We discuss the process
, where
N
is a heavy Majorana neutrino and
. Large cross sections are expected for these processes at high center-of-mass energies, which can be reached at future lepton–lepton ...colliders. The Monte Carlo simulation of the studied processes is produced within the framework of the seesaw type-I model, where the Majorana neutrinos (or heavy neutral leptons, HNL), are introduced in the standard leptonic sector. Recently the possibility to search for the direct HNL production was studied in the
process with the subsequent decay
. In this paper we investigate an alternative process
with the lepton number violation by two units. The similar processes appear in collisions with the same-sign beams,
or
. The cross sections of the processes under consideration are enhanced by the soft photon exchange in the
t
-channel. We calculate the cross sections for the signals and potential Standard Model backgrounds for the
beam collisions at the 1 TeV center-of-mass energy and the
collisions at 3 and 10 TeV. Due to the diagrams with soft
t
-channel photons and respective interference the promptly emitted leptons are produced in the direction close to the corresponding beam. These leptons will be lost in the beam pipe or badly measured by forward detectors. However, the signal events can be well separated from backgrounds using the rest of the event containing the
particles. Finally, the expected upper limits on the mixing parameters
as a function of
M
(
N
) are calculated.
The
process with the subsequent decay of the Higgs boson
is studied, where both
Z
bosons are reconstructed in the final states with two jets. The analysis is performed using Monte Carlo data samples ...obtained with detailed ILD detector simulation assuming an integrated luminosity of 2 ab
–1
, beam polarizations of
, and center-of-mass energy of
GeV for the electron–positron International Linear Collider being currently designed. The analysis is repeated for the case of two 0.9 ab
–1
data samples with polarizations
. Contributions of the potential background processes are studied using all available ILD MC event samples. The largest background comes from the
process supplemented by an energetic photon produced by initial state radiation. To suppress this background, we require that at least one of the
Z
bosons decays to
b
-jets. To reduce the jet reconstruction uncertainties the
variable is used, where
GeV. The
distributions are obtained for the studied signal and backgrounds to estimate the expected accuracy of the
measurement. The accuracy is 22% for the option of the single polarization sample described above and deteriorate to 24% in case of the sample with two polarizations. The proposed method can be applied at any future
collider.
Physics at ILC Drutskoy, A G
Journal of physics. Conference series,
01/2016, Letnik:
675, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The physics case for the International Linear Collider (ILC) project is discussed. The project is proposed to be built in Japan and a final decision has to be taken in 2016 on a government level. The ...initial data taking with e +e - beams is planned at the center-of-mass energy of 500 GeV with following runs at 250 GeV and 350 GeV. Potential physics studies at ILC are discussed with a special attention to the measurements, which are expected to have a better sensitivity at ILC in respect to the LHC experiments.
Using 605 fb(-1) of data collected at the Upsilon(4S) resonance we present a measurement of the inclusive radiative B-meson decay channel, B-->X(s)gamma. For the lower photon energy thresholds of ...1.7, 1.8, 1.9, and 2.0 GeV, as defined in the rest frame of the B meson, we measure the partial branching fraction and the mean and variance of the photon energy spectrum. At the 1.7 GeV threshold we obtain the partial branching fraction BF(B-->X(s)}gamma)=(3.45+/-0.15+/-0.40)x10(-4), where the errors are statistical and systematic.
Equal amounts of matter and antimatter are predicted to have been produced in the Big Bang, but our observable Universe is clearly matter-dominated. One of the prerequisites for understanding this ...elimination of antimatter is the nonconservation of charge-parity (CP) symmetry. So far, two types of CP violation have been observed in the neutral K meson (K0) and B meson (B0) systems: CP violation involving the mixing between K0 and its antiparticle (and likewise for B0 and ), and direct CP violation in the decay of each meson. The observed effects for both types of CP violation are substantially larger for the B0 meson system. However, they are still consistent with the standard model of particle physics, which has a unique source of CP violation that is known to be too small to account for the matter-dominated Universe. Here we report that the direct CP violation in charged B±→K± 0 decay is different from that in the neutral B0 counterpart. The direct CP-violating decay rate asymmetry, (that is, the difference between the number of observed B-→K- 0 event versus B+→K+ 0 events, normalized to the sum of these events) is measured to be about +7%, with an uncertainty that is reduced by a factor of 1.7 from a previous measurement. However, the asymmetry for versus B0→K+ - is at the -10% level. Although it is susceptible to strong interaction effects that need further clarification, this large deviation in direct CP violation between charged and neutral B meson decays could be an indication of new sources of CP violation-which would help to explain the dominance of matter in the Universe.
A detailed study of hadronic interactions is presented using data recorded with the highly granular CALICE silicon–tungsten electromagnetic calorimeter. Approximately 350,000 selected π− events at ...energies between 2 and 10GeV have been studied. The predictions of several physics models available within the GEANT4 simulation tool kit are compared to this data. A reasonable overall description of the data is observed; the Monte Carlo predictions are within 20% of the data, and for many observables much closer. The largest quantitative discrepancies are found in the longitudinal and transverse distributions of reconstructed energy.
We search for bottomonium states in Υ(2S) → (bb)γ decays with an integrated luminosity of 24.7 fb(-1) recorded at the Υ(2S) resonance with the Belle detector at KEK, containing (157.8±3.6)×10(6) ...Υ(2S) events. The (bb) system is reconstructed in 26 exclusive hadronic final states composed of charged pions, kaons, protons, and K(S)(0) mesons. We find no evidence for the state recently observed around 9975 MeV (X(bb)) in an analysis based on a data sample of 9.3×10(6) Υ(2S) events collected with the CLEO III detector. We set a 90% confidence level upper limit on the branching fraction BΥ(2S) → X(bb)γ × ∑(i)BX(bb) → h(i) < 4.9×10(-6), summed over the exclusive hadronic final states employed in our analysis. This result is an order of magnitude smaller than the measurement reported with CLEO data. We also set an upper limit for the ηb(1S) state of BΥ(2S) → ηb(1S)γ × ∑(i)Bηb(1S) → h(i) < 3.7×10(-6).
We have measured the branching fraction of the inclusive radiative
B meson decay
B→
X
s
γ to be
Br(
B→
X
s
γ)=(3.36±0.53(stat)±0.42(sys)
+0.50
−0.54(th))×10
−4. The result is based on a sample of
...6.07×10
6 B
B
̄
events collected at the
ϒ(4
S) resonance with the Belle detector at the KEKB asymmetric
e
+
e
− storage ring.
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