Phenomenology of light- and strange-quark simultaneous production at high energies

This letter presents an extension of EPL116(2017)62001 to light- and strange-quark nonequilibrium chemical phase-space occupancy factors (γ_q,s). The resulting damped trigonometric functionalities relating γ_q,s to the nucleon-nucleon center-of-mass energies (\(\sqrt {{s_{NN}}} \)) looks very similar except different coefficients. The phenomenology of the resulting γ_q,s(\(\sqrt {{s_{NN}}} \)) describes a rapid decrease at \(\sqrt {{s_{NN}}} \) ? 7GeV followed by a faster increase up to ~20 GeV. Then, both γ_q,s become nonsensitive to \(\sqrt {{s_{NN}}} \). Although these differ from γ _s (\(\sqrt {{s_{NN}}} \))obtained at γ _q (\(\sqrt {{s_{NN}}} \))=1, various particle ratios including K⁺/π⁺, K^?/π^?, Λ/π^?, Λ?/π^?, Ξ⁺/π⁺, and Ω/π^?, can well be reproduced, as well. We conclude that γ_q,s(\(\sqrt {{s_{NN}}} \)) should be instead determined from fits of various particle yields and ratios but not merely from fits to the particle ratio K⁺/π⁺.     

Modeling of the internal tracking system of the NICA/MPD detector

The internal tracking system of the NICA/MPD detector is aimed at efficiently detecting the short-lived products of nucleus–nucleus collisions. We consider various geometries of the internal tracking system based on microstrip silicon sensors and simulate its identification power in reconstructing the Λ⁰ hyperons formed in central Au + Au collisions at \(\sqrt {{S_{NN}}} \; = 9\;GeV\).     

Hadron production at forward rapidity in nuclear collisions at RHIC

The main experimental results obtained by the BRAHMS experiment at Relativistic Heavy Ion Collider (RHIC) for Au+Au collisions at \(\sqrt {s_{NN} } \) =62.4, 200 GeV and d+Au collisions at \(\sqrt {s_{NN} } \) = 200GeV are presented. The m _T spectra and the Gaussian-like rapidity densities of produced pions and kaons in Au+Au central collisions at \(\sqrt {s_{NN} } \) = 200 are GeV shown, and their rapidity densities are compared with results from models. The net-proton yield in the same system is compared with that from AGS and SPS energies to study the high energy collision scenario-transparency and stopping. The rapidity, energy and centrality dependence of the nuclear modification factors in both systems are compared with models to differentiate between the initial and final state effect.     

Involution symmetries and the PMNS matrix

The hot and dense matter produced in nucleus–nucleus collisions is supposed to expand according to unified hydrodynamics, one of the few theoretical models that can be worked out exactly. The solution is then used to formulate the rapidity distribution of charged particles frozen out from the fluid on the space-like hypersurface with a fixed temperature, T _FO. A comparison is made between the theoretical predictions and the experimental measurements carried out by PHOBOS Collaboration in the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory (BNL) in different centrality Au–Au and Cu–Cu collisions at \(\sqrt {s_{\text {NN}}} \,=\,19.6\) and 22.4 GeV, respectively. The theoretical results are in good accordance with experimental data.     

Measurement of CP asymmetries in neutralino production at the ILC

We study the prospects to measure the CP-sensitive triple-product asymmetries in neutralino production \(e^{+} e^{-} \to\tilde{\chi}^{0}_{i}\tilde{\chi}^{0}_{1}\) and subsequent leptonic two-body decays \(\tilde{\chi}^{0}_{i} \to \tilde{\ell}_{R} \ell\), \(\tilde{\ell}_{R} \to \tilde{\chi}^{0}_{1} \ell\), for ?=e,μ, within the Minimal Supersymmetric Standard Model. We include a full detector simulation of the International Large Detector for the International Linear Collider. The simulation was performed at a center-of-mass energy of \(\sqrt{s}=500\) GeV, including the relevant Standard Model background processes, a realistic beam energy spectrum, beam backgrounds and a beam polarization of 80% and ?60% for the electron and positron beams, respectively. In order to effectively disentangle different signal samples and reduce SM and SUSY backgrounds we apply a method of kinematic reconstruction. Assuming an integrated luminosity of 500 fb^?1 collected by the experiment and the performance of the current ILD detector, we arrive at a relative measurement accuracy of 10% for the CP-sensitive asymmetry in our scenario. We demonstrate that our method of signal selection using kinematic reconstruction can be applied to a broad class of scenarios and it allows disentangling processes with similar kinematic properties.     

Monte Carlo event generators for NICA/MPD and CBM experiments

An improved version of the Glauber Monte Carlo simulation program is proposed that allows on to estimate the geometric properties of nucleus–nucleus interactions in energy range \(\sqrt {{S_{NN}}} \) of 5 GeV to 20 TeV. It is shown that the geometric properties of interactions at energies of 5–10 GeV (NICA/MPD and CBM) are quite close to those at an energy of 200 GeV (RHIC). The geometric properties can be derived from experimentally observable quantities using different techniques. The most promising of these is the registration of spectator neutrons from nuclear residuals. It is shown that event generators predict different multiplicities of produced neutrons. The registration of neutrons will be a great step in our understanding of the decay of nuclei in highly excited states.     

Constraining spin-one color-octet resonances using CDF and ATLAS data

In this paper, we study the production of spin-one color-octet resonances (colorons) at hadron colliders in a model independent way. We use dijets data measured by CDF (at \(\sqrt{ s}=1.96\) TeV and \(\mathcal{L}=1.13\) pb^?1) and ATLAS (at \(\sqrt{ s}=7\) TeV and \(\mathcal{L}=315\) nb^?1) collaborations at the Tevatron and the LHC respectively to impose limits on the coupling of colorons to fermions. We show that CDF data still produce the more stringent limits on the coloron coupling constant.     

On quantum analogue of dynamical stabilisation of inverted harmonic oscillator by time periodical uniform field

Quantum analogue of stabilised forced oscillations around an unstable equilibrium position is explored by solving the non-stationary Schrödinger equation (NSE) of the inverted harmonic oscillator (IHO) driven periodically by spatial uniform field of frequency \(\Omega \), amplitude \(F_{0}\) and phase \(\phi \), i.e. the system with the Hamiltonian of \(\hat{{H}}=(\hat{{p}}^{2}/2m)-(m\omega ^{2}x^{2}/2)-F_0 x\sin \) \(\left( {\Omega t+\phi } \right) \). The NSE has been solved both analytically and numerically by Maple 15 in dimensionless variables \(\xi = x\sqrt{m\omega /\hbar }\hbox {, }f_0 =F_0 /\omega \sqrt{\hbar m\omega }\) and \(\tau =\omega t\). The initial condition (IC) has been specified by the wave function (w.f.) of a generalised Gaussian type which suits well the corresponding quantum IC operator. The solution obtained demonstrates the non-monotonous behaviour of the coordinate spreading \(\sigma \left( \tau \right) \hbox { =}\sqrt{\big ( {\overline{\Delta \xi ^{2}\big ( \tau \big )} } \big )}\) which decreases first from quite macroscopic values of \(\sigma _{0} =2^{12,\ldots ,25}\) to minimal one of \(\sim \!(1/\sqrt{2})\) at times \(\tau <\tau _0 =0.125\ln \!\left( {16\sigma _0^4 +1} \right) \) and then grows back unlimitedly. For certain phases \(\phi \) depending on the \(\Omega /\omega \) ratio and \(n=\log _2\!\sigma _0 \), the mass centre of the packet \(\xi _{\mathrm {av}}( \tau )= \overline{\hat{{x}}(\tau )} \cdot \sqrt{m\omega /\hbar }\) delays approximately two natural ‘periods’ \(\sim \!(4\pi /\omega )\) in the area of the stationary point and then escapes to ‘\(+\)’ or ‘?’ infinity in a bifurcating way.  For ‘resonant’ \(\Omega =\omega \), the bifurcation phases \(\phi \) fit well with the regression formula of Fermi–Dirac type of argument n with their asymptotic \(\phi ( {\Omega ,n\rightarrow \infty } )\) obeying the classical formula \(\phi _{\mathrm {cl}} ( \Omega )=-\hbox {arctg} \, \Omega \) for initial energy \(E = 0\) in the wide range of \(\Omega =2^{-4},...,2^{7}\).     

Net-proton measurements at RHIC and the quantum chromodynamics phase diagram

Two measurements related to the proton and antiproton production near midrapidity in \(\sqrt {s_{{NN}}} = 7.7\) , 11.5, 19.6, 27, 39, 62.4 and 200 GeV Au+Au collisions using the STAR detector at the Relativistic Heavy Ion Collider (RHIC) are discussed. At intermediate impact parameters, the net-proton midrapidity dv ₁/dy, where v ₁ and y are directed flow and rapidity, respectively, shows non-monotonic variation as a function of beam energy. This non-monotonic variation is characterized by the presence of a minimum in dv ₁/dy between \(\sqrt {s_{NN}} = 11.5\) and 19.6 GeV and a change in the sign of dv ₁/dy twice between \(\sqrt {s_{{NN}}}\) = 7.7 and 39 GeV. At small impact parameters the product of the moments of net-proton distribution, kurtosis × variance (κ σ ²) and skewness × standard deviation (S σ) are observed to be significantly below the corresponding measurements at large impact parameter collisions for \(\sqrt {s_{{NN}}}\) = 19.6 and 27 GeV. The κ σ ² and S σ values at these beam energies deviate from the expectations from Poisson statistics and that from a hadron resonance gas model. Both these measurements have implications towards understanding the quantum chromodynamics (QCD) phase structures, the first-order phase transition and the critical point in the high baryonic chemical potential region of the phase diagram.     

Non-extensivity of the chemical potential of polymer melts

Following Flory’s ideality hypothesis, the chemical potential of a test chain of length n immersed into a dense solution of chemically identical polymers of length distribution P(N) is extensive in n . We argue that an additional contribution \( \delta\) \( \mu_{{{\rm c}}}^{}\)(n) ～ +1/\( \rho\) \( \sqrt{{n}}\) arises (\( \rho\) being the monomer density) for all P(N) if n ? 〈N〉 which can be traced back to the overall incompressibility of the solution leading to a long-range repulsion between monomers. Focusing on Flory-distributed melts, we obtain \( \delta\) \( \mu_{{{\rm c}}}^{}\)(n) \( \approx\) (1 - 2n/〈N〉)/\( \rho\) \( \sqrt{{n}}\) for n ? 〈N〉² , hence, \( \delta\) \( \mu_{{{\rm c}}}^{}\)(n) \( \approx\) -1/\( \rho\) \( \sqrt{{n}}\) if n is similar to the typical length of the bath 〈N〉 . Similar results are obtained for monodisperse solutions. Our perturbation calculations are checked numerically by analyzing the annealed length distribution P(N) of linear equilibrium polymers generated by Monte Carlo simulation of the bond fluctuation model. As predicted we find, e.g., the non-exponentiality parameter K _p \( \equiv\) 1 - 〈N ^p〉/p!〈N〉^p to decay as K _p \( \approx\) 1/\( \sqrt{{\langle N \rangle }}\) for all moments p of the distribution.     

Pion decay constants in a strong magnetic field

Decay constants of the charged and neutral pions in magnetic field are considered in the framework of the effective quark-antiquark lagrangian respecting Gell-Mann–Oakes–Renner (GOR) relations at zero field. The \(\sqrt {\frac{{{e_q}B}}{\sigma }} \) dependence is found in strong fields e_qB ? σ for the neutral pion, while the charged pion constant decreases as \(\sqrt {\frac{\sigma }{{{e_q}B}}} \).     

Influence of photon-neutrino processes on the cooling of a magnetar

The influence of a strongly magnetized dense plasma on the photon-neutrino processes γe ^± → e ^±ν\(\bar \nu \), γ → ν\(\bar \nu \), and γγ → ν\(\bar \nu \) is considered; invariant amplitudes of the γe ^± → e ^±ν\(\bar \nu \) and γγ → ν\(\bar \nu \) reactions are calculated. The contributions from these processes to the neutrino luminosity are calculated in the special case of a cold plasma. Under these conditions, the contribution from the process γ → ν\(\bar \nu \) to the neutrino emissivity is shown to be strongly suppressed compared to the contributions from the photoneutrino and photon conversion processes. Since the neutron star cooling curve can be modified through a change of the neutrino luminosity in a strong magnetic field, the magnetic field strength in the outer crust of the magnetar is assumed to be constrained.     

Signals of leptophilic dark matter at the ILC

Adopting a model independent approach, we constrain the various effective interactions of leptophilic DM particles with the visible world from the WMAP and Planck data. The thermally averaged indirect DM annihilation cross section and the DM–electron direct-detection cross section for such a DM candidate are observed to be consistent with the respective experimental data. We study the production of cosmologically allowed leptophilic DM in association with \(Z\, (Z\rightarrow f\bar{f})\), \(f\equiv q,\,e^-,\, \mu ^-\) at the ILC. We perform the \(\chi ^2\) analysis and compute the 99% C.L. acceptance contours in the \(m_\chi \) and \(\varLambda \) plane from the two-dimensional differential distributions of various kinematic observables obtained after employing parton showering and hadronisation to the simulated data. We observe that the dominant hadronic channel provides the best kinematic reach of 2.62 TeV (\(m_\chi \) = 25 GeV), which further improves to \(\sim \)3 TeV for polarised beams at \(\sqrt{s} = 1\) TeV and an integrated luminosity of 1 ab\(^{-1}\).     

Scalar top quarks production in polarized photon-photon collisions at ILC

We study pair production of scalar top quarks (stop, \(\tilde t_1\)) in polarized photon-photon collisions with the subsequent decay of the top squarks into b quarks and charginos \(\tilde t_1 \to b\tilde \chi _1^ \pm\). We simulate this process by using PYTHIA6.4 for an electron beam energy \(2E_{beam}^e = \sqrt {s_{ee} } = 1000 GeV\). The energy spectrum of back-scattered photons is generated by CIRCE2 program. A set of criteria for physical variables is proposed which leads to a good separation of stop signal events from top quark pair production, being the main background. These criteria allow us to reconstruct the mass of the top squark, provided that the neutralino mass is known.     

Monojet signatures from heavy colored particles: future collider sensitivities and theoretical uncertainties

In models with colored particle \(\mathcal {Q}\) that can decay into a dark matter candidate X, the relevant collider process \(pp\rightarrow \mathcal {Q}\bar{\mathcal {Q}}\rightarrow X\bar{X}\,+\,\)jets gives rise to events with significant transverse momentum imbalance. When the masses of \(\mathcal {Q}\) and X are very close, the relevant signature becomes monojet-like, and Large Hadron Collider (LHC) search limits become much less constraining. In this paper, we study the current and anticipated experimental sensitivity to such particles at the High-Luminosity LHC at \(\sqrt{s}=14\) TeV with \(\mathcal {L}=3\) ab\(^{-1}\) of data and the proposed High-Energy LHC at \(\sqrt{s}=27\) TeV with \(\mathcal {L}=15\) ab\(^{-1}\) of data. We estimate the reach for various Lorentz and QCD color representations of \(\mathcal {Q}\). Identifying the nature of \(\mathcal {Q}\) is very important to understanding the physics behind the monojet signature. Therefore, we also study the dependence of the observables built from the \(pp\rightarrow \mathcal {Q}\bar{\mathcal {Q}} + j \) process on \(\mathcal {Q}\) itself. Using the state-of-the-art Monte Carlo suites MadGraph5_aMC@NLO+Pythia8 and Sherpa, we find that when these observables are calculated at NLO in QCD with parton shower matching and multijet merging, the residual theoretical uncertainties are comparable to differences observed when varying the quantum numbers of \(\mathcal {Q}\) itself. We find, however, that the precision achievable with NNLO calculations, where available, can resolve this dilemma.     

<Emphasis Type="Italic">Z</Emphasis>′ discovery potential at the LHC in the minimal <Emphasis Type="Italic">B</Emphasis>–<Emphasis Type="Italic">L</Emphasis> extension of the standard model

We present the Large Hadron Collider (LHC) discovery potential in the Z′ sector of a \(U(1)_{B\mbox{--}L}\) enlarged Standard Model (that also includes three heavy Majorana neutrinos and an additional Higgs boson) for \(\sqrt{s}=7\), 10 and 14 TeV centre-of-mass (CM) energies, considering both the \(Z'_{B\mbox{--}L}\rightarrow e^{+}e^{-}\) and \(Z'_{B\mbox{--}L}\rightarrow\mu^{+}\mu^{-}\) decay channels. The comparison of the (irreducible) backgrounds with the expected backgrounds for the DØ experiment at the Tevatron validates our simulation. We propose an alternative analysis that has the potential to improve the DØ sensitivity. Electrons provide a higher sensitivity to smaller couplings at small \(Z'_{B\mbox{--}L}\) boson masses than do muons. The resolutions achievable may allow the \(Z'_{B\mbox{--}L}\) boson width to be measured at smaller masses in the case of electrons in the final state. The run of the LHC at \(\sqrt{s}=7\) TeV, assuming at most \(\int\mathcal{L} \sim1\) fb^?1, will be able to give similar results to those that will be available soon at the Tevatron in the lower mass region, and to extend them for a heavier M _Z′.     

NICA at JINR: New prospects for exploration of quark-gluon matter

A new scientific program is proposed at the Joint Institute for Nuclear Research (JINR) in Dubna aimed at studies of hot and dense baryonic matter in the wide energy range from 2 GeV/u kinetic energy in fixed target experiments to $\sqrt {s_{NN} } = 4 - 11$ GeV/u in the collider mode. To realize this program the development of the JINR accelerator facility in high-energy physics (HEP) has been started. This facility is based on the existing superconducting synchrotron??the Nuclotron. The program foresees both experiments at the beams extracted from the Nuclotron, and the construction of a heavy-ion collider??the Nuclotron-based Ion Collider fAcility (NICA) which is designed to reach the required parameters with an average luminosity of L = 10²⁷ cm^?2 s^?1.     

Top quark FCNCs in extended Higgs sectors

The large number of top quarks produced at the LHC and possible future hadron colliders allows to study rare decays of this particle. In many well motivated models of new physics, for example in non-minimal composite-Higgs models, the existence of scalar singlets can induce new flavor-violating top decays surpassing the Higgs contribution by orders of magnitude. We study the discovery prospects of rare top decays within such models and develop new search strategies to test these interactions in top pair-produced events at the LHC. We demonstrate that scales as large as 10–50 TeV can be probed. Improvements by factors of \(\sim 1.5\) and \(\sim 3\) can be obtained at \(\sqrt{s} = 27\) TeV and \(\sqrt{s} = 100\) TeV colliders respectively.     

Fully constrained Majorana neutrino mass matrices using $$\varvec{\varSigma (72\times 3)}$$

In 2002, two neutrino mixing ansatze having trimaximally mixed middle (\(\nu _2\)) columns, namely tri-chi-maximal mixing (\(\text {T}\chi \text {M}\)) and tri-phi-maximal mixing (\(\text {T}\phi \text {M}\)), were proposed. In 2012, it was shown that \(\text {T}\chi \text {M}\) with \(\chi =\pm \,\frac{\pi }{16}\) as well as \(\text {T}\phi \text {M}\) with \(\phi = \pm \,\frac{\pi }{16}\) leads to the solution, \(\sin ^2 \theta _{13} = \frac{2}{3} \sin ^2 \frac{\pi }{16}\), consistent with the latest measurements of the reactor mixing angle, \(\theta _{13}\). To obtain \(\text {T}\chi \text {M}_{(\chi =\pm \,\frac{\pi }{16})}\) and \(\text {T}\phi \text {M}_{(\phi =\pm \,\frac{\pi }{16})}\), the type I see-saw framework with fully constrained Majorana neutrino mass matrices was utilised. These mass matrices also resulted in the neutrino mass ratios, \(m_1:m_2:m_3=\frac{\left( 2+\sqrt{2}\right) }{1+\sqrt{2(2+\sqrt{2})}}:1:\frac{\left( 2+\sqrt{2}\right) }{-1+\sqrt{2(2+\sqrt{2})}}\). In this paper we construct a flavour model based on the discrete group \(\varSigma (72\times 3)\) and obtain the aforementioned results. A Majorana neutrino mass matrix (a symmetric \(3\times 3\) matrix with six complex degrees of freedom) is conveniently mapped into a flavon field transforming as the complex six-dimensional representation of \(\varSigma (72\times 3)\). Specific vacuum alignments of the flavons are used to arrive at the desired mass matrices.