Hadronization
In particle physics, hadronization (or hadronisation) is the process of the formation of hadrons out of quarks and gluons, which due to colour confinement, cannot exist as isolated particles. After high-energy collisions in a particle collider in which quarks or gluons are created, newly-created individual quarks and gluons transform to quarks and gluons confined in hadrons in a conversion that is not yet well understood. In the Standard Model the new particles are presumed to combine with quarks and antiquarks that form colourless combinations, spontaneously created from the vacuum.[1]
Hadronization also occurred shortly after the Big Bang when the quark–gluon plasma cooled to the temperature below which free quarks and gluons cannot exist (about 170 MeV). The quarks and gluons then combined into hadrons.
Phenomenological studies
The QCD (Quantum Chromodynamics) of the hadronization process are not yet fully understood, but are modeled and parameterized in a number of phenomenological studies, including the Lund string model and in various long-range QCD approximation schemes.[1][2][3]
The tight cone of particles created by the hadronization of a single quark is called a jet. In particle detectors, jets are observed rather than quarks, whose existence must be inferred. The models and approximation schemes and their predicted jet hadronization, or fragmentation, have been extensively compared with measurement in a number of high energy particle physics experiments, e.g. TASSO,[4] OPAL[5] and H1.[6]
The top quark does not hadronize
The top quark, however, decays via the weak force with a mean lifetime of 5×10−25 seconds. Unlike all other weak interactions which typically are much slower than strong interactions, the top quark weak decay is uniquely shorter than the time scale at which the strong force of QCD acts, so a top quark decays before it can hadronize.[7] The top quark is therefore almost a free particle.[8][9][10]
Hadronization simulation and models
Hadronization can be explored using Monte Carlo simulation. After the particle shower has terminated, partons with virtualities (how far off shell the virtual particles are) on the order of the cut-off scale remain. From this point on, the parton is in the low momentum transfer, long-distance regime in which non-perturbative effects become important. The most dominant of these effects is hadronization, which converts partons into observable hadrons. No exact theory for hadronization is known but there are two successful models for parameterization.
These models are used within event generators which simulate particle physics events. The scale at which partons are given to the hadronization is fixed by the shower Monte Carlo component of the event generator. Hadronization models typically start at some predefined scale of their own. This can cause significant issue if not set up properly within the Shower Monte Carlo. Common choices of shower Monte Carlo are PYTHIA and HERWIG. Each of these correspond to one of the two parameterization models.
References
- ^ a b Yu; Dokshitzer, L.; Khoze, V.A.; Mueller, A. H.; Troyan, S.I. (1991). Basics of Perturbative QCD. Editions Frontieres.
- ^ Bassetto, A.; Ciafaloni, M.; Marchesini, G.; Mueller, A.H. (1982). "Jet multiplicity and soft gluon factorization". Nuclear Physics B. 207 (2): 189–204. Bibcode:1982NuPhB.207..189B. doi:10.1016/0550-3213(82)90161-4. ISSN 0550-3213.
- ^ Mueller, A.H. (1981). "On the multiplicity of hadrons in QCD jets". Physics Letters B. 104 (2): 161–164. Bibcode:1981PhLB..104..161M. doi:10.1016/0370-2693(81)90581-5. ISSN 0370-2693.
- ^ Braunschweig, W.; Gerhards, R.; Kirschfink, F. J.; Martyn, H.-U.; Fischer, H.M.; Hartmann, H.; et al. (TASSO Collaboration) (1990). "Global jet properties at 14-44 GeV center of mass energy in e+ e- annihilation". Zeitschrift für Physik C. 47 (2): 187–198. doi:10.1007/bf01552339. ISSN 0170-9739.
- ^ Akrawy, M.Z.; Alexander, G.; Allison, J.; Allport, P.P.; Anderson, K.J.; Armitage, J.C.; et al. (OPAL Collaboration) (1990). "A study of coherence of soft gluons in hadron jets". Physics Letters B. 247 (4): 617–628. Bibcode:1990PhLB..247..617A. doi:10.1016/0370-2693(90)91911-t. ISSN 0370-2693.
- ^ Aid, S.; Andreev, V.; Andrieu, B.; Appuhn, R.-D.; Arpagaus, M.; Babaev, A.; et al. (H1 Collaboration) (1995). "A study of the fragmentation of quarks in e− p collisions at HERA". Nuclear Physics B. 445 (1): 3–21. arXiv:hep-ex/9505003. Bibcode:1995NuPhB.445....3A. doi:10.1016/0550-3213(95)91599-h. ISSN 0550-3213.
- ^ Abazov, V.M.; Abbott, B.; Abolins, M.; Acharya, B.S.; Adams, M.; Adams, T.; Aguilo, E.; Ahn, S.H.; Ahsan, M.; Alexeev, G.D.; Alkhazov, G.; Alton, A.; Alverson, G.; Alves, G.A.; Anastasoaie, M.; Ancu, L.S.; Andeen, T.; Anderson, S.; Anzelc, M.S.; Aoki, M.; Arnoud, Y.; Arov, M.; Arthaud, M.; Askew, A.; Åsman, B.; Assis Jesus, A.C.S.; Atramentov, O.; Avila, C.; Ay, C.; Badaud, F. (2008). "Evidence for production of single top quarks". Physical Review D. 78: 012005. arXiv:0803.0739v2. doi:10.1103/PhysRevD.78.012005.
{{cite journal}}: Unknown parameter|displayauthors=ignored (|display-authors=suggested) (help) - ^ Seidel, Katja; Simon, Frank; Tesař, Michal; Poss, Stephane (August 2013). "Top quark mass measurements at and above threshold at CLIC". The European Physical Journal C. 73 (8): 2530. arXiv:1303.3758. Bibcode:2013EPJC...73.2530S. doi:10.1140/epjc/s10052-013-2530-7. ISSN 1434-6044.
- ^ Alioli, S.; Fernandez, P.; Fuster, J.; Irles, A.; Moch, S.; Uwer, P.; Vos, M. (May 2013). "A new observable to measure the top-quark mass at hadron colliders". The European Physical Journal C. 73 (5): 2438. arXiv:1303.6415. Bibcode:2013EPJC...73.2438A. doi:10.1140/epjc/s10052-013-2438-2. ISSN 1434-6044.
- ^ Gao, Jun; Li, Chong Sheng; Zhu, Hua Xing (24 January 2013). "Top-quark decay at next-to-next-to-leading order in QCD". Physical Review Letters. 110 (4): 042001. arXiv:1210.2808. doi:10.1103/PhysRevLett.110.042001. ISSN 0031-9007. PMID 25166153.
- Greco, V.; Ko, C. M.; Lévai, P. (2003). "Parton coalescence and the antiproton/pion anomaly at RHIC". Physical Review Letters. 90 (20): 202302. arXiv:nucl-th/0301093. Bibcode:2003PhRvL..90t2302G. doi:10.1103/PhysRevLett.90.202302. PMID 12785885.
- Fries, R.J.; Müller, B.; Nonaka, C.; Bass, S.A. (2003). "Hadronization in heavy-ion collisions: Recombination and fragmentation of partons hadronization in heavy-ion collisions". Physical Review Letters. 90 (20): 202303. arXiv:nucl-th/0301087. Bibcode:2003PhRvL..90t2303F. doi:10.1103/PhysRevLett.90.202303. PMID 12785886.