Synthesis and characterization of hybrid nanostructures

There has been significant interest in the development of multicomponent nanocrystals formed by the assembly of two or more different materials with control over size, shape, composition, and spatial orientation. In particular, the selective growth of metals on the tips of semiconductor nanorods and wires can act to couple the electrical and optical properties of semiconductors with the unique properties of various metals. Here, we outline our progress on the solution-phase synthesis of metal-semiconductor heterojunctions formed by the growth of Au, Pt, or other binary catalytic metal systems on metal (Cd, Pb, Cu)-chalcogenide nanostructures. We show the ability to grow the metal on various shapes (spherical, rods, hexagonal prisms, and wires). Furthermore, manipulating the composition of the metal nanoparticles is also shown, where PtNi and PtCo alloys are our main focus. The magnetic and electrical properties of the developed hybrid nanostructures are shown

Calibration of ATLAS Tile Calorimeter at Electromagnetic Scale

In this paper we summarize the measurement of the electromagnetic (EM) scale calibration constant for 11% of the Tile Calorimeter modules exposed to electron and muon test beams at CERN SPS accelerator. The Tile Calorimeter modules are currently installed in the ATLAS detector. The analysis presented in this paper takes into account the recent improvements in the Tile Calorimeter cesium calibration, charge injection system calibration and Fit Method energy reconstruction. The overall conversion factor between the measured charge and the energy deposited by measured particles for Tile Calorimeter cells is $1.050pm0.003$~pC/GeV, with spread of $2.4pm0.1$%. We discuss in detail the sources of uncertainties of EM scale calibration constant. We also show, that after inter-calibrating all the Tile Calorimeter cells with a~radioactive cesium source and setting the EM scale in the first calorimeter sampling with electron beams, the values of signals measured in the second and third calorimeter sampling need to be increased by 1--9% to keep the EM scale uniform in the whole calorimeter

Study of jet shapes in inclusive jet production in pppp collisions at =7\sqrt{}=7 TeVTeV using the ATLAS detector

Jet shapes have been measured in inclusive jet production in proton-proton collisions at $\sqrt{}=7$  $TeV$ using $3  pb^{−1}$ of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-$k_t$ algorithm with transverse momentum $30  GeV<<600  GeV$ and rapidity in the region $|y|<2.8$. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the jet shapes present a moderate jet rapidity dependence. Within QCD, the data test a variety of perturbative and nonperturbative effects. In particular, the data show sensitivity to the details of the parton shower, fragmentation, and underlying event models in the Monte Carlo generators. For an appropriate choice of the parameters used in these models, the data are well described

Measurement of underlying event characteristics using charged particles in pppp collisions at s=900\sqrt{s}=900 GeVGeV and 7 TeV with the ATLAS detector

Measurements of charged particle distributions, sensitive to the underlying event, have been performed with the ATLAS detector at the LHC. The measurements are based on data collected using a minimum-bias trigger to select proton-proton collisions at center-of-mass energies of 900 GeV and 7 TeV. The “underlying event” is defined as those aspects of a hadronic interaction attributed not to the hard scattering process, but rather to the accompanying interactions of the rest of the proton. Three regions are defined in azimuthal angle with respect to the highest transverse momentum charged particle in the event, such that the region transverse to the dominant momentum-flow is most sensitive to the underlying event. In each of these regions, distributions of the charged particle multiplicity, transverse momentum density, and average are measured. The data show generally higher underlying event activity than that predicted by Monte Carlo models tuned to pre-LHC data

Measurement of the inclusive isolated prompt photon cross section in pppp collisions at s=7\sqrt{s}=7 TeVTeV with the ATLAS detector

A measurement of the cross section for the inclusive production of isolated prompt photons in $pp$ collisions at a center-of-mass energy $\sqrt{s}=7$ $TeV$ is presented. The measurement covers the pseudorapidity ranges $|^|<1.37$ and $1.52≤|^|<1.81$ in the transverse energy range 15≤^_T<100  $GeV$. The results are based on an integrated luminosity of $880  nb^{−1}$, collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner tracker. Residual background in the selected sample is estimated from data based on the observed distribution of the transverse isolation energy in a narrow cone around the photon candidate. The results are compared to predictions from next-to-leading-order perturbative QCD calculations

Search for pair production of first or second generation leptoquarks in proton-proton collisions at s=7\sqrt{s}=7 TeV using the ATLAS detector at the LHC

This paper describes searches for the pair production of first or second generation scalar leptoquarks using $35  pb^{−1}$ of proton-proton collision data recorded by the ATLAS detector at $\sqrt{s}=7$  TeV. Leptoquarks are searched in events with two oppositely-charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses $M_{LQ}<376 (319)$ GeV and $M_{LQ}<422 (362)$ GeV for first and second generation scalar leptoquarks, respectively, when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5)

Measurement of the b0^0_b lifetime and mass in the ATLAS experiment

A measurement of the $^0_b$ lifetime and mass in the decay channel $^0_→/⁡(^+⁢^−)⁢^0⁡(⁢^−)$ is presented. The analysis uses a signal sample of about 2200 ^0_ and \overline{}^0_ decays that are reconstructed in $4.9  fb^{−1} of ATLAS$ $⁢$ collision data collected in 2011 at the LHC center-of-mass energy of 7 TeV. A simultaneous mass and decay time maximum likelihood fit is used to extract the ^0_ lifetime and mass. They are measured to be $_{}=1.449±0.036⁢(stat)±0.017⁢(syst)  ps$ and $_{}=5619.7±0.7⁢(stat)±1.1⁢(syst)  MeV$

Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics

A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN

Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table, submitted to European Physical Journal

Measurement of the flavour composition of dijet events in pp collisions at root s=7 TeV with the ATLAS detector

This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at &#8730;s=7 TeV using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb−1. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity |y|&#60;2.1. The fit results agree with the predictions of leading- and next-to-leading-order calculations, with the exception of the dijet fraction composed of bottom and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originating from e.g. gluon splitting, is demonstrated. The difference between bottom jet production rates in leading and subleading jets is consistent with the next-to-leading-order predictions