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.