## Unbreakable

14/11/2012

Today, at HCP2012, new results on Higgs boson search were made available by CMS and ATLAS. Of course, well aligned with preceding rumors, all in all these appear rather disappointing. Maybe, beyond the increasing agreement with Standard Model expectations, the most delusional result is that the particle announced on July 4th appears to be completely lonely on a desert ranging till almost 1 TeV, at least if one is looking for other Higgs particles behaving Standard Model-like. $\tau\tau$ decay rate is now aligning with expectations even if there is some room for a different outcome. On the other side, both experiments did not update $\gamma\gamma$ findings. The scenario that is emerging from these results is the theorist’s nightmare. Tomorrow, all this will be collected in single talks by CMS and ATLAS speakers.

In a retrospective we could say that people claiming for a prize to discoverers of the Higgs mechanism seem to be vindicated. There appears no sign of supersymmetry that is more and more relinquished in a nowhere land. But, I would like to point out that, if a supersymmetric theory is the right one, there is just one theory to be singled out exploring the parameter space. It is normal in any case to see such a vast epidemic death of theories. It is also possible that theorists should now do a significant effort for new proposals beyond those largely explored in these last thirty years.

Standard Model is even more resembling a perfect theory really unbreakable and mimicking the success of the Maxwell equations put forward 150 years ago.  But we know it must break…

Finally, I would like to conclude this rather fizzling out post by pointing out a rather funny side of this situation. Tommaso Dorigo has a bet on with Gordon Watts and Jacques Distler amounting to \$1200 on the non-existence of SUSY partners. This bet has not been payed yet as Distler is claiming there are a lot of “juicy rumors” from CERN and the terms are not fulfilled yet (see comments here).  I do not know what rumors Distler is talking about but, unless CERN is not hiding data (that would appear a rather strange behavior at best), maybe it is time to do a check on who the winner could be.

## Kyoto, arXiv and all that

12/11/2012

Today, Kyoto conference HCP2012 has started. There is already an important news from LHCb that proves for the first time the existence of the decay $B_s\rightarrow\mu^+\mu^-$. They find close agreement with the Standard Model (see here). Another point scored by this model and waiting for new physics yet. You can find the program with all the talks to download here. There is a lot of expectations from the update on the Higgs search: The great day is Thursday. Meantime, there is Jester providing some rumors (see here on twitter side) and seem really interesting.

I have a couple of papers to put to the attention of my readers from arXiv. Firstly, Yuan-Sen Ting and Bryan Gin-ge Chen provided a further improved redaction of the Coleman’s lectures (see here). This people is doing a really deserving work and these lectures are a fundamental reading for any serious scholar on quantum field theory.

Axel Weber posted a contribution to a conference (see here) summing up his main conclusions on the infrared behavior of the running coupling and the two-point functions for a Yang-Mills theory. He makes use of renormalization group and the inescapable conclusion is that if one must have a decoupling solution, as lattice computations demand, then the running coupling reaches an infrared trivial fixed point. This is in close agreement with my conclusions on this matter and it is very pleasant to see them emerge from another approach.

Sidney Coleman (2011). Notes from Sidney Coleman’s Physics 253a arXiv arXiv: 1110.5013v4

Axel Weber (2012). The infrared fixed point of Landau gauge Yang-Mills theory arXiv arXiv: 1211.1473v1

## ATLAS and CMS papers published

10/09/2012

Papers by ATLAS and CMS have appeared in Physics Letters B and can be freely downloaded. They report on the discovery of the Higgs-like particle on July 4th.

CMS Collaboration (2012). Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC Physics Letters B DOI: 10.1016/j.physletb.2012.08.021

ATLAS Collaboration (2012). Combined search for the Standard Model Higgs boson using up to 4.9 fb^{−1} of pp collision data at \sqrt{7} TeV with the ATLAS detector at the LHC Physics Letters B DOI: 10.1016/j.physletb.2012.02.044

## QCD 12 and Higgs’ tears

08/07/2012

I have spent this week in Montpellier being a participant to QCD 12, a biannual conference organized by Stephan Narison. It is the third time that I go to Montpellier for this conference and there are always very good reasons for being there. Essentially, the quality of physics and beauty of the city are already worthwhile and sound arguments but also the excellent organization  by the host and the attention reserved to the guests are not the least. This year we have had the blessing of a historical event in physics: The discovery at CERN of the Higgs particle. Stephan organized the event with the webcast from CERN the first two hours on Wednesday and so we heard directly from Gianotti and Incandela what they were seeing at LHC.  The conference is a fair interplay between experiment and theory in a field, QCD, that is very active and with several important open problems. Maybe, we would like to emphasize that is QCD that gives mass to everyday things, and not the Higgs boson, and this means that the solution of the mass gap problem and the developing of proper methods to manage non-perturbative regimes are essential to the understanding of our common perception of reality. Indeed, Roberto Mussa of University of Turin remembered us an argument that  makes Higgs boson essential to everyday life: The stability of matter. Without the Higgs boson quarks would have equal masses and so, proton would decay into neutron. The difference in mass between u and d quarks is essential and this originates from Higgs boson.

In this conference several questions emerged that were absolutely exciting. Hadron spectrum is not so well understood both in the low and high part. There is a plenty of experimental results claiming for an explanation. Labs keep on finding resonances that have not an immediate explanation and make hard the life of us theoreticians. One should compare the situation with the case of electromagnetic interactions where a Rydberg formula was promptly found and understanding of bound states is now quite straightforward. For hadrons we have hard times already to catch what the structure of a resonance is. These difficulties arise from the missing of technique to manage non-perturbative problems in a way similar to the weak coupling limit. Indeed, on Wednesday, some approaches were given to manage this kind of situation and, besides my talk, the most common technique is AdS/QCD starting from Maldacena conjecture. This was also the argument of Stefano Nicotri and Floriana Giannuzzi. They are students of Pietro Colangelo and contributed to the organization of Lecce conference. I have spent a lot of good time with them and so we exchanged a lot of opinions about this matter. On this line, Hans Günter Dosch put all us down showing that the situation with this approach is not so fine. Simply, it appears like a proper model for the mapping between gravity and QCD is lacking yet but, of course, people is actively pursuing it.

A talk that gave me some interesting views was the one by Kenichi Konishi. He pointed out how the confinement can emerge looking at the behavior of the supersymmetric counterpart of Yang-Mills theory. He pointed out the problems with the idea of monopoles, already discussed by Kei-Ichi Kondo at Lecce. And you bet, when one looks at SYM one recover the condensation of a scalar field! Konishi works at University of Pisa where teaches quantum mechanics.

On the line of non-perturbative approaches were the talks by Matteo Giordano and Enrico Meggiolaro. They are trying to re-derive from first principles the Froissart bound. This is a bound on hadronic scattering that can be obtained just using unitarity and dispersion relations. This bound depends crucially on the mass gap of the theory and so, again, we are coping with all the problems given above. Meggiolaro showed that, using lattice computations, the limit can be recovered with the proper constant while Matteo is approaching this problem using AdS/QCD. With Matteo we meet again in Montpellier after four years. We remembered each other immediately and drunk a last beer before leaving on Friday night after the social dinner, with Montpellier streets full of people and pleasant noise.

A talk that I followed with a lot of interest was the one given by Pietro Falgari. He is working on the use of perturbation theory at high-energy in QCD to evaluate the production rate of pairs of top quarks. Even if in this limit perturbation theory can be applied in QCD, they have difficulties mostly related to resum a quite singular series with logarithmic contributions. So, also when perturbation theory applies, QCD does not save us from problems. With Pietro I have spent a lot of time in Montpellier and we left the city together on Saturday with the same flight.

An interesting talk was the one given by Eduardo de Rafael about the determination of the g factor of the muon. This is a truly relevant matter as this measurement can give a clue to new physics. But, as de Rafael pointed out, the critical point is the determination of the hadronic contribution. Presently, there is a 3.6 sigmas discrepancy between the theoretical computed value and the measured one. We cannot be confident that the evaluation of the hadronic part is not correctly accomplished.

Last but not least, the current work of Narison on heavy flavors with sum rules. This approach is now fairly well stable and provides results also better than other non-perturbative techniques. This has been shown in the talk by his collaborator Albuquerque from Sao Paolo. Of course, results like these should be a reference for experiments much in the same way are others as lattice computations. Finally, I would like to cite the talk by Robert Kaminski. He presented the fine work done in collaboration with R. Garcia-Martin J. R. Pelaez, J. Ruiz de Elvira aimed to a precise determination of the properties of f0(600) and f0(980). Their results are striking indeed as they fix very precise values to the mass and width of these resonances, in close agreement with preceding works. It is my personal conviction that a serious theoretical approach should be derive both the mass and the width of these resonances deriving at the same time their structure.

Wednesday was the great day. There was a lot of expectation and the great discovery was in the air predated by a lot of rumors here and there. Our organizers did a great work both providing the webcast from CERN and with a pair of talks on Friday from people of CMS and ATLAS. There has been a religious silence during the talks of Incandela and Gianotti just interrupted by applause at the announcements of the 5 sigmas discovery by the two groups. Following this, we discussed a lot about this matter and, besides it is very standard model-like this particle at the moment, we all were very cautious to claim supersymmetry dead. Rather we would like to know more about the rates in the various channels, results to be known in the near future in order to answer the question put forward by CERN director Rolf-Dieter Heuer: Which one? A girl at my conference asked for other four Higgs and we all know why. Talking with a colleague at ATLAS here in Montpellier, he told me a quite interesting figure for the WW channel but I will not disclose it. Work is in progress yet and data are really too fresh to be discussed. It is a matter of few months and we will know better about the nature of this new particle. Meanwhile, I would like to remember Higgs’ tears after the great announcement and the handshaking with Fabiola Gianotti, after the splendid talk by her, confirming the expectation of almost fifty years of waiting with hopes often not coming up. It is an achievement that very few scientists can claim in their lifetime. The same must apply identically to Englert, Brout, Guralnik, Hagen, and Kibble.

On Friday, the program was concluded by the talks of people from CERN, on behalf of ATLAS and CMS Collaborations. Pushpa Bhat from Fermilab talked on behalf of CMS Experiment while Robert Harrington from Particle Physics Experimental Group of University of Edinburgh talked on behalf of ATLAS Experiment. This was a great conclusion for the Conference, hearing directly from people at CERN, about the great achievement announced on Wednesday.

As a final remark, I would like to thank all people with whom I shared beautiful moments at this conference. Besides people I have already mentioned, I would like to thank Stefano Venditti, Antonio Cassese, Andrey Tayduganov, Federico Mescia, Benjamin Obherof. A great thank goes to Stephan Narison for giving me the chance to give a talk here, for giving me the chance to be chairman for the first time, and for the excellent and really enjoying organization in a beautiful city. See you again!

## A new year full of promises

03/01/2012

We have left 2011 with a lot of exciting results from experiments. Neutrinos appear to move a bit faster than expected and Higgs provided some glimpses at CERN. Of course, this kind of Higgs appears somewhat boring at first being in the range of what Standard Model expected. But it is really too early to say something for sure. We expect definite answer for the next summer with a lot more data analyzed by people at CERN.

With the new year, I would like to point out to my readers a couple of nice papers that are really worthwhile reading. About CUDA and lattice QCD, my Portuguese friends, Pedro Bicudo and Nuno Cardoso,  made a relevant step beyond and made available their code for working for a generic SU(N) gauge group (see here, their code is here). As I have some time I will try their code. The work of these people is excellent and making their code worldwide available is really helpful for all our community.

Finally, Axel Maas put forward a revision of his very good review paper (see here). Axel gave important contributions to the current understanding of Yang-Mills theory and his paper yields a lucid description of these ideas that rely on a large effort on lattice computations and functional methods. Often, I complain about the fact that the community at large seems to not consider these lines of research reliable yet to work with. This is not true as the results they were able to get give since now sound results to work with and the most important of these are that Yang-Mill theory has indeed a mass gap and that this theory appears to display a running coupling reaching zero lowering momenta, a completely unexpected result that goes against common wisdom but this is just what lattice put out.

So, let me wish to you a great 2012 and I hope to share with you the excitement physics research is promising.

Nuno Cardoso, & Pedro Bicudo (2011). Generating SU(Nc) pure gauge lattice QCD configurations on GPUs with
CUDA and OpenMP arXiv arXiv: 1112.4533v1

Axel Maas (2011). Describing gauge bosons at zero and finite temperature arXiv arXiv: 1106.3942v2

## Glimpses of Higgs

13/12/2011

Finally, after some frantic waiting filled with rumors, we heard the truth from people at CERN. And we discovered that rumors were just right. Evidence is mounting for a Higgs particle at around 120-130 GeV, after new data were accounted for. All these evidences point toward a Standard Model Higgs. But some caution words are needed (see Matt Strassler’s post) as a discovery cannot be claimed yet. ATLAS sees a 3.6 sigma overall evidence but, accounting for look elsewhere effect, this go down to 2.5 sigma while CMS has a similar 2.6 sigma going down to 1.9 with look elsewhere effect. This is not enough to rule out a fluctuations but, anyhow, a strong indication where to point researchers attention for the near future. All the matter will be pinned down later next year. From my side, I just note a possible contradiction between the two experiments as ATLAS keeps on claiming an excess around 500-600 GeV, also with increasing number of data and indeed evidence now goes beyond 2 sigma, while, as for today, CMS claims this range ruled out. It is possible that this is another glimpse for a Higgs multiplet as required by supersymmetry. I think that also this matter will be fixed soon next year.

The conference raised a lot of enthusiasm (see here) to some caution (see here) or skepticism (see here).

Fabiola Gianotti, Rolf Heuer and Guido Tonelli

What makes these hints striking is the fact that both experiments see the excess in the same region where the particle was expected and with the proper rates. It should also be said that, with these data and energy, people at CERN have done an excellent work with the analysis of them. But, of course, it is still possible that we are coping with a fluctuation and the particle is hiding elsewhere or is something else. For sure, next year the puzzle will be completed and also this part of the Standard Model will be part of our textbooks in the right way. What we have here is a completely new situation holding the premises for a clear understanding of one of the greatest question of mankind ever. So, when a child will ask to you: “Mom, what are we made of?” this question will have an answer, an answer arising from the work of a lot of smart people running one of the greatest technological achievement of our history: LHC.

## CERN Scientific Policy Committee: Higgs search

02/12/2011

It is now officially published the agenda of the meeting of the Scientific Policy Commitee of CERN (see here) on 12 December. On 13 December it is scheduled a seminar by ATLAS and CMS about Higgs search (see here) by the spokepersons of these experiments: Fabiola Gianotti and Guido Tonelli. As usual, you can follow an ongoing discussion at Philip Gibbs’ blog. Philip promised further combined graphs in real time. Just stay tuned!