Prior to "Quark Matter 2006" predictions within retarded jet absorption scenario at RHIC

Predictions for some experimental physical observables in nucleus-nucleus collisions at RHIC energies are presented. I utilize the previous suggestion that the retarded, by time about 2-3 fm/c, jet absorption in opaque core is a natural explanation of many experimental data. This assumption is applied only to the particles with high transverse momentum above 4 GeV/c resulting from parton fragmentation. I calculate nuclear modification factor $R_{AA}$, $R_{AA}$ in- and out of the reaction plane, azimuthal anisotropy parameter $v_2$, jet suppression $I_{AA}$ for the away side jet and its dependence versus the reaction plane orientation. The systems under consideration are Au+Au, Cu+Cu, at 200 GeV and 62 GeV. Most of numbers are predictions prior to the QM2006.Comment: 10 pages, including 3 figures and 4 tables, Iaa values update

Evidence of finite sQGP formation time at RHIC

We demonstrate that the existence of a finite formation time of strongly interacting plasma in nuclear collisions at RHIC is an inavitable conclusion from recent experimental data. The most striking feature of the experimental data - an absense of absorption of high transverse momentum pions in the rection plane direction for mid-peripheral collisions - points to the presence of a surface zone with no absorption and strong suppression in the inner core. A natural interpretation of such a zone should be the plasma formation time T= 2-3 fm/c. We discuss constraints induced by finite formation time on some physical observables at RHIC. Nuclear modification factor, azimuthal assymetry, di-jet correlations can quantitatively be described by particle production in the early stage of the nuclear collision. A possible impact on azimuthal anisotropy at lower hardon momenta, on interpretation of the non-photonic electrons and J/psi data is also considered.Comment: 8 pages including 5 figures. Proceedings of the 22nd Winter Workshop on Nuclear Dynamics, La Jolla, California, March 11-18, 200

"Jet-Ridge" effect in heavy ion collisions as a back splash from stopped parton

I propose a simple explanation of the ``ridge'' seen in the near-side jet two-particle correlation function in heavy ion collisions at RHIC. This could be a cumulative shock wave produced in liquid-like matter by an energetic stopped parton. Splash of liquid in the direction opposite to the fast penetrating object is a known effect. In nucleus-nucleus collision the trigger is an escaped non-interacting parton. Partner parton could be stopped in the medium forming a conical-like shock wave with density depletion behind the stopped parton. In the proposed scenario shock waves will move in three directions: two waves will form a correlation structure at angles differ from phi = 3.14 radians and are usually called a Mach Cone. The other direction is exactly opposite to the original direction of stopping parton. The wide rapidity distribution of the ridge is caused by the rapidity swing of the away-side jet and longitudinal expansion of the system along the beam direction. The calculation of such a shock wave is very complicated, but some phenomenological observables could be explained and predicted.Comment: 4 pages, 4 figure

Corona effect in AA collisions at 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 LHC energy. Our hypothesis was based on experimental data, which raised the idea of a finite formation time for the produced medium. At RHIC energy and in low density corona region this time reaches about 2 fm/c. All observed high p_t particles are produced in the corona region and have a chance to escape during this 2 fm/c. After that, the formed high density matter absorbs all jets. Following this hypothesis, the nuclear modification factor R_{AA} should be independent on particle momentum and be flat versus p_t. At the same time, we describe the finite azimuthal anisotropy of high p_t particles, v_2. A separate prediction held that, at LHC energy, the formation time in the corona region should be two times smaller, about 1 fm/c. New data at LHC 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 (I would call it as a parton binding energy) 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 RHIC energy, where the cross section follows a power law with about p^{-8} and this shift explains a very slow rise of R_{AA} seen for neutral pions with p_t above 15 GeV/c. We also show that the observed at LHC dependence of v_2 at high p_t and our previous predictions agree.Comment: Published version, 4 pages, 5 figures. Only on-line abstract changed by adding notation "parton binding energy

Identified particle production at high transverse momentum in nucleus-nucleus collisions at RHIC

Experimental results for identified hadron spectra in AA collisions at RHIC are reviewed. Jet suppression in central AuAu collisions at 200 GeV is seen in leading meson and baryon spectra at high p_t. Enhanced baryon production at intermediate p_T (2<p_t<5 GeV/c) is related to quark content but not its mass.In d+Au collisions Cronin enhancement is observed with larger magnitude for baryons than for mesons, but this difference can not explain the baryon-to-meson ratio in Au+Au collisions. In Au+Au the observations at 62.4 GeV and 200 GeV are very similar, but smaller suppresion of the leading particles is seen at low beam energy, which is evidence for a smooth beam energy dependence of the effect. Near and away side jets seen in two-particle correlations are very similar for the leading baryons and mesons.Comment: 4 pages, 7 figures, talk given at the XXXXth Recontres de Moriond on QCD and high energy hadronic interactions, La Thuile, Italy, 12-19 Mar 200

Constraints induced by finite plasma formation time on some physical observables at RHIC

We discuss consequences of finite plasma formation time at RHIC. Nuclear modification factor, azimuthal assymetry, di-jet correlations can quantitatively be described by particle production in the early stage of the nuclear collision. A possible impact on interpretation of the non-photonic electrons and J/psi data is also considered.Comment: 15 pages, 8 figure

Empirical estimation the effects of flow on thermal photon angular distribution and spectra in nucleus-nucleus collisions at RHIC and LHC

Experimental data for hadron radial and elliptic flow are used to investigate their influence on the shape of the thermal photon spectrum at RHIC. Leaving alone the actual mechanism of photon production and its time evolution, we concentrate on the spectrum shape. Radial and longitudinal flow of the bulk can change significantly the observed photon energy spectrum via the Doppler Effect. Experimental thermal photon data are described by local frame temperature parameter which depends on the assumption of longitudinal and radial flow. From the observed hadron elliptic flow we estimate the modulation of radial flow parameter versus the angle relative to the reaction plane. Based on this we calculate elliptic flow parameter for thermal photons, which was found to be very close to that for hadrons. Considering very similar amplitude for hadron elliptic flow at LHC and RHIC, we demonstrate that thermal photons at LHC should show large elliptic flow as well. All of these considerations are also valid for the low invariant mass dilepton pairs.Comment: 4 pages, 2 figures. This work was finished in 2009, but get skeptical reactions. Now, in the scope of new PHENIX results, it should be poste

Prior to "Quark Matter 2006" predictions within retarded jet absorption scenario at RHIC

Predictions for some experimental physical observables in nucleus-nucleus collisions at RHIC energies are presented. I utilize the previous suggestion that the retarded, by time about 2-3 fm/c, jet absorption in opaque core is a natural explanation of many experimental data. This assumption is applied only to the particles with high transverse momentum above 4 GeV/c resulting from parton fragmentation. I calculate nuclear modification factor $R_{AA}$, $R_{AA}$ in- and out of the reaction plane, azimuthal anisotropy parameter $v_2$, jet suppression $I_{AA}$ for the away side jet and its dependence versus the reaction plane orientation. The systems under consideration are Au+Au, Cu+Cu, at 200 GeV and 62 GeV. Most of numbers are predictions prior to the QM2006

The role of electron scattering from registration detector in a MAC-E type spectrometer

There is a proposal to search for a sterile neutrino in a few keV mass range by the "Troitsk nu-mass" facility. In order to estimate sterile neutrino mixing one needs to make precision spectrum measurements well below the endpoint using the existing electrostatic spectrometer with a magnetic adiabatic collimation, or MAC-E filter. The expected signature will be a kink in the electron energy spectrum in tritium beta-decay. In this article we consider the systematic effect of electron backscattering on the detector used in the spectrometer. For this purpose we provide a set of Monte-Carlo simulation results of electron backscattering on a silicon detector with a thin golden window with realistic electric and magnetic fields in the spectrometer. We have found that the probability of such an effect reaches up to 20-30\%. The scattered electron could be reflected backwards to the detector by electrostatic field or by magnetic mirror. There is also a few percent probability to escape from the spectrometer through its entrance. A time delay between the scattering moment on the detector and the return of the reflected electron can reach a couple of microseconds in the Troitsk spectrometer. Such estimations are critical for the planning upgrades of the detector and the registration electronics.Comment: 14 pages, 14 figure

Analysis of published data of electron capture in 7Be in the search for a heavy neutrino in the mass range under 800 keV

We present a reanalysis of the experimental data of electron capture in $^7$Be embedded in Ta which have been published by other authors. Our goal is to set upper limits on a mixture of electron neutrino with a possible right-handed heavy neutrino in the 150--800 keV mass range. In the published experiment a $^7$Li recoil energy spectrum in the 20--200 eV range was measured. In case of electron capture with emission of a heavy neutrino, the recoil spectrum should be shifted to the lower energies. We search for an additional Gauss-shaped structure with the same energy width as the main K-shell transition peak. For this we digitize the published spectrum curve, find the energy resolution, calculate the moving sum of the events along the spectrum in the energy interval of about 3 sigma of energy resolution. Then we use the statistical error of this sum to exclude at some level the appearance of an additional peak. Finally, we present the upper limits at a 95\% confidence level on electron neutrino -- heavy neutrino mixing element, $U^2$, in the mass matrix. New upper limits are at least one order of magnitude lower than the existing data in 300--800 keV mass range.Comment: 4 pages, 2 figure