Friday, 31 October 2008

On CDF Anomaly

Mhm, it seems that I chose the wrong side of the Atlantic. First, the LHC produces a big firework display instead of small black holes, and then the CDF collaboration at the Tevatron discovers new physics. About the CDF anomaly in multi-muon events, see Tommaso's post or the original paper. Together with a few CERN fellows we had an impromptu journal club today, and we have reached the conclusion that, well, we don't know :-). The anomaly occurs in a theoretically difficult region, the B-baryon spectrum is poorly known, the local Monte Carlo magicians are very sceptical about modeling the b-quarks, etc, etc. It does not mean, of course, that one should shrug it off. Whether we want it or not, the CDF anomaly will dominate particle model-building for the next few months.

Meanwhile, there is already one model on the market that, incidentally:-), looks relevant for the anomaly: SuperUnified Theory of Dark Matter. One can immediately cook up $e^N$ variations of that model, but there seem to be 3 basic building blocks:
1) The "visible" sector that consists of the usual MSSM with the supersymmetry breaking scale $M_{MSSM} \sim$ few hundred GeV.
2) The dark sector with a smaller supersymmetry breaking scale $M_{dark} \sim $ GeV. It includes a dark gauge group with dark gauge bosons and dark gauginos, a dark Higgs that breaks the dark gauge group and gives the dark mass to the dark gauge bosons of order 1 dark GeV. In fact it's all dark.
3) The dark matter particle that is charged under the dark group and has a large mass, $M_{DM} \sim $ TeV. Unlike in a typical MSSM-like scenario, dark matter is not the lightest supersymmetric particle, but rather some new vector-like fermion whose mass is generated in the similar fashion as the MSSM mu-term.

The dark group talks to the MSSM thanks to a kinetic mixing of the dark gauge bosons with the Standard Model photon, that is via lagrangian terms of the type $f_{\mu\nu} F_{\mu \nu}$. Such mixing terms are easily written down when the dark group is U(1), although for non-abelian gauge groups there is a way to achieve that too (via higher-dimensional operators). Once the dark gauge boson mixes with the photon, it effectively couples to the electromagnetic current in the visible sector. Thanks to this mixing, the dark gauge boson can decay into the Standard Model particles.

The SuperUnified model is tailored to fit the cosmic-ray positron excess PÀMELA and ATIC/PPB-BETS. The dark matter particle with a TeV scale mass is needed to explain the positron signal above 10 GeV (as seen by PAMELA) all the way up to 800 GeV (as suggested by ATIC/PPB-BETS), see here. The dark gauge bosons with a GeV mass scale play a two-fold role. Firstly, they provide for a long range force that leads to the Sommerfeld enhancement of the dark matter annihilation rate today. Secondly, the 1 GeV mass scale ensures that the dark matter particle does not annihilate into protons/antiprotons or heavy flavors, but dominantly into electrons, muons, pions and kaons. The second point is crucial to explain why PAMELA does not see any excess in the cosmic-ray antiprotons. Supersymmetry does not play an important role in the dynamics of dark matter, but it ensures "naturalness" of the 1 GeV scale in the dark sector, as well as of the electroweak scale in the visible sector. I guess that analogous non-supersymmetric constructions based, for example, on global symmetries and axions will soon appear on ArXiv.

What connects of this model to the CDF anomaly is the prediction of "lepton jets". In the first step, much as in the MSSM, the hadron collider produces squarks and gluinos that cascade down to the lightest MSSM neutralino. The latter mixes into the dark gauginos, by the same token as the dark gauge boson mixes with the visible photon. The dark gaugino decays to the dark LSP and a dark gauge boson. Finally, the dark gauge boson mixes back into the visible sector and decays into two leptons. At the end of this chain we obtain two leptons with the invariant mass of order 1 GeV and a small angular separation, the latter being due the Lorentz boost factor $\gamma \sim M_{MSSM}/M_{dark} \sim 100$.

The perfect timing of the "lepton jets" prediction is unlikely to be accidental. A new spying affair is most welcome, now that the paparazzi affair seems to by dying out. While waiting for CDF to find the traitor and hang him on the top pole, I keep wondering if the SuperUnified model does indeed explain the CDF excess. If you take a look at the invariant mass distribution of the anomalous muon-pair events (right panel) it does not resemble a 2-body decay of a narrow-width particle (for comparison, admire the J/Psi peak in the left panel), which it should if the muons come from a decay of the dark gauge boson. Or am I missing something? Furthermore, it has been experimentally proved that bosons are discovered in Europe, while only fermions can be discovered in the US. This is obviously inconsistent with the Tevatron finding the dark gauge boson ;-)

Thanks to Bob, Jure and Tomas for the input.
See also Lubos' post on the SuperUnified model.
For more details and explanations on the CDF anomaly, see the posts of Peter and Tommaso and John.

16 comments:

Matti Pitkanen said...

TGD has predicted the existence of colored excitations of leptons explaining CDF anomaly already for fifteen years ago.

One of the basic predictions of TGD indeed is that leptons should have colored excitations. Already at seventies a lot of evidence for colored electrons, or rather their pion like bound states, came from anomalous production of electron positron pairs in heavy ion collisions.
For some mysterious reason it was put under the carpet. I have tried to tell about this in blogs-also here-but in vain.


For year ago evidence for muo-pions came. Again it was forgotten although Lubos made some nasty comments on the finding.

X.-G. He, J. Tandean, G. Valencia (2007),
Has HyperCP Observed a Light Higgs Boson?,Phys. Rev. D74.
http://arxiv.org/abs/hep-ph/0610274.

X.-G. He, J. Tandean, G. Valencia (2007),
Light Higgs Production in Hyperon Decay, Phys. Rev. Lett. 98.
http://arxiv.org/abs/hep-ph/0610362.


CDF gives evidence for tau-pion. The lifetime predicted for charged tau-pion obtained by scaling the prediction for pion life-time is correct if one scales down the parameter x in the parameter f(pi)= xm(pi) characterizing pion coupling to axial current by factor .41. To my opinion the case is now closed since the probability that a prediction bringing in nothing new but known masses and weak decay parameters is correct is extremely low. I really hope that people working in the field would be finally mature to take this seriously. If TGD explanation of the anomalous e+e- production would have been taken seriously (for more one and half decades ago), particle physics would look quite different now.

The positron and electron positron cosmic ray anomalies can in turn be seen as evidence for M_89 copy of hadron physics.

See my blog and the chapter Recent Status of Leptohadron Hypothesis of "p-Adic Length Scale Hypothesis and Dark Matter Hierarchy".

Matti Pitkanen said...

Still a comment about leptohadron hypothesis. The surprising finding of PAMELA is that positron fraction (the ratio of flux of positrons to the sum of electron and positron fluxes) increases above 10 GeV. If positrons emerge from secondary production during the propagation of cosmic ray-nuclei, this ratio should decrease if only standard physics is be involved with the collisions. This is taken as evidence for the production of electron-positron pairs, possibly in the decays of dark matter particles.


Leptohadron hypothesis predicts that in high energy collisions of charged nuclei with charged particles of matter it is possible to produce also charged electro-pions, which decay to electrons or positrons depending on their charge and produce the electronic counterparts of the jets discovered in CDF. This proposal - and more generally leptohadron hypothesis - could be tested by trying to find whether also electronic jets can be found in proton-proton collisions. They should be present at considerably lower energies than muon jets.

The simple-minded guess is that for proton-proton collisions the center of mass energy at which the jet formation begins to make itself visible is in constant ratio to the mass of charged lepton. From CDF data this ratio is around sqrt(s)/m(τ) about 10^3. For electropions the threshold energy would be around .5 GeV and for muo-pions around 100 GeV. In fact, I found that I have told in Recent Status of Leptohadron Hypothesis years ago about production of anomalous electron-positron pairs in hadronic reactions [1,2,3,4] as evidence for lepto-hadron hypothesis.

[1] T. Akesson et al (1987), Phys. Lett. B192,
463, T. Akesson et al (1987), Phys. Rev. D36,
2615.


[2] A.T. Goshaw et al (1979), Phys. Rev. Lett. 43,
1065.


[3] P.V. Chliapnikov et al (1984), Phys. Lett. B
141, 276.


[4]S. Barshay (1992) , Mod. Phys. Lett. A, Vol 7, No
20, p. 1843.

Jester said...

That's impressive Matti, everything connects to everything else. Is there anything that you could NOT explain, once it had happened? I would love to smoke the weed that you grow :-]

Ervin said...

Can anyone explain why the CDF anomaly has to be linked to the poorly understood physics of Dark Matter? Are there any hints that strongly support this connection?

With anticipated thanks,

Ervin

Daniel de França MTd2 said...

Jester,

Probably the same kind of string weed. Although his is cultivated at home, not at huge theorical crops.

Jester said...

Ervin, the link is very weak indeed. Assuming thermal origin for dark matter, in order to explain the PAMELA excess one typically has to boost the annihilation rate today. A 1 GeV force carrier could do that, thanks to the Sommerfeld enhancement (though this is just one posssibility, out of many). And CDF sees something weird happening around 1 GeV....

Anonymous said...

Both the Woit and Dorigo links go to Woit's blog.

Coin said...

Hi,

I am confused by the close proximity of these PAMELA and CDF announcements. Both seem to be discussing something along the lines of an unexplained excess of energy or particles, and both are being linked to dark matter models; this "superunified theory of dark matter" is being put forward as appropriate to both situations.

What, if anything, is the connection between the CDF and PAMELA findings? Is it possible that, or is there reason to actively believe that, CDF's muon excess and PAMELA's positron excess have a common cause?

And leaving physics aside for a moment and considering sociology, is it possible that the reason why CDF chose to announce their excess now rather than at some other date was linked to the long-awaited PAMELA announcement?

Jester said...

Coin, from the experimental point of view there is only one connection between PAMELA and CDF: both see an excess in a leptonic final state. Otherwise, the two signal are completely different, in particular, the energy scale is different. It is very likely that two anomalies are not linked in a simple manner, but models that explain both appear more sexy to theorists. As I was trying to explain in the post, in the model of Nima and Neal one auxiliary element to explain PAMELA has the right energy scale (but perhaps not the right characteristics) to explain CDF.

Matti Pitkanen said...

Dear Jester,

this "explains everything argument" is excellent: cheap and extremely user-friendly. People knowing absolutely nothing about my work have been continually using this wonderful argument during these years and the trick works, at least in selected company.

If you want to discuss the hypothesis seriously, it might be a good idea to study the model in detail.


I do not of course explain everything: I just put these anomalies in bigger picture and consider just the basic qualitative features. Remember that I have worked with TGD for 31 years and with leptohadron hypothesis for one and half decades: it gives certain kind of bird's eye of view.


One might understand PAMELA in terms of leptohadron hypothesis. For instance, the collisions of cosmic nuclei with matter generate strong non-orthogonal E and B fields inducing the generation of leptopions decaying into leptobaryons and producing the jets giving rise to electrons and positrons.

I also discuss at my blog the possibility that this process requires a phase transition increasing Planck constant. If so -as the argument suggests- then leptopions would represent one instance of dark matter.

Matti Pitkanen

Jester said...

Matti, it was cheap indeed, but I wanted to be clear what I think about it. These days there many random people (journalists, bank analysts, Goa hippies) visiting this page, and they might get a false impression. Of course, noone serious is going to study your work. The comments you drop here and there reveal that what you're trying promote is just a collection of words that sound technical but make no sense.

If you want to prove that I'm wrong, try to PREDICT some experimental result. For example, the analogous CDF results in the electron final state. Or predict in what other distributions they should they see an excess. Or the SHAPE of the gamma-ray spectrum measured by glast(now fermi).

This is how science works, and there are good reasons why it should be this way. If you correctly predict future experimental result, me and everyone else will crawl at your feet asking for forgiveness. And in the meantime, pls don't spam my comment section.

Jester said...

I wasn't clear enough, Matti. Express yourself on your blog, or in a physics journal, but not here.

De Bunker said...

Coin, when you're looking for ducks, but you've never seen a duck before, you'll ask if everything new you find could be a duck. So, every new unexplained data will be proposed to have something to do with either dark matter or the higgs boson. Sometimes though, the link is tenuous. In fact most experimental excesses are not discoveries of new physics, and eventually go away in the face of more/better data. They've definitely discovered something though. It's possible it's a problem in their track fitting algorithms or detector itself, or more likely some combination of undiscovered b- and c- hadrons. Dark matter or higgs having anything to do with this is a much less likely hypothesis.

Matti Pitkanen said...

A comment about masses of the new particles. The prediction for neutral leptopion mass is 3.6 GeV and same as proposed in the paper of CDF collaboration, which had appeared to the arXiv this morning as I learned from the blog of Tommaso.

The masses suggested in the article for a particle decaying sequentially to the lowest state were 3.6 GeV, 7.3 GeV, and 15 GeV.

p-Adic length scale hypothesis predicts that allowed mass scales come as powers of sqrt(2) and these masses come in good approximation as powers of 2. Several p-adic scales appear in low energy hadron physics for quarks and this replaces Gell-Mann formula for low-lying hadron masses.

Therefore one can ask whether these masses correspond to neutral tau-pion with p= M_k=2^k-1, k=107) and its scaled up variants with p=about 2^k, k= 105, and k=103 (also prime). The prediction for masses would be 3.6 GeV, 7.2 GeV, 14.4 GeV.


Matti Pitkänen

Matti Pitkanen said...

I compared the CDF model with TGD based model of CDF anomaly. In particular, the possibility whether the masses of the proposed three particles coming as powers of 2 could correspond to masses of p-adically scaled variants of tau-pion decaying strongly to the lowest lying states. Strong decays would be of type pi^0 at shorter scale decaying to pi^0+pi^+ + pi^- at longer scale.


This is possible but the model differs several respects from the CDF model. For a detailed model of the strong decay cascade for scaled leptopions see my blog.

Matti Pitkanen said...

Dear Jester,

a comment about the opening angle of the cone with respect to the direction of the first muon.


There were three models to for the production of lepton jets be considered.

a) Virtual pi^(107) decaying to leptohadrons.

b) The formation of coherent state of k=107 pions heated to QCD like plasma state and producing lepton jets as analogs of quark jets.

c) p-Adically scaled on mass shell pi(103) with mass about 8*m(tau) decaying to 3 k=105 pions with masses about 4*m(tau) and 2*m(tau) and pi^0(105) decaying to k=107 pions with masses about 2*m(tau) and m(tau).

The two charged pions decay weakly to tau-nu and mu-nu pairs for k=105 and mu-nu pairs for k=107 cases.

This is the option fixed by the consistency with CDF model and should produce lepton jets as a consequence of the peculiar reaction kinematics forcing the reaction products to be almost at rest. I found that this is indeed the case.

The strong decay for p-adically scaled up neural tau-pion pi(103) with mass equal to 8 m(tau) to pi^0(105)+pi^+(105)+ pi^-(105) followed by similar decay of pi^0(105) to k=103 tau-pions predicts that secondary muons resulting from the decay of second charged pi(105) have opening angle 45 degrees and those resulting from decays of charge pi(107) have opening angle 28.7 degrees. Measured opening angle was 36.8 degrees.

It is essential that the masses of colored neutrinos are small, most naturally same as that of ordinary ones, and that the masses of pi^0(103) and pi^(105) are slightly above the threshold allowing the decay to 3 pions occur with 3 resulting pions almost at rest (otherwise the second charged pion must be virtual and decay electroweakly and on mass shell condition is lost and decay is much more slower).

The model is consistent with all what I know at this moment at both qualitative and quantitative level (assuming that CDF model with masses coming as powers of 2 catches the quantitative aspects). CDF anomaly gives new support for two basic notions of TGD: p-adic length scale hypothesis (actually not hypothesis anymore) and the notion that color is not spinlike quantum number but corresponds to CP_2 partial waves so that both leptons and quarks have colored excitations and QCD like dynamics should appear in variety of p-adic length scales.


I have not yet estimated the total rate for the production of pi^0(103): this requires the use of the formulas developed for electropion production cross section. This obviously gives the final killer test for the model.

For more detailed explanation see my blog
my blog.

Matti