Jet Hadronization in Vacuum and in the Medium Rainer Fries Texas A&M University Quark Matter 2015 Kobe, September 28, 2015 With Kyongchol Han Che Ming Ko

JET collaboration goal: ”… realistic calculations of jet production in a high energy density medium…”  comprehensive modeling of jet showers, including hadron chemistry. Unified approach to hadronization of jets in vacuum and medium  hybrid recombination and string fragmentation model. Develop a hadronization code that can be universally applied to jet showers MCs with and without embedding in a fluid dynamic background event by event. Work with the WSU and LBNL/CCNU groups. Rainer Fries2 QM 2015 The JET Effort on Jet Hadronization Examples for hadron chemistry with high momentum trigers

Rainer Fries3 QM 2015 Work Flow Parton shower MC with space-time information Texas Jet Hadronization Code Thermal partons from background medium. Sampler for iEBE is provided. Output: hadrons associated with the jet log of energy, momentum, flavor removed from the medium

I. Parton Showers Starting point: perturbative parton showers evolved to a scale Q 0. Decay gluons with remaining virtualities into quark-antiquark pairs. Light and strange quarks, chemistry from phase space QM Rainer Fries Force gluon decay For test purposes: e + +e - showers from PYTHIA supplemented by space-time evolution from tracking virtuality of partons.

I. Parton Showers QM Rainer Fries Example: Sample of 10 6 PYTHIA parton showers with E jet = 100 GeV. dN / dz and dN / d 2 P T before vs after gluon decay

I. Parton Showers QM Rainer Fries Distance of quark-antiquark pairs in phase space is the deciding factor for the importance of recombination. Distribution of pair distances in parton showers in phase space (in their center of mass frame) Peaks around ∆r ~ 0.5 fm, ∆k ~0.4 GeV  many partons close in phase space Long tails exist  lonely “remnant” partons

II. Recombination Step Monte Carlo version of the instantaneous recombination model in the Wigner formalism. QM Rainer Fries Force gluon decay Recombine v 1.0: Spherical well Wigner functions according to Greco, Ko and Levai. v2.0: More physical harmonic osciallator Wigner functions. Instantaneous coalescence including resonances Resonances and their decays are important (connections to cluster hadronization) [K. Han, C.M. Ko, R.J.F., arxiv: ]

II. Recombination Instantaneous coalescence for mesons and baryons: Wigner formalism v1.0 hadron & resonance Wigner functions: Step functions a la Greco, Ko, Levai  Evaluated at equal time in the pair or triplet rest frame.  Throw dice to accept or reject a pair or triplet for recombination. QM Rainer Fries [Greco, Ko & Levai, PRL 90, (2003)] [Fries, Greco, Sorensen, Ann. Rev. Nucl. Part. Sci. 58, 177 (2008)]

II. Recombination QM Rainer Fries

III. Remnant Strings Naturally there are remnant quarks and antiquarks which have not found a recombination partner. QM Rainer Fries Force gluon decay Recombine Remnant strings String Decay Why? No confinement in parton shower, quarks can get far away. In reality: colored object needs to stay connected. Return these partons to PYTHIA to connect them with remnant strings.

III. Remnant Strings QM Rainer Fries Check on recombination probability: v2.0; 100 GeV jets

Results: Vacuum QM Rainer Fries Longitudinal structure: dN / dz of stable particles compared to PYTHIA string fragmentation (e+e-). v2.0; 100 GeV jets

Results: Vacuum QM Rainer Fries Transverse structure: dN / d 2 P T of stable particles compared to PYTHIA string fragmentation (e+e-). v2.0; 100 GeV jets Generally good agreement with pure string fragmentation. No precision tuning to data thus far.

Results: Vacuum QM Rainer Fries More complicated systems: dN / dP T of hadrons in p+p. v1.0 Credit: Tan Luo (LBNL/CCNU)

Adding a Medium The space-time picture is complicated and it matters! All relevant partons have to be on the surface of the QGP or outside the QGP to hadronize. Propagate all shower partons to the hadronization hypersurface, or make them part of the medium. QM Rainer Fries QGP T > T c Hadronization T ~ T c Hadronic/vacuum T < T c QGP T > T c Hadronization T ~ T c Hadronic/vacuum T < T c

Adding a Medium QM Rainer Fries t t x x y y

Results With Medium PYTHIA showers propagated to the T = T c hypersurface (E < 600 MeV quarks absorbed in the QGP); sh-sh includes remnant fragmentation. QM Rainer Fries

Results With Medium Medium effects only important for small hadron momenta < 10 GeV as expected. Shower-thermal recombination takes over from pure shower-shower recombination; remnant strings are still important. Ranked list of importance of shower-thermal vs shower-shower: N > K > . Large for nucleons! Geometry matters: jet bulk inside or outside the QGP? Caveat: the plots were made with true in-medium showers but vacuum shower with a very simplistic energy loss model. Results should hold qualitatively. QM Rainer Fries

Results With Medium QM Rainer Fries

Results With Medium Preview: Hadronization for LBNL/CCNU Coupled Linearized Boltzmann- Hydro (see talk by Wei Chen). Hadron suppression/enhancement + azimuthal correlations Calculations with event-by-event hydro medium + v2.0 hadronization + medium modified are on the way. QM Rainer Fries

Summary QM Rainer Fries We have developed an event-by-event hybrid hadronization module for jet Monte Carlos. Quark recombination including resonances, supplemented by string fragmentation. Medium effects on hadronization: include thermal partons sampled from hydro event-by-event. v1.0 is at work in the JET collaboration, v2.0 will be made public soon. We have begun studying systematically observables emerging from our calculations.

Backup QM Rainer Fries

Hadronization Candidates QM Rainer Fries Lund string fragmentation Cluster hadronization Jet recombination