1 / 7

Systematics of Extra Jets in ttbar Events: Analysis and Measurements at DØ

This report outlines the approach taken by DØ to analyze extra jets in ttbar events, specifically within the l+jets channel. We focus on events containing exactly four jets and leverage those with four or more jets to assess Monte Carlo simulations against our measurements. The paper discusses the challenges of defining measurable quantities that are independent of the experiment while providing a methodology to compare data with MC predictions using R ratios. We present our findings and adjustments made to MC parameters to align with observed data, detailing various factors affecting top mass measurements.

dorjan
Download Presentation

Systematics of Extra Jets in ttbar Events: Analysis and Measurements at DØ

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Extra jets in ttbar events Regina Demina University of Rochester 6/27/07

  2. Systematics due to extra jets • DØ’s approach – measure it on ttbar events • In top mass analysis (in l+jets channel) we select events with four and only four jets • We use events with four or more jets to verify our Monte Carlo in how well does it model extra jets • We vary MC parameter to reproduce the data number for the fraction of events that have extra jets in them • It was easier to do in the “pre-matching” era • We varied the fraction of ttj events • Cannot do this anymore

  3. What to measure? • It is difficult to define a measurable quantity that is experiment independent • It is possible to compare data with specific detector MC • Can define • R=N(ttbar +0 jets)/N(ttbar + 1 or more jets) • Measure in ttbar l+jets data • Compare to MC • PYTHIA • ALPGEN tt+0lp, +1lp, +2lp

  4. R=N(j=4)/N(j>4) • The result from l+jets data R=1.71±0.25 Ntags

  5. ALPGEN MC • Divide tt+0lp(excl), tt+1lp(excl), tt+2lp(incl) into l+3particle jets, l+4particle jets, and l+5 or more particle jets Vary the fraction of l+5 particle jets to get the right R R(3pj +4pj) =1.33 R(5pj) =1.56 In data between 1.46 and 1.96

  6. Data to MC comparison Fraction of l+5pj should be varied from -50% of the nominal weight to using 100% of l+5pj.

  7. How to assess systematics on Mt • Compare top mass from 3,4,5 pj and vary within suggested uncertainty to check the effect on top mass • Next look at kinematics of the extra jet • Ej, etaj, DR(j-bjet), DR(j-light jet)

More Related