T2K has made improved measurements of three-flavor neutrino mixing with 19.7(16.3) × 10^20 protons on target in (anti-)neutrino-enhanced beam modes. A new sample of muon-neutrino events with tagged pions has been added at the far detector, increasing the neutrino-enhanced muon-neutrino sample size by 42.5%. In addition, new samples have been added at the near detector, and significant improvements have been made to the flux and neutrino interaction modeling. T2K data continues to prefer the normal mass ordering and upper octant of sin^2θ(23) with a near-maximal value of the charge-parity violating phase with best-fit values in the normal ordering of δCP=−2.18+1.22−0.47, sin^2θ(23)=0.559+0.018−0.078 and Δm(23)^2=(+2.506+0.039−0.052)×10^−3 eV^2.
The T2K Collaboration, "Results from the T2K experiment on neutrino mixing including a new far detector μ-like sample" arXiv:2506.05889 (June 6, 2025).
The preference for the upper quadrant was about 2.3 sigma, and the preference for a normal ordering was about 2.7 sigma. With regard to CP-violation:
The data preferred values of δCP close to −π/2 radians, excluding values around +π/2 radians at >3σ, and excluding the CP-conserving values of 0 and π at 90% confidence. However [with further analysis] . . . the result to no longer exclude δCP = π at 90% confidence. The result was statistically limited and can be expected to improve as more data is accumulated.
5 comments:
what do you think of this
arXiv:2506.05326 (hep-ph)
[Submitted on 5 Jun 2025]
Searching for Hidden Sector Particles at Neutrino Telescopes
Sagar Airen, Zackaria Chacko, Can Kilic, Ram Purandhar Reddy Sudha
We explore the possibility of directly detecting light, long-lived hidden sector particles at the IceCube neutrino telescope. Such particles frequently arise in non-minimal hidden sectors that couple to the Standard Model through portal operators. We consider two distinct scenarios. In the first scenario, which arises from a neutrino portal interaction, a hidden sector particle is produced inside the detector by the collision of an energetic neutrino with a nucleon, giving rise to a visible cascade. This new state then decays into a hidden sector daughter, which can naturally be long-lived. The eventual decay of the daughter particle back to Standard Model states gives rise to a second cascade inside the detector. This scenario therefore gives rise to a characteristic "double bang" signal arising from the two distinct cascades. In the second scenario, which arises from a hypercharge portal interaction, a hidden sector particle is produced outside the detector by the collision of an atmospheric muon with a nucleon. This new state promptly decays into a pair of hidden sector daughters that are long-lived. If both daughters decay into Standard Model states inside the detector, we again obtain a double-bang signal from the two distinct cascades. We explore the reach of IceCube for these two scenarios and show that it has the potential to significantly improve the sensitivity to hidden sector models in the mass range from about a GeV to about 20 GeV.
Comments: 29 pages, 18 figures and 1 table
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)
Report number: UT-WI-41-2024
Dark matter and dark radiation from chiral U(1) gauge symmetry
Xiao He, Takaaki Nomura, Norimi Yokozaki
We consider a simple model of a dark sector with a chiral gauge symmetry. The anomaly-free condition requires at least five chiral fermions. Some of the fermions acquire masses through a vacuum expectation value of a Higgs field, and they are stable due to an accidental symmetry. This makes them dark matter candidates. If the dark sector was once in thermal equilibrium with the Standard Model and dark radiation constraints are included, two-component dark matter may be needed since the number of massless fermions is restricted. To meet the requirements from dark matter direct detection experiments, the main component should be a Majorana fermion, and the secondary component should be a Dirac fermion. The amount of Dirac fermion dark matter must be sufficiently small to satisfy direct detection limits. We also discuss the possibility of testing an invisible dark photon at future lepton collider experiments, taking into account cosmological constraints.
Comments: 15 pages, 6 figures
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)
Cite as: arXiv:2506.04718 [hep-ph]
if X17 exists, it may not be a dark matter particle but it is part of a hidden sector or dark sector with many more particles and new forces separate and feeble interactions with standard model
what is your view of hidden sector physics of which x17 might be the first to be shown to exist.
susy would double these
The signal they're looking for in the first paper has already been largely ruled out by direct dark matter detection experiments, but it doesn't hurt to do additional data analysis of data they're collecting anyway.
The second paper's theory is truly grasping at straws with very little to motivate it.
"if X17 exists, it may not be a dark matter particle"
I agree.
"but it is part of a hidden sector or dark sector with many more particles and new forces separate and feeble interactions with standard model" anything that hasn't been ruled out is possible, but there is really almost nothing to motivate that. Look at muon g-2. The SM has never looked more solid and complete.
SUSY is all but ruled out.
okay
"We explore the possibility of directly detecting light, long-lived hidden sector particles at the IceCube neutrino telescope. Such particles frequently arise in non-minimal hidden sectors that couple to the Standard Model through portal operators. "
if x17 exist " non-minimal hidden sectors that couple to the Standard Model through portal operators"
x17 may be a portal operators
The second paper's theory is truly grasping at straws with very little to motivate it.
its a variation of the dark photon
The dark photon (also hidden, heavy, para-, or secluded photon) is a hypothetical hidden sector particle, proposed as a force carrier similar to the photon of electromagnetism but potentially connected to dark matter.[1] In a minimal scenario, this new force can be introduced by extending the gauge group of the Standard Model of Particle Physics with a new abelian U(1) gauge symmetry. The corresponding new spin-1 gauge boson (i.e., the dark photon) can then couple very weakly to electrically charged particles through kinetic mixing with the ordinary photon[2] and could thus be detected. The dark photon can also interact with the Standard Model if some of the fermions are charged under the new abelian group.[3] The possible charging arrangements are restricted by a number of consistency requirements such as anomaly cancellation and constraints coming from Yukawa matrices.
Positron Annihilation into Dark Matter Experiment, originally runs 1 and 2 were search for dark photon
if x17 exist there are probably more particles
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