Higgs

The LHC restarts — in a manner of speaking —

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As many of you will have already read, the Large Hadron Collider [LHC], located at the CERN laboratory in Geneva, Switzerland, has “restarted”. Well, a restart of such a machine, after two years of upgrades, is not a simple matter, and perhaps we should say that the LHC has “begun to restart”. The process of … Read more

Giving Public Talk Jan. 20th in Cambridge, MA

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Hope all of you had a good holiday and a good start to the New Year! I myself continue to be extraordinarily busy as we move into 2015, but I am glad to say that some of that activity involves communicating science to the public.  In fact, a week from today I will be giving a … Read more

How a Trigger Can Potentially Make or Break an LHC Discovery

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Triggering is an essential part of the Large Hadron Collider [LHC]; there are so many collisions happening each second at the LHC, compared to the number that the experiments can afford to store for later study, that the data about most of the collisions (99.999%) have to be thrown away immediately, completely and permanently within a … Read more

Final Days of Busy Visit to CERN

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I’m a few days behind (thanks to an NSF grant proposal that had to be finished last week) but I wanted to write a bit more about my visit to CERN, which concluded Nov. 21st in a whirlwind of activity. I was working full tilt on timely issues related to Run 2 of the Large Hadron Collider [LHC], currently scheduled to start early next May.   (You may recall the LHC has been shut down for repairs and upgrades since the end of 2012.)

A certain fraction of my time for the last decade has been taken up by concerns about the LHC experiments’ ability to observe new long-lived particles, specifically ones that aren’t affected by the electromagnetic or strong nuclear forces. (Long-lived particles that are affected by those forces are easier to search for, and are much more constrained by the LHC experiments.  More about them some other time.)

This subject is important to me because it is a classic example of how the trigger systems at LHC experiments could fail us — whereby a spectacular signal of a new phenomena could be discarded and lost in the very process of taking and storing the data! If no one thinks carefully about the challenges of finding long-lived particles in advance of running the LHC, we can end up losing a huge opportunity, unnecessarily. Fortunately some of us are thinking about it, but we are small in number. It is an uphill battle for those experimenters within ATLAS and CMS [the two general purpose experiments at the LHC] who are working hard to make sure they have the required triggers available. I can’t tell you how many times people within the experiments — even at the Naturalness conference I wrote about recently — have told me “such efforts are hopeless”… despite the fact that their own experiments have actually shown, already in public and in some cases published measurements (including this, this, this, this, this, and this), that it is not. Conversely, many completely practical searches for long-lived particles have not been carried out, often because there was no trigger strategy able to capture them, or because, despite the events having been recorded, no one at ATLAS or CMS has had time or energy to actually search through their data for this signal.

Now what is meant by “long-lived particles”?

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At the Naturalness 2014 Conference

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Greetings from the last day of the conference “Naturalness 2014“, where theorists and experimentalists involved with the Large Hadron Collider [LHC] are discussing one of the most widely-discussed questions in high-energy physics: are the laws of nature in our universe “natural” (= “generic”), and if not, why not? It’s so widely discussed that one of my concerns coming in to the conference was whether anyone would have anything new to say that hadn’t already been said many times.

What makes the Standard Model’s equations (which are the equations governing the known particles, including the simplest possible Higgs particle) so “unnatural” (i.e. “non-generic”) is that when one combines the Standard Model with, say, Einstein’s gravity equations. or indeed with any other equations involving additional particles and fields, one finds that the parameters in the equations (such as the strength of the electromagnetic force or the interaction of the electron with the Higgs field) must be chosen so that certain effects almost perfectly cancel, to one part in a gazillion* (something like 10³²). If this cancellation fails, the universe described by these equations looks nothing like the one we know. I’ve discussed this non-genericity in some detail here.

*A gazillion, as defined on this website, is a number so big that it even makes particle physicists and cosmologists flinch. [From Old English, gajillion.]

Most theorists who have tried to address the naturalness problem have tried adding new principles, and consequently new particles, to the Standard Model’s equations, so that this extreme cancellation is no longer necessary, or so that the cancellation is automatic, or something to this effect. Their suggestions have included supersymmetry, warped extra dimensions, little Higgs, etc…. but importantly, these examples are only natural if the lightest of the new particles that they predict have masses that are around or below 1 TeV/c², and must therefore be directly observable at the LHC (with a few very interesting exceptions, which I’ll talk about some other time). The details are far too complex to go into here, but the constraints from what was not discovered at LHC in 2011-2012 implies that most of these examples don’t work perfectly. Some partial non-automatic cancellation, not at one part in a gazillion but at one part in 100, seems to be necessary for almost all of the suggestions made up to now.

So what are we to think of this?

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Day 2 At CERN

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Day 2 of my visit to CERN (host laboratory of the Large Hadron Collider [LHC]) was a pretty typical CERN day for me. Here’s a rough sketch of how it panned out: 1000: after a few chores, arrived at CERN by tram. Worked on my ongoing research project #1. Answered an email about my ongoing research … Read more

Off to CERN

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After a couple of months of hard work on grant writing, career plans and scientific research, I’ve made it back to my blogging keyboard.  I’m on my way to Switzerland for a couple of weeks in Europe, spending much of the time at the CERN laboratory. CERN, of course, is the host of the Large Hadron Collider … Read more

Will the Higgs Boson Destroy the Universe???

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No.

The Higgs boson is not dangerous and will not destroy the universe.

The Higgs boson is a type of particle, a little ripple in the Higgs field. [See here for the Higgs FAQ.] This lowly particle, if you’re lucky enough to make one (and at the world’s largest particle accelerator, the Large Hadron Collider, only one in a trillion proton-proton collisions actually does so) has a brief life, disintegrating to other particles in less than the time that it takes light to cross from one side of an atom to another. (Recall that light can travel from the Earth to the Moon in under two seconds.) Such a fragile creature is hardly more dangerous than a mayfly.

Anyone who says otherwise probably read Hawking’s book (or read about it in the press) but didn’t understand what he or she was reading, perhaps because he or she had not read the Higgs FAQ.

If you want to worry about something Higgs-related, you can try to worry about the Higgs field, which is “ON” in our universe, though not nearly as “on” as it could be. If someone were to turn the Higgs field OFF, let’s say as a practical joke, that would be a disaster: all ordinary matter across the universe would explode, because the electrons on the outskirts of atoms would lose their mass and fly off into space. This is not something to worry about, however. We know it would require an input of energy and can’t happen spontaneously.  Moreover, the amount of energy required to artificially turn the Higgs field off is immense; to do so even in a small room would require energy comparable to that of a typical supernova, an explosion of a star that can outshine an entire galaxy and releases the vast majority of its energy in unseen neutrinos. No one, fortunately, has a supernova in his or her back pocket. And if someone did, we’d have more immediate problems than worrying about someone wasting a supernova trying to turn off the Higgs field in a basement somewhere.

Now it would also be a disaster if someone could turn the Higgs field WAY UP… more than when your older brother turned up the volume on your stereo or MP3 player and blew out your speakers. In this case atoms would violently collapse, or worse, and things would be just as nasty as if the Higgs field were turned OFF. Should you worry about this? Well, it’s possible this could happen spontaneously, so it’s slightly more plausible. But I do mean slightly. Very slightly.

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