I. M. Dremin
The equations of in-medium gluodynamics are proposed. Their classical lowest order solution is explicitly shown for a color charge moving with constant speed. For nuclear permittivity larger than 1 it describes the shock wave induced by emission of Cherenkov gluons. Specific effects at LHC energies are described and compared with Mach wave predictions.
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Full quantum calculation of the in-medium Cherenkov gluon emission by gluon current in transparent media without dispersion is discussed.
Full quantum calculation of Cherenkov gluon radiation by quark and gluon currents and a Cherenkov decay of a gluon into a pair of Cherenkov gluons in transparent media is performed. Energy losses due to Cherenkov gluon radiation in high energy nuclear collisions are calculated. The angular distribution of the energy flow due to the radiation of Cherenkov gluons is analyzed.
Color Chiral Cherenkov radiation and energy loss in quark-gluon plasma
本研究引入并探究色手征切伦科夫效应，推导了所有胶子极化的跃迁速率，计算了该效应对夸克-胶子等离子体中部分子能量损失的贡献。
The famous formula for the emission angle of Cherenkov radiation should be modified when applied to hadronic reactions because of recoil effects. They impose the upper limit on the energy of the gluon emitted at a given angle. Also, it leads to essential corrections to the nuclear refractive index value as determined from the angular position of Cherenkov rings.
Beside comparatively low energy Cherenkov gluons observed at RHIC, there could be high energy gluons at LHC, related to the high energy region of positive real part of the forward scattering amplitude. In both cases they give rise to particles emitted along some cone. The characteristics of the cones produced by these two types of gluons are different. Therefore different experiments are needed to detect them. The cosmic ray event which initiated this idea is described in detail.
The coherent hadron production analogous to Cherenkov radiation of photons gives rise to the ring-like events. Being projected on the ring diameter they produce the two-bump structure recently observed for the away-side jets at RHIC. The position of the peaks and their height determine such properties of the hadronic medium as its nuclear index of refraction, the parton density, the free path length and the energy loss of Cherenkov gluons. Beside comparatively low energy gluons observed at RHIC, there could be high energy gluons at LHC, related to the high energy region of positive real part o…
The coherent hadron production analogous to Cherenkov radiation of photons gives rise to the ring-like events. Being projected on the ring diameter they produce the two-bump structure recently observed for the away-side jets at RHIC. The position of the peaks and their height determine such properties of the hadronic medium as its nuclear refractive index, the parton density, the free path length and the energy loss of Cherenkov gluons. Cherenkov gluons may be responsible for the asymmetry of dilepton mass spectra near rho-meson observed in experiment. Beside comparatively low energy gluons ob…
The equations of in-medium gluodynamics are proposed. Their classical lowest order solution is explicitly shown for a color charge moving with constant speed. For nuclear permittivity larger than 1 it describes emission of Cherenkov gluons resembling results of classical electrodynamics. The choice of nuclear permittivity and Lorentz-invariance of the problem are discussed. Effects induced by the transversely and longitudinally moving (relative to the collision axis) partons at LHC energies are described.
Gluon bremsstrahlung induced by multiple parton scattering in a finite dense medium has a unique angular distribution with respect to the initial parton direction. A dead-cone structure with an opening angle $θ^2_0 \approx 2(1-z)/(zLE)$ for gluons with fractional energy $z$ arises from the Landau-Pomeranchuck-Migdal (LPM) interference. In a medium where the gluon's dielectric constant is $ε>1$, the LPM interference pattern is shown to become Cherenkov-like with an increased opening angle determined by the dielectric constant $\cos^2θ_c=z+(1-z)/ε$. For a large dielectric constant $ε\gg 1+2/z^2L…
Some properties of the nuclear matter as revealed by Cherenkov gluons are discussed.
The equations of in-medium gluodynamics are proposed. Their classical lowest order solution is explicitly shown for a color charge moving with constant speed. For nuclear permittivity larger than 1 it describes emission of Cherenkov gluons resembling results of classical electrodynamics. The values of the real and imaginary parts of the nuclear permittivity are obtained from the fits to experimental data on the double-humped structure around the away-side jet obtained at RHIC. The dispersion of the nuclear permittivity is predicted by comparing the RHIC, SPS and cosmic ray data. This is import…
The pseudorapidity distribution of centers of dense isolated groups of particles in HIJING model is determined. It can be considered as the background for Cherenkov gluons. If peaks over this background were found in experiment, they would indicate the onset of new collective effects.
Similar to electromagnetic forces, strong interactions might induce such collective effects as Cherenkov and Mach waves. Their conical structure would be responsible for specific ring-like events. The theoretical and experimental arguments in favor of these phenomena are discussed and their most important features are described.
The collective effect of emission by the forward moving partons of high energy Cherenkov gluons in nucleus-nucleus collisions at RHIC and LHC energies is considered. It can reveal itself as peaks in the pseudorapidity distribution of jets at midrapidities or as a ring-like structure of individual events in event-by-event analysis. The pseudorapidity distribution of centers of dense isolated groups of particles in HIJING model is determined. It can be considered as the background for Cherenkov gluons. If peaks above this background were found in experiment, they would indicate new collective ef…
The quark-gluon medium described by QCD equations is considered at high energies. Within the assumptions of the linear response theory the chromopermittivity of the medium is introduced and it is argued that it exceeds 1 at TeV energies. The dispersion equations show that the proper modes of the medium reveal instability and the parton currents traversing it induce the emission of Cherenkov gluons. Their distributions at LHC can differ from those typical for lower energies of RHIC because they are determined by the high energy dependence of the chromopermittivity while the latter ones arise du…
Cherenkov gluons may be responsible for the asymmetry of dilepton mass spectra near rho-meson observed in experiment. They can be produced only in the low-mass wing of the resonance. Therefore the dilepton mass spectra are flattened there and their peak is slightly shifted to lower masses compared with the in-vacuum rho-meson mass. This feature must be common for all resonances.
The spectrum of Cherenkov gluons is calculated within the framework of in-medium QCD. It is compared with experimental data on the double-humped structure around the away-side jet obtained at RHIC. The values of the real and imaginary parts of the nuclear permittivity are obtained from these fits. It is shown that accounting for an additional smearing due to resonance-like production of final hadrons allows to achieve an agreement with experimental data.
Collective properties of the quark-gluon medium induced by its polarization are described by macroscopic QCD equations. The parton currents traversing it lead to emission of Cherenkov gluons, the wake effect and the transition radiation. Comparison with experimental data of RHIC reveals large value of the chromopermittivity of the medium while cosmic ray data at higher energies (close to LHC) favor much smaller values. The dispersion equations show that the proper modes of the medium are unstable.
Medium Characterization with Hard Probes: From Cherenkov Light in QED to Jet Drift in QCD
本文通过切连科夫光和喷流漂移研究介质特性，利用散射拟合和喷流漂移模拟揭示介质参数对粒子识别和QGP性质的影响。
We compute the energy and momentum deposited by a fast moving parton in a quark-gluon plasma using linear viscous hydrodynamics with an energy loss per unit length profile proportional to the path length and with different values of the shear viscosity to entropy density ratio. We show that when varying these parameters, the transverse modes still dominate over the longitudinal ones and thus energy and momentum is preferentially deposited along the head-shock, as in the case of a constant energy loss per unit length profile and the lowest value for the shear viscosity to entropy density ratio.
I use the space-time distribution of energy and momentum deposited by a fast parton traversing a perturbative quark-gluon plasma as a source term for the linearized hydrodynamical equations of the medium. A method of solution for the medium response is presented in detail. Numerical results are given for different values of the shear viscosity to entropy density ratio, $η/s$, and speed of sound, $c_s$. Furthermore, I investigate the relevance of finite source structure by expanding the source term up to first order in gradients of a $δ$ function centered at the fast parton and comparing the re…
How invisible can QCD axions be? From Supernova emission to Cherenkov signals
研究最大程度隐形的QCD轴子，先分析其在超新星中的产生，推导冷却约束并计算发射光谱，再探讨在切伦科夫探测器中的探测前景，目的是建立QCD轴子可探测性下限。
Gluon helicity distribution in the nucleon from lattice QCD and machine learning
该研究结合格点QCD与机器学习，解决了欧几里得关联污染项问题，首次测定核子光锥胶子螺旋度关联PDF，提供否定胶子负极化的数值证据，提出不依赖不完善参数化的可系统改进的PDF提取方法，助力理解强相互作用自旋效应与核子自旋结构。
Collisional energy loss of a fast particle in a medium is mostly due to the medium polarization by the electromagnetic fields of the particle. A small fraction of energy is carried away by the Cherenkov radiation. In chiral medium there is an additional contribution to the energy loss due to induction of the anomalous current proportional to the magnetic field. It causes the particle to lose energy mostly in the form of the \emph{chiral} Cherenkov radiation. We employ classical electrodynamics, adequate in a wide range of particle energies, to compute the collisional energy loss by a fast part…
Decoding the proton's gluonic density with lattice QCD-informed machine learning
本文利用变分自编码器逆映射器VAIM，基于格点QCD计算的RpITDs重构质子胶子PDF，结果与全局拟合相符并验证了潜在表示的有效性。
We derive the space-time distribution of energy and momentum deposited by a fast parton traversing a weakly coupled quark-gluon plasma by treating the fast part on as the source of an external color field perturbing the medium. We then use our result as a source term for the linearized hydrodynamical equations of the medium. We show that the solution contains a sonic Mach cone and a dissipative wake if the parton moves at a supersonic speed.
To investigate the formation and the propagation of relativistic shock waves in viscous gluon matter we solve the relativistic Riemann problem using a microscopic parton cascade. We demonstrate the transition from ideal to viscous shock waves by varying the shear viscosity to entropy density ratio $η/s$. Furthermore we compare our results with those obtained by solving the relativistic causal dissipative fluid equations of Israel and Stewart (IS), in order to show the validity of the IS hydrodynamics. Employing the parton cascade we also investigate the formation of Mach shocks induced by a hi…
Polarized and unpolarized gluon PDFs: generative machine learning applications for lattice QCD matrix elements at short distance and large momentum
本文用生成式机器学习从格点QCD短距离数据外推胶子关联函数，重建核子极化与非极化胶子PDF，并克服传统函数形式偏差。
The experimental azimuthal dihadron distributions at RHIC show a double peak structure in the away side ($Δϕ= π\pm 1.2$ rad.) for intermediate $p_t$ particles. A variety of models have appeared trying to describe this modification. We will review most of them, with special emphasis in the Conical Flow scenario in which the observed shape is a consequence of the emission of sound by a supersonic high momentum particle propagating in the Quark Gluon Plasma.
We study Mach shocks generated by fast partonic jets propagating through a deconfined strongly-interacting matter. Our main goal is to take into account different types of collective motion during the formation and evolution of this matter. We predict a significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies as compared to the case of jet propagation in a static medium. The observed broadening of the near-side two-particle correlations in pseudorapidity space is explained by the Bjorken-like longitudinal expansion. Three-particle correlation measurements are…
We derive the distribution of energy and momentum transmitted from a primary fast parton and its medium-induced bremsstrahlung gluons to a thermalized quark-gluon plasma. Our calculation takes into account the important and thus far neglected effects of quantum interference between the resulting color currents. We use our result to obtain the rate at which energy is absorbed by the medium as a function of time and find that the rate is modified by the quantum interference between the primary parton and secondary gluons. This Landau-Pomeranchuk-Migdal type interference persists for time scales …
We present results for the process $gg \to γZ g$ within the standard model at hadron colliders. Due to large gluon flux at the LHC and the proposed HE-LHC, this process can have significant cross section at these machines. Several thousand such events have already been produced at the LHC according to the standard model predictions. This process can also be a background to new physics signals. We discuss some of the important features of this process related to the structure of its amplitude. We also compute the total cross section at the hadron colliders and give some important kinematic dist…
The equations for Yang-Mills field in a medium are derived in a linear approximation with respect to the gauge coupling parameter and the external field. The obtained equations closely resemble the macroscopic Maxwell equations. A canonical quantization is performed for a family of Fermi-like gauges in the case of constant and diagonal (in the group indices) tensors of electric permittivity and magnetic permeability. The physical subspace is defined and the gauge field propagator is evaluated for a particular choice of the gauge. The propagator is applied for evaluation of the cross-section of…
The energy and momentum lost by a hard parton propagating through hot and dense matter has to be redistributed during the nuclear medium evolution. Apart from heating the medium, there is the possibility that collective modes are excited leading to the emergence of Mach cones or Cherenkov radiation. Recent two-particle correlation measurements by STAR \cite{Wang:2004kf} and PHENIX \cite{Adler:2005ee} at RHIC indicate that such phenomena may play an important role in understanding the jet-medium interactions. Possible collective modes are discussed and it is demonstrated that Mach cones as crea…
Production and equilibration of quark-gluon plasma are studied within the color flux-tube model, at the RHIC and LHC energies. Non-Abelian relativistic transport equations for quarks, antiquarks and gluons, are solved in the extended phase space which includes coordinates, momenta and color. Before the chromoelectric field is formed, hard and semihard partons are produced via minijets which provide the initial conditions necessary to solve the transport equations. The model predicts that in spite of the vast difference between the RHIC and LHC incident energies, once the local equilibrium is r…
The self-interactions of gluons determine all the unique features of QCD and lead to a dominant abundance of gluons inside matter already at moderate $x$. Despite their dominant role, the properties of gluons remain largely unexplored. Tantalizing hints of saturated gluon densities have been found in $e$+p collisions at HERA, and in d+Au and Au+Au collisions at RHIC. Saturation physics will have a profound influence on heavy-ion collisions at the LHC. But unveiling the collective behavior of dense assemblies of gluons under conditions where their self-interactions dominate will require an Elec…
In this thesis, we present recent advances at the precision frontier of higher-order quantum chromodynamics (QCD) calculations. We consider massless two-loop five-point amplitudes, with a particular focus on diphoton-plus-jet production through gluon fusion. We build a library of infrared functions up to at most next-to-next-to-leading order (NNLO) in QCD, which can be used to validate amplitudes and construct counterterms in subtraction schemes at NNLO. We review progress in the novel use of machine learning technology to optimise the evaluation of amplitudes in hadron collider simulations. W…
Holographic equation of state matched with hadron gas equation as a tool for the study of the quark-gluon plasma evolution
本文提出将全息状态方程与强子共振气体方程匹配，利用机器学习校准参数并结合iEBE-MUSIC等软件包模拟相对论重离子碰撞中夸克-胶子等离子体的演化及强子谱。
We examine experimental signatures of TeV-mass black hole formation in heavy ion collisions at the LHC. We find that the black hole production results in a complete disappearance of all very high $p_T$ ({$> 500$} GeV) back-to-back correlated di-jets of total mass {$M > M_f \sim 1$}TeV. We show that the subsequent Hawking-decay produces multiple hard mono-jets and discuss their detection. We study the possibility of cold black hole remnant (BHR) formation of mass $\sim M_f$ and the experimental distinguishability of scenarios with BHRs and those with complete black hole decay. Finally we point …
The production of Large Extra Dimension (LXD) Black Holes (BHs), with a new, fundamental mass scale of $M_f = 1$ TeV, has been predicted to occur at the Large Hadron Collider, LHC, with the formidable rate of $10^8$ per year in p-p collisions at full energy, 14 TeV, and at full luminosity. We show that such LXD-BH formation will be experimentally observable at the LHC by the complete disappearance of all very high $p_t$ ($> 500$ GeV) back-to-back correlated Di-Jets of total mass $M > M_f = 1$ TeV. We suggest to complement this clear cut-off signal at $M > 2*500$ GeV in the di-jet-correlation f…
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