Anisotropies in the initial energy density distribution of the quark-gluon plasma created in high energy heavy ion collisions lead to anisotropies in the azimuthal distributions of the final-state ...particles known as collective anisotropic flow. Fourier harmonic decomposition is used to quantify these anisotropies. The higher-order harmonics can be induced by the same order anisotropies (linear response) or by the combined influence of several lower order anisotropies (nonlinear response) in the initial state. The mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles are measured as functions of transverse momentum and centrality in Formula omitted collisions at nucleon-nucleon center-of-mass energies Formula omitted and 5.02 Formula omitted with the CMS detector. The results are compared with viscous hydrodynamic calculations using several different initial conditions, as well as microscopic transport model calculations. None of the models provides a simultaneous description of the mixed higher-order flow harmonics and nonlinear response coefficients.
Corrosion on silicon sensors Hartmann, F.; Bergauer, T.; Fontaine, J.C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2006, Letnik:
569, Številka:
1
Journal Article
Recenzirano
The CMS tracking detector uses about 26
000 silicon sensors to equip
206
m
2
of silicon F. Hartmann, et al., Nucl. Instr. and Meth. A 478 (2002); J.L. Agram, et al., Nucl. Instr. and Meth. A 517 ...(2004) 77. During our quality and process control, including long term testing of the silicon sensors, strange stains on the guard and bias rings have been observed. The result of a systematic investigation proved that our detectors are affected by
Al
2
O
3
corrosion after time under voltage in a humid environment. Depth profiling showed that the metal structures are compromised down to the level of
SiO
2
. Finally, significant concentrations of potassium (K) were found precisely at the location of the corrosion, serving as a catalyst for the electrochemical reaction. A systematic study and origin of these stains will be presented.
A measurement is presented of differential cross sections for t-channel single top quark and antiquark production in proton-proton collisions at a centre-of-mass energy of 13 Formula omitted by the ...CMS experiment at the LHC. From a data set corresponding to an integrated luminosity of 35.9 Formula omitted, events containing one muon or electron and two or three jets are analysed. The cross section is measured as a function of the top quark transverse momentum ( Formula omitted), rapidity, and polarisation angle, the charged lepton Formula omitted and rapidity, and the Formula omitted of the Formula omitted boson from the top quark decay. In addition, the charge ratio is measured differentially as a function of the top quark, charged lepton, and Formula omitted boson kinematic observables. The results are found to be in agreement with standard model predictions using various next-to-leading-order event generators and sets of parton distribution functions. Additionally, the spin asymmetry, sensitive to the top quark polarisation, is determined from the differential distribution of the polarisation angle at parton level to be Formula omitted, in agreement with the standard model prediction.
A search is presented for a heavy vector resonance decaying into a Formula omitted boson and the standard model Higgs boson, where the Formula omitted boson is identified through its leptonic decays ...to electrons, muons, or neutrinos, and the Higgs boson is identified through its hadronic decays. The search is performed in a Lorentz-boosted regime and is based on data collected from 2016 to 2018 at the CERN LHC, corresponding to an integrated luminosity of 137 Formula omitted. Upper limits are derived on the production of a narrow heavy resonance Formula omitted, and a mass below 3.5 and 3.7 Formula omitted is excluded at 95% confidence level in models where the heavy vector boson couples predominantly to fermions and to bosons, respectively. These are the most stringent limits placed on the Heavy Vector Triplet Formula omitted model to date. If the heavy vector boson couples exclusively to standard model bosons, upper limits on the product of the cross section and branching fraction are set between 23 and 0.3 Formula omitted for a Formula omitted mass between 0.8 and 4.6 Formula omitted, respectively. This is the first limit set on a heavy vector boson coupling exclusively to standard model bosons in its production and decay.
Imaging with protons at MedAustron Ulrich-Pur, F.; Bergauer, T.; Burker, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2020, Letnik:
978
Journal Article
Recenzirano
Odprti dostop
Ion beam therapy has become a frequently applied form of cancer therapy over the last years. The advantage of ion beam therapy over conventional radiotherapy using photons is the strongly localized ...dose deposition, leading to a reduction of dose applied to surrounding healthy tissue. Currently, treatment planning for proton therapy is based on X-ray computed tomography, which entails certain sources of inaccuracy in calculation of the stopping power (SP). A more precise method to acquire the SP is to directly use high energy protons (or other ions such as carbon) and perform proton computed tomography (pCT). With this method, the ions are tracked prior to entering and after leaving the patient and finally their residual energy is measured at the very end. Therefore, an ion imaging demonstrator, comprising a tracking telescope made from double-sided silicon strip detectors and a range telescope as a residual energy detector, was set up. First measurements with this setup were performed at beam tests at MedAustron, a center for ion therapy and research in Wiener Neustadt, Austria. The facility provides three rooms for cancer treatment with proton beams as well as one which is dedicated to non-clinical research.
This contribution describes the principle of ion imaging with proton beams in general as well as the design of the experimental setup. Moreover, first results from simulations and recent beam tests as well as ideas for future developments will be presented.
Precision machines like electron-positron-colliders and b-factories demand for low material budget and high position resolution when it comes to particle tracking. A low material budget can be ...achieved by using thin double-sided silicon detectors (DSSDs) and lightweight construction. Since thin sensors give low signals, one has to be very careful to achieve high charge collection efficiency, which requires an appropriate sensor design. In this paper we present a detailed investigation of different p-stop patterns used for strip isolation on the n-side of double-sided microstrip sensors with n-type bulk. We designed test sensors featuring the common p-stop, the atoll p-stop and a combined p-stop pattern, and for every pattern four different geometric layouts were considered. These sensors were tested at the Super Proton Synchrotron (SPS) at CERN (Geneva, Switzerland) in a 120GeV/c hadron beam. Then they were irradiated to 700 kGy with a 60Co source and subsequently tested in the same beam as before. One geometric layout of the atoll p-stop pattern turned out to perform best, both before and after irradiation. The conclusions of these tests will be applied to the design of DSSDs for the Belle II experiment at KEK (Tsukuba, Japan).
A search is presented for Formula omitted slepton pairs produced in proton-proton collisions at a center-of-mass energy of 13 Formula omitted. The search is carried out in events containing two ...Formula omitted leptons in the final state, on the assumption that each Formula omitted slepton decays primarily to a Formula omitted lepton and a neutralino. Events are considered in which each Formula omitted lepton decays to one or more hadrons and a neutrino, or in which one of the Formula omitted leptons decays instead to an electron or a muon and two neutrinos. The data, collected with the CMS detector in 2016 and 2017, correspond to an integrated luminosity of 77.2 Formula omitted. The observed data are consistent with the standard model background expectation. The results are used to set 95% confidence level upper limits on the cross section for Formula omitted slepton pair production in various models for Formula omitted slepton masses between 90 and 200 Formula omitted and neutralino masses of 1, 10, and 20 Formula omitted. In the case of purely left-handed Formula omitted slepton production and decay to a Formula omitted lepton and a neutralino with a mass of 1 Formula omitted, the strongest limit is obtained for a Formula omitted slepton mass of 125 Formula omitted at a factor of 1.14 larger than the theoretical cross section.
The standard model (SM) production of four top quarks ( Formula omitted) in proton-proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016-2018 data taking ...of the LHC, corresponds to an integrated luminosity of 137 Formula omitted at a center-of-mass energy of 13 Formula omitted. The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the Formula omitted signal are respectively 2.6 and 2.7 standard deviations, and the Formula omitted cross section is measured to be Formula omitted. The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, Formula omitted, yielding a limit of Formula omitted at Formula omitted confidence level, where Formula omitted is the SM value of Formula omitted. They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework, Formula omitted. Limits are set on the production of a heavy scalar or pseudoscalar boson in Type-II two-Higgs-doublet and simplified dark matter models, with exclusion limits reaching 350-470 Formula omitted and 350-550 Formula omitted for scalar and pseudoscalar bosons, respectively. Upper bounds are also set on couplings of the top quark to new light particles.
A measurement is presented of electroweak (EW) production of a Formula omitted boson in association with two jets in proton-proton collisions at Formula omitted. The data sample was recorded by the ...CMS Collaboration at the LHC and corresponds to an integrated luminosity of 35.9 Formula omitted. The measurement is performed for the Formula omittedjj final state (with Formula omitted indicating a lepton-neutrino pair, and j representing the quarks produced in the hard interaction) in a kinematic region defined by invariant mass Formula omitted and transverse momenta Formula omitted. The cross section of the process is measured in the electron and muon channels yielding Formula omitted per channel, in agreement with leading-order standard model predictions. The additional hadronic activity of events in a signal-enriched region is studied, and the measurements are compared with predictions. The final state is also used to perform a search for anomalous trilinear gauge couplings. Limits on anomalous trilinear gauge couplings associated with dimension-six operators are given in the framework of an effective field theory. The corresponding 95% confidence level intervals are Formula omitted, Formula omitted, and Formula omitted. These results are combined with the CMS EW Formula omitted analysis, yielding the constraint on the Formula omitted coupling: Formula omitted.
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