Saturday 30 May 2015

Weekend Plot: Higgs mass and SUSY

This weekend's plot shows the region in the stop mass and mixing space of the MSSM that reproduces the measured Higgs boson mass of 125 GeV:



Unlike in the Standard Model, in the minimal supersymmetric extension of the Standard Model (MSSM) the Higgs boson mass is not a free parameter; it can be calculated given all masses and couplings of the supersymmetric particles. At the lowest order, it is equal to the Z bosons mass 91 GeV (for large enough tanβ). To reconcile the predicted and the observed Higgs mass, one needs to invoke large loop corrections due to supersymmetry breaking. These are dominated by the contribution of the top quark and its 2 scalar partners (stops) which couple most strongly of all particles to the Higgs. As can be seen in the plot above, the stop mass preferred by the Higgs mass measurement is around 10 TeV. With a little bit of conspiracy, if the mixing between the two stops  is just right, this can be lowered to about 2 TeV. In any case, this means that, as long as the MSSM is the correct theory, there is little chance to discover the stops at the LHC.

This conclusion may be surprising because previous calculations were painting a more optimistic picture. The results above are derived with the new SUSYHD code, which utilizes effective field theory techniques to compute the Higgs mass in the presence of  heavy supersymmetric particles. Other frequently used codes, such as FeynHiggs or Suspect, obtain a significantly larger Higgs mass for the same supersymmetric spectrum, especially near the maximal mixing point. The difference can be clearly seen in the plot to the right (called the boobs plot by some experts). Although there is a  debate about the size of the error as estimated by SUSYHD, other effective theory calculations report the same central values.

38 comments:

Anonymous said...

What do you mean when you write that one cannot calculate the Higgs mass in the SM? If you specify the (renormalized) parameters, you can calculate it. In that regard, the situation in the SM is no different to that in the MSSM.

Anonymous said...

An analogous plot is in fig. 7 here: http://arxiv.org/pdf/1504.08331v1.pdf

The point seems to be that higher order SM corrections to the relation between M_top and y_top were not included in codes that computed loops treating SUSY particles on the same foot as SM particles

Anonymous said...

Its means that the Higgs mass in the Standard model is a function of unknown parameter, i.e the quartic coupling in the Scalar potential lambda. While in the MSSM, the Higgs mass depends upon the Z-boson mass and tan\beta. While this tree level formula does not provide the observed 125 GeV, large radiative corrections could arise as a consequence of the incomplete cancellations between the top and stop loops.
Best,
A.

Jester said...

Thx. To add to that, at the Lagrangian level this means that the quartic Higgs self-coupling is a free parameter in the SM, while it is fixed in terms the SM gauge couplings in the MSSM.

Anonymous said...

I have two comments: 1) I think the error estimate of SuperHD does not include the uncertainty in m_top. 2) in particular for the light susy case, there is no proper error estimate in SupetHD. 3) what is shown, is the average of the stop masses. Thus for 2TeV and maximal mixing, one stop can still be rather light. However, charge and colour breaking minima can be dangerous in that case, see e.g.1405.7376.

Anonymous said...

Sorry, it became three comments...

Anonymous said...

Continuing about calculability - I don't find that satisfactory. The SM and MSSM Higgs masses are both functions of unknown parameters (lambda in the SM and soft-breaking masses and \mu etc in the MSSM) - they are both just as calculable (once you specify or measure all the relevant parameters).

Anonymous said...

Anon--regarding calculability. The scalar self-coupling of the light Higgs in the MSSM is determined by gauge couplings and, unlike the SM, is thus known. You are right that the MSSM Higgs mass depends on soft-breaking masses and \mu, but it is very weakly dependent on them. The only strong dependence turns out to be the stop masses and the mixing parameter (which themselves depend on the soft-breaking masses and mu), and thus the plots are given.

Jester said...

Anon up there: 1) the dashed line in the plot is the 2sigma uncertainty due to the top mass. See also Fig. 1 in 1504.05200: above 2 TeV top mass error dominates, whereas below 2 TeV the theory error dominates. 2) Yes, by construction the EFT approach does not work for light susy. The error quickly becomes very large for susy masses below ~1 TeV.

Filippo said...

Thanks for advertising this!

Anonymous said...

I don't think 'boobs plots' is at all funny, and will make female physicists feel uncomfortable. I know you are in France, but the rest of the world is not French.

Anonymous said...

I understand that this is a blog and you try to be funny but you should refrain from foolish names like 'boobs plots'. Unless you are interesting in losing the female part of readers...

Anonymous said...

>> refrain from foolish names like 'boobs plots'. Unless you are interesting in losing the female part of readers...

I think this is a very sexist statement and here is why:
If some plot would be called 'dick plot' it would certainly not scare away the male readers.
So you are suggesting that females are much more sensitive and thus different from males.
This is obviously sexist.

Anonymous said...

"If some plot would be called 'dick plot' it would certainly not scare away the male readers.
So you are suggesting that females are much more sensitive and thus different from males.
This is obviously sexist."

Calling a plot feature by a body part, male or female, is simply offensive and immature, at the emotional level of an 11-year-old, not that of a professional scientist. It's not funny either.

Jester said...

I fully agree it's not right and I apologize. In the future I will be careful to include in my posts a balanced number of references to male and female organs.

Anonymous said...

"I know you are in France, but the rest of the world is not French." Well, I'm in Finland, and can just now report that surprisingly also here nobody gives a thought about the boobs plot.

Anonymous said...

To bring some balance, here comes the famous dick plot: http://susy2013.ictp.it/lecturenotes/02_Tuesday/SUSY_Phenomenology/Iwamoto.pdf

Anonymous said...

And BTW, the first comment about the boob plot was deeply stereotypical and offensive to French people.

StevieB said...

I'm looking forward to the gender and nationality neutral Uranus plot...

Anonymous said...

That's an optimistic vision of the plot. If you flip it, you'd get something that Landau called "Lifshitz' ass" ("жопа Лифшица" ),
http://ic.pics.livejournal.com/plazmodij/16914310/3846/3846_320.gif
Your previous gem was less ambiguous (luckily), http://resonaances.blogspot.fi/2014/03/weekend-plot-rorschach-test.html

Anonymous said...

Even if the name you're referring to in brackets is a name which is used in "experts' circles", I'm finding this a bit offensive.
It's stuff like this that contributes to keeping the number of women in physics low - but maybe not everyone thinks it should be higher than it is?!

Other than that: I usually like your blog, it's very informative!

Sven said...

Hi,
for the physics of the comparison plot: the fact that a diagrammatic calculation using largely on-shell renormalization (as in FeynHiggs) gives higher Mh values than a DRbar (or even EFT) calculation is well known. On the other hand, SusyHD gives particularly low values, and the error estimate they give is highly debatable, if not to say completely overly "optimistic".
Furthermore, the "pure EFT approach" as in SusyHD works potentially well, when no SUSY particles are observable at the LHC Run II (or even at the HL-LHC) and *everything* is above at least 2 TeV, in my opinion a rather boring scenario (which also does not help with (g-2)_mu and is not very favorable for DM either, to name a few).

As for the naming debate, I consider myself as an expert in this field (having produced many versions of that plot myself), but I have never heard the name "boobs plot". Very strange...

Anonymous said...

I saw so many comments talking about boobs and dick plots and you forget to talk about the physics of the plots.
A.

Jester said...

OK, I changed to "some experts", and we all agree that those who call it this way are childish and immature. Now, no more boobs and weenies, please - the physics here is far more interesting.

RBS said...

So the fleeting beauty Susy is again just around the corner? Or can we find any other ways to nail her down? :)

Anonymous said...

Sorry RBS, but your comment is too sexist. Why should Susy be considered female? I'm sure there are some male readers that would disagree. Also, there is this thing called male beauty as well, which the sexist female proponents are systematically oppressing everywhere.

And don't get me even started on "nail her down" versus "nail him down"... ;)

RBS said...

Indeed we can try to nail SUS(y) down in any of her~his ubiquitous bosonic or fermionic forms. But why do I have this nagging feeling that s~he'll always be found just behind the very next energy threshold? 8-)

Anonymous said...

In semi-quantitative terms, how "unnatural" is a 10 TeV stop?

Jester said...

It corresponds to a 1 in 10000 fine-tuning. Whether this is acceptable or not depends on a personal taste.

Anonymous said...

Mmm. Well we've blown two orders of magnitude past the "1 in 100" figure bandied about shortly after the Higgs discovery, and clearly there's nowhere for the denominator to go but up. My gag reflex was triggered before the LHC turned on, so "taste" along with "beauty" seem to me to have gone the way of empiricism on forefront of HEP theory. I wonder if there's a version of me in some pocket universe who isn't saddened.

LMMI

Ervin Goldfain said...

Jester,

No word on tantalizing hints for heavy gauge bosons at sqrt(s)= 8 TeV from the ATLAS collaboration? As Lubos points out, it may be indeed a "faint" signal for BSM physics, now that CMS has reported similar findings awhile ago.

Can these results also fall in line with the B-meson anomaly?

Cheers,

Ervin

Jester said...

Patience :)

Anonymous said...

Dear Jester, I much appreciate your blog and also the funny sarcastic/goliardic comments as "boobs plot". Maybe it is not a coincidence you choose Jester as your nickname. People who criticize you should consider how much boring are the other blogs and how much time consuming is the daily inspection of the arXiv (if they want a clue beyond the very narrow field of everyone interest).

Anonymous said...

This clearly shows a SUSY discovery will need a 15 TeV collider.

RBS said...

While we're waiting: are there any further possibilites / prospects of upgrading LHC to still higher energies, beyond current plan? Guess it should stay around for a couple of decades given the cost.

Anonymous said...

There is the idea of a high-energy LHC (HE-LHC), up to ~30 TeV collision energy in the same ring, which needs twice the strength of all dipole magnets. Currently the high-luminosity LHC (HL-LHC, same energy but higher collision rate) gets more support, and its timescale would be shorter.
There is also a proposal for a ~100 TeV ring, but funding for such a megaproject is completely unclear.

Plasma wakefield acceleration might change the game in ~20 years. Up to 100 GeV/meter would allow a >10 TeV linear electron/positron collider.

Anonymous said...

I am in general a lurker on this very good blog. There was a term when I was growing up I think quite appropriate to those who take such offense to the b**b plot: Lighten up Francis!

RBS said...

Since mid 19-ies when the elementary zoo started to expand HEP physicists were on the unification mission that was quite successful till now - in the strong, electroweak and finally SM/Higgs advances. Looking forward from here and only on placing a bet level: should any BSM sings be found in this run, would they be in the line of further unification, perhaps shedding some light on future GUT models; or some completely new and unexpected additions to the zoo?