“Tantalising hints” is a phrase high energy physicists have a love-hate relation with, and for good measure. Often all major discoveries remain tantalizing hints for a long time, creating a lot of confusion, generating a lot of debates and then either fade away into oblivion or become something so big that history just cannot ignore it. A recent demonstration of this phenomenon was given at the LHC during the hunt for the Higgs, where what remained as a ‘tantalising signal’ for months, grew steadily and offered the LHC physicists their first opportunity to say ‘Hurrah!’ A similar event may be afoot at the giant Super Cryogenic Dark Matter Search (SuperCDMS ) experiment, located deep inside a tunnel in the Soudan Mine in northern Minnesota. There is a ‘tantalizing hint’ of the detection of a particle which might be the elusive Dark Matter particle.
The recent tidings have excited physicists, as they have detected three events in the detector of a possibly weakly interacting massive particle (WIMP). However, they need more events. The surety of the discovery of these WIMPs is only 99.8 %, which amounts to a wee bit more than what physicists call 3-sigma confidence level. This is at the ‘tantalising hint’ level. At 4-sigma, it gets interesting and only at 5-sigma (which is a massive 99.9997% surety), do physicists say that they have a discovery.
The mass of the particle is somewhere about 8-10 GeV, which is about 8 to 10 times the mass of the proton. That’s low mass in the context and this particle, if present, should turn up in some of the other colliders and detectors, especially the LHC, in the near future.
Theorists are already busy at work figuring out how all of this fits into their theory. Can a supersymmetric theory, a theorist’s dream for a long time, accommodate the particle of mass 10 GeV? If so, which version and how has that version fared at the LHC?
For now, let this hint promote itself to the level of a discovery – we have seen too many tantalizing signals come and then disappear to be hasty.
It’s a pincer attack on new physics. The sister project to the CMS and ATLAS collaborations at the LHC CERN, LHCb has just released new data which spells a death knell for supersymmetry. Okay, that might be a hasty statement, but if the results are really what they are, it’s very unlikely that any ‘reasonable’ model of supersymmetry will be able to survive.
Why the LHCb?
The LHC collaborations CMS and ATLAS have been the mainstay of the group and recently enjoyed huge success in the discovery of the Higgs Boson. Less publicized and more specialist in their study is the LHCb detector and its collaboration. This detector is specialized for measuring certain exotic particles – those made up of at least one bottom quark. Since the bottom quark is very heavy, and heavy particles tend to decay very fast, all particles with the bottom quark are very short-lived making their study very difficult. And this is where LHCb specializes in.
Now the result
LHCb announced a new observation today and it knocks the wind out of supersymmetry. Let me tell you the observation and then tell you what it implies. They observed the decay of a certain particle called the Bs meson (B=Bottom and s=strange). The decay rate of this particle hadn’t been measured before with much accuracy, but today the LHCb collaboration announced that they have measured it and found that it decays into two muons about 3-4 times per billion decays. The ‘bingo’ moment for non-supersymmetric particle physics is that this is exactly what the Standard Model predicts. Right on the dot!
There is another storm brewing. It turns out that the Higgs Boson discovered earlier isn’t behaving as well as it should! Notably, it is not decaying into two tau leptons as often as it should. In fact, it seems that it is not decaying into tau leptons at all. There is a problem!
And the bad news
These two problems are pulling in opposite direction squeezing the super-symmetric space that lies between them. If the Bs decaying into two muons is exactly like what the Standard Model says, then supersymmetry, which predicts a higher decay rate, must obviously be constrained. And very heavily so!
So there it is! Supersymmetry is teetering on the edge of oblivion. But it may yet survive…
The sky is no longer the limit — the limit lies deep within sub-atomic particles. After the glory of the Higgs discovery, the LHC has now set a record for obtaining the hottest temperature mankind has ever seen. The trick — make a hot enough quark-gluon plasma.
At the center of this achievement lies the less talked about detector ALICE (short for A Large Ion Collider Experiment). We get to hear about the CMS and ATLAS detectors, since these are dedicated to the Higgs boson search and its subsequent measurement. The ALICE detector is a heavy-ion detector. Heavy ions, i.e. ions with very high atomic numbers and weights, like Gold and Lead, are collided at high energies. The end products are then analysed.
What the hell is QGP?
The generic end product is quark-gluon plasma (QGP), a soup of quarks, which are building blocks of protons and neutrons, and the so-called gluon particles. This is regarded as another form of matter and this was indeed the state of the Universe just moments after the Big Bang! In QGP, matter behaves like a perfect fluid, with no drag or friction.
Numbers, just for the record
Now, for the record you need numbers. The earlier record was set again by a QGP factory called the Brookhaven National Laboratory and the temperature they attained was a whopping 4-trillion degrees!! That’s a 4 followed by 12 zeroes!
ALICE isn’t quite sure of its figures yet, but the energy to temperature conversion should indicate temperature of close to 5.5 trillion degrees! But the ALICE collaboration wants a few days in order figure out the actual numbers.
The ALICE experiment is colliding beams of lead ions, but the collision between unlike heavy ions is a likely possibility for the future. That will be important to know the dependence of the parameters of the resulting fireball on the geometry of the colliding particles.
The publicized $9 billion papers on the Higgs Boson are out! Both the CMS and the ATLAS collaboration at the LHC, CERN have been working against the clock for the last two months to churn out the result that the world was looking forward to – finding the Higgs Boson. Having found the Higgs Boson and announcing it on the 4th of July at Geneva, the CMS and ATLAS collaborations have now released two papers, both reporting that they have improved upon their earlier presented results.
Stating the Obvious
The 4th July conference had already stated that both the CMS and the ATLAS detectors at LHC have found the Higgs Boson, the long sought after particle responsible for endowing all massive particles with mass. The search has been on since the LHC started running more than two years ago. The long time required just goes to show the magnitude of the search – finding the Higgs Boson wasn’t easy. But make no mistake – the Higgs Boson is definitely there!
Now, these two papers, one by CMS and the other by ATLAS, do something on expected lines – they bump up the significance of the result. This simply means that they make the result more concrete.
Improving the Results
To put in the numbers, the CMS collaboration had quoted a significance of 4.9 sigma or 99.99995% surety of the presence of the Higgs at a mass of 125.3 GeV. They have just bumped up to 5.0 sigma, which means that the surety is not 99.99997% but at a mass of 125.5 GeV. The error bars stay as they are. The decay channels of highest significance are the diphoton (or the gamma-gamma) channel, where the Higgs decaying to two photons, or the ZZ channel, where the Higgs boson decays into two Z-bosons.
The ATLAS collaboration publish a more adventurous result. They have bumped up their significance from the 5.0 sigma announced on 4th July, to the 5.9 sigma! That is a huge improvement, but this also raises a few questions about the analysis of data. How is it that the ATLAS collaboration can bump up their significance so very quickly?
Both collaborations have gracefully dedicated their papers to all those who were associated with the Higgs search, but have passed away and couldn’t see the remarkable results.
All of the questions – and there are many – will be answered in an expected conference in December, when the data collected the LHC in the next three months will be analysed and presented. The LHC is set to go into a period of hibernation after that for about 14 months and expected to resume in 2014.
In the world of high-powered lasers, a new kid is on the block. And it’s damn powerful! The Berkeley Lab Laser Accelerator (BELLA) has developed a laser which can deliver a huge 1 petawatt of power in a single pulse which lasts for 40 femtoseconds. It can do this once every second, making it a one-pulse-per-second laser.
Now, what do those terms with the funny units mean?
A petawatt is a million billion watts – a quadrillion watts, in everyday language. And a femtosecond is a quadrillionth of a second – one part of 1015 parts in a second! No other laser in the world has this high a peak power and still function at that high a pulse rate (1 pulse per second). This is now officially a world record – this is the world’s most powerful laser.
Building an accelerator
Enter the Laser and Optical Accelerator Systems Integrated Studies (LOASIS) program and there is where BELLA really scores. The really powerful laser is a prototype for the ultimate laser that will be built to accelerate particles for an accelerator. This accelerator will use the laser’s energy to speed up electrons and protons.
Conventional particle accelerators, the LHC included, uses electric fields to accelerate the charged particles, while magnetic fields bend them. The laser uses its intense heat to generate plasma. This plasma has a lot of free electrons swimming around and they can absorb energy and be accelerated to very high speeds. The trick is to make all of these electrons accelerate in phase.
Says Wim Leemans of Berkeley Labs Accelerator and Fusion Research Division (AFRD), the dept. responsible for the construction and maintenance of the LOASIS:
BELLA will be an exceptional tool for advancing the physics of laser and matter interactions. The laser’s peak power will give us access to new regimes, such as developing compact particle accelerators for high-energy physics, and tabletop free electron lasers for investigating materials and biological systems.
BELLA laser will be used to build the world’s first plasma accelerator, which will be able to accelerate electrons to 10 GeV. This is about a thousandths of what the LHC produced, but it’s still very high energy achieved on a device a millionth of the size of the LHC. This successful preliminary test of the BELLA laser was part of the LOASIS test which is due to start this autumn.
If you’ve been following our blog for the last few days and been interested in the science posts and those on the Higgs, you’ll know that I was very skeptical about the discovery of the Higgs Boson by the time this presentation comes about. And boy, am I proved wrong! And I am elated about it.
Let’s be honest – it isn’t the Higgs
Okay, to be honest, the exactly correct statement would be this: There is a particle, hitherto unknown, having mass between 125 and 126.5 GeV (giga electronvolt), which has been discovered with 99.999997% certainty. We still don’t know whether this is the Higgs Boson or not – it could just be another particle.
It’s not the Standard Model Higgs
In fact, to make things interesting, this is really not the Standard Model Higgs. So people claiming that this ‘completes’ the Standard Model are, at least partially, incorrect. While the Standard Model predicts – and requires – the Higgs Boson, there is nothing that we know right now that says that this discovered particle is the Higgs.
Furthermore, the Standard Model predicts a Higgs with the mass of about 140 GeV or thereabout. What we have got is something with a mass in the ballpark of 125-126 GeV. Even if this is the Higgs, this is NOT the Standard Model Higgs.
What we really have!
So what have we really got on our plates? What we do know is that there is a particle whose mass is 125 GeV or so and how it decays. We also know how much it decays through the various decay channels – the so-called ‘branching ratios’. We are yet to know the charge of this particle and its parity. We do not know whether this is a fundamental particle (like the electron, with no ‘sub-parts’) or a composite one (i.e. made up of more elementary particles like quarks).
As Fabiola Gianotti, ATLAS spokesperson, said:
We are entering an era of Higgs measurement.
That is a lot of work left. We need to figure out what we are looking at really.
Rolf Heuer, CERN Director General, said that this is like looking at someone from far away and recognizing him/her immediately to be your best friend. But you’re not quite sure. You want that person to be closer to you so that you can make sure that it is indeed your best friend and not his/her twin.
Quite true. We need to take a better look. Translated into the language of high energy physics, that means ‘We need more data’. The saga will continue till the end of this year, then there will be a break and will continue again in 2014.
So, what can it be, if it’s not the Higgs Boson? It can be one of the supersymmetric partners of some already known particle. We don’t really know anything about the energy scale at which super-symmetry sets in or when supersymmetry breaks, but there is a fair possibility that the LHC might be detecting tantalizing hints in the next three months. When it comes back in full force in 2014, running at a higher energy of 14 TeV, compared to 8 TeV currently, we will definitely rule out or embrace supersymmetry at the 5 TeV energy scale.
Don’t worry, if you don’t get this – it’s futuristic talk. We want to talk more about today’s conference and that is what we will do!
Today’s conference: what they really said!
So this particle we are seeing today – let’s just call it Particle X till CERN says that it is indeed the Higgs boson – decays via different modes. A particle decays if it is heavy and there is no law or conservation principle preventing it from decaying. And it can decay via different end products – two Z-bosons, W-bosons, photons, four leptons etc – and all of the decay channels have some probability. One can be more probable than the other, and some channels can have more background noise than others. This happens if, say, a decay product can come from more than one source.
For example, bottom quarks can be produced from a lot of different sources, like all the so-called QCD processes. This masks the signal coming from the Higgs decay. The subtraction of background often leads to subtraction of the signal itself.
In order to cut through this mess, it is imperative that one identifies ‘clean channels’. Two such channels for this particle X are lepton channels and the di-photon channels. Particle X can decay into two muons or two electrons accompanied by the respective anti-neutrinos (don’t bother about those) through the lepton channel and, as the name suggests, into two photons in the di-photon channel. And lo, the signal is the strongest in these two channels. CMS and ATLAS (the two detectors at LHC searching for the Higgs) both have been extremely diligent and successful in looking for signals in these two channels. Both have scored grand success.
Look at the green squiggle dipping down right above the black continuous squiggle. That, the legend on the left reveals, is the signal from the di-photon channel. Look how strong that signal is! This immediately suggests that the particle is a boson (otherwise, if it were a fermion, it would violate fermion number conservation) and that the particle cannot be a spin-1 particle (as the photon is a spin-1 particle and we can either have spin-0 or spin-2 for the initial particle). The Standard Model Higgs is a spin-0 object.
What about the charged lepton channel? The two lepton channel is an indirect way to infer the presence of the ZZ or the WW channel. The neutral Z-boson or charged W-bosons are formed from the decay of the Higgs boson. These then decay into muons and electrons, which are then detected. It turns out that our particle X mimics the Higgs Boson quite closely.
What does CMS say about the different channels?
For the gamma-gamma channel (another name for the diphoton channel), the surety is about 4.1 sigma for the particle X having a mass of 125 GeV.What about Z-channel? It spits out 3.2-sigma confidence level for X having a mass near 125 GeV.
Add these two in quadrature (square each, then add and then take the square root of the sum) and you get 5.2-sigma!! This is winning, as the confidence level required for announcing a discovery is 5-sigma!
More data is expected to bump up the confidence level even further. Particle X could be as certain as 7-sigma by the end of December.
It’s not worth repeating the story for ATLAS as it is very similar.
Being cautious, still
CMS hit it just right when they cautiously put this up as the defining slide, saying “We have observed a new boson with a mass of 125.3 +/- 0.6 GeV at 4.9-sigma significance”.
The conservative 4.9-sigma, instead of a two-channel combined 5.2-sigma is typical amongst high energy physicists. This takes into account other channels and the so-called ‘look-elsewhere effect’. We need not get into that for our purposes here.
Point of disagreement – a potential for trouble?
Now let’s come to the discrepancy between the two collaborations – CMS says that the boson is at 125.3 +/- 0.6 GeV, while ATLAS says that it is at 126.5 GeV. The ATLAS collaboration hasn’t put in the error bars. So what are we supposed to make of this? What about the 1 GeV discrepancy?
We don’t know right now. Rolf Heuer made light of the incident:
We have the Higgs, but which one?
Rolf Heuer’s bag of quotes doesn’t end there, and so we would like to end with one of his gems – one signifying finality:
I said we will have a discovery this year. DONE!
Done, indeed. Congrats to everyone on the CERN team and the worldwide collaborations!
CERN is all set to announce the latest in the Higgs search from the LHC. The press conference will take place in Geneva on the 4th of July, 9 AM local time. This will update the world on the ongoing search for the Higgs Boson, unfortunately dubbed the ‘God Particle’. Results from the 2012 data analyses will be presented and the path forward will also be charted out. More data will be gathered by the time LHC shuts down in December for nearly one-and-half years and we will get to know about the final fate of the Higgs Boson by December.
Interestingly, this will come on the heels of a major high energy conference, being held in Melbourne, Australia, called International Conference of High Energy Physics, 2012 (ICHEP, 2012). Australia not being a ‘member state’ of CERN’s LHC confederacy doesn’t get the honour of hosting a major Higgs update from its own soil. More here: http://techie-buzz.com/science/higgs-boson-cern-conference.html
Inside sources say that the Higgs update will announce the fact that the Higgs is almost discovered but not quite. So to clear the air first up, we ask THE question: Has the Higgs been found? The answer: NO!
No, the Higgs hasn’t been discovered. The ‘excess’ or the odd bump seems to be concentrated consistently at one only energy – 125-126 GeV. This is great news, as the LHC has gone from restricting the mass ranges for the Higgs Boson, excluding different regions with different confidence levels, to precisely pin-pointing a specific mass! That is definite indication that there is indeed some particle at that energy and it could be the Higgs.
Talking about confidence levels, the Geneva press conference is probably going to announce the fact that the Higgs excess has been located with a confidence level of about 3 to 3.5 sigma. While this is significant and worth mentioning, there is no reason to call this a discovery. A discovery requires 5-sigma confidence level. We just don’t have that much data right now to confirm a 5-sigma confidence level. Read this for more: http://techie-buzz.com/science/higgs-boson-discovery-rumors.html
A LOT of Noise!
A final word: A lot of blogs are chattering over the ‘fact’ that the Higgs boson has been discovered. At the risk of sounding utterly repetitive, we venture out “No! The Higgs Boson has not been discovered”. That will require till the end of this year. Believe whom you will.
The latest status of the Higgs Boson search at the LHC will be announced on the 4th of July. The conference will be held in Geneva. Incidentally, the International Conference on High Energy Physics (ICHEP), 2012, will also commence on the same date, but in faraway Melbourne.
The Higgs announcement
The announcement is expected to a big one – especially with the predicted discovery of the Higgs by the end of the year. The status of the Higgs will not be changed to ‘discovered’, but we will get to know how far we have actually reached.
We have already told you why you shouldn’t believe the rumors going around about the Higgs being discovered (LINK). It hasn’t been discovered as yet!
Just to sum up that post in the link, we predict that the CERN conference will announce that the Higgs bump in 8 TeV data matches with the bump in the 7 TeV data. Better make your way to that post!
CERN and murky money matters
CERN’s problem with making the official announcement from ICHEP in Melbourne is that Australia is not a ‘member state’ of CERN. Why make an official announcement in a country that doesn’t foot the bill for running of the LHC? So Geneva it is! And July 4th.
The CERN conference is scheduled for 0900 hours Geneva local time, which is GMT + 2 hours (i.e. it is two hours ahead of GMT) currently, due to daylight savings.
Do stay tuned to our coverage of the announcement.
In a few days, the floodgates will open and you’ll hear about the Higgs Boson being already found. The Holy Grail of particle physics will have been found and only CERN will need to confirm it in their press release. When CERN will deliver the promised press release, they will inevitably say that the Higgs is still far from being discovered and that they have only see a ‘statistically significant fluctuation’ about some energy range. The whole non-high energy physics world will breathe out a collective sigh and, defeated, ask ‘How much longer?’
Higgs Not Discovered!
In order to spare at least our readers from being part of this international collective gasping team, I would like to mention this: The Higgs Boson’s status on its road to being discovered hasn’t changed since the December CERN update. It hasn’t been discovered as yet!
I predict that this is the line that CERN will adopt when it gives the Higgs Boson status update during the International Conference on High Energy Physics (ICHEP) that will be held in Melbourne from the 4th of July to the 11th of July.
The Last Six Months at the LHC
But then what has changed in the last six months? Has the LHC been doing nothing?
The LHC is now operating at a new energy scale. The LHC had been colliding beams at 7 TeV energy last year, and, beginning this year, it has been colliding beams at 8 TeV energy. The good news is that they still see the 125 GeV bump in the 8 TeV data they saw in the 7 TeV data, which has been attributed to the Higgs Boson. This means that the 125 GeV bump is not some random fluctuation, but an actual particle – probably the Higgs.
Why Is It Still Not A Discovery?
However, the data collected is not enough to guarantee a discovery, not even when integrated with the 7 TeV data. The 7 TeV data had yielded a confidence level of 1.9 sigma from the CMS detector and a confidence level of 2.3 sigma from the ATLAS detector. Both numbers are far from the 5 sigma confidence level needed to guarantee a discovery. However, the coincidence of the mass range for the fluctuation in the two detectors is heartening.
As I have explained here, ‘confidence level’ is a quantitative measure which tells physicist how unlikely it is that a certain signal is a mere fluctuation. So 3 sigma means that the chances that a signal is a fluke are less than 0.13%. High Energy physics demands very high rigour at 5-sigma confidence level – that’s the doubts reducing from 0.13% to less than .00007%.
What To Expect From ICHEP
The ICHEP announcement will say that the Higgs has been seen in the same energy range – 125 to 126 GeV mass range – and that the amount of data is not enough to say that it is really there. The 8 TeV data is far too small – giving at most a 1.5 sigma confidence level and no more. Integrated with the 7 TeV data, the confidence levels for both detectors might swell up to 2.5 to 3-sigma (taking into account the look-elsewhere effect), which, though significant, is still not a discovery. Sorry for the disappointment!
The good news is that this is exactly what is to be expected. The Higgs search is expected to end by the end of this year. That is when you will REALLY get to know whether the Higgs actually exists or not.
As for ICHEP and Higgs announcements by CERN, you can rely on us for the information. We will post them as they are announced. Not before!
Experiments may just be showing some chinks in the massive armour of the Standard Model of particle physics. The Stanford Linear Accelerator (SLAC) experiment BaBar has just produced data that contradicts the Standard Model, but the confidence level is still not high enough to warrant the tag of a discovery. So the Standard Model stays where it is, at least for the moment. Physicists are waiting for a confirmation of the same anomalous effect from the Belle experiment.
The Decay Deal
So this is what’s happening. A particle called the B-bar meson (i.e. a bound state of a quark and an anti-quark in which the antiquark is a anti-bottom or b-bar) decays into a D-meson (i.e. a meson containing a down quark) and a tau anti-neutrino and a tau lepton. The problem is not in the decay products but in the rate of decay. The Standard Model predicts very definite rates for particle decays, but the observed decay rate is higher than what the Standard Model predicts. This excess is what has got physicists interested.
The confidence level of the observation is about 3.4 sigma, which is not enough to claim a discovery, which requires 5 sigma. Confidence level is a quantitative measure of how solid a set of data is. The higher the confidence level, the lesser the chances that the result is a mere fluctuation.
There is work to be done, though. Seasoned particle physicists are wary. BaBar spokesperson, Michael Roney, professor at University of Victoria, Canada is visibly enthusiastic:
The excess over the Standard Model prediction is exciting
but then puts up a cautious front with:
But before we can claim an actual discovery, other experiments have to replicate it and rule out the possibility this isn’t just an unlikely statistical fluctuation.
And that’s exactly how these things work.
The LHC Angle to “New Physics”
Incidentally, this one is not coming from the LHC at CERN. LHC has been hard at work and the data it is churning out is killing off one ‘New Physics’ or Beyond Standard Model theory after the other, confirming the Standard Model even further. The greatest confirmation of the accuracy of the Standard Model will come from the Higgs discovery, which is where the irony lies. The irony is that, if the Higgs is discovered at 125-126 GeV range, and this is the likeliest scenario, physics beyond the Standard Model is a definite requirement.
As I mentioned, the wait now is for another experiment to repeat these results. Says Roney:
If they do, the combined significance could be compelling enough to suggest how we can finally move beyond the Standard Model.