Conducting Effective Searches Conducting Effective Searches: Orientation for Search Committees.
Comparing A ccelerator and direct Dark Matter searches
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Transcript of Comparing A ccelerator and direct Dark Matter searches
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Comparing Accelerator and direct Dark Matter
searches
G. Azuelos24 Jul 2014 Dark Matter workshop - Montreal 1
WIMPS: what can we say about their
properties? possible origins? many models
What is an effective theory? Detecting DM from missing
momentum at colliders: LEP, Tevatron, LHC
Validity of effective theory
Some references:• Bai, Fox and Harnik, 1005.3797v2• P. Fox et al., 1103.0240• J. Goodman et al., 1008.1783, 1111.2359• G. Busoni et al., 1307.2253, 1402.1275• O. Buchmueller et al., 1308.6799• M. Papucci et al., 1402.2285• KICP workshop 2013:
https://kicp-workshops.uchicago.edu/DM-LHC2013/presentations.php
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In early universe, WIMPS are in thermal equilibrium and annihilate until the density is too low freeze-out
Some possibilities: LSP: neutralinos, gravitinos LKP: Kaluza-Klein state in Universal Extra dimensions LTP: Little Higgs with T parity also, in Technicolor, composite Higgs models Higgs portal Z’ portal fermion portal useful to have a model-independent approach
In collider experiments: non-interacting, invisible particles missing ET
Properties of WIMPS
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Effective theories
Assume new physics at some high energy scale L Energy scale at which measurement is performed: Q
Observed effect of new physics is small and needs to be calculated at 1st order only
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W
Classic example: Fermi theory: Weak interaction is well approximated, in nuclear physics, by a contact interaction, when, in fact, it is an exchange of a heavy particle
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Propagator of the heavy particle:
valid as long as
Effective approximation
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(weak contact coupling)
(f = scalar mediator)
Mq
q
c
c
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Translate to Direct Detection
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Mq
q
c
ctime
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Different kinematics
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Assuming weak interactions (neutralinos):
spin-independent:
spin-dependent
Wimps interacting with matter
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c c
q q
Z
cc
c c
q q
h,H
c
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q
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spin-dependent cross sections
proton neutron
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Light mediator
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momentum and spin-dependent model
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LEP shines light on Dark Matter
4 effective operators
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• single photon• cm energy ~ 200 GeV• central: 45o < q < 135o
• forward: 12o < q < 32o
• v. forward: 3.8o < q < 8o
simulated conditions, accounting for efficiencies as function of angle and resolutions
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DM nucleon scattering cross section
strong constraints on spin-dependent at low mass: no A2 dependence
also considered… if lepton coupling only limits on annihilation lighter mediator effects
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Operators
DiracComplex scalarsReal scalars
Many curves obtained
for the limits on L and for limits derived on nucleon cross sections for the different operators
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reach at colliders, in EFT
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spin-dependent
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LHC
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ATLAS 1210.4391
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Validity condition of EFT
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Definition: ; Typically expect
• condition for perturbativity:
• mediator heavier than WIMP:
• truncation of propagator expansion:
• s-channel:
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The lower Q, the better the EFT approximation
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Momentum transfer Q
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p4
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RL
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Fraction of cross section for which Q < L :
for scalar operator:
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RL
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for scalar operator:
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Compared to ATLAS
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rUV/eff
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Ratio of cross sections obtained with UV completed theory (s-channel scalar mediator) and with EFT :
The smallet pT and mc are, the better the EFT approximation.
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Beyond Effective Field Theory at the LHC
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• EFT is valid if
• cross section enhanced if mediator is on-shell, for example
• Consider CMS monojet analysis, as basis (7 and 8 TeV analyses)
• Use Monte Carlo (MCFM 6.6) to simulate dark matter monojet process
• includes full effects of mediator propagator and width, in s-channel
• consider axial-vector and vector operators only:
• apply CMS cuts
• one hard jet: pT > 100 GeV
• signal regions (best of their signal regions)
• parton level cuts, with geometric acceptance
• background simulated with MadGraph:
• pythia showering and PGS detector simulation
• compared results with CMS to validate their MC analysis
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Simplified model
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s-channel axial-vector interaction: applies also to Majorana DM, and more interesting spin-dependent limits
EFT valid if M >> Q• Q > 500 GeV when pT(j) > 100 GeV, Etmiss > 400 GeV• find condition: M > 2.5 TeV
EFT OK
within 20%
resonant
production
of mediator
EFT OK
resonant production of mediator
2.5 TeV
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Region 1: Very high mediator mass: EFT OK
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Region II : resonant enhancement
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• On-shell production of mediator if
• production enhanced EFT limit conservative
Limit on L scales as ~ G-1/4 at the resonance peak
Region III for CMS conditions
Region II for CMS conditions
see also Goodman & Shepherd, arXiv:1111.2359
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CMS EXO-12-048 PAS
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Region III: very light mediator – EFT limit too strong
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• In the limit where the mediator is very light, • the cross section does not depend on its mass since
• EFT assumes M is very large (and g small for the same L)
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Comparison to Direct Detection
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O. B
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Recommendations and Conclusion
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Validity of EFT depends a lot on the assumptions and parameters:• 4 parameters:• small dependence on width G in resonance region• LHC should provide limits on L in M-mc plane (in s-channel assumption?)
• for few values of G/M
Complementarity:M. Cahill-Rowley, 1305.6921
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EXTRAS
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tree level coupling to leptons only
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Assume coupling to leptons only
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Limits on Λ
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Upper limits on annihilation cross sections
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Annihilation cross section, compared to astronomical limits
LEP limits better than Fermi for low masses
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With different mediator masses
strong dependence on width, if M > 2 mwimp, since it is produced on-shell
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Wimp-Nucleus cross section
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Annihilation cross section
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Limits on L
monojet limits from CDF• ET(jet) > 80 GeV• Etmiss > 80 GeV• 2nd jet ET < 30 GeV• no add. jet with ET > 20 GeV
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Bai, Fox and Harnik,arXiv:1005.3797
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need quark content of nucleon
spin-independent cross section
very sensitive at low massestests also couplings to higher generations
proton
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Bai, Fox and Harnik,arXiv:1005.3797
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c c
q q
h,H
c
cq
q c c
q q
Z
cc
http://www.worldscientific.com/doi/abs/10.1142/S0218301392000023?queryID=%24%7BresultBean.queryID%7D
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ATLAS 1210.4391
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ATLAS 1210.4391
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ATLAS 1210.4391
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ATLAS mono-Z1404.0051
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CMSEXO-12-048 PAS
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Bai, at DM workshop 2013
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Bai, at DM workshop 2013