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Posts Tagged ‘upgrade’

It is great to be a member of the US LHC blogging team! I have followed my friends’ posts here for a while. I hope I have something to add to the conversation, but I am confident that at least one person will read this regardless of the content because I sent the link to my Mom. (Hi, Mom!)

I’m typing on the flight back to the US from the UK after a week of meetings relating to possible future upgrades of the ATLAS detector that took place at Oxford University. I can imagine you are thinking, “Upgrades?! You people just started taking data! What are you doing already thinking about upgrades?!” I feel that way myself sometimes when numbers like 2017 and 2021 are floating around the room, particularly when I know that collisions are happening that very moment in the center of the ATLAS detector. But it is difficult to imagine a physics scenario where we would not want to see data from the LHC for a few decades. To enable this to happen people had to start thinking about upgrades well before we started taking data.

So, what is the physics landscape? Let us imagine that we find something that we think is the higgs boson. It is going to take quite a bit of data to convince ourselves that what we see is the same higgs boson that is described in our standard model of particle physics, and not some other object, like a higgs described by supersymmetry. This detective work will require high statistics, which means lots of collisions, which means lots of time with the LHC running. If we do not see anything with our first few years of running we will be able to rule out the version of the higgs boson that comes from our standard model and we will have to throw ourselves into hunting for particles and processes that are more difficult to see and, again, require more statistics. We have reasons to believe that we will see something new at the energy that the LHC was designed to deliver, but some of these scenarios will require impressive experimental gymnastics, to say nothing of (seeing a trend here?) high statistics. In order to more efficiently deliver these high statistics, the LHC has plans for upgrades of its own, and ATLAS will need to respond by making changes to the detector that allow us to cope with more extreme running conditions from the collider.

There are a few reasons running for long periods of time require upgrades to ATLAS and the other detectors, even without an upgraded LHC. For one thing, some of the electronics in our detector date back to the late 1990s and we cannot expect them all to survive well into the 2020s. There also will be pretty high flux of particles delivered to the detector over the course of data-taking, particularly to the regions close to the proton-proton interaction point, so replacement parts will be needed. Let me try an analogy: You just bought a car. It would be odd to not get regular oil changes, to keep it running well as long as is possible. And if something happens to the muffler it makes sense to replace it, even if it means spending a bit more money, in order to get the most out of the initial investment. The world has certainly invested in the LHC. (Thank you, world!) Before we go forward with specific upgrade projects we need to convince each other, our funding agencies, and the people who set the budgets of our funding agencies that the projects are justified both scientifically and financially. The peer review process rightfully keeps us on our toes.

In addition to the presentations and discussions at Oxford there were a few free moments during which we were able to explore the area. I visited the pub where J.R.R. Tolkien and C.S. Lewis used to hang out. I also visited the impressive Museum of Natural History. To top it all off, we had our workshop dinner in the Keble College dining hall, which doesn’t sound very impressive until you see the space. Harry Potter could have rounded the corner at any minute and none of us would have blinked.

Thanks for reading!

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Making Improvements

Monday, May 10th, 2010

The LHC has only had collisions for a little over a month now, and I’m as excited as the next scientist about the new data that is coming in.  With it we will hopefully be able to push existing boundaries in new ways.  The detectors are running well and I think that is a testament to all of the years that went into their development.  (Even if some of those years weren’t planned.)

For my first US LHC blog post, I want to write about something I’ve been working on.  Even though things are looking rosy right now, I’m in the business of improvement.  I work on the hadronic calorimeter (HCAL for short) for the CMS detector.  It is a large heavy detector system charged with trying to stop any hadrons (pions, kaons, protons, neutrons, etc.) from the collisions and measure their energy.  The CMS calorimeter is a sandwich of brass and plastic scintillator planes.  We measure the energy of the hadrons based on the amount of light we collect from the scintillator material.

Here is where the improvement comes in.  The HCAL design was essentially finalized in 1997.  That’s right 13 years ago.  And this was after several years of R&D to come up with a good design.  It then had to be manufactured and installed to be ready for what has been a very exciting commencement to data taking.

In the years since the HCAL was specified and built, new and exciting technologies have emerged that could potentially improve the performance of our calorimeter.  One of these is the silicon photomultiplier.  This device could allow us to better measure the light from the scintillators thereby improving our measurement of the hadron energy.  However, because it took 13+ years to get the original HCAL to a fully integrated system, it will probably take several years for the new upgrade to be designed, specified, prototyped and produced and then it must be integrated into the existing CMS detector.  All this means that although beam operations have been going on for months, upgrade plans have been going on for years.

I’m excited about what we can learn from the data being taken now with CMS and the other LHC detectors, and I looking forward to improvements that are coming in the future years to better exploit the discovery potential of this remarkable machine.

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ATLAS Upgrade

Friday, November 6th, 2009

You might think it odd that work has already started to upgrade parts of the ATLAS detector, even before the LHC has started running!

As I wrote in a previous post, one of the key operating parameters for the LHC is luminosity, i.e., the beam intensity. The design calls for a luminosity of 1034/cm2/sec; this means that if you look at the beam head-on, it will contain 1034 protons/sec spread over an area of 1 sq. cm. In reality, each beam consists of 2800 bunches each containing ~1011 protons and about 0.03 mm in radius. Two such bunches collide every 25 nanoseconds, i.e., 40 million times/second; this is known as a bunch crossing.

The number of events that we collect is directly proportional to the luminosity. I had also written that the most common type of events that occur have a very large rate. What this implies is that when two proton bunches collide, most of the time we produce these “ordinary” events. For instance, when the luminosity is 1034, at each bunch crossing we get an average of 23 such events; they are easy to recognize, in the sense that they produce mainly low energy particles. So, when we produce an interesting event, say, a pair of top quarks or a Higgs boson, that event will be sitting atop this low-level “fuzz”. This background produces detectable signals in ATLAS, causing higher load on the trigger system and readout electronics, and pattern recognition problems in the reconstruction software. For instance, the (TRT) sub-detector, could have an occupancy rate as high as 10-20%, i.e., a non-negligible fraction of all wires will register hits; pattern recognition will be tough, but manageable. Other tracking sub-detectors are not a problem since they have much finer granulation (see Seth’s post on tracking). In addition, as particles produced in these “ordinary” events travel through the various sub-systems that are made out of silicon, they cause a slow degradation in them; detectors and electronics are made to resist this deterioration, but they do eventually fail.

When the luminosity starts to increase, as the LHC program calls for, these problems become much more serious. For instance, at a luminosity of 1035, each interesting event will be sitting atop a background of about 400 of these “junk” events; there is no way around it. As for the TRT, you can see that it will be useless.

The upgrade is planned in two phases. In the first phase, corresponding to a luminosity of 3*1034, currently scheduled for 2015 (but will depend on well the LHC performs), we plan to insert an extra layer of silicon sensors between the beam-pipe and the first silicon layer; by then, the first layer’s performance will have deteriorated enough to be noticeable. We will also upgrade some other detectors and electronics that sit close to the beam.

In the second phase, corresponding to a luminosity of 1035, all of the sub-systems that are used for tracking charged particles, i.e., the silicon layers and the TRT, will be replaced. All electronic readout for the detector will be replaced with more sophisticated stuff; the trigger logic and associated electronics will undergo a big overhaul, etc. This is scheduled for 2020.

These upgrades take time and effort, hence the early start. Most groups in the US and UK are already steering resources, in the form of people and money, towards the Phase I upgrade, e.g., my colleague, Hal Evans at Indiana University, is looking at some trigger improvements, and other countries are also joining in. We are used to this mode of operation; at one of my previous experiments (at the accelerator at Cornell University), we were simultaneously, analyzing data collected with version II of the experiment, starting to commission version II.5, and doing R&D on version III!

–Vivek Jain, Indiana University

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The next next thing

Friday, November 21st, 2008

This week I took a brief trip to Fermilab to attend a little bit of a workshop on upgrades to the CMS detector.  Now yes, this is nutty on its face — what are we doing talking about upgrading a detector that has yet to see its first collisions?  How can you know what needs upgrading?  Unfortunately, the time scales for completing such projects are very long, and we need to start planning now.  By 2013 there are supposed to be LHC upgrades to improve the beam focusing at the collision points, and CMS will want to make changes to make the most of this.  That’s only five years away, and given how long it can take to do the R&D work and then actual construction of the detectors, you have to start now.

It definitely would be better to have some real data, and certainly what we learn from collisions as soon as we have them will inform what we do in the upgrade.  However, we already have plenty of information to chew on. We learned a lot in the course of the construction of the detectors, and know that there are specific problems we would like to fix.  The current detector was already designed some years ago, and there have been technical advances that we would like to take advantage of.  (I was struck by one talk about electronics in which it was stated that there is an increased focus on making components with low power consumption; this is an issue on the computing side too.)  And perhaps in the course of the upgrade studies, we’ll learn something that will allow us to operate the current detector and analyze its data in a more clever way.

Due to my own schedule constraints, I could only stay for a day of the workshop, and thus I won’t claim that I did any real work!  However, it sounds like some progress was made.  We expect that we’ll have to rearrange our tracking system, and as part of it we want to be able to have an online track trigger, something we don’t have right now.  That is a very difficult technical problem, but people agreed on a strawman layout for the tracker that people could at least use for studies, and a general strategy for how the triggering could work.

I am slightly embarrassed to admit that this was my first visit to Fermilab in about six months!  The new baby here at home has kept me from traveling around as much as I ought to.  So there were lots of people to see and say hello to (including the guy in the badge office; my ID had expired and got confiscated at the gate!).  There never is enough time in the day at the lab to talk to everyone I want to see.  I’m looking forward to getting back again soon(ish).

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You may ask why one would speak about an upgrade while everyone is still in “acute anticipation” for the first few particles to make it around the machine? Perhaps there are even skeptics who doubt that we may never be able to circulate particles in this giant hole. I was recently browsing through the “LHC the guide” and stumbled upon one of the fascinating facts which may cool down that skepticism. Apparently, during that major tunnel digging, the two ends of the 27-km circular tunnel met up to within 1 cm!

Ok, that said, and if you believe in the “as soon as possible” version of the beam schedule, it is estimated that focusing magnets closest to the interaction point will reach the end of their lifetime circa 2013-14 (or before) due to radiation damage from collision debris. Instead of replacing exact replicas, why not do better. And why not, since these magnets do have the largest impact on the holy grail called luminosity.

So, discussions about the LHC upgrade began a decade ago which is now being coordinated under the CARE-HHH network, you can find all sorts of stuff here: http://care-hhh.web.cern.ch/CARE%2DHHH/default.html
After several workshops debating about what seemed like infinite new ideas, it now boils down to two contenders (both democrats, I think). Ask me in a couple of years and the priorities maybe completely different, physics and/or management. The U.S. folk under the LARP program (https://dms.uslarp.org/) have been very busy on the upgrade program since the beginning. Now more than ever, about 100 physicists from U.S. labs (this is lot for accelerator physics) are working very hard to get those particles circulating and yes, do even better next time around. It is perhaps a bit ironic, since the beginning of the biggest accelerator may also mean the demise of some other smaller siblings – sort of “survival of the fittest”. To be cont’d…

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