118954339
Variable VHE gamma-ray emission from Markarian 501
The blazar Markarian 501 (Mrk 501) was observed at energies above 0.10 TeV with the MAGIC telescope from May through July 2005. The high sensitivity of the instrument enabled the determination of the flux and spectrum of the source on a night-by-night basis. Throughout our observational campaign, the flux from Mrk 501 was found to vary by an order of magnitude. Intra-night flux variability with flux-doubling times down to 2 minutes was observed during the two most active nights, namely June 30 and July 9. These are the fastest flux variations ever observed in Mrk 501. The ~20-minute long flare of July 9 showed an indication of a 4 +/- 1 min time delay between the peaks of F(<0.25 TeV) and F(>1.2 TeV), which may indicate a progressive acceleration of electrons in the emitting plasma blob. The flux variability was quantified for several energy ranges, and found to increase with the energy of the gamma-ray photons. The spectra hardened significantly with increasing flux, and during the two most active nights, a spectral peak was clearly detected at 0.43 +/- 0.06 TeV and 0.25 +/- 0.07 TeV, respectively for June 30 and July 9. There is no evidence of such spectral feature for the other nights at energies down to 0.10 TeV, thus suggesting that the spectral peak is correlated with the source luminosity. These observed characteristics could be accommodated in a Synchrotron-Self-Compton (SSC) framework in which the increase in gamma-ray flux is produced by a freshly injected (high energy) electron population.
16174766
Detection of VHE radiation from the BL Lac PG 1553+113 with the MAGIC telescope
In 2005 and 2006, the MAGIC telescope has observed very high energy gamma-ray emission from the distant BL Lac object PG 1553+113. The overall significance of the signal is 8.8 σ for 18.8 h observation time. The light curve shows no significant flux variations on a daily time-scale, the flux level during 2005 was, however, significantly higher compared to 2006. The differential energy spectrum between ∼ 90 GeV and 500 GeV is well described by a power law with photon index Γ = 4.2 ± 0.3. The combined 2005 and 2006 energy spectrum provides an upper limit of z = 0.74 on the redshift of the object. Subject headings: PG 1553+113, BL Lac, AGN, VHE gamma-ray, imaging air Cherenkov telescope
107422776
The coming revolution in particle physics: Report of the Fermilab Long Range Planning Committee
In early 2003, the Fermilab Director formed a committee (Appendix A) to examine options for the long-range future of Fermilab. Specifically, the committee was asked to respond to a charge (Appendix B), which laid out the assumptions, which were to underlie our discussions. The committee met a few times during the spring of 2003 and formulated a plan of action. It identified a number of issues that deserved attention, and a subcommittee was formed to focus on each. We agreed that in addressing these key issues, a broader participation was appropriate. The manner in which that was achieved varied from subcommittee to subcommittee to group. In some cases the expanded membership participated in all the discussions, in others, particular presentations were solicited and heard. Some subgroups met regularly over several months, others convened only for a small number of discussions. We have attempted to list participants in Appendix C. General presentations indicating the purpose of the work were given, for example at the Fermilab Users Annual Meeting. Towards the end of the summer some sense of direction developed and a series of open meetings was organized by the different subgroups. These meetings of two and more hour's duration gave the broader laboratory and user community a further chance to react to perceived directions and to make their opinions known. They were extremely well attended. In all, nearly 100 people have participated in the process including the development of initial drafts and proto-recommendations. A larger number attended the various open sessions. It is therefore likely, even expected, that the general thrusts of this report are no surprise. Nevertheless, the committee met in a number of plenary closed sessions including a two-day retreat in which all the issues were discussed and a common view was developed. The Director and Deputy Director heard and interacted with the discussions in most of these meetings. In attempting to converge, we have written the individual chapters from a slightly advocative point of view. In the final discussions and editing, we have attempted some damping. Nevertheless, if all recommendations were accepted, all positive options pursued, any reasonable budget would be exceeded. We have balanced this bottom up approach with a top down development. We tried to extract the essence and to provide a couple of balanced options based on the discussions at the retreat. Healthy, lively, and vigorous exchanges ensued which resulted in multiple rewrites and culminated in the Executive Summary for this document. It is there that you should find the most concise product of this process. In preparing the report, we did consider the potential availability of resources. We have devoted a chapter of the report to discuss the limitations of our efforts. It should be recognized that there are large variances among the public opinions about costs of large elements of the program such as the Linear Collider, or even the Proton Driver. The evolution of the laboratory budget is also very uncertain and depends on many things such as the success in physics terms of the current program. We have therefore taken a relatively optimistic point of view in achieving balance. It is in this sense that the report provides options. At any point in time, the Fermilab Director will need to make choices among the options; we hope that the broad thrusts, which we call out, will be helpful. In the remainder of the report we use chapter 2 to describe the Physics Landscape 2010-2020, which is the basis for what we would like to see happen. In chapter 3 we discuss the Linear Collider, which will be a major component of the laboratory program under any scenario and, if constructed nearby, a dominant one. In chapter 4 we describe a vigorous but evolutionary program to address the key neutrino physics areas, and in chapter 5 we discuss attractive initiatives, which would provide the necessary powerful source of protons and, hence, neutrinos for this program. A strong participation in the machine, the experiment (CMS), and the physics at the Large Hadron Collider is a constant for our deliberations and is discussed in chapter 6. Astroparticlephysics, which was introduced to the Laboratory twenty years ago, continues to develop and its growth is discussed in chapter 7. Accelerator research and development, the underpinning of our science core is addressed in chapter 8, and its sister discipline, detector research and development, is covered in chapter 9. In chapter 10 we examine the interdisciplinary science close to our field, which encircles our laboratory. In chapter 11 we outline some of the resource issues and the extent to which they were addressed before we present the conclusions.
115883664
Time-of-flight measurement in the DZero Central Fiber Tracker
We continue evaluation of the new electronics developed for the Central Fiber Tracker and Preshower detectors. With the custom TriP chip and MCM II we have measured the position of the hits along the fiber by comparing the time of arrival of the photons at the VLPC with the expected timing relative to the beam. The measured rms resolution at the center of the fibers is 46cm for hits with more than 8 photo-electrons and is dominated by the statistics of photon arrival time. The corresponding resolution near the ends of the fibers (where more photoelectrons are collected) is calculated to be of order 27cm. With a second submission of the TriP chip to add the time-of-flight measuring capability we will effectively double the number of channels in the central fiber tracker. This capability will increase the maximum luminosity at which D0 can do tracking from {approx} 100 {center_dot} 10{sup 30}cm{sup -2}s{sup -1} to {approx} 200 {center_dot} 10{sup 30} cm{sup -2}s{sup -1} (at a bench mark tracking specification). The cost of replacing the electronics is of order $500K and the necessary lead time is 1.5 years.