Paper page for 3D jet substructure measurements in pp collisions at 200 GeV from the Run12 dataset

PA : 
Monika Robotkova, Georgi Ponimatkin and Jana Bielchikova - NPI Prague
Raghav Kunnawalkam Elayavalli - Yale and BNL (now Vanderbilt)
Helen Caines - Yale
Joern Putschke - Wayne State

PRL Title : First measurements of variation of the splitting kinematics within the jet clustering tree in pp collisions

PRL Abstract : Jets serve as the experimental proxy for hard scattered quarks and gluons in high energy colliders where they copiously produced. We present the first fully corrected, multi-dimensional measurements of the splitting dynamics within jets in $pp$ collisions at $\sqrt{s} = 200$ GeV with STAR. Correlations between the SoftDrop groomed splitting fraction $z_{\rm{g}}$, and the groomed jet radius $R_{\rm{g}}$ at the leading hard splitting for varying jet momenta and resolution parameters showcase varying jet shower topologies. We extend beyond the first split in the jet shower and present the $z_{g}$ and $R_{g}$ at the first, second and third splits along the hard branch for various jet and initiator prong momenta. These measurements signify a transition of the splitting kinematics from perturbative to non-perturbative like splittings as we travel along the jet shower  


PRL Conclusions : In this letter, we have presented for the first time two sets of differential measurements of the substructure of jets produced in pp collisions at sqrts=200 GeV with the STAR experiment. We showed an inherent correlation between the opening angle and momentum fraction for the first hardest SoftDrop branching in jet, where wide angle splittings are significantly asymmetric in their momentum sharing whereas collinear emissions have greater momentum sharing on average. These correspond to an experimental observation of perturbative-QCD like splittings in soft radiation at wide angles in contrast with hard collinear splittings where one expects a large dominance of non-perturbative effects that alter the shape of the splitting kinematics. We also observed a similar effect along the jet clustering tree where the mean momentum fractions of the first, second and third splits increases consecutively as a result of their emission phase-space being reduced as we follow the harder branch in the jet clustering tree. Both sets of differential measurements show a weak dependence on the jet pT and resolution parameters leading to the conclusion that tagging a jet based on a specific shower topology requires a simultaneous handle on both the momentum and angular substructure scales. These measurements are a first step in highlighting the transition of the energy scales within a jet from hard pQCD to soft npQCD and finally hadronization and promises further exploration of jet topology tagging and QGP tomography in heavy ion collisions.

PRD Title : Systematic exploration of a dynamically evolving jet shower via multi-differential measurements in pp collisions at RHIC

PRD Abstract : Jets are collimated sprays of hadrons and serve as an experimental tool for studying the dynamics of quarks and gluons in relativistic hadron colliders. Differential measurements of jet structure enable a systematic exploration of the parton shower evolution starting from the perturbative QCD description of DGLAP splitting functions and ending with non-perturbative parts of the shower and finally hadronization mechanisms. Following previously published measurements of the SoftDrop splitting observables, we present the first fully corrected correlations between jet substructure observables for jet varying transverse momenta and resolution parameters in $pp$ collisions at $\sqrt{s} = 200$ GeV with the STAR detector. These substructure observables characterize the momentum scale in the splits such as the groomed splitting fraction $z_{\rm{g}}$, splitting scale $k_{\rm{T}}$, modified mass drop $\mu$ and we study their evolution with respect to the the groomed jet radius $R_{\rm{g}}$, representing an angular scale at the first split. To quantify the evolution of the splitting kinematics along the jet shower, we present an experimental measurement of the $z_{g}$ and $R_{g}$ at the first, second and third splittings along the harder branch differentially as a function of the jet and initiator prong transverse momenta for varying jet resolution parameters. Both sets of 3-D substructure measurements point to a strong dependence on the angular phase-space available for radiation with a weak dependence on the jet momentum and resolution parameters.


PRD Conclusions : We presented the first set of differential jet substructure measurements at p+p collisions at RHIC. The measurements are fully corrected for detector effects via a 2+1 D unfolding which is employed for the first time at STAR involving both a Bayesian method and ensemble correction for the jet spectra. For the splitting observables at the first split, we observe a strong dependence of the momentum fraction (z_{g}) and splitting scale (k_{T}) on the groomed jet opening angle (R_{g}) and weak dependence on pT,jet, which allows us to isolate soft splits by selecting wide angle splits. The mass drop observable on the other hand shows a weaker dependence on the R_{g} which highlights the impact of hadronization mechanisms to this observable. We also presented the fully corrected iterative SoftDrop z_{g} and R_{g} distributions for the first, second and third splits along the jet clustering tree. These measurements are presented as a function of both the jet p_{T} and the initiator prong p_{T}. With the initiator prong p_{T}, we are able to directly compare splittings at a fixed momentum scale of the mother whereas the overall jet energy scale can be varied. We observe a significant modification of the shape of z_{g} and R_{g} as we travel along the jet shower from the first to the third splits due to a constriction of the available phase space for radiations. This is the exact same observation seen in the correlation between z_{g} and R_{g} at the first splits as the such an evolution can be connected to the jet's virtuality and its subsequent evolution from hard scattering scale ($Q^{2}$) to the hadronization scale ($\Lambda_{\rm{QCD}}$). The fully corrected data are compared to leading order MC event generators which showcase an overall qualitative agreement with the data albeit slight differences at the first split which are reduced for second and third splits. These data allow for a detailed comparison with MC generators with varying perturbative (parton showers) and non-perturbative (hadronization, multi-parton interactions) implementations to highlight the transition between the two regions of the jet shower. This technique opens up the exciting possibility of space-time tomography in Au+Au collisions and enables differential measurements of jet energy loss for specific substructure.

JetCorr PWGC paper preview request presentation : from Monika - https://drupal.star.bnl.gov/STAR/system/files/HP_meeting_6_16_v3.pdf

PWGC paper preview presentation : TBD

GPC members :

Analysis Code :

Analysis note :
1. Raghav - iterative softdrop analysis note - pdf
2. Monika - 3D correlations at the first split - pdf
Analysis details :
datasets, event selection and jet cuts - https://drupal.star.bnl.gov/STAR/blog/elayavalli/run12-pp-analysis

Preliminary Results :
Both sets of final unfolded measurements were first shown at DIS 2021 by
Monika https://drupal.star.bnl.gov/STAR/blog/robotmon/differential-measurements-jet-sub-structure-observables-and-their-correlation-pp-colli and
Raghav https://drupal.star.bnl.gov/STAR/blog/elayavalli/run12-iterative-splitting-fully-unfolded-preliminary-figures

Public Presentations On Behalf of STAR Collaboration: 
Monika DIS 21 - https://indico.bnl.gov/event/9726/contributions/46219/
Raghav DIS 21 - https://indico.bnl.gov/event/9726/contributions/46218/
Raghav BOOST 21 - https://indico.cern.ch/event/1037559/contributions/4440988/ 
Monika ICNFP 21 - https://indico.cern.ch/event/1025480/contributions/4456972/
Raghav Jets and 3D Imaging 21 - https://indico.bnl.gov/event/10555/contributions/54713/

Public Proceedings :
Monika DIS -
Monika ICNFP - 
Raghav DIS - https://arxiv.org/abs/2107.14557

JetCorr Presentations : 
Raghav
1. March 2021 collaboration meeting iterative splitting systematics - https://drupal.star.bnl.gov/STAR/system/files/ppRun12_iterative_substructure_systematics_update_2March2021_v0.pdf
2. 3D correction procedure and systematics study - https://drupal.star.bnl.gov/STAR/system/files/jetcorr_pp_iterative_substructure_analysis_update_raghav_15Oct2020_v0.pdf
3. Sept 2020 Collaboration meeting procedure updates - https://drupal.star.bnl.gov/STAR/system/files/STAR_Collab_pp_iterative_substructure_analysis_update_raghav_15Sept2020_v0.pdf
4. Iterative analysis first look at unfolding data - https://drupal.star.bnl.gov/STAR/system/files/pp_iterative_jetsubstructure_raghav_31March2019_v1.pdf
5. Matching metric and first look at closure - https://drupal.star.bnl.gov/STAR/system/files/jetcorr_pp_iterative_substructure_analysis_update_raghav_9dec2019_v0.pdf
Monika
1. Collaboration meeting -
2. 3D unfolding correction and systematics - https://drupal.star.bnl.gov/STAR/system/files/colab_meeting_030521_Robotkova.pdf
3. observables and first look - https://drupal.star.bnl.gov/STAR/system/files/jetcorr_Robotkova.pdf