118567857
PROPOSAL OF AN INVERSE LOGARITHM SCALING LAW FOR THE LUMINOSITY EVOLUTION
A scaling law for the time-dependence of the dynamic aperture, i.e., the region of phase space where stable motion occurs, was proposed in previous papers, about ten years ago. It was showed that dynamic aperture has a logarithmic dependence on time, which would be suggested by some fundamental theorems of the theory of dynamical systems. Such a scaling law was recently extended also to the intensity evolution in a storage ring. In this paper, inspired by these results, and inverse logarithm scaling law for the luminosity in a circular collider is proposed. Such a time-dependence is then tested against the data from the LHC physics runs and also with some examples from other machines. The results are presented and discussed in detail.
121335136
Design and field measurement of the BEPC-II interaction region dual-aperture quadrupoles
With the Beijing Electron Positron Collider upgrade project (BEPC-II), two dual-aperture septum-style quadrupole magnets are used in the interaction region for the final focusing of the electron and positron beams. The BEPC-II lattice design calls for the same high quality integral quadrupole field and large good field region in both apertures for each magnet. Two-dimensional contour optimization and pole-end chamfer iteration are used to minimize the systematic harmonic errors. Unexpected non-systematic errors induced by the unsymmetrical structure and the manufacturing errors are compensated with the pole-end shimming. Magnet measurements with rotating coils are performed to guide and confirm the magnet design. This paper discusses the design consideration, optimizing procedure and measurement results of these dual-aperture magnets.
38643705
BEPCII Interaction Region Design and Construction Status
BEPC (Beijing Electron Positron Collider) is now upgrading to a double-ring collider which requires a new storage ring to be built in the existing tunnel. A new and compact interaction region (IR) has been designed to allow a peak luminosity of 1033cm-2s-1from an equal beam energy of 1.89 GeV, a crossing angle, 93 bunches with maximum beam current of 0.91 A . The multi-purpose superconducting magnets and conventional dual aperture quadrupoles are used as final focusing quadrupole in the interaction region. The two beams collide at the interaction point with a crossing angle of ± 11 mrad and further beams separation is enhanced with the help of a septum bending magnet which locates just beyond the superconducting magnet and acts on the outgoing beam lines only. This paper will describe the IR design and the construction status.
123625266
Interaction region design and realization for the Beijing Electron Positron Collider
The Beijing Electron Positron Collider (BEPC) has been upgraded as a double-ring factory-like collider (BEPCII). A compact interaction region (IR), which is the most complicated region in the BEPCII, has been designed to afford a peak luminosity of 1 x 10(33) cm(-2) s(-1) with an equal beam energy of 1.89 GeV, a cross angle of +/-11 mrad, 93 bunches and maximum beam current of 0.91 A. All the components of the IR have been fabricated successfully. The design and realization of the interaction region for the BEPCII will be introduced in detail. (C) 2009 Elsevier B.V. All rights reserved.
120440896
Longitudinal Single Bunch Instability Caused by Wake Field of Electron Cloud
The electron cloud accumulated in the vicinity of positron beam generates longitudinal electric field during the passage of bunch. The longitudinal interaction between bunch and electron cloud can lead to the distortion of the bunch shape. We use a simple analytic formula to calculate the longitudinal electric field due to electron cloud. Based on the longitudinal wake field, the macro-particle tracking method is used to simulate the variation of bunch longitudinal profile in different electron cloud densities and the simulation also shows that the synchrotron oscillation tune is slightly shifted by the wake field. By comparing the simulation results and the analytical estimation from potential distortion theory, the longitudinal wake field from electron cloud can be seen as a potential well effect.
119013150
Looking for parity nonconservation from strong interactions beyond QCD
Quantum Chromodynamics (QCD), the gauge eld theory describing the strong interactions of colored quarks and gluons in the Standard Model 12 , has been extraordinarily successful in describing physics in both non-perturbative and perturbative regimes. Using the positivity of the Euclidean path integrand for Yang-Mills theory, Vafa and Witten proved that QCD does not spontaneously break parity or CP if = 0 3 . CP conservation in the strong interactions is necessitated by the extreme smallness of experimental upper bounds on the neutron electric dipole moment a . It has been suggested that heavy ion collisions may form metastable phases which allow for parity nonconservation 5 . An induced charge separation along the angular momentum vector of the collision would create an electric dipole moment of the hot gluon matter. There are ongoing searches by the STAR collaboration 6 at the Relativistic Heavy Ion Collider (RHIC) to establish such an eect. Also, parityviolating eects can be induced by topological solutions in QCD.
119248652
MAJORANA Collaboration's Experience with Germanium Detectors
The goal of the \textsc{Majorana} \textsc{Demonstrator} project is to search for 0$\nu\beta\beta$ decay in $^{76}\mathrm{Ge}$. Of all candidate isotopes for 0$\nu\beta\beta$, $^{76}\mathrm{Ge}$ has some of the most favorable characteristics. Germanium detectors are a well established technology, and in searches for 0$\nu\beta\beta$, the high purity germanium crystal acts simultaneously as source and detector. Furthermore, p-type germanium detectors provide excellent energy resolution and a specially designed point contact geometry allows for sensitive pulse shape discrimination. This paper will summarize the experiences the \textsc{Majorana} collaboration made with enriched germanium detectors manufactured by ORTEC$^{\circledR}$. The process from production, to characterization and integration in \textsc{Majorana} mounting structure will be described. A summary of the performance of all enriched germanium detectors will be given.
119301804
The Majorana Demonstrator: A Search for Neutrinoless Double-beta Decay of 76Ge
Neutrinoless double-beta decay is a hypothesized process where in some even-even nuclei it might be possible for two neutrons to simultaneously decay into two protons and two electrons without emitting neutrinos. This is possible only if neutrinos are Majorana particles, i.e. fermions that are their own antiparticles. Neutrinos being Majorana particles would explicitly violate lepton number conservation, and might play a role in the matter-antimatter asymmetry in the universe. The observation of neutrinoless double-beta decay would also provide complementary information related to neutrino masses. The Majorana Collaboration is constructing the Majorana Demonstrator, a 40-kg modular germanium detector array, to search for the Neutrinoless double-beta decay of 76Ge and to demonstrate a background rate at or below 3 counts/(ROI-t-y) in the 4 keV region of interest (ROI) around the 2039 keV Q-value for 76Ge Neutrinoless double-beta decay. In this paper, we discuss the physics of neutrinoless double beta decay and then focus on the Majorana Demonstrator, including its design and approach to achieve ultra-low backgrounds and the status of the experiment.
119237175
Taking a Razor to Dark Matter Parameter Space at the LHC
Dark matter (DM) has been searched for at colliders in a largely model independent fashion by looking for an excess number of events involving a single jet, or photon, and missing energy. We investigate the possibility of looking for excesses in more inclusive jet channels. Events with multiple jets contain more information and thus more handles to increase the signal to background ratio. In particular, we adapt the recent CMS "razor" analysis from a search for supersymmetry to a search for DM. We consider simplified models where DM is a Dirac fermion that couples to the quarks of the Standard Model (SM) through exchange of vector or axial-vector mediators or to gluons through scalar exchange. We consider both light and heavy (leading to effective contact interactions) mediators. Since the razor analysis requires multiple jets in the final state, the data set is complementary to that used for the monojet search and thus the bounds can be combined.
53131853
Testing electroweak baryogenesis with future colliders
A bstractElectroweak Baryogenesis (EWBG) is a compelling scenario for explaining the matter-antimatter asymmetry in the universe. Its connection to the electroweak phase transition makes it inherently testable. However, completely excluding this scenario can seem difficult in practice, due to the sheer number of proposed models. We investigate the possibility of postulating a “no-lose” theorem for testing EWBG in future e+e− or hadron colliders. As a first step we focus on a factorized picture of EWBG which separates the sources of a stronger phase transition from those that provide new sources of CP violation. We then construct a “nightmare scenario” that generates a strong first-order phase transition as required by EWBG, but is very difficult to test experimentally. We show that a 100 TeV hadron collider is both necessary and possibly sufficient for testing the parameter space of the nightmare scenario that is consistent with EWBG.