Monika Mittal Shanghai Jiao Tong University, China

Transcription

1 + Interview for Chung-Yao Chao Fellowship 2017 Shanghai Jiao Tong University, China 25th April 2017

2 + About myself 2 Ø Working as post-doc fellow at SJTU, China ü ATLAS experiment at Large Hadron Collider ü Supervisor: Prof. Jun Guo, Prof. Haijun Yang April 2017 onwards ü Measurement of differential production cross-section and search for anomalous quartic gauge coupling by studying the vector boson scattering in ZZ(à 4l)+2j final state using pp collision data of ATLAS experiment. Ø PhD in experimental high energy physics Dec 2010-Mar 2016 ü CMS experiment of Large Hadron Collider ü Panjab University, Chandigarh, India ü Thesis supervisor: Prof. Manjit Kaur (PU) and Prof. Shashi Dugad (TIFR) ü Thesis Title: Study of pure electroweak production production Z [à µµ] boson in association with two jets [at COM = 8 TeV] ü Projects: v Cross-section measurement of EW production of Z boson v HCAL Outer (HO) upgrade project. v Cross-section measurement of Zà ee process at COM energy 13 TeV. Ø Post-graduate (honors school Physics) with distinction from Panjab University

3 + Publications 3

4 Eur. Phys. J. C 75 (2015) 66 + Pure EW production of Z boson 4 Ø Cross-section measurement for the pure electroweak production of Zà µµ at LHC using CMS detector at 8 TeV. Ø Key signature ü Di-jet system with large rapidity gap and large invariant mass. ü Color exchange suppressed between the two jets: low hadronic activity. Ø These events provide an ideal testing ground for the study of the VBF processes including the search for the Higgs boson and searches beyond SM. Ø Very rare processes ü Possible with high center of mass energy and luminosity provided by LHC. Ø Lowest cross-section measurement at 8 TeV. Ø Contribution ü Framework development for 8 TeV ü Main analyzer for the analysis. ü Event selection optimization ü background estimate and its modeling ü Compared cut based and MVA based approaches. ü Data unfolding, systematics uncertainties and cross section measurement.

5 + Continued 5 Ø For the measurement of cross-section two approaches are followed: ü Cut Based Method v Variables are optimized to achieve maximal sensitivity i.e. maximizing the quantity signal/background ü MVA: Boosted decision tree σ = 174 ± 15 (stat) ± 40 (syst) fb = 174 ± 42 (total) fb Study of charged hadronic activity:

6 + Ø CMS PAS SMP Differential Drell-Yan cross section DYà ee differential cross-section measurement at 13 TeV using pp data from CMS experiment.. ü ü ü Ø Provide test of the Standard Model Effective input for PDF constraints Important for various LHC physics searches, pose dominating background. Contribution ü Framework development for 13 TeV analysis with start of Run 2. ü Event selection optimization and N-1 variable studies. ü Electron scale and smearing corrections. ü Data unfolding and peak cross-section measurement.

7 + HCAL Outer (HO) detector 7 Ø Results made from physic analysis make sense and lead to new discoveries if and only if the data collected by the detector is of high quality Ø Acts as a tail catcher for the barrel calorimeter Ø Pose additional interaction length in central region Ø Improves jet energy resolution Hcal Outer Ø HO initially used Hybrid Photo Diodes (HPDs) to detect the scintillation light but found to be they are not optimal Ø CMS replaced the HPDs with Silicon Photo-Multiplier (SiPM).

8 + Contribution towards HO 8 Ø Test beam participation: ü Setup and data analysis ü Troubleshooting ü Measurement of scale factor, calibration constant and linearity of response ü Saturation of SiPM using Light Mixers CMS DN-2015/015 Ø The expected performance of HO (during Run 2) is ensured by studying the effects of saturation of SiPM and qadc due to very high p T jets ü HO in all rings would sustain at 13 TeV without significant effects of saturation when operated at the gain of 6 fc/p.e. Ø Participated in quality control and burn-in of HO hardware, the extraction and installation of readout modules in the CMS detector for HO YB-1 and HO-YB-2. Ø Installation of HO and online validation of the detector lead to proper functioning. ü Checking all the fiber links. Ø Commissioning of new HO detector using the Cosmic data. CMS DN-2014/019

9 + Achievements 9 Ø CMS Achievement award 2014 ü Awarded by CMS Collaboration, Geneva. Ø Best speaker award ü Awarded at CHASCON Conference at Chandigarh in 2014 Ø Best speaker award ü Awarded at IX Experimental High Energy Physics School, IIT Madras 2013 Ø Senior/Junior Research Fellowship ü Awarded by University Grant Commission, Delhi Ø Qualified National Eligibility Test for lectureship in India

10 + Future Plan 10 Ø Vector boson scattering (with heavy bosons) is an important process in the SM. ü Rare process ß à benchmark SM measurement accessible only at LHC. ü Involving Higgs boson interactions ß à Understanding the nature of EWSB. ü Involving quartic gauge coupling ß à Search for anomalous interactions in the EWK sector. Ø I will mainly focus on the differential production cross-section of ZZ(à 4l) + 2j final state which is not explored yet due to its lower production cross-section. Ø Fully reconstructed events ß à golden channel for discovery ü Challenging due to high QCD backgrounds. Ø Goal would be to perform the complete analysis, involving MC truth study of the signal events, signal selection, data-driven background estimate, and limit settings. Ø Long term: using pp collision data collected at ATLAS detector at 13 TeV ü The results can be re-interpreted for the evidence of the EWK ZZjj production and possibility to measure its properties. Ø Study the performance of Monitored Drift tubes in additional muon stations BME and BOE that close the gaps in the middle and outer layers projectively.

11 + Backup slides 11

12 + Contribution towards HO 12 Ø Test beam setup and analysis, changing the detector configuration as per run plan and trouble shooting HO detector. Ø Measurement of scale factor and calibration constants. Ø Study of linearity of HB+HO response for hadron showers. Ø Saturation of SiPM using light mixers was studied for HO. Ø The result were accepted by CMS HCAL Collaboration and For Run II in CMS SiPM in HO were installed with ü No light mixer for R1 and R2 ü Notre Dame light mixer for R0

13 + Backgrounds 13 DY+Jets Diboson TTJets à Major contribution from DY +Jets à Relatively Small contribution from Di-bosons and TTJets. à Negligible contribution from QCD

14 + Topological variables 14 M jj, y*, and R pt hard were used further and optimised to have maximum signal significance.

15 + SiPM Dynamic Range 15 ü The effective surface area of SiPM is 3 x 3 mm 2 and consist of 3600 pixels ü The area of each such pixel is 50 x50 µm 2 out of which only the center area is active 35 x 35 µm 2. ü The number of pixel fires determines the dynamic range. Each photon should hit a separate pixel. ü Number of incident photon is small, probability of more than one photon falling on the same pixel is small ü With increasing number of photons, number of pixel tends to saturate

16 + Need/Study of Light Mixer 16 Ø Ring 0 fibre bundle extends over SiPM edge ( due to 2 layers) ü inhomogeneous response Ø Direct coupling of ODU fibre bundle results in dark areas ü reduces effective number of pixel Light Mixer