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A. Belyaev

Publications and source records attributed to A. Belyaev.

At least 73 records · Page 4Linked to original sources
arXiv2012

Production of Sigma{\pm}pi?pK+ in p+p reactions at 3.5 GeV beam energy

We study the production of Sigma^+-pi^+-pK^+ particle quartets in p+p reactions at 3.5 GeV kinetic beam energy. The data were taken with the HADES experiment at GSI. This report evaluates the contribution of resonances like Lambda(1405$, Sigma(1385)^0, Lambda(1520), Delta(1232), N^* and K^*0 to the Sigma^+- pi^-+ p K+ final state. The resulting simulation model is compared to the experimental data in several angular distributions and it shows itself as suitable to evaluate the acceptance corrections properly.

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arXiv2012

Higgs Phenomenology of Minimal Universal Extra Dimensions

The minimal model of Universal Extra Dimensions (MUED) is briefly reviewed. We explain how the cross-sections for Higgs production via gluon fusion and decay into two photons are modified, relative the the Standard Model (SM) values, by KK particles running in loops, leading to an enhancement of the gg to h to two photons and gg to h to W+W- cross-sections. ATLAS and CMS searches for the SM Higgs in these channels are reinterpreted in the context of MUED and used to place new limits on the MUED parameter space. Only a small region of between 1 and 3 GeV around mh = 125 GeV for 500 GeV < 1/R < 1600 GeV remains open at the 95 % confidence level.

hep-ph↗
arXiv2011

Inclusive dielectron spectra in p+p collisions at 3.5 GeV

We present the inclusive invariant-mass, transverse momentum and rapidity distributions of dielectrons (e$^{+}$e$^{-}$ pairs) in p+p interactions at 3.5 GeV beam kinetic energy. In the vector-meson mass region, a distinct peak corresponding to direct $ω$ decays is reconstructed with 2% mass resolution. The data is compared to predictions from three model calculations. Due to the large acceptance of the HADES apparatus for $e^{+}e^{-}$ invariant masses above 0.2 GeV/$c^{2}$ and for transverse pair momenta p$_{t}$ $ <$ 1 GeV/$c$, acceptance corrections are to a large extent model independent. This allows us to extract from dielectron data for the first time at this energy the inclusive production cross sections for light vector mesons. Inclusive production cross sections for $π^o$ and $η$ mesons are also reported. The obtained results will serve as an important reference for the study of vector meson production in proton-nucleus and heavy-ion collisions. Furthermore, using this data, an improved value for the upper bound of the branching ratio for direct $η$ decays into the electron-positron channel is obtained.

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arXiv2011

Dielectron production in Ar+KCl collisions at 1.76A GeV

We present results on dielectron production in Ar+KCl collisions at 1.76A GeV. For the first time $ω$ mesons could be reconstructed in a heavy-ion reaction at a bombarding energy which is well below the production threshold in free nucleon-nucleon collisions. The omega multiplicity has been extracted and compared to the yields of other particles, in particular of the phi meson. At intermediate e+e- invariant masses, we find a strong enhancement of the pair yield over a reference spectrum from elementary nucleon-nucleon reactions suggesting the onset of non-trivial effects of the nuclear medium. Transverse-mass spectra and angular distributions have been reconstructed in three invariant mass bins. In the former unexpectedly large slopes are found for high-mass pairs. The latter, in particular the helicity-angle distributions, are largely consistent with expectations for a pair cocktail dominated at intermediate masses by delta Dalitz decays.

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arXiv2011

Cross section in deuteron-proton elastic scattering at 1.25 GeV/u

First results of the differential cross section in dp elastic scattering at 1.25 GeV/u measured with the HADES over a large angular range are reported. The obtained data corresponds to large transverse momenta, where a high sensitivity to the two-nucleon and three-nucleon short-range correlations is expected.

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arXiv2011

Single and double pion production in np collisions at 1.25 GeV with HADES

The preliminary results on charged pion production in np collisions at an incident beam energy of 1.25 GeV measured with HADES are presented. The np reactions were isolated in dp collisions at 1.25 GeV/u using the Forward Wall hodoscope, which allowed to register spectator protons. The results for np -> pppi-, np -> nppi+pi- and np -> dpi+pi- channels are compared with OPE calculations. A reasonable agreement between experimental results and the predictions of the OPE+OBE model is observed.

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arXiv2011

Hyperon production in Ar+KCl collisions at 1.76A GeV

We present transverse momentum spectra, rapidity distribution and multiplicity of Lambda-hyperons measured with the HADES spectrometer in the reaction Ar(1.76A GeV)+KCl. The yield of Xi- is calculated from our previously reported Xi-/(Lambda+Sigma0) ratio and compared to other strange particle multiplicities. Employing a strangeness balance equation the multiplicities of the yet unmeasured charged Sigma hyperons can be estimated. Finally a statistical hadronization model is used to fit the yields of pi-, K+, K0s, K-, phi, Lambda and Xi-. The resulting chemical freeze-out temperature of T=(76+-2) MeV is compared to the measured slope parameters obtained from fits to the transverse mass distributions of the particles.

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arXiv2010

Higgs phenomenology in the minimal $B-L$ extension of the Standard Model at LHC

We present some phenomenology of the Higgs sector of the Minimal $B-L$ U(1) Extension of the Standard Model at the Large Hadron Collider. In this model, the existence of an extra gauge boson ($Z'$) and an extra scalar (heavy Higgs) are predicted as naturally related with the breaking of the $B-L$ (baryon minus lepton number) symmetry. For this, we have started by deriving the unitarity bounds in the high energy limit for the Minimal $B-L$ Model parameter space. This was accomplished by analysing the full class of Higgs and would-be Goldstone boson two-to-two scatterings at tree level (exploiting the Equivalence Theorem). Hence, we studied some peculiar signature that could be observed at the CERN machine in the search of both light and heavy Higgs bosons.

hep-ph↗
arXiv2010

The Z' boson of the minimal B-L model at future Linear Colliders in e+e- --> mu+mu-

We study the capabilities of future electron-positron Linear Colliders, with centre-of-mass energy at the TeV scale, in accessing the parameter space of a $Z'$ boson within the minimal $B-L$ model. We carry out a detailed comparison between the discovery regions mapped over a two-dimensional configuration space ($Z'$ mass and coupling) at the Large Hadron Collider and possible future Linear Colliders for the case of di-muon production. As known in the literature for other $Z'$ models, we confirm that leptonic machines, as compared to the CERN hadronic accelerator, display an additional potential in discovering a $Z'$ boson as well as in allowing one to study its properties at a level of precision well beyond that of any of the existing colliders.

hep-ph↗
arXiv2010

Tree Level Unitarity Bounds for the Minimal B-L Model

We have derived the unitarity bounds in the high energy limit for the minimal B-L extension of the Standard Model by analysing the full class of Higgs and would-be Goldstone boson two-to-two scatterings at tree level. Moreover, we have investigated how these limits could vary at some lower critical value of the energy.

hep-ph↗
arXiv2010

New Physics at the LHC. A Les Houches Report: Physics at TeV Colliders 2009 - New Physics Working Group

We present a collection of signatures for physics beyond the standard model that need to be explored at the LHC. First, are presented various tools developed to measure new particle masses in scenarios where all decays include an unobservable particle. Second, various aspects of supersymmetric models are discussed. Third, some signatures of models of strong electroweak symmetry are discussed. In the fourth part, a special attention is devoted to high mass resonances, as the ones appearing in models with warped extra dimensions. Finally, prospects for models with a hidden sector/valley are presented. Our report, which includes brief experimental and theoretical reviews as well as original results, summarizes the activities of the "New Physics" working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 8-26 June, 2009).

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arXiv2009

Phenomenology of the minimal B-L extension of the Standard Model

We present the Large Hadron Collider (LHC) discovery potential in the $Z'$ and heavy neutrino sectors of a $U(1)_{B-L}$ enlarged Standard Model also encompassing three heavy Majorana neutrinos. This model exhibits novel signatures at the LHC, the most interesting arising from a $Z'$ decay chain involving heavy neutrinos, eventually decaying into leptons and jets. In particular, this signature allows one to measure the $Z'$ and heavy neutrino masses involved. In addition, over a large region of parameter space, the heavy neutrinos are rather long-lived particles producing distinctive displaced vertices that can be seen in the detectors. Lastly, the simultaneous measurement of both the heavy neutrino mass and decay length enables an estimate of the absolute mass of the parent light neutrino. For completeness, we will also compare the LHC and a future Linear Collider (LC) discovery potentials.

hep-ph↗
arXiv2009

Future perspectives at SIS-100 with HADES-at-FAIR

Currently, the HADES spectrometer undergoes un upgrade program to be prepared for measurements at the upcoming SIS-100 synchrotron at FAIR. We describe the current status of the HADES di-electron measurements at the SIS-18 and our future plans for SIS-100.

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arXiv2009

Charged pion production in C+C and Ar+KCl collisions measured with HADES

Results of a study of charged pion production in 12C+12C collisions at incident beam energies of 1A GeV and 2A GeV, and 40Ar+natKCl at 1.76AGeV, using the spectrometer HADES at GSI, are presented. We have performed a measurement of the transverse momentum distributions of pi+- mesons covering a fairly large rapidity interval, in case of the C+C collision system for the first time. The yields, transverse mass and angular distributions are compared with a transport model as well as with existing data from other experiments.

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arXiv2009

Measurement of charged pions in 12C + 12C collisions at 1A GeV and 2A GeV with HADES

We present the results of a study of charged pion production in 12C + 12C collisions at incident beam energies of 1A GeV and 2A GeV using the HADES spectrometer at GSI. The main emphasis of the HADES program is on the dielectron signal from the early phase of the collision. Here, however, we discuss the data with respect to the emission of charged hadrons, specifically the production of pi+- mesons, which are related to neutral pions representing a dominant contribution to the dielectron yield. We have performed the first large-angular range measurement of the distribution of pi+- mesons for the 12C + 12C collision system covering a fairly large rapidity interval. The pion yields, transverse-mass and angular distributions are compared with calculations done within a transport model, as well as with existing data from other experiments. The anisotropy of pion production is systematically analyzed.

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arXiv2008

Technicolor Walks at the LHC

We analyze the potential of the Large Hadron Collider (LHC) to observe signatures of phenomenologically viable Walking Technicolor models. We study and compare the Drell-Yan (DY) and Vector Boson Fusion (VBF) mechanisms for the production of composite heavy vectors. We find that the heavy vectors are most easily produced and detected via the DY processes. The composite Higgs phenomenology is also studied. If Technicolor walks at the LHC its footprints will be visible and our analysis will help uncovering them.

hep-ph↗
arXiv2008

Dictionary of LHC Signatures

We report on a plan to establish a "Dictionary of LHC Signatures", an initiative that started at the WHEPPX workshop in January 2008. This study aims towards the strategy on distinguishing of 3 classes of dark matter motivated scenarios such as R-parity conserved supersymmetry, Little Higgs models with T-parity conservation and Universal Extra Dimensions with KK-parity for generic cases of their realization in wide range of the model space. Discriminating signatures are tabulated and will need a further detailed analysis.

hep-ph↗