On the latest anomaly in LHCb

[...So, Resonaances is back with its trademark pessimism and frustration. But here is a post with a glimmer of hope and a bit more substance...]

LHCb recently reported an anomaly in the angular distribution of  B0 → K*0 (→K+π-) μ+ μ- decays. The discreet charm of flavor physics is that even trying to understand which process is being studied may  give you a serious migraine. So let's first translate to English.  B0 is a pseudoscalar meson made of an anti-b- and a d-quark that is easily found in the junk produced by LHC collisions. K*0, actually K*0(892) because they come in variety of masses,  is a vector meson made of an anti-s and a d-quark which promptly decays to a usual charged kaon and a pion.  B0 → K*0(→K+π-) μ+ μ-, in the following simply referred to as B → K*μμ, is a rare decay  occurring with the branching fraction of order 10^-7. Of course there's also the conjugate process where each particle is replaced with its anti-particle, and the two are dumped together in the LHCb analysis.  Some properties of this decay have been studied before at the B-factories, Tevatron, and LHC, without finding anything unexpected. The new thing about the latest LHCb analysis is that they study the full monty differential distribution with respect to the 4 variables characterizing this four-body decay process: 3 angles θK,θl and φ (see the picture) and the invariant mass q^2 of the di-muon pair.  A parametrization of that differential distribution is

Basically, LHCb measured all these Sn and FL coefficients as a function of q^2.  The largest anomaly is observed at low q^2 in the parameter S5 (also presented as  P5' which is S5 rescaled a function of FL).  LHCb quantifies it is a 3.7 sigma deviation from the Standard Model in the region 4.3≤q^2≤8.68 GeV^2;  this is downgraded to 2.5 sigma if the look-elsewhere effect is taken into account.  Theorists fitting the data quote the deviation between 1 and  4.5 sigma, depending on theoretical assumptions and how the data are sliced and cooked.

The interesting question is whether new physics could be responsible for the anomaly. To go beyond a yes/no answer one has to, unfortunately, go through a bit of technicalities.  At the parton level, the relevant process is the b→sμ+μ- decay.  Theorists computing the  B → K*μμ decay thus start from an effective interaction Lagrangian with  4-fermion and dipole operators involving  the b- and s-quarks. The operators relevant for this process are

where Λref≈35 TeV. This set of operators allows one to describe the B → K*μμ  decays in a completely model independent way, whether within the Standard Model or in some new physics scenario. In the Standard Model a subset of these operators is generated (see the diagrams) with the coefficients C7, C9 and C10 of order 1 (the suppression scale of the effective operators is tens of TeV due to the loop suppression, and also due to the CKM suppression via the small Vbs matrix element; this is why B → K*μμ is so sensitive to new physics). New physics could provide additional contributions to these 3 operators or produce the C' operators that are not generated in the Standard Model at all. For example, the tree-level exchange of a Z' boson coupled to leptons and, in a flavor violating way, to quarks could affect C9 and C9'; the dipole operators C7 and C7' could be generated e.g. by loop diagrams with  a charged Higgs boson, and so on. Now, all of these operators affect the angular distribution of B → K*μμ decays, in particular they can shift the anomalous observable S5/P5'. But one should be careful not to screw up the other observables that remain in a good agreement with the Standard Model. Moreover, the same operators also affect  countless other processes in the B-meson sector, including the well measured branching fractions for  B → Xs γ  and  Bs→μμ decays.  Thus, it is a non-trivial question whether a consistent solution to the anomaly can be found.  The answer is that that, indeed, there do exist regions in the parameter space where the fit to the data is much better than in the Standard Model. According to this paper, the best scenario is the one where new physics generates simultaneously C9 and C9', with the contribution to C9 similar in size but opposite in sign to the Standard Model effective contribution. Other combinations of the operators can also improve the fit,  but the gain is less striking.

 

So, the verdict is... well, at this point the anomaly is not utterly solid yet.  One warning flag is that it shows up in a complicated angular analysis rather than in a clean and simple observable, which gives  more opportunities for theories and experimenters alike to commit a subtle error in the analysis. Moreover, in order to explain the anomaly, new physics contributions to the B → K*μμ amplitude need to be of the same order of magnitude as the Standard Models ones, which requires a certain degree of conspiracy. Most likely, the experimental data and the Standard Model predictions will approach each other when more data is analyzed,  as it has happened countless times in the past.   Nevertheless, we're looking forward to the future updates on B → K*μμ with a little more anticipation than usual. Note that the current LHCb analysis includes only the 7 TeV run data;  the twice as large 8 TeV sample is still waiting to see the light...

[Most pictures stolen from Nicola Serra's talk at EPS] 

A kingdom for a scale

The recent hiatus, so far the longest in the history of Résonaances, was caused by a unique combination of work, travel, frustration, depression, and sloth. Sorry :-|  A day may come when this blog will fall silent forever; but it is not this day ;)
 
After the first run of the LHC particle physics finds itself in an unprecedented situation. During most of  the history of the discipline we had a high energy scale that allowed us to organize our theoretical and experimental efforts. It first appeared back in the 1930s when Fermi wrote down his theory of weak interactions which contained a 4-fermion operator mediating the beta decay of the neutron. For dimensional reasons, 4-fermion operators appear in the Lagrangian divided by an energy scale squared, and in the case of the Fermi operator  this scale is what we now know as the electroweak scale v=174 GeV. This scale come with well defined physical consequences. Scattering amplitudes in the Fermi theory misbehave at energies above v, and some new physics must appear to regulate them. Later several details of this picture were modified. In particular, it was found that the Fermi  4-fermion operator is a low energy effective description of the exchange of a W boson between pairs of fermions. However the argument for new physics near the electroweak scale remained in place, this time to regulate the W and Z bosons scattering amplitudes. That's why even before the LHC kicked off  we could give an almost risk-free promise that it was going to discover something.

Now things have changed dramatically. The LHC has explored the energy range up to about 1 TeV and definitively crossed the electroweak scale. The promised new physics phenomenon was found: a spin-0 boson coupled to mass,  as predicted in the Standard Model. This little addition miraculously cures all the woes of the theory. Ignoring gravity, the Standard Model with the 125 GeV Higgs boson can be extended to arbitrarily high scales. Only the coupling of matter to gravity guarantees some new phenomena, like maybe strong gravitational effects and production of black holes. But that should happen at an immensely high scale of 10^19 GeV that we may never be able to reach in collider experiments. We are not sure if  there is any other physical scale between the electroweak and Planck scale. There's no well defined energy frontier we can head toward. Particle physics no longer has  a firm reference point. An artist's view of the current situation is this:

There's actually one important practical consequence.  Regardless how high energy collider we build next: 30 TeV, 100 TeV, or 1000 TeV,  we cannot be sure it will discover any new phenomena rather than just confirm the old theory in the new energy range. 

This is not to say that the Standard Model must be valid all the way to the Planck scale. On the contrary we have strong hints it is otherwise. The existence of dark matter, the observations of  neutrino oscillations, the matter-antimatter asymmetry in the Universe, and the cosmological inflation, they all require some physics beyond the Standard Model. However none of the above points to a concrete scale where new phenomena must show up. The answers may be just behind the corner  and be revealed by the run-II of the LHC. Or the answer may be due to Planck-scale physics and will never be directly explored; or else it may be due to very light and very weakly coupled degrees of freedom that should be probed by other means than colliders. For example, for dark matter particles we know theoretically motivated models with the mass ranging from sub-eV (axions) to the GUT scale (wimpzillas), and there is no mass  between these two extremes that is clearly favored from the theory point of view.  The case of the neutrino oscillations is a bit different because, as soon as we prove experimentally that neutrinos are Majorana particles, we will confirm  the existence of a set of dimension-5  operators beyond the Standard Model, the so-called Weinberg operators of the form (H L)^2/Λ. Then the scale Λ is the maximum energy scale where new physics (singlet Majorana neutrinos or something more complicated) has to show up. This is however little consolation given the scale emerging from neutrino experiments is Λ∼10^15 GeV, obviously beyond the direct reach of accelerators in a foreseeable future.   

So, while pushing up the energy frontier in accelerators will continue, I think that currently searching high and low for a new scale is the top priority. Indeed, increasing the collision energy has become an expensive and time consuming endeavor; we will achieve an almost factor of 2 increase in 2 years, and, optimistically, we can hope for another factor of 2 at the time scale of ∼25 years. On the other hand, indirect sensitivity to high scales via searches for  higher dimensional operators beyond the standard model can often be improved by orders of magnitude in the near future. The hope is that Fermi's trick will work again and we may discover the new scale indirectly, by means of experiments at much lower energies. There are literally hundreds of dimension-6 operators beyond the standard model that can be searched for in experiments. For example, operators involving the Higgs fields would affect the Higgs couplings measured, and in this case the LHC and later the ILC can probe the operators suppressed by up to ∼10 TeV. Flavor and CP violating processes offer an even more sensitive probe, with the typical sensitivity between 10 and 10^5 TeV. Who knows, maybe the recent anomaly in B→K*μμ decays is not yet another false alarm, but an effect of the flavor violating dimension-6 operators of the form


with Λ of order 30 TeV.  And if not,  there are hundreds other doors to knock on.  Demonstrating the presence of a nearby new physics scale would surely bring back momentum to the particle physics program. At least, we would know where we stand, and how big a collider we must build to be guaranteed new physics.  So yes, a kingdom and on my part I'm adding the hand of a princess too..

Planck about inflation

The CMB spectrum measured by the Planck satellite points to a perfectly boring universe: the vanilla ΛCDM cosmological model, no hint of new light degrees of freedom beyond the standard model, no hint of larger-than-expected neutrino masses, etc.  However at the quantitative level things are a bit more interesting, as Planck has considerably narrowed down the parameter space of inflation. We may not be far from selecting a small class out the huge zoo of inflationary models.

Simplest models of inflation involve a scalar field with a potential. During inflation, the value of the scalar field is such that the potential is large and positive, effectively acting as a cosmological constant that supports a faster-than-light expansion of the universe. The potential should be almost but not exactly flat, so that the scalar field slowly creeps down the potential slope; once it falls into the minimum inflation ends and the modern history begins. Clearly,  that sounds like a spherical cow model rather than a fundamental picture. However, the  single-field slow-roll inflation works surprisingly well at the quantitative level. There is no sign of isocurvature perturbations that would point to a more complicated inflaton sector.  There is no sign of running of the spectral index that would point to departures from the slow-roll conditions.   There is no sign of  non-gaussianities, that would point to large self-interactions of the inflaton field. There is no sign of wiggles in the CMB spectrum that would point to some violent events happening during inflation.  One can say that the slow-roll inflation is like a spherical cow model that correctly predicts not only the milk yield, but also the density, hue, creaminess, and even the timbre of moo the cow makes when it's being milked.  

Let's look into more details of the slow-roll inflation. Assuming the standard kinetic term for the inflaton field φ, the model is completely characterized by the scalar potential V(φ). The important parameters are the first and second derivatives of the potential at the time when the observable density fluctuations are generated.  Up to normalization, these derivatives are the slow-roll parameters ε and η (see the equation box for a precise definition). Both have to be much smaller than 1, otherwise the inflaton field evolves too quickly to support inflation. Several observables measured by Planck depend primarily on ε and η. In particular, the spectral index, which measures the departure of the primordial density fluctuation spectrum from scale invariance, is given by  ns - 1=2η-6ε. Since Planck measured ns=0.9603±0.0073, we know the order of magnitude of the slow-roll parameters: either ε or η or both have to be of order 0.01. 

Another important observable that depends on the slow roll parameters is the tensor-to-scalar ratio r. The system of an inflaton coupled to gravity  has 3 physical degrees of freedom: the scalar mode linked to curvature perturbations, and the tensor mode corresponding to gravitational waves. The scalar mode was detected in a distant past by the COBE satellite and its amplitude As is of order 10^-10. The tensor mode has not been detected so far.  From the box you see that the amplitude At of the tensor mode  is directly sensitive to the value of the inflaton potential, and for the slow-roll inflation it is expected to be somewhat smaller than As.  In fact, the relative amplitude of tensor and scalar fluctuations is a direct measure of the parameter ε: r=At/As = 16ε. Now, the latest limit from Planck is r≲0.11 at 95% confidence level and,  given we expect ε∼0.01 to fit the spectral index, it is already a non-trivial constraint on the shape of the inflaton potential. That's why in the plot of the best-fit area in the ns vs. r plane many inflationary models fall into the excluded region.  Basically, power-law potentials V(φ)∼φ^n that are too steep, n≳2, are excluded. The quadratic potential  V(φ) = m^2 φ^2, perhaps the most popular one,  is on the verge of being excluded.  What survives are power-law potentials with n≲2, or hilltop models where  inflation happens near a maximum of the potential.   The latter is predicted e.g. in the so-called natural inflation where the inflaton is a  Goldstone boson with a periodic cosine potential.  

So, the current situation is interesting but unsettled.  However, the limit r≲0.11 may not be the last word, if the Planck collaboration manages to fix their polarization data. The tensor fluctuations can be better probed via the B-mode of the CMB polarization spectrum, with the sensitivity  of Planck often quoted around r∼0.05. If indeed the parameter ε is not much smaller than 0.01, as hinted by the spectral index, Planck may be able to pinpoint the B-mode and measure  a non-zero tensor-to-scalar ratio. That would be a huge achievement because we would learn the absolute scale of inflation, and get a glimpse into  fundamental physics at 10^16 GeV!.  Observing no signal and setting stronger limits would also be interesting, as it would completely exclude power-law potentials. We'll see in 1 year.

See the original Planck paper for more details.

More mess with dark matter detection

In theory, the algorithm for detecting dark matter is straightforward: 1) wait until a dark matter particle hits a nucleus in your detector hard enough to produce a visible recoil,  2) count the events and collect the Nobel prize, or set a limit on the dark matter scattering cross section on nucleons. The reality is more complex. Typical models of dark matter models predict  the largest signal near the energy threshold of the detector where it is susceptible to all kinds of spooky background and noise.  For this reason, the field of dark matter detection, with multiple contradictory claims and a good deal of bad blood, reminds of medieval England at the time of the Wars of the Roses. The latest claim of a dark matter signal from the CDMS experiment brings a new hope but also adds to the confusion.

For most of the previous decade CDMS was the most sensitive direct detection experiment. Their primary target was germanium, but they also had a number of silicon target detectors. The latter are more advantageous to study light dark matter - with mass of order 10 GeV -  because silicon nuclei are lighter than the germanium ones, and thus are more prone to get a kick from a light dark matter particle. In the analysis of 56 kg*days of data collected in 2006-2007, posted on arXiv just yesterday, no event passes the cuts designed to separate dark-matter-like recoils from background. To everyone's surprise,  CDMS just announced that in the 124 kg*day of data collected in 2007-2008  three events  the cuts, while the expected background is 0.4 event. In the past, several underground experiments (DAMA, CoGeNT, CRESST) have detected an excess of events, but it's the first time an excess of this magnitude appears in a  low-background apparatus. The probability for the background to produce 3 events is 5%, which would amount to a 2 sigma fluctuation.  On the other hand, testing the background hypothesis against the one of light dark matter with the mass of 9 GeV and the cross section of 2*10^-41cm^2 prefers the latter  at the 3 sigma level, apparently because the recoil energies and the ionization yields of the events perfectly fit the dark matter hypothesis. Statistics is not an exact science, so you can take either of these two numbers as an estimate of the significance of the CDMS signal, depending on your priors and your allegiance. The significance is probably smaller than 3 sigma anyway if the latest data are combined with the previous silicon and germanium data,  which show no signal in the low mass range.    

However, the precise significance is not the most important issue here; in the end, we sometimes shrug off 9 sigma signals. To the right, what looks like Pollock's painting is in fact a summary of best-fit signal regions and limits from various underground experiments  in the dark matter mass vs. cross section parameter space. The most worrying aspect of the CDMS result is that the signal region seems comfortably excluded by the limits from Xenon-10 and Xenon-100 experiments (the green lines in the plot). To reconcile these results one must either assume a serious  systematic issue with the xenon analyses, or consider more exotic dark matter models, for example the xenophobic ones where the  effective coupling to xenon nuclei  is suppressed. On the other hand, the region of the parameter space preferred by CDMS is consistent with the earlier detection claim by the germanium target detector CoGeNT. 

So, dark matter, a fluke, or a fundon? Unfortunately, the past experience with direct detection experiments suggests that we will not learn the definitive answer anytime soon.

First results of AMS-02

Today we saw the first physics results from the AMS-02 collaboration. AMS is a particle detector attached to the International Space Station where it collects more than 10 billion cosmic ray events per year. The data released today concern the energy spectrum of cosmic ray positrons. Before discussing the AMS results it's worth taking a historical detour to understand the wider context.

The Universe we see is made of matter, but some small amounts of antimatter are being constantly produced by all sorts of violent processes: the scattering of high energy cosmic rays on the interstellar medium, the creation of  electron-positron pairs in the electromagnetic field of pulsars,  proton-proton collisions at the LHC, etc. Another possible production mechanism is annihilation of dark matter in the center of our galaxy, hence the interest of particle physicists in the subject.  Dark matter may show up as an excess of high-energy positrons over the background predicted from common astrophysical processes. Assuming we understand the background.

Until a few years ago the common lore was that the dominant production of positrons in our galaxy is via the scattering of high energy cosmic protons off particles in the galactic disc. This predicts the positron fraction decreasing with energy. For this reason, when back in summer 2008 PAMELA  reported a sharp rise of the positron fraction between 10 and 100 GeV we thought  for a moment we had a smoking-gun signal of dark matter. Later, the Fermi satellite confirmed the excess and showed that the rise extends at least up to 200 GeV. However, now we don't consider the excess an evidence of dark matter. One reason is that models of dark matter that quantitatively explain the PAMELA and Fermi signal are rather baroque. Firstly, one needs a large annihilation cross section, of order 10^-24 cm^3/sec, 2 orders of magnitude larger than the one required for dark matter to be a thermal relic. Moreover, dark matter needs to annihilate mostly into leptons  and, unlike what happens in typical models, very little into hadrons (as no excess in the cosmic ray antiproton spectrum is observed).  Another reason for skepticism is  that any dark matter model explaining PAMELA and Fermi is in tension with constraints on the gamma ray flux from the galactic center and from the dwarf galaxies. In the meantime, astrophysicists went back to the drawing board and proposed more ordinary sources of high energy positrons. The current lore is that a few nearby pulsars could be responsible for the observed rise of the positron fraction. Thus, after the initial excitement, things have settled down in a limbo: we're sure the  positron excess is real, but we cannot prove that it's a signature of dark matter, and neither we can prove that it isn't.

So, what have we learned today? Qualitatively, not much, quantitatively, a bit. AMS, with its full-fledged multi purpose detector, has better particle identification capabilities compared to the previous missions, which allows them to reduce systematic errors in the positron fraction down to 1% at low energies (compared to 2% in PAMELA) and explore a larger energy range. Currently, their positron measurement extends up to 350 GeV, so almost a factor of 2 beyond the highest data point from Fermi. AMS shows that the rise continues at least up to 250 GeV. The flux of high energy positrons seems to be isotropic, although their current constraints on the dipole component do not yet exclude a local (pulsar) origin of the positron flux. They also see a hint of flattening of the positron fraction above 250 GeV, although at this point this is not significant. If the positron excess originates from annihilation of dark matter particles with the mass of several hundred GeV one should see a drop in the positron spectrum at energies above the dark matter mass, but it is not said pulsars or other astrophysical phenomena could not produce a similar drop. (Note also that  a sharp drop in the positron spectrum will typically be accompanied by a similar feature in the electron+positron spectrum, but according to the measurements by Fermi nothing dramatic is happening up to 1 TeV.)

So, AMS-02 made some bold claims today. Dark matter is mentioned 9 times in the  press release, supersymmetry twice. They say that “...over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter...”. However this is just a lot of smoke without fire. There's absolutely no way that measurements of the  positron spectrum may give us a reliable evidence for dark matter: not now, and not anytime soon. We simply have no robust way of telling a dark matter signal from a boring astrophysics background in that channel, because we don't know the shape nor the normalization of the background.  It doesn't mean that AMS cannot provide a tantalizing signature of dark matter in the future. The most important thing we learned today is that AMS works and exceeds in precision the previous instruments (which wasn't that obvious: it's the first time a serious experiment is performed on a space station, and besides the mission underwent a dramatic downgrade shortly before the launch). We're waiting most eagerly on the AMS measurements of the antiproton  and anti-deuterium spectra. A correlated excess in several channels could give us more confidence in the dark matter origin. Until that happens, the history has taught us to be skeptical about any evidence of dark matter from astrophysics experiments.

You can find the AMS paper here. See also Matt's blog. Reading the mainstream press it seems that Sam Ting with some help from CERN succeeded in fooling the journalists. I'm glad  that CERN already shook off the faster-than-light neutrinos trauma and is ready for another hoopla.... life is going to be  more interesting for bloggers :-) 

April Fools'13: Peter Higgs arrested in Argentina

Higgs with the corpus delicti.

Unbelievable but true.  It happened last Saturday but only now credible reports are beginning to emerge. Peter Higgs, the physicist who first postulated the existence of a boson discovered last year at the LHC,  was arrested in the Buenos Aires airport on a way back from a symposium in his honor at the University of Rosario. Reportedly, a total of 1.25kg of cocaine was found sewn into plush models of elementary particles that Higgs carried in his luggage. Higgs denies any involvement in drug trafficking, maintaining that the plush models were a gift from a young woman attending his lecture in Rosario. The whole story bears some resemblance to the case of Paul Frampton, another theoretical particle physicist arrested in Argentina last year.  
Given the limited information,  one should not jump into conclusions. Higgs might have been a victim of a set-up: it is odd that two British physicists get arrested in Buenos Aires one after another in such similar circumstances. But, maybe, we should pose ourselves the question whether there exists a deeper relationship between the cocaine trade and theoretical particle physics? The recent dramatic events (and some of the particle physics literature too) certainly  make such a relationship plausible.  

I will update on this story as soon as new facts come to life.

Evening update: This article is an April Fools joke, one in a very bad taste as typical for this blog. Consequently, the current head count of  1 theoretical particle physicist in Argentinian jails remains up to date. So far. On the other hand, I think the idea of smuggling cocaine in plush models of elementary particles is absolutely brilliant :-) 

Besides

The greatest hits of the passing month in HEP were the Higgs update from the LHC and the release cosmological results from Planck. But winter conferences is quite generally  the time for experiments to dump new results.  Here's a short summary of the recent important announcements that might have escaped you in the general turmoil.   

•  CP violation in D meson decays from LHCb
  A year ago LHCb surprised everybody with an evidence for CP asymmetry in D meson decays. More precisely, they measured the asymmetry between the D0→π+π- and D0bar→π+π- decay widths,  and also between the D0→K+K- and D0bar→K+K- widths, finally quoting the difference ΔAcp between these two asymmetries so as to reduce systematic errors.  Although the standard model prediction for this observable cannot be reliably calculated with present techniques, more or less informed estimates locate the asymmetry in the 0.01-0.1% ballpark. The previous LHCb result was ΔAcp=(-0.82±0.21)%, which prompted some cautious talk of new physics.  The recent update  LHCb not only takes advantage of the increased statistics (from 0.6 to 1fb-1), but also adds a new category of events where the flavor of the initial-state D-meson is tagged using the muon from the semileptonic B decay that decayed into a D-meson (see the diagram on the right-hand side of the picture, only the prompt category with the pion tagging was used in the previous analysis).  The new LHCb result is a dramatic U-turn. The asymmetry in the prompt category went down to ΔAcp=(-0.34±0.18)%, while the asymmetry in the semileptonic category is measured with the opposite sign: ΔAcp=(0.49±0.33)%. The naive average of the 2 results yields  ΔAcp=(-0.15±0.16)%,   which means that not only the hint of new physics but also the evidence for CP violation in the D-meson sector have been completely wiped out.  For a detailed description of the analysis see here  and here.  
• Dijet bump from CDF.
  In fact, in March we witnessed a real chainsaw massacre of hints of physics beyond the standard model: Neff in Planck, h→γγ in CMS, ΔAcp in LHCb, and finally the 145 GeV dijet bump  at the Tevatron have all gone away.  The last one is actually a pleasant surprise. Recall, that 2 years ago CDF found a dijet bump near 145 GeV in events featuring a W boson and 2 jets with the significance larger than 4 sigma. If confirmed, the bump would mean a new particle at the weak scale: maybe a hadrophilic Z' boson, maybe a technipion, etc. But D0 did not confirm the bump, and there was a danger that the disagreement between the Tevatron experiments would never be resolved. Moreover,  testing this anomaly at the LHC will probably never be possible due to an overwhelming standard model background of  W+jets events. It seemed that we would have to live with this ghost forever. Luckily, CDF went back to the analysis and found a bug. The main culprit seems to be a difference in the detector response to quark and gluon jets, not taken into account in the previous analysis. Also, CDF improved modeling of the  multijets background where one of the jets fakes a lepton from  W boson decay. Once these improvements are included, the 145 GeV bump vanishes completely. One less thing to worry about. More importantly, the fact that CDF now understands well the W+jets spectrum adds some more confidence to Tevatron Higgs searches which rely in part on similar analysis techniques.   
• μ → e γ  from MEG. 
  On the precision front, there was an important update from the MEG experiment which searches μ → e γ decays.  The standard model predicts this decay should be too rare to be observable  (a tiny branching fraction is induced via the neutrino mixing). On the other hand, it is straightforward to produce a large branching fraction in models with new sources of lepton flavor violation, including supersymmetric and composite Higgs models. The latest MEG update sets the limit on the branching fraction at  5.7x10^­‐13 at 90% CL, which represents a factor of 4 improvement of the previous limit. In any case, precision measurements of rare SM processes seem to be the most promising way to go ahead for particle physics. Indeed, our options to increase collider energies are very limited, whereas in many areas precision can be improved by orders of magnitude at a much lower cost. The hope is that one of these days one of these experiments will observe a non-standard process which will give us a clue about physics beyond the standard model. 
•  Stops from the LHC. 
  Searches for supersymmetry no longer provoke a nervous anticipation, rather a weary frustration at the more and more stringent limits. Two important updates using the full 8 TeV dataset came shortly before the Moriond conference. One is from ATLAS searching for direct production of stop pairs, where each stop  decays to a top quark and an invisible neutralino.  The limit on the stop mass is almost 700 GeV, except in the kinematic region where the sum of top and neutralino masses is very close to the stop mass.  Another important update is the CMS search for pair production of gluinos, where each gluino decays via an off-shell stop to 2 top quarks and an invisible neutralino. In this case, the limit on the gluino mass reaches 1.3 TeV. The limits may be somewhat improved in the future by including more channels, but they already give the feeling of the final reach of the 8 TeV LHC. The two searches mentioned above are important for theorists because they probe the presence of stops near the TeV scale, which is the necessary condition for supersymmetry to address the naturalness problem of electroweak symmetry breaking.  Taken together, the SUSY results gradually force us to accept that supersymmetry cannot completely explain naturalness; even if it's just behind the corner it is getting more and more in difficult in most realizations to avoid fine-tuning at the 1-10% level.  See here for more details of the CMS and ATLAS analyses.