| 1. |
|
|
| 2. |
- Abelev, Betty, et al.
(författare)
-
Long-range angular correlations on the near and away side in p-Pb collisions at root S-NN=5.02 TeV
- 2013
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 719:1-3, s. 29-41
-
Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 < P-T,P-assoc < P-T,P-trig < 4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and p(T) bins, and the widths show no significant evolution with event multiplicity or p(T). These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
|
|
| 3. |
- Abelev, Betty, et al.
(författare)
-
Measurement of prompt J/psi and beauty hadron production cross sections at mid-rapidity in pp collisions at root s=7 TeV
- 2012
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; :11
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE experiment at the LHC has studied J/psi production at mid-rapidity in pp collisions at root s = 7 TeV through its electron pair decay on a data sample corresponding to an integrated luminosity L-int = 5.6 nb(-1). The fraction of J/psi from the decay of long-lived beauty hadrons was determined for J/psi candidates with transverse momentum p(t) > 1,3 GeV/c and rapidity vertical bar y vertical bar < 0.9. The cross section for prompt J/psi mesons, i.e. directly produced J/psi and prompt decays of heavier charmonium states such as the psi(2S) and chi(c) resonances, is sigma(prompt J/psi) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 8.3 +/- 0.8(stat.) +/- 1.1 (syst.)(-1.4)(+1.5) (syst. pol.) mu b. The cross section for the production of b-hadrons decaying to J/psi with p(t) > 1.3 GeV/c and vertical bar y vertical bar < 0.9 is a sigma(J/psi <- hB) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 1.46 +/- 0.38 (stat.)(-0.32)(+0.26) (syst.) mu b. The results are compared to QCD model predictions. The shape of the p(t) and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the b (b) over bar pair total cross section and d sigma/dy at mid-rapidity.
|
|
| 4. |
- Abelev, Betty, et al.
(författare)
-
Underlying Event measurements in pp collisions at root s=0.9 and 7 TeV with the ALICE experiment at the LHC
- 2012
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; :7
-
Tidskriftsartikel (refereegranskat)abstract
- We present measurements of Underlying Event observables in pp collisions at root s = 0 : 9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum p(T),L-T in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different p(T) thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track p(T) threshold considered. Data are compared to PYTHIA 6.4, PYTHIA 8.1 and PHOJET. On average, all models considered underestimate the multiplicity and summed p(T) in the Transverse region by about 10-30%.
|
|
| 5. |
- Andres, J, et al.
(författare)
-
Transition structures for hydride transfer reactions in vacuo and their role in enzyme catalysis
- 1996
-
Ingår i: Journal of Molecular Structure: THEOCHEM. - : Elsevier. - 0166-1280. ; 371, s. 299-312
-
Forskningsöversikt (refereegranskat)abstract
- A general discussion as to the role of in vacuo transition structure in enzyme catalysis is presented. Quantum mechanical aspects are emphasized. The transition structures defined as saddle points of index one (SPi-1) for the hydride transfer step on different model enzyme systems from flavoproteins to dehydrogenases have been characterized with analytical gradients at different levels of theory: semi-empirical; ab initio with different basis sets within the Hartree-Fock scheme; density functional theory using different approaches. Quantum chemical characteristics of the SPi-1 are used to discuss hydride transfer step in enzyme catalyzed reactions and mechanistic implications. With the exception of dihydrofolate reductase, the results for all other systems studied suggest that the endo relative orientation imposed by the active site on the reactants is essential for polarizing the CdHt bond and situating the system in the quadratic region of the endo SPi-1. The geometry and transition vector components are both model independent and weakly dependent on the level of theory used in their determination. Comparisons of the SPi-1 geometries with available X-ray coordinates show that the SPi-1 can be fitted without any stress at the active site. The geometrical arrangement of the SPi-1 results in optimal frontier LUMO orbital interactions, and the transition vector amplitudes show primary and secondary isotope effects to be strongly coupled. A comparison between simple and sophisticated molecular models shows that there is a minimal molecular model associated with geometrical parameters describing the essentials of the chemical interconversion step. For hydride transfer, the corresponding transition vector is an invariant feature.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Arteca, Gustavo A., et al.
(författare)
-
Constructing quantum mechanical models from diabatic schemes : external field modulation of effective energy barriers for bond breaking/formation processes
- 2014
-
Ingår i: Journal of Mathematical Chemistry. - : Springer Science and Business Media LLC. - 0259-9791 .- 1572-8897. ; 52:9, s. 2395-2410
-
Tidskriftsartikel (refereegranskat)abstract
- We have recently proposed an approach where chemical transformations can be described as quantum processes involving the modulation of entangled states by an applied external field (Arteca and Tapia in Phys Rev A 84:012115, 2011). In practical implementations, we gain insight into these processes by using simple quantum-mechanical models derived from diabatic schemes. In this context, reactant, product, and, eventually, intermediate species, are assigned to diabatic basis functions, and then entangled by an external field into a quantum state from which all observable properties of the chemical reaction should emerge. Here, we extend our previous model for bond breaking/formation in diatomic molecules (Arteca et al. in J Math Chem 50:949, 2012). We consider the entire manifold of semiclassical models defined by only two diabatic basis functions: a harmonic well for the "molecular" bound state, and an exponential potential energy function for the asymptotically separated fragments (the "product" channel). Using a two-parameter space to describe all models, we determine how the topology of the total energy function is affected by the shape of the applied field. We show that strong and weak local couplings with the external field modify substantially the occurrence of energy barriers, in contrast to using the uniform (i.e., space-invariant) coupling employed in previous works.
|
|
| 10. |
- Arteca, Gustavo A., et al.
(författare)
-
Constructing quantum mechanical models starting from diabatic schemes : Quantum states for simulations bond break/formation-I. Feshbach-like quantum states and electronuclear wave functions
- 2012
-
Ingår i: Journal of Mathematical Chemistry. - : Springer Science and Business Media LLC. - 0259-9791 .- 1572-8897. ; 50:4, s. 949-970
-
Tidskriftsartikel (refereegranskat)abstract
- A quantum description adapted to scrutinize chemical reaction mechanisms obtains by implementing an electronuclear separation via quantum numbers method; truly diabatic base states obtain that sustain quantum states expressed as linear superpositions. A proto-type bond breaking/formation case: H-2(+) double left right arrow H(1s) + H+ test possibilities via mathematical modeling. Asymptotic states (vertical bar H > circle times vertical bar H+>) and (vertical bar H+> circle times vertical bar H >) and basis states for quantized electromagnetic radiation complete the model; Feshbach-resonance-like quantum states obtain that play pivotal roles gating association/dissociation processes. A fixed grid of floating Gaussian orbitals permits actual computations compatible with this method. The information therefrom gleaned is used to construct model Hamiltonians easily adaptable to second quantization formalisms. Theoretical developments and non-routine computations results can directly be related to experiment.
|
|
