Cross Sections

Cross Sections DEPARTMENT OF PHYSICS AND ASTRONOMY UNIVERSITY OF ROCHESTER WINTER 2002 Diagram credit: Fermilab Physics and Astronomy • WINTER 2002 Message from the Chair —Arie Bodek Over the years we have given high tradition that Len established at Roch- Because of the great success of last priority to the training of our under- ester in this area of physics. year’s sesquicentennial celebration, the graduate and graduate students. This We wish to take this opportunity to University has initiated a new tradition attention has not gone unnoticed and thank all our alumni who have contrib- of hosting a Meliora has just been recognized in a nation- uted generously to the support of the Weekend reunion every wide survey of U.S. graduate students department. By completing the form on year. The theme this conducted in 2001. The Department of the last page of our newsletter, or by past fall was Freedom. Physics and Astronomy at Rochester was responding to our recent appeal for Several of our alumni ranked second nationwide in overall assistance, you can continue (or begin) attended and visited the graduate-student satisfaction. that tradition of giving that will assure department during our After an exhaustive search, it is a the future excellence of the department. open-house festivities. pleasure to report our success in the Other ways to help our cause is to We encourage all our alumni and friends recent recruitment of Alice Quillen, our inform any promising students about to continue this tradition, come for the newest faculty member, who is an our summer undergraduate research weekend, and visit us during Meliora experimenter in astrophysics. She has program (REU), and to encourage stu- Weekend (or anytime!). just joined our astrophysics group as dents interested in careers in physics to Several of our faculty and students assistant professor of physics and as- apply for graduate study at Rochester. have received awards during this past tronomy and will be on campus starting All application material for these pro- academic year. Among the faculty, Kevin January 2002. grams is available on our Web pages McFarland was named a Cottrell Scholar The department suffered a major loss (www.pas.rochester.edu). If you know of by the Research Corporation of America, this past year with the passing of Len any exceptional undergraduates whom and five faculty were elected Fellows of Mandel, one of the world’s leading ex- we should consider either for our REU the American Physical Society. Among perts in the field of quantum optics. Len program or for graduate school, we our students, graduate student Un Ki was an admired teacher and a brilliant would appreciate it if you would please Yang received an award from the Amer- experimenter, and was elected posthu- send their names and e-mail addresses ican Korean Physics Association, Michael mously to the National Academy of Sci- to Barbara Warren ([email protected]. Fitch was awarded the 2001 URA/ ence. A search is currently under way edu), and we will contact them directly. Fermilab award for best Ph.D. thesis, and for a new faculty member in experimental Any help from our alumni along these undergraduate Albert Wang was named quantum optics to continue the strong lines would be welcomed. a finalist for the APS 2001 Apker award. Cross Sections On the Cover Editors: Eric Blackman and Ashok Das The diagram on the cover illustrates a The reason is that the Standard Model Published by the Department of Physics and As- remarkable recent result in high-energy of particle physics has been so successful tronomy of the University of Rochester, and distrib- particle physics from Fermilab’s NuTev in so many ways that any such “appar- uted to alumni and friends free of charge. Copies collaboration. The analysis, led by Roch- ent” disagreements are unusual. Is there may be obtained by writing to CROSS SECTIONS, ester’s Kevin McFarland, suggests that a previously unrecognized problem with Department of Physics and Astronomy, University Neutrinos simply do not behave as ex- our understanding of the theory, or per- of Rochester, P.O. Box 270171, Rochester, NY pected. The vertical axis gives the extent haps more likely, is there an as yet un- 14627-0171. to which the combined electroweak force seen particle? The story is discussed behaves as a mixture of the electromag- further on page 5. Important notices: Area code for Rochester netic force (parity conserving) and the The Department of Physics and has changed to 585. Department phone: (585) weak force (parity violating). The dis- Astronomy and its alumni continue to 275-4351 and fax: (585) 275-8527. crepancy between theory, results for lead cutting-edge research efforts across If you change your mailing address, please other particles, and the NuTev neutrino a broad range of fields. Other examples contact Bob Knox with your new whereabouts findings has surprised many in the of such endeavors are also presented in ([email protected]). Also let him know high-energy physics community and has the science highlights section. your current e-mail address. received widespread public attention. 2 SCIENCE HIGHLIGHTS Physics and Astronomy • WINTER 2002 New Power from Fractal Mathematics: Predicting Extremes Graduate student Subhadip Raychaud- is by measuring the height of a roomful huri, undergraduate Corry Przybyla, pro- of people. Although the tallest person in fessor Yonathan Shapir, and mathematics the world probably isn’t in the room, professor Michael Cranston continue to extreme-value statistics offers a way to demonstrate the power of fractal math estimate how tall that tallest person is for modeling physical systems. Most re- likely to be. Again the key is the idea of cently, the group has been able to formu- fractal scaling, across both space and late a prediction for when a single point time. A pattern that can be scaled is one on a surface will erode to a critical depth. that has the same shape no matter how [Raychaudhuri, Cranston, Przybyla, close you may “zoom in” on it. The basic Shapir, PRL 87, 136101 (2001)]. Predict- pattern repeats on any scale at which The next step in the research was to ing when the lowest point in a surface you view. Fractals display infinite scal- model the growth or erosion process will erode to a critical depth or when the ing. Likewise, when a surface grows or backward in time to determine what a highest point will build up to a critical is eroded, its overall pattern repeats small section of the surface originally height is challenging. The group has used with time. Consequently, a magnified looked like, by studying the way the “extreme-value statistics” to determine piece of the surface will look just like whole surface wound up. With input the probability of extreme events, such the whole surface after a long period of from Michael Cranston, the team was as to forecast severe weather conditions erosion or accumulation. able to generalize the way the extreme or predict floods. “This is the first time The team visualized how the roughness points wound up by solving a mathemat- we’ve had a way to predict how these of a surface changed as it wore away— ical model that should work for other extreme points grow based on nothing by an acid, for instance—or accumulated, fractal surfaces. more than the roughness of the surface such as inside a battery. They concluded Subhadip and Corry then ran com- they’re on,” says Yonathan. An extreme that the extreme point of a section puter simulations of different growth point could be the deepest point of rust changed in a nonlinear way with the and erosion processes thousands of in a steel girder or the highest point of roughness. The section could then be times to gather enough statistics for the metal accumulation inside a battery that scaled to the whole of the surface af- extreme points. Their results confirmed leads to a short. Understanding such fected by the corrosion or accumulation. the fractal-based predictions. issues can lead to better designs of In essence, the height of the tallest per- Yonathan emphasizes that the power material and more reliable devices. son in the world could be extrapolated of the widely applicable technique is its The process is akin to trying to find by scaling up the relationship between ability to determine when an extreme how tall the tallest person in the world the average and the tallest to account point will hit a critical height with much for the world’s population. more accuracy than just trial and error. Evidence Found for Spinning Black Hole University alumnus Todd Strohmayer J1655-40. During x-ray flares in 1996, (Ph.D. ’92) has found that a blinking x- a small percentage of the x-ray light, ray source near the center of the Milky within a narrow frequency range, turned Way has given the best evidence to date on and off about 450 times per second. that black holes spin [Strohmayer, ApJ Given that the mass of the presumed 552, L49 (2001)]. black hole is known from properties of Theorists are almost certain that black the binary system, the extremely rapid holes of stellar mass rotate because they variability could only come from ma- form during the collapse of a rotating terial orbiting very close to the black heavy star and conserve angular momen- hole. A maximally spinning black hole tum. But measuring the actual spin of a provides the smallest radius for the last black hole is tricky. stable orbit of material, and this is the Image credit: NASA Todd’s evidence comes from a phe- only consistent interpretation of the Drawing of inner region of accretion nomenon observed during two blasts of data.

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