14665617
Comment on "Chiral symmetry and the intrinsic structure of the nucleon"- by D.B.Leinweber,A.W.Thomas and R.D.Young
Some remarks are presented on a recent paper (Leinweber,Thomas and Young, Phys.Rev.Lett. 86, 5011, 2001). In particular a statement of the above paper on the fact that the ratio between the magnetic moments of proton and neutron should remain constant at -3/2, independent of the change of the quark mass is discussed on the basis of the general parameterization.
46402346
Field theory and the nonrelativistic quark model: A parametrization of the baryon magnetic moments and masses.
We show that the results of calculations of physical quantities (e.g., the magnetic moments and the masses) in a relativistic field theory can be parametrized in a way typical of the nonrelativistic quark model (NRQM). For a relativistic field theory that, as QCD, satisfies the two properties that (a) the electromagnetic current is carried only by the quarks and (b) flavor breaking is due only to the mass difference between the quarks, the most general expression of the magnetic moments of the baryon octet contains ten different types of terms and therefore ten parameters. If one neglects terms that break flavor at an order higher than the first, the ten terms reduce to seven and these are determined from the seven known magnetic moments. We find that (1) among the seven parameters determined by fitting exactly the data, the two parameters characteristic of the simplest NRQM description are indeed the largest ones (their values, in spite of the presence of five more parameters, are almost unchanged with respect to the NRQM), and (2) the {Sigma}{sup 0}{r arrow}{Lambda}{gamma} rate (to first order in flavor breaking) is related to the magnetic moments of the octet baryons; the prediction is consistent with themore » present data on the rate. For the masses, in the flavor-breaking approximation to first order, we obtain a five-parameter formula containing the Gell-Mann--Okubo relation of the octet and the two equal-spacing relations of the decuplet.« less
27222284
Relation of constituent quark models to QCD: Why several simple models work "so well"
We discuss the relationship between exact QCD and constituent quark models (nonrelativistic, bag, or others) to clarify why different models work reasonably in many cases. For this we use the general parametrization method [G. Morpurgo, Phys. Rev. D {bold 40}, 2997 (1989)] now expressed in terms of the standard current quark fields ({ital m}{sub {ital u}} and {ital m}{sub {ital d}} a few MeV; {ital m}{sub {ital s}}{approx_equal}150 MeV, at the usual mass renormalization point {ital q}=1 GeV). The method provides for several quantities the most general exact form of the spin-flavor structure derivable from the QCD Lagrangian. We can thus determine for many important quantities (masses of lowest baryons and mesons, baryon magnetic moments, semileptonic decays, etc.), from a fit to the data, the coefficients of the parametrization, the same ones that a direct QCD calculation, if feasible, would give. It turns out that only a few coefficients are relatively important. Because different models, each with its few free parameters, can produce these terms by some choice of parameters, one can see why models so different as the nonrelativistic or quasichiral models work {open_quote}{open_quote}well.{close_quote}{close_quote} Finally, expressing the coefficients in the general parametrization dimensionally in terms of current quark massesmore » and {Lambda}, we find that the {ital m}{sub {ital s}} expansion of broken SU(3){times}SU(3) is just an expansion in {Delta}{ital m}/({xi}{Lambda}){approx_equal}{ital m}{sub {ital s}}/({xi}{Lambda}){approx_equal}0.3. The {xi}{close_quote}s determined from different data are rather close (from 2.3 to 3.7). The resulting effective light quark masses in constituent models are of order ({xi}{Lambda}). None of the above conclusions depend on whether or not the chiral limit {ital m}{sub {ital u}},{ital m}{sub {ital d}},{ital m}{sub {ital s}}{r_arrow}0 is mathematically sound. {copyright} {ital 1996 The American Physical Society.}« less
43348861
Smallness of gluon coupling to constituent quarks in baryons and validity of nonrelativistic quark model.
A study of the parametrization of baryon masses and other quantities leads to a ratio {approx}1/5 for two-gluon-exchange versus one-gluon-exchange terms between two constituent quarks in a baryon. This fact (plus the factor 3 reduction from each additional order in flavor breaking) explains the success, to a part per thousand, of a new baryon mass formula (Phys. Rev. Lett. 68, 139 (1992)). It also explains why the results of SU(3) that neglect second-order flavor breaking (such as the Gell-Mann--Okubo baryon mass formula) work much better than expected. Finally the general parametrization, plus the above reduction factors, clarify why the naive'' nonrelativistic quark model (NRQM) is quantitatively fairly good. The reasons are twofold: (a) The structure of the general parametrization (an exact consequence of any QCD-like relativistic field theory) is similar to that of the NRQM; (b) the smallness of the gluon coupling and the reduction factor due to flavor imply that the additive (one-body) terms in the parametrization prevail on the two-body terms and the latter on the three-body ones, the typical feature of the naive'' NRQM.
26628556
Electromagnetic mass differences of the octet and decuplet baryons.
The general parametrization method (Phys. Rev. D 40, 2997 (1989)), an exact consequence of any QCD-like relativistic field theory, is used to parametrize the electromagnetic mass differences of the baryons. First we show that the Coleman-Glashow relationship, derived neglecting flavor breaking, continues to hold if all flavor-breaking terms are kept, except the three-quark ones; this may explain why the formula agrees so well with the data. In addition, neglecting only three-quark terms, we reproduce some equalities between electromagnetic mass differences of {bold 8} and 1{bold 0} baryons derived a long time ago (A. Gal and F. Scheck, Nucl. Phys. B2, 110 (1967)) by the nonrelativistic quark model (NRQM). Also these equalities, now testable due to the improved knowledge of decuplet masses, are well satisfied; they now appear as a general consequence of a relativistic QCD-like field theory, not just of the NRQM.
35083522
Field theory and the nonrelativistic quark model: A parametrization of the meson masses.
We apply the method developed in previous papers (Phys. Rev. D 40, 2997 (1989); 40, 3111 (1989)) to write a general parametrization of the masses of the lowest meson nonets. We compare the mass formulas obtained in this way with those used currently in a nonrelativistic quark model (NRQM). As in the previous work, the aim is to separate the features specific to the NRQM from those that follow from a relativistic field theory satisfying a few rather general conditions (satisfied by QCD). For the meson masses it turns out that the formulas obtained from field theory have essentially the same structure and number of parameters as those in the NRQM. This explains the good fit that the NRQM provides in this case; the internal {ital v}/{ital c} of the {ital q{bar q}} pair is irrelevant. As a by- product, the mixing angle for the {ital I}=0 mesons (e.g., {eta} and {eta}{prime}) predicted from the masses turns out to be model independent to first order in flavor breaking. We discuss the question of the linear versus quadratic or, say, square-root mixing angles.
36021315
The detector safety system for LHC experiments
The Detector Safety System (DSS), currently being developed at CERN under the auspices of the Joint Controls Project (JCOP), will be responsible for assuring the protection of equipment for the four Large Hadron Collider (LHC) experiments. Thus, the DSS will require a high degree of both availability and reliability. After evaluation of various possible solutions, a prototype is being built based on a redundant Siemens PLC front-end, to which the safety-critical part of the DSS task is delegated. This is then supervised by a PVSS SCADA system via an OPC server. The PLC front-end is capable of running autonomously and of automatically taking predefined protective actions whenever required. The supervisory layer provides the operator with a status display and with limited online reconfiguration capabilities. Configuration of the code running in the PLCs will be completely data driven via the contents of a "configuration database." Thus, the DSS can easily adapt to the different and constantly evolving requirements of the LHC experiments during their construction, commissioning, and exploitation phases.
55438680
THE ELECTRICAL CIRCUIT DESCRIPTION FOR THE LHC
The LHC is a very complex machine, made of about 8000 superconducting magnets along a circumference of 26.7 km. The magnets are powered in about 1700 different electrical circuits with currents ranging from 60 A (for small corrector magnets) up to 13 kA for the main dipoles and quadrupoles. The layout of the powering system reflects the complexity of the accelerator. About 80000 high current connections will have to be made. A minor fault in a circuit or one of the superconducting connections would have severe consequences for accelerator operation. For the integration of the electrical equipment, for supporting the assembly and verifying the correctness of the electrical circuits, all relevant information should be included in one coherent database. A simple method for the description of the electrical circuits is proposed, while an associated tool is translating this input into database information and back, checking the circuit description at the same time for inconsistencies. Out of the database information, electrical drawings and detailed views of the electrical connections at every LHC interconnection point can be recreated. This paper describes the approach and outlines several possible applications.
20972059
Measurements of impedance distributions and instability thresholds in LEP
The distribution of reactive and resistive components of the transverse impedance around the circumference of LEP has been obtained by exciting the beam and measuring the variations of phase advance and of closed orbit displacements with beam current. Tune shifts with current and instability thresholds were determined for two machine lattices with different beta functions and momentum compaction for various values of bunch length and synchrotron frequency. These measurements are particularly interesting for LEP2, which will require larger bunch currents to achieve the design luminosity.
56290660
The Software for the CERN Detector Safety System
The CERN Detector Safety System (DSS) has been developed to monitor the state of the LHC detectors and protect their components against emer gency situations which other less reliable systems could possibly fail to handle, or which were not co vered by any other system. The DSS consists of two main components: a PLC-based Front-End and a supervisor Back-End. The two parts communicate via the OPC mechanism. The Front-End is the core of the DSS, to which all the runtime safety-critical actions are delegated. These are encoded in an "Alarm-Action Matrix", that can be seen as a set of user-defined rules relating the Input Channels (analogue and digital senso rs) to the Output Channels (actuators, typically on/off interlock switches). One of the user requireme nts is the possibility of modifying these rules at any time, without stopping the system. New Input and Output Channels can also be incrementally added to the system without perturbing the prev iously existing part. To fulfil these requirements without detriment to the safety-critical part, the PLC software has been designed in a completely datadriven way. This approach allowed the PLC code to be kept as simple as possible and independent from the user-defined rules. The rules, as well as the parameteri zation for the Input and Output Channels, are stored into PLC "datablocks", whose contents drive the execution of the PLC code. The supervisor Back-End, based on the CERN-chosen PVSS SCADA system, represents both the “Configuration Interface” and the “Operator Display” for the DSS. The User is able to define and parameterize Input and Output Channels and to modify the set of rules defining the Alarm-Action Matrix. These modifications, after passing some c onsistency checks, are accepted by the Back-End, permanently stored in PVSS "datapoints", and finally mirrored into the PLC datablocks via the OPC mechanism. In addition to this, the Back-End is constantly informed, again through OPC, of any changes in the status of the monitored system . The Back-End then displays all the relevant information to the User, both via an alarm screen and via an interactive synoptic system. This paper describes in greater details some of the ideas behind the design and the implementation of this system.
5752960
THE CERN DETECTOR SAFETY SYSTEM FOR THE LHC EXPERIMENTS
The Detector Safety System (DSS), developed at CERN in common for the four LHC experiments under the auspices of the Joint Controls Project (JCOP), will be responsible for assuring the equipment protection for these experiments. Therefore, the DSS requires a high degree of both availability and reliability. It is composed of a Front-end and a Back-end part. The Front-end is based on a redundant Siemens PLC, to which the safetycritical part of the DSS task is delegated. The PLC Frontend is capable of running autonomously and of automatically taking predefined protective actions whenever required. It is supervised and configured by the CERN-chosen PVSS SCADA system via a Siemens OPC server. The supervisory layer provides the operator with a status display and with limited online reconfiguration capabilities. Configuration of the code running in the PLCs is completely data driven via the contents of a “Configuration Database”. Thus, the DSS can easily adapt to the different and constantly evolving requirements of the LHC experiments during their construction, commissioning and exploitation phases. Currently, the DSS is being installed and commissioned for the construction of the CMS and LHCb experiments.