In CMS, my focus was on EWK precision measurements associated with single vector boson production (W, Z/Drell-Yan) in the dimuon channel in order to improve the understanding of the SM. The Drell-Yan differential cross section measurement requires understanding the performance of the CMS detector over the full mass range from 15 GeV to 1500 GeV. I have led the Drell-Yan working group, which consists of more than twenty physicists since 2010. I performed a differential cross section measurement (dσ/dM, where M is the dimuon invariant mass) with 36 /pb data collected in 2010 [3]. I have extended the measurement with the more than 100 times larger dataset collected in 2011 (5/fb) and 2012 (20/fb). We measured the double differential cross section measurement (d2σ/dM/dY) where Y is the absolute dimuon rapidity [4] [5]. This provides direct constraints for the PDFs in the low and high dimuon invariant mass regions. Previously the PDF sets have used fixed target data and this will be the first high precision collider data leading to significant improvements with PDFs. PDF is dominant systematic uncertainty for many physics analyses, hence its improvement is one of the highest priority physics research topics at the LHC. In parallel I was involved in two other physics analyses. The dimuon spectrum for new physics was analyzed, in particular for a new heavy gauge boson, Z´, which is predicted by many new physics models like grand unified theories and the Randall-Sundrum model of extra dimensions. I have contributed on understanding backgrounds in the analysis [6]. In addition, I have produced Z´ projection at 14 TeV with various future LHC dataset scenarios (300, 1000 and 3000 /fb) and it will be included in the 2013 Snowmass white paper [7].
I have been selected to have many leadership responsibilities in the CMS collaboration and these have been executed very successfully. I started my leadership in a small team, and was promoted step by step to the larger and higher level groups. My first responsibility in physics research was the trigger efficiency measurement and coordination of the muon trigger team in the Vector Boson Task Force (VBTF) for the 2010 ICHEP conference. CMS had the first 7 TeV dataset with 3/pb and the VBTF proposed to measure the inclusive W and Z cross section as the first 7 TeV result in competition with other experiments in the LHC [8]. After this successful leading role in the VBTF, I was selected to manage the Drell-Yan differential cross section measurement, as a co-convener and I have coordinated this group very productively. This group has produced 3 journal papers and many public CMS notes. Thanks to these past productive coordination efforts, I became a subgroup co-convener in the SM Physics (SMP) group. In this group, I coordinated all EWK analyses of associated single vector boson (W or Z/Drell-Yan) production, including inclusive W and Z cross section, Drell-Yan differential cross section, W charge asymmetry, forward-backward asymmetry of Drell-Yan process, etc. I have coordinated many journal publications and public CMS notes, and many analyses were underway in the pipeline for public results when I stepped down. After the position, I was selected as the co-convener of the Luminosity POG in 2014. A responsibility of the Luminosity POG is to secure flawless determination of the absolute luminosity in CMS, both real-time and an overall normalization to physics analyses. Currently I am an coordinator of muon object activity in the SMP group.
For the detector research, I have focused on various parts of the online and offline software. In particular I have made major contributions to, and I am an expert in, the muon trigger algorithm and trigger online monitoring system. Due to the amount of data and limitations of the Data Acquisition system at the CMS detector, the trigger is very challenging and requires continuous development as the luminosity increases. The CMS trigger system consists of two parts: Level-1 (L1) based on custom electronics and the High-Level Trigger (HLT) relying upon software algorithms. I am an expert and a developer of the muon HLT, in particular the muon Level-3 (L3) algorithm which uses both information from the tracker and the muon detectors. The muon L3 algorithm I developed, the so-called “Cascade” is the sequential combination of three different muon L3 algorithms. The Cascade significantly improved the performance compared to each single L3 algorithm without significantly increasing the decision time. From the beginning of Run I (2010-2012) data taking in 2010, it is the default muon HLT algorithm in CMS and used in all data. Due to the critical nature of the trigger system in real time an online monitoring system has been established and is an essential element of trigger operation which is monitored and reported by the central shifters. I developed the entire muon HLT online data quality monitoring (DQM) software, which was the standard procedures for HLT data certification and HLT menu validation in the Trigger Performance Group during Run I. Moreover, I took a leadership role in the muon HLT online DQM development and my performance in that activity led to being the co-coordinator to lead the entire activities of the trigger online DQM group. As a co-convener, I have successfully coordinated the monitoring of trigger online operation from 2009 to 2011 for all data taking. In this role I was responsible for providing HLT certification, which is essential in selecting sub-datasets for physics analyses [9] [10]. During LHC long shutdown I (2013-2014) led the upgrade of the L3 muon trigger for Run II operation from 2015. In RunII, LHC data is under higher pile-up condition and the improvement of the L3 muon trigger was essential to be robust the performance under the high pile-up condition. The L3 muon trigger showed the performance in 2015, expected from the upgrade project.
[3] CMS Collaboration, “Measurements of the Drell-Yan Cross Sections in pp Collisions at sqrt(s) = 7 TeV”, JHEP 10 (2011) 007
[4] CMS Collaboration, “Measurement of the differential and double-differential Drell-Yan cross section in proton-proton collisions at sqrt(s) = 7 TeV", JHEP 12 (2013) 030
[5] CMS Collaboration, “Measurement of differential and double-differential Drell-Yan cross sections in proton-proton collisions at sqrt(s) = 8 TeV", EPJC 75 (2015) 147
[6] CMS Collaboration, “Search for physics beyond the standard model in dilepton mass spectra in proton-proton collisions at sqrt(s) = 8 TeV", JHEP 04 (2015) 025
[7] CMS Collaboration, “Projected Performance of an Upgraded CMS Detector at the LHC and HL-LHC: Contribution to the Snowmass Process", CMS Note-13-002 (2013), arXiv:1307.7315
[8] CMS Collaboration, "Measurements of Inclusive W and Z Cross Sections in pp Collisions at sqrt(s) = 7 TeV”, JHEP 01 (2011) 080
[9] CMS Collaboration, “Performance of CMS Muon Reconstruction in Cosmic-Ray Events”, J.Instrum. 5 (2010) T03022
[10] CMS Collaboration, “Commissioning of the CMS High-Level Trigger with Cosmic Rays”, J. Instrum. 5 (2010) T03005