Large-angle pp elastic and quasielastic (p,2p) scattering have been simultaneously observed in hydrogen and each of several nuclear targets (Li, C, Al, Cu, Pb) at incident proton momenta of 6, 10, and 12 GeV/c. The nuclear transparency is the ratio of such a cross section in a nucleus to the free pp cross section. The transparency of aluminum increases with incident momentum by more than a factor of 2 from 6 to 9.5 GeV/c and falls significantly between 9.5 and 12 GeV/c. This occurs in a region where the free-proton nucleon-absorption cross section exhibits little energy dependence. QCD predicts an increase in transparency with energy.PACS numbers: 13.75. Cs, 12.38.Qk, 13.85.Dz, 25.40.Ve This Letter describes the first results from a program of study at the Brookhaven National Laboratory Alternating-Gradient Synchrotron which investigates the effects of "color transparency." Quasielastic pp scattering from each of several nuclei is compared to pp elastic scattering in hydrogen at three energies. These data are analyzed with a simple model in which the quasielastic cross section is assumed to factor into the product of three terms, a single-particle nuclear momentum distribution, a free pp cross section, and a factor T which we refer to as the transparency of the nucleus. In the absence of Fermi motion the transparency would beData are presented for pp elastic and quasielastic scattering near 90° cm. (center of mass) at incident proton energies of 6, 10, and 12 GeV/c, corresponding to t [(four-momentum transfer) 2 ] of -4.8, -8.5, and -10.4 GeV 2 .The cross section (da/dt) for pp elastic scattering at large transverse momentum and at fixed cm. angle is characterized by an s [(center-of-mass energy) 2 ] dependence which oscillates around the nominal s~] 0 form predicted by the dimensional scaling law of Brodsky and Farrar. l The form of this energy dependence can be related to the probability of finding protons with all of their quarks confined to a region of space which is proportional to 1A/7. This implies that for large s these initial-and final-state protons are very small.It has been pointed out by Mueller 2 and others that small protons which participate in such processes are characterized by color-charge and color-field distributions confined to ever smaller dimensions as s increases. In high-/ quasielastic scattering this implies that the cross section for soft initial-and final-state interactions with other nucleons in the nucleus will vanish as the energy scale increases. It has thus been predicted that at high energy the transparency of nuclei should approach unity. This is in sharp contrast to a more conventional Glauber picture 3 of absorption in which the transparency would be expected to be energy independent.The apparatus consists of a large-angle magnetic spectrometer with a 4.5° aperture. 4 Large proportional chambers measure the trajectories of recoil tracks opposite the spectrometer. When configured for incident momentum of 10 GeV/c, the spectrometer has Ap/p = 1% and A0 = 1 mr and the recoil-...

Model organisms are widely used in research as accessible and convenient systems to study a particular area or question in biology. Traditionally only a handful of organisms have been widely studied, but modern research tools are enabling researchers to extend the set of model organisms to include less-studied and more unusual systems. This Forum highlights a range of 'non-model model organisms' as emerging systems for tackling questions across the whole spectrum of biology (and beyond), the opportunities and challenges, and the outlook for the future.

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We measured simultaneously pp elastic and quasielastic ͑ p, 2p͒ scattering in hydrogen, deuterium, and carbon for momentum transfers of 4.8 to 6.2 ͑GeV͞c͒ 2 at incoming momenta of 5.9 and 7.5 GeV͞c and center-of-mass scattering angles in the range u c.m. 83.7 ± 90 ± . The nuclear transparency is defined as the ratio of the quasielastic cross section to the free pp cross section. At incoming momentum of 5.9 GeV͞c, the transparency of carbon decreases by a factor of 2 from u c.m. Ӎ 85 ± to u c.m. Ӎ 89 ± . At the largest angle the transparency of carbon increases from 5.9 to 7.5 GeV͞c by more than 50%. The transparency in deuterium does not depend on incoming momentum nor on u c.m. . [S0031-9007 (98)07818-1] PACS numbers: 24.85. + p, 25.40. -h, 24.10. -iNuclear transparency is a measure of the initial and final state interactions that the incoming and outgoing protons undergo before and after the main ͑p, 2p͒ reaction. Conventional theoretical calculations of the nuclear transparency within the Glauber picture [1,2] predict that above an incident momentum of approximately 5 GeV͞c the nuclear transparency does not depend on the incoming momentum nor on the pp c.m. scattering angle, u c.m. . The expectation from QCD based models of proton dynamics in hard exclusive interactions is that the initial and final state scattering may be smaller than the Glauber theory would predict. It is also expected that nuclear transparency should increase with incoming momentum reaching an asymptotic value of 1. These QCD phenomena have been referred to as color transparency [3].

Background: Photosystem II is an essential component of oxygenic photosynthesis.Results: Photosystem II is specifically decreased in rubredoxin mutants of the green alga Chlamydomonas reinhardtii, the cyanobacterium Synechocystis sp. PCC 6803, and the plant Arabidopsis thaliana.Conclusion: Rubredoxin is required for photosystem II, and not photosystem I, accumulation in these organisms.Significance: Rubredoxin was likely important in the evolution of oxygenic photosynthesis.

We report a study of 20 exclusive reactions measured at the AGS at 5.9 GeV/c incident momentum, 90" center of mass. This experiment confirms the strong quark flow dependence of two-body hadronhadron scattering at large angle. At 9.9 GeVIc an upper limit had been set for the ratio of cross sections for (pp + pp)/(pp i pp) at 90' c.m.. with the ratio less than 4%. The present experiment was performed a t lower energy to gain sensitivity, but was still within the fixed angle scaling region. A ratio R(pp/pp) % 1/40 was measured a t 5.9 GeV/c, 90" c.m. in comparison to a ratio near 1.7 for small angle scattering. In addition, many other reactions were measured, often for the first time at 90" c.m. in the scaling region, using beams of T * . K*, p, and p on a hydrogen target. There are similar large differences in cross sections for other reactions: R ( K -p + T + C -/ K -~ i n-C') % 1/12, for example. The relative magnitudes of the different cross sections are consistent with the dominance of quark interchange in these 90" reactions, and indicate that pure gluon exchange and quark-antiquark annihilation diagrams are much less important. The angular dependence of several elastic cross sections and the energy dependence a t a fixed angle of many of the reactions are also presented. PACS number(s): 13.75.-n, 13.85.Dz, 13.85.Fb GeV/c, the depentcurrent address: ~~~~~~d university, cambridge, MA dence of the cross sections flattened in the region of 90" 02139. c.m. These observations indicate that large angle scat- §Current address: University of Arizona, Tucson, AZ 85721. tering for Q2 > 5 ( G e v /~)~ has different dynamics from "current address: Niels Bohr Institute, Copenhagen, small angle scattering. Moreover, the observed power Denmark. of the energy dependence agrees well with dimensionalThe reactions are written as (beam + target) -+ (spectrometer particle + side particle). Reactions 1, 2, 3, 17, and 18 were measured with either final-state particle in the spectrometer. Meson-baryon reactions1 =+P -+ P+ 2 n-p + pn-3 K + p -+ pK+ 4 K -p -+ pK-5 n+p -+ PP+ 6

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We report on recent progress in the design of the proposed MATHUSLA Long Lived Particle (LLP) detector for the HL-LHC, updating the information in the original Letter of Intent (LoI), see CDS:LHCC-I-031, arXiv:1811.00927. A suitable site has been identified at LHC Point 5 that is closer to the CMS Interaction Point (IP) than assumed in the LoI. The decay volume has been increased from 20 m to 25 m in height. Engineering studies have been made in order to locate much of the decay volume below ground, bringing the detector even closer to the IP. With these changes, a 100 m x 100 m detector has the same physics reach for large cτ as the 200 m x 200 m detector described in the LoI and other studies. The performance for small cτ is improved because of the proximity to the IP. Detector technology has also evolved while retaining the strip-like sensor geometry in Resistive Plate Chambers (RPC) described in the LoI. The present design uses extruded scintillator bars read out using wavelength shifting fibers and silicon photomultipliers (SiPM). Operations will be simpler and more robust with much lower operating voltages and without the use of greenhouse gases. Manufacturing is straightforward and should result in cost savings. Understanding of backgrounds has also significantly advanced, thanks to new simulation studies and measurements taken at the MATHUSLA test stand operating above ATLAS in 2018. We discuss next steps for the MATHUSLA collaboration, and identify areas where new members can make particularly important contributions.