Showing papers in "Nuovo Cimento Della Societa Italiana Di Fisica A-nuclei Particles and Fields in 2012"
TL;DR: In this paper, the authors review the state of the art concerning the contribution of quarks to various nucleon properties, including the electric and magnetic form factors, and the level of agreement between theory and experiment is very satisfactory and gives considerable confidence in their capacity to make reliable calculations within nonperturbative QCD.
Abstract: We review the state of our knowledge concerning the contribution of strange quarks to various nucleon properties. In the case of the electric and magnetic form factors, the level of agreement between theory and experiment is very satisfactory and gives us considerable confidence in our capacity to make reliable calculations within non-perturbative QCD. In view of the importance of the scalar form factors to the detection of dark matter candidates such as neutralinos, we place a particular emphasis on the determination of the pi-N and strange quark sigma commutators.
15 citations
11 citations
TL;DR: In this article, the authors review the most popular models proposed to explain the anomalous forward-backward asymmetry in t tbar production at the Tevatron and discuss their viability in view of recent LHC data.
Abstract: We review the most popular models proposed to explain the anomalous forward-backward asymmetry in t tbar production at the Tevatron. We discuss their viability in view of recent LHC data. We summarise their predictions for charge asymmetries at the LHC.
4 citations
TL;DR: In this article, the top forward-backward asymmetry (FBA) reported by CDF and D0 Collaborations in the effective lagrangian approach was studied using dimension-6 effective largrangians.
Abstract: We study the top forward-backward asymmetry (FBA $\equiv A_{\rm FB}$) reported by CDF and D0 Collaborations in the effective lagrangian approach. Using dimension-6 effective largrangians for $q \bar{q} \rightarrow t \bar{t}$, we study the $t\bar{t}$ production cross section and the $A_{\rm FB}$, and a few observables: the FB spin-spin correlation that is strongly correlated with the $A_{\rm FB}$, and longitudinal top polarization as a new probe of chiral structures for possible new physics scenarios.
3 citations
TL;DR: The MOLLER experiment as mentioned in this paper measured the weak charge of the electron with a precision of 2.3% by measuring the parity-violating asymmetry in electron-electron (M\oller) scattering.
Abstract: The MOLLER experiment will measure the weak charge of the electron, $Q^e_W = 1 - 4\sin^2\theta_W$, with a precision of 2.3% by measuring the parity-violating asymmetry in electron-electron (M\oller) scattering. This measurement will provide an ultra-precise measurement of the weak mixing angle, $\sin^2\theta_W$, which is on par with the two most precise collider measurements at the Z$^0$-pole. The precision of the experiment, with a fractional accuracy in the determination of $\sin^2\theta_W$ $\approx 0.1$%, makes it a probe of physics beyond the Standard Model with sensitivities to mass scales of new physics up to 7.5 TeV.
3 citations
TL;DR: In this article, the existence of electric dipole moments (EDM) for fundamental particles signals time-reversal symmetry (T) violation accompanied by violation of parity (P); only upper limits have been established to date.
Abstract: The existence of electric dipole moments (EDM) for fundamental particles signals time-reversal symmetry (T) violation accompanied by violation of parity (P); only upper limits have been established to date. Time-reversal violation in turn implies CP violation under the assumption that CPT is a good symmetry. The neutron is an attractive system for an EDM search, both because it is neu- tral and because a neutron EDM would be relatively easier to interpret than the comparable quantity for a nucleus or even an atom. We introduce briefly the key experimental requirements for such search and describe some aspects of the neutron EDM experiment planned for the Spallation Neutron Source at the U.S. Oak Ridge National Laboratory.
3 citations
TL;DR: In this article, the P2 experiment at Mainz was equipped with two different types of polarimeters, a double scattering Mott polarimeter and a Moller polarimeter with trapped polarized hydrogen atoms.
Abstract: We plan to equip the P2 experiment at Mainz with two different types of polarimeters, a so-called double scattering Mott polarimeter and a Moller polarimeter with trapped polarized hydrogen atoms (Hydro-Moller polarimeter).
We believe that both polarimeters have the potential to achieve an accuracy in the determination of the effective analyzing power of less than 0.5%.
2 citations
TL;DR: In this article, the authors present the preliminary results of the measurement of the azimuthal asymmetries in the process e+e^- -> qqbar -> pi pi X, where the two pions are produced in opposite hemispheres.
Abstract: Transversity distribution describes the quark transverse polarization inside a transversely polarized nucleon. It is the less known leading-twist piece of the QCD description of the partonic structure of the nucleon. Transversity can be extracted from semi-inclusive deep inelastic scattering (SIDIS) where, however, it couples to a new, unknown fragmentation function, called Collins function. We present the preliminary results of the measurement of the azimuthal asymmetries in the process e^+e^- -> qqbar -> pi pi X, where the two pions are produced in opposite hemispheres. These preliminary results are based on a data sample of about 45 fb^{-1}, collected by the BABAR experiment at a center-of-mass energy of 10.54 GeV, and are compared with the Belle measurements.
2 citations
2 citations
TL;DR: In this article, two different techniques of electron target polarimetry for solid targets (iron or supermendure) have been proposed: brute force and classic Møller target polarization in a foil plane and a strong magnetic field in a plane perpendicular to the foil plane.
Abstract: — In Møller polarimetry for solid targets (iron or supermendure), there are only two different techniques of electron target polarization. The first one is a “classic” technique of the Møller target polarization in a foil plane. The second one is the so-called “brute force” technique of the electron target polarization in a strong magnetic field (about 3 T) in a plane perpendicular to the foil plane. Both the techniques can be used for different experiments for electron beam polarization measurements.
2 citations
TL;DR: In this article, analogies and differences between physical conditions of electron-positron plasma in the early universe and in sources of gamma-ray bursts (GRBs) are discussed.
Abstract: Electron-positron plasma is believed to play an imporant role both in the early Universe and in sources of Gamma-Ray Bursts (GRBs). We focus on analogies and differences between physical conditions of electron-positron plasma in the early Universe and in sources of GRBs. We discuss: a) dynamical differences, namely thermal acceleration of the outflow in GRB sources vs. cosmological deceleration; b) nuclear composition differences as synthesis of light elements in the early Universe and possible destruction of heavy elements in GRB plasma; c) different physical conditions during last scattering of photons by electrons. Only during the acceleration phase of the optically thick electron-positron plasma the comoving observer may find it similar to the early Universe. This similarity breaks down during the coasting phase. Reprocessing of nuclear abundances may likely take place in GRB sources. Heavy nuclear elements are then destroyed, resulting mainly in
protons with small admixture of helium. Unlike the primordial plasma which recombines to form neutral hydrogen, and emits the Cosmic Microwave Background
Radiation, GRB plasma does not cool down enough to recombine.
TL;DR: In this paper, the authors present recent progress in the computation of next-to-leading order (NLO) QCD corrections for the production of an electroweak vector boson in association with jets at hadron colliders.
Abstract: In this contribution we present recent progress in the computation of next-to-leading order (NLO) QCD corrections for the production of an electroweak vector boson in association with jets at hadron colliders. We focus on results obtained using the virtual matrix element library BlackHat in conjunction with SHERPA, focusing on results relevant to understanding the background to top production. The production of a vector boson in association with several jets at the Large Hadron Collider (LHC) is an important background for other Standard Model processes as well as new physics signals. In particular, the production of a W boson in association with many jets is an important background for processes involving one or more top quarks. Precise predictions for the backgrounds are crucial to measurement of top-quark processes. Vector boson production in association with multiple jets is also a very important background for many SUSY searches, as it mimics the signatures of many typical decay chains. Here we will discuss how polarization information can be used as an additional handle to differentiate top pair production from 'prompt' W-boson production. More generally, ratios of observables, for example for events containing a W boson versus those containing a Z boson, are expected to be better-behaved as many uncertainties cancel in such ratios. Precise calculation of ratios, along with measurement of one of the two processes in the ratio, can be used in data-driven techniques for estimating backgrounds.
TL;DR: In this article, a method for measuring nuclear-spin-dependent atomic parity violation without nuclear spin independent background is presented, which can be achieved by observing interference of parity-conserving and parity-violating two-photon J=0-to-1 transitions driven by collinear photons of the same frequency in the presence of an external static magnetic field.
Abstract: We present a method for measuring nuclear-spin-dependent atomic parity violation without nuclear-spin-independent background. Such measurements can be achieved by observing interference of parity-conserving and parity-violating two-photon J=0-to-1 transitions driven by collinear photons of the same frequency in the presence of an external static magnetic field.
TL;DR: In this article, the authors examine a selection of the past years' collider-QCD developments, attempting to place them in the context of the above “headline” developments.
Abstract: The past 18 months have seen considerable excitement in the field of collider particle physics. Among the topics that deserve a mention, one might include the measurement of an unexpectedly large tt forward-backward asymmetry at the Tevatron [1, 2], CDF’s anomalous bump in W + dijet production [3], the LHC’s exclusion of huge swathes of supersymmetric parameter space [4, 5] and hints of the Higgs boson from both the Tevatron and the LHC [6-8]. The purpose of this talk is to examine a selection of the past years’ collider-QCD developments, attempting to place them in the context of the above “headline” developments. To guide us through this exercise, let us start by recalling that hard collider events can be broken up into various components: the non-perturbative structure of the proton, e.g. encoded in parton distribution functions and as relevant also to multiple semi-soft interactions; the “hard” process, amenable to fixed-order perturbative calculation, usually involving at most a handful of partons; the fragmentation of those partons, often implemented as a parton shower; and the hadronisation process, by which partons turn into the hadrons that are observed experimentally. All of these elements must be dealt with correctly (and together) if one is to fully predict the properties of events at
TL;DR: In this article, a model which describes the time-dependent CP formalism in $D^0$ decays has been proposed, which can be used to measure the value of the parameter $x, one of the two parameters defining charm mixing.
Abstract: A model which describes the time-dependent CP formalism in $D^0$ decays has recently been proposed. There it has been highlighted a possible measurement of the angle $\beta_c$, in the charm unitarity triangle, using the decays $D^0\to K^+ K^-$ and $D^0\to \pi^+ \pi^-$, and a measurement of the mixing phase $\phi_{MIX}$. The same method can be used to measure the value of the parameter $x$, one of the two parameters defining charm mixing. We numerically evaluate the impact of a time-dependent analysis in terms of the possible outcomes from present and future experiments. We consider the scenarios of correlated $D^0$ mesons production at the center of mass energy of the $\Psi(3770)$ at Super$B$, uncorrelated production at the center of mass energy of the $\Upsilon(4S)$ at Super$B$ and Belle II, and LHCb. Recently a hint of direct CP violation in charm decays was reported by the LHCb collaboration, we estimate the rate of time-dependent asymmetry that could be achieved using their available data, and we generalise the result for the full LHCb program. We conclude that LHCb is already able to perform a first measurement of $\beta_{c,eff}$, and slightly improve the present constraints on the parameters $x$ and $\phi_{MIX}$. A more precise determination of $\beta_{c,eff}$, $\phi_{MIX}$ and $x$ will require a larger data sample, and most probably the cleaner environment of the new high luminosities $B$-factories (both Super$B$ and Belle II) will be needed. We show that Super$B$ will be able to measure $\beta_{c,eff}$ and $\phi_{MIX}$ with a precision of $1.4^o$ and improve the precision on $x$ by a factor of two.
TL;DR: The ATLAS experiment will participate in the Heavy Ion program at the Large Hadron Collider (LHC) and will use its large acceptance, high granularity calorimeters, silicon tracking detectors, and muon spectrometers to study hard scattering processes and jet quenching, quark production and suppression, and global observables in Pb+Pb collisions as discussed by the authors.
Abstract: The ATLAS experiment will participate in the Heavy Ion program at the Large Hadron Collider (LHC) and will use its large acceptance, high granularity calorimeters, silicon tracking detectors, and muon spectrometers to study hard scattering processes and jet quenching, quarkonia production and suppression, and global observables in Pb+Pb collisions. The longitudinal and fine transverse segmentation of the ATLAS electromagnetic calorimeter gives ATLAS unique capabilities for measuring complete jets and photons. Brookhaven National Laboratory, Columbia University, Iowa State University, and Stony Brook University propose a focused program to take advantage of ATLAS’s strengths to study the physics of high-energy parton interactions with the quark-gluon plasma (QGP), the physics of Debye screening of Q-Q̄ states in the QGP, and the physics of initial particle production and thermalization to characterize the properties of the QGP created in heavy ion collisions at the LHC. The proposed program can be accomplished for modest cost, will provide substantial physics impact and will have a positive impact on the physics program at the Relativistic Heavy Ion Collider (RHIC) due to the strong involvement of the proposing institutions in the RHIC program. Participation of US groups will strengthen the existing (and growing) ATLAS heavy ion program by bringing physics and analysis expertise developed at RHIC and will allow the US Nuclear Physics program to participate in an experiment that will have subtantial physics impact on the heavy ion community.
TL;DR: In particular, strong constraints come from lepton flavour violating processes, like mu-to-e gamma as discussed by the authors, which is a type of lepton flavor violating process, and the results of the analysis and the main results are presented in Section 2.1.
Abstract: The recent measurements of the neutrino reactor angle require a re-examination of flavour models based on discrete groups. Indeed, when these models deal with the Tri-Bimaximal, the Bimaximal and the Golden Ratio mixing patterns, some tensions arise in order to accommodate the reactor angle. In particular, strong constraints come from lepton flavour violating processes, like mu -> e gamma. We present the analysis and the main results.
TL;DR: In this article, the authors examine the value of certain concepts highly regarded in the past decade, that concern neutrino propagation, models for the leptonic mixing, interpretations of neutrinoless double beta decay and of SN1987A observations.
Abstract: — We examine the value of certain concepts highly regarded in the past decade, that concern neutrino propagation, models for the leptonic mixing, interpretations of neutrinoless double beta decay and of SN1987A observations. We argue that it would useful to strengthen the role of the discussions among experts of neutrino physics, regarding the hypotheses underlying the theoretical investigations.
TL;DR: In this article, the authors present results on how to observe the analog Hawking radiation in Bose-Einstein condensates by a direct measurement of the density correlations due to the phonon pairs (Hawking quantapartner) created by the acoustic horizon.
Abstract: Summary. — Observing quantum particle creation by black holes (Hawking radi- ation) in the astrophysical context is, in ordinary situations, hopeless. Nevertheless the Hawking effect, which depends only on kinematical properties of wave prop- agation in the presence of horizons, is present also in nongravitational contexts, for instance in stationary fluids undergoing supersonic flow. We present results on how to observe the analog Hawking radiation in Bose-Einstein condensates by a direct measurement of the density correlations due to the phonon pairs (Hawking quanta-partner) created by the acoustic horizon.
TL;DR: In this article, the status and prospects of low energy flavor observables that are highly sensitive to New Physics effects are reviewed, and the implications for possible New Physics in b {yields} s transitions coming from the recent experimental results on the B{sub s} mixing phase, the branching ratio of the rare decay B {sub s] {Y yieldss} {mu}{sup +}{mu}sup -}, and angular observables in the B {y yields} K* {mu}
Abstract: In this talk, I review the status and prospects of several low energy flavor observables that are highly sensitive to New Physics effects. In particular I discuss the implications for possible New Physics in b {yields} s transitions coming from the recent experimental results on the B{sub s} mixing phase, the branching ratio of the rare decay B{sub s} {yields} {mu}{sup +}{mu}{sup -}, and angular observables in the B {yields} K* {mu}{sup +}{mu}{sup -} decay. Also the recent evidence for direct CP violation in singly Cabibbo suppressed charm decays and its interpretation in the context of New Physics models is briefly discussed.