dominates at large Q^2. The electromagnetic corrections give rise to an angular correlation between the lepton and hadron scattering planes with harmonics sensitive to the real and imaginary parts of the DVMP amplitude. These corrections constitute a few percent effect in the kinematics of the forthcoming MINERvA experiment at Fermilab and should be taken into account in precise tests of GPD parametrizations. For virtualities Q^2~100 GeV^2 these corrections become on a par with \nuDVMP handbag contributions.
We study the helicity-independent generalized parton distributions of nucleons in the zero skewness case, based on a particular light-front quark model derived in a soft-wall AdS/QCD approach.