It is Wednesday evening, after a day of sitting in discussions where the last batch of ATLAS results were approved to be shown at EPS. These included our Higgs searches. I can only reveal the results on Friday, which is why you aren't reading this before then. But I am writing it beforehand for a good reason, which I'll explain at the end.

First the data. Here's the ATLAS Higgs search summary plot.





What you see is a dotted line going zig-zag from left to right, with a green band centred on it and a yellow band centred on that. This represents the expected sensitivity of ATLAS to the existence of the Standard Model Higgs boson*.

The horizontal, straight, dotted line tells you where the Higgs boson should appear, for a particular Higgs boson mass (M H on the horizontal axis).

So where the dotted lines cross tells you that by now, with the amount of data we have analysed, we should have ruled out** possible Higgs bosons with masses between about 130 GeV and 200 GeV, and also between about 320 GeV and 460 GeV. If we had done this, it would be a big extension of the previous exclusion limits and would really be squeezing the possible hiding places for the Higgs. The green and yellow bands tell you what the uncertainties are on this exclusion range. Random fluctuations in the data mean we have a 68% chance of excluding stuff within the green band, and a 95% chance excluding stuff within the yellow band (one and two sigma respectively). All this, of course, is if there is no Higgs boson.

Now look at the solid black line zig-zag. This is what the data actually say.

We have excluded at 95% confidence a Standard Model Higgs with a mass between 155 GeV and 190 GeV, and similarly between 285 295 GeV and 450 GeV. Some of this range was already excluded by the Tevatron experiments, but this is still a big advance. In fact around 290 GeV we are doing "better" than expected, which could of course just be to do with fluctuations in the data.

But it gets even more interesting about 155 GeV. Below here, we are not doing as well as we should.

This means one of three things:

(1) We were unlucky, and an upward random fluctuation in the background messed up our sensitivity.

(2) We did something wrong and failed to find it yet (these are still preliminary results, though they have been reviewed by the ATLAS collaboration).

(3) A Higgs boson, or something very much like it, is lurking in there somewhere below 155 GeV and is starting to emerge, blinking, into the light.

I am writing this now because I want to say what I think about our own data before I see what the Tevatron experiments, or our friends across the LHC, CMS, are going to say. By the time you read this, I will probably know. But here you get my judgement of what our stuff means, independent of any bias from other experiments.

If they show exclusion limits going down below 155 GeV, this means ATLAS was unlucky (or wrong) and the Higgs has less room to breath.

If they show exclusion limits which they didn't expect to go below 155 GeV, this means they are not sensitive enough to say anything about the ATLAS result in this region.

If they show exclusion limits which, like us, they expected to go below 155 GeV but which don't, then the chances that this is the first sign of the Higgs boson emerging into the light are increased.

It's not decisive, but from the ATLAS data alone the odds have shifted in favour of the Higgs being around. When CMS and the Tevatron show their data, the odds will either shift back again, or shift further in favour of the Higgs. I don't know yet. But in contrast to some previous occasions, it's now getting really interesting.

The ATLAS Higgs results are being reported by Kyle Cranmer (New York University) at 15:00 CEST, (after which I will post this article) just before CMS. All the Higgs results from the Large Hadron Collider will be summarised in the plenary later by Bill Murray (STFC Rutherford Appleton Laboratory). They are the result of a massive amount of work by hundreds of people on the LHC machine and on ATLAS.

* Standard Model - not some fancy variant with extra generations or something. This is serious.

** At 95% confidence level