1 Dark Matter: Indirect Detection & LHC searches

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1 Dark Matter: Indirect Detection & LHC searches Nicole Bell The University of Melbourne, Australia in collaboration with Ahmad Galea, Amelia Brennan (Melbourne) Thomas Jacques, James Dent, Lawrence Krauss (Arizona) Tom Weiler (Vanderbilt)

Transcript of 1 Dark Matter: Indirect Detection & LHC searches

Page 1: 1 Dark Matter: Indirect Detection & LHC searches

Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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Dark Matter:Indirect Detection & LHC searches

Nicole BellThe University of Melbourne, Australia

in collaboration with

Ahmad Galea, Amelia Brennan (Melbourne) Thomas Jacques, James Dent, Lawrence Krauss (Arizona)

Tom Weiler

(Vanderbilt)

Page 2: 1 Dark Matter: Indirect Detection & LHC searches

Nicole Bell, U. Melbourne The LHC, Particle Physics & the Cosmos, Auckland, 13 July 2012

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production (collider searches)

annihilation (indirect detection)

scattering(direct

detection)

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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annihilation (indirect detection)

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modes are

important!

production (collider searches)

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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Indirect detection ~

dark matter annihilation

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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Parameterize the annihilation cross section as:

<v> = a + bv2 + …

a -- from s-wave (L=0) annihilationb -- both s-wave and p-wave (L=1) contributions

The Lth partial wave contribution is suppressed as v2L

In galactic halos, v~ 10-3c, so only the s-wave contribution will be significant.

However, in many models, s-wave annihilation to a fermion pair is helicity suppressed by a factor of 2

DMf mm

Annihilation cross section

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Majorana neutralinos annihilate to a fermion pair via:

• t- and u-channel exchange of sfermions helicity suppressed

• s-channel exchange of Zhelicity suppressed

• s-channel exchange of higgs suppressed by yukawa couplings

2 vevfm

Example: SUSY

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Cao, Ma, Shaughnessy, PLB 2009.Dark matter = gauge-singlet Majorana fermion =

Example of suppressed annihilation

SUSY analogue

Annihilation of bino dark matter to fermions via exchange of sfermions

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Emission of a photon can lift this suppression: Bergstrom, PLB 225, 372, 1989;Flores, Olive, Rudaz, PLB 232, 377, 1989;Bringmann, Bergstrom, Edsjo, 2008; Barger, Gao, Keung, Marfatia, 2009,…

Lifting the suppression (photons)

The photon carries away a unit of angular momentum no longer helicity suppressed.

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Lifting the suppression (photons)

Final state radiation (FSR) “Virtual internal bremsstrahlung”

(VIB) Effect most pronounced for near-degenerate

and

(i.e. coincides with the co-annihilation region)

Bringmann, Bergstrom, Edsjo, 2008

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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Bergstrom, Bringmann, Edsjo, PRD 2008

Bringmann, Huang, Ibarra, Weniger, arXiv:1203.1312

Bremsstrahlung

signals Gamma rays Positrons

Supposed FERMI gamma ray line at ~130GeV fit by bremsstrahlung signal with m~150GeV, arXiv:1203.1312

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

11Lifting the suppression: electroweak (W,Z) bremsstrahlung

Radiating a W or Z boson can also lift the suppression Both VIB and FSR are present similar to

brem, except for W/Z mass effects.

distinct phenomenology: W and Z bosons decay to charged leptons, neutrinos, gammas, and hadrons hadron production even for “leptophillic” models

Bell, Dent, Jacques & Weiler, PRD 2010.

Bell, Dent, Galea, Jacques, Krauss & Weiler, PLB 2011, arXiv:1104.3823

Ciafaloni, Cirelli, Comelli, De Simone, Riotto & Urbano, JCAP 2011

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

12W brem

rate larger than photon brem

rate, except near threshold

Bell, Dent, Galea, Jacques, Krauss and Weiler, arXiv:1104.3823

Adding all the bremsstrahlung processes:

(in the limit where the W/Z mass is negligible)

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Ratio of eW and e+e-

cross sections

• Annihilation to e+e-, e+e-Z & eW dominates over e+e-• Enhancement by up to three orders of magnitude!

(v~10-3c, Galactic halo)

Bell, Dent, Galea, Jacques, Krauss and Weiler, arXiv:1104.3823

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Annihilation spectra:

/ W/ Z brem

p

γ

ν

e

Bell, Dent, Jacques & Weiler, arXiv:1101.3357

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Maximum allowed brem

cross sections

Bremsstrahlung can’t make significant contribution to e+ flux, without overproducing pbar

/pp

Bell, Dent, Jacques & Weiler, arXiv:1101.3357

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Kachelriess, Serpico and Solberg PRD 2009.

Models with no helicity suppression

EW-brem still occurs, but is subdominant

W/Z decays ensures there is at least a minimal yield of hadrons, photons, charged leptons and neutrinos.

neutrinos-only

(+ W/Z brem)

electrons-only e+e- (+ W/Z brem)

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Neutrinos from the Sun• Dark matter accumulates in the centre of Sun • Capture rate and (if in equilibrium) the annihilation rate

controlled by WIMP-nucleon scattering cross section• Neutrinos are the only annihilation products able to escape• Hard spectra (WW) more detectable than soft spectra (bb)• EW brem annihilation mode distinctive hard spectra

(D.Hooper)

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Solar WIMP limits-

limits depend on the assumed annihilation spectrum

IceCube, arXiv:1112.1840

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Neutrinos from the Sun –

EW brem

Bell, Brennan, Jacques, arXiv:1206.297

EW brem relative muon track rates - IceCube

EW brem

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LHC dark matter searches with electroweak bremsstrahlung

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The dominant DM production process at the LHC may be:

But this process is invisible to the detectors (DM stable, weakly interacting)

We need a visible particle in the final state, to recoil against some missing transverse energy,

e.g.

qq

boson gauge qq

Dark matter visible as high pT state + missing ET

Dark matter at the LHC

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gauge boson is a gluon or photon monojet or monophoton searchesFox, Harnik, Koop, Tsai, 1109.4398, 1103.0240Beltran, Hooper, Kolb, Krusberg, Tait, 1002.4137Frandsen, et al, 1204.3839CMS collaboration, 1204.0821, 1206.5663ATLAS collaboration, 1106.5327…

gluon radiation – high cross section & large backgrounds

monophoton– complementary to (but less constraining than) monojets

electroweak channels? – relatively low backgrounds

Dark matter at the LHC

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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Consider the Z decay to muons:

Signature: pair of high pT muons which reconstruct to a Z, recoiling against missing ET.

We consider bremsstrahlung of Z bosons

Z easily reconstructed invariant mass

Leptonic Z decays backgrounds are low purely EW channel competitive with hadronic jet searches

Z bremsstrahlung

Zqq

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Signal: pair of muons + missing ET Zqq

Backgrounds

EW backgrounds:

QCD backgrounds:

ZZ background has large missing ET & is kinematically most similar to our signal

Z+jets is a large background, but can be removed with kinematic cuts

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similar model as before, but now we take the scalar to be

charged under SU(3), c~(3,2,1/3),

(i.e.

and

are analogous to the neutralino and squark. But, importantly, note we don’t have a gluon.)

Z bremsstrahlung

example model

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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(Includes a cut on invariant mass of the muon pair, and an inclusive muon pT cut of 50 GeV)

Signal and Backgrounds –

before cuts

Bell, Dent, Galea, Jacques, Krauss & Weiler, in preparation

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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signal/background –

as function of R cut

Z boosted muons co-linear signal has small R

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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Cuts: - missing ET > 100 GeV- R < 1

Signal and Backgrounds –

after cuts

Bell, Dent, Galea, Jacques, Krauss & Weiler, in preparation

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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Muon

pT

Missing ET

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Signal falls away for large dark matter mass

(note: couplings chosen to be consistent with relic density)

m=500 GeV

m=300 GeV

m=1000 GeV

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Comparison with monojet

searchesAt 7 TeV, 1fb-1, and same model parameterssimilar sensitivity

Monojet analysisFox et al.arXiv:1109.4398

Z brem analysisBell, Dent, Galea, Jacques, Krauss, Weiler, in preparation

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Nicole Bell, CoEPP, The University of Melbourne The LHC, Particle Physics and the Cosmos, 13 July 2012

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Electroweak bremsstrahlung - indirect detection Annihilation to a fermion pair is often helicity suppressed Internal bremsstrahlung of , W & Z removes the suppression;

Allows indirect detection of otherwise unobservable physics Interesting multimessenger signals. Antiproton limits important. Distinctive neutrino signal for solar WIMP searches

Conclusions

Electroweak bremsstrahlung - colliders Signal is a gauge boson plus missing transverse energy Large signal/background Complementary to monojet and monophoton searches

3-body final states are important for dark matter searches