Search for Dark Matter and Extra Dimensions

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Search for Dark Matter and Extra Dimensions

IV Jornadas del CPAN - 26-28 November - Granada

Valerio Rossetti

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IV Jornadas del CPAN [email protected] 2

Introduction

● This talk is about the ATLAS searches for new phenomena in the final states with large Missing Transverse Energy (MET) and one high

momentum jet or photon

● IFAE has been playing a leading role in the mono-jet and mono-photon analyses from the first publications until now

● Link to all ATLAS public results

● OUTLINE

● Introduction to new-physics scenarios

– Large Extra Dimensions

– Dark Matter production

– Gravitino production in GMSB

● Mono-jet analysis: results and interpretations

– 4.7fb-1 at 7TeV

– 10.5fb-1 at 8TeV

● Mono-photon: results and interpretations

– 4.6fb-1 at 7TeV

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Search for extra dimensions

M_pl² ~ M_D²⁺ⁿ Rⁿ

● A low-energy effective field theory (as in Nucl.Phys. B544 (1999) 3-38) is implemented with different Kaluza Klein exitation modes of the Graviton.

→ jet

→ MET

● Extra-dimensions are contemplated in many BSM scenarios.

● The model proposed by Arkani-Hamed, Dimopoulos, Dvali (ADD) (Phys.Lett.B429:263-272,1998) postulate new compactified extra dimentions.

● The Graviton field can propagate through the EDs, and the gravity scale can be much closer to those of the SM.

● Graviton could be produced at LHC in association with a parton or a photon (monojet or monophoton signature).

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Search for Dark Matter at LHC

D1 D5 D8 D9 D11

● WIMPs can be produced at LHC in different final states depending on the model

● Assuming a coupling with quark or gluon, WIMP production can be detected through an ISR of a parton or a photon

● Different effective operators are considered

● Results can be compared with direct and indirect detection

● A ~23% of the universe is composed by unknown non-luminous matter. This is confirmed by:

● Radial speed measurement in galaxies

● Measures of the expansion of the universe

● Many lines of reasoning suggests that the DM is weakly interacting massive particles (WIMP)

Phys.Rev.D82:116010,2010

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Gravitino production in GMSB

● GMSB scenario with very light gravitino (spin 3/2) as LSP with mass O(10^-4 - 10^-5 eV)

● Gravitino is a DM candidate, but too light to be the unique. (hep-ph/1004.4213)

● Current limits from LEP and Tevatron: M_G > 1.37*10^-5 eV

● Gravitino mass gives access to the SUSY breaking scale

● Gravitino production at LHC in association with squark/gluino has a monojet signature

LEP : √F > 240 GeV

http://arxiv.org/pdf/hep-ph/0610160v2

Assuming g→Gg and q→Gq

with Br=1

~ ~ ~ ~

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ATLAS at LHC

Pile-up in 7 and 8TeV data

2011 @ 7TeV Delivered 5.6fb^-1 Recorded 5.2fb^-1

2012 @ 8TeV Delivered 21.6fb^-1 Recorded 20.2fb^-1 (until Nov. 19th)

More detailed status by V. Mitsou tomorrow

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Mono-jet: background estimation

jet jet

Z W

l

^(missed)

ν ν

ν

http://arxiv.org/abs/1210.4491 Submitted to JHEP

W→eν CR

W→μν CR

● Using 4.7fb^-1 of 7TeV recorded in 2011

● SELECTION (signal region)

● MET, jet1 pT > 120, 220, 350, 500GeV

● Njets ≤ 2

● Δφ(jet2,MET) > 0.5

● Veto on identified electrons or muons

● Z/W+jets → Main background (~97% of the total)

● Estimated using Z→ll and W→lν control regions with identified leptons

The analysis has been also published with

● 33pb^-1 of 2010 data Phys.Lett.B 705 (2011)

● 1fb^-1 of 2011 data ATLAS-CONF-2011-096 (2011)

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Mono-jet: results

● Other backgrounds estimation (~3% of total BG):

● QCD and non-collision BG from data (backup slides)

● Top, Dibosons from MC

● Very precise total background estimation

● total uncertainty 3.2% (for MET>120GeV)

● Data in agreement with SM expectation

Model independent observed limits (95%CL) on non-SM processes:

σ x A x ε < 1.92 pb (MET>120GeV selection) σ x A x ε < 6.9 fb (MET>500GeV selection)

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Mono-jet: ADD extra dimensions

● Limits on ADD scenario with n compact extra dimensions

● Low effective field theory (as in arXiv:hep-ph/9811291)

● The phase space s > M_D² is sensitive to the unknown ultraviolet behavior of the theory.

The fraction of visible cross section with s > M_D² provides a measure of the reliability of the effective theory. This fraction goes from 2% to 50% for n=3 to 6

● Limits on M_D computed from LO and NLO signal cross sections on the full fase space

M_pl² ~ M_D²⁺ⁿ Rⁿ

The observed limits account for experimental uncertainties only. The effect of the theoretical uncertainty is shown changing the cross section by 1 sigma.

Same for the other interpretations

^

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Mono-jet: WIMP production limits

● Different effective interactions are taken into account

● Limits in WIMP-nucleon scattering cross section and compared

with direct detection experiments D1

D5 D8 D9 D11 p

p

DM

WIMP production at LHC

p p

DM DM

Direct detection

90% CL limits to be compared with other experiments

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Mono-jet: WIMP annihilation limits

● Results are translated into cross section of WIMPs annihilation to light quarks

following arXiv:1109.4398 [hep-ph]

● Limits compared with FERMI LAT (assuming universality of light and b quarks)

● Below 10 GeV for D5 and 70 GeV for D8, the ATLAS limits are below the values needed for WIMPs to make up the cold dark matter abundance in the early universe

q

q DM

DM

Indirect detection WIMPs annihilation

95% CL limits to be compared with other experiments

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Monojet analysis at 8TeV

● Analysis repeated using 10.5fb^-1 of 8TeV data

● ATLAS-CONF-2012-147

● No significant changes in the selection and BG estimation

● Good understanding of the BG processes

Transverse Mass For W→μν selection

Di-muon inv. Mass For Z→μμ selection

W→μν CR Z→μμ CR W→eν CR

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● Good agreement between data and estimated SM BG

● No evidence of new physics

● Statistical uncertainty on the MC is dominant for the regions with higher MET: 16% for MET>500GeV

Model independent observed limits (95%CL) σ x A x ε < 2.8 pb (MET>120GeV selection) σ x A x ε < 20 fb (MET>500GeV selection)

Monojet analysis at 8TeV

ATLAS-CONF-2012-147

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● Limits on gravitino production are extracted with:

● Narrow width approximation

● Assuming g→Gg and q→Gq with Br=1

● Different configurations of gluino/squark masses are considered:

● Squark/gluino with masses 200 < m <2400GeV

● m_g = K m_s with K = ¼, ½, 1, 2, 4

● Gravitino masses smaller than 10^-4eV are excluded for m_g/s<1.25TeV

● One order of magnitude higher than LEP / Tevatron results

● Limits on the SUSY breaking scale √<F> = 645 GeV

NWA is considered valid for Γ < 1/4 M (above the dotted line)

~ ~ ~ ~

Monojet: gravitino interpretation

ATLAS-CONF-2012-147

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Mono-photon analysis

SELECTION:

● MET > 150GeV

● Photon pT > 150GeV

● Njets ≤ 1

● Δφ(jet,MET) > 0.5

● Veto on electrons or muons

arXiv:1209.4625 [hep-ex] Submitted to PRL

SM backgrounds (% after all cuts)

● ~68% Z(→νν)+photon (main irreducible BG)

● ~17% W(→lν)+photon (missed e/μ, τ(→had.))

● ~13% Z/W+jet (fake photon, missed e/μ)

● ~2% Multijets, photon+jet, Z(→ll)+photon

Non collision BG from:

● Calorimeter noise spikes

● Beam halo muons

● Cosmic muons

Negligible after cleaning cuts Analysis with 4.6fb^-1 of 7TeV data

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Mono-photon: BG estimation

CR with γ+μ+MET

● The BG estimation follows closely the monojet analysis

● More challenging because of the limited statistics in the CRs, and the fake photons coming from jets and electrons.

● Z/W + γ BG estimated through a CR with:

● Identified muons (inverting the muon veto)

● All other cuts as for the SR

● Z/W + jet BG estimated with rate of fake photons from data:

● jet→γ fake rate from a CR with di-jet events

● e→γ fake rate from “tag and probe” on Z(→ee) events

● Multijet (QCD) and γ+jet BG estimated with extrapolation from CR (as for the monojet)

● Top, WW, WZ, ZZ: MC based estimation

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Mono-photon: results

● The dominant uncertainty is the statistical error of the data in the CRs (13%)

● Systematic uncertainties are estimated for:

● Parton shower and hadronization model (7%)

● Lepton/photon identification and scale (1.5%)

● Jet and MET energy scale and resolution (1%)

● Data in agreement with SM expectations

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Mono-photon: exclusion limits

Model independent observed limits (95%CL) on non-SM processes:

σ x A x ε < 6.8fb

NLO theory

M_pl² ~ M_D²⁺ⁿ Rⁿ

The observed limits account for

experimental uncertainties only. The effect of the theoretical uncertainty is shown changing the cross section by 1 sigma

● Results are translated into limits on M_D scale in ADD models

● Limits on these models are less powerful than mono-jet but potentially probe different mechanisms and new phenomena in a different final state

● The phase space with s > M_D² is sensitive to the unknown ultraviolet behaviour of the theory as for the monojet limits. See slide 9.

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Mono-photon: exclusion limits

● WIMP-nucleon cross section

● Limits on these models are less powerful than mono-jet but it confirms the sensitivity of collider results for low WIMP masses.

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Search summary (SUSY searches)

Monojet result

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Search summary (non SUSY)

Monojet result Monophoton result

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Conclusions

● Mono-jet and mono-photon are important striking signatures for many BSM scenarios.

● The analyses performed so far with 7TeV and part of the 8TeV data have shown no deviation from the SM predictions.

● Results have been interpreted in terms of limits in different scenarios. Other interpretations in terms of stop production, neutralino-squark production, invisible Higgs have being studied (see backup slides)

● Analysis the full 8TeV dataset with more interpretations will come in 2013.

● In 2015 new opportunity for discoveries @ 13TeV collisions.

● These are very exiting times for particle physics! New phenomena can be behind the corner.

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Backup slides

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Other mono-jet interpretation:

stop/sbottom searches

arXiv:1112.4461v2 [hep-ph]

ISR jet

Soft b/c jet MET

● Scenario with very heavy gluino and first generation squarks, and lighter stop and sbottom

● Monojet final state unique access to compressed SUSY scenarios with Mstop/sbottom ~ M_LSP

● The monojet selection can be optimized for this specific final state

● Ongoing work at IFAE

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Other mono-jet interpretation:

invisible Higgs

arXiv:1112.4496

(using 1 fb^-1 ATLAS 7 TeV mono-jet analysis)

● Mono-jet final states can constrain invisible Higgs branching fractions

● Connection to DM phenomenology

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Gravitino limits

Limits for m(squark)!=m(gluino)

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Monojet analysis at 8TeV:

limits on LED and WIMP production

● Limits on ADD extra dimension model and WIMP production with the 8 TeV analysis

● The limits are not improved (except in the case of extra dimensions with n = 6) due to the lack of sufficient statistics in the MC samples employed for the

background predictions.

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26/11/12 [email protected] 28

Data-driven QCD estimation for the monojet analysis (8TeV)

2^nd jet is lost 3^rd jet is lost

● Two kinds of QCD multi-jet events: di-jet and tri-jet

● Using CRs with di-jets and tri-jet events, and

extrapolating the pt of the 2^nd or 3^rd leading jet below the 30GeV threshold

● In both cases the pt extrapolation has big uncertainties from the choice of the fit range, the fitted function and the subtraction of the other processes

Di-jet CR Tri-jet CR

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Monojet analysis at 7 and 8TeV

● Tables with expected and observed number of events in the analyzed 7 and 8 TeV datasets.

● Data and SM predictions are in agreement.

● The statistical uncertainty from the MC is dominant in the case of the 8TeV analysis and is quoted

separately in the table.

4.7fb^-1 @ 7TeV

10.5fb^-1 @ 8TeV