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SUMMARY:Exact Event Time Reconstruction for Time-of-Flight Particle Identi
 fication
DTSTART;VALUE=DATE-TIME:20261030T071500Z
DTEND;VALUE=DATE-TIME:20261030T073000Z
DTSTAMP;VALUE=DATE-TIME:20261030T205450Z
UID:indico-contribution-6385@cern.ch
DESCRIPTION:Speakers: Semyon Yurchenko (Saint Petersburg State University\
 , Laboratory of ulta-high energy physics)\nPrecise determination of the ev
 ent collision time t_{0} is essential for particle identification with tim
 e-of-flight detectors. In the ALICE experiment\, the event time can be rec
 onstructed from measured TOF signals by comparing them with expected fligh
 t times under different particle-mass hypotheses [1\,2]. The corresponding
  optimization problem is combinatorial\, and practical reconstruction proc
 edures therefore employ restricted hypothesis searches and rejection crite
 ria. \n\nWe present an exact polynomial-time method for global minimizatio
 n of the event-time objective function. The algorithm determines the optim
 al particle hypotheses together with the corresponding t0 without exhausti
 ve enumeration of all hypothesis assignments. The method was validated aga
 inst brute-force enumeration at low multiplicity\, where identical particl
 e assignments\, event times\, and objective-function values were obtained.
  It was further benchmarked against the event-time reconstruction procedur
 e implemented in the ALICE O2 framework [3\,4] using simulated pp and Pb-P
 b events. For typical events\, the optimized O2 procedure remains highly c
 ompetitive in execution time\, while the exact method provides a guarantee
 d global optimum and can therefore serve as a reference for validating heu
 ristic reconstruction approaches. \n\nWe also demonstrate ambiguous event 
 configurations for which the restricted search converges to a suboptimal s
 olution\, producing a shifted reconstructed event time and incorrect parti
 cle assignments\, whereas the exact algorithm recovers the global minimum.
  The proposed method can therefore be used both as a validation tool and a
 s a component of future hybrid event-time reconstruction algorithms.\n\nRe
 ferences\n\n[1] ALICE Collaboration\, “Determination of the event collis
 ion time with the ALICE detector at the LHC\,” European Physical Journal
  Plus 132\, 99 (2017). doi:10.1140/epjp/i2017-11279-1\n\n[2] A. Alici for 
 the ALICE Collaboration\, “Particle identification with the ALICE Time-O
 f-Flight detector at the LHC\,” Nuclear Instruments and Methods in Physi
 cs Research A 766\, 288–291 (2014). doi:10.1016/j.nima.2014.05.059\n\n[3
 ] G. Eulisse and D. Rohr for the ALICE Collaboration\, “The O2 software 
 framework and GPU usage in ALICE online and offline reconstruction in Run 
 3\,” EPJ Web of Conferences 295\, 05022 (2024). doi:10.1051/epjconf/2024
 29505022\n\n[4] ALICE O2\, TOF EventTimeMaker implementation and documenta
 tion. EventTimeMaker.h\n\nhttps://indico.particle.mephi.ru/event/626/contr
 ibutions/6385/
LOCATION: Conference Hall 5
URL:https://indico.particle.mephi.ru/event/626/contributions/6385/
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