6 research outputs found
The heavy quark search at the LHC
We explore further the discovery potential for heavy quarks at the LHC, with
emphasis on the and of a sequential fourth family associated with
electroweak symmetry breaking. We consider QCD multijets, ,
and single backgrounds using event generation based on
improved matrix elements and low sensitivity to the modeling of initial state
radiation. We exploit a jet mass technique for the identification of
hadronically decaying 's and 's, to be used in the reconstruction of the
or mass. This along with other aspects of event selection can reduce
backgrounds to very manageable levels. It even allows a search for both
and in the absence of -tagging, of interest for the early running of
the LHC. A heavy quark mass of order 600 GeV is motivated by the connection to
electroweak symmetry breaking, but our analysis is relevant for any new heavy
quarks with weak decay modes.Comment: 12 pages, 7 figure
t' at the LHC: the physics of discovery
A search for a fourth family at the LHC is presently a low priority, but we
argue that an effective search can be conducted early with only a few inverse
femtobarns of data. We discuss a method based on invariant masses of single
jets for identifying the 's originating from heavy quark decays. This can
significantly increase signal to background in the reconstruction of the
mass. We also study the various types of physics that can impact the background
estimate, most notably higher order effects, initial state radiation, and
models of the underlying event.Comment: 16 pages, 12 figures, small improvements, version to appear in JHE
Mediated definite delegation: Certified Grid jobs in ALICE and beyond
Grid computing infrastructures need to provide traceability and accounting of their users activity and protection against misuse and privilege escalation, where the delegation of privileges in the course of a job submission is a key concern. This work describes an improved handling of Multi-user Grid Jobs in the ALICE Grid Services. A security analysis of the ALICE Grid job model is presented with derived security objectives, followed by a discussion of existing approaches of unrestricted delegation based on X.509 proxy certificates and the Grid middleware gLExec. Unrestricted delegation has severe security consequences and limitations, most importantly allowing for identity theft and forgery of jobs and data. These limitations are discussed and formulated, both in general and with respect to an adoption in line with Multi-user Grid Jobs. A new general model of mediated definite delegation is developed, allowing a broker to dynamically process and assign Grid jobs to agents while providing strong accountability and long-term traceability. A prototype implementation allowing for fully certified Grid jobs is presented as well as a potential interaction with gLExec. The achieved improvements regarding system security, malicious job exploitation, identity protection, and accountability are emphasized, including a discussion of non-repudiation in the face of malicious Grid jobs