The CMS drift tubes (DT) muon detector, built for withstanding the LHC expected integrated and instantaneous luminosities, will be used also in the High Luminosity LHC (HL-LHC) at a 5 times larger ...instantaneous luminosity and, consequently, much higher levels of radiation, reaching about 10 times the LHC integrated luminosity. Initial irradiation tests of a spare DT chamber at the CERN gamma irradiation facility (GIF++), at large (∼O(100)) acceleration factor, showed ageing effects resulting in a degradation of the DT cell performance. However, full CMS simulations have shown almost no impact in the muon reconstruction efficiency over the full barrel acceptance and for the full integrated luminosity. A second spare DT chamber was moved inside the GIF++ bunker in October 2017. The chamber was being irradiated at lower acceleration factors, and only 2 out of the 12 layers of the chamber were switched at working voltage when the radioactive source was active, being the other layers in standby. In this way the other non-aged layers are used as reference and as a precise and unbiased telescope of muon tracks for the efficiency computation of the aged layers of the chamber, when set at working voltage for measurements. An integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC run has been absorbed by this second spare DT chamber and the final impact on the muon reconstruction efficiency is under study. Direct inspection of some extracted aged anode wires presented a melted resistive deposition of materials. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway. Strategies to mitigate the ageing effects are also being developed. From the long irradiation measurements of the second spare DT chamber, the effects of radiation in the performance of the DTs expected during the HL-LHC run will be presented.
The mass and width of the W boson are measured using e+e– → W+W– events from the data sample collected by the OPAL experiment at LEP at centre-of-mass energies between 170 GeV and 209 GeV. The mass ...(mW) and width (ΓW) are determined using direct reconstruction of the kinematics of W+W– → and W+W– → events. When combined with previous OPAL measurements using W+W– → events and the dependence on of the WW production cross-section at threshold, the results are determined to be where the first error is statistical, the second systematic and the third due to uncertainties in the value of the LEP beam energy. By measuring in the channel using several different determinations of the direction of jets with differing sensitivities to soft particles, a limit is also obtained on possible final-state interactions due to colour reconnection effects inW+W– → events. The consistency of the results for the W mass and width with those inferred from other electroweak parameters provides an important test of the Standard Model of electroweak interactions.
An investigation of the effects of substrate type and various treatments on carbon nanotubes (CNT) growth, using an evaporated Ni thin film as a catalyst, is presented. Barrier layers of SiO
2, Si
3N
...4, and TiN on Si were used as substrates. The catalyst-insulating substrate systems have been processed in several gaseous atmospheres (Ar, NH
3 and H
2) and in the temperature range 700–900
°C, in order to obtain the most appropriate morphology, size and density of catalyst particles as seeds for the subsequent CNT growth. On this kind of substrates, the smallest nanoparticles were obtained on SiO
2 layers, in H
2 or NH
3 atmosphere even at 700
°C. However, the best vertically aligned and well-graphitized CNT resulted from the NH
3 annealing process, followed by the CNT deposition at 900
°C in C
2H
2 and H
2.
On TiN conducting substrates, the best vertically aligned CNT were deposited using a shorter annealing step and a deposition process at reduced pressure. The samples were characterized by means of scanning electron microscopy (SEM) and Raman spectroscopy analysis.
Field Emission (FE) properties of vertically aligned Carbon Nanotubes (CNTs) grown in a nanoporous anodic aluminium oxide (AAO) template have been investigated. A 50-μm-thick AAO template was ...fabricated by electrochemical techniques. The nanotubes were synthesized in a CVD quartz hot wall furnace using C
2H
2/N
2 mixtures as feeding gas.
I–V measurements have been performed on samples after the nanotubes growth (type I samples) and after a partial Al
2O
3 removal (type II samples) in order to obtain segments of nanotubes protruding from the nanopores. The effects of the conditioning process and adsorbates release have been investigated. The emission curves have been analysed in the framework of the Fowler–Nordheim model. For the
β factor enhancement, a different dependence on time has been evidenced for two types of investigated samples and has been tentatively correlated with materials modifications occurring under the HV polarisation (in case of type I samples) and with the damage induced by chemical etching (in case of type II samples). The values of emitted current density (up to 40
mA/cm
2) and the emission properties indicate that the proposed preparation methodology is suitable for the realization of robust and efficient CNT-based field emission devices and electron sources.
A search is made for charged Higgs bosons predicted by Two-Higgs-Doublet extensions of the Standard Model (2HDM) using electron-positron collision data collected by the OPAL experiment at
, ...corresponding to an integrated luminosity of approximately 600 pb
−1
. Charged Higgs bosons are assumed to be pair-produced and to decay into
,
τν
τ
or AW
±
. No signal is observed. Model-independent limits on the charged Higgs-boson production cross section are derived by combining these results with previous searches at lower energies. Under the assumption
, motivated by general 2HDM type II models, excluded areas on the
plane are presented and charged Higgs bosons are excluded up to a mass of 76.3 GeV at 95 % confidence level, independent of the branching ratio BR(H
±
→
τν
τ
). A scan of the 2HDM type I model parameter space is performed and limits on the Higgs-boson masses
and
m
A
are presented for different choices of tan
β
.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Hadronic event shape distributions from e
+
e
−
annihilation measured by the OPAL experiment at centre-of-mass energies between 91 GeV and 209 GeV are used to determine the strong coupling
α
S
. The ...results are based on QCD predictions complete to the next-to-next-to-leading order (NNLO), and on NNLO calculations matched to the resummed next-to-leading-log-approximation terms (NNLO + NLLA). The combined NNLO result from all variables and centre-of-mass energies is
while the combined NNLO + NLLA result is
The completeness of the NNLO and NNLO + NLLA results with respect to missing higher order contributions, studied by varying the renormalization scale, is improved compared to previous results based on NLO or NLO + NLLA predictions only. The observed energy dependence of
α
S
agrees with the QCD prediction of asymptotic freedom and excludes the absence of running.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Different electrochemical regimes and porous alumina were applied for template synthesis of cobalt nanowire (nw) arrays, revealing several peculiar cases. In contrast to quite uniform filling of ...sulfuric acid alumina templates by alternating current deposition, nonuniform growth of the Co nw tufts and mushrooms was obtained for the case of oxalic acid templates. We showed herein for the first time that such configurations arise from the spontaneous growth of cobalt nw groups evolving from the cobalt balls at the Al/alumina interface. Nevertheless, the uniform growth of densely packed cobalt nw arrays, up to tens of micrometers in length, was obtained via long-term direct current galvanostatic deposition at low current density using oxalic acid templates one-side coated by conducting layer. The unique point of this regime is the formation of hexagonal lattice Co nws with a preferred (100) growth direction.
Measurement of αs with radiative hadronic events Ainsley, C.; Åkesson, P.F.; Alexander, G. ...
The European physical journal. C, Particles and fields,
2008/1, Letnik:
53, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Hadronic final states with a hard isolated photon are studied using data taken at centre-of-mass energies around the mass of the Z boson with the OPAL detector at LEP. The strong coupling α
s
is ...extracted by comparing data and QCD predictions for event shape observables at average reduced centre-of-mass energies ranging from 24 GeV to 78 GeV, and the energy dependence of α
s
is studied. Our results are consistent with the running of α
s
as predicted by QCD and show that within the uncertainties of our analysis event shapes in hadronic Z decays with hard and isolated photon radiation can be described by QCD at reduced centre-of-mass energies. Combining all values from different event shape observables and energies gives α
s
(M
Z
)=0.1182±0.0015(stat.)±0.0101(syst.).
The Compact Muon Solenoid (CMS) experiment prepares its Phase-2 upgrade for the high-luminosity era of the LHC operation (HL-LHC). Due to the increase of occupancy, trigger latency and rates, the ...full electronics of the CMS Drift Tube (DT) chambers will need to be replaced. In the new design, the time bin for the digitization of the chamber signals will be of around 1 ns, and the totality of the signals will be forwarded asynchronously to the service cavern at full resolution. The new backend system will be in charge of building the trigger primitives of each chamber. These trigger primitives contain the information at chamber level about the muon candidates position, direction, and collision time, and are used as input in the L1 CMS trigger. The added functionalities will improve the robustness of the system against ageing. An algorithm based on analytical solutions for reconstructing the DT trigger primitives, called Analytical Method, has been implemented both as a software C++ emulator and in firmware. Its performance has been estimated using the software emulator with simulated and real data samples, and through hardware implementation tests. Measured efficiencies are 96 to 98% for all qualities and time and spatial resolutions are close to the ultimate performance of the DT chambers. A prototype chain of the HL-LHC electronics using the Analytical Method for trigger primitive generation has been installed during Long Shutdown 2 of the LHC and operated in CMS cosmic data taking campaigns in 2020 and 2021. Results from this validation step, the so-called Slice Test, are presented.
Data collected around
GeV by the OPAL experiment at the LEP e
+
e
−
collider are used to study the mechanism of baryon formation. As the signature, the fraction of Σ
−
hyperons whose baryon number ...is compensated by the production of a
or
antihyperon is determined. The method relies entirely on quantum number correlations of the baryons, and not rapidity correlations, making it more model independent than previous studies. Within the context of the JETSET implementation of the string hadronization model, the diquark baryon production model without the popcorn mechanism is strongly disfavored with a significance of 3.8 standard deviations including systematic uncertainties. It is shown that previous studies of the popcorn mechanism with
and
correlations are not conclusive, if parameter uncertainties are considered.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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