Understanding the role of parton mass and Casimir color factors in the quantum chromodynamics parton shower represents an important step in characterizing the emission properties of heavy quarks. ...Recent experimental advances in jet substructure techniques have provided the opportunity to isolate and characterize gluon emissions from heavy quarks. In this Letter, the first direct experimental constraint on the charm-quark splitting function is presented, obtained via the measurement of the groomed shared momentum fraction of the first splitting in charm jets, tagged by a reconstructed D^{0} meson. The measurement is made in proton-proton collisions at sqrts=13 TeV, in the low jet transverse-momentum interval of 15≤p_{T}^{jet ch}<30 GeV/c where the emission properties are sensitive to parton mass effects. In addition, the opening angle of the first perturbative emission of the charm quark, as well as the number of perturbative emissions it undergoes, is reported. Comparisons to measurements of an inclusive-jet sample show a steeper splitting function for charm quarks compared with gluons and light quarks. Charm quarks also undergo fewer perturbative emissions in the parton shower, with a reduced probability of large-angle emissions.
Abstract
A new experiment collects data, since November 2019, at a depth of 210 m.w.e. in the Callio Lab in the Pyhasalmi mine in Finland. The setup, called NEMESIS (New Emma MEasurementS Including ...neutronS), incorporates infrastructure from the EMMA experiment with neutron and large-area plastic scintillator detectors. The experiment’s primary aim is to combine muon tracking with position-sensitive neutron detection to measure precision yields, multiplicities, and lateral distributions of high-multiplicity neutron events induced by cosmic muons in various materials. The data are relevant for background evaluation of the deep-underground searches for Dark Matter (DM), neutrino-less double beta decay, etc. Preliminary analysis revealed anomalies in muon-suppressed neutron multiplicity spectra collected during a 344-day run (live time) with a 565 kg Pb target. The spectra, otherwise well described by an exponential fit, show three peaks at high multiplicities. Although still at a low statistical significance, these small excesses match the outcome of an earlier measurement. The nature of the anomalies remains unclear, but, in principle, they may be a signature of self-annihilation of a WIMP with a mass close to 13 GeV/c
2
. With that assumption, the expected cross-section would be around 10
−42
cm
2
for Spin-Dependent or 10
−46
cm
2
for Spin Independent interactions. We propose verifying this hypothesis with an upgraded NEMESIS experiment, able to collect an order of magnitude more data than this measurement. Based on the statistical uncertainty, analysis of the event rate indicates that cross-section limits for DM mass range of approximately 3-40 GeV/c
2
can be investigated with such a setup.
We present the behavior of the cost-effective Planacon MCP-PMTs with 25μm pore diameter in the presence of axial magnetic fields up to 0.5 T. Having a batch of 62 devices of the same type, two ...MCP-PMTs were selected and their gain variation measured in different magnetic fields. These two otherwise identical devices satisfied the selection criteria by requiring the lowest (1.15 kV) and one of the highest (1.4 kV) bias voltage values to achieve a given gain. Both MCP-PMTs have a nearly identical tolerance of the strong magnetic field despite the significant difference in the bias voltage. This clarifies the mechanism of the B-field influence on the MCP-PMT gain, emphasizing the importance of the intrinsic parameters of the MCP emissive coating rather than external parameters, such as the total bias voltage. By evaluating the dependence of both gain and timing parameters on the magnetic field strength, we confirm the operability of such MCP-PMTs in strong magnetic fields in spite of the relatively large pore diameter and low bias voltage required for a given gain.
Underground multi-muon experiment EMMA Kuusiniemi, P.; Bezrukov, L.; Enqvist, T. ...
Astrophysics and space sciences transactions,
04/2011, Letnik:
7, Številka:
2
Journal Article
Recenzirano
Odprti dostop
EMMA is a new experiment designed for cosmic-ray composition studies around the knee energy operating at the shallow depth underground in the Pyhäsalmi mine, Finland. The array has sufficient ...coverage and resolution to determine the multiplicity, the lateral density distribution and the arrival direction of high-energy muons on an event by event basis. Preliminary results on the muon multiplicity extracted using one detector station of the array are presented.
A new low-background laboratory has been constructed in the Pyhäsalmi mine in central Finland and was commissioned in the beginning of 2017. The underground experimental hall is located at a depth of ...1436 m corresponding to about 4100 m of water equivalent (m.w.e.). We describe the equipment of the laboratory and the backgrounds arising from the natural rock radioactivity and the flux of cosmic ray muons at the experimental hall location. The high-sensitivity experiments operating at the low-background laboratory are briefly described.
The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities ( ) in proton-proton collisions at three center-of-mass energies, Formula omitted 0.9, ...2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 Formula omitted 0.3 % (stat) 8.8 % (sys) and 61.2 Formula omitted 0.3 % (stat) 7.6 % (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The production of the strange and double-strange baryon resonances (..., ...) has been measured at mid-rapidity (... ...) ...in proton-proton collisions at ... ... 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the ... pentaquark, decaying in the ... channel, has been carried out but no evidence is seen.
The production of the strange and double-strange baryon resonances (Formula: see text, Formula: see text) has been measured at mid-rapidity (Formula: see textFormula: see text) in proton-proton ...collisions at Formula: see text Formula: see text 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the Formula: see text pentaquark, decaying in the Formula: see text channel, has been carried out but no evidence is seen.
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