Archive for BICEP3

Still no Primordial Gravitational Waves…

Posted in Astrohype, Bad Statistics, The Universe and Stuff with tags , , , , , , on October 27, 2021 by telescoper

During March 2014 this blog received the most traffic it has ever had (reaching almost 10,000 hits per day at one point). The reason for that was the announcement of the “discovery” of primordial gravitational waves by the BICEP2 experiment. Despite all the hype at the time I wasn’t convinced. This is what I said in an interview with Physics World:

It seems to me though that there’s a significant possibility of some of the polarization signal in E and B [modes] not being cosmological. This is a very interesting result, but I’d prefer to reserve judgement until it is confirmed by other experiments. If it is genuine, then the spectrum is a bit strange and may indicate something added to the normal inflationary recipe.

I also blogged about this several times, e.g. here. It turns out I was right to be unconvinced as the signal detected by BICEP2 was dominated by polarized foreground emission. The story is summarized by these two news stories just a few months apart:

Anyway, the search for primordial gravitational waves continues. The latest publication on this topic came out earlier this month in Physical Review Letters and you can also find it on the arXiv here. The last sentence of the abstract is:

These are the strongest constraints to date on primordial gravitational waves.

In other words, seven years on from the claimed “discovery” there is still no evidence for anything but polarized dust emission…

BICEP3 Cometh…

Posted in The Universe and Stuff with tags , , , , , on January 6, 2016 by telescoper

Back in the office after the Christmas and New Year break, with a mountain of stuff to work through..

Anyway, I saw this paper on the arXiv yesterday and thoought I’d share it here. It’s from a paper by Wu et al. entitled Initial Performance of BICEP3: A Degree Angular Scale 95 GHz Band Polarimeter.  The abstract follows:

BICEP3 is a 550 mm aperture telescope with cold, on-axis, refractive optics designed to observe at the 95 GHz band from the South Pole. It is the newest member of the BICEP/Keck family of inflationary probes specifically designed to measure the polarization of the cosmic microwave background (CMB) at degree-angular scales. BICEP3 is designed to house 1280 dual-polarization pixels, which, when fully-populated, totals to 9× the number of pixels in a single Keck 95 GHz receiver, thus further advancing the BICEP/Keck program’s 95 GHz mapping speed. BICEP3 was deployed during the austral summer of 2014-2015 with 9 detector tiles, to be increased to its full capacity of 20 in the second season. After instrument characterization measurements were taken, CMB observation commenced in April 2015. Together with multi-frequency observation data from Planck, BICEP2, and the Keck Array, BICEP3 is projected to set upper limits on the tensor-to-scalar ratio to r 0.03 at 95% C.L..

It all looks very promising, with science results likely to appear later this year, but who will win the race to find those elusive primordial B-modes?