arXiv subjects

B. L. Ioffe

Publications and source records attributed to B. L. Ioffe.

At least 37 records · Page 2Linked to original sources

arXiv2004

On the chiral phase transition in hadronic matter

A qualitative analysis of the chiral phase transition in QCD with two massless quarks and non--zero baryon density is performed. It is assumed that at zero baryonic density, ρ=0, the temperature phase transition is of the second order. Due to a specific power dependence of baryon masses on the chiral condensate the phase transition becomes of the first order at the temperature T=T_{ph}(ρ) for ρ>0. At temperatures T_{cont}(ρ) > T > T_{ph}(ρ) there is a mixed phase consisting of the quark phase (stable) and the hadron phase (unstable). At the temperature T = T_{cont}(ρ) the system experiences a continuous transition to the pure chirally symmetric phase.

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arXiv2004

Production of light antinuclei in heavy ion collisions

The antideuteron and antihelium-3 production rates at high-energy heavy ion collisions are calculated in the framework of fusion mechanism. It is supposed, that anti-p,n,d,^3He participating in the fusion are moving in the mean field of other fireball constituents. It is demonstrated that at high energies, where many pions are present in the fireball, the number of produced anti-d and ^3He is determined by the balance between created and desintegrated (mainly in collisions with pions) anti-d and ^3He. The explicit formulae for coalescence parameters are presented and compared with the data.

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arXiv2004

Charmonium polarization in e^+e^- and heavy ion collisions

In e^+e^- annihilation at \sqrt{s}=10.6 GeV Belle Collaboration found, that J/psi mesons are predominantly produced in association with an extra \bar{c}c pair. The possible mechanisms of J/psi production are discussed and the probability of the associate production of \bar{c}c pair is estimated. The choice between these mechanisms can be done by measuring J/psi polarization. It is suggested, that in case of heavy ion collisions one may expect remarkable transverse polarization of produced J/psi, if quark-gluon plasma if formed. The measurement of asymmetry of e^+e^-(μ^+μ^-) angular distribution in J/psi-> e^+e^-(μ^+μ^-) decay is a useful tool for detection of quark-gluon plasma formation in heavy ion collisions.

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arXiv2003

Formation of antideuterons in heavy ion collisions

The antideuteron production rate at high-energy heavy ions collisions is calculated basing on the concept of anti-d formation by antinucleons which move in the mean field of the fireball constituents (mainly pions). The explicit formula is presented for the coalescence parameter B_2 in terms of deuteron binding energy and fireball volume.

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arXiv2003

Quarkonium polarization in heavy ion collisions as a possible signature of the quark--gluon plasma

The polarization of quarkonium states produced in hadron collisions exhibits strong non-perturbative effects - for example, at small transverse momentum $p_t$ charmonia appear unpolarized, in sharp contradiction to the predictions of perturbation theory. The quark--gluon plasma is expected to screen away the non-perturbative physics; therefore those quarkonia which escape from the plasma should possess polarization as predicted by perturbative QCD. We estimate the expected $J/ψ$ polarization at small $p_t$, and find that it translates into the asymmetry of the $e^+e^- (μ^+μ^-)$ angular distribution $W(θ) \sim 1 + αcos^2θ$, with $α\simeq 0.35 ÷0.4$.

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arXiv2003

On recent puzzles in the production of heavy quarkonia

Recently, several surprising experimental observations in the production of heavy quarkonium have been reported. In $e^+e^-$ annihilation at $\sqrt{s}=10.6$ GeV, Belle Collaboration finds that $J/ψ$ mesons are predominantly produced in association with an extra $\bar{c}c$ pair, with $σ(e^+e^- \to J/ψ\bar{c}c) / σ(e^+e^- \to J/ψX) = 0.59^{+0.15}_{-0.13}\pm 0.12$, and the BaBar collaboration reports that the produced $J/ψ$'s have mostly longitudinal polarization. In $\bar{p}p$ collisions at the Tevatron, the CDF Collaboration reported an excess of $J/ψ$ and $ψ^{\prime}$ mesons at high $p_{\perp}$ over the perturbative QCD predictions; non--perturbative approach of NRQCD can accomodate the magnitude of the production cross section but not the observed experimentally polarization of quarkonia. In this note we propose possible solutions to these puzzles, and devise further experimental tests.

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arXiv2003

Comment on "Vector and axial-vector mesons at finite temperature"

It is shown, that the correlators of vector and axial-vector currents at finite temperature T in order T^2 reduce to mixing of vacuum VV and AA correlators with universal mixing coefficient given by the parameter ε= T^2/6 F^2_π, unlike the claim in the recent paper by Mallik and Sarkar [1].

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arXiv2002

Gluon condensate in charmonium sum rules with 3-loop corrections

Charmonium sum rules are analyzed with the primary goal to obtain the restrictions on the value of dimension 4 gluon condensate. The moments M_n(Q^2) of the polarization operator of vector charm currents are calculated and compared with experimental data. The 3-loop (alpha_s^2) perturbative corrections, the gluon condensate contribution with alpha_s corrections and dimension 6 operator G^3 contribution are accounted. It is shown that the sum rules for the moments do not work at Q^2=0, where the perturbation series diverges and G^3 contribution is large. The domain in the plane (n, Q^2), where the sum rules are legitimate, is found. Strong correlation of the values of gluon condensate and MS-bar charm quark mass quark is determined. The absolute limits are found to be for gluon condensate <(alpha_s/pi)G^2>=0.009+-0.007 GeV^4 and for charm quark mass m(m)=1.275+-0.015 GeV in MS-bar scheme.

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arXiv2002

Recent progress in QCD at low energies

The recent results in QCD at low energies are reported. The theoretical analysis of hadronic tau-decay is performed in complex q^2-plane. The terms of perturbation theory (PT) up to alpha^3_s are accounted, the terms of operator product expansion (OPE) -- up do dimension 8. The momenta of charmed quark vector current polarization operator are analyzed in 3 loops with account of dimension 4 and 6 OPE terms. The main conclusion is that in the range of low-energy phenomena under consideration PT and OPE are in good agreement with experiment starting from Q^2=-q^2 ~ 1 GeV^2. The values of alpha_s(m^2_tau), alpha_s ^2, <(alpha_s/pi)G^2> and m_c(m_c)were found.

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arXiv2002

Distribution of valence quarks in hadrons in QCD: theoretical method of calculations

The general method for calculation of valence quark distributions in hadrons at intermediate $x$ is presented. The imaginary part of virtual photon forward scattering amplitude on quark current with hadron quantum number is considered in the case, when initial and final virtualities of the current $p^2_1$ and $p^2_2$ are different, negative and large: $\mid p^2_1\mid, \mid p^2_2\mid\gg R^{-2}_c$, where $R_c$ is confinement radius. The operator product expansion (OPE) in $p^2_1,p^2_2$ up to dimension 6 operators is performed. Double dispersion representations in $p^2_1, p^2_2$ of the amplitude in terms of physical states contributions are used. Equalling them to those calculated in QCD by OPE the desired sum rules for quark distributions in mesons are found. The double Borel transformations are applied to the sum rules, killing non-diagonal transition terms, which deteriorated the accuracy in the previous calculations of quark distributions in nucleon. Leading order perturbative corrections are accounted. Valence quark distributions in pion, longitudinally and transversally polarized $ρ$-mesons and proton are calculated at intermediate $x$, $0.2 \la x \la 0.7$ and normalization points $Q^2 = 2-5 GeV^2$ with no fitting parameters. In cases of pion and proton the results are in agreement with found correspondingly from the data on the Drell-Yan process and deep inelastic scattering. Valence quark distributions in transversally and longitudinally polarized $ρ$-mesons are essentially different one from another and also differ from those in pion.

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arXiv2002

Valence quark distributions in nucleon at low $Q^2$ in QCD

Valence u- and d-quarks distributions in proton are calculated in QCD at low $Q^2$ and intermediate x, basing on the operator product expansion (OPE). The imaginary part of the virtual photon scattering amplitude on quark current with proton quantum numbers is considered. The initial and final virtualities $p^2_1$ and $p^2_2$ of the currents are assumed to be large, negative and different, $p^2_1 \not= p^2_2$. The OPE in $p^2_1$, $p^2_2$ up to dimension 6 operators was performed. Double dispersion representations in $p^2_1, p^2_2$ of the amplitudes in terms of physical states contributions are used. Putting them to be equal to those calculated in QCD, the sum rules for quark distributions are found. The double Borel transformations are applied to the sum rules. Leading order perturbative corrections are accounted. Valence quark distributions are found: $u(x)_v$ at $0.15<x<65$,~ $d(x)_v$ at $0.25<x<0.55$ with an accuracy $\sim 30%$ in the middles and $\sim 50%$ at the ends of these intervals. The quark distributions obtained are in agreement with those found from the analysis of hard processes data.

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arXiv2002

Condensates in Quantum Chromodynamics

The paper presents the short review of our to-day knowledge of vacuum condensates in QCD. The condensates are defined as vacuum averages of the operators which arise due to nonperturbative effects. The important role of condensates in determination of physical properties of hadrons and of their low-energy interactions in QCD is underlined. The special value of quark condensate, connected with the existence of baryon masses is mentioned. Vacuum condensates induced by external fields are discussed. QCD at low energy is checked on the basis of the data on hadronic tau-decay. In the theoretical analysis the terms of perturbation theory (PT) up to alpha^3_s are accounted, in the operator product expansion (OPE) - those up to dimension 8. The total probability of the decay tau->hadrons (with zero strangeness) and of the tau-decay structure functions are best described at alpha_s(m^2_tau) = 0.330+-0.025. It is shown that the Borel sum rules for tau-decay structure functions along the rays in the q^2-complex plane are in agreement with the experiment with the accuracy ~2% at the values of the Borel parameter |M^2|> 0.8 GeV^2. The magnitudes of dimensions 6 and 8 condensates were found and the limitations on gluonic condensates were obtained. The sum rules for the charmed quark vector currents polarization operator was analysed in 3 loops (i.e., in order alpha^2_s). The value of charmed quark mass (in MS-bar regularization scheme) was found to be: m_c(m_c) = 1.275+-0.015 GeV and the value of gluonic condensate was estimated: <(alpha_s/pi)G^2> = 0.009+-0.007 GeV^4. The general conclusion is: QCD described by PT + OPE is in a good agreement with experiment at Q^2 >~ 1 GeV^2.

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arXiv2002

Landau's Theoretical Minimum, Landau's Seminar, ITEP in the Beginning of the 1950's

I recollect on the organization of the Landau school and describe the early history of the ITEP Theory Department, as well as the history of creation of famous Landau, Abrikosov, and Khalatnikov's papers, and Landau's papers on P-parity violation and CP-conservation. The recollections carry an imprint of the epoch long gone ..."

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arXiv2001

Phenomenological analysis of K+ meson production in proton-nucleus collisions

Total and differential cross sections from literature, on the production of K+ mesons in pA interactions at projectile energies between T=0.8 and 2.9 GeV, covering the transition across the free nucleon-nucleon threshold at 1.58 GeV, have been investigated. From the target-mass dependence of the production cross sections no evidence for the expected change of the dominant reaction mechanism from two-step to direct kaon production was found. At T=1.0 GeV the A dependences of the total cross sections and of the most recent data from COSY-Juelich, differential cross sections measured under forward angles, are strongly different. The invariant K+ production cross sections show an overall exponential scaling behavior with the squared four-momentum transfer between the beam proton and the produced K+ meson for t< -0.05 GeV^2 independent of the beam energy and emission angle. The data from COSY-Juelich reveal a strongly different t dependence in the region of t>0 GeV^2. Further data at forward angles and different beam energies should be taken in order to explore this region of kinematically extreme conditions.

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arXiv2001

The check of QCD based on the tau-decay data analysis in the complex q^2-plane

The thorough analysis of the ALEPH data on hadronic tau-decay is performed in the framework of QCD. The perturbative calculations are performed in 3 and 4-loop approximations. The terms of the operator product expansion (OPE) are accounted up to dimension D=8. The value of the QCD coupling constant alpha_s(m_tau^2)=0.355 pm 0.025 was found from hadronic branching ratio R_tau. The V+A and V spectral function are analyzed using analytical properties of polarization operators in the whole complex q^2-plane. Borel sum rules in the complex q^2 plane along the rays, starting from the origin, are used. It was demonstrated that QCD with OPE terms is in agreement with the data for the coupling constant close to the lower error edge alpha_s(m_tau^2)=0.330. The restriction on the value of the gluonic condensate was found <(alpha_s/pi)G^2>=0.006 pm 0.012 GeV^2. The analytical perturbative QCD was compared with the data. It is demonstrated to be in strong contradiction with experiment. The restrictions on the renormalon contribution were found. The instanton contributions to the polarization operator are analyzed in various sum rules. In Borel transformation they appear to be small, but not in spectral moments sum rules.

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arXiv2001

Chiral effective theory of strong interactions

The review of chiral effective theory (CET) is given. CET is based on quantum chromodynamics and describes the processes of strong interaction at low energies. It is proved, that CET comes as a consequence of the spontaneous violation of chiral symmetry in QCD - the appearance of chiral symmetry violating vacuum condensates. The Goldstone theorem for the case of QCD is proved and the existence of the octet of massless Goldstone bosons (pi, K, eta) is demonstrated in the limit of massless u,d,s quarks (or the triplet of massless pions in the limit m_u,m_d->0). It is shown, that the same phenomenon - the appearance of quark condensate in QCD - which causes the Goldstone bosons, results in appearance of violating chiral symmetry massive baryons. The general form of CET Lagrangian is derived. Few examples of higher order corrections to tree diagrams in CET are given. The Wess-Zumino term (of order p^4 term in CET Lagrangian) is presented. Low energy sum rules are presented. QCD and CET at finite temperature are discussed. In the framework of CET the T^2 correction to quark condensate in QCD at finite temperature T is calculated and the results of higher order temperature corrections are demonstrated. These results indicate on phase transition in QCD at T \sim 150-200 MeV. The mixing of current correlators in order T^2 is proved.

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arXiv2000

Valence quark distributions in mesons in generalized QCD sum rules

The method for calculation of valence quark distributions at intermediate $x$ is presented. The imaginary part of the virtual photon forward scattering amplitude on the quark current with meson quantum number is considered. Initial and final virtualities $p^2_1$ and $p^2_2$ of the currents are assumed to be large, negative and different, $p^2_1 \not= p^2_2$. The operator product expansion (OPE) in $p^2_1, p^2_2$ up to dimension 6 operators is performed. Double dispersion representations in $p^2_1, p^2_2$ of the amplitude in terms of physical states contributions are used. Equalling them to those calculated in QCD by OPE the desired sum rules for quark distributions in mesons are found. The double Borel transformations are applied to the sum rules, killing non-diagonal transition terms, which deteriorated the accuracy in the previous calculations of quark distributions in nucleon. Leading order perturbative corrections are accounted. Valence quark distributions in pion, longitudinally and transversally polarized $ρ$-mesons are calculated at intermediate $x$, $0.2 \la x \la 0.7$ and normalization points $Q^2 = 2-4 GeV^2$ with no fitting parameters. The use of the Regge behaviour at small $x$ and quark counting rules at large $x$ allows one to find the first and the second moments of valence quark distributions. The obtained quark distributions may be used as an input for evolution equations. In the case of pion the quark distribution is in agreement with those found from the data on the Drell-Yan process.

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arXiv2000

The V-A sum rules and the Operator Product Expansion in complex q^2-plane from tau-decay data

The operator product expansion (OPE) for the difference of vector and axial current correlators is analyzed for complex values of momentum q^2. The vector and axial spectral functions, taken from hadronic tau-decay data, are treated with the help of Borel, Gaussian and spectral moments sum rules. The range of applicability, advantages and disadvantages of each type are discussed. The general features of OPE are confirmed by the data. The vacuum expectation values of dimension 6 and 8 operators are found to be O_6=-(6.8\pm 2.1)*10^{-3} GeV^6, O_8=(7\pm 4)*10^{-3} GeV^8.

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