11,757 research outputs found
Beauty Photoproduction at HERA II with the ZEUS Experiment.
No full textIn this thesis the beauty photoproduction cross section has been measured with the ZEUS detector at HERA II using e+p data collected in 2004 corresponding to an integrated luminosity of 33 pb-1. Beauty production has been studied in the photoproduction regime, in which the boson exchanged between the proton and the positron is an almost real photon (virtuality, Q2 0 GeV2). Events were selected in which a bb pair is produced and at least one of the pair decays semi-leptonically into a muon. The beauty content of the sample was extracted using a combination of el (transverse momentum of the muon with respect to the closest jet) and impact parameter (distance of closest approach of the muon track to the primary vertex) methods. Measurements of the total and differential cross sections for beauty production were made. The measured cross sections are in good agreement with NLO QCD predictions and with the HERA I results that were obtained from a luminosity 3 times larger than that of the present measurement, using only the P 1 variable to separate the beauty signal from charm and light flavours and fixing the charm-to-light-flavour ratio from external measurements. An external constraint for the charm contribution is not needed in this analysis since its fraction is extracted from the fit to these data
Impact of future HERA data on the proton PDF uncertainties using the ZEUS NLO QCD fit
No full textThe high precision and large kinematic coverage of the data from the HERA-1 running period (1994-2000) have already allowed precise extractions of proton parton distribution functions. The HERA-II program is now underway and is expected to provide a substantial increase in the luminosity collected at HERA. In this paper, the first estimate of the impact of future data from HERA, on the proton PDF uncertainties, is presented. Next-to-leading order QCD predictions for inclusive jet cross sections at the LHC are presented using the projected PDFs
Measurement of the neutral current reaction at high Q2 in the H1 experiment at HERA II
No full textThis thesis presents inclusive ep double and single differential cross section measurements for neutral current deep inelastic scattering of longitudinally polarized leptons on protons as a function of the negative four-momentum transfer squared Q2 and the Bjorken variable x. The data were collected in the years 2003-2007 in the H1 experiment at HERA with positively and negatively longitudinally polarized lepton beams of 27 GeV and a proton beam of 920 GeV corresponding to the centre-of-mass energy of sqrt{s} = 319 GeV. The integrated luminosity is about 330 pb^{-1}. An overview of the phenomenology of the deep inelastic scattering is given and the experimental apparatus is described. The NC cross section measurement procedure is presented and discussed in details. The measured cross sections are used to investigate electroweak effects at high Q2. The proton structure function xF_3, sensitive to the valence quarks in the proton, is measured. The polarization effects sensitive to the chiral structure of neutral currents are investigated. The Standard Model predictions are found to be in a good agreement with the measurement
Interview with Roberto Hera
No full textInterview conducted in English.Interview conducted at Lānaʻi City, Lānaʻi.Roberto Hera, second of four children, was born in 1936 in Kealakekua, Kona, Hawaiʻi, where his maternal grandparents farmed coffee. His mother, Marcellina Hera, was raised and educated on the Big Island of Hawaiʻi. His father, Florentino Hera, originally from Cebu, Philippines, received a degree in engineering from the University of Chicago. In 1937, the Heras moved to Lānaʻi where Florentino Hera was employed as an agricultural engineer by the Hawaiian Pineapple Company. He also served as branch manager of the Filipino Federation of America. Roberto Hera was raised and educated on Lānaʻi. Following his high school graduation in 1954, he attended college for a short while, worked in Honolulu, and entered military service. Returning to Lānaʻi in the mid-1960s, he started his decades-long career with Dole Pineapple Company. He worked in virtually every department until his retirement in 1990 as a superintendent. After a few years with the Nature Conservancy, he was coaxed to return to Dole as Director of Facilities. Retired for a second time in 1999, he remains active with ʻIke Aina, Native Hawaiian Land Trust, on Lānaʻi. He has seven children, thirteen grandchildren, and three great-grandchildren
Photoproduction generators at HERA
No full textA study of photoproduction Monte Carlo generators available for HERA
physics has been made. Using parameters determined for deep inelastic
scattering at SPS energies, global event distribution have been studied
for a number of photoproduction sub-processes
Physics with polarized protons at HERA
No full textThe operation of HERA with polarized proton and electron beams will allow to study a wide variety of observables in polarized electron-proton collisions at #sq root#(s)=300 GeV. The physics prospects of this project have been elaborated in detail in a dedicated working group, whose results we summarize in this report. We show that several important and often unique measurements in spin physics could be made at HERA. These include measurements of the polarized structure function g_1(x,Q"2) at low x, a direct determination of the polarized gluon distribution #DELTA#G(x,Q"2) for the region 0.002<x<0.2 from polarized di-jet rates and hadrons with high p_t, polarized quark distributions from weak structure functions and semi-inclusive asymmetries, parton distributions in the polarized photon and information on the helicity structure of possible new physics at large Q"2. HERA could therefore make a significant contribution to our understanding of spin effects in high energy collisions and to the spin structure of the nucleon. (orig.)Available from TIB Hannover: RR 2999(97-233) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Photoproduction physics at HERA
No full textThis report contains five articles about experiments on photoproduction at the HERA storage ring. These concern total cross sections, the behavior and the parton structure of the photon, as well as hard scattering in diffractive dissociation of quasi-real photons. (HSI)Available from TIB Hannover: RA 2999(94-215) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Vector meson production at low x from gauge/gravity duality
No full textWe use gauge/gravity duality to study vector meson (J/?, ? 0 , ?, ?) production in electron-proton scattering, in the limit of high center of mass energy at fixed momentum transfer, corresponding to the limit of low Bjorken x, where the process is dominated by pomeron exchange. Our approach considers the pomeron at strong coupling, described by the graviton Regge trajectory in AdS space with a hard-wall to mimic confinement effects. Both the proton and vector mesons are described by simple holographic wave functions in AdS. This model agrees with HERA H1 data with a ? 2 per degree of freedom below one on total cross-sections, and below two on differential cross-sections, confirming the success of previous studies that model low x DIS and DVCS using gauge/gravity duality
Inclusive photoproduction of hadrons at HERA. - Direct photon production at LEP and HERA
No full textMatrix element calculations for the decay of the Z into one isolated photon plus n jets are reviewed. The problem of photon isolation with respect to quark, antiquark and gluon is discussed in detail. Experimental results of the LEP collaborations are compared to the theory. Theoretical results for #gamma#+n jet production in deep inelastic ep collisions at HERA are presented also. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(94-136) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Recognition of two distinct elements in the RNA substrate by the RNA-binding domain of the T. thermophilus DEAD box helicase Hera
No full textDEAD box helicases catalyze the ATP-dependent destabilization of RNA duplexes. Whereas duplex separation is mediated by the helicase core shared by all members of the family, flanking domains often contribute to binding of the RNA substrate. The Thermus thermophilus DEAD-box helicase Hera (for “heat-resistant RNA-binding ATPase”) contains a C-terminal RNA-binding domain (RBD). We have analyzed RNA binding to the Hera RBD by a combination of mutational analyses, nuclear magnetic resonance and X-ray crystallography, and identify residues on helix α1 and the C-terminus as the main determinants for high-affinity RNA binding. A crystal structure of the RBD in complex with a single-stranded RNA resolves the RNA–protein interactions in the RBD core region around helix α1. Differences in RNA binding to the Hera RBD and to the structurally similar RBD of the Bacillus subtilis DEAD box helicase YxiN illustrate the versatility of RNA recognition motifs as RNA-binding platforms. Comparison of chemical shift perturbation patterns elicited by different RNAs, and the effect of sequence changes in the RNA on binding and unwinding show that the RBD binds a single-stranded RNA region at the core and simultaneously contacts double-stranded RNA through its C-terminal tail. The helicase core then unwinds an adjacent RNA duplex. Overall, the mode of RNA binding by Hera is consistent with a possible function as a general RNA chaperone
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