Quantum Diaries

The leaves were not so green when I ran here yesterday.

On a much needed vacation day away from Fermilab, I went for a nice run in one of my favorite nearby places, the east side of the Fabyan Forest Preserve. The leaves on the trees were bursting with fall color – a brilliant yellow that seemed to light up the woods. There are many trails snaking around the area, and I certainly prefer running on dirt trails rather than asphalt, sidewalks, or even a track.  Getting dirty running through a little mud, up and down hills, and jumping a log here and there builds character.

I’ve read that smells can be a powerful trigger of memories.  The slight musty odor of fallen leaves starting to decay certainly is a sign of autumn, but it means more than that to me – it smells like cross country running season.  Cross country races typically start in late August when summer can still be going strong.  But once the leaves start changing color and that smell wafts into your nose, the season is in full swing and the big championship races are on the horizon.  Having run cross country in high school (winning a PA state championship) and at Penn State (where our team finished 10th in the national championship race my 5th year and I was an Academic All-American), that smell stirs my soul and always puts an extra kick in my step even after 20+ years.

Breathe deep – it’s that time of year again.

I think I will need another day off soon to run through the woods before the trees lose all of their leaves.

For many people in the US, receiving a summons for jury duty causes immediate groaning and thinking of ways to avoid it.  While it seems like an inconvenient disruption to our daily routine, jury duty is an essential part of our legal system in which “trial by jury” may not be fully appreciated unless you’re the one on trial.

I had jury duty last week and I was selected to serve for a civil (not criminal) case.  One party sued the other to recover money paid as a result of damage to a car from an automobile accident; the other party counter-sued for damages to his car, so our jury actually had two cases to decide simultaneously.  (Thankfully no one was injured in the crash.)  Unfortunately, there was no “hard data” to examine – no photographs of the intersection, no measurements of skid marks, no police or eyewitness testimony.  It was a “he said, she said” case where we essentially had to decide what was likely to have happened and which driver was more believable.

The trial lasted only 2.5 hours or so before we started deliberating in the late afternoon, but we needed over 3 hours to reach a verdict around 7 pm.  I don’t think the judge or attorneys expected us to take so long, but the 12 of us were evenly split at the start.  We had some good discussions (and pizza) before reaching a unanimous decision that both parties  did share responsibility for the accident and should receive only half of the money they were seeking.  Although it seemed like we simply “split the baby” in our verdict, there was no way we could decide differently with the data we were given.

I’m glad that science is not conducted like court cases.  When you need data to test a theory or make a measurement, you do an experiment.  (And others will do it, too, to try to reproduce your results.)  There’s no judge telling you to reach a conclusion without information you may want.

I heard that a lot last weekend while I was in State College, PA – home of my undergrad alma mater Penn State University.  I met up with several former college roommates to cheer on the Nittany Lions in their football game against Iowa.  The weather was miserable for the game – chilly and raining the whole time – and unfortunately Penn State lost.  It’s particularly disheartening to see your team lose after spending 4 hours in the rain.  Only a small fraction of 109,000 people in the stands were Iowa fans happy with the result.

Nevertheless, it was nice to catch up with friends I don’t see often, especially since I don’t attend our football weekend every year.  We fly or drive in from all over the country.  This year I flew from Chicago to Newark where my friend living in Brooklyn picked me up and drove to State College along I-80.  I do miss the lush woods and rolling hills in central Pennsylvania.  The leaves were just beginning to change colors; they will look great in a couple of weeks.  It started to smell like fall, too, reminding me of cross-country running season.  I ran cross-country and track at Penn State and we pounded out a lot of miles on the roads and trails in Happy Valley.   It’s great to go back to see how some things have changed while others have stayed the same.  (The Skellar never changes.)

Bringing home a couple boxes of stickies from the Diner made my wife and kids smile.  (If you’ve had them, you know what I’m talking about.  If you haven’t had them, you’re missing out.)  Too bad we ate them all already.  That’s motivation to start planning the next trip.

This picture shows the luminosity at the CDF and D0 detectors for each bunch crossing as well as the intensities of the 36 proton and antiproton bunches.

Yahoo! We just succeeded putting in our first colliding beam store since the long shutdown ended! The initial luminosity was only ~20% of the norm before the shutdown, but the proton and antiproton intensities were intentionally low.  All of the accelerators still need more tune-up work, but delivering the first collisions after a shutdown is a big stepping stone. The experiments need colliding beams to shake out their detectors, too.

While this first store spins, we can catch our breath, get a good night’s sleep (I hope), and prepare for the additional tune-up work.

We’re back!

My daughters and I have been watching flyovers of the International Space Station (ISS) in the early night sky.  We usually walk to the playground of their school for a less obstructed view.  The website spaceweather.com has a “Satellite Flybys” link that is very easy to use.  Simply type in your ZIP code and up pops a few days’ worth of flyover information for several satellites including when and where to look and the apparent magnitude (brightness) of the satellite.   (It can show flyovers outside of the US, too.)  Whether or not you can see a particular satellite depends on where it is in its orbit relative to the Sun and you.  The International Space Station can easily be the brightest object in the night sky – except for the Moon.  There are many more satellites that can be visible, but that website only shows the most interesting ones.

There was a good show on Tuesday evening – ISS and Space Shuttle Discovery close together in the sky.  Discovery had undocked from ISS about 5 hours before we saw them.  Although I’m only a novice photographer, I was able to take some photographs with an 8 second exposure time to get their streaks in the sky. (See a couple of them below.)  We enjoyed watching the show – too bad it only lasted 2 minutes before they disappeared into the Earth’s shadow.

Although the flyovers are brief, they make for great conversation:  How do the astronauts get up there?  Can they see us?  How do they eat, sleep, go to the bathroom?  What do they do all day?  Are there aliens?  Did you want to be an astronaut when you were little?  (Yes.)  I love those discussions much more than watching the flyovers themselves.

Discovery and ISS rising. If you look closely, you can also see the blinking lights from a passing airplane. (Click to enlarge.)

Discovery and ISS setting behind a tree. (Click to enlarge.)

No, no, no – the world isn’t coming to an end – just summer and the Fermilab shutdown!

The daylight hours are noticeably shorter, my kids have been back to school for over 1 week, and I wore my long Sporthill pants on an early morning run this week (it got down to 42 degF in Batavia).  Sigh…although it was a cool summer here, it was still summer.  I wish I were still on the beach.

The shutdown work is wrapping up, too.  The last 2 Tevatron houses that were warmed up for repairs are cooling back down to 80 degK.  Hopefully the cooldown of the whole ring to 4 degK can begin soon afterward.  Although the Main Injector may not be able to deliver us any beam until late next week, I would like to get the Tevatron cold as soon as practical so we can begin powering the superconducting magnets fully to look for any electrical problems.  We have already begun “conditioning” the electrostatic separators used the kick the proton and antiproton beams onto different orbits such that they collide only in the centers of the experiments.  Conditioning them means running them at higher voltages than usual (and maybe causing some electrical discharges, not unlike drawing a spark when dragging your feet on a carpet and then touching a metal object on a dry winter day) so that they will less likely to do that at the slightly lower voltages used for regular operation.  There is plenty of preparation and check-out work to be done without beam.

We’ve also been making plans for the needed studies once we get beam.  The machine won’t be quite the same as it was before the shutdown; although we haven’t made any significant changes, unrolling > 90 magnets will cause some minor changes that we’ll need to understand when tuning up.  Once beam is available, Tevatron experts will be taking shifts in the MCR (Main Control Room) 24 hours a day taking data, implementing changes, and verifying all systems are functional for colliding-beam operation.  We estimate it may take 5-7 days of shift work to recommission the Tevatron before returning to regular operation.  Perhaps we will try a low-luminosity proton-antiproton store ~3 days after we first get beam to check our progress and to allow the CDF and D0 experiments to test their detectors after 3 months without collisions.  They did plenty of work on their systems, too, during the shutdown, so they need time to make sure they are ready to handle efficiently all the collisions we give them.  After that first colliding beam store, we will evaluate it, get feedback from the experiments, and continue tweaking the machine for a day or two before trying another proton-antiproton store.  Once we’re satisfied, we’ll stop taking shifts and let the MCR crews get back to putting in the stores themselves.  The start-up can be a gradual process because it takes all the machines some time the return to their peak performance and hopefully beyond!

I’m looking forward to having a smoothly running accelerator complex in a few weeks so the experiments can get back to collecting lots of data for their physics analyses!

The summer is flying by too quickly!  The “12-week” shutdown of the Fermilab accelerator complex is about 2/3 complete – here’s an update on the Tevatron maintenance.

A view of the open interface between 2 Tevatron magnets.

In an earlier post, I wrote we needed to warm up 6 “houses” to room temperature to fix leaking components.  Well, after technicians did some more leak-checking in the first week of the shutdown, it looked like we needed to warm up 2 more houses!  Fortunately, we discovered one of those extra houses had an “outside air leak” that was readily repaired by applying some epoxy on a thin pipe to prevent air from getting in – no need to warm up that house!  Unfortunately, during the repair of an outside air leak on another (still cold) house, too much air got sucked into the beampipe and froze on the 80 degK surface.  That house had to be warmed up to melt the iceball.  You win some, you lose some.

Overall, I think the work is going rather well.  Six houses have been warmed up, another is on its way to 300 degK, and one last (I hope) house is still on the schedule.  Of the six warmed-up houses, one has been repaired and already cooled back down to liquid nitrogen temperature 80 degK.  Three more are ready for cool-down – hopefully they will be cold next week.  So far, only 1 of the leaks was internal to a magnet that required replacing the entire component.  The others have been fixed by replacing valves or seals accessible from the outside of the magnets.  In addition, no new electrical problems developed during the warm-ups.  It’s good news that the techs have only needed to fix the problems we expected and not any new ones that cropped up along the way.

A quadrupole magnet whose corroded stands needed to be replaced.

The survey and alignment group has unrolled over 60 Tevatron magnets to bring them back within our desired tolerance of < 1mrad.  Eight magnets need new stands since they can no longer be adjusted properly for alignment.

All in all – the shutdown work has been proceeding smoothly.  Five weeks from now, I hope we are recommissioning a leak-free, well-aligned Tevatron.  We will be pulling our own long shifts tuning up the machine with beam to return to normal operation providing high-luminosity proton-antiproton collisions to the CDF and D0 experiments!

We had been waiting several months to learn how hard CERN would push the LHC for its initial running after repairing the damage from last September’s catastrophic event – now we know:

Link to CERN press release

3.5 TeV per beam is half of their design energy, but still > 3 times the Tevatron beam energy.  Personally, I think it is prudent to be cautious and advance slowly as they gain experience and confidence.  The accelerator operators need to test many new systems and verify their reliability for the longer term.  At this point, establishing some operational baselines for both the accelerator and the experiments is more important than pushing the energy and risking another incident causing extended downtime. You can’t do the physics if you’re not running.  The performance will improve thanks to hard work from many people – I’ve seen it happen here at Fermilab.

Last week I attended the 2009 meeting of American Physical Society’s Division of Particles and Fields (APS DPF) at Wayne State University in Detroit.  Most of the conference is devoted to recent experimental and theoretical high-energy physics developments with a smattering of related topics here and there.  I was a co-convener for the Accelerator Physics parallel sessions and I also gave a talk on the recent performance and prospects for the Tevatron.  There were over 300 people registered with lots of topics to cover – almost too many, really, since there were many parallel sessions in the afternoons and not enough time to circulate and explore them.  I was disappointed that only a few experimental  HEP folks attended any of the accelerator sessions.  My co-convener (Pavel Snopok) and I invited speakers to give more general talks than they might give at an accelerator physics conference in hopes of attracting some HEP physicists.  Too bad – too many sessions, not enough time.

One session that I did attend (in part) was for Education and Outreach in HEP.  Physicists are becoming better at communicating with the public, and there are some very good educational programs that involve high school students and teachers.  Fermilab’s own Kathryn Grim gave an overview of the web-based opportunities that are available, like Facebook, Twitter, and blog sites such as Quantum Diaries, and how people are using it.  I find it truly amazing how fast Facebook and Twitter usage is growing.

The conference dinner was held at the Henry Ford Museum in Dearborn.  What a cool place!  Although I lived in Ann Arbor for nearly 8 years, I had never gone to that museum before.  It had much more than old cars – planes, trains, farm equipment, industrial machines.  I should take my family to visit there sometime soon.  I’m sure the girls would love the old camping vehicles and enjoy lunch at the Wienermobile Cafe!

Hey, Nicole!  Too bad we never crossed paths!  How’d that happen?

After a spring that turned out to be more hectic than I expected, I am finally getting back to working on a physics analysis with the CDF detector. I am trying to measure the mass and lifetime of a particle called the B_c meson – a bound state of a bottom quark and a charm quark.  There is nothing surprising (yet?) about the B_c – it should and does exist, but we need to measure its properties experimentally to confirm or refute the predictions.  Hints of the B_c were first reported by experiments at the LEP electron-positron collider, but its existence was solidly established by CDF several years ago.  Currently, the Tevatron is the only accelerator that can produce the B_c, so both CDF and D0 are studying it.

As with most unstable particles, we only measure the trajectories and energies (or momenta) of the particle’s decay products, not the particle itself.  The B_c can decay into many different states, but I am using the B_c → J/ψ π decay channel; the J/ψ is a charm-anticharm quark meson that itself decays into a pair of muons, while the π (pion) is a well-known up-down quark meson (the pion decays, too, but usually not before we measure its momentum).   We can use conservation of energy and momentum to reconstruct the mass of the B_c.  Seeing how far the J/ψ π origin point (vertex) is from the collision point of the incoming proton and antiproton beams indicates how far the B_c traveled before decaying – for the B_c, most decay before traveling even a few hundred microns, corresponding to a lifetime of less than 1 ps = 1 trillionth of a second.

The J/ψ is a particularly useful particle in experimental high-energy physics – its decay to two muons is often used as a “trigger” to help record the process of interest.  We start with a sample of events with a J/ψ and then search for events containing a π that also originates from the same point as the J/ψ muons.  Most events passing our selection criteria are background that is difficult to eliminate.  For any given event, we don’t know if it contains a true B_c → J/ψ π (our signal) or something that just looks like one.  We need to look at events where there is no signal to understand how the background affects the mass and lifetime measurements.  We then combine the data from the selected events (signal + background) to make the measurements.

In the end, there will likely be only a couple hundred signal events scattered among the hundreds of thousands of background.  It’s not easy to extract those measurements, especially the lifetime.  Convincing myself and my colleagues  that we understand the background will be challenging.  I sure wish I had more time to spend on the analysis – it’s hard to make steady progress when working on it only a morning here or an afternoon there.  In a moment like this, I envy students who can spend nearly all their time on their physics analyses.