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ENERGY RECEPTION AND TRANSFER IN PHOTOSYNTHESIS

Description: The basic information about the path of carbon in photosynthesis is reviewed together with the methods that were used to discover it. This has led to the knowledge of what is required of the photochemical reaction in the form of chemical species. Attention is then directed to the structure of the photochemical apparatus itself insofar as it is viewable by electron microscopy, and some principoles of ordered structure are devised for the types of molecules to be found in the chloroplasts. From the combination of these, a structure for the grana lamella is suggested and a mode of function proposed. Experimental test for this mode of function is underway; one method is to examine photoproduced unpaired electrons. This is discussed.
Date: September 23, 1958
Creator: Calvin, Melvin
Partner: UNT Libraries Government Documents Department

Photoproduction of hybrid mesons

Description: In this contribution the author discusses prospects for photoproducing hybrid mesons at CEBAF, based on recent model results and experimental indications of possible hybrids. One excellent opportunity appears to be a search for I = 1, J{sup PC} = 2{sup +{minus}} ``b{sub 2}{sup o}`` hybrids in (a{sub 2}{pi}){sup o} through diffraction photoproduction. Other notable possibilities accessible through {pi}{sup +}; {pi}{sub J}{sup +}(1770) in f{sub 2}{pi}{sup +} and (b{sub 1}{pi}){sup +}; {pi}{sup +}(1800) in f{sub 0}{pi}{sup +}, f{sub 2}{pi}{sup =}, {rho}{sup +}{omega} and ({rho}{pi}){sup +}; a{sub 1} in f{sub 1}{pi}{sup +} and f{sub 2}{pi}{sup +}; and {omega} in ({rho}{pi}){sup o}, {omega}{eta} and K{sub 1}K.
Date: November 1, 1998
Creator: Barnes, T.
Partner: UNT Libraries Government Documents Department

Background Enhancement of CPT Reach at an Asymmetric Phi Factory

Description: Photoproduction of neutral-kaon pairs is studied from the perspective of CP and CPT studies. Interference of the P and S waves, with the former due to diffractive phi production and the latter to f{_}0/a{_}0 production, is shown to enhance the CPT reach. Results are presented of Monte Carlo studies based on rates expected in future experiments.
Date: June 1, 2001
Creator: Isgur, Nathan; Kostelecky, Alan & Szczepaniak, Adam
Partner: UNT Libraries Government Documents Department

Biological Systems for Hydrogen Photoproduction (Presentation)

Description: This presentation summarizes NREL biological systems for hydrogen photoproduction work for the DOE Hydrogen and Fuel Cells Program Annual Merit Review and Peer Evaluation Meeting, May 14-18, 2012. General goal is develop photobiological systems for large-scale, low cost and efficient H{sub 2} production from water (barriers AH, AI and AJ). Specific tasks are: (1) Address the O{sub 2} sensitivity of hydrogenases that prevent continuity of H{sub 2} photoproduction under aerobic, high solar-to-hydrogen (STH) light conversion efficiency conditions; and (2) Utilize a limited STH H{sub 2}-producing method (sulfur deprivation) as a platform to address or test other factors limiting commercial algal H{sub 2} photoproduction, including low rates due to biochemical and engineering mechanisms.
Date: May 1, 2012
Creator: Ghirardi, M. L.
Partner: UNT Libraries Government Documents Department

Properties of the Lambda(1405) Measured at CLAS

Description: The nature of the {Lambda}(1405), and its place in the baryon spectrum has remained uncertain for decades. Theoretical studies have shown that it may possess strong dynamical components which are not seen in other well-known baryons. Using the CLAS detector system in Hall B at Jefferson Lab, we have measured the photoproduction reaction {gamma} + p {yields} K{sup +} {Lambda}(1405) with high statistics and over different {Sigma}{pi} decay channels. The reconstructed invariant mass distribution (lineshape) has been measured, as well as the differential cross sections for the {Lambda}(1405), {Sigma}(1385), and {Lambda}(1520). Our analysis method is discussed and our near-final results for the {Lambda}(1405) lineshape and differential cross section are presented.
Date: April 1, 2012
Creator: Moriya, Kei & Schumacher, Reinhard
Partner: UNT Libraries Government Documents Department

Light Vector Meson Photoproduction off of H at Jefferson Lab and rho-omega Interference in the Leptonic Decay Channel

Description: Recent studies of light vector meson production in heavy nuclear targets has generated interest in {rho}-{omega} interference in the leptonic e{sup +}e{sup -} decay channel. An experimental study of the elementary process provides valuable input for theoretical models and calculations. In experiment E04-005 (g12), high statistics photoproduction data has been taken in Jefferson Lab's Hall B with the Cebaf Large Acceptance Spectrometer (CLAS). The invariant mass spectrum is fitted with two interfering relativistic Breit-Wigner functions to determine the interference phase. Preliminary analysis indicate a measurable {rho}-{omega} interference.
Date: December 1, 2011
Creator: Djalali, Chaden
Partner: UNT Libraries Government Documents Department

Upper limits for the photoproduction cross section for the Phi--(1860) pentaquark state off the deuteron

Description: We searched for the {Phi}{sup --}(1860) pentaquark in the photoproduction process off the deuteron in the {Xi}{sup -} {pi}{sup -} decay channel using CLAS. The invariant mass spectrum of the {Xi}{sup -} {pi}{sup -} system does not indicate any statistically significant enhancement near the reported mass M = 1.860 GeV. The statistical analysis of the sideband-subtracted mass spectrum yields a 90% confidence level upper limit of 0.7 nb for the photoproduction cross section of {Phi}{sup --}(1860) with a consecutive decay into {Xi}{sup -} {pi}{sup -} in the photon energy range 4.5 GeV < E{sub {gamma}} < 5.5 GeV.
Date: January 1, 2012
Creator: Egiyan, Hovanes
Partner: UNT Libraries Government Documents Department

Hadron Spectroscopy Program with CLAS g12

Description: Some conclusions from this presentation are: (1) previous CLAS result on exotic {pi}{sub 1}(1600)/{alpha}{sub 2}(1320) in photoproduction confirmed with higher statistics; (2) previous CLAS result on {gamma}p {yields} pentaquark not confirmed with higher statistics; (3) high luminosity allows exploitation of rare topologies {gamma}p {yields} {phi}{pi}{sup 0}p, {phi}{eta}p, {phi}{omega}p; (4) no observation of any {Xi}* states above 1530 MeV recoiling off of K{sup +}K{sup +} lepton detection permits high statistic study of pseudoscalar dalitz decay; and (5) first observation of {eta}' Dalitz decay, {rho}-{omega} interference via e{sup +}e{sup -} channel.
Date: December 1, 2011
Creator: Weygand, Dennis
Partner: UNT Libraries Government Documents Department

Probing small x parton densities in ultraperipheral AA and pAcollisions at the LHC

Description: We calculate photoproduction rates for several hard processes in ultraperipheral proton-lead and lead-lead collisions at the LHC with {radical}s{sub NN} = 8.8 and 5.5 TeV respectively which could be triggered in the large LHC detectors. We use ATLAS as an example. The lead ion is treated as a source of (coherently produced) photons with energies and intensities greater than those of equivalent ep collisions at HERA.We find very large rates for both inclusive and diffractive production which will extend the HERA x range by nearly an order of magnitude for similar virtualities. We demonstrate that it is possible to reach the kinematic regime where nonlinear effects are larger than at HERA.
Date: September 15, 2005
Creator: Strikman, Mark; Vogt, Ramona & White, Sebastian
Partner: UNT Libraries Government Documents Department

Observation of Two-source Interference in the Photoproduction Reaction AuAu --> AuAu rho 0

Description: In ultra-peripheral relativistic heavy-ion collisions, a photon from the electromagnetic field of one nucleus can fluctuate to a quark-antiquark pair and scatter from the other nucleus, emerging as a {rho}{sup 0}. The {rho}{sup 0} production occurs in two well-separated (median impact parameters of 20 and 40 fermi for the cases considered here) nuclei, so the system forms a 2-source interferometer. At low transverse momenta, the two amplitudes interfere destructively, suppressing {rho}{sup 0} production. Since the {rho}{sup 0} decays before the production amplitudes from the two sources can overlap, the two-pion system can only be described with an entangled non-local wave function, and is thus an example of the Einstein-Podolsky-Rosen paradox. We observe this suppression in 200 GeV per nucleon-pair gold-gold collisions. The interference is 87% {+-} 5%(stat.) {+-} 8% (syst.) of the expected level. This translates into a limit on decoherence due to wave function collapse or other factors, of 23% at the 90% confidence level.
Date: March 2, 2009
Creator: Coll, STAR
Partner: UNT Libraries Government Documents Department

Coherent rho 0 photoproduction in bulk matter at high energies

Description: The momentum transfer {Delta}k required for a photon to scatter from a target and emerge as a {rho}{sup 0} decreases as the photon energy k rises. For k > 3 x 10{sup 14} eV, {Delta}k is small enough that the interaction cannot be localized to a single nucleus. At still higher energies, photons may coherently scatter elastically from bulk matter and emerge as a {rho}{sup 0}, in a manner akin to kaon regeneration. Constructive interference from the different nuclei coherently raises the cross section and the interaction probability rises linearly with energy. At energies above 10{sup 23} eV, coherent conversion is the dominant process; photons interact predominantly as {rho}{sup 0}. We compute the coherent scattering probabilities in slabs of lead, water and rock, and discuss the implications of the increased hadronic interaction probabilities for photons on ultra-high energy shower development.
Date: January 9, 2009
Creator: Couderc, Elsa & Klein, Spencer
Partner: UNT Libraries Government Documents Department

Photoproduction at RHIC and the LHC

Description: The strong electromagnetic fields carried by relativistic highly charged ions make heavy-ion colliders attractive places to study photonuclear interactions and two-photon interactions. At RHIC, three experiments have studied coherent photoproduction of {rho}{sup 0}, 4{pi}, J/{psi}, e{sup +}e{sup -} pairs, and e{sup +}e{sup -} pairs where the electron is bound to one of the incident nuclei. These results show that photoproduction studies are possible, and demonstrate some of the unique possibilities due to the symmetric final states and the ion targets. The LHC will reach photon-nucleon energies many times higher than at HERA; these collisions can be used to measure the gluon distributions in nuclei at very low Bjorken-x, where shadowing and gluon saturation may become important; LHC {gamma}{gamma} collisions may also be attractive places to search for some types of new physics. ATLAS, CMS and ALICE are all planning to study photoproduction. After introducing the principles of photoproduction at hadron colliders, I will review recent results from RHIC on meson and e{sup +}e{sup -} production, and then discuss prospects for studies at the LHC.
Date: October 6, 2008
Creator: Klein, Spencer
Partner: UNT Libraries Government Documents Department

A Non-parametric approach to measuring the K- pi+ amplitudes in D+ ---> K- K+ pi+ decay

Description: Using a large sample of D{sup +} {yields} K{sup -}K{sup +}{pi}{sup +} decays collected by the FOCUS photoproduction experiment at Fermilab, we present the first non-parametric analysis of the K{sup -}{pi}{sup +} amplitudes in D{sup +} {yields} K{sup -}K{sup +}{pi}{sup +} decay. The technique is similar to the technique used for our non-parametric measurements of the D{sup +} {yields} {bar K}*{sup 0} e{sup +}{nu} form factors. Although these results are in rough agreement with those of E687, we observe a wider S-wave contribution for the {bar K}*{sub 0}{sup 0}(1430) contribution than the standard, PDG [1] Breit-Wigner parameterization. We have some weaker evidence for the existence of a new, D-wave component at low values of the K{sup -}{pi}{sup +} mass.
Date: December 1, 2006
Creator: Link, J.M.; Yager, P.M.; /UC, Davis; Anjos, J.C.; Bediaga, I.; Castromonte, C. et al.
Partner: UNT Libraries Government Documents Department

A non-parametric approach to measuring the k- pi+ amplitudes in d+ --> k- k+ pi+ decay

Description: Using a large sample of D{sup +} {yields} K{sup -}K{sup +}{pi}{sup +} decays collected by the FOCUS photoproduction experiment at Fermilab, we present the first non-parametric analysis of the K{sup -} {pi}{sup +} amplitudes in D{sup +} {yields} K{sup -}K{sup +}{pi}{sup +} decay. The technique is similar to the technique used for our non-parametric measurements of the D{sup +} {yields} {bar K}*{sup 0} e{sup +}{nu} form factors. Although these results are in rough agreement with those of E687, we observe a wider S-wave contribution for the {bar K}*{sub 0}{sup 0}(1430) contribution than the standard, PDG [1] Breit-Wigner parameterization. We have some weaker evidence for the existence of a new, D-wave component at low values of the K{sup -} {pi}{sup +} mass.
Date: December 1, 2006
Creator: Link, J.M.
Partner: UNT Libraries Government Documents Department

Photoproduction amplitudes of P(sub)11 and P(sub)33 baryon resonances in the quark model

Description: Predictions are made for the photoproduction amplitudes of low-lying N^(1/2)+ (P(sub)(11)) and delta^(3/2)+ (P(sub)(33)) resonances, using a quark model with relativistic corrections to the transition operator, and mixed nonrelativistic wavefunctions which are correctly orthogonal to the ground states.These amplitudes are also calculated using relativized model wavefunctions. The results for the Roper resonance N(1440) are in marked disagreement with the data.
Date: January 1, 1992
Creator: Capstick, Simon
Partner: UNT Libraries Government Documents Department

Observation of pi+pi-pi+pi- photoproduction in ultraperipheral heavy-ion collisions at sqrt sNN = 200 GeV at the STAR detector

Description: We present a measurement of {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -} photonuclear production in ultra-peripheral Au-Au collisions at {radical}s{sub NN} = 200 GeV from the STAR experiment. The {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -} final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -} invariant mass spectrum of the coherent events exhibits a broad peak around 1540 {+-} 40 MeV/c{sup 2} with a width of 570 {+-} 60 MeV/c{sup 2}, in agreement with the photoproduction data for the {rho}{sup 0}(1700). We do not observe a corresponding peak in the {pi}{sup +}{pi}{sup -} final state and measure an upper limit for the ratio of the branching fractions of the {rho}{sup 0}(1700) to {pi}{sup +}{pi}{sup -} and {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -} of 2.5% at 90% confidence level. The ratio of {rho}{sup 0}(1700) and {rho}{sup 0}(770) coherent production cross sections is measured to be 13.4 {+-} 0.8{sub stat.} {+-} 4.4{sub syst.}%.
Date: July 5, 2010
Creator: Collaboration, STAR & Abelev, Betty
Partner: UNT Libraries Government Documents Department

Reply to Comment on"Coherent rho0 photoproduction in bulk matter at high energies"

Description: In their interesting comment on 'Coherent {rho}0 photoproduction in bulk matter at high energies', Rogers and Strikman point out that, at high energies, q{bar q} dipoles with small separations (d) become more important, and that most of the growth of the cross-section is 'driven by the increasingly large contributions from small size (high mass) configurations'; at photon energies of 10{sup 20} eV, over half of the total cross-section is due to dipoles smaller than 0.25 fm. They state that charm production will increase, and may be as much as 30% of the cross-section. The coherent photoproduction of heavier states requires higher energies than coherent {rho} photoproduction, because the formation length scales as 1/M{sup 2}. For the J/{psi}, the required photon energy is 14 times higher than for the {rho}. We agree that higher-mass states become important at higher energies. However, at this point, additional factors come into play; as we note after Eq. (7), our calculation is only properly normalized when the conversion probability is relatively small. At the energies where coherent production of high mass states is possible, the coherent {rho} production probability is large, and it is necessary to consider reverse reactions such as vector meson 'back-propagation' into real photons. The diagonal transitions found in generalized vector meson dominance, such as from a {rho} to a {phi} or J/{psi} may also become important, and a recursive technique appears needed to solve the problem. To the extent that the higher mass states limit the growth of the low-mass cross-section, coherent {rho} photoproduction will be smaller than we calculated. However, the high-mass fractions quoted by Rogers and Strikman are considerably smaller than the fractional difference between the two hadronic models we considered: the Glauber model and the ERR calculations. The presence of higher mass states in our Glauber calculation would ...
Date: January 27, 2010
Creator: Couderc, E. & Klein, S.
Partner: UNT Libraries Government Documents Department

Stage I to Proposal #144: A Simple Spectrometer to Measure Photoproduction of Vector Mesons and Pions at High Energy

Description: In NAL Proposal No.144, we described a three magnet system, consisting of a forward focussing spectrometer made up of two large aperture magnets, M1 and M2, and a solenoid magnet from the PPA to detect the recoil proton. This spectrometer will enable us to study seven experimental reactions at the same time with high precision.
Date: May 1, 1972
Creator: Margolis, B.; Patel, P.M.; Ross, W.; Stairs, D.G.; U., /McGill; Bird, L. et al.
Partner: UNT Libraries Government Documents Department