119533012
On Power Suppressed Operators and Gauge Invariance in SCET
The form of collinear gauge invariance for power suppressed operators in the soft-collinear effective theory is discussed. Using a field redefinition we show that it is possible to make any power suppressed ultrasoft-collinear operators invariant under the original leading order gauge transformations. Our manipulations avoid gauge fixing. The Lagrangians to O(lambda^2) are given in terms of these new fields. We then give a simple procedure for constructing power suppressed soft-collinear operators in SCET_II by using an intermediate theory SCET_I.
119428056
B decay shape variables and the precision determination of |V(cb)| and m(b)
We present expressions for shape variables of B decay distributions in several different mass schemes, to order $\alpha_s^2\beta_0$ and (Lambda_{QCD}/mb)^3. Such observables are sensitive to the b quark mass and matrix elements in the heavy quark effective theory, and recent measurements allow precision determinations of some of these parameters. We perform a combined fit to recent experimental results from CLEO, BABAR, and DELPHI, and discuss the theoretical uncertainties due to nonperturbative and perturbative effects. We discuss the possible discrepancy between the OPE prediction, recent BABAR results and the measured branching fraction to D and D* states. We find |Vcb| = (40.8 +- 0.9) x 10^{-3} and mb^{1S} = 4.74 +- 0.10 GeV, where the errors are dominated by experimental uncertainties.
118299841
Subtractions for SCET Soft Functions
We present a method to calculate the soft function in Soft-Collinear Effective Theory to NLO for N-jet events, defined with respect to arbitrarily complicated observables and algorithms, using a subtraction-based method. We show that at one loop the singularity structure of all observable/algorithm combinations can be classified as one of two types. Type I jets include jets defined with inclusive algorithms for which a jet shape is measured. Type II jets include jets found with exclusive algorithms, as well as jets for which only the direction and energy are measured. Cross sections that are inclusive over a certain region of phase space, such as the forward region at a hadron collider, are examples of Type II jets. We show that for a large class of measurements the required subtractions are already known analytically, including traditional jet shape measurements at hadron colliders. We demonstrate our method by calculating the soft functions for the case of jets defined in eta-phi space with an out-of-jet pT cut and a rapidity cut on the jets, as well as for the case of 1-jettiness.
34485941
Fluctuating annihilation cross sections and the generation of density perturbations
Fluctuations in the mass and decay rate of a heavy particle which for some period dominates the energy density of the Universe are known to lead to adiabatic density perturbations. We show that generically the annihilation cross section of the same particle also receives fluctuations, which leads to entropy perturbations at freeze-out. If the particle comes to dominate the energy density of the Universe and subsequently decays, this leads to an additional source of adiabatic density perturbations. On the other hand, nonadiabatic density perturbations result when the particle does not decay but contributes to the observed dark matter.
118867883
Enhanced nonperturbative effects in Z decays to hadrons
We use soft collinear effective field theory (SCET) to study nonperturbative strong interaction effects in Z decays to hadronic final states that are enhanced in corners of phase space. These occur, for example, in the jet energy distribution for two jet events near E_J=M_Z/2, the thrust distribution near unity and the jet invariant mass distribution near zero. The extent to which such nonperturbative effects for different observables are related is discussed.
119263456
Factorization of boosted multijet processes for threshold resummation
Explicit applications of factorization theorems for processes at hadron colliders near the hadronic end point have largely focused on simple final states with either no jets (e.g., Drell-Yan) or one inclusive jet (e.g., deep-inelastic scattering and prompt photon production). Factorization for the former type of process gives rise to a soft function that depends on time like momenta, whereas the soft function for the latter type depends on null momenta. We derive in soft-collinear effective theory a factorization theorem that allows for an arbitrary number of jets, where the jets are defined with respect to a jet algorithm, together with any number of nonstrongly interacting particles. We find the soft function in general depends on the null components of the soft momenta inside the jets and on a timelike component of the soft momentum outside of the jets. This generalizes and interpolates between the soft functions for the cases of no jets and one inclusive jet. We verify consistency of our factorization theorem to O(α s ) for any number of jets. While in this paper we demonstrate consistency only near the hadronic end point, we keep the kinematics general enough (in particular allowing for nonzero boost) to allow for an extension to partonic threshold resummation away from the hadronic end point.
126269166
Handling of beam impurities in gamma-spectroscopy experiments at REX-ISOLDE (CERN)
The REX-ISOLDE facility at CERN delivers a great variety of radioactive ion beams with energies up to 3.0 MeV/u and therefore allows nuclear structure physics experiments far from the valley of stability. A crucial point for the experimentalist is the knowledge of beam contaminations, either from the bunching and charge-breeding procedure (residual gas ions) or directly from the ion-production process (isobaric contaminants), whose sources are discussed as well as possible ways of elimination during the postacceleration. Methods to analyse the beam composition in the relevant energy range are presented on the basis of two specific experiments using the MINIBALL detector array with an emphasis on the experimental challenges in Gamma-spectroscopy experiments and data analysis.