Designing Klod detector prototypes and results of their experimental tests

The projected KLOD facility is intended for finding and investigating the ultrarare decay K _L ⁰ → π⁰ν$ \bar \nu $ \bar \nu ; its branching ratio predicted by the Standard Model is Br = (3.0 ± 0.6) × 10⁻¹¹. Designing and testing the prototype of the decay-volume veto system and beam veto calorimeter, which are the most important detectors of the facility, are considered. It is shown that the proposed beam veto calorimeter is able to detect γ rays with a high efficiency at the neutron flux of 300 MHz.     

Beam-induced radiation in the compact muon solenoid tracker at the Large Hadron Collider

The intense radiation environment at the Large Hadron Collider, CERN at a design energy of $ \sqrt s $ \sqrt s = 14 TeV and a luminosity of 10³⁴ cm⁻² s⁻¹ poses unprecedented challenges for safe operation and performance quality of the silicon tracker detectors in the CMS and ATLAS experiments. The silicon trackers are crucial for the physics at the LHC experiments, and the inner layers, being situated only a few centimeters from the interaction point, are most vulnerable to beam-induced radiation. We have recently carried out extensive Monte Carlo simulation studies using MARS program to estimate particle fluxes and radiation dose in the CMS silicon pixel and strip trackers from proton-proton collisions at $ \sqrt s $ \sqrt s = 14 TeV and from machine-induced background such as beam-gas interactions and beam halo. We will present results on radiation dose, particle fluxes and spectra from these studies and discuss implications for radiation damage and performance of the CMS silicon tracker detectors.     

Measurement of D* mesons in jets from p + p collisions at ?s \sqrt s = 200 GeV

We report the measurement of charged D* mesons in jets produced in proton-proton collisions at a center of mass energy $ \sqrt s $ \sqrt s = 200 GeV with the STAR experiment at RHIC. The production rate is found to be N(D*⁺ + D*⁻)/N (jet) = 0.015 ± 0.008 (stat) ± 0.007 (sys) for D* mesons with fractional momenta 0.2 < z < 0.5 in jets with 11.5 GeV mean transverse energy. This rate is consistent with perturbative QCD evalulation of gluon splitting into a pair of charm quarks and subsequent hadronization.     

Production of strange secondaries in high-energy Σ<Superscript>−</Superscript><Emphasis Type="Italic">A</Emphasis> collisions

The WA89 Collaboration experimental data on production of Λ, Σ⁻, Σ⁺, Ξ⁻, Ω⁻ baryons, $ \bar \Lambda $ \bar \Lambda and $ \bar \Xi ^ + $ \bar \Xi ^ + antibaryons in Σ⁻ collisions with C and Cu targets at 345 GeV/c ($ \sqrt {s_{\Sigma N} } $ \sqrt {s_{\Sigma N} } ≈ 25.5 GeV) in the frame of the Quark-Gluon String Model is described. The comparison of the theoretical results with the experimental data is discussed. Finally, some relations among the values of the model parameters obtained with the help of quark combinatorics are presented.     

The p/π ratio pT dependence in the RHIC range of baryo-chemical potential

The BRAHMS measurement of proton-to-pion ratios in Au+Au and p+p collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 62.4 GeV and $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV is presented as a function of transverse momentum and collision centrality within the pseudorapidity range 0 ≤ η ≤ 3. The baryo-chemical potential, μ _B , for the indicated data spans from μ _B ≈ 26 MeV ($ \sqrt {s_{NN} } $ \sqrt {s_{NN} } 200 GeV, η ≈ 0) to μ _B ∼ 260 MeV ($ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 62.4 GeV, η ≈ 3) [1]. The p/πratio measured for Au+Au system at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } 62.4 GeV, η ≈ 3 reaches astounding value of 8–10 at p _T > 1.5 GeV/c. For these energy and pseudorapidity interval no centrality dependency of p/π ratio is observed. Moreover, the baryon-to-meson ratio of nucleus-nucleus data are consistent with results obtained for p+p interactions.     

Neutron diffraction studies of the negative thermal expansion in a layered indium selenide crystal

The neutron diffraction patterns have been analyzed for a layered single crystal and a powder of the γ-polytype of indium selenide in the temperature range 10–300 K. In the temperature range 10–50 K, the excitation of bending vibrations due to the charge density waves changes the phonon spectrum and gives rise to a negative thermal expansion in the plane of layers, i.e., α_‖c = −2.2 × 10⁻⁶ K⁻¹, which is characteristic of two-dimensional structures. The average (over the range T = 50–300 K) coefficients of thermal expansion along the principal crystallographic directions have been calculated: $ \bar \alpha _{ \bot c} $ \bar \alpha _{ \bot c} = 10.48 × 10⁻⁶ K⁻¹ and $ \bar \alpha _{\parallel c} $ \bar \alpha _{\parallel c} = 12.97 × 10⁻⁶ K⁻¹, which agree with the X-ray diffraction data previously obtained by the authors at T = 290 K.     

ESR in the Earth’s magnetic field as a cause of dislocation motion in NaCl crystals

The resonance displacements of the dislocations, l ∼ 100 μm, in NaCl crystals placed in the crossed Earth’s magnetic field B _Earth and the ac field $ \tilde B $ \tilde B ≈ 3 μT of the variable frequency ν ∼ 10⁶ Hz have been discovered in the absence of any other impact on the crystals. Two peaks of the mean dislocation path l(ν) with the maxima at ν₁ = 1.3 MHz and ν₂ = 3 MHz have been observed for the field $ \tilde B $ \tilde B oriented along the vertical and horizontal components of B _Earth, respectively. The effect is explained by the depinning of the dislocations from the impurity centers after their structural transformation due to the ESR in the dislocation-impurity system in the crossed fields. The subsequent motion of the dislocations proceeds under the action of internal stress in the crystals. A physical model has been proposed to explain the strong anisotropy of the effect with respect to the mutual orientation of the dislocation lines and magnetic fields.     

Two-photon decays of pseudotensor mesons <Emphasis Type="Italic">π</Emphasis><Subscript>2</Subscript>(1670), <Emphasis Type="Italic">π</Emphasis><Subscript>2</Subscript>(2250), and <Emphasis Type="Italic">π</Emphasis><Subscript>2</Subscript>(2510)

In terms of relativistic and gauge-invariant spectral-integral technique, we calculate amplitude for the π ₂ → γγ decay as a three-step transition π ₂ → q $ \bar q $ \bar q (2⁻⁺) → γ + q $ \bar q $ \bar q (1⁻⁻) → γγ. Using wave functions of the q $ \bar q $ \bar q components of photon (hep-ph/0406320) and those of pseudotensor mesons π ₂(1670), π ₂(2000), π ₂(2250), and π ₂(2510) (hep-ph/0511109), we obtain the following values for partial widths: Γ _{π2(1670)→γγ} = 0.072 ± 0.007 keV, Γ _{π2(2000)→γγ} = 0.037 ± 0.004 keV, Γ _{π2(2250)→γγ} = 0.027 ± 0.003 keV, and Γ _{π2(2510)→γγ} = 0.022 ± 0.002 keV. In the calculations, we use the momentum operator expansion, and, in this connection, discuss the problem of nilpotent operators inherent in the considered amplitude. It should be emphasized that measurement of two-photon decays of the π ₂ states can give valuable information about the long-range quark-antiquark forces which, as one may guess, are related to the quark confinement.     

Directed flow of identified particles from Au+Au collisions at RHIC

We present the measurement of directed flow (v ₁) for the identified particles, namely, Λ, $ \bar \Lambda $ \bar \Lambda and K _s ⁰, as a function of rapidity and centrality in Au+Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV and 62.4 GeV. The measurement is based on the run IV data obtained by the STAR experiment at RHIC. In order to enhance event plane resolution, we use tracks reconstructed from the Forward Time Projection Chambers (FTPCs), together with the sideward deflection of spectator neutrons measured by the STAR’s Shower Maximum Detector at Zero Degree Calorimeters (ZDC-SMDs). We find that for 200 GeV, proton and antiproton v ₁ is less than 1%, the K _s ⁰ Λ, $ \bar \Lambda $ \bar \Lambda v ₁ is less than 2%; for 62 GeV, proton v ₁ is less than 1% and antiproton is less than 2%, v ₁ for K _s ⁰, Λ, $ \bar \Lambda $ \bar \Lambda is less than 2% in Au+Au collisions at 200 GeV.     

Production of π<Superscript>−</Superscript> mesons in CTa interactions at a momentum of 4.2 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

New experimental data on π⁻-meson production in interactions between carbon and tantalum nuclei at amomentumof 4.2 GeV/c per nucleon are presented. These results are compared with predictions based of themodel of quark-gluon strings (QGS) that is adapted to intermediate energies ($ \sqrt 4 $ \sqrt 4 ≤ 4 GeV). It is shown that the QGS model only qualitatively reproduces the behavior of experimental kinematical features of π⁻ mesons.     

Systematic study of photon production at forward rapidity in STAR

We present the measurement of multiplicity and pseudorapidity distributions of photons production at forward rapidity (−2.3 ≤ η ≤ −3.8) for Cu + Cu collisions at $ \sqrt {S_{NN} } $ \sqrt {S_{NN} } = 62.4 and 200 GeV. Photons are measured using the Photon Multiplicity Detector (PMD) in STAR experiment at RHIC. The distributions of (η−η _beam), where η _beam is beam rapidity is presented. Pseudorapidity distributions of photons at forward rapidities, when ob-served in the frame of one of the colliding particles show the signature of energy independent scaling at forward rapidities known as Limiting Fragmentation. Measurement of inclusive photons reflect the distribution for π ⁰ as most of the photons come from π ⁰ decay. Gluon saturation at initial conditions of the collisions is one of the possible explanations for this scaling. Study of system-size and incident energy dependence of this phenomenon help us understand the mechanisms better. The system-size and energy dependence of the widths of scaling in pseudorapidity and comparison with model predictions are presented.     

Internal waves in a compressible two-layer model atmosphere: Hamiltonian description

We consider slow, compared to the speed of sound, motions of an ideal compressible fluid (gas) in a gravitational field in the presence of two isentropic layers with a small specific-entropy difference between them. Assuming the flow to be potential in each of the layers (v _{1, 2} = ▿ϕ_{1, 2}) and neglecting the acoustic degrees of freedom (div($ \bar \rho $ \bar \rho (z)▿ϕ_{1, 2}) ≈ 0, where $ \bar \rho $ \bar \rho (z) is the average equilibrium density), we derive the equations of motion for the boundary in terms of the shape of the surface z = η(x, y, t) itself and the difference between the boundary values of the two velocity field potentials: ψ(x, y, t) = ψ₁ − ψ₂. We prove the Hamilto nian structure of the derived equations specified by a Lagrangian of the form ℒ = ∫$ \bar \rho $ \bar \rho (η)η _t ψdxdy − ℋ{η, ψ}. The system under consideration is the simplest theoretical model for studying internal waves in a sharply stratified atmosphere in which the decrease in equilibrium gas density due to gas compressibility with increasing height is essentially taken into account. For plane flows, we make a generalization to the case where each of the layers has its own constant potential vorticity. We investigate a system with a model dependence $ \bar \rho $ \bar \rho (z) ∝ e ^−2αz with which the Hamiltonian ℋ{η, ψ} can be represented explicitly. We consider a long-wavelength dynamic regime with dispersion corrections and derive an approximate nonlinear equation of the form u _t + auu _x − b[−$ \hat \partial _x^2 $ \hat \partial _x^2 + α²]^1/2 u _x = 0 (Smith’s equation) for the slow evolution of a traveling wave.     

Dielectron widths of the <Emphasis Type="Italic">S</Emphasis>-, <Emphasis Type="Italic">D</Emphasis>-vector bottomonium states

The dielectron widths of Y(nS)(n = 1, …, 7) and vector decay constants are calculated using the relativistic string Hamiltonian with a universal interaction. For Y(nS) (n = 1, 2, 3) the dielectron widths and their ratios are obtained in full agreement with the latest CLEO data. For Y(10580) and Y(11020) a good agreement with experiment is reached only if the 4S-3D mixing (with a mixing angle θ = 27°± 4°) and 6S-5D mixing (with θ = 40°±5°) are taken into account. The possibility to observe higher “mixed D-wave” resonances, $ \tilde \Upsilon $ \tilde \Upsilon (n ³ D ₁) with n = 3, 4, 5 is discussed. In particular, $ \tilde \Upsilon $ \tilde \Upsilon (≈11120), originating from the pure 5³ D ₁ state, can acquire a rather large dielectron width, ∼130 eV, so that this resonance may become manifest in the e ⁺ e ⁻ experiments. On the contrary, the widths of pure D-wave states are very small, Γ _ee (n ³ D ₁)≤ 2 eV.     

Fine and hyperfine structure of the muonic <Superscript>3</Superscript>He ion

On the basis of quasipotential approach to the bound state problem in QED we calculate the vacuum polarization, relativistic, recoil, structure corrections of orders α ⁵ and α ⁶ to the fine structure interval ΔE ^fs = E(2P _3/2) − E(2P _1/2) and to the hyperfine structure of the energy levels 2P _1/2 and 2P _3/2 in muonic ₂³He ion. The resulting values ΔE ^fs = 144 803.15 μeV, Δ$ \tilde E $ \tilde E ^hfs(2P _1/2) = −58 712.90 μeV, Δ$ \tilde E $ \tilde E ^hfs(2P _3/2) = −24 290.69 μeV provide reliable guidelines in performing a comparison with the relevant experimental data.     

Supersymmetric quantum mechanics living on topologically non-trivial Riemann surfaces

Supersymmetric quantum mechanics is constructed in a new non-Hermitian representation. Firstly, the map between the partner operators H ^(±) is chosen antilinear. Secondly, both these components of a super-Hamiltonian $ \mathcal{H} $ \mathcal{H} are defined along certain topologically non-trivial complex curves r ^(±)(x) which spread over several Riemann sheets of the wave function. The non-uniqueness of our choice of the map $ \mathcal{T} $ \mathcal{T} between ‘tobogganic’ partner curves r ⁽⁺⁾(x) and r ⁽⁻⁾(x) is emphasized.     

Parton structure of the Pomeron in hard single-Pomeron exchange process with μ<Superscript>+</Superscript>μ<Superscript>−</Superscript> pair production on the CMS (LHC)

Process of the μ⁺μ⁻ pair production in hard single-Pomeron exchange is studied on the CMS (LHC) at the energy range $ \sqrt s $ \sqrt s = 7 and 14 TeV. Using H1(DESY) data for quark/antiquark parton distributions in the single-Pomeron, calculations were performed to predict the quark/antiquark component of the parton distribution. The estimations show that the quark/antiquark contribution does not exceed ∼5%. Using CMSSW package the events of the process were reconstructed. The method for estimation of the valent quark/antiquark contribution in the parton structure of the single-Pomeron is developed. This method could be used at the experimental data performance obtained on the CMS detector.     

Measurement of ω/? → e+e? in proton + proton collisions at ?s \sqrt s = 200 GeV at RHIC-PHENIX

The PHENIX experiment at RHIC has measured ω and ϕ meson production using di-electron decay mode over a psude-rapidity range of |η| ≤ 0.35 and a transverse momentum range of 0 < p _T < 5 GeV/c in proton + proton collisions at $ \sqrt s $ \sqrt s = 200 GeV. The spectra of production cross section as a function of p _T for ω and ϕ → e ⁺ e ⁻ show good agreement with other hadornic decay channels ω → π ⁰ γ, ω ⁰ π ⁺ π ⁻ and ϕ → K ⁺ K ⁻, respectively.     

Application of genetic programming for proton-proton interactions

The aim of the present work is to use one of the machine learning techniques named the genetic programming (GP) to model the p-p interactions through discovering functions. In our study, GP is used to simulate and predict the multiplicity distribution of charged pions (P(n _ch )), the average multiplicity (〈n _ch 〉) and the total cross section (σ _tot ) at different values of high energies. We have obtained the multiplicity distribution as a function of the center of mass energy ($ \sqrt s $ \sqrt s ) and charged particles (n _ch ). Also, both the average multiplicity and the total cross section are obtained as a function of $ \sqrt s $ \sqrt s . Our discovered functions produced by GP technique show a good match to the experimental data. The performance of the GP models was also tested at non-trained data and was found to be in good agreement with the experimental data.     

ψ′ to J/ψ ratio measurements in PHENIX at RHIC

The ratio of the ψ′ over the J ψ production cross section in the dielectron channel has been measured in $ \sqrt s $ \sqrt s = 200 GeV p + p collisions with the PHENIX detector at RHIC. The analysis is based on fitting of the dielectron invariant mass spectra in the area around the J ψ and ψ′ signals in order to extract a ratio ψ′ over J ψ of 0.019 ± 0.005 (stat) ± 0.002 (sys) and a fractional feed-down contribution to J ψ from ψ′ of 8.6 ± 2.5%.