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Advancing gravitational wave predictions from cosmological first-order phase transitions
No full textUsing semi-analytical models, we investigate the power spectrum of gravitational waves generated by sound waves in the plasma during a first-order phase transition in new unexplored scenarios. (i) The phase transition is accompanied by a change of the equation of state from that of pure radiation. This causes the peak of the spectrum to shift to smaller frequencies as the equation of state becomes softer and suppresses the amplitude of the power spectrum as a consequence of both sound and gravitational waves propagating across a non-conformal fluid.
(ii) In addition, we investigate the novel limit of large bubbles, by which we mean that the mean bubble spacing is a non-negligible fraction of the Hubble length , i.e. . Since the amplitude of the gravitational wave
signal increases with , this is also the loud signal regime. In this regime the effects of gravity, hitherto neglected, become relevant. We carry out the calculation in cosmological perturbation theory expanding in the parameter , or bubble over Hubble radius.
General relativistic contributions at the next-to-leading order suppress the gravitational wave peak amplitude, with respect to the leading order contribution, by an amount that scales as and also depends on other transition parameters.
This work improves the current estimation of the gravitational waves power spectrum
from first order phase transitions and expands the possible scenarios of transitions that can
be tested by gravitational wave detectors
Recent results in heavy-flavour physics from CMS
No full textRecent CMS results on heavy-flavour physics are discussed. The analyses are based on the data collected during Run 1 and Run 2 of the CERN LHC in pp collisions at 7 and 13 TeV, respectively. The total charm quark pair production cross section is measured with the lowest extrapolation factor to date, and simultaneous production of Y meson and Z boson is observed. The three vector states of B mesons are fully exclusively reconstructed for the first time and their masses are measured
Group photo of the Invisibles25 conference participants
No full textThe Invisibles Workshop 2025 will take place at CERN from September 1st to September 5th, 2025. The Invisibles25 Workshop aims at a broad audience working in the areas of neutrino, dark matter, astroparticle physics, cosmology. It is organized by the Horizon Europe Programme Marie Curie Staff Exchange ASYMMETRY, and it continues the series of “Invisibles” events started in 2012 (Horizon 2020 Marie Curie ITN networks Invisibles, Elusives, and Hidden and Horizon 2020 RISE network InvisiblesPlus)
Search for Supersymmetry with compressed spectra with ATLAS
No full textSupersymmetry (SUSY) models with featuring small mass splittings between one or more particles and the lightest neutralino could solve the hierarchy problem as well as offer a suitable dark matter candidate consistent with the observed thermal-relic dark matter density. However, the detection of SUSY higgsinos at the LHC remains challenging especially if their mass-splitting is O(1 GeV) or lower. Searches are developed using the LHC ATLAS Run 2 dataset to overcome the challenge. Novel techniques are developed exploiting machine-learning techniques, low-momentum tracks with large transverse impact parameters, or topologies consistent with VBF production of the supersymmetric particles. Results are interpreted in terms of SUSY simplified models and, for the first time since the LEP era, several gaps in different ranges of mass-splittings are excluded
Development and characterization of hybrid MCP-PMT with embedded Timepix4 ASIC used as pixelated anode
No full textWe present a novel single-photon detector based on a vacuum tube incorporating a photocathode, a microchannel plate (MCP), and a Timepix4 CMOS ASIC functioning as a pixelated anode. Designed to handle photon rates up to 1 billion per second across a active area, the detector achieves outstanding spatial and temporal resolutions of and below r.m.s., respectively. The Timepix4 ASIC comprises approximately 230,000 pixels, each integrating analog and digital front-end electronics. This enables data-driven acquisition and supports data transmission rates up to 160 Gb/s. External FPGA-based electronics manage both configuration and readout. In order to test the timing performance of the Timepix4 ASIC we performed preliminary characterization of an assembly bonded to a thick n-on-p silicon sensor using a pulsed infrared laser, which demonstrated a per-pixel timing resolution of , with cluster-based averaging methods improving to below . Six prototype detectors incorporating different MCP stack configurations and end-spoiling depths were produced by Hamamatsu Photonics. We report on their characterization, including dark count rates, gain, and spatial and timing resolutions, assessed both in laboratory conditions and during a test-beam campaign at CERN’s SPS facility
Evaluation of a caesium fountain frequency standard for antihydrogen spectroscopy
No full textThe performance of a caesium fountain frequency reference for use in precision measurements of trapped antihydrogen in the ALPHA experiment at CERN is evaluated. A description of the fountain is provided together with a characterisation of systematic effects. The impact of the magnetic environment in the Antimatter Factory, where the fountain is installed, on the performance of the fountain is considered and shown to be insignificant. The systematic fractional frequency uncertainty of the fountain is . The short-term frequency stability of the measured frequency from the ALPHA-HM1 maser is , whereas the fountain itself shows a stability limit of . We find a fractional frequency difference of (1.0 ± 2.2 (stat.) ± 6.5 (syst.)) in a comparison with Terrestrial Time via a GNSS Common View satellite link between January 2023 and June 2024. The fountain enables a significant increase in frequency precision in antihydrogen spectroscopic measurements, and paves the way for improved limits on matter–antimatter comparisons
DUNE@CERN team
No full textDUNE members and collaborators involved with activities at the CERN Neutrino Platfor