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 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

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

Search for supersymmetry in final states with jets, missing transverse momentum and one isolated lepton in s=7 TeV\sqrt{s}=7 TeV pp collisions using 1 fb−11 fb^{−1} of ATLAS data

We present an update of a search for supersymmetry in final states containing jets, missing transverse momentum, and one isolated electron or muon, using $1.04  fb^{−1}$ of proton-proton collision data at $\sqrt{s}=7  TeV$ recorded by the ATLAS experiment at the LHC in the first half of 2011. The analysis is carried out in four distinct signal regions with either three or four jets and variations on the (missing) transverse momentum cuts, resulting in optimized limits for various supersymmetry models. No excess above the standard model background expectation is observed. Limits are set on the visible cross section of new physics within the kinematic requirements of the search. The results are interpreted as limits on the parameters of the minimal supergravity framework, limits on cross sections of simplified models with specific squark and gluino decay modes, and limits on parameters of a model with bilinear -parity violation

Measurement of the isolated diphoton cross section in pppp collisions at s=7 TeV\sqrt{s}=7 TeV with the ATLAS detector

The ATLAS experiment has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at $\sqrt{s}=7  TeV$. The full data set acquired in 2010 is used, corresponding to an integrated luminosity of 37  $pb^{−1}$. The background, consisting of hadronic jets and isolated electrons, is estimated with fully data-driven techniques and subtracted. The differential cross sections, as functions of the di-photon mass ($m_{⁢}$), total transverse momentum ($p_{T,⁢}$), and azimuthal separation ($⁢_{⁢}$), are presented and compared to the predictions of next-to-leading-order QCD

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 $_{}=5619.7±0.7⁢(stat)±1.1⁢(syst)  MeV$

Measurement of the inclusive ±^± and /∗/^* cross sections in the and and decay channels in ⁢⁢ collisions at s=7 TeV\sqrt{s}=7 TeV with the ATLAS detector

The production cross sections of the inclusive Drell-Yan processes $^±→ℓ⁢$ and $/^*→ℓ⁢ℓ (ℓ=, )$ are measured in proton-proton collisions at $\sqrt{s}=7  TeV$ with the ATLAS detector. The cross sections are reported integrated over a fiducial kinematic range, extrapolated to the full range, and also evaluated differentially as a function of the $$decay lepton pseudorapidity and the$$ boson rapidity, respectively. Based on an integrated luminosity of about $35  pb^{−1}$ collected in 2010, the precision of these measurements reaches a few percent. The integrated and the differential $^±$ and $/^*$ cross sections in the and channels are combined, and compared with perturbative QCD calculations, based on a number of different parton distribution sets available at next-to-next-to-leading order