The Higgs Boson may have finally have been caught or, may be, not! Only a clutch of scientists with direct access to latest LHC data knows whether the Higgs has been found or not! Whatever the result be, one thing is for sure the Higgs hunt is nearly over. CERN researchers have restricted the Higgs mass to a window of only 30 GeV, taking into results from the Large Electron Positron (LEP) collider, the Tevatron and, of course, from the LHC itself.
The Higgs, if present in Nature, has got extremely little energy space to hide in. At a conference in Paris, held today (18th November), ATLAS and CMS researchers got together and erased out a HUGE range for the possible mass of the Higgs. A large swathe from 141 to 476 GeV was wiped out in one fell swoop. Says Guido Tonelli, the spokesman for CMS
We’ll know the outcome within weeks.
This is surely going to increase the pulse rate of any particle physicist in the world.
What happens if the Higgs is not found? A lot of problems for the Standard Model. The Higgs boson is the simplest way to generate masses for fermions (like electrons and protons) and bosons (like W and Z bosons). There are other possibilities, but this one Higgs model is the simplest and most beautiful of all the possible models. However, as Feynman would say, if theory disagrees with experiment, then it’s wrong and it doesn’t matter how beautiful the theory might be.
For long, has the Higgs mass been pinned at about 140 GeV. There is still a strong possibility that the Higgs, if found, will be of this mass. We may be on the brink of history.
The tantalizing possibility of new physics may just be around the corner. The LHCb preliminary results surely hint towards that possibility with the first ever detection of CP violation in the charm quark sector. We reported this big news here and in this editorial piece, we intend to elaborate on what the results mean or might imply in layman’s terms.
We will follow the following sequential treatment of the entire subject:
What is CP symmetry and what does its violation mean?
What is baryon asymmetry and what does CP violation have anything to do with this?
What are the generations of quarks?
What decay process are we looking at?
What about the Standard Model? What does this predict?
What are the experimental results and how might we interpret them?
If you think you know any of the sections, you might skip it. Let’s begin our journey.
1. CP Violation
There are certain symmetries that exist in Nature. Many of the symmetries are continuous symmetries, like the rotational symmetry for a sphere. No matter how small an angle of rotation you give to the sphere, it will still look the same. This is not true for an equilateral triangle, whose rotation angle has to be 600 in order for it to look the same. The first one is a continuous symmetry and the latter a discrete one.
Having known what symmetry means, we can look for symmetries in a quantity called the Lagrangian. A Lagrangian reflects all the possible dynamics of a system, (which are manifested through its derivatives). Symmetries of the Lagrangian can be both continuous and discrete. In the Lagrangian for the electromagnetic field, apart from a lot of continuous symmetries, there is also the symmetry of charges. Namely, if you replace all charges with their opposite (i.e. positive charges with negative and vice-versa), the Lagrangian will still be the same. CP (Charge-Parity) symmetry means that whatever operation you perform, if you replace the particles with the anti-particles (charge’) and then switched their positions or reflect them (parity), then no experiment will be able to tell the difference.
CP violation refers to the breaking of this symmetry. Some experiments can differentiate between the above mentioned configurations and, thus, CP is violated. Most notable violation of CP symmetry is given by the weak interaction. This violation is explicitly put in the Lagrangian, which is otherwise CP invariant.
2. Baryon Asymmetry and CP violation
We see that the Universe, as we know it today, is made up of matter and not anti-matter. If there is nothing to differentiate between matter and anti-matter (the labels of particle and anti-particle are human constructs and nothing physically differentiates them), we couldn’t possibly have had more matter than anti-matter. One of the unsolved mysteries is then this: Why is there so much more matter than anti-matter in the Universe. This is known as Baryon Asymmetry puzzle’.
One of the theoretical ways to resolve this is to look for CP violation (see previous section) signatures. CP violating processes can produce more matter particles and hinder the production of anti-matter particles, treating them on unequal footing as explained above. Even though there are models without CP violation, which predict the Baryon Asymmetry, none of them is as beautiful as the Standard Model with the CP violation plugged in. For this to work for every particle, the Baryon number conservation has to be perturbatively broken. In the Standard Model framework, this is not possible. The mechanism for CP violation generating excess baryons is not understood as of now.
3. Generations of Quarks
There are three generations of quarks in the Standard Model. Later generations of quarks are heavier than earlier generations. The three generations are given below.
Most matter is made up of just up and down quarks (the lightest of the lot), given that the proton and neutron are made up of these quarks. The charm quark is a second generation quark and is quite heavy. The heaviest is the top quark, which is so heavy that it cannot exist long enough to form a bound state. We can only identify the top quark by its decay signature.
For our current purposes, only the first two generations of quarks are important. The charm quark, being heavy can decay into strange, anti-strange and up quarks or into down, anti-down and up quarks. The up and down, being the lightest of the lot, doesn’t decay into anything. We shall find out the effect of this decay in the next section.
There may finally be some great news coming out of LHC. After a string of negative results, LHC presents the first ever signals of CP violation in the charm quark sector. This might explain the very origin of matter, in the sense that it explains why matter dominates the Universe. Curiously, the awesome result comes from LHCb, one of the side’ experiments and not from the premier ATLAS and CMS collaborations.
This is what LHCb is saying. The observed asymmetries in the decay processes have been noticed in the charm-quark section, giving rise to the D-mesons. The D-mesons are a bound state of the charm quarks, which is one of the heaviest quarks in the Standard Model. The two relevant quarks are the D0 (D-zero) made up of a charm and an anti-up quark and the D0bar (D-zero bar) made up of anti-charm and an up quark. The LHCb looked into the decay of these relatively stable bound states into CP invariant states, like the Kaons or the pions. The D0 should decay into Ï€+Ï€– or Îº+Îº–, and so should the D0bar at equal rates, if CP were an exact symmetry. What the LHCb found was that this is not the case and the deviation in the rates is substantial and LHCb claims a 3.5 sigma confidence level on this!
The amount of deviation
The Standard Model does predict that CP is not an exact symmetry in the quark sector, but only an approximate one. Still it gives a value of mixing, based on the famous Cabbibo angle, which is close to zero. What LHCb found was that this mixing value is close to 0.82% +/- 0.24%, which is a significant deviation from the Standard Model (at a 3.5 sigma confidence level).
These are still preliminary results. The LHCb is not as sophisticated as the ATLAS or CMS and cannot handle the high beam luminosities that the premier detectors can. Thus, it has collected less data than either of ATLAS and CMS. Less data also means more noise or spurious signals.
More data and analysis will establish this newfound signature of Beyond Standard Model (BSM) physics.
Special Relativity may have saved itself from disaster. According to a scientist, the OPERA collaboration overlooked a crucial correction to the result, which exactly matches the discrepancy observed. It involved the effect of time dilation of the clocks aboard the GPS satellite.
Ronald Van Elburg says that the two frames of reference the Gran Sasso laboratory on the ground and the clocks on the GPS satellite in orbit around the Earth – are in relative motion with respect to each other and thus special relativity effects come into the picture. The time of flight, thus, needs to be corrected for this factor too.
From the perspective of the clock, the detector is moving towards the source and consequently the distance travelled by the particles as observed from the clock is shorter
Magnitude of the Effect
Now, for the crucial magnitude of this effect. Van Elburg presents the analysis which shows that this timing should account for 32 ns for the time of flight. Further, this happens at CERN as well as the Gran Sasso Lab in Italy and thus, the number has to be doubled, yielding 64 ns, which exactly compensates the noticed discrepancy of 60 ns.
This solution has recently been released and is yet to be verified properly. The effect seems too obvious and it seems unlikely that OPERA has not taken it into account. OPERA has not responded as yet.
A theoretical attack on the results
Recently, there has been a theoretical attack on the experimental result by Sheldon Glashow (Nobel Laureate, Physics) and his Boston University colleague, Andrew Cohen. They dismiss the results by showing that if the result were true, no high energy neutrino would reach the detector at Gran Sasso. The fact that they detect high energy neutrino (above 12.5 GeV) means that the neutrinos are not travelling faster than light. This is not an experimental result, but a theoretical bound.
We’ll just have to wait and watch. The van Elburg paper is a pre-print and is not yet peer-reviewed.
Now, you can participate in the unraveling of the greatest mysteries ever on your Android phone. Oxford University has come up with a Large Hadron Collider (LHC) app for Android mobiles. The app is nicely named LHSee’ and gives the user a nice chance to explore the Large Hadron Collider in full 3D glory and detail. You can download the app here.
So, the Higgs Boson particle is still elusive and the LHC is hot in pursuit of the mysterious Boson. Not that you can do much about that sitting at home (or maybe you can donate you’re your computer’s processing power to CERN), but you can certainly get a sense of what is going on at the LHC on a regular basis.
Not as easy as Angry Birds
The bad news is that the details are really involved and you’ll probably take some time to take in everything. The Oxford bundle comes with a host of educational resources, besides the simulation. You’ll be able to learn more about ATLAS, one of the premier detectors at the LHC. It even has a game Hunt the Higgs, which we hope will become as popular as Angry Birds. So, while the LHC is busy colliding protons at monumental energies, you’ll be challenged with picking up the different proton-proton collisions from the jumbled mess. If you spot the Higgs, do give yourself a pat on the back.
CERN’s huge LHC now comes in your phone. That’s another reason for a physicist to buy an Android phone, if you don’t already have one. The biggest search in the history of humanity now occurs on your phone. Feel proud about that! High energy physics has never been this much fun!
It’s the Big Boy’s 57th birthday and this is as good a time as it has ever had! CERN, the premier high energy research institute, the home of the Large Hadron Collider (LHC), has got its hands full at the moment. With the Higgs search nearing a climactic ending and the recent neutrino results from OPERA, CERN has no need or time to look back. The future is bright and beautiful, not to mention potentially revolutionary. But look back, we must, for the last 57 years have been glorious ones too!
The fact that you’re reading this very article is also thanks to CERN, since it invented the World Wide Web. It established hypertext protocols. It is now leading in ushering in the next generation of computing concepts like GRID computing. It has also revolutionized the art of making strong magnets a necessity in high-energy colliders and a mainstay of the medical diagnostic industry. While the Tevatron had pioneered in this field, the research carried on by CERN has far outrun Tevatron’s. Today, CERN’s coding wing is one of the best in the world, once again showing that, even in the fringe fields, CERN’s contributions have been revolutionary.
The Real Deal
Of course, these are mere morsels compared to the achievements by CERN in its main field of interest high energy physics. It has confirmed or demolished one idea after the other in the last six decades and is on the verge of another such feat right now. It has discovered neutral currents’ (1973), a vital component in the theory of weak interaction. It established weak interaction theory with the discovery of the W and Z bosons a decade later (1983). Tevatron was just being established at Fermilab at this time. It would then, in one fell swoop, usher in American dominance in the particle physics world and leave the European counterpart far behind. However, it was only at CERN’s historic Large Electron-Positron Collider (LEP) that the neutrino families were discovered (1989). LEP’s results now form the stepping stone for anyone entering the phenomenological field of high-energy physics.
The world-famous CP-violation effect was also directly noted at CERN in 1999, eliminating any shred of doubt that anyone might have had.
Of course, now it is breaking all barriers in Collider Physics with the LHC running at full blast and expected to go a couple of notches higher. Whether Higgs is found or not, LHC will have discovered major physics.
Here’s wishing CERN a very happy birthday. In the world of blazing fast results from higher and higher energy domains, CERN remains indomitable and will remain so for many years to come.
It’s the end of an era, as the Tevatron at Fermilab retires. It has done everything that was expected of it and much much more. It has probably even saved your life, or the life of someone you know. It was the big thing, eclipsed by the next big thing. The Tevatron is really that Wise Old Man, who has done some wonderful things during his lifetime, hung around and supported everyone around him when there was no one else and is now being neglected in his old age, because someone else has stolen the limelight. The Tevatron was the mainstay of the physics community for nearly 25 years until the super-powerful Large Hadron Collider (LHC) at CERN came along. Even then, Tevatron’s edge had only slightly withered and it could still give the LHC a run for its money, while breathing its last.
The Tevatron was the old world’s greatest accelerator till the LHC came along. Stationed at Fermilab, it could easily produce energies in excess of 512 GeV (512 Billion Electron Volts). Constructed in 1983, it was fondly called the Energy Doubler’ owing to the successive increases of energy as upgrades came in. Its aim was simple verify the Standard Model.
The Standard Model is a mainstay of particle physics. It is the theoretical framework, which describes all the interactions in the Universe, with the sole exception of gravity, which is well-described by the classical General Theory of Relativity. It is the fruit of over six decades of intense work by the most brilliant minds of the 20th century, starting from the 1920’s and ending in the late 1980’s. What the theoretical framework needed was the experimental verification of the heavy particles that it predicted. Could the beautiful theory, constructed by considering the most wonderful aspects of symmetries in Nature, stand up to the test of reality? Tevatron was the only way to know.
The First Big Break – A Top Achievement
The first big break came in 1995 with the discovery of the top quark. The top quark is one of the six types of quarks predicted and belonged to the third generation of the quarks (Graphic above).This means that it is one of the heaviest particles known and is extremely difficult to produce and even harder to detect. According to Einstein’s famous relation E=mc2, we need a minimum energy mc2 to create a particle of mass m’. The problem is that a particle cannot be created in isolation; it comes in with an antiparticle, which has the same mass ‘m’. Thus, you can’t produce just a top, but a top-antitop pair, which means that you need at least 2mc2 to produce the top quark. As a rule of thumb, the energy of the beams colliding within the accelerator has to be about twice the needed energy. For the top quark (rest mass energy of nearly 175 GeV), this amounts to 700 GeV minimum. It had to be the Tevatron.
However, energy scale is not the only thing that the Tevatron redefined. It redefined the sensitivity of the detectors. Its detectors – the CDF and the D0 (D-Zero) – were the most sensitive in the world before the ones at LHC came along. The massive top quark immediately decays into lighter quarks, mainly the bottom quark. The decay happens so very fast that without great detectors, the top quark would’ve remained elusive. It could only have been the Tevatron.
Now, running at nearly 2 TeV, the Tevatron regularly produces the top quark. The exact mass of the top was also provided by Tevatron in 2007 to an accuracy of 1%.
What about the Bottom-Strange particles, you ask? Well, it had to be the Tevatron with the answer. Regular matter particles, called baryons, are made up of quarks. Certain particles, called mesons, are made up of just two quarks, in contrast to protons or neutrons, which are made up of 3 quarks. Each meson contains one quark and one anti-quark. The Standard Model predicts that such particles will undergo baryonic oscillation’ before decaying. Simply put, in a bound state of Bottom and Anti-strange quarks (remember, a quark-anti-quark combination), the bottom will go to anti-bottom and anti-strange will go to strange. They will zip in between these two states, before ultimately decaying into lighter particles. This is a firm prediction of the Standard Model. In 2006, Tevatron’s CDF made measurements of this process. As I said before, it could only have been the Tevatron.
After the astonishing result from the OPERA collaboration of detecting neutrinos travelling faster than speed of light, Fermilab wants to double-check the claim. This is an inevitable step in the direction of validating the apparent finding. If Fermilab’s MINOS data doesn’t find anything that replicates the OPERA observations with high enough confidence, then the OPERA result, despite its hype, will become null and void.
Here’s the reason why, despite the care and beauty of the OPERA experiment, it needs independent corroboration: every scientific result must be reproducible. Fermilab has an advantage over other neutrino research labs in the world since it already has the data sets from the famous MINOS experiment.
MINOS was Fermilab’s version of the Super Kamiokande experiment,. Neutrinos come in three flavours or types electron, muon and tau. The curious thing is that neutrinos can oscillate’ or change between these types. An electron neutrino can become a muon neutrino. A theoretical mechanism, known as the see-saw mechanism, explains this, using certain unknown parameters, which need to be supplied experimentally. Super Kamiokande performed experiments in 1998 and confirmed the phenomenon of oscillation and measured the mixing angle’ too. Fermilab repeated this experiment and found consistent results. This was the MINOS experiment, MINOS standing for Main Injector Neutrino Oscillation Search.
Well known to scientists in the neutrino field, but virtually unthinkable to the outside world, is that fact that MINOS had actually detected neutrinos moving faster than light. However, these couldn’t survive analysis and presented only a 1.6 to 2 sigma confidence level, below the 3 sigma needed for validation and way below the 5 sigma needed for labeling it as a discovery. MINOS now plans to sift through their data and put it through rigorous analysis. MINOS should take less than 6 months, since the data is already available to them.
It won’t matter if the OPERA experiment isn’t proved wrong. If Fermilab and T2K don’t reproduce the data, OPERA will be up for grabs. Einstein, thou be stillâ€¦ at least for 6 months.
So CERN has stunned us with a result and this one doesn’t even come from the LHC. The premier European high energy research institute has detected neutrinos that seem to move at a speed greater than that of light, violating one of the most sacred pillars of physics Einstein’s Special Relativity. You must have read about it we posted it here. So what about these faster-than-light neutrinos? Why are so many people all excited about them?
In this article, I will try and explain that, touching upon four crucial points. First we need to understand why people are not ready to believe the result in the first place. Next, we’ll understand whether this is believable or not. Is CERN just tricking us or have they put real hard work behind this before publishing it? Next, we shall talk about the implications of this result, if it is proved right. Lastly, we discuss how there can still be flaws and where some glitches might be found in the coming days.
Unlike the popular media, scientists are treading softly on this result. They are not yet ready to say that Einstein was wrong, although that is what it would imply. They are merely reporting facts at this moment, stating the results as got in the experiment. The result is very possibly wrong, but let’s take a closer look.
What on earth are Neutrinos?
The real heroes of this story, Neutrinos are the slipperiest of all known particles. They carry no charge, almost no mass and interact extremely feebly with other matter and that too via the weak interaction. They’re nearly impossible to detect. They leave no tracks in bubble chambers (no charge), don’t interact with each other to form clumps (no strong interactions, like those of protons and neutrons) or speak with normal matter particles. Scientists were forced to assume its existence to solve a puzzle (the beta decay problem), and, even though neutrinos have been detected after that by several detectors, their properties remain largely mysterious. They are giving a headache once more.
Why are people not ready to believe it?
Simply put, it’s Einstein. People are not expecting anything new and now they find this! This is just too unexpected. Why take a result so flagrantly conflicting with all known physical results at face value? Wellâ€¦
Is this result Believable?
As an answer the first of our questions, I would go with a Yes‘. The result is totally believable in the sense that the experiment and analysis seem water-tight at this moment. Scientists of the OPERA collaboration have been looking at the data for three years! They have done everything scientifically possible to discredit their own finding, but have only managed to strengthen it.
Remember, we told you in the particle physics articles, what confidence level means? A confidence level, quoted as some n-sigma, n’ being an integer, refers to the amount of confidence the experimenter has on his/her own results. A 3-sigma result is one which is significant enough to be considered a potential for detection’. This means that the doubts are less than 0.3%. We’re just getting warmed up! For a discovery’ we need a minimum of 5-sigma, which is a confidence level of 99.9999%.
The current results are a 6-sigma, at 99.999999% confidence level, high and above the threshold required to get a discovered’ tag!! This still doesn’t mean that it is true. It just means that the possibility that this is merely a statistical fluctuation is extremely small. They two are very close, but not the same.
The real motivation for believing in what CERN has found is the methodology they’ve applied in finding out the results. They had found this result 3 years back, but never jumped the gun in publishing it. They checked and re-checked everything, found crucial error bars and found that this result survives. They added more parameters contributing smaller errors, hoping that they’ll somehow add up and then give the necessary’ error bars. They didn’t.
We’ll just talk about the use of GPS and cesium atomic clocks to measure time and how accurately the distance was measured. Since velocity is simply distance divided by time, we need both parameters accurately.
Particles travelling faster than the speed of light have been found. This startling claim comes from a source as respectable as CERN. This was supposedly observed in a neutrino experiment carried out by CERN. However, it is too early to confirm this startling result.
UPDATE: The ‘discovery’ was made by the OPERA experiment while the neutrinos were beamed from Geneva to a lab in Gran Sasso in Italy. The pre-print of the report, prepared by CERN and published today (23rd September) can be found here: http://arxiv.org/abs/1109.4897
Faster Than The Speed of Light? Real Life Tachyons?
Albert Einstein and his Special Theory of Relativity taught us that nothing having mass can travel at the speed of light or above. Massless particles can travel only at the speed of light. Thus, nothing can travel faster than the speed of light.
CERN’s scientists have now found that neutrinos, one of the most enigmatic particles, have breached this barrier. Neutrinos have nearly no mass, no charge and interact negligibly with ordinary matter. It is due to these properties that they cannot be easily detected. The scientists claim that a neutrino beam fired near Geneva to a lab 730 kilometers away in Italy reached its destination 60 nanoseconds earlier than expected. The experimental and statistical errors combine to deduct 10 nanoseconds, which still leaves 50 nanoseconds unexplained and makes this result significant. There are obvious checks and re-checks being performed.
CERN is now depending on the colliders in America and the T2K neutrino experiment in Japan to reinforce its findings. The findings may need many runs and checks to be confirmed. Once confirmed, it raises many questions, including why such an effect wasn’t noticed before. The big question would be this: What happens to Special Relativity, which is an extremely reliable theory?
John Ellis, a theoretical physicist at CERN, gauges the magnitude of the find, if found true:
This would be such a sensational discovery if it were true that one has to treat it extremely carefully.
About the implication for Special Relativity, Ellis says that It has worked perfectly till now”.
Jury Out On Relativity? Not Really!
A knee-jerk reaction would provoke statements about revolutionizing the whole of physics, since stars to elementary particles, all rely on the Special Theory of Relativity. It has been wonderfully accurate, especially when combined with Quantum Mechanics to form Quantum Field Theory. Personally, at this moment, I don’t think this will throw Relativity out, even if the result is correct – Relativity is too beautiful and has been proved too correct in too many situations for that drastic step. I would even stick my neck out and add that this observation is some sort of experimental glitch and that faster-than-light particles have not really been detected. However, only more tests will testify to that.
The grand old man of physics has been challenged by a tiny, nearly massless particle.