Two-proton correlations in <Superscript>4</Superscript>He<Emphasis Type="Italic">p</Emphasis> interactions at a primary momentum of 5 GeV/<Emphasis Type="Italic">c</Emphasis>

Correlations of secondary protons in ⁴Hep interactions are investigated in an exclusive experiment with the aid of a 2-m liquid-hydrogen bubble chamber exposed to an alpha-particle beam of momentum 5 GeV/c the kinetic energy of primary protons in the rest frame of the nucleus is T_p=620 MeV). By using data obtained in 4π geometry for six basic channels of ⁴Hep interaction that lead to the production of two protons, the total correlation function for the pp system is determined, along with two-proton correlation functions for individual channels. Experimental results are compared with the predictions of the modified Lednicky-Lyuboshitz model. The value of R=1.6±0.3 fm is obtained for the root-meansquare spacetime radius of pp emission in ⁴Hep interactions. The dependence of the correlation function on the total momentum of two emitted protons and on the momentum-transfer direction is investigated.     

Study of collective flow effects in CC collisions at a momentum of 4.2 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

Directed (in-plane) flows of protons, pions, and projectile light fragments (d, t, ³He, ⁴He) have been observed by investigating the dependence of the mean transverse momentum in the reaction plane 〈p _x 〉 on the rapidity y in the c.m. system for CC collisions at a momentum of 4.2 GeV/c per nucleon. The comparison of our in-plane-flow results of protons with flow data for various projectile/target configurations was made using the scaled flow F _s = F/(A _P ^1/3 + A _T ^1/3 ). F _s demonstrates a common scaling behavior for flow values from different systems. From azimuthal distributions of protons and π^? mesons, out-of-plane (squeeze-out) flow effects have been observed and the parameter a₂ (the measure of the anisotropic emission strength) has been extracted. The quark-gluon string model reproduces the experimental results quite well.     

Measurement of light scalar mesons in many-body decays in the PHENIX experiment at the Relativistic Heavy-Ion Collider

The unique design of the PHENIX detector at the Relativistic Heavy-Ion Collider allows one to detect neutral and charged particles produced in high-energy collisions of heavy ions. This circumstance made it possible to measure many-particle decays of light mesons, such as K _S ⁰ →π⁰π⁰, η→π⁰π^?π⁺, and η→γγ in p + p, d + Au and Au + Au collisions at the energy \(\sqrt {S_{NN} }\) = 200 GeV. The latest results of measuring the differential production cross sections, ratios of particle yields (K _S ⁰ /π⁰ and η/π⁰), and the nuclear modification factors (\(R_{dA}^{K_S }\), R _dA ^η , R _AA ^η ) in a wide range of transverse momenta (from 2 to 12 GeV s^?1) are reported.     

Measurement of the azimuthal anisotropy coefficient <Emphasis Type="Italic">v</Emphasis><Subscript>2</Subscript> for the emission of α particles in nucleus-nucleus collisions at energies 1.88–10.6 GeV/nucleon

The azimuthal anisotropy of the emission of α particles in collisions of the ²²Ne, ²⁴Mg, ⁵⁶Fe, and ¹⁹⁷Au nuclei with photoemulsion nuclei has been measured at projectile energies E_pr = 1.88–10.6 GeV/nucleon. The results are compared with similar measurements for protons. It has been found that the ratio of the azimuthal anisotropy coefficients v₂ for α particles and protons is equal to 6 ± 2 at low energies E_pr ≈ 2 GeV/nucleon, whereas these coefficients coincide with each other for energies E_pr ≥ 4 GeV/nucleon. This difference may indicate that, at low projectile energies, α particles are formed predominantly at the early stage of a collective flow. Formation of α particles for E_pr ≥ 4 GeV/nucleon likely occurs at the stage of nuclear matter scattering.     

Corona effect in <Emphasis Type="Italic">AA</Emphasis> collisions at the LHC

Following our earlier finding based on RHIC data on the dominant jet production from nucleus corona region, we reconsider this effect in nucleus–nucleus collisions at the LHC energies. Our hypothesis was based on experimental data, which raised the idea of a finite formation time for the produced medium. At the RHIC energy and in low-density corona region, this time reaches about 2 fm/c. Following this hypothesis, the nuclear modification factor R _AA at high p _t should be independent on particle momentum, and the azimuthal anisotropy of high p _t particles, v ₂, should be finite. A separate prediction held that, at the LHC energy, the formation time in the corona region should be about 1 fm/c. New LHC data show that R _AA is not flat and is rising with p _t . We add to our original hypothesis an assumption that a fast parton traversing the produced medium loses the fixed portion of its energy. A shift of about 7 GeV from the original power law p ^?6 production cross section in pp explains well all the observed R _AA dependencies. The shift of about 7 GeV is also valid at the RHIC energy. We also show that the observed at the LHC dependence of v ₂ at high p _t and our previous predictions agree.     

Die Winkelverteilung der Protonen der Reaktion B11 (d,p 0,1 B12 im Energiebereich von 0,7 ... 1,7 MeV

Angular distributions of the protons in this low-energy region have been measured by only few groups for obvious reasons: the energy of the emitted protons is very low. It will be shown that by using non-supported targets of B¹¹ with very little oxygen contamination the angular distributions can be obtained between approximately 5 and 165 degrees (cm.,p ₀-group) and between 20 and 165 degrees (cm.,p ₁) with high accuracy. The Butler-fits givel=1,r _B =5.2 fm forp ₀ andl=1,r _B =4.7 fm forp ₁. All angular distributions seem to exhibit strong participation of non-stripping mechanism.     

Forward particle production in proton–nucleus interactions at momenta of 25 and 50 GeV/<Emphasis Type="Italic">с</Emphasis> and сarbon–nucleus interactions at an energy of 25 GeV per nucleon

Relative yields of high-x _F charged hadrons (π ^±, К^±, р, \(\overline p \), and d) in proton–nucleus interactions at incident-proton momenta of 25 and 50 GeV/c were measured at an angle of 0° in the momentum range between 15 and 40 GeV/c. An upper limit on the forward production of two protons in proton–nucleus interactions at 50 GeV/c was estimated. The properties of a carbon beam with an energy of 25 GeV per nucleon and fragment yields in its interaction with nuclear targets were measured within a short exposure.     

Messung der Kernradiusdifferenzen von46Ti,48Ti und50Ti durch elastische Elektronenstreuung

Ratios of differential cross sections for elastic electron scattering from⁴⁶Ti,⁴⁸Ti and⁵⁰Ti have been measured at 29 MeV and 58 MeV. A partial wave analysis, carried out for static Fermi-type nuclear charge distributions, yields differences of the r.m.s. radiiR _m ofR _m ⁴⁸ ?R _m ⁴⁶ =(?0,00₅±0,02₇) fm andR _m ⁵⁰ ?R _m ⁴⁶ =(0,00₃±0,02₁) fm, if the skin thickness parameterz of the charge density is assumed to be constant. If allowance is made for a change inz ofΔz/z=±5% and ±10%, then the errors increase by ±0,01₃ fm and ±0,02₈ fm, respectively. This indicates a relatively small change in nuclear r.m.s. radii below the magic neutron number N=28.     

Successes and failures with hard probes

The two major pillars of searches for the Quark Gluon Plasma have been: J/Ψ suppression, proposed in 1986, and observed at both SPS fixed target energies and at RHIC; and, more recently, the suppression of π ⁰ with p _T ≥3 GeV/c by a factor ～5 in Au+Au central collisions, observed at RHIC in 2001, which had been predicted in advance as a consequence of Landau-Pomeranchuck-Migdal coherent (gluon) bremsstrahlung by the outgoing hard-scattered partons traversing the medium. However, new effects were discovered and the quality of the measurements greatly improved so that the clarity of the original explanations has become obscured. For instance: J/Ψ suppression is the same at SpS and RHIC. Is it the QGP, comovers, something else? QCD provides beautiful explanations of π ⁰ and direct γ measurements in p–p collisions but precision fits of the best theories of π ⁰ suppression barely agree with the Au+Au data. Better data are needed for 10<p _T <20 GeV/c, systematic errors are needed in theory calculations, the values of parameters of the medium such as \(\langle\hat{q}\rangle\) derived from precision fits are the subject of controversy. Baryons are much less suppressed than mesons, leading to an anomalous \(\bar{p}/\pi\) ratio for 2≤p _T ≤4.5 GeV/c, but beautiful theoretical explanations of the effect such as recombination do not work in detail. Heavy quarks seem to be suppressed the same as the light quarks, naively arguing against the bremsstrahlung explanation and suggesting exotic, possible transformational explanations. Di-hadron correlations reveal a trigger side ridge, possible Mach cones on the away side, vanishing and reappearance of away jets, both wide and normal jet correlations with and without apparent loss of energy. Can this all be explained consistently? Preliminary results of direct γ production in Au+Au appear to indicate a suppression approaching that of π ⁰ for p _T ≈20 GeV/c and a possibly thermal component for 1≤p _T ≤ 3 GeV/c. What are the implications? Are fragmentation photons a problem? Regeneration of direct γ by outgoing partons is predicted, leading to negative v ₂—is there evidence for or against it? STAR and PHENIX have different observations relevant to the existence of monojets in d+Au collisions. Will new data clarify the situation? When? etc. These and other issues will be discussed with a view to identify which conclusions are firm and where further progress towards real understanding is required.     

Kinetic freeze-out s pectra of identified particles produced in p–Pb collisions at $$\sqrt {s_{NN} }$$ = 5.02 TeV

We study the transverse momentum spectra of identified pions (π^– + π⁺), kaons ((K ^– + K ⁺), K ₀ ^s ), protons (p + p?) and lambda hyperons (Λ + Λ?) produced at mid-rapidity (0 < y _cm < 0.5) in most central (0?5)% p–Pb collisions at \(\sqrt {s_{NN} }\) = 5.02 TeV in comparison with a Unified Statistical Thermal Freeze-out Model (USTFM). The measurements for pions are reported upto p _T = 3 GeV, the kaons (K ^– + K ⁺) are reported upto p _T = 2.5 GeV, K ₀ ^s is reported upto p _T = 7 GeV, and the baryons (protons and lambda hyperons) are reported upto p _T = 3.5 GeV. A good agreement is seen between the calculated results and the experimental data points taken from the ALICE experiment. The transverse momentum spectra are found to be flatter for heavy particles than for light particles. Bulk freeze-out properties in terms of kinetic freeze-out temperature and the transverse collective flow velocity are extracted from the fits of the transverse momentum spectra of these hadrons. The effect of resonance decay contributions has also been taken care of.     

The decoupling problem at RHIC

We investigate whether it is possible to dynamically generate from classical transport theory the observed surprising R_out ≈ R_side in Au+Au at \(\sqrt s = 130A\) GeV at RHIC [1,2]. We obtained covariant solutions to the Boltzmann transport equation via the MPC technique [3], for a wide range of partonic initial conditions and opacities. We demonstrate that there exist transport solutions that yield a freezeout distribution with R _out < R _side for K _⊥ ? 1.5 GeV. These solutions correspond to continuous evaporation-like freezeout, where the emission duration is comparable to the source size. Naively this would mean R _out > R _side. Nevertheless, our sources exhibit R _out < R _side because they are narrower in the‘out’ than in the‘side’ direction and, in addition, a positive x _out-t correlation develops reducing R _out further.     

Inclusive neutral-pion production in <Emphasis Type="Italic">d</Emphasis>C and <Emphasis Type="Italic">d</Emphasis>Cu interactions at a momentum of 4.5 GeV/. per nucleon

The cross sections for inclusive neutral-pion production in the reactions d + C → π⁰ + x and d + Cu → π⁰ + x at a momentum of 4.5 GeV/c per nucleon were measured over the kinematical region specified by the inequalities Θ_π≤16° and E_π≥2 GeV (in the laboratory frame). From the ratio of the cross sections for neutral-pion generation on carbon and copper nuclei, the exponent n in the parametrization Ed³σ/d³p ～ A _T ⁿ is obtained as a function of the cumulative number X in the range 0.6 ≤ X ≤ 1.8 and as a function of the square of the transverse momentum in the range 0.04 ≤ P _t ² ≤ 0.40 (GeV/c)². The probabilities of the formation of six-quark configurations in the D, ⁴He, and ¹²C nuclei are estimated. The double-differential cross section for the reaction d + C → π⁰ + x is determined for the first time by using a data sample containing more than 40 000 neutral pions.     

Quark see-saw,Higgs mass and vacuum stability

The issue of vacuum stability of standard model (SM) is discussed by embedding it within the TeV scale left–right quark see-saw model. The Higgs potential in this case has only two coupling parameters (λ₁, λ₂) and two mass parameters. There are only two physical neutral Higgs bosons (h,H), the lighter one being identified with the 126 GeV Higgs boson. We explore the range of values for (λ₁, λ₂) for which the vacuum is stable for all values of the Higgs fields till 10¹⁶ GeV. Combining with the further requirement that the scalar self-couplings remain perturbative till 10¹⁶ GeV, we find (i) an upper and lower limit on the second Higgs (H) mass to be within the range: 0.4 ≤ (M_H/v_R) ≤ 0.7, where v_R is the parity breaking scale and (ii) the masses of heavy vector-like top, bottom and τ partner fermions (P₃, N₃,E₃) have an upper bound ≤ v_R. These predictions can be tested at LHC and future higher energy colliders.     

Role of the Δ-isobar excitation mechanism in the reaction pp → {pp}<Subscript><Emphasis Type="Italic">s</Emphasis></Subscript>π<Superscript>0</Superscript>

The mechanism of Δ-isobar excitation in the intermediate state of the reaction pp → {pp}_sπ⁰, where {pp}_s is a pair of protons in state ¹S₀ at excitation energy E _pp < 3 MeV, is used to calculate the differential cross section of this reaction in the energy range of 0.3–1 GeV. It is shown that the main contribution is made by three partial waves in the pp channel: ³ P ₀, ³ P ₂ and ³ F ₂. The model explains the position of the peak observed at a beam energy of GeV and a zero diproton scattering angle, but cannot describe its absolute value.     

Surface Microparticles in Liquid Helium. Quantum Archimedes’ Principle

Deviations from Archimedes’ principle for spherical molecular hydrogen particles with the radius R₀ at the surface of ⁴He liquid helium have been investigated. The classical Archimedes’ principle holds if R₀ is larger than the helium capillary length L_cap ? 500 μm. In this case, the elevation of a particle above the liquid is h₊ ~ R₀. At 30 μm < R₀ < 500 μm, the buoyancy is suppressed by the surface tension and h₊ ~ R³₀/L²_cap. At R₀ < 30 μm, the particle is situated beneath the surface of the liquid. In this case, the buoyancy competes with the Casimir force, which repels the particle from the surface deep into the liquid. The distance of the particle to the surface is h_- ~ R^5/3_c/R^2/3₀ if R₀ > R_c. Here, \({R_c} \cong {\left( {\frac{{\hbar c}}{{\rho g}}} \right)^{1/5}} \approx 1\), where ? is Planck’s constant, c is the speed of light, g is the acceleration due to gravity, and ρ is the mass density of helium. For very small particles (R₀ < R_c), the distance h_ to the surface of the liquid is independent of their size, h_ = R_c.     

Investigation of <Emphasis Type="Italic">pn</Emphasis> correlations in <Superscript>4</Superscript>He<Emphasis Type="Italic">p</Emphasis> interactions at a momentum of 5 GeV/<Emphasis Type="Italic">c</Emphasis>

Proton-neutron correlations in ⁴Hep interactions are studied in an exclusive experiment by using a 2-m bubble chamber exposed to a 5-GeV/c beam of α particles (the kinetic energy of the protons in the nucleus rest frame is T _p = 620 MeV). Data on the production of pn pairs in 4π geometry for three channels, where it is possible to reconstruct the neutron momentum unambiguously, are used to determine the pn correlation function in ⁴Hep interactions. The experimental results are compared with the predictions of a modified Lednicky-Lyuboshitz model. The value obtained for the root-mean-square radius of the pn-emission region is R _pn = 2.1 ± 0.3 fm. The dependence of the correlation function on the modulus of the total momentum of the emitted nucleon pair and on the direction of the momentum transfer is studied. An indication that the emission of a pn pair proceeds predominantly through the production of a virtual deuteron is obtained.     

Messungen an 19,8 GeV-Protonen und ihren Wechselwirkungen in Emulsionen

In Ilford K 5-emulsions 190 nuclear interactions produced by 19.8 GeV protons have been analysed systematically. The mean interactionlength was found to be 34.7±2.5 cm, the mean number of shower particles isn _s=4.5±0.2, the mean number of heavy particlesN _h=9.0±0.6. The integral momentum spectrum between the emission angles of 31° and 55° in the centre of mass system shows a steep descent beyond 0.3 GeV/c with an exponent of ?1.5±0.3, the mean momentum isP ^*=0.60±0.05 GeV/c and the mean inelasticity was found to beK=0.37±0.06. Scattering measurements could be done successfully up to an energy of 20 GeV. The scattering constant was found to beK(t)=20.4t ^0.055 (t in μ). Moreover there was found in treating errors that only the nonoverlapping cells are statistically independent, i.e. the standard deviation must be calculated only with half of the number of second differences.     

Properties of proton clusters in inelastic CC interactions accompanied by the production of Λ and <Emphasis Type="Italic">K</Emphasis><Superscript>0</Superscript> particles at <Emphasis Type="Italic">p</Emphasis> = 4.2 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

Within a new relativistically invariant approach, the properties of proton clusters that are formed together with Λ and K⁰ particles in inelastic CC interactions at p=4.2 GeV/c per nucleon are investigated in the space of relative 4-velocities. The observed proton clusters are shown to be characterized by high values of the mean kinetic energy of the protons in the cluster rest frame: 〈T _p 〉=100±2 MeV.     

Production of light vector mesons in heavy-ion nuclear collisions at RHIC,measured by the PHENIX spectrometer

The production cross sections of ω and ? mesons in p + p, d + Au, and Au + Au collisions at energies √S _NN = 63 and 200 GeV have been measured in the PHENIX experiment at RHIC. The results of the measurements in different hadronic and dielectron decay channels are in agreement within the measurement error. The nuclear modification factors R _AA measured for both mesons are consistent with the results previously obtained for light neutral mesons. The position and width of the meson mass peaks reconstructed in hadronic decay channels are in agreement with the results of measurements in vacuum.     

Determination of low-energy parameters of neutron-proton scattering on the basis of modern experimental data from partial-wave analyses

The triplet and singlet low-energy parameters in the effective-range expansion for neutron-proton scattering are determined by using the latest experimental data on respective phase shifts from the SAID nucleon-nucleon database. The results differ markedly from the analogous parameters obtained on the basis of the phase shifts of the Nijmegen group and contradict the parameter values that are presently used as experimental ones. The values found with the aid of the phase shifts from the SAID nucleon-nucleon database for the total cross section for the scattering of zero-energy neutrons by protons, σ ₀ = 20.426 b, and the neutron-proton coherent scattering length, f = ?3.755 fm, agree perfectly with experimental cross-section values obtained by Houk, σ ₀ = 20.436 ± 0.023 b, and experimental scattering-length values obtained by Houk and Wilson, f = ?3.756 ± 0.009 fm, but they contradict cross-section values of σ ₀ = 20.491 ± 0.014 b according to Dilg and coherent-scattering-length values of f = ?3.7409 ± 0.0011 fm according to Koester and Nistler.