arXiv subjects

M. Strikman

Publications and source records attributed to M. Strikman.

At least 163 records · Page 9Linked to original sources

arXiv2003

Hard Photodisintegration of a Proton Pair in 3He

Hard photodisintegration of the deuteron has been extensively studied in order to understand the dynamics of the transition from hadronic to quark-gluon descriptions of the strong interaction. In this work, we discuss the extension of this program to hard photodisintegration of a $pp$ pair in the $^3$He nucleus. Experimental confirmation of new features predicted here for the suggested reaction would advance our understanding of hard nuclear reactions. A main prediction, in contrast with low-energy observations, is that the $pp$ breakup cross section is not much smaller than the one for $pn$ break up.In some models, the energy-dependent oscillations observed for $pp$ scattering are predicted to appear in the $γ^3{\rm He} \to p p + n$ reaction. Such an observation would open up a completely new field in studies of color coherence phenomena in hard nuclear reactions. We also demonstrate that, in addition to the energy dependence, the measurement of the light-cone momentum distribution of the recoil neutron provides an independent test of the underlying dynamics of hard disintegration.

nucl-th↗

arXiv2003

The universal psi-prime-prime to psi-prime ratio as unambiguous signature for hard physics in nuclear reactions and in decays of beauty hadrons

We suggest the ratio of the $ψ''(3770)/ψ'(3686)$ production cross sections as an unambiguous probe of the dominance of hard, point-like physics in charmonium production. If hard physics dominates the charmonium production the ratio : ${σ(ψ'')\overσ(ψ')}\approx {Γ(ψ''\to l^+l^-)\over Γ(ψ'\to l^+l^-)} \approx 0.1$ is independent of the process. We argue that since the dominant $D\bar D$ decay mode of the $ψ''$-meson can be detected with a high efficiency at the current facilities the effective counting rate for the $ψ''$ production should be comparable to that of the $ψ'$ and hence it could be observed at the $B$-factories. Even in hadron induced processes the ratio will not be changed significantly by final state interactions due to the similar mass and size of these two charmonium states. A possible exception are the charmonium state interactions with low energy particles -- comovers -- which are especially relevant for the heavy ion collisions.

hep-ph↗

arXiv2003

Coherent Photoproduction from Nuclei

We argue that study of the cross section of coherent photo(electro) production of vector mesons off nuclear targets provides an effective method to probe the leading twist hard QCD regimes of color transparency and perturbative color opacity as well as the onset of black body limit (BBL) in the soft and hard QCD interactions. In the case of intermediate energies we use the Generalized Vector Dominance Model to take into account coherence effects for two distinctive limits - the soft interactions for production of $ρ$ and $ρ'$-mesons and the color transparency regime for production of charmonium states. We demonstrate that GVDM describes very well $ρ$-meson coherent photoproduction at $6 \leq E_γ \leq 10$ GeV and predict an oscillating energy dependence for the coherent charmonium production. In the limit of small $x$ we find that hard QCD leads to onset of the perturbative color opacity even for production of very small onium states, like $Υ$. The advantages of the process of coherent dijet photoproduction and hard diffractive processes in general for probing the onset of BBL and measuring the light-cone wave function of the photon in a hard scattering regime where decomposition over twists becomes inapplicable are explained. We apply this analysis to the study of the photon induced coherent processes in Ultra Peripheral Collisions of ions at LHC and demonstrate that the counting rates will be sufficient to study the physics of color opacity and color transparency at the energies beyond the reach of the electron-nucleon(nucleus) colliders.

hep-ph↗

arXiv2003

Onset of Perturbative Color Opacity at Small x and Upsilon Coherent Photoproduction off heavy nuclei at LHC

We study photon-induced coherent production of Upsilon in ultraperipheral heavy ion collisions at LHC and demonstrate that the counting rates will be sufficient to measure nuclear shadowing of generalized gluon distributions. This will establish the transition from the regime of color transparency to the regime of perturbative color opacity in an unambiguous way. We argue that such measurements will provide the possibility to investigate the interaction of ultra-small color dipoles with nuclei in QCD at large energies, which are beyond the reach of the electron-nucleon (nucleus) colliders, and will unambiguously discriminate between the leading twist and higher twist scenarios of gluon nuclear shadowing.

hep-ph↗

arXiv2003

DVCS on spinless nuclear targets in impulse approximation

Within the impulse approximation, we derive expressions for the amplitude of deeply virtual Compton scattering on spinless nuclei in terms of the generalized parton distributions of the nucleon. As an application, nuclear effects in the beam-charge and single-spin asymmetries are discussed.

hep-ph↗

arXiv2003

Probing coherent charmonium photoproduction off light nuclei at medium energies

We demonstrate how the elementary amplitudes $γN\to ΨN$, the amplitude of the nondiagonal $J/ψN\Leftrightarrow ψ' N$ transition, and the total $J/ψN$ and $ψ' N$ cross sections can be determined from measurements of the coherent $J/ψ$ and $ψ'$ photoproduction off light nuclei at moderate energies. For this purpose we provide a detailed numerical analysis of the coherent charmonium photoproduction off silicon within the generalized vector dominance model (GVDM) adjusted to account for the physics of charmonium models and color transparency phenomenon.

hep-ph↗

arXiv2003

Cross Section Oscillations in the Coherent Charmonium Photoproduction off Nuclei at Moderate Energies

We calculate the coherent charmonium photoproduction at intermediate energies accounting for the physics of the charmonium bound states and the dependence of the cross section on the region occupied by color using a correspondingly adjusted generalized vector dominance model (GVDM). In the photon energy domain where the coherence lengths are comparable to the average internucleon distances in nuclei and the nuclear radii we found that significant oscillations of the total and forward photoproduction cross sections governed by the longitudinal nuclear form factor are strongly modified by the charmonium rescatterings accounting for the nondiagonal transitions related to the color screening phenomenon. We discuss how these oscillations can influence the determination of the genuine charmonium-nucleon cross sections in the forthcoming SLAC E160 experiment on low energy J/psi and psi' photoproduction off nuclei.

hep-ph↗

arXiv2002

Modelling generalized parton distributions to describe deeply virtual Compton scattering data

We present a new model for generalized parton distributions (GPDs), based on the aligned jet model, which successfully describes the deeply virtual Compton scattering (DVCS) data from H1, ZEUS, HERMES and CLAS. We also present an easily implementable and flexible algorithm for their construction. This new model is necessary since the most widely used models for GPDs, which are based on factorized double distributions, cannot, in their current form, describe the DVCS data when employed in a full QCD analysis. We demonstrate explicitly the reason for the shortcoming in the data description. We also highlight several non-perturbative input parameters which could be used to tune the GPDs, and the $t$-dependence, to the DVCS data using a fitting procedure.

hep-ph↗

arXiv2002

Predictions of the Generalized Glauber Model for the coherent $ρ$-production at RHIC and the STAR data

We calculate the rapidity distribution and the total cross section of coherent and incoherent $ρ$-production in the heavy ion ultraperipheral collisions (UPC) at $\surd s_{NN}=130$ GeV using the generalized vector dominance model(GVDM) and the Gribov- Glauber approach. We find the coherent cross section of $ρ$-production $σ_{coh}=490$ mb compared to the $σ_{coh}=370\pm 170\pm 80$ mb recently reported by the STAR collaboration at RHIC. The predicted cross section inside the acceptance of the experiment, $|y|\le 1$, agrees with the data. It is emphasized that measurements of the rapidity distribution will provide a much more stringent test of the model.

hep-ph↗

arXiv2002

Coherence Effects in Diffractive Electroproduction from Nuclei

We argue that study of the cross section of coherent photo(electro) production of $ρ,ρ^{\prime}, ...$-mesons provides an effective method to probe onset of black body limit(BBL) in the soft and hard QCD interactions. We illustrate the expected features of the onset of BBL using generalized vector dominance model(GVDM). We show that this model describes very well $ρ$-meson coherent photoproduction at $6 \leq E_γ \leq 10$ GeV. The advantages of the process of coherent dijet production and hard diffractive processes in general for probing the onset of BBL and measuring the light-cone wave function of the photon in a hard scattering regime where decomposition over twists becomes inapplicable are explained. We argue also that the regime of color fluctuations manifests itself at intermediate energies in exclusive and semiexclusive photoproduction of vector mesons and that the color transparency(CT) should reveal itself in these processes at $Q^2$ of the order of a few GeV$^2$.

hep-ph↗

arXiv2002

Spontaneously Broken Chiral Symmetry and Hard QCD Phenomena

These are the mini-proceedings of the workshop ``Spontaneously Broken Chiral Symmetry and Hard QCD Phenomena" held at the Physikzentrum Bad Honnef from July 15 to 19, 2002. Every author presents a summary of his talk. The transparencies of all speakers and further information on the workshop can be found on the website: http://www.tp2.ruhr-uni-bochum.de/hardreactions.html

hep-ph↗

arXiv2002

Novel hard semiexclusive processes and color singlet clusters in hadrons

Hard scattering to a three cluster final state is suggested as a method to probe configurations in hadrons containing small size color singlet cluster and a residual quark-gluon system of a finite mass. Examples of such processes include $e + N \to e+ p +M_X (Λ+M_X'), p+p \to p+p+M_X(p+Λ+M_X')$ where $M_X(M_X')$ could be a pion(kaon) or other state of finite mass which does not increase with momentum transfer ($Q^2$). We argue that different models of the nucleon may lead to very different qualitative predictions for the spectrum of states $M_X$. We find that in the pion model of nonperturbative $q \bar q$ sea in a nucleon the cross section of these reactions is comparable to the cross section of the corresponding two-body reaction. Studies of these reactions are feasible using both fixed target detectors (EVA at BNL, HERMES at DESY) and collider detectors with a good acceptance in the forward direction.

hep-ph↗

arXiv2002

A new hard QCD phenomenon - proton diffraction into three jets

We argue that the process of the proton diffraction into three jets in proton-nucleus scattering at LHC will allow to investigate the light-cone wave function of protons, generalized gluon densities in nuclei at small x, as well as the interplay of the color transparency and opacity phenomena.

hep-ph↗

arXiv2002

Novel QCD phenomena in pA collisions at LHC

We discuss novel QCD phenomena in pA collisions at LHC energies such as the possibility to invesigate the behaviour of hard processes at $x $ as low as $10^{-7}$, signals for onset of the black body limit in the hard processes and in the nucleon fragmentation, multijet production.

hep-ph↗

arXiv2002

Coulomb induced diffraction of energetic hadrons into jets

The electromagnetic (e.m.) current conservation and renormalizability of QCD are used to calculate the amplitude of energetic hadron(photon) diffraction into several jets with large relative transverse momenta off the nucleon(nucleus) Coulomb field. Numerical estimates of the ratio of e.m. and strong amplitudes show that within the kinematic range where the leading twist approximation for the strong amplitude is applicable, the e.m. contribution can be neglected. In pA scattering at LHC and in the fragmentation of a photon into two jets in ultraperipheral AA collisions in the black limit (which maybe realistic at LHC) e.m. contribution may win.

hep-ph↗

arXiv2002

Signals for black body limit in coherent ultraperipheral heavy ion collisions

We argue that study of total cross section of photoabsorption and coherent photoproduction of $ρ,ρ^{\prime}$-mesons in ultraperipheral heavy ion collisions (UPC) is effective method to probe onset of black body limit(BBL) in the soft and hard QCD interactions. We illustrate the expected features of the onset of BBL using generalized vector dominance model. We show that this model describes very well $ρ$-meson coherent photoproduction at $6 \leq E_γ \leq 10 GeV$. In the case of $ρ$-meson production we find a UPC cross section which is a factor $\sim 1.5 $ larger than the one found by Klein and Nystrand. The advantages of the process of coherent dijet production to probe onset of BBL in hard scattering regime where decomposition over the twists becomes inapplicable are explained and relative importance of the $γ+Pomeron$ and $γ+γ$ mechanisms is estimated.

hep-ph↗

arXiv2002

Coherent QCD phenomena in the Coherent Pion-Nucleon and Pion-Nucleus Production of Two Jets at High Relative Momenta

We use QCD to compute the cross section for coherent production of a di-jet (treated as a $q\bar q$ moving at high relative transverse momentum,$κ_t $). In the target rest frame,the space-time evolution of this reaction is dominated by the process in which the high $κ_t$ $q\bar q$ component of the pion wave function is formed before reaching the target. It then interacts through two gluon exchange. In the approximation of keeping the leading order in powers of $α_s$ and all orders in $α_{s}\ln(κ_{t}^2/k_{0}^2),$ the amplitudes for other processes are shown to be smaller at least by a power of $α_{s}$. The resulting dominant amplitude is proportional to $z(1-z) κ_t^{-4}$ ($z$ is the fraction light-cone(+)momentum carried by the quark in the final state) times the skewed gluon distribution of the target. For the pion scattering by a nuclear target, this means that at fixed $x_{N}= 2κ_{t}^2/s$ (but $κ_{t}^2\to \infty$) the nuclear process in which there is only a single interaction is the most important one to contribute to the reaction. Thus in this limit color transparency phenomena should occur.These findings are in accord with E971 experiment at FNAL. We also re-examine a potentially important nuclear multiple scattering correction which is positive and $\propto A^{1/3}/κ_t^4$. The meaning of the signal obtained from the experimental measurement of pion diffraction into two jets is also critically examined and significant corrections are identified.We show also that for values of $κ_t$ achieved at fixed target energies, di-jet production by the e.m. field of the nucleus leads to an insignificant correction which gets more important as $κ_t$ increases.

hep-ph↗

arXiv2002

Investigation of the high momentum component of nuclear wave function using hard quasielastic A(p,2p)X reactions

We present theoretical analysis of the first data on the high energy and momentum transfer (hard) quasielastic $C(p,2p)X$ reactions. The cross section of hard $A(p,2p)X$ reaction is calculated within the light-cone impulse approximation based on two-nucleon correlation model for the high-momentum component of the nuclear wave function. The nuclear effects due to modification of the bound nucleon structure, soft nucleon-nucleon reinteraction in the initial and final states of the reaction with and without color coherence have been considered. The calculations including these nuclear effects show that the distribution of the bound proton light-cone momentum fraction $(α)$ shifts towards small values ($α< 1$), effect which was previously derived only within plane wave impulse approximation. This shift is very sensitive to the strength of the short range correlations in nuclei. Also calculated is an excess of the total longitudinal momentum of outgoing protons. The calculations are compared with data on the $C(p,2p)X$ reaction obtained from the EVA/AGS experiment at Brookhaven National Laboratory. These data show $α$-shift in agreement with the calculations. The comparison allows also to single out the contribution from short-range nucleon correlations. The obtained strength of the correlations is in agreement with the values previously obtained from electroproduction reactions on nuclei.

nucl-th↗