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Members discuss the Higgs discovery July 6, 2012

Posted by admin in : Cosmology, Gravitation, and Relativity (CGR), Nuclear and Particle Physics (NPP) , trackback Bookmark and Share

This is certainly an exciting development at CERN! My group and I are in the four lepton working group.  We apply a multivariate analysis to data and simulations to arrive at our results, which is in agreement and supports what was shown by Fabiola.

We see excesses in the gamma-gamma and four lepton channel, but not the bbar or WW channels at least in the 2011 dataset.  It may be just statistics, or the way the data is analyzed in the other channels, but the branching ratios for a Higgs boson are predicted with great confidence (only the mass is a free parameter in the SM).  The WW and bbar and tau channels have large bf, larger than gamma-gamma and 4 lepton.  The former channels have larger backgrounds and it is harder to tease out any excess.  So that may explain this question (in my mind at least it is a bit puzzling).  Also, the gamma-gamma channel can have heavy states contributing to the process that signals new physics beyond even the Higgs, if this result holds up.  And note that we don’t yet have enough data to determine the intrinsic spin or parity of whatever particle may be attributed to this excess.

What this all means is that, in my opinion, we will need to wait until more data is collected before a definitive statement can be made about a Higgs or not. Now the real work begins.  What is this new particle?  Is it the Standard Model Higgs boson?  Is it one of several new states? Is it a scalar or pseudoscalar?  Etc. Etc.  Very exciting times!

Professor O. Keith Baker, Yale University

SUSY among all the other ideas out there (extra-dimensions, branes, etc.) is the unique one that is brought to the fore by the light mass Higgs boson that seems just around the corner from having a final discovery announcement. None of the other candidates for what comes after the Higgs discovery have any such implications to my knowledge.

SUSY is also he only one that is brought to the fore if multiple Higgs bosons are ultimately found. SUSY actually requires multiple Higgs bosons and their superpartners.

The SUSY extension of the Standard Model that has been most extensively studied is called the `Minimal SUSY Standard Model’ or MSSM. As there are literally scores and scores of undetermined parameters, it is not definitive about the likely mass hierarchy of the Higgs family. There is also the NMSSM (the `next to mimimal supersymmetrical Standard Model) which has even more parameters and thus is even less definitive about the properties of any Higgs families. In fact, Superstring/M-Theory suggests that even the NMSSM is not the complete story.

There is a Minimal Supersymmetric Standard Model wiki page that has a pretty good discussion of its properties. There can be found here a discussion of the need for why at least a second Higgs boson must exist in the context of the MSSM. Also there is this lecture available on You Tube.

While the MSSM is not so predictive about the masses, it does make very definite predictions about the charges and coupling to the electroweak forces by members of the Higgs family.

Professor S. James Gates, University of Maryland-College Park

As a theorist I’d say that SUSY has “nice” properties of stabilizing the vacuum, but it also restricts the theoretical hand from just adding anything to the theory arbitrarily. For example one might ask where does the SM Lagrangian (without SUSY) for the Higgs come from (it’s just a polynomial interaction) as it does not seem to be based on a principle like the gauge principle that is used in other interactions or SUSY. The answer is that “well it works” to give spontaneously broken symmetry but there may be many ways to get into this spontaneously broken phase theoretically. Gauge theories and SUSY can control, through symmetry, what the interactions look like which also forces certain particles for consistency. That is why SUSY needs more than one Higgs for example. This makes SUSY, in some sense (limited to our imaginative ways to use SUSY) easier to rule out if Nature has no need for SUSY. But even as SUSY starts to experimentally manifest itself (and I believe it will soon), the next big question is “what breaks SUSY?”.

Professor Vincent Rodgers, University of Iowa

Even if this thing is the Higgs, this discovery itself cannot be the only new physics.  The hierarchy problem in physics (the divergence of the Higgs mass at much higher energies) requires something that stabilizes it.  The most likely candidate, as far as I can tell, is SUSY, just as Professor Gates wrote.

In SUSY, there are an additional four Higgs bosons, at least in the SUSY models I am familiar with.  So Rolf’s statement about which Higgs refers to this dilemma.  Is this thing reported on yesterday the SM Higgs, or one of the SUSY Higgs? If the latter, then there should be more waiting to be found.

SUSY is not the only solution to the hierarchy problem.  But it is probably the most developed theoretically.  In my opinion, the simplest SUSY models seem to be ruled out over much of its parameter space by some precision experiments like edm expts.  Jim may want to clarify this for me.  So if SUSY exists, it is likely some of the MSSM models, or beyond.  Also, as I understand the theory, a heavy Higgs comes into tension with SUSY.  If this 125-126 GeV thing is a Higgs, it is in a difficult but doable region for MSSM of some sort.

Professor O. Keith Baker, Yale University

The whole event was really thrilling, and I was especially glad to see the payoff from our efforts to enhance and better model the ATLAS detector’s performance in intense luminosity conditions. This demonstrates that we are ready not only for discoveries, but also for the following studies to more conclusively identify this new boson.

I concur with our theorists that even if this is a Higgs discovery, our job of explaining how the SM works so well in this energy regime will be far from finished — a lot of my recent work at ATLAS has been related to this area of SUSY and other “exotic model” searches.

But, like Keith, I am especially interested in the couplings of this new particle to third-generation fermions, where the little data ATLAS and CMS have — and it’s far too little for me to place bets yet — do leave room for a lot of surprises to come in.

The implication for hadron collider physicists of my generation — the ones too late to discover the top quark, who relentlessly probed it at the Tevatron and LHC to check for any deviations from SM predictions — is that a new space has opened up for similar tests. Once again, we can easily envision likely ways to make significant contributions to our understanding of the particle universe (hurray!).

Professor Ayana Arce, Duke University

The discovery of the Higgs-like particle is the culmination of a lot of efforts for many years by so many people. I started on the ATLAS Experiment in 1998, I contributed to various aspects of the ATLAS experiments and held many positions in the ATLAS Collaboration. I was ATLAS Higgs working group convener in 2008-2010. In this capacity, I led and directed the analysis efforts of the ATLAS Higgs working group. So, I can confidently say that my work contributed directly in the search and discovery of this new particle. It is a significant achievement that will lead to the capacity building and training for younger students, an improvement understanding of fundamental physics, and ultimately technological spin-offs to the benefits of humanity. It is truly a great pleasure for me to work with so many people across the world and to participate directly in such a monumental discovery that may revolutionize our lives in the years to come.”

Dr. Ketevi A. Assamagan, Permanent Staff Physicist, Brookhaven National Laboratory

At last – there is exciting and long awaited news of a new Higgs-like boson. South Africans scientists, students and computer experts have participated in these exciting developments. “It’s a global experiment, and we have six of our Universities participating at CERN” says Prof Jean Cleymans, leader of the SA-CERN programme, which launched almost four years ago.

The Department of Science and Technology selected CERN as one of its global large-scale infrastructure projects; it supports scientists in the South Africa-CERN consortium to participate in experiments to investigate the existence of the Higgs boson particle and other expected discoveries. The Department is proud of these scientists who are part of this major scientific breakthrough and celebrates this achievement with the rest of the world.

Tantalizing hints of a new particle with a mass around 126 GeV were reported in December 2011. ATLAS and CMS, two of the CERN experiments, have today not only confirmed these hints with data taken in 2012, but also done so with sufficient confidence (5 sigma each) to claim a new particle has been observed. A 5 sigma confidence means that the error due to statistical fluctuations has a probability of less than 1 in 1.7 million (or rolling a dice eight times to get a six each time). Furthermore, the new particle interacts similarly to the Higgs boson. The Higgs boson is reputed to endow mass to other particles. This new Higgs-like boson will now be subjected to intense and detailed study, over some decades, and while exploring this, we may make further surprising discoveries.

Although we don’t have a crystal ball to predict the full benefits to science and society, we note that most of today’s understanding of nature and the development of technology began with the discovery of the now familiar particles like the electron. We are at a new beginning. The LHC may also shed light on the primordial state of matter, shortly after the Big Bang, and on dark matter and dark energy.

The LHC at CERN is a global experiment, and South African participation at CERN enables the highest quality scientific research, manpower development, technology transfer and innovation. The South African computing Grid was established as a result of the CERN involvement. This is a combination of fast networks and high performance computing clusters. It forms the basis of data processing and analysis for CERN. It will also provide valuable lessons for the SKA and data intensive computing in general. Other spinoffs are expected in diagnostic and therapeutic medicine, remote sensing and nuclear technology, to name a few other fields.

Statement by SA-CERN Programme

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Comments»

1. Tristan Hubsch - July 12, 2012

OF COURSE, it would be wonderful if the observed Higgs particle is only one of many—for which then there’d be a chance to support supersymmetry… For my own part, I’d like that and shan’t bet against it. Let’s just stay aware of all the (many) other options, as are being explored.

After such a long time, there is NEW experimental data!!!

2. Alphonso Hamilton II - July 15, 2012

Susy in my opinion seems to be one of the best models when investigating the Higgs particle. The flow of data is artistic in nature and show us that there is possibilities of other particles far pass the Higgs boson. CERN will soon have data that I believe will close the gap in our mathematical data and reality. Absolutely exciting times to be living in……MUCH SUCCESS TO ALL INVOLVED @ CERN & OTHERS