The Beamline's Baby Steps

January 22, 2005

So if the beamline was "born" on December 3 when we sent the first protons through the entire beamline, then the baby took it first steps today when we put a target in the way of those protons, and finally produced a neutrino beam.  We are still not ready to start the official “run”, but we want to test what we already have in place to make a neutrino beam, and a few things need to be finished before we can run at the high intensity we ultimately have to achieve.

So the goal of these three days (Friday through Sunday) is to produce a neutrino beam that is strong enough that we can see neutrino events at what is called the "Near Detector".  Although it's almost a thousand times closer than the "Far Detector", it is a whole kilometer away from the proton target, and is located about 900 feet of earth after the last neutrino could have been produced.   So imagine that first step as going through 900 feet of earth, and imagine how excited all the people working on the detector and the beamline will be to see that first step really happen, and you can imagine how my day went today. 

At about 2:00 this afternoon, the folks working on the beamline sent the first batch of protons down the beamline, and they hit that target on the very first try!  To really make a neutrino beam though, you have to not only hit the target and make a huge spray of particles that decay to neutrinos, but then you have to focus that spray of particles.  By about 2:30 this afternoon we were sending 200 thousand amps of current through magnets called "horns" (because of their funky horn-like shape), which is what it takes to do the focusing. 

Luckily you can see that you're making neutrinos by looking at the other particles that get produced when the particles decay to neutrinos:  those other particles are called muons, and we saw these really intense muon fluxes right away, when they put the current in our two horns just as the spray was passing through them. 

To see the neutrino interactions, though, we had to look at the detector signals, and we had to look in the right window of time after the protons hit the target. This means all the detector measurements have to be processed and you have to “throw out” all the signals that occur at the wrong time. After we were looking at the muon monitors for several low intensity spills a bunch of us were saying “you should be seeing neutrinos by now, look at all those muons!”.

Sure enough, at about 2:45 the first “beam neutrino” event was found, and there was cheering all over the 12^th floor control room. From looking at the time that the neutrino event really occurred, it turned out to have shown up on only the 4^th time that current was sent through the horns (2:19PM)—amazing!

So once again, I find these kid analogies helpful (if inaccurate) for describing what is going on…you are so excited for a few hours after your child takes her (or his) first steps, but then pretty soon it’s old news and you want to see how far the baby can actually go! So in the same way, as excited as we were to see that very first event, pretty soon people were not jumping up and down for single events, but they were thrilled to be making distributions of the dozens of events we were getting that afternoon.  These distributions prove once and for all that these neutrinos really were coming from our beamline, not only because when in time they arrived, but the direction that they were coming from was pointing exactly where we expected (the plot I show here was made by 7PM Friday night!  ds/dz=1 means the outgoing muon from the neutrino interaction was pointed exactly along the beam direction...0 would be perpendicular, and notice the scale only goes from 0.8 to 1.0!)

.

And once again, we all celebrated with champagne, and the next days will filled with more detailed studies of how this beamline is really working. It might seem strange that I’m writing so often about celebrating with champagne, but to be honest, “firing up” a new experiment is something people get to do only a few times in their entire career, so believe me, we celebrate every step! 

Read the Fermilab Today article about this here

Comments

[mike]

Where on the web can I monitor the progress of the CNBGS?

[Debbie]

The CNGS (CERN to Gran Sasso) neutrino beam has a very spiffy web page at

http://proj-cngs.web.cern.ch/proj-cngs/

There are lots of publications that you can reach starting there, and there is a good selection of articles written for the non-specialist at

http://proj-cngs.web.cern.ch/proj-cngs/Publications/Publications.htm#NonSpecialist

Of course if you're a specialist there are articles for you there too!

Enjoy,
Debbie

[~DS~]

BTW, I didn't see any trackback info to auto-notify when your blog's been mentioned on other blogs.

[Aaron]

This sounds dumber every time I think it, but I have to ask. How do you make a beam of particles that barely interact with anything? There's no way to make them change direction!

[Debbie]

It's not dumb at all, it's what makes doing this so hard. The way to make a beam of neutrinos is to first make a beam of particles whose direction you CAN change (i.e. a beam of charged particles, namely pions and kaons), focus that beam so the particles are all pointed in the same right direction, and then when these particles decay, the things they decay to are also going in that same right direction.