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Searching for pair production of SUSY particles in leptonic final states at the CMS experiment
No full textThe most recent results for searches of pair production of charged and neutral electroweak SUSY particles are presented. The analyses are performed in the final states containing one or more leptons, and presence of a boosted Higgs boson. The results are based on proton-proton collisions recorded at sqrt(s) = 13 TeV with the CMS detector using the full Run 2 dataset of 137 fb-1
Chiral photoelectron angular distributions from ionization of achiral atomic and molecular species
No full textWe show that the combination of two achiral components—an atomic or molecular target plus a circularly polarized photon—can yield chirally structured photoelectron angular distributions. For photoionization of CO, the angular distribution of carbon -shell photoelectrons is chiral when the molecular axis is neither perpendicular nor (anti)parallel to the light propagation axis. In photo-double-ionization of He, the distribution of one electron is chiral if the other electron is oriented like the molecular axis in the former case and if the electrons are distinguishable by their energy. In both scenarios, the circularly polarized photon defines a plane with a sense of rotation and an additional axis is defined by the CO molecule or one electron. This is sufficient to establish an unambiguous coordinate frame of well-defined handedness. To produce a chirally structured electron angular distribution, such a coordinate frame is necessary but not sufficient. We show that additional electron-electron interaction or scattering processes are needed to create the chiral angular distribution
Origin of the high Seebeck coefficient of the misfit cobaltate from site-specific valency and spin-state determinations
No full textLayered misfit cobaltate [Ca2CoO3]0.62[CoO2], which emerged as an important thermoelectric material [A. C. Masset et al. Phys. Rev. B 62, 166 (2000)], has been explored extensively in the last decade for the exact mechanism behind its high Seebeck coefficient. Its complex crystal and electronic structures have inhibited consensus among such investigations. This situation has arisen mainly due to difficulties in accurate identification of the chemical state, spin state, and site symmetries in its two subsystems (rocksalt [Ca2CoO3] and triangular [CoO2]). By employing resonant photoemission spectroscopy and x-ray absorption spectroscopy along with charge transfer multiplet simulations (at the Co ions), we have successfully identified the site symmetries, valencies, and spin states of the Co in both layers. Our site-symmetry observations explain the experimental value of the high Seebeck coefficient and also confirm that the carriers hop within the rocksalt layer, which is in contrast to earlier reports where hopping within triangular CoO2 layer has been held responsible for the large Seebeck coefficient
Search for Axion-Like Particles produced in collisions at Belle II
No full textWe present a search for the direct production of a light pseudoscalar decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process in the mass range {0.2} \,< m_a < {9.7}\,{\text{GeV/c}^2} using data corresponding to an integrated luminosity of . Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axion-like particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength of ALPs to photons at the level of . The limits are the most restrictive to date for 0.2\,<\,m_a\,<\,5\,{\text{GeV/c}^2}
Beyond the Standard Models with Cosmic Strings
No full textWe examine which information on the early cosmological history can be extracted from the potential measurement by third-generation gravitational-wave observatories of a stochastic gravitational wave background (SGWB) produced by cosmic strings. We consider a variety of cosmological scenarios breaking the scale-invariant properties of the spectrum, such as early long matter or kination eras, short intermediate matter and inflation periods inside a radiation era, and their specific signatures on the SGWB . This requires to go beyond the usually-assumed scaling regime, to take into account the transient effects during the change of equation of state of the universe. We compute the time evolution of the string network parameters and thus the loop-production efficiency during the transient regime, and derive the corresponding shift in the turning-point frequency. We consider the impact of particle production on the gravitational-wave emission by loops. We estimate the reach of future interferometers LISA, BBO, DECIGO, ET and CE and radio telescope SKA to probe the new physics energy scale at which the universe has experienced changes in its expansion history. We find that a given interferometer may be sensitive to very different energy scales, depending on the nature and duration of the non-standard era, and the value of the string tension. It is fascinating that by exploiting the data from different GW observatories associated with distinct frequency bands, we may be able to reconstruct the full spectrum and therefore extract the values of fundamental physics parameters
PB method and multi-jet production
No full textTransverse momentum dependent (TMD) parton distributions obtained from the Parton Branching (PB) method are combined with next-to-leading-order (NLO) calculations of jet production to obtain predictions for LHC jet final states. In addition, a new initial state Parton Shower, which is based on the TMD distributions, and final state Parton Showers are included together with hadronization. We compare our predictions with jet and Z+jet measurements performed at the LHC, finding good agreement. We present first results for multi-jet merging with PB-TMDs, illustrating the application of the method to differential jet rates and transverse momentum spectra
Reconciling hints on axion-like-particles from high-energy gamma rays with stellar bounds
No full textIt has been recently claimed by two different groups that the spectral modulation observed in gamma rays from Galactic pulsars and supernova remnants can be due to conversion of photons into ultra-light axion-like-particles (ALPs) in large-scale Galactic magnetic fields. While we show the required best-fit photon-ALP coupling, GeV, to be consistent with constraints from observations of photon-ALPs mixing in vacuum, this is in conflict with other bounds, specifically from the CAST solar axion limit, from the helium-burning lifetime in globular clusters, and from the non-observations of gamma rays in coincidence with SN 1987A. In order to reconcile these different results, we propose that environmental effects in matter would suppress the ALP production in dense astrophysical plasma, allowing to relax previous bounds and make them compatible with photon-ALP conversions in the low-density Galactic medium. If this explanation is correct, the claimed ALP signal would be on the reach of next-generations laboratory experiments such as ALPS II
Robust spin-ice freezing in magnetically frustrated HoGeTiO pyrochlore
No full textStructural analysis of spin frustrated HoGexTiO (x = 0, 0.1, 0.15 & 0.25) pyrochlore oxides has been performed using high resolution x-ray diffraction pattern and low temperature synchrotron x-ray diffraction pattern. The effect of positive chemical pressure on the spin dynamics ofHoGexTiO has been analysed through the study of static (M–T and M–H; magnetisation against temperature & magnetisation against magnetic field) and dynamical (ac susceptibility) magnetic measurements. In lower temperature regime (~2 K), such systems are predominantly governed by competing exchange (J) and dipolar (D) magnetic interactions. Magnetic measurements indicate that the application of increased chemical pressure in HoTiO matrix propels the system towards diminished ferromagnetic interaction. Dipolar coupling constant remains almost unchanged but Curie–Weiss temperature reduces to −0.04 K from 0.33 K (for an applied magnetic field; H = 100 Oe) with increasing x in HoGexTiO. Positive chemical pressure establishes the dominance of Ho–Ho antiferromagnetic interaction J over dipolar interaction D. Spin relaxation feature corresponding to thermally activated single ion freezing (T~15 K) is shifted towards lower temperature. This chemical pressure-driven T shift is ascribed to the alteration in crystal field effect, which reduces the activation energy for singe ion spin freezing. The reduction in the activation energy indicates crystal field-phonon coupling in HoGexTiO system. The robustness in spin ice freezing (second spin relaxation feature in ac susceptibility curve) remains unaffected with increasingly chemical pressure. This spin freezing ('2 in-2 out' spin arrangement in tetrahedra) is related to quantum tunneling phenomenon, at T ~ 2 K. It indicates that majority of spins still follow the 'ice rule' in HoGexTiO even after the application of chemical pressure
