1 / 20

Electron performance and related physics results Paul Bell representing

Electron performance and related physics results Paul Bell representing M. Backes, P. Bell, W. Bell, S. Gadomski, J. Gramling, M. Goulette, C. Mora Herrera, A. Katre, K.Nikolics, E Benhar Noccioli, G. Pásztor, X. Wu Monday June 18 th 2012 Chateau de Bossey. Overview.

weylin
Download Presentation

Electron performance and related physics results Paul Bell representing

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. Electron performance and related physics results Paul Bell representing M. Backes, P. Bell, W. Bell, S. Gadomski, J. Gramling, M. Goulette, C. Mora Herrera, A. Katre, K.Nikolics, E Benhar Noccioli, G. Pásztor, X. Wu Monday June 18th 2012 Chateau de Bossey

  2. Overview • Electron performance studies • Electron related physics measurements: • - Standard Model measurements • Future plans: • - Higgs searches • - Diboson physics • - Tribosons, anomalous couplings and the • ATLAS Forward Physics (AFP) project Understanding ATLAS Measuring the Standard Model Finding the missing pieces…

  3. Part 1: Electron performance

  4. Electrons in ATLAS: A one page introduction EM calorimetry Inner Detector Tracker Electrons reconstructed by matching tracks to calorimeter energy deposits and identified by cutting on track and shower properties

  5. Electron performance G. Pásztor, E. Benhar Noccioli, K. Nikolics, E. Berglund, V. Dao, J. Navarro, A. Robichaud Véronneau Recent Geneva contributions: E. Niccioli improves efficiency measurement at low ET using J/y events (for use in Higgs to 4-leptons analysis, see later) K. Nikolics extends the data measurement to high ET range beyond 50 GeV Methods documented in 2010 performance paper edited by G. Pásztor, precision and performance continually improves Precise determination of electron performance (for electrons with energy from few GeV to few TeV) essential for SM measurements and searches for new physics Electron performance = - Precision of energy and momentum measurement - Efficiency of electron triggering, reconstruction and identification

  6. Bremsstrahlung Track Refitting G. Pásztor, E. Benhar Noccioli Calo electron’s original path Photon emission reconstructed path Electrons in Inner Detector suffer significant energy loss via Bremsstrahlung (> 2 radiation lengths of material at some h) Spoils 4 momentum measurement and determination of track parameters Geneva group contributed to validation of method to “refit” tracks to compensate for Brem effects => Better track cluster matching (=higher efficiency), improved four momentum calculation, more precise track parameters. Biggest improvements at low pT WITHOUT REFITTING WITH REFITTING

  7. E/Gamma Trigger P Bell, A. Katre, J. Gramling, V. Dao L1 Hardware (Calorimeter) Output < 60kHz L2 software (custom algos) Output < 5kHz EF software (as offline) Output < 400Hz (30% e/g) Electron and photon triggers are used to record the data for many analyses, from SM to Higgs to SUSY P. B deputy convener of trigger E/g group since 1st March: responsible for developing, maintaining and monitoring (A.Katre, J.Gramling) electron & photon triggers For 2012: a major reoptimisation of selection cuts in order to remain efficient at high pile-up

  8. Part 2: Electron-related (Standard Model) physics measurements

  9. Inclusive electron cross-section M. Backes, P. Bell, S. Gadomski, C. Mora-Herrara, G. Pásztor,X. Wu • - At low pT electron production • is dominated by heavy flavour (HF) • production and decay • - Goal of analysis was to extract • this HF signal from QCD fakes • and photon conversions and measure its • cross section as function of pT • Electron measurement compared to results • in muon channel and to predictions of MC • generators and theoretical calculations • Good agreement with calculations at next • to leading log (NLL) level in pQCD • Importance of NLL terms can be seen • Published summer 2011: • part of theses of M. Backes & C. Mora-Herrara

  10. Vector bosons 1/2 W. Bell, E. Berglund, J. Garcia Navarro Take ratio: experimental uncertainties cancel Precision testing ground for SM and QCD: cross-sections measured to few % precision, pQCD calculations available at NNLO Several analyses with 2010 data set: Inclusive measurements: fiducial, differential & total cross sections Production with associated jets: fiducial & differential cross-sections Major contributions to electron efficiencies

  11. Vector bosons 2/2 W. Bell, E. Berglund, J. Garcia Navarro • - Measure ratio of cross sections • R = s (W + 1 jet) / s (Z + 1 jet) • as function of jet pT • Represents a higher precision test • of SM than individual V + jet • measurements due to cancellation • of experimental and theoretical • uncertainties

  12. High-Mass Drell-Yan cross-section measurement P. Bell, S. Gadomski, G. Pásztor, M. Goulette, K. Nikolics, X. Wu Opposite sign dielectron pairs are produced across a wide range of invariant mass (Mee) by the Drell Yan process pp → Z/g* → e+e- Cross-section at the Z peak (66 < Mee < 116 GeV) measured in several analyses already Current analysis measures cross section as function of Meeat high mass: 116 – 1500 GeV Measurement based on full 2011 dataset (5fb-1), a collaboration between Geneva, Mainz and Liverpool (~10 people) Geneva group: coordination, background estimation, electron efficiencies at high pT, unfolding Paper currently in approval process NB: shares many experimental similarities with search for a resonance at high Mee (the Z’)…

  13. Z’ search P. Bell, S. Gadomski, G. Pásztor, M. Goulette, K. Nikolics, X. Wu • Geneva methods for QCD background estimation used also in the Z’ searches • Published with 1fb-1 and 5fb-1 of data • No new physics observed: present upper • limit on cross-section as a function of Z’ mass • This in turn gives a lower limit on Z’ mass Observed (expected) 95% CL lower mass limits (TeV)

  14. Part 3: Future plans: Higgs or no Higgs?

  15. Higgs search in H → ZZ* → 4 leptons channel G. Pásztor, E. Benhar Noccioli, T. Bernasconi • Sensitive to H over wide mass range: • 110 – 600 GeV • Golden channel due to high mass • resolution but small branching fraction • Look for signal in 4-lepton invariant mass • distribution • Geneva recently joined the effort: • Maximising performance for low pT • electrons (Brem track refitting, efficiency • studies at low pT) • Methods for estimating background • contribution in electron channel

  16. Higgs search in H → ZZ* → 4 leptons channel G. Pásztor, E. Benhar Noccioli, T. Bernasconi 2011 results: Exclude mass ranges 134-156, 182-233, 256- 265, 268-415 at 95% CL Small excesses found around 3 mass values (inc 125GeV) but none statistically significant • Future plans: • Discover the Higgs ! • Prepare measurements of Higgs’ properties: mass, angular distributions (spin)…

  17. Dibosons • The SM Higgs is required to preserve unitarity in • the scattering of longitudinally polarised bosons • If no Higgs field is discovered, new physics may be • found in studying such scattering processes • Di-vector boson production via vector boson fusion • provides ideal environment to test composite • and SM Higgs theories • Composite Higgs models: allow the Higgs boson • to  be  expressed  as  lightest  iso‐singlet of  a • QCD-like  extension to SM • can exist at low mass with less “fine-tuning”

  18. Tribosons: Wgg productions • - W + 2 photon production will be the first • triboson process observable: a genuinely new • SM measurement • ~ 3 sigma SM significance in 2011, should be • measurable in 2012 • Sensitive to the quartic gauge coupling WWgg: • present in the SM but may receive extra • “anomalous” contributions from new physics: • allows to set limits on these • anomalous quartic gauge couplings • AQGCs in general are said to “offer a window” • on the Higgs sector due to their connection to • the scattering processes • Anomalous contributions show up in • high-mass tails of distribution of diphoton • invariant mass • Several orders of magnitude higher • sensitivity than at LEP

  19. The Atlas Forward Physics (AFP) Project AFP: Install forward detectors to “tag” protons from diffractive events • Sensitivity to anomalous gauge couplings is • one of the physics motivations (also diffractive • Higgs production, SUSY…) • Can access WWgg via pp  WWpp process • Sensitivity to WWgg AQCS an order of • magnitude higher again than via Wgg production • Geneva recently joined the AFP project

  20. Summary • Geneva group has made and continues to make a major contribution to the understanding of electron performance • These performance studies have been vital to many SM analyses and more recently to the search for the SM Higgs boson • The group has played and is playing a leading role in many analyses using electrons in the final state: • the inclusive electron cross section measurement • the cross section measurements of W and Z bosons • the high-mass Drell Yan cross section measurement (and the Z’ search) • A careful choice of future analyses should ensure our role in the discovery of new physics which must appear at LHC energies, whether it is the SM Higgs or something else!

More Related