141 research outputs found
Recent results from ZEUS
No full textRecent results on deep inelastic scattering from the ZEUS collaboration are reviewed. These include studies of neutral and charged currents at high Q"2, fragmentation and perturbative QCD, and information on the quark and gluon content of the proton. Information on the gluon density in the proton is obtained from a wide variety of processes, leading to a consistent picture of a steep rise of the gluon density at low x. Preliminary measurements of F_2 extending to new regimes at both high and low Q"2 and x are presented based on 1994 data. Analysis of events with a large rapidity gap with respect to the direction of the proton beam is consistent with factorisation of the cross-section into a flux factor and a structure function, and can be interpreted as an indication of point-like constituents inside the pomeron. (orig.)Available from TIB Hannover: RA 2999(95-158) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Hypergraph patterns and collaboration structure
No full textHumans collaborate in different contexts such as in creative or scientific projects, in workplaces and in sports. Depending on the project and external circumstances, a newly formed collaboration may include people that have collaborated before in the past, and people with no collaboration history. Such existing relationships between team members have been reported to influence the performance of teams. However, it is not clear how existing relationships between team members should be quantified, and whether some relationships are more likely to occur in new collaborations than others. Here we introduce a new family of structural patterns, m-patterns, which formalize relationships between collaborators and we study the prevalence of such structures in data and a simple random-hypergraph null model. We analyze the frequency with which different collaboration structures appear in our null model and show how such frequencies depend on size and hyperedge density in the hypergraphs. Comparing the null model to data of human and non-human collaborations, we find that some collaboration structures are vastly under- and overrepresented in empirical datasets. Finally, we find that structures of scientific collaborations on COVID-19 papers in some cases are statistically significantly different from those of non-COVID-19 papers. Examining citation counts for 4 different scientific fields, we also find indications that repeat collaborations are more successful for 2-author scientific publications and less successful for 3-author scientific publications as compared to other collaboration structures.</p
DataSheet1_Hypergraph patterns and collaboration structure.PDF
No full textHumans collaborate in different contexts such as in creative or scientific projects, in workplaces and in sports. Depending on the project and external circumstances, a newly formed collaboration may include people that have collaborated before in the past, and people with no collaboration history. Such existing relationships between team members have been reported to influence the performance of teams. However, it is not clear how existing relationships between team members should be quantified, and whether some relationships are more likely to occur in new collaborations than others. Here we introduce a new family of structural patterns, m-patterns, which formalize relationships between collaborators and we study the prevalence of such structures in data and a simple random-hypergraph null model. We analyze the frequency with which different collaboration structures appear in our null model and show how such frequencies depend on size and hyperedge density in the hypergraphs. Comparing the null model to data of human and non-human collaborations, we find that some collaboration structures are vastly under- and overrepresented in empirical datasets. Finally, we find that structures of scientific collaborations on COVID-19 papers in some cases are statistically significantly different from those of non-COVID-19 papers. Examining citation counts for 4 different scientific fields, we also find indications that repeat collaborations are more successful for 2-author scientific publications and less successful for 3-author scientific publications as compared to other collaboration structures.</p
First measurement of the proton structure function F_2 with the ZEUS detector
No full textThis thesis describes the methods and results of the first measurement of the proton structure function F_2 by the ZEUS collaboration. The ZEUS detector is one of two large general purpose detectors at the electron-proton colliding facility HERA located at DESY in Hamburg Germany. HERA provides collisions of 26.6 GeV electrons with 820 GeV protons, resulting in a center of mass energy an order of magnitude higher than previous fixed target electron scattering experiments. The kinematics at HERA allows the measurement of F_2 in a region of x and Q"2 phase space previously unexplored. A total integrated luminosity of 24.7 nb"-"1, collected during the fall of 1992, was used for the measurement of F_2. The results reported here extend the measurement of F_2 to lower values of x by two orders of magnitude. In the parton model the behavior of F_2 at low x is highly dependent on the unknown gluon distribution and the absence of data leads to significantly different expectations of the neutral current cross sections at low x. A measurement of F_2 at low x constrains the gluon distribution. The results show a strong rise at low x. (orig.)Available from TIB Hannover: RN 2821(94-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Nachweis von Elektronen aus der e-p Streuung mit dem Hadron-Elektron-Separator im ZEUS-Experiment
No full textThis thesis describes results from the first operation of the Hadron Electron Separator (HES). It is a large area (10 m"2) silicon detector consisting of 10,412 silicon diodes used as particle detectors. It is situated inside the ZEUS Rear Calorimeter. The individual diodes have a size of 3x3.3 cm"2 and a thickness of 400 #mu#m. Distinguishing electrons and hadrons is possible by measuring the energy deposit in the individual diodes. As the deposited energy is proportional to the number of particles contained in an electromagnetic or hadronic shower, these two types of showers can be distinguished by their different showering behaviour. The HES is situated at a depth of 3.3 radiation units inside the calorimeter. During the year 1992, 2,016 HES diodes had been installed in an area close to the beampipe. All of these diodes were included in the readout chain and systematic checks of the performance were made with the first data. An algorithm was developed to identify electrons and to calculate the center of gravity of an electromagnetic shower. Due to the smaller granularity of the HES compared to the calorimeter cells an improved position resolution was achieved. In addition, the HES provided an estimate of the efficiency of electron recognition by comparision with other methods of electron identification. Clear signals for electrons were seen and it was also possible to detect neutral pions in the energy range from 2 to 7 GeV by their decay into two photons. Even with the limited statistics in 1992, it was already possible to select a sample of electrons originating from deep inelastic scattering. This sample was used to determine the proton structure function F_2 and the analysis done with the HES extends the analyses published by the ZEUS collaboration to lower values of x and Q"2. In the meantime all 10,048 diodes have been installed. (orig.)Available from TIB Hannover: RN 2821(94-09) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Measurement of the inclusive φ cross-section in pp collisions at √s=7 TeV
No full textThe cross-section for inclusive φ meson production in pp collisions at a centre-of-mass energy of √s = 7 TeV has been measured with the LHCb detector at the Large Hadron Collider. The differential cross-section is measured as a function of the φ transverse momentum pT and rapidity y in the region 0.6< pT <5.0 GeV/c and 2.44< y <4.06. The cross-section for inclusive φ production in this kinematic range is σ(pp→φX)=1758±19(stat) +43−14(syst)±182(scale) μb, where the first systematic uncertainty depends on the pT and y region and the second is related to the overall scale. Predictions based on the Pythia 6.4 generator underestimate the cross-section
First observation of Bs → J/ψf0(980) decays
No full textUsing data collected with the LHCb detector in proton–proton collisions at a centre-of-mass energy of 7 TeV, the hadronic decay is observed. This CP eigenstate mode could be used to measure mixing-induced CP violation in the system. Using a fit to the π+π− mass spectrum with interfering resonances gives . In the interval ±90 MeV around 980 MeV, corresponding to approximately two full f0 widths we also find , where in both cases the uncertainties are statistical and systematic, respectively
Measurement of the D+/- production asymmetry in 7 TeV pp collisions
No full textThe asymmetry in the production cross-section \sigma of D+/- mesons, A_P = (\sigma(D+) - \sigma(D-))/(\sigma(D+) + \sigma(D-)), is measured in bins of pseudorapidity \eta and transverse momentum p_T within the acceptance of the LHCb detector. The result is obtained with a sample of D+ -> K_S pi+ decays corresponding to an integrated luminosity of 1.0 fb^-1, collected in pp collisions at a centre of mass energy of 7 TeV at the Large Hadron Collider. When integrated over the kinematic range 2.0 K_S pi+ decay is negligible. No significant dependence on \eta or p_T is observed
Measurement of the polarization amplitudes and triple product asymmetries in the B0s → Φ Φ decay
No full text<p>Using 1.0 fb−1 of pp collision data collected at a centre-of-mass energy of s√=7 TeV with the LHCb detector, measurements of the polarization amplitudes, strong phase difference and triple product asymmetries in the B0s→ϕϕ decay mode are presented. The measured values are</p>
<p>|A0|2=0.365±0.022(stat)±0.012(syst),|A⊥|2=0.291±0.024(stat)±0.010(syst),cos(δ∥)=−0.844±0.068(stat)±0.029(syst),AU=−0.055±0.036(stat)±0.018(syst),AV=0.010±0.036(stat)±0.018(syst).</p>
Measurement of the CP-violating phase \phi s in Bs->J/\psi\pi+\pi- decays
No full textMeasurement of the mixing-induced CP-violating phase phi_s in Bs decays is of prime importance in probing new physics. Here 7421 +/- 105 signal events from the dominantly CP-odd final state J/\psi pi+ pi- are selected in 1/fb of pp collision data collected at sqrt{s} = 7 TeV with the LHCb detector. A time-dependent fit to the data yields a value of phi_s=-0.019^{+0.173+0.004}_{-0.174-0.003} rad, consistent with the Standard Model expectation. No evidence of direct CP violation is found
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