Vertex Reconstruction Using a Single Layer Silicon Detector

Typical vertex finding algorithms use reconstructed tracks, registered in a multi-layer detector, which directly point to the common point of origin. A detector with a single layer of silicon sensors registers the passage of primary particles only in one place. Nevertheless, the information available from these hits can also be used to estimate the vertex position, when the geometrical properties of silicon sensors and the measured ionization energy losses of the particles are fully exploited. In this paper the algorithm used for this purpose in the PHOBOS experiment is described. The vertex reconstruction performance is studied using simulations and compared with results obtained from real data. The very large acceptance of a single-layered multiplicity detector permits vertex reconstruction for low multiplicity events where other methods, using small acceptance subdetectors, fail because of insufficient number of registered primary tracks.Comment: accepted for publication in Nucl. Instr. Meth.

The Casimir force in noncommutative Randall-Sundrum models

In this paper we study the effect of spacetime noncommutativity in the 5-dimensional Randall-Sundrum brane worlds on the Casimir force acting on a pair of parallel plates. We show that the presence of a noncommutative scale length affects the nature of the Casimir force for small plate separation. Using accurate experimental bounds for the Casimir force in parallel plate geometry, we find an upper bound for the noncommutative cutoff of the order of $10^{3}$ TeV, and that the size of the interbrane distance in RSI model is approximately given by $kR\lesssim20.5$ and $kR\lesssim18.4$ for $k=10^{19}$ GeV and $k=10^{16}$GeV, respectively.Comment: 20 pages, 5 figures, accepted for publication in Phys. Rev.

Entropy of the Randall-Sundrum black brane world to all orders in the Planck length

We study the effects, to all orders in the Planck length from a generalized uncertainty principle (GUP), on the statistical entropy of massive scalar bulk fields in the Randall-Sundrum black brane world. We show that the Bekenstein-Hawking area law is not preserved, and contains small corrections terms proportional to the black hole inverse area.Comment: 19 pages, 1 figure. (v2): section 4 improve

Lorentz-covariant deformed algebra with minimal length

The $D$-dimensional two-parameter deformed algebra with minimal length introduced by Kempf is generalized to a Lorentz-covariant algebra describing a ($D+1$)-dimensional quantized space-time. For D=3, it includes Snyder algebra as a special case. The deformed Poincar\'e transformations leaving the algebra invariant are identified. Uncertainty relations are studied. In the case of D=1 and one nonvanishing parameter, the bound-state energy spectrum and wavefunctions of the Dirac oscillator are exactly obtained.Comment: 8 pages, no figure, presented at XV International Colloquium on Integrable Systems and Quantum Symmetries (ISQS-15), Prague, June 15-17, 200

Status and Performance of New Silicon Stripixel Detector for the PHENIX Experiment at RHIC: Beta Source, Cosmic-rays and Proton Beam at 120 GeV

We are constructing a Silicon Vertex Tracker detector (VTX) for the PHENIX experiment at RHIC. Our main motivation is to enable measurements of heavy flavor production (charm and beauty) in p+p, p+d and A+A collisions. Such data will illuminate the properties of the matter created in high-energy heavy-ion collisions. The measurements also will reveal the distribution of gluons in protons from p+p collisions. The VTX detector consists of four layers of barrel detectors and covers |eta|< 1.2, and almost a 2pi in azimuth. The inner two silicon barrels consist of silicon pixel sensors; their technology accords with that of the ALICE1LHCB sensor-readout hybrid. The outer two barrels are silicon stripixel detectors with a new "spiral" design, and a single-sided sensor with 2-dimensional (X, U) readout. In this paper, we describe the silicon stripixel detector and discuss its performance, including its response to electrons from a beta source (90Sr), muons from cosmic-rays, and a 120 GeV proton beam. The results from the proton beam demonstrate that the principle of two-dimensional position sensitivity based on charge sharing works; the signal-to-noise value is 10.4, the position resolution is 33.6 um for X-stripixel (35.2 um for U-stripixel), and the tracking efficiencies in the X- and U-stripixels are, over 98.9 +/- 0.2%. The stripixel detector within the VTX project is in the pre-production phase.Comment: Accepted for publication in Journal of Instrumentation (JINST). Invited talk at Pixel 2008 International Workshop, September 23-26, 2008, Fermilab, Batavia, Illinois, U.S.

8Be cluster emission versus alpha evaporation in 28Si + 12C

The possible occurence of highly deformed configurations in the $^{40}$Ca di-nuclear system formed in the $^{28}$Si + $^{12}$C reaction is investigated by analyzing the spectra of emitted light charged particles. Both inclusive and exclusive measurements of the heavy fragments (A $\geq$ 10) and their associated light charged particles (protons and $\alpha$ particles) have been made at the IReS Strasbourg {\sc VIVITRON} Tandem facility at bombarding energies of $E_{lab}$ ($^{28}$Si) = 112 MeV and 180 MeV by using the {\sc ICARE} charged particle multidetector array. The energy spectra, velocity distributions, in-plane and out-of-plane angular correlations of light charged particles are compared to statistical-model calculations using a consistent set of parameters with spin-dependent level densities. This spin dependence approach suggests the onset of large nuclear deformation in $^{40}$Ca at high spin. This conclusion might be connected with the recent observation of superdeformed bands in the $^{40}$Ca nucleus. The analysis of $\alpha$ particles in coincidence with $^{32}$S fragments suggests a surprisingly strong $^{8}$Be cluster emission of a binary nature.Comment: 39 pages 15 figure

Status and overview of development of the Silicon Pixel Detector for the PHENIX experiment at the BNL RHIC

We have developed a silicon pixel detector to enhance the physics capabilities of the PHENIX experiment. This detector, consisting of two layers of sensors, will be installed around the beam pipe at the collision point and covers a pseudo-rapidity of | \eta | < 1.2 and an azimuth angle of | \phi | ~ 2{\pi}. The detector uses 200 um thick silicon sensors and readout chips developed for the ALICE experiment. In order to meet the PHENIX DAQ readout requirements, it is necessary to read out 4 readout chips in parallel. The physics goals of PHENIX require that radiation thickness of the detector be minimized. To meet these criteria, the detector has been designed and developed. In this paper, we report the current status of the development, especially the development of the low-mass readout bus and the front-end readout electronics.Comment: 9 pages, 8 figures and 1 table in DOCX (Word 2007); PIXEL 2008 workshop proceedings, will be published in the Proceedings Section of JINST(Journal of Instrumentation

Fission and cluster decay of 76^{76}Sr nucleus in the ground-state and formed in heavy-ion reactions

Calculations for fission and cluster decay of $^{76}Sr$ are presented for this nucleus to be in its ground-state or formed as an excited compound system in heavy-ion reactions. The predicted mass distribution, for the dynamical collective mass transfer process assumed for fission of $^{76}Sr$, is clearly asymmetric, favouring $\alpha$-nuclei. Cluster decay is studied within a preformed cluster model, both for ground-state to ground-state decays and from excited compound system to the ground-state(s) or excited states(s) of the fragments.Comment: 14 pages LaTeX, 5 Figures available upon request Submitted to Phys. Rev.

Minimal Length and the Quantum Bouncer: A Nonperturbative Study

We present the energy eigenvalues of a quantum bouncer in the framework of the Generalized (Gravitational) Uncertainty Principle (GUP) via quantum mechanical and semiclassical schemes. In this paper, we use two equivalent nonperturbative representations of a deformed commutation relation in the form [X,P]=i\hbar(1+\beta P^2) where \beta is the GUP parameter. The new representation is formally self-adjoint and preserves the ordinary nature of the position operator. We show that both representations result in the same modified semiclassical energy spectrum and agrees well with the quantum mechanical description.Comment: 14 pages, 2 figures, to appear in Int. J. Theor. Phy