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SUMMARY:Fragmentation of isospin-symmetric $^{20}$Ne at the LHC: a challen
 ge and an opportunity
DTSTART;VALUE=DATE-TIME:20261029T133500Z
DTEND;VALUE=DATE-TIME:20261029T135000Z
DTSTAMP;VALUE=DATE-TIME:20261018T174714Z
UID:indico-contribution-6302@cern.ch
DESCRIPTION:Speakers: Igor Pshenichnov (INR RAS\, MIPT(NRU))\nIn 2025\, da
 ta on $^{16}$O–$^{16}$O and $^{20}$Ne–$^{20}$Ne collisions were collec
 ted at the LHC for the first time. Unlike in the LHC runs with $^{208}$Pb 
 beams conducted since 2010\, a significant fraction of spectator fragments
  emitted in collisions of light isospin-symmetric nuclei\, such as $^{16}$
 O and $^{20}$Ne\, also have equal numbers of neutrons and protons. Consequ
 ently\, these fragments exhibit magnetic rigidity similar to that of beam 
 nuclei. As the transverse momenta of spectator fragments are expected to b
 e close to the nominal beam momentum\, such $2Z=A$ secondary nuclei may ci
 rculate in the LHC. This poses a challenge for tuning the collider beam op
 tics to suppress the circulation of $2Z=A$ fragments\, in order to prevent
  their collisions with beam nuclei and reduce contamination of the $^{16}$
 O–$^{16}$O and $^{20}$Ne–$^{20}$Ne data due to beam transmutation [1].
 \n\nThe cross sections of production of $^2$H\, $^4$He\, $^{6}$Li\, $^{10}
 $B\, $^{12}$C\, and $^{14}$N spectator fragments in $^{16}$O–$^{16}$O we
 re estimated [2] with the Abrasion-Ablation Monte Carlo for Colliders mod
 el with pre-equlibrium Minimum Spanning Tree clustering (AAMCC-MST) [3]. 
 While contamination of $^{16}$O–$^{16}$O data is considered negligible b
 ased on recently collected data [4]\, this has not yet confirmed for $^{2
 0}$Ne–$^{20}$Ne collisions.\n\nWe report the results of AAMCC-MST modell
 ing of the production of spectator neutrons\, protons\, as well as $^2$H\,
  $^4$He\, $^{6}$Li\, $^{10}$B\, $^{12}$C\, $^{14}$N\, $^{16}$O\, and $^{18
 }$F fragments in $^{20}$Ne–$^{20}$Ne collisions at $\\sqrt{s_{NN}}=5.36$
  TeV. Prior to simulating $^{20}$Ne fragmentation at the LHC\, we validat
 ed AAMCC-MST using data on fragmentation of $\\sim 0.4A$–5$A$ GeV $^{20}
 $Ne and $^{22}$Ne projectiles in nuclear emulsion and on elemental targets
  [5\,6]. Three density profiles for $^{20}$Ne and $^{22}$Ne were employed
 : a deformed Woods–Saxon\, a five–$\\alpha$ bi-pyramidal configuration
 \, and a spherical profile for $^{20}$Ne. Calculations were also performed
  with and without MST clustering. Comparisons of results obtained with dif
 ferent calculation options demonstrate the sensitivity to both the details
  of the nuclear structure of $^{20\,22}$Ne and the fragmentation modelling
 .\n\nIn all previous studies of neon fragmentation\, neither protons nor n
 eutrons were registered. The data on spectator neutrons and protons from $
 ^{20}$Ne–$^{20}$Ne collisions collected by the ALICE Zero Degree Calorim
 eters (ZDC) [7] will provide a unique opportunity to study fragmentation o
 f isospin-symmetric $^{20}$Ne. Following validation of fragmentation model
 s with these new data\, new methods of luminosity monitoring and centralit
 y determination for collisions of light nuclei can be developed with invol
 ving both neutron and proton ZDCs.\n\nReferences\n\n[1] G. Nijs\, W. van d
 er Schee\, Phys. Lett. B 872 (2026) 140061\n\n[2] A. Svetlichnyi\, S. Sa
 venkov\, R. Nepeivoda\, I. Pshenichnov\, Physics 5 (2023) 38\n\n[3] R. N
 epeivoda\, A. Svetlichnyi\, N. Kozyrev\, I. Pshenichnov\, Particles 5 (
 2022) 40\n\n[4] A. Hayrapetyan\, V. Makarenko\, A. Tumasyan et al.\, Ph
 ys. Rev. Lett. 136 (2026) 162301\n\n[5] N.N. Abd-Allah\, M. Mohery\, Cze
 choslov. J. Phys. 51 (2001) 1189\n\n[6] A.T. Neagu\, E. Firu\, M. Haidu
 c\, J. Phys. G Nucl. Part. Phys. 40 (2013) 035102\n\n[7] C. Oppedisano\, 
 R. Arnaldi\, E. Chiavassa\, Nucl. Phys. B - Proc. Suppl. 197 (2009) 206\
 n\nhttps://indico.particle.mephi.ru/event/626/contributions/6302/
LOCATION:Sevastopol Hotel
URL:https://indico.particle.mephi.ru/event/626/contributions/6302/
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