Data From LHC and Tevatron Shows No Signs of the Existence Of Extra Dimensions

Negative results are important and the LHC just shows that. While the LHC hasn’t been able to find the Higgs Boson with absolute certainty as yet, it has done physics great service by eliminating a lot of different possibilities and put stringent bounds on existing theories. The CMS collaboration at LHC has just released a paper reporting their findings related to the existence of hidden extra dimensions. This is crucial to the very fabric of string theory.

The CMS detector at LHC

The CMS hasn’t found anything in their data that indicates that extra dimensions exist. The team has looked at the energy range of 2.3 to 3.8 TeV, which is the typical collision energy of protons, when the LHC runs at 7 TeV beam energy. The LHC recently upgraded to 8 TeV, 1 TeV up from the usual, but there is little hope of finding things at that energy. We can only wait till the LHC resumes its run after the break it is scheduled to take in a few days. It will be back at 14 TeV and maybe then we can get something on extra dimensions.

And the Tevatron adds to the misery…

Not only the LHC, even the Tevatron data eliminates the presence of extra dimensions, at least at low energies. The Tevatron is dead, but the data is still there and the D-Zero detector team is looking at the energy range around 260 GeV and have found nothing.

So far, the theoretical bounds on the energies at which particles might couple to extra dimensions have large errors. So this result really tells us what the lower limit for any experiment searching for extra dimensions should be.

The LHC is continuing to negate anything beyond the Standard Model. It has got good data to verify the one last piece of the Standard Model – the Higgs Boson – and the search is in its last few days. It seems that the emergence of physics beyond the Standard Model, except in the neutrino sector, isn’t happening at the moment.

Analysis of Tevatron Data Favors Low-Mass Higgs Boson; Confirms LHC Observations

A full analysis of the Tevatron data collected over ten years – a mind boggling 500 trillion proton-antiproton collision events – yields a narrower range for the Higgs mass. A new statistical fluctuation, seen with a confidence level of 2.2 sigma, narrows the range of the particle causing the fluctuation to between 115 GeV to 135 GeV. A GeV is a Giga electron Volts or a billion electron volts. These are pretty strong bounds on the mass. Furthermore, the entire regions between 147 to 179 GeV can be safely eliminated. This analysis confirms what the LHC data says – the Higgs is a low mass Higgs with a mass of about 125-126 GeV and the mass range above 141 GeV is eliminated with 95% confidence.

The local significances of the Higgs signature, both from the LHC and the Tevatron. Notice the continuous black line rising way above the dotted black line within the 115 to 127 GeV range. The horizontal light across the graph is the Standard Model prediction probability. The actual observed probability has to be greater than this line.

Excluded ranges and the range to look out for

The data, collected from CDF and DZero detectors of the now-deceased Tevatron, combines well with the LHC data, specifically with that supplied by the ATLAS detector, to restrict the Higgs mass between 115 GeV and 129 GeV. This also provides more confidence to the 3.6 sigma peak announced during the 13th December 2011 CERN broadcast. Kindly check the link here for very specific details of the seminar: http://techie-buzz.com/science/higgs-boson-cern-seminar-results.html

However, this result shows that the LHC and the Tevatron results match and that’s great, but it doesn’t get us any closer to actually finding the Higgs. Of course, if the Tevatron had disagreed, then we would’ve been in serious trouble.

Bottom line

Two things come out of this confirmation: The Higgs is most probably a low mass Higgs, having a mass of about 125-126 GeV. This is pretty interesting in itself, since this is not just the boring Standard Model Higgs, but gives an inkling of the success of supersymmetric theories. Secondly, the “look elsewhere” effect may not be as significant as was previously thought, now that the bounds are tighter. The “look elsewhere effect” takes into account the probability of finding the Higgs at every point within a certain range and not just at a very small interval. This considerably reduces the significance of the observed bump in general. Since the “look elsewhere effect” may decrease its contribution, concentrating on local significances may be quite the right thing to do!

Of course, the game will only be decided by the LHC. We expect to have enough data to pinpoint the Higgs by the end of this year, before the LHC goes into hibernation for 15 months. The game is heating up and getting interesting. Stay tuned…

CP Violation: Tevatron Detector Data Reconfirms What The LHC Had Already Said

The Tevatron at Fermilab may not be active any longer, but the data it has collected over its lifetime is still capable of inspiring great thoughts. The data, now fully analysed, has revealed what the LHCb had already found earlier, thus giving more credence to hypothetical ideas. The data yields answers to questions as basic as “Why is there matter in the Universe?”.

The CDF detector

CP Violation

In November 2011, we had reported about a reported CP violation in the charm quark sector. We inferred that by looking at the so-called D0-D0 bar mixing. The news can be found here. A more detailed discussion and explanation of the various things is given here.

So, let me just quote the basic figure. The LHCb quotes a figure of 0.82% deviation from the expected value of zero, from the Standard Model. A non-zero value of CP violation goes towards answering the question of why matter won over anti-matter, when equal amounts of the two were produced right after the Big Bang. Now, the CDF gives the same hints.

The CDF quotes a deviation of 0.67 % from zero. The result says -0.67% +/- 0.16%. Alongwith the LHCb results, the CP Violation stands at 3.8 sigma confidence level.

The Standard Model predicts that if CP violation is detected, it might signal the existence of new particles. So far, we have no data to indicate that so far!

Fund Crunch Forces Fermilab To Scavenge The Tevatron

Shortage of funds has hit the scientific laboratories badly. This is quite evident from the attitude Fermilab has towards the deceased Tevatron. Fermilab is planning to recycle many parts of the once-biggest particle  collider for other experiments. It’s to save cost, they clarify.

The CDF detector in Tevatron is now being raided for valuable, and not-so-valuable, parts.

Parts, parts…

Of course, there is nothing wrong in that – in fact, this is a good practice. However, given the amount of history the Tevatron has, many people are frowning. The ex-spokesperson for the CDF detector at Tevatron, Rob Roser says:

Some parts are worth pennies, but in this budgetary climate, even pennies are worth saving

The Tevatron was the biggest beast in the particle physics world till the Large Hadron Collider (LHC) came onto the scene. It has fulfilled all of the expectations and has done more. It discovered the top quark, accurately measured the mass of the W and Z bosons and was instrumental in the Higgs search, especially in the low mass range. The Tevatron probed the Higgs decaying to two photon channel and, now it seems that this is the most promising channel.

However, now the collider parts are being utilized for some other experiments. Demands are being met for photomultiplier tubes (PMT’s). These are used to catch light as particles deposit energy while travelling through the detector material.

Tevatron after death: Just some squiggly lines on the ground?

Looking into the Future

There are other things planned in the near future. Fermilab is all set for lepton colliders, which will collide particles like electrons and positrons, or muons-antimuons. The muons can change to electrons and this process will be studied in greater detail by the new lepton collider. This process should answer certain questions about the electroweak force and put strong bounds on the different constants in the electroweak theory, especially the magnetic moment of the muon. This is the so-called ‘g-2’ (g minus two) experiment. The muonic magnetic moment, supposed to be just 2, is actually a bit more. The difference between the electronic and muonic magnetic moments is due to the difference in masses. The electron to muon process should involve hadronic processes as well and this new experiment could yield very strong bounds on these hadronic processes. The hadronic processes from leptonic processes can indicate supersymmetry and, thus, can tell tales about Physics beyond the Standard Model.

There are also many long baseline Neutrino experiments planned. Fermilab’s own MINOS experiment has to be upgraded and the data made more precise.

Even in death, the Tevatron is fuelling research, this time donating parts of itself for future experiments. Scavenging may be a strong term to use for Fermilab and what it is doing to the Tevatron, but there is no doubt that the desecration of the giant will disappoint a few.

Reference and more info from: http://www.nature.com/news/physicists-raid-tevatron-for-parts-1.10078

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.

The LHC

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.

New Particle Discovered At Fermilab; Existence Confirmed

This time it appears to be genuine. Fermilab has indeed detected a new particle the Xi-sub-b baryon.

A few days ago Fermilab got the entire physics community excited by announcing that it was almost sure of a discovery of a new particle the W/Z-bar boson. We covered the sensational news here. It turns out that it was not the case.

The CDF detector, where the new particle was detected

The particle

A baryon is a particle (technically, a bound state’) of three quarks. A proton is an example and is made up of two up and one down quark. Apart from these two types, there are four more types of quarks top(some people call it truth’), bottom (some prefer beauty’), strange and charm. The top quark is the most massive, followed by bottom, charm and strange in that order. The Xi-sub-b baryon has an up quark, a strange quark and a bottom quark. The discovery was made yesterday and reported today in Fermilab’s press release.

The standard model list for the quarks and all other fundamental particles.

The Xi-sub-b baryon is extremely unstable, being able to travel just a fraction of a millimetre before disintegrating into lighter particles. The particle was detected in the CDF detector.

Confidence levels

There have been 25 isolated detections, or events, that confirm the existence of the new particle. As we mentioned in earlier posts, the criteria for a discovery is confidence level’. We need a minimum of five-sigma confidence level, or a confidence of more than 99.997% that a certain detection is genuine. Here, Fermilab, after data analysis, puts the confidence level at seven sigma, much higher than the threshold!

The details of the discovery have been sent to Physical Review Letters (PRL) for publication.

Eureka Moment Claims Rejected: No New Particle Discovered At Fermilab

It is disappointing news for the particle physics community coming out of Fermilab, we’re afraid. Fermilab has confirmed that the earlier bump seen in the data, presumed to be a new particle, is not significant enough to be considered a detection. We broke the news in emphatic fashion of a new particle discovered in Fermilab in an earlier post.

Story So Far

We had reported that there was a bump found at about 145 GeV with a 5 GeV spread. Data acquired from proton-antiproton collisions with semi-leptonic dijet emissions showed a peak at 145 GeV. The curve was Gaussian in nature with a spread of 5 GeV on either side of the peak. Initial analysis showed that the curve had a three-sigma confidence level (More on confidence levels later). There was thus a strong possibility that a new particle was on the way, since no boson is known having a mass of 145 GeV. The new particle was named as the Z’ or the W’ (Z-primed or W-primed) boson. The Standard Model, wildly successful in particle physics, did not predict this and to fit this in would have required a serious rethinking of known physics. Physicists were naturally excited.

This detection was made at Fermilab at their CDF detector.

The CDF detector

Fermilab was the biggest particle accelerator till the Large Hadron Collider came onto the scene. It has been a major progressive force for particle physics over the last three decades, also serving to etch the American superiority in the particle physics arena. It is however expected to be closed down forever late this year. Data recovered from it over the years is still being analysed, and as such will continue for the next five years. One of the two detectors at Fermilab the CDF had detected the anomalous bump of our present interest.

So What’s Wrong?

There are two problems with the CDF data it cannot be corroborated and it falls outside the required confidence levels.

Problem 1:

The DZero Detector

The other detector at Fermilab, named DZero, repeated the experiment, but failed to come up with any conclusive evidence of detection. The negative DZero result would definitely cast shadows over the CDF discovery. Scientists are now baffled as to how the two detectors extremely alike could give such widely varying results under the same experimental conditions. However this is a very good safeguard.

 

Problem 2: Remember that earlier we had said something about a three-sigma confidence level? It means that the data is reliable and the chances of it being wrong are one-in-a-thousand (99.9% accurate). Confidence levels measure reliability of data. For a discovery to be accepted by the scientific community, the event must have at least a five-sigma confidence level or higher, which means that doubts must reduce to less than one-in-a-million. The problem with the current bump is that it lies just below the five-sigma confidence level.

Graph for the DZero Results.

Take a look at the above graph. Never mind the mathematics and abstruse symbols. Know that the horizontal axis represents the mass of the particles and the vertical axis represents the number of particles detected. At the 145-150 GeV range (point 145 GeV on the horizontal axis), you’d have expected a curve if the previous CDF results were replicated. This is marked with the dotted curve. There is nothing there as far as DZero is concerned. The red regions represent detections and these are in complete agreement with the Standard Model. There is no anomaly to be seen anywhere.

On both counts, the bump is rejected as a new discovery.

What changes then?

Practically nothing changes. The 145 GeV particle, if discovered, would have been interesting, as the Standard Model doesn’t predict it. Further, it could have provided a mechanism for particles acquiring mass without the need of the Higgs boson (essentially becoming the new God particle’). With it being ruled out, the Standard Model stands as it is with the Higgs mechanism being the most favoured mechanism for mass generation.

The discovery would have been exciting, but the field’s exciting even without it. After all, science is like this. DZero spokesperson Stefan Soldner-Rembold  put it approproiately in a Fermilab press conference:

This is exactly how science works. Independent verification of any new observation is the key principle of scientific research.

So very true!

The “God Particle”: Higgs Boson Mystery Might Be Solved by 2012, Says CERN

The mystery of the Higgs boson, the so called God Particle, will be solved by 2012. This claim came from CERN a couple of days back. CERN spokesperson, Fabiola Gianotti, said:

By the end of 2012 we will either discover the Standard Model Higgs Boson, if it exists, or we will rule it out

Make or (almost) break:

This has caused quite a bit of excitement in the physics quarters, with people betting both ways, but leaning towards a successful search. The Higgs boson is supposed to endow all particles in the universe with mass. The mass of a particle depends on the strength of interaction with the Higgs field. Whereas a photon (particle of light) doesn’t interact with the field at all, an electron neutrino (a very light particle) interacts very weakly, while a proton (comparatively heavy) interacts much more strongly. The mechanism by which an interacting particle gets mass is called the Higgs mechanism, after the British physicist Peter Higgs, who first proposed it. Since then, the Higgs has been hot property in the particle physics arena, and has evoked strong interest outside it too. Probably, it is the most popular boson after the photon. The Higgs fits in nicely with the present Standard Model. The only problem is that it hasn’t been detected as yet.

A Simulated Higss event at LHC

If the Higgs boson were found, it would put an everlasting stamp of approval on the Standard Model. However, an unsuccessful search will not invalidate the Standard Model, as some people believe. There are many less known mechanisms not involving the Higgs, which describes how particles get mass.

The LHC:

The LHC was built with a primary aim of detecting the Higgs, especially with the Tevatron at Fermilab, the biggest collider before the LHC, shutting down in 2011. The enthusiasm to get at the Higgs is palpable within the science community and the desperation can be felt by the leakage of a memo at CERN a few days back. ATLAS, CERN has however invalidated the memo, which stated that a Higgs signature has been found.

The CMS Detector at the LHC, CERN

Smashing protons (and heavier nuclei) travelling at velocities close to that of light, scientists hope to recreate the conditions that supposedly existed right after the Big Bang. The LHC recently crossed the 7 TeV energy limit and also set a new record for beam intensity. This is, however, just half of its maximum capability. Scientists are busy acquiring and sifting through data of the order of terabytes, looking for a sign of the elusive Higgs and any of its heavier super-symmetric partners that the Standard Model predicts will have to exist, if the Higgs exists.

There will be an answer. Whether that answer will please Standard Model physicists is another question, and we will have to wait till 2012 for that.

Watch this space for more…

Eureka Moment: New Particle Discovered At Tevatron?

This is big, really big! This may be the biggest news to hit the particle physics world in the the last 50 years. Scientists, analyzing the data collected at the Tevatron, Fermilab, have detected an anomaly that could well usher in a new dawn in theoretical physics and change the Standard Model as we know it now. The observation was a bump in the data, but in the ‘wrong’ place.

Tevatron
Tevatron

Scientists are excited about a Gaussian peak that has been observed on Wednesday, 6th April, centered at about 150 GeV with a spread of 2.5 GeV, corresponding to nearly 300 events.

Data Analysis:

Physicists are generally quite skeptical about any news of big breakthroughs. This ensures that the discoveries are really authentic. Most ‘discoveries’ are just mistakes in the code being used for data-analysis, or some human error or plain background fluctuations. All of these have to be ruled out. Coding errors can be ruled out by using many orthogonal samples of data, called ‘control sets’. Background fluctuations take a bit more effort, but routine analysis can eliminate it almost completely. A peak left after background elimination cannot be discarded.

Notwithstanding the fact that physicists are extremely skeptical, almost all major discoveries in high energy physics have been accidental. The key to such a discovery is rigorous analysis of data.

Is this the Higgs Boson?

The knee-jerk reaction was to suspect the discovery of the Higgs, the bosonic particle that is believed to endow all fundamental particles with mass. The Higgs boson, however, is ruled out, because if the Higgs could be produced at 140 GeV at a non-negligible rate, then we expect to see the characteristic decay jets, which would consist, mainly, of bottom quarks. However, such jets have not been observed, ruling out this possibility.

Higgs Event at CMS
Higgs Event at CMS, LHC

Is this a new force of nature?

It is too early to comment. The discovery of a new particle – a new boson – has to be confirmed. Only further investigation can answer this question.

What could fit the fill?

A new particle, which was coincidentally proposed in a paper a few days back, could fit the bill. The particle is called the Z’ boson, as compared to the Z boson. The Z’ boson is expected to decay via semi-leptonic (i.e. a mixture of hadrons and leptons) channels. Semi-leptonic jets have been observed. So, maybe, the Z’ is the ‘new’ particle.

Decay event for the Higgs
Higgs Decay

Confidence Levels:

The result now stands with a 3-sigma confidence level. This means that the possibility of ruling out the observation as a statistical fluctuation is less than 1 percent. Physicists look for a 6-sigma confidence level, which means that the doubts should reduce to less than 0.003%. To attain this level of confidence, scientists will need more sets of data and rigorous analysis of the same.

More data is on the way. As Prof. Nima Arkani-Hamed of the Institute for Advanced Studies, Princeton, notes, LHC should come up with much more data and copious events, if this is indeed a real discovery.

An Event at the Large Hadron Collider
A Collision Event at the Large Hadron Collider

One thing is for sure: this is exciting. If this is true, this is pure gold for particle physicists.

UPDATE: Fermilab rejects new particle discovery after extensive data analysis. Read here.