IFJ PAN: increasingly smaller chances for "new physics"

Traces "new physics", beyond the Standard Model, they could hide in the processes associated with the decays of baryons. However, an analysis by IFJ PAN scientists has shown that some of the rarest baryon decays show no anomalous.

Baryons are conglomerates of three quarksow, ktore can decay into smaller particles. Typically, such processes proceed in pairs, or resonantly. Sometimes, however, it happens that a baryon decays into several daughter particles not in a cascade of events, but at once, in one fell swoop – or, as physicists call it: non-resonantly. As explained by the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Krakow, developed since poł century Standard Model – the most perfect tool for cooThe modern physics tools used to describe the phenomena occurring in theod elementary particles – predicts that non-resonant baryon decaysow are extremely rare. Depending on the type of baryon, they should appear once in billions of casesoin or at an even lower frequency.

– If the frequency of some decaysoin non-resonant was different from that predicted by the Standard Model, could indicate the existence of hitherto unknown processesoin and particles, and therefore o "new physics". That’s why non-resonant decays have been attracting our attention for a long time,” explains Prof. H. K., quoted in the release. Mariusz Witek of IFJ PAN.

Prof. Witek headed a five-person group of Krakow physicistsow, dealing with the search for non-resonant decaysoin a baryonoin the alluring Lambda c in data collected in 2011 and 2012 at the international LHCb experiment at the Large Hadron Collideroin Geneva. The results of this analysis were published in the journal "Physical Review".

Why the attention of the Krakow researchers was attracted to Lambda c baryons – that is, particles built from quarksoin the lower d, gorny u and alluring c? As IFJ PAN explains in the announcement, the most massive t-quark decays so quickly that in ogole does not combine with other quarks – and therefore does not form a baryonoin whichowhose decays could be recorded. Baryon decaysow with the second-mass beauty quark b was analyzed earlier, m.in. because the signals indicative of their occurrence were somewhat easier to pick up. The Krakow group contributed here swoj contribution, contributing to the detection of an interesting deviation from theoretical predictions.

In the baryon groupoin containing heavy quarks unexplored alluring baryons still remained.

– The Standard Model predicts that non-resonant baryon decaysoin Lambda c, ktowhich result in three particles: a proton and two muons, should occur about once every hundreds of billions ofoin the decay ofow. This is a much rarer phenomenon than baryon decaysow with the beauty quark b, ktors we have dealt with before,” emphasizes Dr. hab. Marcin Chrząszcz (IFJ PAN).

– Measurements and analysis are now much more difficult, having to look at the many times larger group of events recorded in the LHCb experiment. It’s worth doing, however, because the reward is to come across a trail of much more subtle processesow. If any discrepancy with predictions could be observed here, it would most likely be a harbinger of a "new physics" – physicist adds.

In the case of such rare phenomena, theosignalow evidence of non-resonant baryon decaysoin Lambda c from background noise proved to be an arduous and time-consuming task. Nonetheless, the Krakow physicists managed to improve the g a hundredfoldorna limit on the incidence of decayoin non-resonant. It has been estimated at less than one case in hundreds of millions ofow.

– Consideration of further data, including from the second cycle of the LHC gas pedal, should already screw up theotce improve our result by a factor of 10. So we would already be very close to the predictions of the Standard Model. If in baryon decaysoLambda c manifests any "new physics", this will be the last call for it to reveal a. So far, not the slightest trace of it is visible,” concludes Prof. Witek.

During the analysis, the Krakow researchers observed roalso resonant decays, in which theohe Lambda c baryon decayed into a proton and an omega meson. As they admit, some surprise was the lack of signaloin evidence of yet another resonant decay path: for proton and meson rho. However, the result turned out to be consistent with theoretical predictions.

Sourceosource: PAP – Science in Poland, fot. IFJ PAN, CERN, The LHCb Collaboration. On the gothat the signal of a non-resonant decay into a proton and two muons, below the signal for resonant decay involving the omega meson.