Measurement of differential cross sections of isolated-photon plus heavy-flavour jet production in pp collisions at √s=8 TeV using the ATLAS detector

This Letter presents the measurement of differential cross sections of isolated prompt photons produced in association with a b-jet or a c-jet. These final states provide sensitivity to the heavy-flavour content of the proton and aspects related to the modelling of heavy-flavour quarks in perturbative QCD. The measurement uses proton–proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of up to 20.2 fb−1. The differential cross sections are measured for each jet flavour with respect to the transverse energy of the leading photon in two photon pseudorapidity regions: |ηγ | < 1.37 and 1.56 < |ηγ | < 2.37. The measurement covers photon transverse energies 25 < Eγ T < 400 GeV and 25 < Eγ T < 350 GeV respectively for the two |ηγ | regions. For each jet flavour, the ratio of the cross sections in the two |ηγ | regions is also measured. The measurement is corrected for detector effects and compared to leading-order and nextto-leading-order perturbative QCD calculations, based on various treatments and assumptions about the heavy-flavour content of the proton. Overall, the predictions agree well with the measurement, but some deviations are observed at high photon transverse energies. The total uncertainty in the measurement ranges between 13% and 66%, while the central γ + b measurement exhibits the smallest uncertainty, ranging from 13% to 27%, which is comparable to the precision of the theoretical predictions

LOCALIZATION OF POLYPEPTIDES IN ISOLATED CHLOROSOMES FROM GREEN PHOTOTROPHIC BACTERIA BY IMMONUGOLD LABELING ELECTRON-MICROSCOPY

Chlorosomes were prepared from Chloroflexus aurantiacus, Chlorobium limicola f. thiosulfatophilum and Prosthecochloris aestuarii by sucrose density gradient centrifugation. Two preparation methods were used. The first was applied to all three organisms and yielded chlorosomes without cytoplasmic membrane (CM) components. The second, which included a cross-linking step, was applied to Cf. aurantiacus and P. aestuarii only and yielded chlorosomes affixed to small inner CM patches. For the P. aestuarii sample this second method also yielded rod-elements, which were released from the inside of the chlorosomes. Antisera, raised against chlorosome polypeptide chains (18, 11 and 5.7 kDa), isolated from CM-free Cf. aurantiacus chlorosomes or a mixture of 24 and 24.5 kDa reaction center (RC) polypeptides isolated from Cf. aurantiacus inner CM, were incubated with the two different Cf. aurantiacus chlorosome samples and analyzed by gold-labeling, electron microscopy (EM). Three antisera (anti-18 kDa, anti-11 kDa and anti-5.7 kDa) showed specific interaction with the chlorosomal envelope, whereas the anti-RC serum exhibited specificity for the CM. This result demonstrates for the first time that the 5.7 kDa polypeptide is in the chlorosomal envelope. Previous work had placed the polypeptide as a structural component of the intrachlorosomal rod-elements (Feick, R.G. and Fuller, R.C. (1984) Biochemistry 23, 3693-3700). Affinity-purified antibodies raised against a 7.5 kDa polypeptide isolated from Cb. limicola CM-free chlorosomes were incubated with Cb. limicola and P. aestuarii chlorosome samples. The antibodies showed considerable affinity for the chlorosomal envelopes but far less towards the CM components and hardly any for the rod-elements