arXiv subjects

N. N. Nikolaev

Publications and source records attributed to N. N. Nikolaev.

At least 37 records · Page 2Linked to original sources

arXiv2018

Phase Measurement for Driven Spin Oscillations in a Storage Ring

This paper reports the first simultaneous measurement of the horizontal and vertical components of the polarization vector in a storage ring under the influence of a radio frequency (rf) solenoid. The experiments were performed at the Cooler Synchrotron COSY in Jülich using a vector polarized, bunched $0.97\,\textrm{GeV/c}$ deuteron beam. Using the new spin feedback system, we set the initial phase difference between the solenoid field and the precession of the polarization vector to a predefined value. The feedback system was then switched off, allowing the phase difference to change over time, and the solenoid was switched on to rotate the polarization vector. We observed an oscillation of the vertical polarization component and the phase difference. The oscillations can be described using an analytical model. The results of this experiment also apply to other rf devices with horizontal magnetic fields, such as Wien filters. The precise manipulation of particle spins in storage rings is a prerequisite for measuring the electric dipole moment (EDM) of charged particles.

physics.acc-ph↗

arXiv2017

Non-exponential decoherence of radio-frequency resonance rotation of spin in storage rings

Precision experiments, such as the search for electric dipole moments of charged particles using radiofrequency spin rotators in storage rings, demand for maintaining the exact spin resonance condition for several thousand seconds. Synchrotron oscillations in the stored beam modulate the spin tune of off-central particles, moving it off the perfect resonance condition set for central particles on the reference orbit. Here we report an analytic description of how synchrotron oscillations lead to non-exponential decoherence of the radiofrequency resonance driven up-down spin rotations. This non-exponential decoherence is shown to be accompanied by a nontrivial walk of the spin phase. We also comment on sensitivity of the decoherence rate to the harmonics of the radiofreqency spin rotator and a possibility to check predictions of decoherence-free magic energies.

physics.acc-ph↗

arXiv2017

Phase locking the spin precession in a storage ring

This letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV/$c$ bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate ($\approx 121$ kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. In particular, the rotation rate shows a sinusoidal function of the horizontal polarization phase (relative to the rf solenoid), which was controlled to within a one standard deviation range of $σ= 0.21$ rad. The minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753 kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a requirement for the use of storage rings to look for an intrinsic electric dipole moment of charged particles.

physics.acc-ph↗

arXiv2017

Spin tune mapping as a novel tool to probe the spin dynamics in storage rings

Precision experiments, such as the search for electric dipole moments of charged particles using storage rings, demand for an understanding of the spin dynamics with unprecedented accuracy. The ultimate aim is to measure the electric dipole moments with a sensitivity up to 15 orders in magnitude better than the magnetic dipole moment of the stored particles. This formidable task requires an understanding of the background to the signal of the electric dipole from rotations of the spins in the spurious magnetic fields of a storage ring. One of the observables, especially sensitive to the imperfection magnetic fields in the ring is the angular orientation of stable spin axis. Up to now, the stable spin axis has never been determined experimentally, and in addition, the JEDI collaboration for the first time succeeded to quantify the background signals that stem from false rotations of the magnetic dipole moments in the horizontal and longitudinal imperfection magnetic fields of the storage ring. To this end, we developed a new method based on the spin tune response of a machine to artificially applied longitudinal magnetic fields. This novel technique, called \textit{spin tune mapping}, emerges as a very powerful tool to probe the spin dynamics in storage rings. The technique was experimentally tested in 2014 at the cooler synchrotron COSY, and for the first time, the angular orientation of the stable spin axis at two different locations in the ring has been determined to an unprecedented accuracy of better than $2.8μ$rad.

physics.acc-ph↗

arXiv2015

Toward polarized antiprotons: Machine development for spin-filtering experiments

The paper describes the commissioning of the experimental equipment and the machine studies required for the first spin-filtering experiment with protons at a beam kinetic energy of $49.3\,$MeV in COSY. The implementation of a low-$β$ insertion made it possible to achieve beam lifetimes of $τ_{\rm{b}}=8000\,$s in the presence of a dense polarized hydrogen storage-cell target of areal density $d_{\rm t}=(5.5\pm 0.2)\times 10^{13}\,\mathrm{atoms/cm^{2}}$. The developed techniques can be directly applied to antiproton machines and allow for the determination of the spin-dependent $\bar{p}p$ cross sections via spin filtering.

physics.acc-ph↗

arXiv2014

Color screening, absorption and $σ_{tot}^{pp}$ at LHC

We show that a growth of the proton-proton total cross section with energy can be entirely attributed to the purely perturbative mechanism. The infrared regularization at rather short distances, $R_c\simeq 0.3$ fm, allows to extend the BFKL technique from deep inelastic to hadron-hadron scattering. With the account of the absorption corrections our results are in agreement with the LHC data on $σ_{tot}^{pp}$.

hep-ph↗

arXiv2012

Drell-Yan lepton pair production at high energies in the Parton Reggeization Approach

According to extensive theoretical studies of the high energy limit of QCD, inelastic interactions are dominated by the multi-Regge final states. The appropriate gauge-invariant objects, which simultaneously incorporate the transverse momentum degrees of freedom, are Reggeized gluons, quarks and antiquarks. In the present communication we extend parton Reggeization approach to Drell-Yan production of massive lepton pairs. The basic ingredient is a process of Reggeized quark-antiquark annihilation, which is described by the Reggeon-Reggeon-photon effective vertex. We calculate transverse-momentum and invariant-mass distributions of Drell-Yan lepton pairs measured at the CERN SPS, FNAL Tevatron and CERN LHC in the different ranges of energy and rapidity. We focus on angular distributions of Drell-Yan leptons in different kinematical ranges. The obtained results are compared with the existing data and a good agreement is found. The predictions for future experiments for Drell-Yan lepton pair production at the CERN LHC have been made.

hep-ph↗

arXiv2009

The BFKL-Regge factorization and $F_2^b$, $F_2^c$, $F_L$ at HERA: physics implications of nodal properties of the BFKL eigenfunctions

The asymptotic freedom is known to split the leading-$\log$ BFKL pomeron into a series of isolated poles in the complex angular momentum plane. One of our earlier findings was that the subleading hard BFKL exchanges decouple from such experimentally important observables as small-$x$ charm, $F_2^c$, and the longitudinal, $F_L$, structure functions of the proton at moderately large $Q^2$. For instance, we predicted precocious BFKL asymptotics of $F_2^c(x,Q^2)$ with intercept of the rightmost BFKL pole $α_{\Pom}(0)-1=Δ_{\Pom}\approx 0.4$. On the other hand, the small-$x$ open beauty photo- and electro-production probes the vacuum exchange for much smaller color dipoles which entails significant subleading vacuum pole corrections to the small-$x$ behavior. In view of the accumulation of the experimental data on small-$x$ $F_{2}^{c}$, $F_{2}^{b}$ and $F_{L}$ we extend our early predictions to the kinematical domain covered by new HERA measurements. Our parameter-free results agree well with the determination of $F_2^c$, $F_L$ and published H1 results on $F_2^b$ but slightly overshoot the very recent (2008, preliminary) H1 results on $F_2^b$.

hep-ph↗

arXiv2009

Measurement of the Spin-Dependence of the pbar-p Interaction at the AD-Ring

We propose to use an internal polarized hydrogen storage cell gas target in the AD ring to determine for the first time the two total spin-dependent pbar-p cross sections sigma_1 and sigma_2 at antiproton beam energies in the range from 50 to 450 MeV. The data obtained are of interest by themselves for the general theory of pbar-p interactions since they will provide a first experimental constraint of the spin-spin dependence of the nucleon-antinucleon potential in the energy range of interest. In addition, measurements of the polarization buildup of stored antiprotons are required to define the optimum parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to feed a double-polarized asymmetric pbar-p collider with polarized antiprotons. Such a machine has recently been proposed by the PAX collaboration for the new Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. The availability of an intense stored beam of polarized antiprotons will provide access to a wealth of single- and double-spin observables, thereby opening a new window on QCD spin physics.

nucl-ex↗

arXiv2009

Beauty, charm and $F_L$ at HERA: new data vs. early predictions

One of the well known effects of the asymptotic freedom is splitting of the leading-$\log$ BFKL pomeron into a series of isolated poles in complex angular momentum plane. Following our earlier works we explore the phenomenological consequences of the emerging BFKL-Regge factorized expansion for the small-$x$ charm ($F_2^c$) and beauty ($F_{2}^{b}$) structure functions of the proton. As we found earlier,the color dipole approach to the BFKL dynamics predicts uniquely decoupling of subleading hard BFKL exchanges from $F_2^c$ at moderately large $Q^{2}$. We predicted precocious BFKL asymptotics of $F_2^c(x,Q^2)$ with intercept of the rightmost BFKL pole $α_{\Pom}(0)-1=Δ_{\Pom}\approx 0.4$. High-energy open beauty photo- and electro-production probes the vacuum exchange at much smaller distances and detects significant corrections to the BFKL asymptotics coming from the subleading vacuum poles. In view of the accumulation of the experimental data on small-$x$ $F_{2}^{c}$ and $F_{2}^{b}$ we extended our early predictions to the kinematical domain covered by new HERA measurements.Our structure functions obtained in 1999 agree well with the determination of both $F_2^c$ and $F_2^b$ by the H1 published in 2006 but contradict to very recent (2008, preliminary) H1 results on $F_2^b$. We present also comparison of our early predictions for the longitudinal structure function $F_L$ with recent H1 data (2008) taken at very low Bjorken $x$. We comment on the electromagnetic corrections to the Okun-Pomeranchuk theorem.

hep-ph↗

arXiv2009

Polarizing a stored proton beam by spin flip?

We discuss polarizing a proton beam in a storage ring, either by selective removal or by spin flip of the stored ions. Prompted by recent, conflicting calculations, we have carried out a measurement of the spin flip cross section in low-energy electron-proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. The measured cross sections are too small for making spin flip a viable tool in polarizing a stored beam. This invalidates a recent proposal to use co-moving polarized positrons to polarize a stored antiproton beam.

nucl-ex↗

arXiv2006

Unitarity constraints for DIS off nuclei: predictions for electron-ion colliders

Future electron-ion colliders (eIC) will focus on the unitarity properties of deep inelastic scattering (DIS) in the limit of strong nuclear absorption. Strong nuclear shadowing and a large abundance of coherent diffraction are the most striking consequences of unitarity, and here we report quantitative predictions for these effects in the kinematical range of the planned eIC.

hep-ph↗

arXiv2006

Unitarity cutting rules for the nucleus excitation and topological cross sections in hard production off nuclei from nonlinear k_t-factorization

At the partonic level, a typical final state in small-x deep inelastic scattering off nuclei and hard proton-nucleus collisions can be characterized by the multiplicity of color-excited nucleons. Within reggeon field theory, each color-excited nucleon is associated with the unitarity cut of the pomeron exchanged between the projectile and nucleus. In this communication we derive the unitarity rules for the multiplicity of excited nucleons, alias cut pomerons, alias topological cross sections, for typical hard dijet production processes. We demonstrate how the coupled-channel non-Abelian intranuclear evolution of color dipoles, inherent to pQCD, gives rise to the reggeon field theory diagrams for final states in terms of the uncut, and two kinds of cut, pomerons. Upon the proper identification of the uncut and cut pomeron exchanges, the topological cross sections for dijet production follow in a straightforward way from the earlier derived nonlinear k_t - factorization quadratures for the inclusive dijet cross sections. The concept of a coherent (collective) nuclear glue proves extremely useful for the formulation of reggeon field theory vertices of multipomeron - cut and uncut - couplings to particles and between themselves. A departure of our unitarity cutting rules from the ones suggested by the pre-QCD Abramovsky-Kancheli-Gribov rules, stems from the coupled-channel features of intranuclear pQCD. We propose a multiplicity re-summation as a tool for the isolation of topological cross sections for single-jet production.

hep-ph↗

arXiv2006

Quenching of Leading Jets and Particles: the p_t Dependent Landau-Pomeranchuk-Migdal effect from Nonlinear k_t Factorization

We report the first derivation of the Landau-Pomeranchuk-Migdal effect for leading jets at fixed values of the transverse momentum p_t in the beam fragmentation region of hadron-nucleus collisions from RHIC (Relativistic Heavy Ion Collider) to LHC (Large Hadron Collider). The major novelty of this work is a derivation of the missing virtual radiative pQCD correction to these processes - the real-emission radiative corrections are already available in the literature. We manifestly implement the unitarity relation, which in the simplest form requires that upon summing over the virtual and real-emission corrections the total number of scattered quarks must exactly equal unity. For the free-nucleon target, the leading jet spectrum is shown to satisfy the familiar linear Balitsky-Fadin-Kuraev-Lipatov leading log(1/x) (LL-1/x) evolution. For nuclear targets, the nonlinear k_t-factorization for the LL-1/x evolution of the leading jet sepctrum is shown to exactly match the equally nonlinear LL-1/x evolution of the collective nuclear glue - there emerges a unique linear k_t-factorization relation between the two nonlinear evolving nuclear observables. We argue that within the standard dilute uncorrelated nucleonic gas treatment of heavy nuclei, in the finite energy range from RHIC to LHC, the leading jet spectrum can be evolved in the LL-1/x Balitsky-Kovchegov approximation. We comment on the extension of these results to, and their possible reggeon field theory interpretation for, mid-rapidity jets at LHC.

hep-ph↗

arXiv2006

Polarization Buildup of Stored Protons and Antiprotons: Filtex Result and Implications for Pax at Fair

The spin filtering by a multiple passage of a stored beam through a polarized internal gas target is a unique possibility of polarizing high luminosity beam of antiprotons to a high degree of polarization. Apart from the polarization by the spin-dependent transmission, a unique geometrical feature of spin filtering in storage rings is a scattering of stored particles within the ring \cite{Meyer}. A rotation of the spin in the scattering process affects the polarization buildup. We report here a fully quantum-mechanical evolution equation for the spin-density matrix of a stored beam which incorporates the scattering within the ring. We show how dramatically the interplay of the transmission and scattering within the ring changes from polarized electrons to polarized protons in the atomic target. After discussions of the FILTEX results on filtering of stored protons \cite{FILTEX}, we comment on the strategy of spin filtering of antiprotons for the PAX experiment at GSI FAIR \cite{PAX-TP}.

hep-ph↗

arXiv2006

Glue in the pomeron from nonlinear k_\perp-factorization

We derive the nonlinear k_\perp-factorization for the spectrum of jets in high-mass diffractive deep inelastic scattering as a function of three hard scales - the virtuality of the photon Q^2, the transverse momentum of the jet and the saturation scale Q_A. In contrast to all other hard reactions studied so far, we encounter a clash between the two definitions of the glue in the pomeron -- from the inclusive spectrum of leading quarks and the small-βevolution of the diffractive cross section. This clash casts a further shadow on customary applications of the familiar collinear factorization to a pQCD analysis of diffractive deep inelastic scattering.

hep-ph↗

arXiv2005

Spin Filtering in Storage Rings

The spin filtering in storage rings is based on the multiple passage of a stored beam through a polarized internal gas target. Apart from the polarization by transmission, a unique geometrical feature of interaction with the target in such a filtering process, pointed out by H.O. Meyer \cite{Meyer}, is a scattering of stored particles within the beam. A rotation of the spin in the scattering process affects the polarization buildup. We derive here a quantum-mechanical evolution equation for the spin-density matrix of the stored beam which incorporates scattering within the beam. We show how the interplay of transmission and scattering with the beam changes from polarized electrons to polarized protons in the atomic target. After discussions of the FILTEX results on the filtering of stored protons \cite{FILTEX}, we comment on the strategy of spin filtering of antiprotons for the PAX experiment at GSI FAIR \cite{PAX-TP}.

hep-ph↗

arXiv2005

Nonlinear $k_{\perp}$-factorization: a new paradigm for an in-nucleus hard QCD

We review the origin, and salient features, of the breaking of the conventional linear $k_{\perp}$-factorization for an in-nucleus hard pQCD processes. A realization of the nonlinear $k_{\perp}$-factorization which emerges instead is shown to depend on color properties of the underlying pQCD subprocesses. We discuss the emerging universality classes and extend nonlinear $k_{\perp}$-factorization to AGK unitarity rules for the excitation of the target nucleus.

hep-ph↗