89 research outputs found
Characterization and minimization of the half-integer stop band with space charge in hadron synchrotrons
No full textThis work characterizes the half-integer stop band for various beam distributions in hadron synchrotrons using simulation models with self-consistent space charge and experimental data. Synchrotrons for hadron beams are an important tool in fundamental research (particle and nuclear physics) and applied sciences (medical technology, materials science, industry). However, they are subject to undesirable effects, which degrade the quality of the beam. In any hadron synchrotron, the half-integer resonance is among the strongest effects that limit the maximum achievable beam intensity. The heavy-ion superconducting synchrotron SIS100, currently under construction at GSI, together with the already operating SIS18 synchrotron at GSI, should provide intense beams for future FAIR experiments. Using SIS100 as an example, this work develops a quantitative framework for characterizing the half-integer stop band for realistic, Gaussian-like distributed bunched beams in simulations. The developed framework is tested in a dedicated experiment in SIS18. In any synchrotron, gradient errors in quadrupole magnets induce the half-integer resonance. Due to the half-integer resonance, the beam intensity is limited, which is often referred to as the space-charge limit. To minimize the half-integer stop band for a bunched beam, and hence increase the maximum achievable intensity, lattice corrections are applied. Including space charge in the optimization procedure yields results equivalent to a conventional lattice correction. We validate in long-term simulations, that conventional correction tools are sufficient for increasing the gradient-error-induced space-charge limit of synchrotrons. This study identifies the tune areas affected by the half-integer resonance for varying space-charge strengths. The role of synchrotron motion in providing continuous emittance growth across the bunch is investigated. A key insight of this analysis is that, for bunched beams, a relatively small gradient error can result in a large half-integer stop-band width. The maximum achievable bunch intensity is thus reduced significantly. This contrasts with the findings in existing studies in literature based on more simplified beam distributions, where the space-charge limit does not depend on the strength of gradient errors. The reason for the discrepancy is identified in the increasing stop-band width for Gaussian distributions when space charge becomes stronger, which appears on time scales relevant for synchrotrons
Upgrade of the LHCb ECAL monitoring system
No full textDuring the LHCb running in 2011 and 2012 it was found that the precision of PMT gain monitoring with LED system is affected by radiation damage of the long light guides transporting LED light to calorimeter cells. It was decided to replace in 2014 the present light guides to new ones that should be made of radiation tolerant quartz fibers. After the replacement, the system requires full tuning. It includes adjustment of the LED flash agnitudes and delays, and, after that, adjustment of the PIN diode system. My work was the following: to adjust the PIN signal amplitudes. This included a rough equalization of the amplitudes of signal from the 4 or 2 LEDs served by each PIN diode (achieved by mechanical adjustment of positions of corresponding fibers with respect to the PIN), and then reducing the PIN signal amplitude to the middle of the ADC range when necessary (total of 40 resistive attenuators were produced for this); to find timing corrections for ADCs digitizing the PIN signals; perform a PMT gain measurements using photo statistics. The procedure of determination of timing correction from ECAL step runs was implemented. Finally, it was shown that the ECAL sensitivity degradation can be explained by the degradation of ECAL cells more than PMTs'
Partial-wave analysis of τ−→π−π−π+ντ at BELLE
No full textWe present preliminary results of a partial-wave analysis of τ − → π−π−π+ντ in data from the Belle experiment at the KEKB e+e− collider. We demonstrate the presence of the a1(1420) and a1(1640) resonances in tauon decays and measure their masses and widths. We also present validation of our findings using a model-independent approach. Our results can improve modeling in simulation studies necessary for measuring the tauon electric and magnetic dipole moments and Michel parameters
Characterization and minimization of the half-integer stop band with space charge in a hadron synchrotron
No full textIn any hadron synchrotron, the half-integer resonance is among the strongest effects limiting the achievable maximum beam intensity. The heavy-ion superconducting synchrotron SIS100, currently under construction at GSI, should provide intense beams for the future FAIR experiments. Using SIS100 as an example, this paper develops a quantitative framework for characterizing the half-integer stop band for realistic, Gaussian-like distributed bunched beams. This study identifies the tune areas affected by the gradient-error-induced half-integer resonance for varying space charge strengths. A key insight of our analysis is that, for bunched beams a relatively small gradient error can result in a large half-integer stop band width. The achievable maximum bunch intensity, often referred to as space charge limit, is thus reduced significantly. This contrasts the findings in existing studies in literature based on more simplified beam distributions. The reason for discrepancy is identified in the increasing stop band width for Gaussian distributions when space charge becomes stronger, which appears on longer time scales as relevant for synchrotrons. The role of synchrotron motion in providing continuous emittance growth across the bunch is scrutinized. To minimize the half-integer stop band for a bunched beam, and hence increase the space charge limit, lattice corrections are applied: Including space charge in the optimization procedure recovers results equivalent to conventional lattice correction. Therefore, we find that conventional correction tools are well suited to increase the gradient-error-induced space charge limit of synchrotrons
Partial wave analysis of at Belle
No full textWe present simulation studies in preparation for analyzing
in data from the Belle experiment at the KEK
collider. Analyzing this decay can shed light on the
and resonances and yield results that
improve measurement of the electric and magnetic dipole moments. We show
that we can achieve a higher signal efficiency than previous analyses of the
same decay. We also demonstrate that neural networks can model our complicated
six-dimensional background distributions and that quasi-model-independent
partial-wave analysis can extract resonance masses, widths, and production
amplitudes and phases.Comment: submitted to Proceedings of Science, ICHE2022 poster session, 4
pages, 2 figure
Simulation Study of the Space Charge Limit in Heavy-ion Synchrotrons
No full textThe SIS100 synchrotron as a part of the new FAIR accelerator facility at GSI
should be operated at the "space charge limit" for light and heavy ion beams.
Beam losses due to space charge induced resonance crossing should not exceed a
few percent during a full cycle. The recent advances in the performance of
particle tracking tools with self-consistent solvers for the 3D space charge
forces now allow us to reliably identify low-loss areas in tune space,
considering the full 1s (160'000 turns) accumulation plateau in SIS100. A
realistic magnet error model, extracted from precise bench measurements of the
SIS100 main dipole and quadrupole magnets, is included in the simulations.
Previously such beam dynamics simulations required non-self-consistent space
charge models. By comparing to the self-consistent simulations results we are
now able to demonstrate that the predictions from such faster space charge
models can be used to identify low-loss regions with sufficient accuracy.
The findings are applied by identifying a low-loss working point region in
SIS100 for the design FAIR beam parameters. The bunch intensity at the space
charge limit is determined. Several counter-measures to space charge are
proposed to enlarge the low-loss area and to further increase the space charge
limit.Comment: 17 pages, 24 figure
The Belle II vertex detector integration
No full textThe Belle II experiment comes with a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric collider with energies tuned to (4 ) resonance sqrt() = 10.588 GeV. The accelerator has successfully completed the first phase of commissioning in 2016 and the first electron–positron collisions in Belle II took place in April 2018. Belle II features a newly designed silicon vertex detector based on DEPFET pixel and double-sided strip layers. Currently, a subset of the vertex detector is installed (Phase 2 of the experiment). Installation of the full detector (Phase 3) will be completed by the end of 2018.
This paper describes the Phase 2 arrangement of the Belle II silicon vertex detector, with focus on the interconnection of detectors and their integration with the software framework of Belle II. Alignment issues are discussed based on detector simulations and first acquired data
Measurement of and with a semileptonic tagging method
No full textInternational audienceThe experimental results on the ratios of branching fractions and , where denotes an electron or a muon, show a long-standing discrepancy with the Standard Model predictions, and might hint to a violation of lepton flavor universality. We report a new simultaneous measurement of and , based on a data sample containing events recorded at the resonance with the Belle detector at the KEKB collider. In this analysis the tag-side meson is reconstructed in a semileptonic decay mode and the signal-side is reconstructed in a purely leptonic decay. The measured values are and , where the first uncertainties are statistical and the second are systematic. These results are in agreement with the Standard Model predictions within , and standard deviations for , and their combination, respectively. This work constitutes the most precise measurements of and performed to date as well as the first result for based on a semileptonic tagging method
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