And Strange and Charm Baryons in Pp and Pbpb with CMS

0 + 퐵푠 , 퐷푠 , and strange and charm baryons in pp and PbPb with CMS

Zhaozhong Shi on behalf of the CMS Collaboration

Massachusetts Institute of Technology

Heavy-Flavour Hadronization in pp and Heavy Ion Collisions at the LHC

03/03/2020

Zhaozhong Shi CERN HF Hadronization Workshop 1 Heavy Quark Production in High Energy QCD

➡ Heavy quarks are predominately produced through gluon fusion 푔푔 → 푄푄ത at the LHC

➡ Heavy quarks hadronize in vacuum via the fragmentation mechanism ➡ The hadronization of partons in general is non-perturbative

Zhaozhong Shi CERN HF Hadronization Workshop 2 Heavy Quark Hadronization in pp and pA Collisions • In high energy pp collisions ➡ Test the calculations of perturbative QCD ➡ Used as a baseline reference for other collisions systems

• In high energy pA collisions ➡ Understand the initial state cold nuclear matter (for instance, nuclear shadowing) effect on final state hadron spectra ➡ Test the validity of QCD factorization theorem in pA collisions

• Phenomenological models for hadronization ➡ Lund String Model ➡ Statistical Hadronization Model ➡ Quark Coalescence Model

Zhaozhong Shi CERN HF Hadronization Workshop 3 Heavy Quark Hadronization in AA Collisions • In high energy AA collisions ➡ Hot and dense strongly interacting medium with color degree of freedom named Quark- Gluon Plasma (QGP) is created ➡ Heavy quark produced via hard scattering in the initial stage of the collisions, calculable in pQCD with NPDF information ➡ Heavy quark traverse and lose a significant fraction of their energies through the medium before hadronization • In-medium energy loss mechanism of heavy quarks Collisional Radiative

• Relevant physics ➡ Flavor dependence of energy loss ➡ Dead cone effect [1] [1] Phys. Lett. B 519 (2001) 199

Zhaozhong Shi CERN HF Hadronization Workshop 4 Effects of the QGP Medium on the Hadronization of Partons • In the thermally and chemically equilibrated QGP medium ➡ Temperature > strange quark mass ➡ Strange quark production is enhanced via 푔푔 → 푠푠ҧ ➡ Expected strangeness enhancement in charm and bottom hadronization via the recombination mechanism [2] ➡ The baryon to meson ratio is expected to enhance in PbPb collisions compared to pp due to the quark coalescence effect

• Goal: Understand the effects of the QGP medium on the hadronization of heavy quarks

[2] Phys. Rev. C79 (2009) 044905

Zhaozhong Shi CERN HF Hadronization Workshop 5 Experimental Observables for Heavy Quark Hadronization • Differential cross sections ➡ Directly measured by experiments ➡ Test the calculations of perturbative QCD in pp collisions

• Nuclear modification factor ➡ Understand the initial state effects on the hadron spectra in pA collisions ➡ Understand the effect of the QGP medium on the spectra in AA collisions - Energy loss - Recombination and fragmentation ➡ Constrain the theoretical model calculations

• Ratios of baryon-to-meson and strange-to-nonstrange spectra in different collision systems ➡ Remove energy loss of heavy quarks effect ➡ Cancellation of some systematic uncertainties ➡ Sensitive to hadronization mechanism at low 푝푇

Zhaozhong Shi CERN HF Hadronization Workshop 6 The CMS Detector

• Excellent vertexing and tracking capabilities • Dedicated triggers for open heavy flavor physics • No hadronic PID necessary for particle reconstructions

Zhaozhong Shi CERN HF Hadronization Workshop 7 The CMS Datasets and Trigger System Datasets • LHC Run II 2015 pp, 2016 pPb at 5.02 TeV, Run I PbPb at 2.76 TeV, and Run II PbPb at 5.02 TeV • Minimum biased sample for 푝푇 < 20 GeV/c and triggered samples for 푝푇 > 20 GeV/c • Dedicated HLT D-meson filters to enhance the statistics of very high 푝푇 D mesons • High multiplicity trigger to select high multiplicity pPb events comparable to peripheral PbPb

Triggering system Hardware Level 1 Track Selections 푫ퟎ Selections Jet Trigger Selections in Software Triggers

0 Level 1 (L1) jet algorithm Track seed 푝푇 cut applied: 퐷 online reconstruction with online background 푝푇 > 2 GeV/c for pp/pPb Loose selections based 0 subtraction 푝푇 > 8 GeV/c for PbPb on 퐷 vertex displacement Zhaozhong Shi CERN HF Hadronization Workshop 8 Light Flavor Hadron Reconstructions 푽ퟎ Mesons 0 + − 퐾푠 (푑푠ҧ − 푠푑ҧ) → π π Branching ratio = 0.692 Λ0(푢푑푠) → π−푝+ Branching ratio = 0.639 푉0 particles are reconstructed by combining a pair of opposite charged particles

π- Strange Baryons • Topological variables Ξ−(푑푠푠) → Λ0π− Branching ratio = 0.999 applied to optimally - - + π /K p Ω−(푠푠푠) → Λ0퐾− Branching ratio = 0.678 select candidates

0 • No hadronic particle Λ Ξ− and Ω− baryons are reconstructed by - - identification Ξ /Ω combining a charged track with a Λ0 candidate

Phys. Lett. B 768 (2017) 103

Zhaozhong Shi CERN HF Hadronization Workshop 9 Light Flavor Nuclear Modification Factor RpPb

Phys. Lett. B 768 (2017) 103

0 0 • For 푝푇 < 2 GeV/c, the Λ /2퐾푠 ratio decreases as the multiplicity increases. This is consistent to the radial flow interpretation in hydrodynamics. 0 0 • For 푝푇 > 2 GeV/c, the Λ /2퐾푠 ratio increases as the multiplicity increases. This is consistent to the recombination effect in hadronization • The uncertainties of Ξ−/Λ0 ratio is too high to draw any conclusion • These results shed light on hydrodynamic like behavior in small systems.

Zhaozhong Shi CERN HF Hadronization Workshop 10 퐷0 푐푢ത Reconstruction and Selections • Primary vertex reconstruction several tracks • 퐷0 candidates (vertex) reconstruction pairing two tracks + kinematic fitter • 퐷0 candidates selection (TMVA Rectangular Cuts) decay topology ➡ Pointing angle (α) < ~0.12 ➡ 3D decay length (d0) significance > ~4 ➡ Secondary vertex probability > ~0.1 ➡ Distance of Closest Approach (DCA) < ~0.008 cm

푫ퟎ → 푲−흅+ channel 푓(푐 → 퐷0)~50% Branching Ratio = 3.93% 푐τ ≃120 μm

Zhaozhong Shi CERN HF Hadronization Workshop 11 Extraction of Prompt Faction from Data • Data-driven way to extract the prompt fraction of 푫ퟎ ➡ Fit the DCA of the data with prompt and non-prompt 퐷0 DCA Monte Carlo templates ➡ Correct the inclusive 퐷0 spectrum with the prompt fractions in pp and PbPb

Phys. Lett. B 782 (2018) 474

Zhaozhong Shi CERN HF Hadronization Workshop 12 퐷0 Invariant Mass Extraction 푫ퟎ invariant mass distributions are fitted by • Double Gaussian (Signal) • 3rd order polynomial (Combinatorial) • Single Gaussian (K-π swapped: candidates with wrong mass assignment) ➡ Not using PID

Phys. Lett. B 782 (2018) 474

Zhaozhong Shi CERN HF Hadronization Workshop 13 Prompt 퐷0 Meson Spectra in pp and PbPb

0 • 퐷 푝푇 spectrum in pp collisions agrees reasonably well with FONLL calculations and is systematically below the GM-VFNS calculations with uncertainties 푑σ 1 푑푁 • 푝푝 > 푃푏푃푏 → charm quarks lose energy in PbPb collisions Phys. Lett. B 782 (2018) 474 푑푝푇 푇퐴퐴 푑푝푇 1 푑푁0−10% 1 푑푁0−100% • 푃푏푃푏 < 푃푏푃푏 → Charm quarks lose more energy in more central collisions 푇퐴퐴 푑푝푇 푇퐴퐴 푑푝푇 Zhaozhong Shi CERN HF Hadronization Workshop 14 + Prompt 퐷푠 푐푠ҧ Reconstruction and Selections + Optimization of 푫풔 Candidate Selections + • 퐷푠 candidates selection (TMVA Rectangular Cuts) decay topology ➡ Pointing angle (α) fixed at < ~0.12 ➡ 3D decay length significance ➡ Secondary vertex probability + + + + − 푫풔 → 흅 흓 → 흅 푲 푲 channel + 푓(푐 → 퐷푠 )~10% Branching Ratio = 2.27% 푐τ ≃150 μm

CMS-PAS-HIN- 18-017

Zhaozhong Shi CERN HF Hadronization Workshop 15 + Prompt 퐷푠 Meson 푝푇 Spectra in pp and PbPb + 0 • Semi-data driven way to obtain the nonprompt fraction for 퐷푠 from the nonprompt 퐷 measurement corrected fragmentation fraction, branching ratio and relative 푝푇 shape according to PYTHIA

CMS-PAS-HIN- 18-017

+ • The 퐷푠 푝푇 spectrum in pp agrees reasonably well with the PYTHIA 8 predictions within + statistical uncertainties at high 푝푇 but PYTHIA 8 fails to predict the 퐷푠 푝푇 spectrum in PbPb + • 퐷푠 푝푇 spectrum in PbPb lies below its spectrum in pp, which is due to the energy loss of charm quark inside the QGP medium

Zhaozhong Shi CERN HF Hadronization Workshop 16 + 0 Prompt 퐷푠 /퐷 Ratios in pp and PbPb + • Precise measurements of prompt 푫풔 and 푫ퟎ mesons productions in both pp above 2 GeV/c and PbPb above 6 GeV/c

• No significant strangeness enhancement at intermediate 푝푇 6 – 40 GeV/c in PbPb + ퟎ compared to pp within 푫풔 /푫 uncertainties

• Both TAMU and PHSD agree reasonably + 0 well with 퐷푠 /퐷 in pp

• PHSD predictions are comparable to + ퟎ the 푫풔 /푫 double ratio CMS-PAS-HIN- T. Song et al., Phys. Rev. C 93 (Mar, 2016) 034906 18-017 M. He and R. Rapp, Phys. Letts .B 795 (2019) 117 – 121

Zhaozhong Shi CERN HF Hadronization Workshop 17 + Prompt Λ푐 푢푑푐 Reconstruction and Selections + Optimization of 휦풄 Candidate Selections + • 훬푐 candidates selection (TMVA Rectangular Cuts) decay topology • Optimization on each 푝푇 bin pp PbPb ➡ 2D Pointing angle (α) ➡ 3D Pointing angle (α) ➡ 2D decay length significance ➡ 3D decay length significance ➡ Vertex probability ➡ Vertex probability ➡ Daughter track 푝푇 ratio ➡ Daughter track 푝푇 ratio

+ + − + 휦풄 → 풑 푲 흅 channel + 푓(푐 → 훬푐 )~10% Branching Ratio = 6.28% 푐τ ≃60 μm

Phys. Lett. B 803 (2020) 135328

Zhaozhong Shi CERN HF Hadronization Workshop 18 + 훬푐 Baryon Spectra in pp and PbPb

Phys. Lett. B 803 (2020) 135328

+ • The 훬푐 푝푇 spectrum in pp collisions agrees reasonably well with the PYTHIA 8 predictions within uncertainties + • 훬푐 푝푇 spectrum in PbPb lies below the pp in the 푝푇 range of 10 – 20 GeV/c, which indicates the energy loss of charm quarks in the QGP medium + • 훬푐 production is more suppressed in the central collisions than the peripheral collisions

Zhaozhong Shi CERN HF Hadronization Workshop 19 + 0 Λ푐 /퐷 Ratio in pp and PbPb Collisions • No significant contribution from quark coalescence effect on charm hadronization + 0 comparing the Λ푐 /퐷 ratio in 푝푇 range of 10 – 20 GeV/c in pp and PbPb collisions + 0 • Λ푐 /퐷 has no significant 푝푇 dependence within uncertainties, which is consistent to the predictions of shape from PYTHIA 8 but with different offset values • PYTHIA 8 with color reconnection agrees with the central values of the experimental data but has a decreasing trend as 푝푇 increases, which not shown from the data • Solid line (include fragmentation and coalescence effects): predict a strong 푝푇 + 0 dependence on Λ푐 /퐷 • Dashed line (include excited charm baryon states beyond PDG): provide reasonable Phys. Lett. B 803 (2020) 135328 description to the pp data for 푝푇 < 10 GeV/c

Zhaozhong Shi CERN HF Hadronization Workshop 20 퐵+ Mesons Decay Chains and Full Reconstructions • 퐵+: via the decay channel 퐵+ → J/ψ퐾+ → μ+μ−퐾+ (Branching Ratio = 1.01×10−3).

Non-prompt J/ψ Decay μ Hadronize • Not using hadronic PID μ B+ • Precise vertexing and tracking b quarks → B mesons K • Statistically enriched and Secondary Vertex dedicated dimuon triggered Primary Vertex cτ = O(500) μm datasets

Phys. Rev. Lett. (2017) 119

Zhaozhong Shi CERN HF Hadronization Workshop 21 + 퐵 푝푇 Spectra in pp and PbPb

• 퐵+ 푝 spectrum in pp collisions is overall consistent 푇 Phys. Rev. Lett. (2017) 119 with the FONLL calculations within uncertainties + • 퐵 푝푇 spectrum in PbPb collisions has similar trend as pp. However, the spectrum lies below the pp collisions at the same 푝푇, which suggests the shift of the spectrum to the left due to the energy loss of beauty quarks in the QGP medium created in PbPb collisions

Zhaozhong Shi CERN HF Hadronization Workshop 22 퐵+ Nuclear Modification Factor • Supression of 푩+ meson production in PbPb collisions → b quarks lose energy in the QGP

• No obvious 풑푻 dependence at 7 – 50 GeV/c

• Consistent with most theoretical predictions at 7 – 50 GeV/c

M. He et al., Phys. Lett. B 735 (2014) 445 M. Djordjevic, Phys. Rev. C 94 (2016) 044908 X. Jiechen et al., JHEP 2 (2016) 169 Phys. Rev. Lett. (2017) 119 W. A. Horowitz, Phys. Rev. D 91 (2015) 085019 P. B. Gossiaux et al, Nucl. Phys., A931 (2014) 581

Zhaozhong Shi CERN HF Hadronization Workshop 23 0 퐵푠 Full Reconstruction Strategies 0 0 + − + − −3 • 퐵푠 : using the decay channel 퐵푠 → 퐽/휓휙 → 휇 휇 퐾 퐾 (Branching Ratio = 1.08×10 ) 0 ∗ 2 0 ➡ 퐵 → 퐽/ψ퐾 rejected with 푚퐾퐾 − 푚휙 < 0.015 GeV/c → No non-prompt 퐵푠 background Non-prompt J/ψ Decay μ QGP • Not using hadronic PID Hadronize μ • Precise vertexing and tracking K B s • b quarks → B mesons Statistically enriched and Secondary Vertex K dedicated dimuon triggered Primary Vertex cτ = O(500) μm datasets

Phys. Letts. B. 796, 168

Zhaozhong Shi CERN HF Hadronization Workshop 24 0 퐵푠 Spectra in pp and PbPb

Phys. Letts. B. 796, 168

0 • 퐵푠 푝푇 differential cross section in pp collisions is overall consistent with the FONLL calculations within uncertainties 0 • 퐵푠 푝푇 spectrum in PbPb collisions has similar trend as pp within uncertainties

Zhaozhong Shi CERN HF Hadronization Workshop 25 0 + Heavy Flavor Beauty Sector: 퐵푠 /퐵 Ratio in pp and Pbpb

ퟎ • Hint of less suppression of 푩풔 mesons compared to 푩+ mesons in PbPb collisions → potentially due to strangeness enhancement and the recombination effect in QGP

• Substantial statistical and systematic ퟎ uncertainties in 푩풔 measurement

Phys. Letts. B. 796, 168 M. He et al., Phys. Lett. B 735 (2014) 445 – 450 X. Jiechen et al., JHEP 2 (2016) 169

Zhaozhong Shi CERN HF Hadronization Workshop 26 0 + Heavy Flavor Beauty Sector: 퐵푠 /퐵 Ratio in pp and Pbpb

• Cancelations of correlated systematic uncertainties of ퟎ + 푩풔 and 푩

ퟎ + • Indication of greater 푩풔 /푩 ratio than unity

M. He et al., Phys. Lett. B 735 (2014) 445 – 450 Phys. Letts. B. 796, 168 X. Jiechen et al., JHEP 2 (2016) 169

Zhaozhong Shi CERN HF Hadronization Workshop 27 Summary I – The Charm Sector

• D-meson 푝푇 spectrum in pp collisions agrees reasonably well with the PYTHIA predictions 0 + + • Suppressions of 퐷 , 퐷푠 , and Λ푐 baryon in PbPb compared to pp are observed • No significant strangeness enhancement at intermediate 푝푇 6 – 40 GeV/c in PbPb compared to + ퟎ pp within 푫풔 /푫 uncertainties

+ • Λ푐 baryon spectrum in pp collisions agrees reasonably well with the PYTHIA predictions + • More suppression for Λ푐 production at the central collisions than the peripheral collisions, + 0 • Λ푐 /퐷 ratio in PbPb is the same pp within for 10 − 20 GeV/c within uncertainties, which suggests no significant contributions from the quark-coalescence effect in this 푝푇 range + 0 • No significant 푝푇 dependence for Λ푐 /퐷 ratio in pp collisions is observed from 5 to 20 GeV/c

Zhaozhong Shi CERN HF Hadronization Workshop 28 Summary II – The Beauty Sector

• B mesons 푝푇 spectra are consistent with FONLL calculations

• Suppressions for B mesons productions in PbPb collisions

• Indication of flavor dependence of parton energy loss

ퟎ • First 푩풔 measurement in PbPb collisions

ퟎ + • Hint of greater 푩풔 /푩 ratio than unity, potentially due strangeness enhancement effect and quark coalescence mechanism

• More precise and differential B mesons measurements with 2017 pp and 2018 PbPb datasets in the future

Zhaozhong Shi CERN HF Hadronization Workshop 29 Thank You for Your Attentions

This MIT group’s work was supported by US DOE-NP and NSF-GRFP

Zhaozhong Shi CERN HF Hadronization Workshop 30 Back Up

Zhaozhong Shi CERN HF Hadronization Wokshop 31 Light Flavor Hadron Spectra

Zhaozhong Shi CERN HF Hadronization Workshop 32