Exotic is the word! Italian physicists have discovered traces of rare nuclei containing an exotic form of matter – hyperons. They have just discovered a hydrogen nucleus with 6 nucleons, which includes 4 neutrons, 1 proton (and thus hydrogen) and one uncharged hyperon called lambda!!
The exotic side of the Universe
Hyperons are particles, which are made up of quarks, just like protons. But, unlike protons, they are short-lived, much heavier and contain the so-called strange quark. They are thus called strange baryons! If a nucleus contains such hyperons, the nucleus is called ‘hypernucleus’.
The Italian scientists have found a hypernucleus called ‘hydrogen six Lambda’ (6ΛH, Λ=Greek letter, Lambda), which means that it is a hydrogen nucleus (i.e. has 1 proton), with six nucleons altogether (i.e. 5 particles other than the proton) and that one of them is the Lambda baryon. This says that the other four particles are all neutrons. The 6ΛH was predicted in 1963, but only now have physicists at Instituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Frascati (INFN-LNF) working on this experiment called FINUDA found a signature of it. The finding is due to appear in an issue of the Physical Review Letters (PRL).
The hyperon makes it possible to detect this hydrogen nucleus having as many as 4 neutrons. Hydrogen five (5H), i.e. without the Lambda, exists for just 10-22 s, which is too short to measure leave alone trap and study the nucleus. The presence of the strange particle boosts the lifetime by a factor of a trillion, taking it to 0.1 nanosecond, which is long enough for physicists to measure and study. Note that this timescale is still way too small for daily life!
Producing the hyperhydrogen
The hyperhydrogen is produced in an indirect way. The FUNIDA collider collides electron-positron beams. This gives rise to a phi-meson (with a small probability). This phi-meson can decay into two other mesons – the K meson and the anti-K meson. When the anti K-meson (which contains a strange quark) interacts with a lithium nucleus, it can produce a 6ΛH and pi-plus meson. When physicists detect the pi-plus meson, they know that a 6ΛH has been created.
FUNIDA experiments have also been able to produce 4ΛH, having 2 neutrons. They are produced more readily than 6ΛH and can be studied with greater ease as they exist for a longer time than the 6ΛH.
Clues into strangeness
Physicists are hoping that such studies will yield valuable clues into the nature of strange forms of matter. Another interesting challenge will be to synthesize nuclei having two strange particles, rather than just one! Producing helium or lithium nuclei with strange particle is also on the cards.
The Higgs search gets hotter and hotter. Recent analysis of old data have raised the confidence level of the Higgs detection from the older value of 3.8-sigma overall to a much healthier 4.3-sigma, as indicated by the two papers sent for publication, one by CMS and the other by ATLAS. The Compact Muon Solenoid (CMS) detector group had given the confidence level of 2.5-sigma. Now, with the analysis of more data, they have pushed it up to 3.1-sigma. Remember that a 5-sigma confidence level is what you need for tagging something as a discovery – so 4.3-sigma, though exciting, is not momentous.
There – but not quite there
The results overwhelmingly predict a Higgs mass in the range of 124-126 GeV, which is exactly what scientists had reported on December 13th.
A 5-sigma means that one is 99.99997% sure, while a 4.3-sigma result means that scientists are 99.996% sure that the identified peak is the Higgs peak.
This is just an improvement over the ‘initial’ December announcements by CERN. The data is not new, since the LHC hasn’t been taking any since November, but a more thorough analysis has been done and this is what it says. I suspect that this is as far as CERN can go at the moment with the Higgs confidence levels, and they will require much more data to be completely sure.
The 3.8-sigma confidence levels shouldn’t be taken too seriously. There have been peaks of this confidence level, but they had vanished. Fortunately, this hasn’t.
A new chapter
We should have to wait another year or so before the LHC can give something definite on the Higgs search. Now that the LHC is temporarily closed down for mandatory maintenance efforts, the big bosses, meeting at Charminox, France, are discussing the energy and the luminosity it will be tuned to when it opens later this year. The scale up to 8 TeV in energy is expected, but the luminosity is not yet revealed.
The largest structure ever in the history of mankind is being built for the smallest particle of matter known to mankind. Called the KM3Net Telescope, the structure will be a neutrino detector, taller than the Burj Khalifa, but buried under 3200 meters of water! The whole structure is the latest in the series of larger and larger neutrino detectors and will be the product of a pan-European contribution. It will be the second largest structure in human history, second only to the Great Wall of China.
The super-structure will consist of long cables, holding an optical modulus at the end of each. Each of these optical moduli is a standalone sensing unit, sensitive to light. It will consist of 31 photo-multiplier tubes (or PMTs), which are sensitive light-detectors. All of this will be sealed up as one unit inside a 17-inch glass sphere. The detector will consist of a huge number of such optical moduli!
Why neutrinos are such a headache!
Neutrinos are notoriously hard to detect. They interact only via the weak force (which is also responsible for the decay of heavy nuclei) with other particles and no other force. They leave no trails in the conventional detector chambers, as they are not charged. They do not affect other matter gravitationally, as they are massless (or have extremely small mass!). In order to detect them, the best strategy is to let it hit a proton and convert it into a neutron. This liberates a positron (or anti-electron). The positron emitted travels at such high speeds that it emits radiation called Cherenkov radiation. (Cherenkov radiation is the radiation emitted by a charged particle when it moves faster then light in that medium. Thus, here the electrons/positrons have to move faster than light moves in water). This radiation is detected by the PMT’s. The radiation comes in the form of a cone. This is how the neutrino is indirectly detected.
The KM3Net project is also a Cherenkov type detector, like the famous T2K detector in Japan, which is the largest right now.
Tall, Taller – Tallest!
The whole structure will be taller than the Burj Khalifa, the tallest building in the world. But, this will not be noticed, because it will be underwater. The chamber will be filled with water, as it has a high density of protons. It is meant to detect neutrinos coming through the Earth, and through the sea-floor. This is possible, since neutrinos interact very weakly.
Sometimes mountains have to be moved before the truth can emerge.
The Higgs search is not yet over and is all set to go on at LHC, CERN. This is the natural consequence of the CERN official seminar.
The Higgs has been definitely observed at the energy 126 GeV at a 3.6 2.3-sigma confidence level at ATLAS, combining all decay channels!
The data presented at ATLAS, by ATLAS boss Fabiola Gianotti, is more-or-less in line with Standard Model expectations.
Result from ATLAS:
The Higgs officially lies between 114 GeV to 141 GeV. The rest of the mass range has been eliminated with 95% confidence level.Several channels like the Higgs-> WW* has been excluded.
The mass range between 113 t0 115.5 GeV has been excluded, as has been the range from 131-453 GeV, with the exception of a window from 237-251 GeV at 95% confidence.
The Higgs-> gamma-gamma is a very promising channel and this suggests the 126 GeV figure for the mass of the Higgs.This suggests the presence of a ‘low-mass’ Higgs, which is quite in line with the Standard Model. More data in 2012 will help CERN make a more definitive statement.
Bottom Line: Local Significance – 3.6-sigma; Global Significance – 2.3-sigma at 126 GeV
Result from CMS:
The CMS results ruled out a high mass Higgs, much like the ATLAS results. 270-440 GeV was excluded and the Higgs->gamma-gamma channel gave very clear results. This low mass Higgs is very consistent with the previously announced ATLAS results, which is extremely good news. There were excess events noticed between 110-130 GeV, in the tau-tau and bottom-bottom decay channels; this eliminates 134-158 GeV mass range.
A curious 4-lepton excess was noticed at 125 GeV, which is bang on target, if you take the ATLAS results (above) at face-value. This is again, very good news. The Higgs-> WW and Higgs-> ZZ excludes 129-270 GeV mass range. Multiple channel “modest excess” was noticed just below 129 GeV!
Bottom Line: Local Significance – 2.6-sigma; Global Significance – 1.9-sigma at 124 GeV
The global results take into account the so-called ‘look elsewhere’ effect, which means that it factors in the chances of observing this same local excess at any point within a certain range and also in all channels.
The CERN announcement
CERN announced today that the Higgs has been observed’, but not detected’. The subtle difference between these two words lies in mathematics. When CERN says that they have observed the Higgs, it means that they are 99.73% sure that the Higgs is there. This is, however, not enough to guarantee the tag of a discovery. For that, the confidence level has to go up to 5-sigma, which gives a 99.99994% surety. This is very important, since 3-sigma effects have been known to go away in the past.
The non-discovery of the Higgs, as yet
The only reasonable explanation for the less-than-discovery tag at the moment is because LHC still doesn’t have enough data or rather, not enough data has been crunched.
This is surely great news for the particle physics community. The Higgs may be there in this and there are strong indications from both ATLAS and CMS that it is there and this means that the Standard Model has passed its stringent test yet! However, the mass is still to be ascertained exactly. The error bars haven’t been fully established.
So, the wait continues.
The Super Symmetric Models
This mass of the Higgs Boson, if actually true, is extremely exciting. It lends credibility to the cMSSM models, which is one of the basic Super Symmetric Models. There were widespread news reports that LHC has ruled out super-symmetric models or at least the simplest ones. Not quite! The cMSSM can accommodate a Higgs of 121 GeV mass and no higher. However, a small tweaking of the parameters yield a different version of the theory, which can very well accommodate a 125 GeV Higgs.
Another revolution may be just around the corner! Watch out!
The Higgs seems to be playing the game better than ever, peeking out once in a while, but not for long enough time! Initial analysis of the data from both ATLAS and CMS indicate an excess in the gamma-gamma channel for the Higgs at about 125-126 GeV. ATLAS detects this at a high 3.5 sigma confidence level and CMS comes in at a more tentative 2 sigma confidence level. This is good enough to tag it as a proper observation. None is good enough to warrant the tag of a discoveryof the Higgs, which requires 5 sigma confidence levels.
Both ATLAS and CMS observations are in the gamma-gamma or diphoton channel.
We had told you about the Higgs search coming to an end here and also that there is a joint seminar in CERN on the 13th of this month. The announcement at this seminar is expected to be the definitive on the Higgs search. It will make or break the Higgs, and, thus, a part of the Standard Model as well.
125 GeV Higgs more interesting than a 140 GeV one!
In a way, a 125-GeV Higgs would be awesome news for physicists, since this mass would require corrections to the Standard Model, since the vacuum becomes unstable at high energies. A 140 GeV Higgs would’ve been more mundane, and would’ve been the simplest of all the scenarios.
The situation is a bit ironic really. The Tevatron had almost eliminated the Higgs gamma-gamma channel decay process. Many scientists were convinced that the gamma-gamma channel was no good, and if the Higgs is found, it will be via the ZZ or WW channels. Though this is not incorrect, the gamma-gamma channel has given one of the strongest signals of the Higgs till date and right before the big announcement at the seminar.
It is unlikely that CERN will say anything about this before the 13th December announcement. Fingers crossed!
There is palpable tension at CERN for sure people might not sleep till Tuesday, the 13th. The premier particle physics laboratory is all set to hold a special seminar that day, possibly to announce latest in the search for the Higgs boson. The search is nearing an end and this is expected to be a landmark announcement, possibly one that can either confirm or rule out the Higgs boson.
The 13th December joint announcement might be the last one on the Higgs. We are hoping for either a confirmation or nullification.
We had covered a seminar given jointly by the ATLAS and CMS collaborations last month here and we had told you that the search was nearing an end.
The latest news yet!
The mass ranges for finding the Higgs has been narrowed down to just 30 GeV between 114 to 144 GeV, as per the simplest version of the Standard Model. The finding of the Higgs boson is a crucial step, as it would be the final confirmation of the tremendous success of the Standard Model.
The Standard Model
The Standard Model of particle physics is a framework based on very fundamental principles of physics. It describes the interaction between different particles and the three forces electromagnetism, weak and strong. Although there are a number of freely adjustable parameters, the Standard Model has been the most successful theory of physics ever. The progress of physics in this direction has been extremely rapid, especially in the 1950’s to the 1990’s. Each of the particles predicted by the Standard Model has been detected, giving both theorists and experimentalists enormous confidence that this is the correct model. Theory has always been immediately confirmed by experiments, and they have invariably confirmed the Standard Model predictions! All that remains is finding the Higgs and this one last piece is playing hard-to-get.
Many physicists are tensed about the prospect of there being no Higgs! Many others, among them notably Nobel Prize winner Steven Weinberg, feels that it would be exciting if the Standard Model Higgs is not found! There are many alternative models and these would then gain center stage.
All in all, it is safe to say that this one announcement may be the fork in the path for physics going forward. Higgs or no Higgs – that is the question. The answer comes on the 13th!
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.
It was just yesterday, yet we have come so far! The first proton beams at a respectable 7 TeV energy was started only on 30th March, 2010. It has been hardly a year and a half and so much has already been achieved. This was the basic message sent out by CERN speakers Frederick Bordry and Rolf Heuer, also the Director of CERN at the Lepton Photon Conference, 2011, being held at Tata Institute of Fundamental Research, Mumbai, India.
There are a lot of projects on the horizon, both short time and long time. Obviously, the long term projects are ambitious and a bit ambiguous as of now. However, as Heuer said, they are practical. We should not be afraid that it is not easy, he said.
Among the many new developments happening or proposed at LHC is the development of magnets that can generate extremely high magnetic fields, called high-field magnets. These will be required to increase the energy of a beam, without lengthening the collider tunnel. Prof. Michael Peskin of SLAC, who was in the audience, asked if this is a dream or a programamidst chuckles, to which Bordry replied that it was certainly a realistic program.
The LHC is expected to have a long shutdown period from 2013 to mid 2014 for repairs and maintenance work.
New physics and monster accelerators
A number of new projects are upcoming, even though they haven’t been officially sanctioned. Yesterday’ it was the synergy of the Tevatron, HERA and SLAC that led to the discovery of the Standard Model, said Heuer, adding that the LHC results will guide the way at the energy frontier.
About the Higgs search, Heuer said that while finding the Higgs will be a discovery, not finding the Higgs and ruling it out will also be a major discovery. People should not say that these scientists are searching for nothing, he quipped. Not finding the Higgs will be a major result, since it will completely destroy the Standard Model, allowing other models of physics to come into the limelight.
Among a plethora of futuristic plans announced, the most spectacular was the announcement of a hadron-lepton collider the LHeC. The LHC is a hadron-hadron collider. It can collide protons together or lead/silver nuclei etc. A hadron-lepton collider will be able to collide a proton, and say an electron. The energy per beam of the LHeC will be 16.5 TeV, combining to give a massive 33 TeV in total. The LHeC design is on my desk right now, but I shouldn’t be mentioning that here, he remarked drawing loud laughter from the global audience. As far as LHC physics is concerned, he said that 2012 will be a decisive year. The TeV results will either lead to the discovery of new particles and some new physics will be known or it will be a reformulation of the physics we already know. Both will be progressive steps for particle physics.
Heuer spoke at length on the building of the linear accelerators International Linear Collider (ILC) and the Compact LInear Collider (CLIC). Today, we need to keep our choices openwas Heuer’s advice.
On the question of collaboration, Heuer said that CERN was throwing its doors open to non-European countries. The E’ in CERN is going from European’ to Everybody’. We’re not changing our name, however, said Heuer.
Exciting times in particle physics beckon us! As usual this sentiment was put emphatically in Heuer’s own words -We are just beginning to explore 95% of the universe.
I’ll let the scientist in Heuer have the final word on this report. When asked if he’ll be bothered if the next big accelerator is located in the US, instead of at CERN, Heuer put it beautifully, I don’t care where the collider is! I only care about the science coming out of it.
The scientific enterprise is a greater binding factor than anything else. It’s a silent messenger of world peace, uniting the world in the pursuit of truth and never advertising that facet.
If a high energy collision means fast billiard balls colliding or a train wreck, this article is tailor made for you. As the world, or at least the 0.042% of it who are interested in particle physics, gets their opinions ready about the yet unsuccessful Higgs search at the Large Hadron Collider (LHC), CERN, we thought it might be a good idea to explain what physicists mean by what they say. However, we don’t want to explain why they speak that way.
Here we will list out a few things you’ve heard and are likely to hear in the coming days, along with what they might possibly mean.
Units and Particles:
In particle physics, people prefer to use units of energy, instead of that of mass to measure mass. The idea is a good one, since we can use Einstein’s relation E=mc2 directly. The unit of energy is an electron volt or eV. If you force an electron to go through one volt, then it has the energy of 1 eV. It’s too small to use, so people use 1Mega eV (MeV) 1 million eV, or 1Giga eV (GeV) 1 billion eV. If that is not large enough, the LHC demands that we use 1 Tera eV (TeV) or 1 million million eV. The LHC is currently operating at 7 TeV.
The more important point to note about energy is what is considered big! How much really is 1 TeV of energy in human scales? It’s much less than the kinetic energy of a house-fly! So why is it called high-energy physics? It’s because this energy is carried by particles that are really really small! If a proton having 3 TeV of energy is scaled up to our scales, then we would each have energy exceeding that of a Supersonic jet plane. There’s a large amount of energy packed into a small volume.
About particles, there are just two types Fermions and Bosons. Know that fermions don’t like hanging out together, while bosons have no such ego issues. You can stuff a lot of bosons at one place, while that is impossible in case of fermions. Leptons are one kind of fermions, which are electron-like. Photons are bosons. (As to why this happens, it’s related to the Pauli Exclusion Principle, a fundamental result from quantum mechanics, responsible for single-handedly creating all of chemistry! Fermions follow Pauli Principle, bosons do not).
This is probably the most important phenomenon in this story, so pay attention. This is the deal. Every modern physical theory has some symmetry associated with it. For example, if you made all the positive charges in the Universe negative and the negative charges positive, the Universe will still look exactly like it does. Here’s the crucial part with every (continuous) symmetry, is associated a quantity that is conserved, or doesn’t change value. Example: Take time translation. If time were to flow backwards, at the microscopic scale, we would notice nothing. This symmetry leads to conservation of energy. Symmetry breaking refers to the fact that under certain circumstances, a physical theory loses the symmetry it started out with. We can then distinguish between different states. We can choose.
A Useful Analogy
The best analogy I’ve heard asks you to picture a round table with 10 people sitting equally spaced from each other. There is one glass of water kept identically placed between each two adjacent persons, making it 10 glasses in total. Assuming that the glasses are all identical, one can go and reach out for either one there is no preferred choice as yet. (Situation 1 in the graphic below.) But, say someone does pick up a glass say the glass placed to his/her right.(Situation 2 in the graphic below.) Then, everybody will HAVE to pick the glass to his/her right (assuming that no one wants chaos!). Now, you can differentiate between this system and another such system in which someone went for the glass on the left. Symmetry breaking has allowed us to identify a parameter, which had earlier left the system invariant. The word spontaneous’ is clear from this context. The perturbation has to come from within the system and everyone will choose a glass. The symmetry has been spontaneously broken!
In physics too, there arises situations in which the ground state (or state of lowest energy) of a theory is invariant under certain symmetries. This symmetry can, however, be broken and spontaneously, too if the system interacts with a field. It can be shown that this leads to two distinguishable states one having mass. Physicist believe that this is how mass is generated. The interaction field is named Higgs field’ and the force carrying boson associated with the field (as with any force field) is the Higgs Boson.
We could like to conclude this brief glossary of explanations here. Know that these explanations are highly simplified and the whole picture is much richer in beauty and technical details than this. Unfortunately, I won’t be able to communicate that beauty to a person, not having enough background in physics (being a major in physics is a must) and maths. If you already have a background, you’ve probably already seen a bit of the beauty. Go in search of more.
The world is not only queerer than we suppose, remember; it is much queerer than we can possibly suppose. In the words of the immortal Richard Feynman, I think Nature’s imagination is so much greater than Man’s, She’s never going to let us relax.
Links to related articles:
The Higgs search being unsuccessful so far, ATLAS and CMS collaborations of CERN jointly announce. Initial report here.
The figures and numbers (statistics) from the CERN announcement here.