18986664
Discovery Potential of the Standard Model Higgs Boson Through H -> WW Decay Mode with the ATLAS Detector at LHC
We report results of a study of the Standard Model Higgs boson discovery potential through the W-pair leptonic decay modes with the ATLAS detector at LHC at 14 TeV center-of-mass energy. We used MC samples with full detector simulation and reconstruction of the ATLAS experiment to estimate the ATLAS detection sensitivity for the reaction of pp -> H -> WW -> e\nu \mu\nu with no hard jet or two hard jets in the final states. The prospects for the Higgs boson searches at ATLAS are presented, including trigger efficiencies and data-driven methods to estimate the backgrounds using control samples in data. With 10/fb of integrated luminosity, one would expect to discover a Standard Model Higgs boson with ATLAS detector in Higgs boson mass range 135 < m_H < 190 GeV. If the Higgs boson does not exist, we will extend and confirm the exclusion produced by the Tevatron Higgs boson search result, which has ruled out the Higgs boson mass range of 160 < m_H < 170 GeV at 95% confidence level. If Higgs boson would be discovered, ATLAS could measure its mass with a precision of about 2 and 7 GeV for Higgs boson mass around 160 GeV and 130 GeV, respectively.
16109424
Frequency scanned interferometry for ILC tracker alignment
In this paper, we report high-precision absolute distance and vibration measurements performed with frequency scanned interferometry using a pair of single-mode optical b ers. Absolute distance was determined by counting the interference fringes produced while scanning the laser frequency. A high-nesse Fabry-Perot interferometer was used to determine frequency changes during scanning. A dual-laser scanning technique was used to cancel drift errors to improve the absolute distance measurement presicion. Under realistic conditions, a precision of 0.16 microns was achieved for absolute distance of 0.41 meters. Numerical simulation of an optical alignment system for a single silicon ladder, cylinder is also presented. The motivation for this project is to design a novel optical system for quasi-real time alignment of tracker detector elements used in High Energy Physics (HEP) experiments. A.F. Fox-Murphy et.al. from Oxford University reported their design of a frequency scanned interferometer (FSI) for precise alignment of the ATLAS Inner Detector [1, 2]. Given the demonstrated need for improvements in detector performance, we plan to design and prototype an enhanced FSI system to be used for the alignment of tracker elements in the next generation of electron-positron Linear Collider detectors. Current plans for future detectors require a spatial resolution for signals from a tracker detector, such as a silicon microstrip or silicon drift detector, to be approximately 7-10 m [3]. To achieve this required spatial resolution, the measurement precision of absolute distance changes of tracker elements in one dimension should be on the order of 1 m . Simultaneous measurements from hundreds of interferometers will be used to determine the 3-dimensional positions of the tracker elements. The University of Michigan group has constructed several demonstration Frequency Scanned Interferometer (FSI) systems with the laser light transported by air or single-mode optical b er, using single-b er and dual-laser scanning techniques for initial feasibility studies. Absolute distance was determined by counting the interference fringes produced while scanning the laser frequency. The main goal of the demonstration systems was to determine the potential accuracy of absolute distance measurements that could be achieved under both controlled and realistic conditions. Secondary goals included estimating the eects of vibrations and studying error sources crucial to the absolute distance accuracy. Two multiple-distance-measurement analysis techniques were developed to improve distance precision and to extract the amplitude and frequency of vibrations. Under laboratory conditions, a measurement precision of 50 nm was achieved for absolute distances ranging from 0.1 meters to 0.7 meters by using the rst multipledistance-measurement technique. The second analysis technique has the capability to measure vibration frequencies ranging from 0.1 Hz to 100 Hz with amplitude as small as a few nanometers, without a priori knowledge[4]. The multiple-distance-measurement analysis techniques are well suited for reducing vibration eects and uncertainties from fringe & frequency determination, but do not handle well the drift errors such as from thermal eects. In this paper, we describe a dual-laser system intended to reduce the drift errors and show some results under realistic conditions. Numerical simulation of an optical alignment system for a single silicon ladder and for cylinders is also presented.
16647938
Searches for Gauge-Mediated SUSY Breaking Topologies with the L3 Detector at LEP
Searches for topologies predicted by gauge‐mediated SUSY breaking models were performed using data collected with the L3 detector at LEP. All possible lifetimes of the next‐to‐lightest SUSY particle (NLSP), neutralino or scalar tau, were considered. No evidence for these new phenomena was found and limits on the production cross sections and sparticle masses were derived. A scan over the parameters of the minimal GMSB model was performed, leading to lower limits of 62.2 GeV, 11 TeV, and 0.07 eV on the NLSP mass, the mass scale parameter Λ, and the gravitino mass, respectively. The status of the LEP combined searches is also discussed.
17682877
Impact of Tracker Design on Higgs and Slepton Measurements
We have studied the impact of charged track resolution on Higgs mass and production cross section measurement in the process e+e− → Z0H,Z0 → + −,H → X for Higgs masses between 120 and 160 GeV, and on smuon mass measurement using smuon pair production for three different mass pairs, assuming the International Linear Collider(ILC) is operated at 500 GeV center of mass energies (CME) with integrated luminosities of 500 fb−1. The effect of initial state radiation (ISR), beamstrahlung and beam energy spread on Higgs and smuon mass measurement are also estimated. Using fast Monte Carlo simulations of the 2001 North American baseline detector designs (LD and SD), we find that the ISR and beamstrahlung have significant impact on Higgs and smuon mass measurement; Charged track momentum resolution affect Higgs mass significantly with better track performance yielding better Higgs mass resolution and precision for the track momentum resolution improvement up to a factor of about 5; Track momentum resolution has little effect on the measurement precision of the Higgsstrahlung cross section, the branching ratio of H → CC, the smuon and neutralino masses; Beam energy spread better than about 0.2% has little effect on Higgs, smuon and neutralino masses; The SD detector provides a more accurate measurement than the LD of the Higgs mass.
10348258
Studies of boosted decision trees for MiniBooNE particle identification
Boosted decision trees are applied to particle identification in the MiniBooNE experiment operated at Fermi National Accelerator Laboratory (Fermilab) for neutrino oscillations. Numerous attempts are made to tune the boosted decision trees, to compare performance of various boosting algorithms, and to select input variables for optimal performance.
14942523
Studies of stability and robustness for artificial neural networks and boosted decision trees
In this paper, we compare the performance, stability and robustness of Artificial Neural Networks (ANN) and Boosted Decision Trees (BDT) using MiniBooNE Monte Carlo samples. These methods attempt to classify events given a number of identification variables. The BDT algorithm has been discussed by us in previous publications. Testing is done in this paper by smearing and shifting the input variables of testing samples. Based on these studies, BDT has better particle identification performance than ANN. The degradation of the classifications obtained by shifting or smearing variables of testing results is smaller for BDT than for ANN.
17081750
String Field Theory and Tachyon Dynamics
In this thesis we present some works done during my doctoral studies. These results focus on two directions. The first one is motivated by tachyon dynamics in open string theory. We calculate the stress tensors for the p-adic string model and for the pure tachyonic sector of open string field theory (OSFT). We give the energy density of lump solutions and attempt to evaluate the evolution of the pressure in rolling tachyon solutions. We discuss the relevance of the pressure calculation for the identification of the large time solution with a gas of closed strings. In the second direction, we give some results in closed string field theory (CSFT). We considered marginal deformations in CSFT. The marginal parameter, called a, is that associated with the dimension-zero primary operator cWcX&X. We use this marginal operator to test the quartic structure of CSFT and the feasibility of level expansion. We check the vanishing of the effective potential for a. In the level expansion the quartic terms generated by the cubic interactions must be cancelled by the elementary quartic interaction of four marginal operators. We confirm this prediction, thus giving evidence that the sign, normalization, and region of integration Vo, 4 for the quartic vertex are all correct. This is the first calculation of an elementary quartic amplitude for which there is an expectation that can be checked. We also extend the calculation to the case of the four marginal operators associated with two space coordinates. We then try to search a critical point of the tachyon potential in CSFT. We include the tachyon, the dilaton, and massive fields in the computation. Some evidence is found for the existence of a closed string tachyon vacuum. It seems that this critical point becomes more shallow when higher level contributions are considered. We also relate fields in the sigma model and those in CSFT. Moreover, large dilaton deformations are studied numerically. Finally, we use the low-energy effective field equations that couple gravity, the dilaton, and the bulk closed string tachyon to study the end result of the physical decay process associated with the instability of closed string tachyon. We establish that whenever the tachyon induces the rolling process, the Einstein metric undergoes collapse while the dilaton rolls to strong coupling. Some more general potentials and the possible cosmological application are discussed. Thesis Supervisor: Barton Zwiebach Title: Professor of Physics
18014891
Twisted bundles on noncommutative T4 and D-brane bound states
We construct twisted quantum bundles and adjoint sections on noncommutative $T^4$, and investigate relevant D-brane bound states with non-Abelian backgrounds. We also show that the noncommutative $T^4$ with non-Abelian backgrounds exhibits SO$(4,4|Z)$ duality and via this duality we get a Morita equivalent $T^4$ on which only D0-branes exist. For a reducible non-Abelian background, the moduli space of D-brane bound states in Type II string theory takes the form $\prod_a (T^4)^{q_a}/S_{q_a}$.
16912746
Towards an Efficient Prototype of a RPC Detector Readout System for the Daya Bay Neutrino Experiment
The Daya Bay RPC (Resistive Plate Chamber) readout system is responsible for collecting event data created by muons entering the detector systems from above. The readout system should be capable of converting analog signals from the RPC detectors into digital signals, which are buffered and uploaded for readout by the online DAQ (Data Acquisition) system. The RPC readout system will report trigger information to a master trigger system. The numerous and relatively minute pulses from the RPC detectors require accurate signal discriminating and reliable data transmission. This article provides a brief overview of the Daya Bay RPC detector and then outlines the design and performance of the prototype RPC readout system.
18270173
Identified particle production in p + p and d +Au collisions at RHIC
The BRAHMS experiment at RHIC has measured the transverse momentum spectra of charged pions, kaons and (anti-)protons over a wide range of rapidity in d+Au and p+p collisions at √SNN = 200 GeV. The nuclear modification factor R dAu at forward rapidity shows a clear suppression for π + . The measured net-proton yields in p+p collisions are compared to PYTHIA and HIJING/B and seem to be better described by the latter.
855249
EXACT SEIBERG WITTEN MAP AND INDUCED GRAVITY FROM NONCOMMUTATIVITY
We find a closed form for Seiberg–Witten (SW) map between ordinary and noncommutative (NC) Dirac–Born–Infeld actions. We show that NC Maxwell action after the exact SW map can be regarded as ordinary Maxwell action coupling to a metric deformed by gauge fields. We also show that reversed procedure by inverse SW map lead to a similar interpretation in terms of induced NC geometry. This implies that noncommutativity in field theory can be interpreted as field-dependent fluctuations of spacetime geometry, which genuinely realizes an interesting idea recently observed by Rivelles.