arXiv subjects

M. Lublinsky

Publications and source records attributed to M. Lublinsky.

At least 19 recordsLinked to original sources

arXiv2022

Nuclei in the toy world: beyond the Pomeron in zero transverse dimensions

We explore possible extensions of the $t$-channel and $s$-channel unitary model of high energy evolution in zero transverse dimensions appropriate to very high energy/atomic number where the dipole density in a toy hadron is parametrically high.We suggest that the appropriate generalization is to allow emission of more than one dipole in a single step of energy evolution. We construct explicitly such a model that preserves the $t$-channel and s-channel unitarity and have the correct low density limit, and study the particle multiplicity distribution resulting from this evolution. We consider initial conditions of a single dipole and many dipoles at initial rapidity. We observe that the saturation regime in this model is preceded by a parametric range of rapidities $\frac{1}{\alpha_s}\ln\frac{1}{\alpha_s}<Y<\frac{1}{\alpha_s}\ln\frac{1}{\alpha_s^2}$, where the saturation effects are still unimportant, but multiple emissions determine the properties of the evolution. We also discuss the influence of the saturation on the parton cascade and, in particular, find that in the saturation regime the entropy of partons becomes $S \approx \h \ln N$ where $N$ is the mean multiplicity.

hep-ph↗

arXiv2015

Hanbury-Brown-Twiss measurements at large rapidity separations, or can we measure the proton radius in p-A collisions?

We point out that current calculations of inclusive two-particle correlations in p-A collisions based on the Color Glass Condensate approach exhibit a contribution from Hanbury-Brown-Twiss correlations. These HBT correlations are quite distinct from the standard ones, in that they are apparent for particles widely separated in rapidity. The transverse size of the emitter which is reflected in these correlations is the gluonic size of the proton. This raises an interesting possibility of measuring the proton size directly by the HBT effect of particle pairs produced in p-A collisions.

hep-ph↗

arXiv2013

QCD Reggeon Calculus From KLWMIJ/JIMWLK Evolution: Vertices, Reggeization and All

We show explicitly how the high energy QCD evolution generated by the KLWMIJ Hamiltonian can be cast in the form of the QCD Reggeon Field Theory. We show how to reduce the KLWMIJ Hamitonian to physical color singlet degrees of freedom. We suggest a natural way of defining the Pomeron and other Reggeons in the framework of the KLWMIJ evolution and derive the QCD Reggeon Field Theory Hamiltonian which includes several lowest Reggeon operators. This Hamiltonian generates evolution equations for all Reggeons in the case of dilute-dense scattering, including the nonlinear Balitsky-Kovchegov equation for the Pomeron. We also find explicit expressions for the Reggeon conjugate operators in terms of QCD operators, and derive their evolution equations. This provides a natural and unambiguous framework for reggeization procedure introduced in \cite{BW, BE}. The Bartels triple Pomeron vertex is inherited directly from the RFT Hamiltonian. For simplicity in the bulk of the paper we work in the large $N_c$ limit.

hep-ph↗

arXiv2012

Classicalization and Unitarity

We point out that the scenario for UV completion by "classicalization", proposed recently is in fact Wilsonian in the classical Wilsonian sense. It corresponds to the situation when a field theory has a nontrivial UV fixed point governed by a higher dimensional operator. Provided the kinetic term is a relevant operator around this point the theory will flow in the IR to the free scalar theory. Physically, "classicalization", if it can be realized, would correspond to a situation when the fluctuations of the field operator in the UV are smaller than in the IR. As a result there exists a clear tension between the "classicalization" scenario and constraints imposed by unitarity on a quantum field theory, making the existence of classicalizing unitary theories questionable.

hep-th↗

arXiv2011

Universal hydrodynamics and charged hadron multiplicity at the LHC

Time evolution of a "little bang" created in heavy ion collisions can be divided into two phases, the pre-equilibrium and hydrodynamic. At what moment the evolution becomes hydrodynamic and is there any universality in the hydrodynamic flow? To answer these questions we briefly discuss various versions of hydrodynamics and their applicability conditions. In particular, we elaborate on the idea of "universal" (all-order resumed) hydrodynamics and propose a simple new model for it. The model is motivated by results obtained recently via the AdS/CFT correspondence. Finally, charged hadron multiplicities in heavy ion collisions at the RHIC and LHC are discussed. At the freezout, the multiplicities can be related to total entropy produced in the collision. Assuming the universal hydrodynamics to hold, we calculate the entropy production in the hydro stage of the collision. We end up speculating about a connection between the multiplicity growth and the temperature dependence of the QGP viscosity.

hep-ph↗

arXiv2006

Treading on the cut: Semi inclusive observables at high energy

We develop the formalizm for calculating semi inclusive observables at high energy in the JIMWLK/KLWMIJ approach. We consider several examples including diffractive processes, elastic and inclusive over the target degrees of freedom, scattering with fixed total transverse momentum transfer and inclusive gluon production. We discuss evolution of these observables with respect to various rapidity variables involved in their definitions (total rapidity, rapidity gap, width of diffractive interval etc.). We also discuss the dipole model limit of these observables and derive closed simple (as opposed to functional) differential equations in this approximation. We point out that there are some interesting differences between the full JIMWLK/KLWMIJ evolution and the dipole model evolution of diffractive cross section. In particular we show that in the dipole approximation the target does not diffract beyond the valence rapidity interval, consistently with the intuition suggested by the Pomeron fan diagramms. On the other hand such diffractive processes do exist in the full JIMWLK/KLWMIJ approach, albeit suppressed by the factor 1/N_c^2.

hep-ph↗

arXiv2004

Higher Order Effects in Non Linear Evolution from a Veto in Rapidities

Higher order corrections to the Balitsky-Kovchegov equation have been estimated by introducing a rapidity veto which forbids subsequent emissions to be very close in rapidity and is known to mimic higher order corrections to the linear BFKL equation. The rapidity veto constraint has been first introduced using analytical arguments obtaining a power growth with energy, Q_s (Y) ~ exp(lambda Y), of the saturation scale of lambda ~ 0.45. Then a numerical analysis for the non-linear Balitsky-Kovchegov equation has been carried out for phenomenological rapidities: when a veto of about two units of rapidity is introduced for a fixed value of the coupling constant of alpha_s = 0.2 the saturation scale lambda decreases from ~ 0.6 to ~ 0.3, and when running coupling effects are taken into account it decreases from ~ 0.4 to ~ 0.3.

hep-ph↗

arXiv2004

Search for Chargino and Neutralino Production at sqrt(s) = 192-209 GeV at LEP

Approximately 438 pb-1 of e+e- data from the OPAL detector, taken with the LEP collider running at centre-of-mass energies of 192-209 Gev, are analyzed to search for evidence of chargino pair production, e+e- -> tilde chi^+_1 tilde chi^-_1, or neutralino associated production, e+e- -> tilde chi^0_2 tilde chi^0_1. Limits are set at the 95% confidence level on the product of the cross-section for the process e+e- -> tilde chi^+_1 tilde chi^-_1 and its branching ratios to topologies containing jets and missing energy, of jest with a lepton and missing energy, and on the product of the cross-section for e+e- -> tilde chi^0_2 tilde chi^0_1 and its branching ratio to jets. R-parity conservation is assumed throughout this paper. When these results are interpreted in the context of the Constrained Minimal Supersymmetric Standard Model, limits are also set on the masses of the tilde chi^+-_1, tilde chi^0_1 and tilde chi^0_2, and regions of the parameter space of the model are ruled out. Nearly model-independent limits are also set at the 95% confidence level on sigma(e+e- -> tilde chi^+_1 tilde chi^-_1) with the assumption that each chargino decays via a W boson, and on sigma(e+e- -> tilde chi^0_2 tilde chi^0_1) with the tilde chi^0_2 assumed to decay via a Z^0.

hep-ex↗

arXiv2003

A Linear Evolution for Non-Linear Dynamics and Correlations in Realistic Nuclei

A new approach to high energy evolution based on a linear equation for QCD generating functional is developed. This approach opens a possibility for systematic study of correlations inside targets, and, in particular, inside realistic nuclei. Our results are presented as three new equations. The first one is a linear equation for QCD generating functional (and for scattering amplitude) that sums the 'fan' diagrams. For the amplitude this equation is equivalent to the non-linear Balitsky-Kovchegov equation. The second equation is a generalization of the Balitsky-Kovchegov non-linear equation to interactions with realistic nuclei. It includes a new correlation parameter which incorporates, in a model dependent way, correlations inside the nuclei. The third equation is a non - linear equation for QCD generating functional (and for scattering amplitude) that in addition to the 'fan' diagrams sums the Glauber-Mueller multiple rescatterings.

hep-ph↗

arXiv2003

Quark-Antiquark Exchange in $γ^* γ^*$ Scattering

We calculate the high energy behavior of quark-antiquark exchange in $γ^* γ^*$ elastic scattering by summing, to all orders, the leading double logarithmic contributions of the QCD ladder diagrams. Motivation comes from the LEP data for $σ_{tot}^{γ^* γ^*}$ which indicate the need for secondary reggeon exchange. We show that, for large photon virtualities, this exchange is calculable in pQCD. This applies, in particular, to parts of the LEP kinematic region.

hep-ph↗

arXiv2003

QCD Saturation and Photoproduction on Proton and Nuclei Targets

We calculate inclusive photoproduction cross-sections for both proton and nuclei targets, using a saturation model derived from an approximate solution to the Balitsky-Kovchegov nonlinear evolution equation. This paper extends our hypothesis, that one can successfully use the dipole picture and saturation models to describe soft processes, instead of the soft Pomeron Regge parametrization. Our fit is compatible with our previous fit to DIS data, and utilizes the same phenomenological parameters as in our paper devoted to soft hadronic interactions. Using the Glauber formalism, and no additional parameters, we calculate the cross-sections for photoproduction on various nuclei, and compare our results with the relevant data.

hep-ph↗

arXiv2003

Hard-soft Pomeron transition from QCD saturation in the dipole picture

We pose the question: how far can we push the QCD dipole model and the idea of QCD saturation to the kinematical regions traditionally associated with soft nonperturbative physics? The answer is that it works sufficiently well allowing a smooth transition from hard (BFKL) pomeron to the soft one.

hep-ph↗

arXiv2003

J/ψPhoto- and DIS Production via Nonlinear Evolution

We apply our solution of the nonlinear evolution equation to the case of $J/ψ$ photo and DIS production on nucleons and nuclei targets. The uncertainty in the $J/ψ$ wave function normalization due to Fermi motion is treated as a free parameter. We obtain good reproduction of the HERA experimental data on a proton target. Calculations of $J/ψ$ mesons coherent production on nuclei targets are presented and discussed. Our analysis supports the conclusions reached in our previous studies, stressing the importance of nonlinear evolution in the kinematical domain of high-density QCD.

hep-ph↗

arXiv2003

The Dipole Picture and Saturation in Soft Processes

We attempt to describe soft hadron interactions in the framework of saturation models, one based upon the Balitsky-Kovchegov non-linear equation and another one due to Golec-Biernat and Wüsthoff. For $pp$, $Kp$, and $πp$ scattering the relevant hadronic wave functions are formulated, and total, elastic cross-sections, and the forward elastic slope are calculated and compared to experimental data. The saturation mechanism leads to reasonable reproduction of the data for the quantities analyzed, except for the forward elastic slope, where the predicted increase with energy is too moderate.

hep-ph↗

arXiv2002

Diffractive dissociation from non-linear evolution in DIS on nuclei

The process of single diffractive dissociation off nuclei is considered on a basis of solutions to the nonlinear evolution equation. The relevant saturation scales $Q_{s A}^D(x,x_0)$ are determined and their dependences on Bjorken $x$, atomic number $A$, and minimal rapidity gap $Y_0\equiv \ln 1/x_0$ are investigated. The solutions are shown to posses the geometrical scaling in a broad kinematic region for $x$ well below $x_0$. A detailed theoretical discussion of saturation scale and scaling is presented. The ratio $σ^{diff}/σ^{tot}$ is computed for several nuclei. We predict that at $x\simeq 10^{-4}$ this ratio is of the order 25% which is much larger to the one of proton. This result indicates a possibility to observe a very strong nuclear shadowing.

hep-ph↗

arXiv2002

Towards a new global QCD analysis: low x DIS data from non-linear evolution

A new approach to global QCD analysis is developed. The main ingredients are two QCD-based evolution equations. The first one is the Balitsky-Kovchegov nonlinear equation, which sums higher twists while preserving unitarity. The second equation is linear and it is responsible for the correct short distance behavior of the theory, namely it includes the DGLAP kernel. Our approach allows extrapolation of the parton distributions to very high energies available at the LHC as well as very low photon virtualities, $Q^2\ll 1 {\rm GeV^2}$. All existing low $x$ data on the $F_2$ structure function is reproduced using one fitting parameter. The resulting $χ^2/df=1$. Analyzing the parameter $λ\equiv \partial\ln F_2/\partial(\ln 1/x)$ at very low $x$ and $Q^2$ well below $1 {\rm GeV^2}$ we find $λ\simeq 0.08 - 0.1$. A result which agrees with the "soft pomeron" intercept without involving soft physics.

hep-ph↗

arXiv2002

Possible large mass effects in direct determination of the CKM elements in top decays

We discuss the possibility that mass effects, beyond phase space, may have substantial influence on the direct determination of $V_{tq}$ in decays of top quarks. In principle, our results are valid both for singly produced top and for $t {\bar t}$ pair production. The mass effect is practically irrelevant for the extraction of $V_{tb}$ from Tevatron data, but it may have implications for higher energy multi-jet top decay.

hep-ph↗

arXiv2001

Non-linear evolution and high energy diffractive production

The ratio of the diffractive production to the total cross section in DIS is computed as a function of the produced mass. The analysis is based on the solution to the non-linear evolution equation for the diffraction dissociation in DIS. The obtained ratios almost do not depend on the central mass energy in agreement with the HERA experimental data. This independence is argued to be a consequence of the scaling phenomena displayed by the cross sections. As a weakness point a significant discrepancy between the data and the obtained results is found in the absolute values of the ratios. Several explanatory reasons are discussed.

hep-ph↗