118379671
The application of gauge invariance and canonical quantization to the internal structure of gauge field systems
It is unavoidable to deal with the quark and gluon momentum and angular momentum contributions to the nucleon momentum and spin in the study of nucleon internal structure. However, we never have the quark and gluon momentum, orbital angular momentum and gluon spin operators which satisfy both the gauge invariance and the canonical momentum and angular momentum commutation relation. The conflicts between the gauge invariance and canonical quantization requirement of these operators are discussed. A new set of quark and gluon momentum, orbital angular momentum and spin operators, which satisfy both the gauge invariance and canonical momentum and angular momentum commutation relation, are proposed. The key point to achieve such a proper decomposition is to separate the gauge field into the pure gauge and the gauge covariant parts. The same conflicts also exist in QED and quantum mechanics and have been solved in the same manner. The impacts of this new decomposition to the nucleon internal structure are discussed.
119391728
Quantum Version of Gauge Invariance and Nucleon Internal Structure
The conflict between cononical commutation relation and gauge invariance, which both the momentum and angular momentum of quark and gluon should satisfy, is clarified. The quantum version of gauge invariance is studied. The gauge independence of the matrix elements of quark momentum and angular momentum operators between physical states are proved. We suggest to use the canonical quark momentum and angular momentum distributions to describe the nucleon internal structure in order to establish an internal consistent description of hadron spectroscopy and hadron structure. The same problem for the atomic spectroscopy and structure is discussed.
121445421
Study of Topological Structure of Vacuum by Lattice QCD
Overlap fermions and improved 5Li cooling are compared, which exhibits that these two filter methods can produce similar structures. Then the overlap fermions and improved 5Li cooling are combined to calculate the topological charge and identify the structure of the vacuum. The results are consistent with instanton liquid model.
117634870
Some properties of pi meson in nuclear matter with finite density
In the GCM we study some properties of pi meson as the Goldstone bosons in a nuclear matter with finite density. Using the effective action in a nuclear matter, we calculate the decay constant and pi mass as functions of the chemical potential. The relation between the chemical potential and the density of a nuclear matter is firstly given here. We find that f(pi) and m(pi) monotonously decrease as nuclear matter density increases. The result is consistent with the usual assumption that the chiral symmetry is gradually restored as the density of a nuclear matter increases.
124731696
The effective gluon propagator in the global color symmetry model
It is shown that the effective gluon propagator in the global color symmetry model can be calculated in the instanton dilute liquid approximation. The calculated effective gluon propagator is consistent with the general command on the qualitative features of the gluon propagator, i.e., (i) the gluon propagator is significantly enhanced at small space-like k(2), and (ii) for k(2) > 1.5 GeV2 the perturbative results are quantitatively reliable.
123819304
QCD INTERACTION IN PION-DEUTERON ELASTIC-SCATTERING
The pion-deuteron elastic scattering matrix element is under consideration in the framework of QCD. The interactions including the perturbative effect and nonperturbative contributions of gluon condensate and quark condensate in the scattering process are discussed. The interaction operators are given.
118391627
Measurement of hadron composition in charged jets from pp collisions with the ALICE experiment
Abstract We report the first measurement of charged pion, kaon and (anti-)proton production in jets from hadron colliders. The measurement was carried out with the ALICE detector using 2 × 10 8 minimum bias pp collisions at a centre-of-mass energy of s = 7 TeV at the LHC. We present the π, K and p transverse momentum ( p T ) spectra, as well as the spectra of the reduced momentum ( z ch ≡ p T track / p T,jet ch ), in charged jets of p T between 5–20 GeV/c. The measurement is compared to Monte Carlo calculations.
120618992
Eigenvalue Distribution of Large $N$ Random Matrix--- A Direct Diagrammatic Proof to Marchenko-Pastur Law ---
In various theoretical models, large N limit has been a very useful tool, both at a qualitative and a quantitative level [1]. It works as a great approximation, even when the actual dimension of the matrix is not a very large number, such as Nc = 3 in QCD [2, 3] and Nf = 3 in neutrino anarchy [4]. It is thus useful to understand the behavior of large N random matrices as much as possible. In random matrix theory, there is a powerful law— Marchenko-Pastur (MP) law [5]—that governs the asymptotic eigenvalue distribution of large-dimension random matrices. In this paper we provide an alternative proof to it. We first state Marchenko Pastur law in Section II. Then in Section III, we present a detailed proof of MP law using Feynman diagrams. We extend our proof to symmetric matrix case in Section IV. Section V is our conclusion.
119681467
Exploring the performance limits of the ALICE Time Projection Chamber and Transition Radiation Detector for measuring identified hadron production at the LHC
The Time Projection Chamber (TPC) and Transition Radiation Detector (TRD) are the 
main tracking and particle identification devices in the ALICE experiment at the CERN 
LHC. This thesis studies aspects of their performance beyond the original designs. This 
includes extending the TPC momentum measurement for cosmic rays to sub-TeV scale, 
investigating a robust identification method for electrons and hadrons by the TRD, and 
developing new approaches to characterize the TPC and TRD signals. These studies lead 
to an intriguing observation of the transition radiation from sub-TeV cosmic muons, and 
a universal method -- the TPC coherent fit -- to extract yields of different particle species 
with momentum from 0.5 to above 20 GeV/c. 
 
With the TPC coherent fit, transverse momentum spectra (0.6 < pt < 20 GeV/c) of pions, 
kaons and protons at mid-rapidity (|y|<~0.8) in pp collisions at sqrt(s) = 2.76 and 7 TeV and 
Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV at the LHC are measured. In this unified approach 
both the anomalous enhancement of the proton-to-pion ratio at moderate pt (2-8 GeV/c) 
(the so-called baryon anomaly) and the nuclear modification of particle yields up to 
high pt (> 10 GeV/c) in Pb-Pb collisions are observed. The particle production is also 
studied in jets from pp collisions at 7 TeV and the results are well described by Perugia-0 
tune of PYTHIA6.
195751286
The HERMES Recoil Detector : Particle Identification and Determination of Detector Efficiency of the Scintillating Fiber Tracker
HERMES is a fixed target experiment using the HERA 27.6 GeV polarized electron/positron beams. With the polarized beams and its gas targets, which can be highly polarized, HERMES is dedicated to study the nucleon spin structure. One of its current physics programs is to measure deeply virtual Compton scattering (DVCS). In order to detect the recoiling proton the Recoil Detector was installed in the target region in the winter of 2005, taking data until the HERA-shutdown in the summer of 2007. The Recoil Detector measured energy loss of the traversing particles with its sub-detectors, including the silicon strip detector and the scintillating fiber tracker. This enables particle identification for protons and pions. In this work a systematic particle identification procedure is developed, whose performance is quantified. Another aspect of this work is the determination of the detector efficiency of the scintillating fiber tracker. Kurzfassung HERMES ist ein Fixed-Target-Experiment zur Untersuchung des Nukleonenspins. Der 27.6 GeV polarisierter Elektron-/Positron-Strahl von HERA wurde auf das hoch polarisierbare Gastarget geleitet. Eines der aktuellen Physikprogramme bei HERMES ist die Messung der tief virtuellen Compton-Streuung (DVCS). Um das rückgestreute Proton nachzuweisen wurde im Winter 2005 der Recoil-Detektor um das Target installiert, der bis zum HERA-Shutdown im Sommer 2007 Daten genommen hat. Der Recoil-Detektor maß den Energieverlust der durchgehenden Teilchen mittels eines Silizium-Streifen-Detektors und eines Trackers aus szintillierenden Fasern. Er ermöglicht so eine Teilchenidentifizierung für Protonen und Pionen. In dieser Arbeit wurde ein systematisches Teilchenidentifizierungsverfahren entwickelt, dessen Leistung quantitativ beschrieben wird. Ein anderer Aspekt dieser Arbeit ist die Bestimmung der Detektoreffizienz des Szintillierenden-Fasern-Trackers.
119116044
Energy loss signals in the ALICETRD
Abstract We present the energy loss measurements with the ALICE TRD in the β γ range 1–10 4 , where β = v / c and γ = 1 / 1 − β 2 . The measurements are conducted in three different scenarios: (1)with pions and electrons from testbeams; (2)with protons, pions and electrons in proton–proton collisions at center-of-mass energy 7 TeV; (3)with muons detected in ALICE cosmic runs. In the testbeam and cosmic ray measurements, ionization energy loss (d E /d x ) signal as well as ionization energy loss plus transition radiation (d E /d x +TR) signal are measured. With cosmic muons the onset of TR is observed. Signals from TeV cosmic muons are consistent with those from GeV electrons in the other measurements. Numerical descriptions of the signal spectra and the β γ - dependence of the most probable signals are also presented.