maxwells_daemon: (South Park Tim)
2013-04-02 03:27 pm

Exciting non-discovery from the LHC

In my occasional efforts to keep you abreast of the latest results from the LHC, you might find this paper on heffalon production of interest - even if a day late. I thought the experimental methodology exceptionally robust, though there is an acknowledged fine-tuning problem with their theoretical model. C. Robin, W. T. Pooh, and Piglet will have to wait for the LHC energy upgrade in 2015 for their next chance at the Nobel (though I think it was Piglet alone who first proposed the heffalon hypothesis).
maxwells_daemon: (Kzin)
2012-11-15 05:44 pm

PCC Elections

I enjoy elections and think it is important to vote. So much so, I vote in two different countries where I am eligible to vote.

But I don't agree with today's PCC (Police and Crime Commissioner) elections. I think criminal justice is the one of the worst things to make directly elected (just look at elected prosecutors and judges in the US). So, I've been wondering what to do. Many people have suggested not voting or (better) deliberately spoiling their ballot as a protest. On the other hand one of the candidates does seem better qualified than the rest, so it would be a pity not to register my opinion. [*]

In the end, I went and marked "scrap PCC" (ie. spoilt) as my first choice and my preferred candidate (Tim Starkey, Labour) as second choice. I don't know whether that will be counted the way I want, but it's the best I can do. (They could discard the whole ballot as spoilt, or count my second choice as a first choice.)

The polling station was empty (apart from the tellers, one of whom was off making tea) when I went in at 5pm, so I guess most people are not voting. I told the teller that I was sorry that they had to be there, but he said he enjoyed elections. Even more than me, it seems!

* Also, The Economist argues "If turnout in next week’s elections is really low, England and Wales (Scotland is sensibly sticking with police authorities) could end up with mighty figures who feel untrammelled by public scrutiny."
maxwells_daemon: (Default)
2012-07-04 12:52 pm

Discovery, but is it a Higgs?

After months of equivocation ("hints"), we can finally say that we have discovered something.

It was all very exciting. I'm not used to hearing applause in the middle of a physics presentation. And the second time (ATLAS), they were applauding the number ("5.0 sigma") that I helped determine.

ATLAS see a 5.0σ excess, and CMS see 4.9σ. Each alone would probably be enough to claim a discovery. (According to particle physics convention, one needs >5σ. It is arguable whether one needs to include the "look-elsewhere effect", which reduces the significance to 4.2σ-ish, but one can either combine ATLAS+CMS (as some blogs are already doing), or use CMS to limit the ATLAS search range (or vice versa) so each doesn't need to look elsewhere.)

There certainly was an observation of a Higgs, but that was Peter Higgs, who attended the presentation. But we can't say that what ATLAS and CMS have discovered is a Standard Model Higgs boson. The observations are compatible with a Higgs (though both ATLAS and CMS see a few more decays to two photons than might be expected, which is what pushed us over the 5σ line), but now we need to measure its properties to see whether it's a SM Higgs, some other sort of Higgs, or something entirely new different.
maxwells_daemon: (Default)
2011-12-13 07:08 pm
Entry tags:

Higgs excitement

Today was an exciting day. Finally we can see our our new Higgs search results public, and we can see what CMS have seen and compare. As everyone keeps emphasising, we haven't discovered the Higgs. ATLAS has seen a fairly large "excess" and CMS have a couple of moderate excesses, one of which matches ours at a mass of 126 GeV.

You might want to stop reading here, as it's all science (too much science for LJ?) from here on in...

The two most telling plots are these:

which give the significance (actually (im)probability that there is no Higgs at each mass) of the ATLAS and CMS results, separated into different channels (ways the Higgs can decay) and combined (in black) within each experiment. Those plots are the ones to look at to answer the question "did we see anything?", so probably most interesting at this stage (nothing to do with the fact that I worked most on this one for ATLAS, though I was a small cog in an enormous machine).

If this is a hint of the Higgs, then ATLAS was rather lucky to get such a large signal (though it is still not so large to be suspicious). If this is a statistical fluctuation, then ATLAS was really unlucky (as our spokesperson put it "if it's background, it will be really difficult to kill"). CMS's smaller signal was neither lucky or unlucky.

These numbers have to be corrected for the "look-elsewhere effect" (the fact that we are looking for the Higgs at many different masses and if we look often enough we are bound to see a statistical fluctuation) - unfortunately this was not included in all the internet rumours that prefigured the announcements, so today may have been a bit of a let-down for some people. There is actually a philosophical problem with that correction: should we count everywhere we looked, or just the area that we are still looking (and haven't excluded). ATLAS and CMS actually took different options in their conclusions (probably because it doesn't make much difference for ATLAS, so they can be conservative, while CMS have nothing very exciting to say if they follow us).

So ATLAS/CMS see a significance of 2.5/1.9 sigma (0.6%/3% probability that this is just chance, not a Higgs) or 2.3/0.6 sigma (1%/27%) for a Higgs at around 124/126 GeV, depending on how you calculate the look-elsewhere effect. It is quite incorrect to try to combine these numbers without detailed study (several of the uncertainties are correlated between ATLAS and CMS - it took months for ATLAS and CMS to combine their previous Higgs results), but that hasn't stopped the blogosphere. If you were to naively combine the larger set of numbers you reach 3.1 sigma (0.1%), which in our field is sufficient to claim "evidence" (still well short of 5 sigma required for an "observation"). But I couldn't possibly comment.

For me, the fact that we see an excess at the same place in so many channels (3 channels in ATLAS, 1-3 in CMS, not to mention various sub-channels), makes me quite hopeful that this is something real. Each channel looks for different things (and the two experiments have different detectors and analysis techniques), so it is unlikely to be a mistake. That means it can probably only be a fluke if this isn't really a Higgs. Next year we hope to have lots more data (and at a higher energy), so we should be able to pin it down soon.
maxwells_daemon: (South Park Tim)
2011-12-11 03:54 pm

The Asimov data set

I've been a fan of Isaac Asimov since I was a teenager. I read all his short stories and novels I could get my hands on, and it was probably his essays on science that did the most to get me interested in physics. So I have found it immensely cool that his name is being bandied about in so many discussions in the ATLAS combined Higgs search group.

It is all down to a paper by some of my colleagues (two of whom I am working with now, and another who helped introduce me to another piece of statistics I am working on). They dubbed a representative data set, used to calculate expected sensitivities, the "Asimov data set" and cite Asimov's short story, Franchise (I should probably add something to Wikipedia). I remember the story well: it's about someone chosen by Multivac (a global supercomputer) as the sole voter, because his views are representative of the whole population.

Since it has come up in so many discussions over the last year, I've followed the evolution of the term: "Asimov dataset", "Asimov likelihood", "Asimov method", "Asimov distribution", or just "the Asimov". I get a little thrill each time I hear a new one (I know, I'm a real fanboy).

Despite this, what I've been doing in the Higgs group is to cross-check the asymptotic results, which use the Asimov method, using more traditional methods (known as "ensemble pseudo-experiments", or more informally as "toy Monte Carlo"). They don't rely on assumptions like large statistics (as did Multivac, or Hari Seldon, for that matter), but do require a large amount of computer time to generate many random pseudo-experiments. I developed a way to run these on the Grid. With hundreds of thousands of machines round the world, I have used 8 years of CPU time to generate 8 million toys in a few days.

This sort of thing went into the results that generated some excitement in the summer (eg. p14-16 of the EPS conference presentation). I'm not allowed to say what we will show on Tuesday, but it should be worth watching.
maxwells_daemon: (Default)
2011-03-27 09:40 pm

ATLAS shifts

I'm on shift controlling LHC's ATLAS detector! There are about 15 of us, but I'm in charge of the Run Control system that is in overall control, so I say I'm the most important.

I must say that, compared to DELPHI and BaBar, the ATLAS control room looks like a control room should with everyone in serried ranks facing the giant screen wall at the front. Like Mission Control, only with events and trace plots instead of trajectories and delta-Vs. Here's me on the web-cam (first row, second set of desks).

ATLAS Control Room web-cam

Since people have asked: I've done well at not creating a black hole and gobbling up the world. But in fact, my job would be to detect the black hole when the LHC produces one, so I guess I failed at that.

I did start a couple of runs, the last of which lasted for 23 hours (and included some Van der Meer scans - named for the Nobel laureate, who recently died - where we could see the beams being moved back and forth on the beam position monitors).

Unfortunately these are 2.76 TeV collision-energy runs, which we are doing primarily for comparison with December's heavy-ion data, and not of such interest to what I'm doing. Maybe when I'm on shift next week, we'll take some 7 TeV data.

LHC just declared stable beams, and we're off again! Woot!
maxwells_daemon: (Home Computer 2004)
2011-02-15 07:02 pm


There's good news and bad news.

The good news is much-anticipated: the first new TiVo model in the UK for a decade, and it arrived today! (According to the engineer, I'm the first customer to get one in Oxford.) It is very whizzy with dual-tuner HD recording direct from the cable and integration with the on-demand services, YouTube, etc. It has some annoying features (especially having to enter a PIN every time one wants to watch a recorded 15-rated programme before the watershed) and lacks some things my old TiVos could do (notably copying recordings to PC and no hacking), but is mostly a big improvement.

The bad news has been long-dreaded: the day mine arrived, TiVo announced that they'll soon stop sending schedule information to old TiVos, rendering them near-useless. This is very sad, especially for people who can't get a new TiVo (it is expensive, since you have to get Virgin's top TV package, and only available in cabled areas). Hopefully an alternative way of providing the schedules can be worked out by all the TiVo hackers who want to keep their TiVos going (this has been done elsewhere, so it's probably feasible). I'm almost tempted to help, since I'll miss hacking the new TiVo. (I did a lot of work on my old Palm phone after I moved to Android, but that was just to transfer stuff over - transferring from old to new TiVo is more limited.)

[ETA: a search just revealed that I previously posted about TiVo in 2004, excited by the (until-now unrealised) possibility for a new TiVo model. So I've been anticipating this for at least 7 years!]
maxwells_daemon: (Beaker)
2010-10-16 02:33 pm

Proud of the BBC

Mitch Benn's Proud of the BBC is great (thanks to [ profile] bibliogirl for the first recommendation). Go watch it now.

That's a fantastic song, but I'm not sure I can fully get behind the sentiment. Most of my BBC favourites are from some time ago. There are many excellent British programmes not on that list, mostly made by Channel 4. I am watching much more US TV nowadays, mainly because the BBC is producing much less good drama these days. (I don't even have an LJ icon from a BBC programme.) Maybe I can say I'm proud of what the BBC was and proud when it still, too rarely, produces something brilliant.

Qualifications aside, [ profile] jinty alerted me to a meme that seems to be developing and I feel well-justified in spreading. Here are the programmes listed in the song that I have seen. )
maxwells_daemon: (butter)
2010-06-11 09:51 pm


Cool look at Diamond, the synchrotron at my workplace. The Blade Runner soundtrack led to wistful thoughts: where's my flying car? (Maybe that's how they took the aerial shots.) Why isn't RAL infested with killer sexbots? Why can't I find a better life offworld?
maxwells_daemon: (Dr Bunsen)
2010-05-27 07:11 pm


I don't travel much, except to the usual places (and not much of even that of late), Geneva and San Francisco. But today I'm at DESY in Hamburg, so here are a few trivial observations.

Hamburg has lots of trees. This was obvious even from the plane.

DESY is like CERN on a weekend, but with German instead of French. And lots of trees. (Until recently, DESY had one of the major world accelerators, HERA. I imagine that when HERA was operational DESY was much busier.) The style of buildings, rooms, streets, etc is very like CERN. (One of my RAL colleagues told me that DESY was "like RAL, only more run-down", but I really don't see that.) I guess that won't mean much to anyone without a familiarity with particle physics labs, but maybe with some google-streetviewing, I could demonstrate - a project for later, perhaps.

In Germany, people rap on the table instead of clapping at the end of a talk. I vaguely remember this from a meeting I organised in Karslruhe, many years ago, but it came as a surprise. I think I like it.
maxwells_daemon: (Beaker)
2010-04-21 12:21 am

The joys of being a floating voter

I like my role as an undecided voter in a marginal constituency. It almost feels like my decision will make a difference this time.

OK, I'm not entirely undecided, but I'm still allowing for the possibility that Andrew Smith can persuade me back into the Labour fold. That is hampered by the fact that I've never actually heard any of the Oxford East candidates speak (except Andrew Smith on TV, when he was a minister): since I work outside Oxford, I've only ever managed to get to the Wantage hustings near my work. That's always been Conservative (never one of the options I'd support), apart from when Robert Jackson defected to Labour.

This time a friend directed me to the Climate Question Time tomorrow (Wednesday) evening, so I should finally get to see the candidates debate. Hurrah! No sign of debates on other topics, but I still hold out hope. The Party Leaders' TV debates are good too of course, but we vote for MPs, not PMs.
maxwells_daemon: (Kzin)
2010-04-17 03:05 pm

Happy Birthday, Kzin!

I don't know exactly when his birthday is, but we were told that he was 13 weeks old when we got him, so he is about a year old now, and officially no longer a kitten but a grown up cat. He's certainly now a cat about town, a cat of the world, a cat who knows what's what. But even so, after a hard day's prowling the garden and environs, he still jumps on my lap and insists on being stroked. Or playing fetch with his toy mouse. Or peering between the banisters at me as I go down stairs and bumping noses (though this is rarer, as usually he'll follow me down). Or collapsing on my feet, rolling on his back, paws folded in, the unbearable cuteness of it making it impossible not to tickle his tummy.

So, I should post some photos as demonstration of what a beautiful grown up cat he is. He's not actually changed much for the last few months, though he is looking much more svelt with all the exercise he's getting. Unfortunately, my phone camera doesn't have a flash, making it difficult to capture a black cat in all his beauty in the house. This is the best I have, with [ profile] freya_9 last month:
From Tim's Photos
Maybe someone who has caught Kzin on virtual film can post a photo in the comments?
maxwells_daemon: (Dr Bunsen)
2010-04-01 12:36 pm


We only got our first physics data from the LHC on Tuesday, and they are already planning its successor!
maxwells_daemon: (Dr Bunsen)
2009-12-18 04:35 pm


Here's how we feel about all the beautiful collision data ATLAS has taken over the last few weeks.

ATLAS Armenteros Plot

(This is an "Armenteros Plot" of -pT+ vs (pL+ - pL-) / (pL+ + pL-) (where pT and pL are the momenta (of the positive/negative daughter), respectively transverse and longitudinal to the decaying particle's direction), and shows the decays of K0s (in the smile) and Λs (right eye) and anti-Λs (left eye). It was included in today's ATLAS Report on first collision data, though in a less cheerful form.)

maxwells_daemon: (Dr Manhatten)
2009-11-21 01:36 am

The LHC is back!

First beam splash events of 2009 have been recorded this evening in ATLAS (follow link to event displays). Woot!

This is where we were last year, just before the accident. Hopefully we can soon move onto colliding beams, initially at 450GeV per beam, allowing us to better calibrate the detector. If all goes well, we hope to get 3.5TeV per beam, and the start of real physics, either just before, or just after Christmas.

The first event appears on the screens in the ATLAS control room
My colleagues celebrating the first event in the ATLAS control room
maxwells_daemon: (Me in Toronto. Can't you tell?)
2009-11-19 01:08 pm

!tang apology

I die! There is a great celebration in the land as news of my demise spreads. Workers up tools to dance in the streets, lighting bonfires to burn my effigy. Crops are not harvested, production lines grind to a halt, investments left to fail. As the cities burn and civilisation crumbles, starvation is not far behind. Cursing my name, all that I stood for, and all that I caused, all die! O the embarrassment!

(I've had plenty to apologise for of late, but this one isn't specific. See here for an explanation. Feel free to come up with your own.)
maxwells_daemon: (Dr Bunsen)
2009-11-14 02:27 pm

Giving What We Can

This seems like a good way to encourage people to make significant contributions to helping tackling poverty. The web site also has useful resources to help decide on the most effective charities.

Web site: Giving What We Can
BBC News article

Good work, Toby!
maxwells_daemon: (Willow)
2009-07-19 01:05 am


We were becoming quite worried. For two days, the only signs of Kzin were occasional rustle, occasionally eaten food, and used litter tray.

Then this evening, while we were watching Weeds, [ profile] emily_shore noticed him sitting on his bed watching us. We kept still as he wandered around the room. He became very interested by both our slippers (not on feet) and then alternated between interest and trepidation as we proffered, then wiggled fingers and toes. After some time of this, I got a kitten toy (sparkly rattly ball with feather on a stick) and enticed him with jiggles, then rapid movements and all. We all had fun as he batted, pounced, and chased for much of the evening, slowly gaining confidence. We both took photos, though he's barely visible in mine (poor light - see how I need a gPhone!), so you'll have to wait for [ profile] emily_shore's. Later, when Emily had gone, he even consented to being stroked a few times, while purring continuously (even for a minute after he'd moved out of stroking range).

There's still some way to go (sitting in lap, other people, especially [ profile] jackfirecat, and other parts of the house), but it's surprising how rapidly he gained confidence after hiding for so long. I hope he doesn't forget tomorrow.