CMS - Theoretical research
Our theorists are reknown experts in theory of nuclear collisions and phenomenology of proton and heavy ion scattering.
Among group's theoretical activities studies of collective effects in pp and AA, of high multiplicities in pp, elastic scattering of protons should be stressed.
Collective effects in pp and AA
Properties of dense strongly interacted matter formed in AA scattering heavily depend on time passed after collision. Experimental studies indicate that properties of that matter can not be factorized to a trivial superposition of pp. According to present consensus in a theory of strong interactions different stages of collision may be distinguished, which is presented on a figure below.
roup participants take part in a studies of theory and phenomenology of collective physics in AA. In particular, phenomenological model for strongly interacted matter by a means of chromopermetivity, which is an non-abelian analog of dielectric permitivity in electromagnetism, has been presented. Also possibility of Cherenkov gluon emission is investigated.
1) Дремин И. М., Леонидов А. В. «Кварк-глюонная среда» УФН 180 1167–1196 (2010) in russian
2) Дремин И.М. «Когерентное адронное излучение при сверхвысоких энергиях.» Письма в ЖЭТФ 1216 (1977) in russian
3) I. M. Dremin The medium in heavy-ion collisions Nucl. Phys. A 785 (2007), 369
4) I. M. Dremin, M. R. Kirakosyan, A. V. Leonidov, A. V. Vinogradov “Cherenkov Glue in Opaque Nuclear Medium” Nucl. Phys. A826: 190-197, 2009
5) I.M. Dremin, The wake in mid-central nuclear collisions. Mod. Phys. Lett. A25 (2010) 591
Also group studied turbulent corrections to polarization of a quark-gluon plasma.
1) M. R. Kirakosyan, A. V. Leonidov, B. Muller «Turbulence-Induced Instabilities in EP and QGP» Acta Physica Polonica B, vol. 6, p 403, (2013)
2) I. M. Dremin, M. R. Kirakosyan, A. V. Leonidov «On Collective Properties of Dense QCD Matter» Advances in High Energy Physics vol. 2013 (2013), 706531
It is shown that the soft mechanism of multiparticle production by Lund hadronic strings formed by colliding constituent degrees of freedom generates a shape of angular correlations similar to the ridge structure observed in the pp collisions at 7 TeV at the LHC.
1) I.M. Dremin, V.T. Kim «Towards a common origin of the elliptic flow, ridge and alignment» JETP Lett. 92 (2010) 720
2) M.Yu. Azarkin, I.M. Dremin, A.V. Leonidov «Soft ridge in proton-proton collisions» Mod.Phys.Lett.A26:963-966,2011; Erratum-ibid.A26:1309,2011
There is recent activity in a study of collective effects in a early stages of collision. In a collaboration with a collegues from BNL dilepton and photon production in glasma was considered. Besides, transition to a limit of anisotropic hydrodynamics on early stages of a collision is studied.
1) M. Chiu, T. K. Hemmick, V. Khachatryan, A. Leonidov, J. Liao, L. McLerran «Production of Photons and Dileptons in the Glasma» Nuclear Physics A 900, 16-37, 2013
2) A. V. Leonidov, A. Radovskaya - in prepararion
Multiparticle production of hadrons
Mechanism of multiparticle production is highly important in a collisions of high energy particles. Study of such processes gives us possibility to get information of a matter structure on a very small scales, of a new forms of matter that may be formed in extreme conditions, of assymptotic properties of strong interactions, of quark confinement etc. Understanding of processes of multiparticle production in strong interaction is also important to distinguish effects that may or may not be explained by a standart model, so it is also crucial for a planning of new experiments.
In a seminal paper of I. M. Dremin and D. S. Chernyavskiy was originally considered one-mesonic approximation and its application to calculations of nonelastic peripheral hadron scattering. Method shortly became fundamental multiperipheral and multireggeon models.
1) И.М. Дремин, Д.С. Чернавский, Периферические взаимодействия нуклонов при энергии 7 БэВ, ЖЭТФ 38 (1960) 229. in russian
2) I.M. Dremin, A.M. Dunaevskii, The multiperipheral cluster theory and its comparison to experiment. Phys. Rep. 18C (1975) 159.
Also let us mention work of I. M. Dremin on investigation of multiparticle production by a means of analysis of probability-generating functions in perturbative QCD. System of equations for jet evolution was analised for both fixed and running coupling. Systematic approach for analysis of equations with a running coupling by expanding integrand in series has been considered, which resulted in modification of perturbative expansion for observables. Comparison with experiment was presented.
1) Дремин И. М. "Множественное рождение частиц и квантовая хромодинамика" УФН 172 551–571 (2002)
2) I. M. Dremin, C. S. Lam, V. A. Nechitailo «High Order Perturbative QCD Approach to Multiplicity Distributions of Quark and Gluon Jets» Phys.Rev.D61:074020,2000
3) I.M. Dremin, J.W. Gary «Hadron multiplicities» Phys. Rep. 349 (2001) 301.
Innovative approach to extraction of correlations from particle flow in high energy collisions problem using wavelet has been considered.
1) И.М. Дремин, О.В. Иванов, В.А. Нечитайло «Вейвлеты и их использование» УФН 171 465–501 (2001)
2) И.М. Дремин «Дальние корреляции частиц и вейвлеты» УФН 170 1235–1244 (2000)
General behavior of correlations and fluctuations in multiparticle production was investigated, the notions of intermittency and fractality as related to high energy physics were considered.
1) Де Вольф Э А, Дремин И М, Киттель В "Поведение корреляций и флуктуаций в процессах рождения адронов при высоких энергиях" УФН 163 (1) 3–62 (1993)
2) E.A. De Wolf, I.M. Dremin, W. Kittel «Scaling laws for density correlations and fluctuations in multiparticle dynamics»
The multiplicity distributions of charged particles at Tevatron (p\bar p) and LHC (pp) energies were analysed in the framework of the independent pair parton interactions (IPPI) model. It was shown that the number of soft pair parton interactions (and therefore the density of the partonic medium) is large and increases with energy. This growth depends on the width of the rapidity window. The similar conclusions were obtained in the multiladder exchange model (QGSM).
I.M. Dremin, V.A. Nechitailo «Soft multiple parton interactions as seen in multiplicity distributions at Tevatron and LHC» Phys. Rev. D (2011)
It has been shown that yield of charm particles in cosmic rays is higher than it is expected in a simple perturbative QCD calculations.
I.M. Dremin, V.I. Yakovlev «Charm in cosmic rays (The long-flying component
of EAS cores)» Astroparticle physics 26 (2006) 1.
We founded an indication that the rates of different hard processes observed by CMS and ALICE universally depend on underlying event charged-particles multiplicity until it becomes four times more than average. It was shown that the increase of the overlap area of colliding protons was not sufficient for explanation of the rate of jet production in events with charged-particle multiplicity three times higher than average and some new mechanisms are necessary like interaction of protons in rare configurations of higher than average gluon density. Such mechanisms are not included in the present Monte Carlo event generators.
M.Yu. Azarkin, I.M. Dremin, M. Strikman «Jets in multiparticle production in and beyond geometry of proton-proton collisions at the LHC» Phys. Lett. B 735 (2014) 244.