Transformation in the particle zoo
Evidence of a long-sought effect in CERN data

Date:
August 18, 2021
Source:
University of Bonn
Summary:
An international study has found evidence of a long-sought effect in
accelerator data. The so-called 'triangle singularity' describes how
particles can change their identities by exchanging quarks, thereby
mimicking a new particle. The mechanism also provides new insights
into a mystery that has long puzzled particle physicists: Protons,
neutrons and many other particles are much heavier than one would
expect. This is due to peculiarities of the strong interaction
that holds the quarks together. The triangle singularity could
help to better understand these properties.



FULL STORY ==========================================================================
An international study led by the University of Bonn has found evidence
of a long-sought effect in accelerator data. The so-called "triangle singularity" describes how particles can change their identities by
exchanging quarks, thereby mimicking a new particle. The mechanism also provides new insights into a mystery that has long puzzled particle
physicists: Protons, neutrons and many other particles are much heavier
than one would expect. This is due to peculiarities of the strong
interaction that holds the quarks together. The triangle singularity
could help to better understand these properties. The publication is
now available in Physical Review Letters.


==========================================================================
In their study, the researchers analyzed data from the COMPASS experiment
at the European Organization for Nuclear Research CERN in Geneva. There, certain particles called pions are brought to extremely high velocities
and shot at hydrogen atoms.

Pions consist of two building blocks, a quark and an anti-quark. These
are held together by the strong interaction, much like two magnets whose
poles attract each other. When magnets are moved away from each other,
the attraction between them decreases successively. With the strong
interaction it is different: It increases in line with the distance,
similar to the tensile force of a stretching rubber band.

However, the impact of the pion on the hydrogen nucleus is so strong
that this rubber band breaks. The "stretching energy" stored in it is
released all at once. "This is converted into matter, which creates
new particles," explains Prof. Dr. Bernhard Ketzer of the Helmholtz
Institute for Radiation and Nuclear Physics at the University of
Bonn. "Experiments like these therefore provide us with important
information about the strong interaction." Unusual signal In 2015,
COMPASS detectors registered an unusual signal after such a crash test. It seemed to indicate that the collision had created an exotic new particle
for a few fractions of a second. "Particles normally consist either of
three quarks -- this includes the protons and neutrons, for example --
or, like the pions, of one quark and one antiquark," says Ketzer. "This
new short-lived intermediate state, however, appeared to consist of
four quarks." Together with his research group and colleagues at the
Technical University of Munich, the physicist has now put the data
through a new analysis. "We were able to show that the signal can also
be explained in a different way, that is, by the aforementioned triangle singularity," he stresses. This mechanism was postulated as early as
the 1950s by the Russian physicist Lev Davidovich Landau, but has not
yet been proven directly.

According to this, the particle collision did not produce a tetraquark
at all, but a completely normal quark-antiquark intermediate. This,
however, disintegrated again straight away, but in an unusual manner:
"The particles involved exchanged quarks and changed their identities in
the process," says Ketzer, who is also a member of the Transdisciplinary Research Area "Building Blocks of Matter and Fundamental Interactions"
(TRA Matter). "The resulting signal then looks exactly like that from a tetraquark with a different mass." This is the first time such a triangle singularity has been detected directly mimicking a new particle in this
mass range. The result is also interesting because it allows new insights
into the nature of the strong interaction.

Only a small fraction of the proton mass can be explained by Higgs
mechanism Protons, neutrons, pions and other particles (called hadrons)
have mass. They get this from the so-called Higgs mechanism, but obviously
not exclusively: A proton has about 20 times more mass than can be
explained by the Higgs mechanism alone. "The much bigger part of the mass
of hadrons is due to the strong interaction," Ketzer explains. "Exactly
how the masses of hadrons come about, however, is not yet clear. Our data
help us to better understand the properties of the strong interaction,
and perhaps the ways in which it contributes to the mass of particles." ========================================================================== Story Source: Materials provided by University_of_Bonn. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. G. D. Alexeev, M. G. Alexeev, A. Amoroso, V. Andrieux,
V.

Anosov, A. Antoshkin, K. Augsten, W. Augustyniak,
C. D. R.

Azevedo, B. Badełek, F. Balestra, M. Ball, J. Barth,
R. Beck, Y.

Bedfer, J. Berenguer Antequera, J. Bernhard, M. Bodlak,
F. Bradamante, A.

Bressan, V. E. Burtsev, W.-C. Chang, C. Chatterjee,
M. Chiosso, A. G. Chumakov, S.-U. Chung, A. Cicuttin,
P. M. M.

Correia, M. L. Crespo, D. D'Ago, S. Dalla Torre, S. S.

Dasgupta, S. Dasgupta, I. Denisenko, O. Yu. Denisov,
S. V.

Donskov, N. Doshita, Ch. Dreisbach, W. Du"nnweber,
R. R. Dusaev, A. Efremov, P. D. Eversheim,
P. Faccioli, M. Faessler, M. Finger, M. Finger, H. Fischer,
C. Franco, J. M. Friedrich, V. Frolov, F.

Gautheron, O. P. Gavrichtchouk, S. Gerassimov, J. Giarra, I.

Gnesi, M. Gorzellik, A. Grasso, A. Gridin, M. Grosse Perdekamp,
B. Grube, A. Guskov, D. von Harrach, R. Heitz, F. Herrmann,
N. Horikawa, N. d'Hose, C.-Y. Hsieh, S. Huber, S. Ishimoto,
A. Ivanov, T. Iwata, M. Jandek, V.

Jary, R. Joosten, P. Jo"rg, E. Kabuss, F. Kaspar, A. Kerbizi,
B. Ketzer, G. V. Khaustov, Yu. A. Khokhlov,
Yu. Kisselev, F. Klein, J. H. Koivuniemi,
V. N. Kolosov, K. Kondo Horikawa, I.

Konorov, V. F. Konstantinov, A. M. Kotzinian,
O. M.

Kouznetsov, A. Koval, Z. Kral, F. Krinner, Y. Kulinich, F. Kunne, K.

Kurek, R. P. Kurjata, A. Kveton, K. Lavickova, S. Levorato,
Y.-S.

Lian, J. Lichtenstadt, P.-J. Lin, R. Longo,
V. E. Lyubovitskij, A.

Maggiora, A. Magnon, N. Makins, N. Makke, G. K. Mallot, A.

Maltsev, S. A. Mamon, B. Marianski, A. Martin, J. Marzec, J.

Matousek, T. Matsuda, G. Mattson, G. V. Meshcheryakov,
M. Meyer, W. Meyer, Yu. V. Mikhailov, M. Mikhasenko,
E. Mitrofanov, N.

Mitrofanov, Y. Miyachi, A. Moretti, A. Nagaytsev, C. Naim,
D. Neyret, J.

Novy', W.-D. Nowak, G. Nukazuka, A. S. Nunes, A. G.

Olshevsky, M. Ostrick, D. Panzieri, B. Parsamyan, S. Paul,
H. Pekeler, J.-C. Peng, M. Pesek, D. V. Peshekhonov,
M. Peskova', N. Pierre, S. Platchkov, J. Pochodzalla,
V. A. Polyakov, J. Pretz, M.

Quaresma, C. Quintans, G. Reicherz, C. Riedl, T. Rudnicki,
D. I.

Ryabchikov, A. Rybnikov, A. Rychter, V. D. Samoylenko,
A. Sandacz, S. Sarkar, I. A. Savin, G. Sbrizzai,
H. Schmieden, A. Selyunin, L.

Sinha, M. Slunecka, J. Smolik, A. Srnka, D. Steffen, M. Stolarski,
O.

Subrt, M. Sulc, H. Suzuki, P. Sznajder, S. Tessaro, F. Tessarotto,
A.

Thiel, J. Tomsa, F. Tosello, A. Townsend, V. Tskhay, S. Uhl,
B. I.

Vasilishin, A. Vauth, B. M. Veit, J. Veloso, B. Ventura,
A. Vidon, M. Virius, M. Wagner, S. Wallner, K. Zaremba,
P. Zavada, M. Zavertyaev, M. Zemko, E. Zemlyanichkina,
Y. Zhao, M. Ziembicki. Triangle Singularity as the Origin
of the a1(1420). Physical Review Letters, 2021; 127 (8) DOI:
10.1103/PhysRevLett.127.082501 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210818135226.htm

--- up 14 weeks, 5 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)