New degrees of freedom can be optimized in mask shapes when the source is also adjustable, because required image symmetries can be provided by the source rather than the collected wavefront. The optimized mask will often consist of novel sets of shapes that are quite different in layout from the target IC patterns. This implies that the optimization algorithm should have good global convergence properties, since the target patterns may not be a suitable starting solution. We have developed an algorithm that can optimize mask and source without using a starting design. Examples are shown where the process window obtained is between 2 and 6 times larger than that achieved with standard RET methods. The optimized masks require phase shift, but no trim mask is used. Thus far we have only optimized 2D patterns over small fields (periodicities of 1im or less). We also discuss mask optimization with fixed source, source optimization with fixed mask, and the re-targeting of designs in different mask regions to provide a common exposure level.
We have observed a signal of 55 isolated /-conversion pairs produced in a wide-band neutrino beam using the Fermilab 15-ft bubble chamber filled with a heavy Ne-H2 mixture. The signal is consistent with coherent neutral-current single-/* 0 production followed by decay of the /r° with one of the decay ys being lost. This signal corresponds to a rate of (2.0 ± 0.4) x 10~* 4 of the total v^ charged-current cross section at our average E v of 20 GeV. From this result, we obtain a value of /J~0.98±0.24 for the weak-neutral-current isovector axial-vector coupling.PACS numbers: 13.15.Cj Neutral-current coherent K° production, first suggested by Nachtmann 1 and Lackner 2 and later refined by Rein and Sehgal, 3 occurs predominantly through the interaction of the isovector axial-vector current, the longitudinal part of which behaves like a /r° and scatters elastically from a nucleus exchanging a pomeronlike particle. The importance of coherent x° production is that a precise measurement of the cross section can provide a direct measurement of the isovector axial-vector neutral-current coupling. Using the notation of Hung and Sakurai, 4 one can write the axial-vector weak current as Ja^PAlT 1 + SAl' m0 , where P is the isovector axialvector coupling constant and S is the isoscalar axialvector coupling constant. The standard model of electroweak interactions predicts that ^ = 1 and 5=0.Evidence for neutral-current coherent single-/r° production by neutrinos has been reported by three groups. 5 " 8 Weak coherent x° production was first observed by the Aachen-Padova group, 5 who reconstructed K°ys at an average neutrino energy of 2 GeV. This has been confirmed by Gargamelle data with single fs at a similar low neutrino energy. The third group used a high-energy neutrino beam along with a highly segmented calorimeter. They were forced to rely on a statistical method to identify candidate events. We have directly observed a signal of isolated photon-conversion pairs in a heavy-liquid bubble chamber exposed to a wide-band neutrino beam «£' v >=20 GeV). This signal can be explained by coherent TT 0 production with only one of the 7t° decay photons being observable.The data for the present experiment were taken in the Fermilab 15-ft bubble chamber filled with a heavy Ne-H2 mixture and exposed to a single horn-focused wide-band v^ beam. The heavy neon mixture is ideal for identifying electrons and /s since its radiation length is -40 cm.In the heavy mixture a n can sometimes appear to be a single y. This occurs when a y either fails to convert in the visible volume or converts inside the radiation shower caused by the earlier conversion of the other y. The short conversion length in our liquid ensures that the probability for a ;r°-decay y to convert in the visible volume is large ( -95%); however, as the energy of the it 0 increases, the opening angle between the two decay fs decreases thus increasing the probability for the two conversions to overlap. From examining a large sample of converted y's, criteria were deduced concerning...
This Letter compares neutral-current and charged-current scaling-variable distributions in neutrino-nucleon interactions induced by a narrow-band beam at Brookhaven National Laboratory; the x distribution of neutral-current events has been reported previously. The first measurement of flux-normalized neutrino cross sections from a narrow-band beam in the energy range E v =3-9 GeV is also presented.
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