Quantum Diaries

Hi blog-enthusiasts,

So much has happened with the LHC over the past year or so since I started blogging. We’ve recorded splash events, first collisions, stable running and accelerated beams, and now machine operations are going full steam ahead at record breaking energies. Although I’ve enjoyed sharing my thoughts and updates, all good things must come to an end.

Thanks to all my readers who’ve kept up on my posts. I know they’ve been sparse over the past month but I’ve realized that I can’t really do justice to the LHC blog and do the rest of my work. I hope you’ve enjoyed reading what I’ve had to say and best of luck to the rest of the bloggers!

Regina

It’s been a while since I’ve blogged and to my readers I apologize. I have been working on my leptoquark analysis, which is rolling right along. I’ll be sure to share that at a more appropriate time but I thought it would be fun to take note of what I do on an average work day. So why not today…

9:30-ish A.M. – arrive at Brookhaven National Lab. Usually I go to Stony Brook, but today I’m working with one of the post-docs at BNL on how to estimate QCD background.** Upon arriving, we get a quick coffee and get caught up on this weekend’s US Open tennis championships. Discussion of my analysis code ensues.

**ASIDE: QCD (Quantum ChromoDynamics) is the theory of strong interactions. Of the forces we study at the LHC, this is the least exactly understood. It relates to all quark/gluon (color charged) interactions. QCD has two peculiarities: confinement and asymptotic-freedom. In short, confinement means that as you move two quarks away from each other the force between them gets larger (like a rubber band). This explains why you never see single quarks, instead you see showers of quarks (called jets). As they move away from each other, more quarks pop out. Asymptotic-freedom means that high energy quarks and gluons interact less. At a hadron collider, the most prominent thing you get out are jets. They are a significant background that you have to remove to do an analysis. It’s also difficult to simulate just based on the sheer number of jets that come out. My advisor once told me that the least expensive way to simulate all the QCD background needed  is to build a collider and take data. **

10:30 A.M. – After getting some unexpected results in my electron analysis, the anonymous post-doc confirms that there is indeed a bug in my analysis code. This is what I spend the vast majority of my time doing. Writing and debugging code to perform an analysis on data and simulated data. He has written a modified version on my electron selection code, so I work to combine the two.

11:15 A.M. – We get into a discussion about what the electron/photon (called e/gamma) group has defined as an appropriate selection criteria for the electrons I want to include in my analysis. I want to use a standard selection criteria but the standards vary in the early days of data-taking. We decide that the best approach is to use the selection criteria of my greatest background: W bosons produced with jets.

12:15 P.M. – Lunch time. We join the other ATLAS scientists at BNL on the walk over to the cafeteria. The cafeteria contains your standard fare. I usually go for an egg-salad sandwich. The days I go to BNL, I don’t make my own lunch. The discussion flows from the fate of the Tevatron to the post-doc’s baby girl and back to the US Open (I’m a big tennis fan… go figure).

1:00 P.M.: Head back from lunch, and start the discussion of QCD estimation. Unfortunately the bug in my code and discussion of selection criteria for electrons took up the morning, but that leaves the afternoon for some strong force fun. **So how do we do this ** The discussion takes a while, but once it’s done….

**Another Aside!: QCD estimation is done a couple of different ways. It gets pretty detailed, but here is a brief overview. You look at two different regions: an area that you believe to be signal poor and QCD background rich, and the other signal rich and QCD background poor. You can then pick selection variables that are uncorrelated: like a lepton ID variable, and a Missing Energy variable (from neutrinos). You can then plot the values of the events in terms of the two variables and come with four regions: an area that is signal for both variables, an area that passes signal cuts for one variable but not the other (2 of these), and an area that fails the signal cuts for both variables. From these numbers and ratios you can predict the amount of QCD you should get. –I’ll note again, this is simplified, but the general idea is there.**

2:45 P.M.: I now get to write the code that makes these plots 🙂 And spend the rest of the afternoon doing so.

6:45 P.M.: I get home in time to see the US Open men’s championship get rain delayed, so I pop open my laptop and start coding again. I have a farewell party for a friend who graduated and is moving to Germany tonight, so I can’t work too much longer.

-Regina

Over the weekend the LHC was able to deliver our first pb^-1 of data! Milestones keep rolling on by and the data keeps rolling in. This is a big first step in getting what will hopefully be lots and lots of data. I’ve included a link to the ATLAS luminosity plot for your viewing pleasure. (CMS has one too… but I’m on ATLAS :))

To anyone who isn’t a particle physicist an inverse picobarn (pb^-1) is a pretty bizarre unit. I’ll start out with the base unit: the barn (b). It’s a measurement of area, proportional to m^2 or cm^2. The barn unit comes from when nuclear physics was in its infancy and refers to a uranium nucleus which is as big as a barn (1 barn = 10^-24 cm^2). (I still think physicists should hire writers to come up with this stuff… anywho, back to the post).

An inverse barn (or b^-1) in the particle physics world is a measure of collision events in an area of a barn. Throw in a metric prefix (pico which is 10^-12*base unit) and now you’re all caught up to speed. But what does that mean really? Fermilab has over an inverse femtobarn (fb^-1, which means 1000x an inverse picobarn) of data but of course they’ve been running their collider for over a decade. We’ll still need much more data to do searches for things like the Higgs, but very early searches are definitely underway – not to mention all the Standard Model physics and calibration that’s going on too.

So cheers to the first pb-1 of data… I can’t wait to start analyzing.

-Regina

Lots of us bloggers have been talking about ICHEP which is going on this week. I’m not attending the conference, although some of the work I’ve been doing is :).
Now I’ve been turning my attention back to my physics analysis.  As of about a week ago we have 200 nb-1 (now closer to 300 nb-1) of data – which is about 1/50th of what I hope to get for an analysis.

I briefly mentioned that I’ll be doing a search in a previous post. Now I’d like to share a bit what this particle beast is. A leptoquark carries quantum numbers for both quarks and leptons. It would decay by generation such that it mixes families of quarks and leptons. So why do we think it exists? In a word: Symmetry.

Physicists love symmetry (and symmetry breaking :)). Symmetry in forces (like electricity and magnetism), symmetry in families and generations of particles, symmetries everywhere. Since the quarks and leptons in the Standard Model have the same family structure it seems like there should be something that ties them together, like leptoquarks.

Granted this is a bit of an oversimplification, theorists have put in lots of work into understanding how these particles work. And now I’m going to be looking for them.

I’ll be giving updates over the next few months explaining more about these particles over the coming weeks.

-Regina

Sorry for the hiatus, blog enthusiasts! I’m taking some time to catch-up while watching the fireworks out of my window on July 4th. Tis the season for summer conferences. The one in particular that I’m involved in is ICHEP (International Conference on High Energy Physics) is coming up at the end of July, which means all the papers have to be approved by ATLAS by the end of June (which just so happened to be last week – hooray independence  ;)). This year the conference is in Paris and there we’ll show the first physics results from the LHC. ATLAS alone has over 40 papers submitted. In particular I’ve been looking at material mapping using photons.

So what is material mapping?… sounds like something cartographers do.
We have lots of computer simulations of the ATLAS detector. To double check to make sure we’ve taken into account every cable we look to see that the particles interact the way we expect them to. Photons, for example, when they to through material convert predictably into an electron/positron pair. When I say predictably, I mean based on the amount of material they go through. We find these electron/positron pairs because they have a displaced vertex (an electron/positron which are close to each other and when you draw a line back from their tracks the origin isn’t the main interaction point). The more material in the way, the faster they convert. So we make sure our Monte Carlo simulations predict where most of the conversions occur to make sure we understand the detector.

I’ll try to provide a link to show a picture of the material map once they have been approved for public viewing.

Until then, Happy July 4th!

Fireworks

Regina

I was going out to dinner last night with some of my colleagues and the topic of new physics results at the Tevatron (specifically DZero) came up. I’m always happy to hear about new physics happenings  because it’s too easy to get so caught up in your work that you don’t notice other work being done around you. I know a couple of other bloggers have already posted it, but I’m still excited about it. And maybe a little out of the loop since it’s my last week at CERN and I’ve been really focused on getting a functioning analysis together :).

So for those of you that haven’t heard/read… there’s some interesting stuff happening with CP violation at the Tevatron. Here’s some background:
The Tevatron produces copious amounts of particles called B mesons. B mesons (quark-antiquark b – d or s pairs) oscillate between themselves and their antiparticles (Something I’m happy to elaborate on if anyone is interested). This oscillation can violate CP (charge conjugation and parity symmetry) thus preferring one state in the matter/antimatter system vs. the other.  (This also happens in the kaon system, and was one of the first pieces of experimental evidence that CP was violated). According to the standard model, this asymmetry is supposed to be very small (on the order of 10-4) – so small the Tevatron experiments can not measure it accurately. However that’s not what they found…
There is evidence that the asymmetry is about 100x larger than expected or 3.2 sigma (or 3.2 standard deviations). Now that’s not enough away from the predicted value to claim discovery just yet (need 5 sigma to be really sure). But it’s a very interesting result. Here’s a link to the arXiv paper

The New York Times also published a nice article.  You know you’ve hit the big time, when the NYT has an article about it ;). Although I dislike it when physicists talk about finding faces or toes of god.

-Regina

Dear LHC,

Sorry it’s been a while since I’ve visited — I may say I enjoy going to meetings in my pjs but you’re always on my mind. I’ve been devoting hours and hours to your service since I’ve been gone. Things are different now, I’ve traveled 4,000 miles to see you, and now I’m back – basking in the glow of your status:

Beam Setup: Injection Probe Beam

I know that last week you were able to reach luminosities higher than ever before, more than doubling our data set size. Those collisions were – for lack of a better phrase – the bees knees.

But I have another request… I’m on shift this week and next week. You’ll see me over at the LAr desk (well maybe not over the monitors… – (it’s sad when I make short jokes on myself)). So far, I’ve been waiting patently – taking calibration run after calibration run, and cosmic run after cosmic run. But I’ve seen that all before, and it just doesn’t do it for me any more.  I would really appreciate it if you were able to squeeze the beam – like I know you’re able to – for me(*). I see the daily plan… so I know you’re thinking about it too.

Sincerely your devoted follower,

Regina

(*) (the proton beam starts fairly broad, the LHC then has magnets to focus it which means higher luminosity (more protons per unit area)- or more collisions and therefore more data)

“If they could teach Koko the gorilla sign language, surely I could teach you rudimentary physics.”
-Sheldon to Penny (last Monday night’s episode)

Sure, they routinely throw up things like the Schrodinger equation and make references to things like quantum mechanics… and whether or not I may laugh periodically… I really dislike The Big Bang Theory (BBT from here on out).

Don’t get me wrong, I know people who love it – my parents for example. When I tell them I went to trivia night, they say things like “Oooh! that’s just like on the BBT”. They ask which of my friends is like Leonard or Sheldon and ask me if the equations they randomly throw up on the screen are actually physics equations. Of course my parents think I’m pretty smart, and they have met some of my physicist friends.

It’s not the science of BBT that I have problems with. It’s how the only physicists in the show are nerdy, socially awkward, and intolerant. Granted Sheldon (the stereotype of stereotypes) is kind of the jerk of the group, but he likens someone who for all intent and purposes is reasonably intelligent to a gorilla… but Penny can’t be smart, she’s pretty and blonde, and likes shoes. >Sigh<

Screen shot from the BBT

“Newton was a smart cookie… ooh is that where Fig Newtons come from?” – Penny

Granted the goal is to be funny, but I hate how the show only has socially incompetent and extraordinarily nerdy guys. And how they make physics completely inaccessible to anyone who doesn’t wear glasses. Sheldon starts teaching Penny physics with a history lesson starting 3000 years ago and chastises her for not taking notes. Instead he could tell her to looking around and see nature. Physics is the study of how nature works. (But that’s not Sheldon’s character… he wants physics to be inaccessible).

I have 20/20 vision, enjoy shoes, hair cuts, showering daily, monkey pants, Glee, and books that don’t have an equation in the text… so do lots of my (physics) friends.  I think lots of people are pushed away from physics at an early age because of shows like this. And it’s self fulfilling: only a certain type is portrayed therefore only that certain type feels welcome… so only a certain type becomes physicists.

Of course, at the end of the day, the BBT is a comedy show. But that doesn’t mean that the writers can’t do something positive for physics… like maybe have a woman physicist on the show who isn’t a sociopath, or a guy who has interests outside of physics.

Granted it’s not just this show in particular. One of my childhood favorites – Saved by the Bell – always has the science teacher as a nerdy, white guy in a lab coat who was really really weird (this was also true of the math teacher… whereas the history/English/art teachers were always women… way to break down barriers Saved by the Bell…). I guess that wasn’t enough of a deterrent for me, but I also had a really cool science teacher in 4th grade. She told me that the world needed little girls like me to go into science. I remember the conversation to this day – I think at the time, I wanted to be an astronaut :).

There are lots of programs out there to try to combat this stereotype (as an undergrad, I was involved in Expanding your Horizons and Girl scout Badge day both of which were targeted on getting girls interested in science), but social “norms” are entrenched in everything that we see and do. The only real way to promote change is to talk to normal guys, girls and minorities face to face and tell them that science is for everyone – not just the socially awkward.

And that’s why I dislike the Big Bang Theory 🙂

– Regina

The past few weeks have been really busy. Of course the flood of data and the prospects of an analysis are driving the work, so it’s a welcome change. I’ll also be heading over to CERN in about a week to go on shift. I’ll be there for about a month, and am excited to get back to where the action is. This is however, if planet earth doesn’t have other plans for me. I have to say, I’ve had flights get cancelled before, but I can honestly say, never because of a volcano eruption.

Geneva's on top :).. notice Reykjavík isn't cancelled

My sympathies are with the people who are stranded, I know I’ve received about 10 emails saying people had to phone into meetings because they couldn’t get back to CERN. I’ll have to keep everyone update on my status… it looks like most airports should be open on Tuesday (my flight leaves Sunday).

Until then, analyses await… and with those analyses come one word: Grid.
The Grid is the mechanism by which we do large scale computing. Instead of running an analysis on a local computer (which has limited capabilities), I send a “job” to a set of computers which copies the conditions of my work area, and breaks the large job into a bunch of smaller ones so it can run over the data set faster. I say this in confidence… I’ve now sent 3000 jobs to the grid. I <3 analyzing 🙂 I usually send my jobs to BNL (Brookhaven National Lab) and I’ve never had  a problem… but now I’m getting  the following message:

WARNING : Your job might be delayed since BNL is busy. There are 10398 jobs already queued by other users while 292 jobs are running. Please consider replicating the input dataset to a free site or avoiding the –site/–cloud option so that the brokerage will find a free site

I guess lots of people are running over data. Although it’s annoying to have to wait, it makes me happy to think about all the activity that’s been happening.

I think the pictures says it all. This is the beginning of a new era of discovery for particle physics. Excellent job by all my fellow collaborators on ATLAS and the LHC! Hopefully much more data is soon to come. It makes me very excited about the future.

Here is where our public event displays are located.

7 TeV Collision Event