Advertisement

Using γ + jets production to calibrate the Standard Model \( Z\left( { \to v\bar{v}} \right) \) + jets background to new physics processes at the LHC

  • S. Ask
  • M. A. Parker
  • T. Sandova
  • M. E. Shea
  • W. J. Stirling
Article

Abstract

The irreducible background from Z (→ νν) + jets, to beyond the Standard Model searches at the LHC, can be calibrated using γ + jets data. The method utilises the fact that at high vector boson p T (≫ M Z), the event kinematics are the same for the two processes and the cross sections differ mainly due to the boson-quark couplings. The method relies on a precise prediction from theory of the Z/γ cross section ratio at high p T, which should be insensitive to effects from full event simulation. We study the Z/γ ratio for final states involving 1, 2 and 3 hadronic jets, using both the leading-order parton shower Monte Carlo program Pythia8 and a leading-order matrix element program gambos. This enables us both to understand the underlying parton dynamics in both processes, and to quantify the theoretical systematic uncertainties in the ratio predictions. Using a typical set of experimental cuts, we estimate the net theoretical uncertainty in the ratio to be of order ±7%, when obtained from a Monte-Carlo program using multiparton matrix-elements for the hard process. Uncertainties associated with full event simulation are found to be small. The results indicate that an overall accuracy of the method, excluding statistical errors, of order 10% should be possible.

Keywords

QCD Phenomenology Supersymmetry Phenomenology 

References

  1. [1]
    ATLAS collaboration, G. Aad et al., Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in \( \sqrt {s} = 7 \) TeV proton-proton collisions, Phys. Lett. B 701 (2011) 186 [arXiv:1102.5290] [SPIRES].ADSGoogle Scholar
  2. [2]
    ATLAS collaboration, Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in \( \sqrt {s} = 7 \) TeV proton-proton collisions, ATLAS-CONF-2011-086 (2011).Google Scholar
  3. [3]
    CMS collaboration, Data-driven estimation of the invisible Z background to the SUSY MET plus jets search, PAS-SUS-08-002 (2008).Google Scholar
  4. [4]
    CMS collaboration, V. Khachatryan et al., Search for supersymmetry in pp collisions at 7 TeV in events with jets and missing transverse energy, Phys. Lett. B 698 (2011) 196 [arXiv:1101.1628] [SPIRES].ADSCrossRefGoogle Scholar
  5. [5]
    CMS collaboration, S. Chatrchyan et al., Search for new physics with jets and missing transverse momentum in pp collisions at \( \sqrt {s} = 7 \) TeV , submitted to JHEP, arXiv:1106.4503 [SPIRES].
  6. [6]
    CDF collaboration, T. Aaltonen et al., First observation of vector boson pairs in a hadronic final state at the Tevatron collider, Phys. Rev. Lett. 103 (2009) 091803 [arXiv:0905.4714] [SPIRES].ADSCrossRefGoogle Scholar
  7. [7]
    T. Sjöstrand, S. Mrenna and P.Z. Skands, PYTHIA 6.4 physics and manual, JHEP 05 (2006) 026 [hep-ph/0603175] [SPIRES].ADSCrossRefGoogle Scholar
  8. [8]
    T. Sjöstrand, S. Mrenna and P.Z. Skands, A brief introduction to PYTHIA 8.1, Comput. Phys. Commun. 178 (2008) 852 [arXiv:0710.3820] [SPIRES].ADSzbMATHCrossRefGoogle Scholar
  9. [9]
    M. Bahr, S. Gieseke, M. Gigg, D. Grellscheid, K. Hamilton, et al., HERWIG++ physics and manual, Eur. Phys. J. C 58 (2008) 639 [arXiv:0803.0883] [SPIRES].ADSCrossRefGoogle Scholar
  10. [10]
    Z. Bern, G. Diana, L. Dixon, F. Febres Cordero, S. Hoeche, et al., Driving missing data at next-to-leading order, submitted to Phys. Rev. D, arXiv:1106.1423 [SPIRES].
  11. [11]
    T. Gleisberg, S. Hoeche, F. Krauss, M. Schonherr, S. Schumann, et al., Event generation with SHERPA 1.1, JHEP 02 (2009) 007 [arXiv:0811.4622] [SPIRES].ADSCrossRefGoogle Scholar
  12. [12]
    R.K. Ellis,W.J. Stirling and B.R. Webber, QCD and collider physics, Cambridge University Press, Cambridge U.K. (1996).CrossRefGoogle Scholar
  13. [13]
    A. Martin, W. Stirling, R. Thorne and G. Watt, Parton distributions for the LHC, Eur. Phys. J. C 63 (2009) 189 [arXiv:0901.0002] [SPIRES].ADSCrossRefGoogle Scholar
  14. [14]
    F.A. Berends, H. Kuijf, B. Tausk and W. Giele, On the production of a W and jets at hadron colliders, Nucl. Phys. B 357 (1991) 32 [SPIRES].ADSCrossRefGoogle Scholar
  15. [15]
    CTEQ collaboration, H. Lai et al., Global QCD analysis of parton structure of the nucleon: CTEQ5 parton distributions, Eur. Phys. J. C 12 (2000) 375 [hep-ph/9903282] [SPIRES].ADSCrossRefGoogle Scholar
  16. [16]
    M. Glück, E. Reya and A. Vogt, Dynamical parton distributions revisited, Eur. Phys. J. C5 (1998) 461 [hep-ph/9806404] [SPIRES].ADSCrossRefGoogle Scholar
  17. [17]
    G. Aad et al., Measurement of the inclusive isolated prompt photon cross section in pp collisions at \( \sqrt {s} = 7 \) TeV with the ATLAS detector, Phys. Rev. D 83 (2011) 052005 [arXiv:1012.4389] [SPIRES].ADSGoogle Scholar
  18. [18]
    ATLAS collaboration, Measurement of the inclusive isolated prompt photon cross section in pp collisions at \( \sqrt {s} = 7 \) TeV with the ATLAS detector using 35pb −1, ATLAS-CONF-2011-058 (2011).Google Scholar
  19. [19]
    A. Buckley, J. Butterworth, S. Gieseke, D. Grellscheid, S. Hoche, et al., General-purpose event generators for LHC physics, Phys. Rept. 504 (2011) 145 [arXiv:1101.2599] [SPIRES].ADSCrossRefGoogle Scholar
  20. [20]
    M. Cacciari, G.P. Salam and G. Soyez, The anti-k t jet clustering algorithm, JHEP 04 (2008) 063 [arXiv:0802.1189] [SPIRES].ADSCrossRefGoogle Scholar
  21. [21]
    M. Cacciari and G.P. Salam, Dispelling the N 3 myth for the k t jet-finder, Phys. Lett. B 641 (2006) 57 [hep-ph/0512210] [SPIRES].ADSGoogle Scholar
  22. [22]
    M. Cacciari, G.P. Salam and G. Soyez, FastJet, http://fastjet.fr.
  23. [23]
    E. Maina, S. Moretti and D.A. Ross, One loop weak corrections to γ /Z hadroproduction at finite transverse momentum, Phys. Lett. B 593 (2004) 143 [Erratum ibid. B 614 (2055) 216] [hep-ph/0403050] [SPIRES].
  24. [24]
    J.H. Kuhn, A. Kulesza, S. Pozzorini and M. Schulze, Electroweak corrections to hadronic photon production at large transverse momenta, JHEP 03 (2006) 059 [hep-ph/0508253] [SPIRES].ADSCrossRefGoogle Scholar
  25. [25]
    U. Baur, Weak boson emission in hadron collider processes, Phys. Rev. D 75 (2007) 013005 [hep-ph/0611241] [SPIRES].ADSGoogle Scholar
  26. [26]
    G. Bell, J. Kuhn and J. Rittinger, Electroweak Sudakov logarithms and real gauge-boson radiation in the TeV region, Eur. Phys. J. C 70 (2010) 659 [arXiv:1004.4117] [SPIRES].ADSCrossRefGoogle Scholar

Copyright information

© SISSA, Trieste, Italy 2011

Authors and Affiliations

  • S. Ask
    • 1
  • M. A. Parker
    • 1
  • T. Sandova
  • M. E. Shea
    • 1
  • W. J. Stirling
    • 1
  1. 1.Cavendish Laboratory, University of CambridgeCambridgeU.K.

Personalised recommendations