QQbar jet Events Tagged with Dileptons at the LHC

1
QQbarjet Events Tagged with Dileptons at the
LHC

• Camelia Mironov1, Ramona Vogt2,3, Gerd J. Kunde1
• 1 Los Alamos National Lab
• 2 Lawrence Livermore National Lab
• 3 UC Davis

2
Outline

• Intro on heavy quarks and jets
• General considerations
• NLO for heavy quarks and uncertainties
• Present study
• Theoretical setup
• LHC and cuts
• QQbarjet
• Quark perspective
• Hadronic perspective
• Rates at 5.5 and 14TeV

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QQbar jet
LO
NLO

Identify and isolate the three-prong hard
scattered events! Hunt WISELY!

• In the low background region, M12,70GeV,
  identify/reconstruct the QQbarjet, by tagging on
  the dilepton from the simultaneous decay of
  DDbar/BBbar
• Better control on the bkg from dilepton than
  single lepton.

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HOW?

• Isolate LO from NLO contributions
• Look at the kinematics and find a cut

Need a code
(PYTHIA, FONLL, MC_at_NLO,MNR) that considers
NLOinterference terms (FONLL,MC_at_NLO,MNR) t
hat gives angular correlations
(MC_at_NLO and MNR) that has both charm and
bottom
(MNR)
5
HVQMNR a.k.a. MNR
M. Mangano, P. Nason, G. Ridolfi Nucl.Phys.B 373
(1992) 295

• ? Calculates LO and NLO

Q mQ (GeV/c2) ltkTgt (GeV/c) e ?F ?R PDF
charm 1.5 1.0 0.06 1 1 CTEQ6M
bottom 4.75 1.0 0.006 1 1 CTEQ6M
µR2 ?R(mQ2pT2) µF2 ?F(mQ2pT2)

• ? Fragments the heavy quark
• ? Decays the heavy meson B/D?lX

Peterson FF (Phys.Rev.D 27 (1983) 105
e mq2/mQ2
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Present study dileptonQQbarjet _at_ LHC

• Have high luminosity and high collision energy ?
  high rates
• Have excellent detectors for jet, leptons,
  tracking, etc

ALICE
ATLAS
CMS
Name Cut1 Cut2 Cut3 Cut4
M GeV/c2 12,70 12,70 12,70 -
pTlepton1 GeV/c 1.0 3.5 3.5 3.5
?lepton2 0.9 2.4 2.4 2.4
pTlepton2 GeV/c 1.0 3.5 3.5 5.0
?lepton2 0.9 2.4 2.4 3.0
pTdilepton GeV/c 5.0 10 25 25
ee µµ µµ
µe
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QQbar jet quark perspective
NLO - full marker LO - open marker
Different partonic contributions to the total
QQbar momentum cross section. MQQbar is in the
interval 12,70GeV/c2. No cuts are imposed on
the single quarks.

• The NLO contributions are dominant over the whole
  range of the momentum spectrum
• gluon fusion the dominant channel

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QQbar jet dilepton perspective
NLO - full marker LO - open marker
Different partonic contributions to the total
dilepton azimuthal distribution. Cut3 was used.

• LO diagrams give contributions at large ?f (the
  back-to-back topology)
• NLO diagrams span almost the whole phase space.

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QQbar jet dilepton distributions
Dileptons from DDbar decays. Cut systematics.

• highest rates when no mass constraints (Cut4)
• from Cut3 and Cut4 sets low mass dileptons are
  produced from diagrams in which Q and Qbar are
  close in space
• from Cut1 and Cut2 sets low momentum dileptons
  (and implicitly Q and Qbar) are produced far away
  from each other (close to back-to-back).

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QQbar jet dilepton distributions
Dileptons from BBbar decays. Cut systematics.

• highest rates when no mass constraines (Cut4)
• from Cut3 and Cut4 sets low mass dileptons are
  produced from diagrams in which Q and Qbar are
  close in space
• from Cut1 and Cut2 sets low momentum dileptons
  (and implicitly Q and Qbar) are produced far away
  from each other (close to back-to-back).

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QQbar jet rates after angle cut
Differential cross section for bottom and charm
dileptons, with Cut3 and ?flt90o. Left
pp_at_14TeV Right pp_at_5.5TeV
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QQbar jet heavy-ions case
Integrated rates above pTmin for 5.5TeV PbPb. No
energy loss was considered. Scaling A2spp

• A couple of thousand QQbarjet events are
  produced and maybe be identified in the
  semileptonic decay channel

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QQbar jet background

• Physics Background
• Z0/? dileptons
• in M12,70MeV -- small
• Whole M range -- eµ channel
• B-gtJ/? X
• invariant mass cut on the dileptons
• Combinatorial Background
• b/c(-gtlX) misindentified lepton
• two fake leptons
• Same sign dilepton analysis ee, e-e-, µµ,
  µ-µ-
• Bad Karma Background (case study for slide 10)
• pp pileup 25collisions/bunch cross 4310-6
  bbbarjet/event, 2110-6 ccbarjet/event
• AA - a lot of charm and bottom produced each
  event 1.7 bbbarjet/event, 0.8
  ccbarjet/event, for Cut_3 and 5 centr.
• Use azimuthal correlations --gt flat background

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Conclusions

• Propose to hunt for heavy quarks jet events in
  the semileptonic decay channel of the
  BBbar/DDbar.
• Within the present works assumptions, at the
  LHC the production rates are high enough to do
  the analysis
• For the channel considered, have control on the
  background
• To remember
• Nothing is absolute! Best combine methods to
• identify the heavy quark products (vtx
  displacement, decay reco, etc .)
• reconstruct the jet (jet algorithm, angular
  correlations)