Hint Of New Physics At LHC – Explaining the LHCb Results

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.

The actual news piece, which you should read before reading this:  http://techie-buzz.com/science/lhc-newphysics.html
The LHCb detector

Explaining it simply: topics to cover

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.

The generations of quarks, along with the generation of leptons. (Picture courtesy: CERN)

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.

Charming Results from LHCb Conference: Has The LHC Finally Found Some New Physics?

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.

An explanation of the results:  http://techie-buzz.com/science/hint-of-new-physics-at-lhc-explaining-the-lhcb-results.html
The LHCb Detector

What is found wasn’t quite expected!

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 κ+κ, 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.

Here’s more:http://resonaances.blogspot.com/2011/11/lhcb-has-evidence-of-new-physics-maybe.html
An explanation of the results from us:  http://techie-buzz.com/science/hint-of-new-physics-at-lhc-explaining-the-lhcb-results.html

Get The LHC On Your Android Phone, Thanks to Oxford University

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.

Check out the official Oxford University site here:  http://www2.physics.ox.ac.uk/about-us/outreach/public/lhsee

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!

Download link from Android market again:  https://market.android.com/details?id=com.lhsee

Wishing CERN A Very Happy Birthday!

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!

Happy Birthday, CERN

CERN: Needs no description

CERN, an acronym for European Organization for Nuclear Research (the proper acronym is in French Centre Européenne pour la Recherche Nucléaire ), is located in the pristine suburbs of Franco-Swiss border. While today it is known mostly for the LHC and its awesome power, CERN has had huge achievements in the past. It has yielded at least 2 Nobel Prizes in experimental physics, verified the Standard Model beyond doubt and has, along with the Tevatron, been the experimental hub of the particle physics world.

Inventing the WWW

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 ATLAS building

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.

Best wishes and may you have a really long life.

The End Of An Era: Fermilab’s Tevatron Shuts Down – A Tribute

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 Final Hurrah – Webcast Link : http://www-visualmedia.fnal.gov/live/110930Tev.htm

The Tevatron. The accelerating column in below the ground.

The Old Warhorse

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 Standard Model Scheme (Courtesy: Fermilab. Appropriate, isn't it?)

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.

The Top Quark Production and Decay. Note that a single top quark cannot be produced.

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%.

More Success

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.

News From CERN: Israel Become First Non-European Associate Member Of CERN

Israel became the first non-European nation to join CERN. The decision was made at a meeting in Geneva on the 16th of September, 2011. Israel will be an Associate Member’ of the CERN collaboration and will keep that status for a minimum of 24 months.

Israel has been an Observer’ State for the CERN Council since 1991. It was promoted to special Observer’ in 2009. This move was inevitable.

Rolf Heuer (left) and Israel Ambassador, Leshno-Yaar, (right) shake hands at the landmark meeting (Courtesy: CERN)

Road Forward for CERN

Recently, at the Lepton Photon Conference, 2011, held at the Tata Institute of Fundamental Research, Mumbai, India, Rolf Heuer, the Director General of CERN, outlined the road ahead for CERN. He said that there were plans to include non-European nations into CERN in his speech. The E’ in CERN would no longer stand for European’, but would come to mean Everyone’, he said.

Rolf Heuer, DG, CERN and the Israeli Ambassador and Permanent Representative to the United Nations, H.E. Mr. Leshno-Yaar signed the agreement , which admitted Israel to the CERN Associate Membership. The document still needs to be ratified by the Knesset. This officially makes Israel a member for a minimum of 24 months.

Rolf Heuer said of this development:

It is a vital part of our mission to build bridges between nations. This agreement enriches us scientifically, and is an important step in that direction.

Israel had played a major role in the 1990’s, during the historic Large Electron Positron (LEP) Collider Experiment. This was an important milestone in the legacy of CERN.

More than just science

This move will gain Israel more monetary support from CERN to further its own research interests. Israel has supported Palestinian students in research by providing them funding and equipment on the same footing as Israeli students. It has sent mixed Israeli-Palestinian students at the various summer science camps organised by CERN.

The very act of systematically scouring for facts, known as science, might be the adhesive for the world that wise men have been looking for.

CERN’s Press Release:  http://press.web.cern.ch/press/PressReleases/Releases2011/PR18.11E.html

New Physics Should Be Around The Corner, Says Rolf Heuer, Director of CERN; Charts Future After LHC

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.

Projects! Projects!

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.

Rolf Heuer, Director General of CERN, speaking at the Lepton Photon Conference, 2011, at TIFR, Mumbai

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 CMS detector at LHC

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.

International Collaboration

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.

High Energy for Dummies: A Brief Glossary of Technical Jargon Used in Particle Physics

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.

Tunnel of the LHC

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:

Energy units

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.

Particles types

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).

Hullabaloo about Higgs:

This is the biggest name in particle physics you’ve ever heard. The electron is passé, it’s time for the Higgs. Named after Peter Higgs, this particle is supposed to endow all other particles in the Universe with mass. It is a so-called boson, unlike the electron. It is itself massive (meaning that it has mass), theoretically predicted to be about 140 GeV. Through a mechanism, known as the Higgs mechanism, an example of spontaneous symmetry breaking (explanation below) of a field theory, mass is generated.

Spontaneous Symmetry breaking:

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.

Final Word

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.

Latest Results of Higgs Search Presented Jointly By ATLAS and CMS, LHC, CERN at Lepton Photon ’11, Mumbai

The latest results on the Higgs search are out. Results were presented separately by ATLAS and CMS detectors of LHC, CERN today(i.e. 22st August, 2011) at the Lepton-Photon Conference, 2011. In this semi-technical article, we present the most important results in a systematic form. The verdict is, however, out the Higgs hasn’t been found as yet.

Check out our first (non-technical) post on this discovery here. A countdown to the Lepton Photon Conference itself is here.

Higgs Production and Decay channels

There are a few things that should be kept in mind right throughout the article. The Higgs boson is primarily produced by interaction of two gluons. (A gluon is what keeps protons and neutrons in an atomic nucleus together.) This is called gluon-gluon production of the Higgs boson.

Next, the Higgs, being highly massive (i.e. having a high mass) decays into lighter particles. This is what massive particles always do they decay into lighter particles. The only thing is that different particles decay at different rates. Heavier particles will decay much faster than comparatively lighter particles.

Higgs event

The Higgs can decay into a number of lighter products. Each of these products leaves a distinctive signature on the detectors and the different modes of decay are called different decay channels’. The Higgs primarily has a gamma-gamma (Higgs decaying into two gamma ray photons.) channel, a WW and a ZZ channel. These are the main channels of interest. The gamma-gamma channel will be the preferred channel if the Higgs is a comparatively light particle about 100 GeV in mass. If the Higgs decays by producing two Z-bosons (the ZZ channel) or two W-bosons (WW channel) then its mass is above 130 GeV.   In other words, the gamma-gamma channel fixes the upper limit of the Higgs mass at 130 GeV, while the WW and ZZ channels fix the lower energy bound at 130 GeV.

Now, here is the interesting part. The WW or ZZ bosons are themselves quite heavy and decay into a number of products. These decay channels produce characteristic detection patterns in the detectors. Comparing the observed rate of decay into these channels with that of the expected value, the data is reconstructed to see if this indeed was a Higgs event.

Now for more technical details

ATLAS Results

The ATLAS detector found no significant excess in the gamma-gamma channel. The bottom-bottombar (b-bbar) channel (this is what the WW bosons break down into bottom and anti-bottom quarks) gave big excess of Higgs event above the theoretically expected Standard Model(SM) production rates. Even though the excess was nearly 10 times the SM predictions, the sensitivity needs to be improved. Furthermore, Tevatron has a much greater say in the b-bbar channel than the LHC, given that it has recorded much higher number of events and has a higher luminosity at that energy range. The tau-tau (tau is a lepton, an electron like particle) channel gave a 4 to 5 times excess.

The ATLAS detector at LHC, CERN

Overall, there was no significant excess in any of the channels to warrant a discovery. There was no significant excess number of events noticed for the Higgs in the mass range of 110 GeV to 160 GeV. This mass range is tentatively excluded with 95% confidence level. However, at 99% confidence level, there is a window about 142 GeV, which can be a possible detection window. Further experiments will probe this window more thoroughly.

CMS results

CMS detected no excess in the gamma-gamma channel. A slight excess was noticed in the tau-tau channel and this is expected to be an important channel for further investigation, owing to the fact that data reconstruction from this channel points to a Higgs mass of about 140 GeV.

Excess of events in the WW going to lepton-lepton channel suggests a mass range of 130 GeV to 200 GeV. Three pairs of events have been notices at three mass ranges 122, 142 and 165 GeV for the ZZ channel. Only the 142 GeV event is consistent with Standard Model predictions. Happily, this is the very window that wasn’t excluded earlier with 99% confidence level.

Out of theoretically expected mass range exclusion of 145 to 440 GeV, three ranges have been excluded 145 to 216 GeV, 226 to 288 GeV and 310 to 400 GeV. Anything above 400 GeV is unlikely and the crucial 130 to 145 GeV window is still open. These mass ranges have been excluded with 98% confidence level.

Higgs search continues with full force. LHC will provide a lot more data samples in the coming months and this might ultimately lead us to achieve the Holy Grail of Particle Physics.

Higgs Boson Still Not Found: Huge Official Announcement from LHC, CERN


This is the joint announcement made by the ATLAS and CMS teams, LHC, CERN at the Lepton-Photon Conference, 2011 being held at Tata Institute of Fundamental Research (TIFR), Mumbai, India. This is likely to be a disappointment for many around the world, both within and without the particle physics community. The search is however on!

A warmup countdown post to this Lepton Photon Conference, 2011 is here. Semi-technical post showing all relevant results and figures can be found here.

The Higgs Boson

The Higgs Boson, predicted from considerations of symmetry in Quantum Field Theory by Peter Higgs, is the particle theoretically responsible for endowing every other massive particle with mass. It’s a boson with spin zero, with positive parity and charge.

Weak Signals

There were a number of weak signals noticed that preceded the event. These Higgs signatures’ included the W-W or the Z-Z decay channel for the Higgs as the primary decay channel. This means that the Higgs once produced will decay into two W or Z-bosons, which will in turn break up into electron-positron pairs or muon-antimuon pairs. Unfortunately, none of these events could stand up to the rigors of analysis and survive till the 5 sigma confidence level was reached in both ATLAS and CMS detectors, as yet.

No such significant excess has been observed in the lower mass gamma-gamma channel. Also, more exotic branches like the tau-tau and b-bbar (bottom-bottombar quarks) have not offered anything promising.

The results of Tevatron, Fermilab are similarly blank, with no significant excess noticed in any channel.

The Future

This is also an exciting opportunity it opens up new possible physical theories. Spontaneous symmetry breaking, at least what we know of it now, may not be the whole story. There are many rival’ theories of the Standard Model, many requiring no Higgs boson to achieve mass. These Higgless models may become the focus of mainstream research and the LHC may be next used to test the predictions of such theories.

However, it is too early to make such claims. The Higgs search is going on at full blast.

And a Promise

We will bring more articles soon, explaining what this means for the Standard Model and particle physics in general. We will also run an article elucidating the jargon of particle physics. Hold on for that it’ll come sooner that you think.


Actual results from the ATLAS and CMS joint announcement on the Higgs Boson search can be found here. All relevant facts and figures present.