Hadronization and Jet Substructure at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC)

Hadronization and jet substructure at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC)

Joe Osborn Oak Ridge National Laboratory, University of Michigan

March 18, 2020 • Jets are a proxy for partons, and thus provide sensitivity to the underlying partonic dynamics

Jets

• Jet physics is a broad experimental endeavor at RHIC and the LHC • Enabled by more robust comparisons that can be made between theory and experiment with recent jet ﬁnding algorithms

Joe Osborn (ORNL) 1 Jets

• Jet physics is a broad experimental endeavor at RHIC and the LHC • Enabled by more robust comparisons that can be made between theory and experiment with recent jet ﬁnding algorithms • Jets are a proxy for partons, and thus provide sensitivity to the underlying partonic dynamics

Joe Osborn (ORNL) 1 • We can use a perturbative object to learn about nonperturbative physics

Jet Hadronization

• BUT - jets are still formed from ﬁnal-state hadrons! • Nonperturbative elements of QCD still important in understanding perturbative jets

Joe Osborn (ORNL) 2 Jet Hadronization

• BUT - jets are still formed from ﬁnal-state hadrons! • Nonperturbative elements of QCD still important in understanding perturbative jets • We can use a perturbative object to learn about nonperturbative physics

Joe Osborn (ORNL) 2 How do jets really form?

Joe Osborn (ORNL) 2 Jet Formation

q g q q¯ . . . hadrons g q

Joe Osborn (ORNL) 3 Jet Formation

Fragmentation Hadronization

Joe Osborn (ORNL) 3 Fragmentation vs. Hadronization

Fragmentation

• Use jet grooming algorithms to identify “prongs” of jet, as a proxy for partonic splittings

Joe Osborn (ORNL) 4 Fragmentation vs. Hadronization

Fragmentation Hadronization

• Use jet grooming algorithms to identify “prongs” of jet, as a proxy • Use individual hadrons to study for partonic splittings correlations with jet axis

Joe Osborn (ORNL) 4 Fragmentation vs. Hadronization

Fragmentation Hadronization

• Use jet grooming algorithms to identify “prongs” of jet, as a proxy • Use individual hadrons to study for partonic splittings correlations with jet axis

Emphasis on perturbative QCD Emphasis on NONperturbative QCD

Joe Osborn (ORNL) 4 Fragmentation vs. Hadronization

Fragmentation Hadronization

In between??

• Use jet grooming algorithms to identify “prongs” of jet, as a proxy • Use individual hadrons to study for partonic splittings correlations with jet axis

Emphasis on perturbative QCD Emphasis on NONperturbative QCD

Joe Osborn (ORNL) 4 • Jets, as a proxy for a parton, are a tool to connect the perturbative to nonperturbative

• Would allow for complete characterization of parton → hadron

1. A way to connect the initial-state parton to the ﬁnal-state hadrons

2. A way to connect the ﬂavors of the initial-state parton to the ﬁnal-state hadrons

3. Statistics to study multi-diﬀerential correlations

Hadronization: What do we want?

• What is on our wish list to robustly study hadronization?

Joe Osborn (ORNL) 5 • Would allow for complete characterization of parton → hadron

2. A way to connect the ﬂavors of the initial-state parton to the ﬁnal-state hadrons

3. Statistics to study multi-diﬀerential correlations

Hadronization: What do we want?

jet • What is on our wish list to robustly study hadronization? 1. A way to connect the initial-state parton to the ﬁnal-state hadrons • Jets, as a proxy for a parton, are a tool to connect the parton perturbative to nonperturbative

Joe Osborn (ORNL) 5 3. Statistics to study multi-diﬀerential correlations

Hadronization: What do we want?

jet • What is on our wish list to robustly study hadronization? π+ n 1. A way to connect the initial-state 0 Λ η parton to the final-state hadrons up • Jets, as a proxy for a parton, are a tool to connect the parton perturbative to nonperturbative 2. A way to connect the flavors of the initial-state parton to the final-state hadrons • Would allow for complete characterization of parton → hadron

Joe Osborn (ORNL) 5 Hadronization: What do we want?

jet • What is on our wish list to robustly study hadronization? π+ n 1. A way to connect the initial-state 0 Λ η parton to the final-state hadrons up • Jets, as a proxy for a parton, are a tool to connect the parton perturbative to nonperturbative 2. A way to connect the flavors of • Baryon vs. meson the initial-state parton to the final-state hadrons • Resonance production (φ, J/ψ, Υ) • Would allow for complete • Correlations (e.g. kinematic, characterization of PIDed. . . ) parton → hadron • ... 3. Statistics to study multi-differential correlations

Joe Osborn (ORNL) 5 STAR Soft Drop

• New STAR results are ﬁrst study at RHIC of Soft Drop splittings

• Highlight RG , which shows need for more robust theory calculations relating fragmentation and hadronization eﬀects

arXiv:2003.02114

Joe Osborn (ORNL) 6 • Measurement of D0 production as a function of radial dimension + • More exotic Λc hadronization studies

Flavor Dependence - Heavy Quarks

• First study trying to observe the dead cone eﬀect • Suppression of splittings at small angles comparing D0 to inclusive jets

Joe Osborn (ORNL) 7 + • More exotic Λc hadronization studies

Flavor Dependence - Heavy Quarks

27.4 pb-1 (5.02 TeV pp) + 404 µb-1 (5.02 TeV PbPb) 4 < pD < 20 GeV/c CMS T 0 |yD| < 2 D + jet jet |p | > 60 GeV/c 10 T ηjet • First study trying to observe the | | < 1.6 JD

dead cone eﬀect dr dN

JD 1 • Suppression of splittings at small N 1 0 angles comparing D to inclusive PbPb jets pp CCNU PYTHIA PbPb pp (SHERPA) 0 − • Measurement of D production as a 10 1 0 0.1 0.2 0.3 0.4 0.5 function of radial dimension 2 CCNU r pp

PbPb 1

0 0.1 0.2 0.3 0.4 0.5 1.5 r PYTHIA 1 pp 0.5

Generator SHERPA 0 0 0.1 0.2 0.3 0.4 0.5 r arXiv:1911.01461

Joe Osborn (ORNL) 7 Flavor Dependence - Heavy Quarks

• First study trying to observe the dead cone eﬀect • Suppression of splittings at small angles comparing D0 to inclusive jets • Measurement of D0 production as a function of radial dimension + • More exotic Λc hadronization studies

Joe Osborn (ORNL) 7 Flavor Dependence - g → bb¯

• Measurement of bb¯ jets from gluon splitting • Improve understanding of boosted H → bb¯ decays • Improve understanding of bb¯ fragmentation

Phys. Rev. D 99, 052004 (2019)

Joe Osborn (ORNL) 8 • On average, light quark jets produce higher momentum particles than gluon jets

Flavor Dependence - Quark vs. Gluon

) -1 z

( 4 0.49 nb Pb+Pb 10 -1 D

25 pb pp 103 5.02 TeV 102 • Starting to move towards ﬂavor 10 ATLAS γ dependence p = 80-126 GeV, pjet = 63-144 GeV T T 1 0-30% Pb+Pb (×102), γ-tag • Use direct photon tags to 30-80% Pb+Pb (×101), γ-tag 10−1 pp (×100), γ-tag preferentially select light quarks vs. − 2 pp, inclusive jets, pjet = 80-110 GeV 10 T gluons 1.5 10−1 1 pp z -tag γ 1 Pythia8 A14 NNPDF23LO Sherpa CT10

Ratio to 0.5 Herwig H7UE MMHT2014lo 0.016 0.1 1 z Phys. Rev. Lett. 123, 042001 (2019)

Joe Osborn (ORNL) 9 Flavor Dependence - Quark vs. Gluon

) -1 z

( 4 0.49 nb Pb+Pb 10 -1 D

γ produce higher momentum particles 1 Pythia8 A14 NNPDF23LO than gluon jets Sherpa CT10

Ratio to 0.5 Herwig H7UE MMHT2014lo 0.016 0.1 1 z Phys. Rev. Lett. 123, 042001 (2019)

Joe Osborn (ORNL) 9 • Light quark jets produce higher momentum particles than gluon jets • Light quark jets are more collimated than gluon jets

ATLAS Inclusive and LHCb Z+jet

z 10 d

dN ATLAS inclusive jet LHCb Z+jet jet

1 6 EPJ C71, 1795 (2011) s = 8 TeV N 10 Z s = 7 TeV 60 < M µµ < 120 GeV, 2 < η < 4.5 • Compare ATLAS inclusive jet 5 |ηjet| < 1.2, R = 0.6 2.5 < ηjet < 4, R = 0.5 10 ptrack > 0.5 GeV phadron > 0.25 GeV, phadron > 4 GeV T T 25 < pjet < 40 GeV 20 < pjet < 30 GeV to LHCb Z+jet 4 T T 10 40 < pjet < 60 GeV (x10) 30 < pjet < 50 GeV (x10) T T 103 102 10 1 Phys. Rev. Lett. 123, 232001 (2019) 10−1 10−2 10−1 z LHCb quark jet (ﬁlled) - red and black ATLAS gluon jet (open) - blue and green

Joe Osborn (ORNL) 10 ATLAS Inclusive and LHCb Z+jet

z 10 d

dN ATLAS inclusive jet LHCb Z+jet jet

1 6 EPJ C71, 1795 (2011) s = 8 TeV N 10 Z s = 7 TeV 60 < M µµ < 120 GeV, 2 < η < 4.5 • Compare ATLAS inclusive jet 5 |ηjet| < 1.2, R = 0.6 2.5 < ηjet < 4, R = 0.5 10 ptrack > 0.5 GeV phadron > 0.25 GeV, phadron > 4 GeV T T 25 < pjet < 40 GeV 20 < pjet < 30 GeV to LHCb Z+jet 4 T T 10 40 < pjet < 60 GeV (x10) 30 < pjet < 50 GeV (x10) T T • Light quark jets produce 103 higher momentum particles 102 than gluon jets 10 • Light quark jets are more 1 Phys. Rev. Lett. 123, 232001 (2019) collimated than gluon jets − 10 1 10−2 10−1 z LHCb quark jet (ﬁlled) - red and black ATLAS gluon jet (open) - blue and green

Joe Osborn (ORNL) 10 • Both processes light quark jet dominated • Light quark jet structure shows little rapidity dependence • Hint of more collimated jets in Z+jet • Massive Z vs. massless γ?

LHCb Z+jet vs. ATLAS γ-jet

Phys. Rev. Lett. 123, 232001 (2019) • ATLAS midrapidity γ-jet and 4

z 10

d γ

dN ATLAS -jet arXiv:1902.10007 LHCb forward rapidity Z-jet s = 5.02 TeV +jet

Z γ 1 γ / 3 80 < E < 126 GeV, |η | < 2.37 distributions are very similar γ 10 T jet jet N 63 < p < 144 GeV, |η | < 2.1, R = 0.4 T ptrack > 1 GeV T 102

10 LHCb Z-jet s = 8 TeV Z 60 < M µµ < 120 GeV, 2 < η < 4.5 1 50 < pjet < 100 GeV, 2.5 < ηjet < 4, R = 0.5 T phadron > 0.25 GeV, phadron > 4 GeV T 10−1 10−2 10−1 z

LHCb quark jet (ﬁlled) - red ATLAS quark jet (open) - black

Joe Osborn (ORNL) 11 • Hint of more collimated jets in Z+jet • Massive Z vs. massless γ?

LHCb Z+jet vs. ATLAS γ-jet

Phys. Rev. Lett. 123, 232001 (2019) • ATLAS midrapidity γ-jet and 4

z 10

d γ

dN ATLAS -jet arXiv:1902.10007 LHCb forward rapidity Z-jet s = 5.02 TeV +jet

Z γ 1 γ / 3 80 < E < 126 GeV, |η | < 2.37 distributions are very similar γ 10 T jet jet N 63 < p < 144 GeV, |η | < 2.1, R = 0.4 T ptrack > 1 GeV • Both processes light quark T 102 jet dominated • Light quark jet structure 10 LHCb Z-jet s = 8 TeV Z shows little rapidity 60 < M µµ < 120 GeV, 2 < η < 4.5 1 50 < pjet < 100 GeV, 2.5 < ηjet < 4, R = 0.5 dependence T phadron > 0.25 GeV, phadron > 4 GeV T 10−1 10−2 10−1 z

LHCb quark jet (ﬁlled) - red ATLAS quark jet (open) - black

Joe Osborn (ORNL) 11 LHCb Z+jet vs. ATLAS γ-jet

Phys. Rev. Lett. 123, 232001 (2019) • ATLAS midrapidity γ-jet and 4

z 10

d γ

dN ATLAS -jet arXiv:1902.10007 LHCb forward rapidity Z-jet s = 5.02 TeV +jet

Joe Osborn (ORNL) 11 • Perturbative region quite similar between quark and gluon jets

ATLAS Inclusive and LHCb Z+jet

5 ]

-1 10 ATLAS inclusive jet LHCb Z+jet • Transverse momentum 4 EPJ C71, 1795 (2011) s = 8 TeV 10 ηZ [GeV s = 7 TeV 60 < M µµ < 120 GeV, 2 < < 4.5 distributions show smaller T jet jet j |η | < 1.2, R = 0.6 2.5 < η < 4, R = 0.5 dN d 3 track hadron hadron

jet p > 0.5 GeV p > 0.25 GeV, p > 4 GeV

1 10 T T hjT i in Z+jet vs. inclusive jet jet N 25 < p < 40 GeV 20 < p < 30 GeV T T jet at small j 2 40 < pjet < 60 GeV (x10) 30 < pjet < 50 GeV (x10) T 10 T T • Consistent with more 10 collimated light quark vs. gluon jets 1 10−1 Phys. Rev. Lett. 123, 232001 (2019) 10−2 1 2 3 j [GeV] T LHCb quark jet (ﬁlled) - red and black ATLAS gluon jet (open) - blue and green

Joe Osborn (ORNL) 12 • Perturbative region quite similar between quark and gluon jets

ATLAS Inclusive and LHCb Z+jet

5 ]

jet p > 0.5 GeV p > 0.25 GeV, p > 4 GeV

Joe Osborn (ORNL) 12 ATLAS Inclusive and LHCb Z+jet

5 ]

jet p > 0.5 GeV p > 0.25 GeV, p > 4 GeV

1 10 T T hjT i in Z+jet vs. inclusive jet jet N 25 < p < 40 GeV 20 < p < 30 GeV T T jet at small j 2 40 < pjet < 60 GeV (x10) 30 < pjet < 50 GeV (x10) T 10 T T • Consistent with more 10 collimated light quark vs. gluon jets 1 − • Perturbative region quite 10 1 Phys. Rev. Lett. 123, 232001 (2019) similar between quark and 10−2 1 2 3 gluon jets j [GeV] T LHCb quark jet (ﬁlled) - red and black ATLAS gluon jet (open) - blue and green

Joe Osborn (ORNL) 12 ATLAS Inclusive and LHCb Z+jet

r 10 d

dN ATLAS inclusive jet LHCb Z+jet jet

1 EPJ C71, 1795 (2011) s = 8 TeV N ηZ • Comparing ATLAS 4 s = 7 TeV 60 < M µµ < 120 GeV, 2 < < 4.5 10 |ηjet| < 1.2, R = 0.6 2.5 < ηjet < 4, R = 0.5 ptrack > 0.5 GeV phadron > 0.25 GeV, phadron > 4 GeV midrapidity inclusive jets to T T 25 < pjet < 40 GeV 20 < pjet < 30 GeV 3 T T 40 < pjet < 60 GeV (x10) 30 < pjet < 50 GeV (x10) LHCb forward Z+jet shows 10 T T jets are more collimated 102 when tagged with a Z

• Gluon jets “ﬂatter” in radius, 10

while light quark jets are Phys. Rev. Lett. 123, 232001 (2019) 1 “steeper” 0 0.1 0.2 0.3 0.4 r

LHCb quark jet (ﬁlled) - red and black ATLAS gluon jet (open) - blue and green

Joe Osborn (ORNL) 13 • Correlations between xE (proxy for z) and jT

• Correlations between z, jT , and angular production sensitive to 3D polarized FFs

Multi-dimensional Measurements

• We now have statistics to make ]

-1 jet 2 126 < p < 158 GeV ATLAS multi-dimensional measurements! 10 − T -1 0 10% Pb+Pb sNN = 5.02 TeV, 0.49 nb -1 • Provide more information and ) [GeV pp s = 5.02 TeV, 25 pb

r 10

, anti-k R=0.4 T t deeper understanding than p

( 1

D inclusive measurements 10−1 • Correlations between pT and r of − pp Pb+Pb 10 2 1.0 < p < 1.6 GeV 1.6 < pT < 2.5 GeV hadrons within jets 2.5 < pT < 4.0 GeV −3 4.0 < pT < 6.3 GeV 10 6.3 < pT < 10.0 GeV 10.0 < pT < 25.1 GeV T −4 25.1 < p < 63.1 GeV 10 T 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 r

Phys. Rev. C 100, 064901 (2019)

Joe Osborn (ORNL) 14 • Correlations between z, jT , and angular production sensitive to 3D polarized FFs

Multi-dimensional Measurements

• We now have statistics to make multi-dimensional measurements! • Provide more information and deeper understanding than inclusive measurements

• Correlations between pT and r of hadrons within jets

• Correlations between xE (proxy for z) and jT

JHEP 1903, 169 (2019)

Joe Osborn (ORNL) 14 Multi-dimensional Measurements

• We now have statistics to make multi-dimensional measurements! • Provide more information and deeper understanding than inclusive measurements

• Correlations between pT and r of hadrons within jets

• Correlations between xE (proxy for z) and jT

• Correlations between z, jT , and angular production sensitive to 3D polarized FFs

Joe Osborn (ORNL) 14 Future Jet Hadronization Measurements

• Where are we headed, and what Int. J. Mod. Phys. A 30, 1530022 (2015) don’t we have? • Particle ID (tracking, RICH, calorimetry) • Heavy ﬂavor jet tagging • Resonance production within jets

PRL 118, 192001 (2017) (φ, J/ψ, Υ) • Correlations with ﬂavor ID

Joe Osborn (ORNL) 15 • Jet substructure and hadronization a major component of science case

Future Jet Hadronization Measurements

• sPHENIX is a dedicated jet detector being constructed at RHIC • CD3 recently approved, construction is moving forward for installation in 2022

Joe Osborn (ORNL) 16 Future Jet Hadronization Measurements

• sPHENIX is a dedicated jet detector being constructed at RHIC • CD3 recently approved, construction is moving forward for installation in 2022 • Jet substructure and hadronization a major component of science case

Joe Osborn (ORNL) 16 • Hadronization is a major pillar of EIC physics case • Developing ideas in the next decade before EIC will be crucial to maximize science output of this unique QCD machine!

Hadronization at an Electron Ion Collider

• Electron Ion Collider (EIC) will be a QCD physics machine

Joe Osborn (ORNL) 17 Hadronization at an Electron Ion Collider

• Electron Ion Collider (EIC) will be a QCD physics machine • Hadronization is a major pillar of EIC physics case • Developing ideas in the next decade before EIC will be crucial to maximize science output of this unique QCD machine!

Joe Osborn (ORNL) 17 • Entering phase of synthesizing information and asking more fundamental questions • Kinematic correlations between hadrons in jets • Light quark vs. gluon jet hadronization • Heavy quark jet substructure • Many opportunities moving forward, beginning to utilize PID, multidiﬀerential measurements, etc. • Ideas behind hadronization are relatively undeveloped, but there will be signiﬁcant growth with current and future experiments!

Conclusions

• Jet substructure and hadronization has exploded onto the high energy and nuclear physics scene, with wide ranging physics interests

Joe Osborn (ORNL) 18 • Many opportunities moving forward, beginning to utilize PID, multidiﬀerential measurements, etc. • Ideas behind hadronization are relatively undeveloped, but there will be signiﬁcant growth with current and future experiments!

Conclusions

Joe Osborn (ORNL) 18 • Ideas behind hadronization are relatively undeveloped, but there will be signiﬁcant growth with current and future experiments!

Conclusions

• Jet substructure and hadronization has exploded onto the high energy and nuclear physics scene, with wide ranging physics interests • Entering phase of synthesizing information and asking more fundamental questions • Kinematic correlations between hadrons in jets • Light quark vs. gluon jet hadronization • Heavy quark jet substructure • Many opportunities moving forward, beginning to utilize PID, multidiﬀerential measurements, etc.

Joe Osborn (ORNL) 18 Conclusions

Joe Osborn (ORNL) 18 Back Up

Joe Osborn (ORNL) 18 Analysis Details

• Follow similar analysis strategy to ATLAS (EPJC 71, 1795 (2011), NPA 978, 65 (2018)) and LHCb (PRL 118, 192001 (2017)) + − • Z → µ µ identiﬁed with 60 < Mµµ < 120 GeV, in 2 < η < 4.5 jet • Anti-kT jets are measured with R = 0.5, pT > 20 GeV, in 2.5 < η < 4

•| ∆φZ+jet | > 7π/8 and single primary vertex selects 2 → 2 topology

• Charged hadrons identiﬁed with pT > 0.25 GeV, p > 4 GeV, ∆R < 0.5 • Results eﬃciency corrected and 2D Bayesian unfolded

Joe Osborn (ORNL) 19 Jet Substructure

• Searching “ﬁnd fulltext ’jet substructure’ and tc p” on INSPIRE 200 yields number of published papers Papers containing 'jet substructure' 180 Source: INSPIRE • Number of papers per year has 160 exploded in last decade 140 120 • Papers discuss wide range of Number of papers 100 physics interests 80 • Searches for new particles 60 • Heavy ﬂavor jet tagging 40 • BSM searches (e.g. dark matter) 20 0 • Heavy ion collisions 1990 1995 2000 2005 2010 2015 2020 • Machine learning Year • QCD color connections • ...

Joe Osborn (ORNL) 20 Theory Comparisons

• Theory colleagues have already published comparisons to data • Reasonable description of data • However, LHCb data has started a discussion on best (theoretically) tractable ways to study hadronization

Joe Osborn (ORNL) 21 Anti-kT Algorithm

• Sequential recombination algorithm which clusters particles into jets

based on their pT • Widely used as it is both infrared and collinear safe in calculations

• Clusters particles around highest pT particle in a conical shape 2 −2 −2 ∆ij dij = min(p , p ) Ti Tj R2 d = p−2 iB Ti

Joe Osborn (ORNL) 22 Comparisons with PYTHIA (z) z d dN 102 +jet 1 Z N

PYTHIA z d dN LHCb 102 1

s = 8 TeV +jet

Data 1 20 < pjet < 30 GeV Z

T N

10 10−2 10−1 z 1 true PYTHIA LHCb

PYTHIA/Data 0 1 s = 8 TeV − − Data 10 2 10 1 50 < pjet < 100 GeV z T z d

dN −2 −1

10 10 102 z 1 true +jet 1 Z PYTHIA/Data N 0 10−2 10−1 10 z

PYTHIA LHCb • PYTHIA generally underpredicts 1 Data s = 8 TeV 30 < pjet < 50 GeV T the number of high z hadrons

10−2 10−1 z 1 true

PYTHIA/Data 0 −2 −1 10 10 z Joe Osborn (ORNL) 23 Comparisons with PYTHIA (jT ) T j d dN LHCb PYTHIA 10 s = 8 TeV jet +jet 20 < p < 30 GeV Data 1

Z T N 1 T j d dN LHCb PYTHIA −1 10 s = 8 TeV 10 jet +jet 50 < p < 100 GeV Data 1

Z T N 10−2 1

1 2 3 jtrue 10−1 1 T

PYTHIA/Data 0 1 2 3 −2 j [GeV] 10 T

T 1 2 3 j jtrue d dN LHCb 1 T PYTHIA 10 s = 8 TeV

jet PYTHIA/Data +jet 30 < p < 50 GeV Data 0 1 Z T 1 2 3

N j [GeV] 1 T

− • PYTHIA generally gets j shape, 10 1 T with about a 20% diﬀerence in −2 10 normalization 1 2 3 jtrue 1 T

PYTHIA/Data 0 1 2 3 j [GeV] Joe Osborn (ORNL) T 24 Comparisons with PYTHIA (r)

102 r d dN LHCb s = 8 TeV PYTHIA jet +jet 20 < p < 30 GeV 1

Z T Data N

10 102 r d dN LHCb s = 8 TeV PYTHIA jet +jet 50 < p < 100 GeV 1

Z T Data N

0 0.1 0.2 0.3 0.4 0.5 r 1 true 10

PYTHIA/Data 0 0 0.1 0.2 0.3 0.4 0.5 r 102 r d dN LHCb 0 0.1 0.2 0.3 0.4 0.5 PYTHIA s = 8 TeV rtrue jet 1 +jet 30 < p < 50 GeV 1

Z T Data PYTHIA/Data

N 0 0 0.1 0.2 0.3 0.4 0.5 r 10 • PYTHIA generally underpredicts the number of small r hadrons

0 0.1 0.2 0.3 0.4 0.5 r 1 true

PYTHIA/Data 0 0 0.1 0.2 0.3 0.4 0.5 r Joe Osborn (ORNL) 25 • Jet substructure was motivated by new particle searches • However, many ﬁelds of physics at collider facilities quickly realized the potential of these techniques

Symbolic Beginning

PRL 100, 242001 (2010)

• Substructure revolution symbolically initiated by 2010 Butterworth et al PRL • Motivated by searching for highly boosted VH → `±bb¯ production

Joe Osborn (ORNL) 26 Symbolic Beginning

PRL 100, 242001 (2010)

• Substructure revolution symbolically initiated by 2010 Butterworth et al PRL • Motivated by searching for highly boosted VH → `±bb¯ production • Jet substructure was motivated by new particle searches • However, many ﬁelds of physics at collider facilities quickly realized the potential of these techniques

Joe Osborn (ORNL) 26 Jet Substructure Physics at RHIC

• Measurement of jet mass sensitive to both fragmentation and hadronization aspects of jet substructure! • Can study the interplay and connections between both

Joe Osborn (ORNL) 27 Jet Substructure at the LHC

• Searches for dark matter particles using jet substructure techniques • Soft drop algorithm recursively removes soft, wide angle radiation to better identify tt¯ candidates • Improves searches for new particles

JHEP 1806, 027 (2018)

Joe Osborn (ORNL) 28 Jet Substructure at the LHC

• Jet girth shows transverse momentum weighted width • Indication of how “wide” jets are based on their hadronic constituents • Improves understanding of nonperturbative hadronization dynamics

Joe Osborn (ORNL) JHEP 1810, 139 (2018) 29 Central vs. Forward Jets

0.5 ch ATLAS s = 13 TeV, 33 fb-1 1000 < Jet p / GeV < 1200 0.4 T ) dN / dn

jet Extracted Quark-like Data Extracted Gluon-like Data • Leverage diﬀerent rapidity regions (1/N 0.3 Quarks Pythia 8.186 A14 to extract quark-like and gluon-like Gluons Pythia 8.186 A14 data 0.2 • Investigate radiation pattern diﬀerences between light quarks and 0.1 gluons

0 0 20 40 60

Phys. Rev. D 100, 052011 (2019) nch

Joe Osborn (ORNL) 30 • Hadronization dynamics • Jet properties

• Z+jet is predominantly sensitive to light quark jets • Nearly all other hadronization studies at LHC measure inclusive jets, which are sensitive to predominantly gluon jets • Opportunity to study light quark vs. gluon:

Z+jet

• Why Z+jet?

Joe Osborn (ORNL) 31 • Hadronization dynamics • Jet properties

• Nearly all other hadronization studies at LHC measure inclusive jets, which are sensitive to predominantly gluon jets • Opportunity to study light quark vs. gluon:

Z+jet

• Why Z+jet? 1 PYTHIA 8.2 → • Z+jet is predominantly sensitive to 0.9 qg Z q s = 8 TeV qq→Z g light quark jets 0.8 Forward Z+jet 0.7 0.6

Partonic Fraction 0.5 0.4 0.3 0.2 0.1 0 0 10 20 30 40 50 60 70 80 90 100 pZ [GeV] T

Joe Osborn (ORNL) 31 • Hadronization dynamics • Jet properties

• Opportunity to study light quark vs. gluon:

Z+jet

• Why Z+jet? 1 PYTHIA 8.2 • Z+jet is predominantly sensitive to 0.9 qq→qq s = 8 TeV gg→gg light quark jets 0.8 Midrapidity inclusive jet → 0.7 qg qg • Nearly all other hadronization 0.6

studies at LHC measure inclusive Partonic Fraction 0.5 jets, which are sensitive to 0.4 0.3 predominantly gluon jets 0.2 0.1 0 20 30 40 50 60 70 80 90 100 pjet [GeV] T

Joe Osborn (ORNL) 31 Z+jet

• Why Z+jet? 1 PYTHIA 8.2 → • Z+jet is predominantly sensitive to 0.9 qg Z q s = 8 TeV qq→Z g light quark jets 0.8 Forward Z+jet 0.7 • Nearly all other hadronization 0.6

studies at LHC measure inclusive Partonic Fraction 0.5 jets, which are sensitive to 0.4 0.3 predominantly gluon jets 0.2 • Opportunity to study light quark vs. 0.1 0 gluon: 0 10 20 30 40 50 60 70 80 90 100 pZ [GeV] • Hadronization dynamics T • Jet properties

Joe Osborn (ORNL) 31 Observables

• Measure hadronization observables in two dimensions • Longitudinal momentum fraction z

• Transverse momentum jT • Radial proﬁle r (transverse) Z 0, jet... • Reminder - each of these observables is for a single hadron within the jet pjet · ph trig assoc z = p ·pT 2 • x deﬁned as T |pjet | E trig 2 |pT |

|ph × pjet | jT = |pjet | q 2 2 r = (φh − φjet ) + (yh − yjet ) Joe Osborn (ORNL) 32