Editing Hadronization

{{short description|Process by which hadrons are formed}}
'''Hadronization''' (or '''hadronisation''') is the process of the formation of [[hadron]]s out of [[quark]]s and [[gluon]]s. There are two main branches of hadronization: [[Quark–gluon plasma|quark-gluon plasma]] (QGP) transformation<ref>{{Cite journal|last=Rafelski|first=Johann|year=2015|title=Melting hadrons, boiling quarks|journal=The European Physical Journal A|language=en|volume=51|issue=9|pages=114|doi=10.1140/epja/i2015-15114-0|arxiv=1508.03260 |bibcode=2015EPJA...51..114R |issn=1434-6001|doi-access=free}}</ref> and [[Lund string model|colour string decay]] into hadrons.<ref>{{Cite book|last=Andersson, Bo, 1937-|url=https://www.worldcat.org/oclc/37755081|title=The Lund model|publisher=Cambridge University Press|year=1998|isbn=0-521-42094-6|location=Cambridge, U.K.|oclc=37755081}}</ref> The transformation of quark-gluon plasma into hadrons is studied in [[lattice QCD]] numerical simulations, which are explored in [[Relativistic heavy-ion collisions|relativistic heavy-ion]] experiments.<ref>{{Citation|last=Müller|first=Berndt|title=A New Phase of Matter: Quark-Gluon Plasma Beyond the Hagedorn Critical Temperature|work=Melting Hadrons, Boiling Quarks - From Hagedorn Temperature to Ultra-Relativistic Heavy-Ion Collisions at CERN|pages=107–116|year=2016|editor-last=Rafelski|editor-first=Johann|place=Cham|publisher=Springer International Publishing|language=en|doi=10.1007/978-3-319-17545-4_14|bibcode=2016mhbq.book..107M |isbn=978-3-319-17544-7|doi-access=free|arxiv=1501.06077}}</ref> Quark-gluon plasma hadronization occurred shortly after the [[Big Bang]] when the [[quark–gluon plasma]] cooled down to the [[Hagedorn temperature]] (about 150&nbsp;[[MeV]]) when free quarks and gluons cannot exist.<ref>{{Cite book|last1=Letessier|first1=Jean|url=https://www.cambridge.org/core/product/identifier/9780511534997/type/book|title=Hadrons and Quark–Gluon Plasma|last2=Rafelski|first2=Johann|publisher=Cambridge University Press|year=2002|isbn=978-0-521-38536-7|edition=1|doi=10.1017/cbo9780511534997}}</ref> In string breaking new hadrons are forming out of quarks, antiquarks and sometimes gluons, spontaneously created from the [[vacuum]].<ref name=Yu1991/>

== Statistical hadronization ==
A highly successful description of QGP hadronization is based on statistical phase space weighting<ref>{{Cite journal|last1=Rafelski|first1=Johann|last2=Letessier|first2=Jean|year=2003|title=Testing limits of statistical hadronization|url=https://linkinghub.elsevier.com/retrieve/pii/S0375947402014185|journal=Nuclear Physics A|language=en|volume=715|pages=98c–107c|doi=10.1016/S0375-9474(02)01418-5|arxiv=nucl-th/0209084|bibcode=2003NuPhA.715...98R |s2cid=18970526 }}</ref> according to the Fermi–Pomeranchuk model of particle production.<ref>{{Citation|last=Hagedorn|first=Rolf|title=The Long Way to the Statistical Bootstrap Model|url=http://link.springer.com/10.1007/978-1-4615-1945-4_2|work=Hot Hadronic Matter|series=NATO ASI Series |volume=346|pages=13–46|year=1995|editor-last=Letessier|editor-first=Jean|place=Boston, MA|publisher=Springer US|doi=10.1007/978-1-4615-1945-4_2|isbn=978-1-4613-5798-8|access-date=2020-06-25|editor2-last=Gutbrod|editor2-first=Hans H.|editor3-last=Rafelski|editor3-first=Johann|url-access=subscription}}</ref> This approach was developed, since 1950, initially as a qualitative description of strongly interacting particle production. It was originally not meant to be an accurate description, but a phase space estimate of upper limit to particle yield. In the following years numerous hadronic resonances were discovered. [[Rolf Hagedorn]] postulated the statistical bootstrap model (SBM) allowing to describe hadronic interactions in terms of statistical resonance weights and the resonance mass spectrum. This turned the qualitative Fermi–Pomeranchuk model into a precise statistical hadronization model for particle production.<ref>{{Cite journal|last1=Torrieri|first1=G.|last2=Steinke|first2=S.|last3=Broniowski|first3=W.|last4=Florkowski|first4=W.|last5=Letessier|first5=J.|last6=Rafelski|first6=J.|year=2005|title=SHARE: Statistical hadronization with resonances|url=https://linkinghub.elsevier.com/retrieve/pii/S0010465505000755|journal=Computer Physics Communications|language=en|volume=167|issue=3|pages=229–251|doi=10.1016/j.cpc.2005.01.004|arxiv=nucl-th/0404083|bibcode=2005CoPhC.167..229T |s2cid=13525448 }}</ref> However, this property of hadronic interactions poses a challenge for the statistical hadronization model as the yield of particles is sensitive to the unidentified high mass hadron resonance states. The statistical hadronization model was first applied to relativistic heavy-ion collisions in 1991, which led to the recognition of the first strange anti-baryon signature of quark-gluon plasma discovered at [[CERN]].<ref>{{Cite journal|last=Rafelski|first=Johann|year=1991|title=Strange anti-baryons from quark-gluon plasma|url=https://linkinghub.elsevier.com/retrieve/pii/037026939191576H|journal=Physics Letters B|language=en|volume=262|issue=2–3|pages=333–340|doi=10.1016/0370-2693(91)91576-H|bibcode=1991PhLB..262..333R |url-access=subscription}}</ref><ref>{{Cite journal|last1=Abatzis|first1=S.|last2=Barnes|first2=R.P.|last3=Benayoun|first3=M.|last4=Beusch|first4=W.|last5=Bloodworth|first5=I.J.|last6=Bravar|first6=A.|last7=Caponero|first7=M.|last8=Carney|first8=J.N.|last9=Dufey|first9=J.P.|last10=Evans|first10=D.|last11=Fini|first11=R.|year=1990|title=Λ and production in sulphur-tungsten interactions at 200 GeV/c per nucleon|url=https://linkinghub.elsevier.com/retrieve/pii/037026939090282B|journal=Physics Letters B|language=en|volume=244|issue=1|pages=130–134|doi=10.1016/0370-2693(90)90282-B}}</ref>

==Phenomenological studies of string model and fragmentation==
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 [[Quantum chromodynamics|QCD]] approximation schemes.<ref name=Yu1991>{{cite book |last1=Yu |first2=L. |last2=Dokshitzer |first3=V.A. |last3=Khoze |first4=A. H. |last4=Mueller |first5=S.I. |last5=Troyan |title=Basics of Perturbative QCD |publisher=Editions Frontieres |year=1991}}</ref><ref name=Bassetto1982>{{cite journal |last1=Bassetto |first1=A. |last2=Ciafaloni |first2=M. |last3=Marchesini |first3=G. |last4=Mueller |first4=A.H. |title=Jet multiplicity and soft gluon factorization |journal=Nuclear Physics B  |volume=207 |issue=2 |year=1982 |issn=0550-3213 |doi=10.1016/0550-3213(82)90161-4 |pages=189–204 |bibcode=1982NuPhB.207..189B }}</ref><ref name=Mueller1981>{{cite journal |last=Mueller |first=A.H. |year=1981 |title=On the multiplicity of hadrons in QCD jets |journal=Physics Letters B |volume=104 |issue=2 |pages=161–164 |issn=0370-2693 |doi=10.1016/0370-2693(81)90581-5 |bibcode=1981PhLB..104..161M}}</ref>

The tight cone of particles created by the hadronization of a single [[quark]] is called a [[Jet (particle physics)|jet]].  In [[particle detector]]s, 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]],<ref>{{cite journal |last1=Braunschweig |first1=W. |last2=Gerhards |first2=R. |last3=Kirschfink |first3=F. J. |last4=Martyn |first4=H.-U. |last5=Fischer |first5=H.M. |last6=Hartmann |first6=H. |last7=Hartmann |first7=J. |last8=Hilger |first8=E. |last9=Jocksch |first9=A. |last10=Wedemeyer |first10=R. |display-authors=6 |collaboration=TASSO Collaboration |title=Global jet properties at 14-44&nbsp;GeV center of mass energy in e<sup>+</sup>&nbsp;e<sup>−</sup> annihilation |journal=Zeitschrift für Physik C  |volume=47 |issue=2 |year=1990 |issn=0170-9739 |doi=10.1007/bf01552339 |pages=187–198|s2cid=124007688 }}</ref> [[OPAL detector|OPAL]]<ref>{{cite journal |last1=Akrawy |first1=M.Z. |last2=Alexander |first2=G. |last3=Allison |first3=J. |last4=Allport |first4=P.P. |last5=Anderson |first5=K.J. |last6=Armitage |first6=J.C. |last7=Arnison |first7=G.T.J. |last8=Ashton |first8=P. |last9=Azuelos |first9=G. |last10=Baines |first10=J.T.M. |display-authors=6 |collaboration=OPAL Collaboration |title=A study of coherence of soft gluons in hadron jets |journal=Physics Letters B  |volume=247 |issue=4 |year=1990 |issn=0370-2693 |doi=10.1016/0370-2693(90)91911-t | pages=617–628| bibcode=1990PhLB..247..617A |s2cid=121998239 |url=https://cds.cern.ch/record/209874 }}</ref> and [[H1 (particle detector)|H1]].<ref>{{cite journal |last1=Aid |first1=S. |last2=Andreev |first2=V. |last3=Andrieu |first3=B. |last4=Appuhn |first4=R.-D. |last5=Arpagaus |first5=M. |last6=Babaev |first6=A. |last7=Baehr |first7=J. |last8=Bán |first8=J. |last9=Ban |first9=Y. |last10=Baranov |first10=P. |display-authors=6 |collaboration=H1 Collaboration |title=A study of the fragmentation of quarks in e<sup>&minus;</sup>&nbsp;p collisions at HERA |journal=Nuclear Physics B  |volume=445 |issue=1 |year=1995 |issn=0550-3213 |doi=10.1016/0550-3213(95)91599-h |pages=3–21 |bibcode=1995NuPhB.445....3A |arxiv=hep-ex/9505003|s2cid=18632361 }}</ref>

Hadronization can be explored using [[Monte Carlo method|Monte Carlo]] simulation. After the [[particle shower]] has terminated, [[parton (particle physics)|partons]] with virtualities (how far [[On shell and off shell|off shell]] the [[virtual particle]]s 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 generator]]s which simulate particle physics events. The scale at which [[parton (particle physics)|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.

==The top quark does not hadronize==
The [[top quark]], however, decays via the [[weak force]] with a mean lifetime of 5×10<sup>−25</sup> 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.<ref>{{cite journal |last1=Abazov |first1=V.M. |last2=Abbott |first2=B. |last3=Abolins |first3=M. |last4=Acharya |first4=B.S. |last5=Adams |first5=M. |last6=Adams  |first6=T. |last7=Aguilo |first7=E. |last8=Ahn |first8=S.H. |last9=Ahsan |first9=M. |last10=Alexeev |first10=G.D. |last11=Alkhazov |first11=G. |last12=Alton |first12=A. |last13=Alverson |first13=G. |last14=Alves |first14=G.A. |last15=Anastasoaie |first15=M. |last16=Ancu |first16=L.S. |last17=Andeen |first17=T. |last18=Anderson |first18=S. |last19=Anzelc |first19=M.S. |last20=Aoki |first20=M. |last21=Arnoud |first21=Y. |last22=Arov |first22=M. |last23=Arthaud |first23=M. |last24=Askew |first24=A. |last25=Åsman |first25=B. |last26=Assis Jesus |first26=A.C.S. |last27=Atramentov |first27=O. |last28=Avila |first28=C. |last29=Ay |first29=C. |last30=Badaud |first30=F. |display-authors=6 |year=2008 |title=Evidence for production of single top quarks |journal=Physical Review D |volume=78 |issue=1 |page=012005 |arxiv=0803.0739 |doi=10.1103/PhysRevD.78.012005|bibcode=2008PhRvD..78a2005A |s2cid=204894756 }}</ref> The [[top quark]] is therefore almost a free particle.<ref>{{cite journal |last1=Seidel |first1=Katja |last2=Simon |first2=Frank |last3=Tesař |first3=Michal |last4=Poss |first4=Stephane |date=August 2013 |title=Top quark mass measurements at and above threshold at CLIC |journal=The European Physical Journal C |volume=73 |issue=8 |page=2530 |doi=10.1140/epjc/s10052-013-2530-7 |issn=1434-6044 |arxiv=1303.3758 |bibcode=2013EPJC...73.2530S|s2cid=118529845 }}</ref><ref>{{cite journal |last1=Alioli |first1=S. |last2=Fernandez |first2=P. |last3=Fuster |first3=J. |last4=Irles |first4=A. |last5=Moch |first5=S. |last6=Uwer |first6=P. |last7=Vos |first7=M. |date=May 2013 |title=A new observable to measure the top-quark mass at hadron colliders |journal=The European Physical Journal C |volume=73 |issue=5 |page=2438 |doi=10.1140/epjc/s10052-013-2438-2 |arxiv=1303.6415 |issn=1434-6044 |bibcode=2013EPJC...73.2438A|s2cid=20136858 }}</ref><ref>{{cite journal |last1=Gao |first1=Jun |last2=Li |first2=Chong Sheng |last3=Zhu |first3=Hua Xing |date=2013-01-24 |df=dmy-all |title=Top-quark decay at next-to-next-to-leading order in QCD |journal=Physical Review Letters |volume=110 |issue=4 |page=042001 |doi=10.1103/PhysRevLett.110.042001 |pmid=25166153 |issn=0031-9007 |arxiv=1210.2808|bibcode=2013PhRvL.110d2001G |s2cid=5101838 }}</ref>

==References==
{{Reflist|25em}}
{{Wiktionary}}
* {{cite journal |last1=Greco |first1=V. |last2=Ko |first2=C. M. |last3=Lévai |first3=P. |year=2003 |title=Parton coalescence and the antiproton/pion anomaly at RHIC |journal=Physical Review Letters |volume=90 |issue=20 |page=202302 |doi=10.1103/PhysRevLett.90.202302 |bibcode=2003PhRvL..90t2302G |pmid=12785885 |arxiv=nucl-th/0301093|s2cid=35617853 }}
* {{cite journal |last1=Fries |first1=R.J. |last2=Müller |first2=B. |last3=Nonaka |first3=C. |last4=Bass |first4=S.A. |year=2003 |title=Hadronization in heavy-ion collisions: Recombination and fragmentation of partons hadronization in heavy-ion collisions |journal=Physical Review Letters |volume=90 |issue=20 |page=202303 |doi=10.1103/PhysRevLett.90.202303|arxiv = nucl-th/0301087 |bibcode=2003PhRvL..90t2303F |pmid=12785886|s2cid=912540 }}

[[Category:Quantum chromodynamics]]
[[Category:Experimental particle physics]]