arXiv subjects
Publications and source records attributed to D. J. Summers.
One often wishes to quickly add a few overlined characters such as anti-B0 or anti-neutrino to a Microsoft Word document. Underlined characters are straightforward but overlined characters require equation editor which makes small picture files. The font here allows one to directly add overlined English and the most used overlined Greek characters to Microsoft Word documents on Apple Macintosh computers.
The first acceleration stage for this muon collider scenario includes twenty passes through a single two GeV Linac. Teardrop shaped arcs of 1.8 Tesla fixed field magnets are used at each end of the Linac. This dogbone geometry minimizes muon decay losses because muons pass through shorter arcs when their gamma boost is low. Two 2200 meter radius hybrid rings of fixed superconducting magnets and iron magnets ramping at 200 Hz and 330 Hz are used as part of the second stage of muon acceleration. Muons are given 25 GeV of RF energy per orbit. Acceleration is from 250 GeV/c to 2400 GeV/c and requires a total of 86 orbits in both rings; 82% of the muons survive. The total power consumption of the iron dipoles is 4 megawatts. Stranded copper conductors and thin magnetic laminations are used to reduce power losses.
Two 2200m radius hybrid rings of fixed superconducting magnets and iron magnets ramping at 200 Hz and 330 Hz are used to accelerate muons. Muons are given 25 GeV of RF energy per orbit. Acceleration is from 250 GeV/c to 2400 GeV/c and requires a total of 86 orbits in both rings; 82% of the muons survive. The total power consumption of the iron dipoles is 4 megawatts. Stranded copper conductors and thin Metglas laminations are used to reduce power losses.
Limits at the 10**-4 level are reported for rare and forbidden decays of the D0 charm meson to a pair of leptons and either a vector meson or two pseudoscalar mesons. Of these searches, 18 are investigations of decays without previous published results; several others have significantly improved sensitivity over previous results.
E769 has just recorded on tape the interactions of 500 million pions, kaons, and protons. A Cerenkov counter and a TRD were used to tag beam particle types in both positive and negative 250 GeV/c hadron beams. Thin foil Be, Al, Cu, and W targets were used with a spectrometer including silicon microstrips to look for charm decay vertices. Preliminary results show D0 --> K- pi+ and D+ --> K- pi+ pi+ mass peaks. As the event reconstruction progresses on numerous parallel microprocessors, we intend to explore the pT, xF, A, and flavor dependence of the production of charmed mesons and baryons.
We report the results of a blind search for flavor-changing neutral current, lepton-flavor violating, and lepton-number violating decays of D+, D(s)+, and D0 mesons (and their antiparticles) into modes containing muons and electrons. Using data from Fermilab charm hadroproduction experiment E791, we examine the pi l l and K l l decay modes of D+ and D(s)+ and the l+ l- decay modes of D0. No evidence for any of these decays is found. Therefore, we present branching-fraction upper limits at 90% confidence level for the 24 decay modes examined. Eight of these modes have no previously reported limits, and fourteen are reported with significant improvements over previously published results.
Experiment 791 at Fermilab's Tagged Photon Laboratory has just accumulated a high statistics charm sample by recording 20 billion events on 24000 8mm tapes. A 500 GeV/c pi- beam was used with a fixed target and a magnetic spectrometer which now includes 23 silicon fixed target and a magnetic spectrometer which now includes 23 silicon microstrip planes for vertex reconstruction. A new data acquisition system read out 9000 events/sec during the part of the Tevatron cycle that delivered beam. Digitization and readout took 50 uS per event. Data was buffered in eight large FIFO memories to allow continuous event building and continuous tape writing to a wall of 42 Exabytes at 9.6 MB/sec. The 50 terabytes of data buffered to tape is now being filtered on RISC CPUs. Preliminary results show D0 --> K- pi+ and D+ --> K- pi+ pi+ decays. Rarer decays will be pursued.
We have integrated a system of 16 RISC CPUs to help reconstruct and analyze a 1.3 Terabyte data set of 400 million high energy physics interactions. These new CPUs provided an affordable means of processing a very large data set. The data was generated using a hadron beam and a fixed target at Fermilab Experiment 769. Signals were recorded on tape from particles created in or decaying near the target and passing though a magnetic spectrometer. Because all the interactions were independent, each CPU could completely reconstruct any interaction without reference to other CPUs. Problems of this sort are ideal for multiple processors. In the offline reconstuction system, we used Exabyte 8mm video tape drives with an I/O capacity of 7 Terabytes per year and a storage capacity of 2.3 Gigabytes per tape. This reduced tape mounts to one or two per day rather than one or two per hour as would be the case with 9-track tapes. The ETHERNET network used to link the CPUs and has an I/O capacity of 15 Terabytes per year. The RISC CPUs came in the form of commercially supported workstations with little memory and no graphics to minimize cost. Each 25 MHz MIPS R3000 RISC CPU processed data 20 times faster than 16MHz Motorola 68020 CPUs that were also used. About 8000 hours of processing was needed to reconstruct the data set. A sample of thousands of fully reconstructed particles containing a charm quark has been produced.
To collect data for the study of charm particle decays, we built a high speed data acquisition system for use with the E791 magnetic spectrometer at Fermilab. The DA system read out 24000 channels in 50 uS. Events were accepted at the rate of 9000 per second. Eight large FIFOs were used to buffer event segments, which were then compressed and formatted by 54 processors housed in 6 VME crates. Data was written continuously to 42 Exabyte tape drives at the rate of 9.6 Mb/s. During the 1991 fixed target run at Fermilab, 20 billion physics events were recorded on 24000 8 mm tapes; this 50 Tb (Terabyte) data set is now being analyzed.
We introduce a variable useful for measuring masses of particles pair produced at hadron colliders, where each particle decays to one particle that is directly observable and another particle whose existence can only be inferred from missing transverse momenta. This variable is closely related to the transverse mass variable commonly used for measuring the $W$ mass at hadron colliders, and like the transverse mass our variable extracts masses in a reasonably model independent way. Without considering either backgrounds or measurement errors we consider how our variable would perform measuring the mass of selectrons in a mSUGRA SUSY model at the LHC.
We motivate the study of ``Minijets'' (that is jets soft with respect to the hard scattering, but hard with respect to Λ_QCD) as a means to study the underlying QCD colour flow in events. We discuss, with the aid of a simplistic model, currently available events in which minijets are observed, that is the events have high multiplicity, as a means of understanding the physics of minijets. We encourage both theoreticians and experiments to continue the study of minijets.
We compute the W transverse momentum distribution at large transverse momentum at fixed next-to-leading order (i.e. O(alpha_s^2) and find good agreement with the preliminary measurements reported by D0. We find that the W transverse momentum distribution is typically significantly larger than the exclusive one-jet rate for a given value of p_T^W or E_T^jet, mainly because two or more jet events are excluded. As a consequence, we find that theoretically the W+1 jet to W+0 jet ratio R^10 is smaller than the analogous quantity defined in terms of p_T^W, R^W. This hierarchy is preserved under changes of renormalisation/factorisation scales, strong coupling constant and jet algorithm. However, this appears to be in contradiction with the preliminary experimental results which suggest R^10 > R^W.
We present asymmetries between the production of D+ and D- mesons in Fermilab experiment E791 as a function of xF and pt**2. The data used here consist of 74,000 fully-reconstructed charmed mesons produced by a 500 GeV/c pi- beam on C and Pt foils. The measurements are compared to results of models which predict differences between the production of heavy-quark mesons that have a light quark in common with the beam (leading particles) and those that do not (non-leading particles). While the default models do not agree with our data, we can reach agreement with one of them, PYTHIA, by making a limited number of changes to parameters used.
We calculate decays of a Standard Model Higgs boson to a virtual massive particle and discuss how this depends on the massive particle total width. If the partial width of Higgs to a virtual massive particle can be measured this gives a measurement of that massive particle's width. We discuss how one would go about measuring these partial widths of a Higgs experimentally, and how this could lead to a measurement of the $W$ boson and $t$ quark width. For the latter extreme dependence on the Higgs mass and the small $H\to tt^*$ branching ratios mean that little can be learnt about the $t$ quark width. For the former there is also large dependence on the Higgs mass; however this can be removed by taking the ratio of $H\to WW^*$ decays to $H\to ZZ^*$ decays. This ratio also has the advantage of being fairly insensitive to physics beyond the Standard Model. Unfortunately, for Higgs masses of interest the $H\to ZZ^*$ branching ratio is small enough that we require many 1000's of tagged Higgs decays before an accurate measurement of the $W$ width can be made. This is likely to be hard experimentally.
We present a simple method of removing the singularities associated with soft photon emission to all orders in perturbation theory through exponentiation, while keeping a consistent description of hard photon emission. We apply this method to the process e+ e- --> mu+ mu- + n photons where we include both Z^0 and photon exchange and retain the muon mass dependence. The photonic radiation is allowed to be radiated off any charged leg, and so we include all initial and final state radiation, as well as all interference effects. The effect of exponentiation is to suppress soft photon emission over the cross-section you would obtain from working at strictly leading order. We also show how one would extend the method to treat the collinear singularity; and remove the associated leading mass logarithms.