Jet Trimming

Initial state radiation, multiple interactions, and event pileup can contaminate jets and degrade event reconstruction. Here we introduce a procedure, jet trimming, designed to mitigate these sources of contamination in jets initiated by light partons. This procedure is complimentary to existing methods developed for boosted heavy particles. We find that jet trimming can achieve significant improvements in event reconstruction, especially at high energy/luminosity hadron colliders like the LHC.Comment: 20 pages, 11 figures, 3 tables - Minor changes to text/figure

D^* production from e^+e^- to ep collisions in NLO QCD

Fragmentation functions for D mesons, based on the convolution of a perturbative part, related to the heavy quark perturbative showering, and a non-perturbative model for its hadronization into the meson, are used to describe D^* production in e^+e^- and ep collisions. The non-perturbative part is determined by fitting the e^+e^- data taken by ARGUS and OPAL at 10.6 and 91.2 GeV respectively. When fitting with a non perturbative Peterson fragmentation function and using next-to-leading evolution for the perturbative part, we find an epsilon parameter sensibly different from the one commonly used, which is instead found with a leading order fit. The use of this new value is shown to increase considerably the cross section for D^* production at HERA, suggesting a possible reconciliation between the next-to-leading order theoretical predictions and the experimental data.Comment: 20 pages, LaTeX2e, 8 Postscript figure

A Short Review on Jet Identification

Jets can be used to probe the physical properties of the high energy density matter created in collisions at the Relativistic Heavy Ion Collider (RHIC). Measurements of strong suppression of inclusive hadron distributions and di-hadron correlations at high $p_{T}$ have already provided evidence for partonic energy loss. However, these measurements suffer from well-known geometric biases due to the competition of energy loss and fragmentation. These biases can be avoided if the jets are reconstructed independently of their fragmentation details - quenched or unquenched. In this paper, we discuss modern jet reconstruction algorithms (cone and sequential recombination) and their corresponding background subtraction techniques required by the high multiplicities of heavy ion collisions. We review recent results from the STAR experiment at RHIC on direct jet reconstruction in central Au+Au collisions at $\sqrt {s_{NN}}= 200$ GeV.Comment: Proceedings for the invited talk of Hot Quarks 2008, Estes Park, CO 18-23 August 200

RR Lyrae variables in the globular cluster M3 (NGC5272). I. BVI CCD photometry

New BVI CCD photometry is presented for 60 RR Lyrae variables in the globular cluster M3. Light curves have been constructed and ephemerides have been (re)-derived for all of them. Four stars (i.e. V29, V136, V155 and V209), although recognized as variables, had no previous period determinations. Also, the period derived for V129 is significantly different from the one published by Sawyer-Hogg (1973). Light curve parameters, i.e. mean magnitudes, amplitudes and rise-times, have been derived. The discussion of these results in the framework of the stellar evolution and pulsation theories will be presented in a forthcoming paper.Comment: 19 pages, latex, uses mn.sty, 12 encapsulated figures, to be published in MNRAS, text and figures also available at http://www.bo.astro.it/bap/BAPhome.html or via anonymous ftp at ftp://boas3.bo.astro.it/bap/files (bap98-12-textfig.ps

Star-to-star Na and O abundance variations along the red giant branch in NGC 2808

We report for the first time Na and O abundances from high-resolution, high S/N echelle spectra of 20 red giants in NGC 2808, taken as part of the Science Verification program of the FLAMES multi-object spectrograph at the ESO VLT. In these stars, spanning about 3 mag from the red giant branch (RGB) tip, large variations are detected in the abundances of oxygen and sodium, anticorrelated with each other; this is a well known evidence of proton-capture reactions at high temperatures in the ON and NeNa cycles. One star appears super O-poor; if the extension of the Na-O anticorrelation is confirmed, NGC 2808 might reach O depletion levels as large as those of M 13. This result confirms our previous findings based on lower resolution spectra (Carretta et al. 2003) of a large star-to-star scatter in proton capture elements at all positions along the RGB in NGC 2808, with no significant evolutionary contribution. Finally, the average metallicity for NGC 2808 is [Fe/H]= -1.14 +/- 0.01 dex (rms=0.06) from 19 stars.Comment: 12 pages, 3 figures, accepted for publication in ApJ Letter

Measurement of heavy-flavor production in Pb-Pb collisions at the LHC with ALICE

A Large Ion Collider Experiment (ALICE) at the Large Hadron Collider (LHC) has been built in order to study the Quark-Gluon Plasma (QGP) created in high-energy nuclear collisions. As heavy-flavor quarks are produced at the early stage of the collision, they serve as sensitive probes for the QGP. The ALICE detector with its capabilities such as particle identification, secondary vertexing and tracking in a high multiplicity environment can address, among other measurements, the heavy-flavor sector in heavy-ion collisions. We present latest results on the measurement of the nuclear modification factor of open heavy-flavors as well as on the measurement of open heavy-flavor azimuthal anisotropy v2 in Pb-Pb collisions at sqrt(s) = 2.76 TeV. Open charmed hadrons are reconstructed in the hadronic decay channels D0->Kpi, D+->Kpipi, and D*+->D0pi applying a secondary decay-vertex topology. Complementary measurements are performed by detecting electrons (muons) from semi-leptonic decays of open heavy-flavor hadrons in the central (forward) rapidity region.Comment: 10 pages, 6 figures. Talk given by Robert Grajcarek at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

The small x gluon and b\bar{b} production at the LHC

We study open b\bar{b} production at large rapidity at the LHC in an attempt to pin down the gluon distribution at very low x. For the LHC energy of 7 TeV, at next-to-leading order (NLO), there is a large factorization scale uncertainty. We show that the uncertainty can be greatly reduced if events are selected in which the transverse momenta of the two B-mesons balance each other to some accuracy, that is |\vec p_{1T}+\vec p_{2T}| < k_0. This will fix the scale \mu_F \simeq k_0, and will allow the LHCb experiment, in particular, to study the x-behaviour of gluon distribution down to x ~ 10^{-5}, at rather low scales, \mu ~ 2 GeV. We evaluate the expected cross sections using, for illustrative purposes, various recent sets of Parton Distribution Functions.Comment: 13 pages, 5 figure

Transverse Momentum Distribution in b-> s Gamma

We present the complete calculation of the transverse momentum distribution for the decay b->s Gamma. The contributions of the leading operator O_7 are computed: infrared logarithms are resummed with next-to-leading accuracy, according to usual techniques of resummation. Non logarithmic terms are evaluated to O(alpha_S) by calculating one loop diagrams.Comment: Talk given 10th International QCD Conference (QCD 03), Montpellier, France, 2-9 Jul 2003. 4 page