Searches for Dark Forces with KLOE

Searches for Dark Forces with KLOE

Anthony Palladino

on behalf of the KLOE/KLOE-2 Collaborations

37^th International Conference on High Energy Physics (ICHEP) Valencia

5 July 2014

Some open questions in physics

Several puzzlingastrophysicalmeasurements andparticle physicsquestions...

• e⁺/e⁻ excess in cosmic ray flux as compared to proton/antiproton flux (PAMELA)

• 511 keV gamma ray signal from the galactic center (INTEGRAL)

• totale⁺/e⁻ flux (ATIC, Hess, Fermi)

• DAMA/LIBRA annual modulation

• positron spectrum in primary cosmic rays (AMS)

• gµ−2 discrepancy

• some relation to parity violation?

...each of these effects could be explained by the existence of a U boson with mass less than 2 proton masses.

Dark photon (U or A

)

Neutral dark vector boson,U, with mixing:

Lmix=−₂F_µν^QEDF_Dark^µν

Could appear as a resonance in a final-state`<sup>+</sup>`⁻ invariant mass spectrum.

KLOE has performed the following searches:

• φ→ηU , U→e⁺e⁻

• e⁺e⁻→Uγ, U→µ⁺µ⁻

• e⁺e⁻→Uγ, U→e⁺e⁻

• e⁺e⁻→Uh⁰ , U→µ⁺µ⁻ , h⁰ invisible

`⁺=e⁺,µ⁺

`⁻=e⁻,µ⁻

γ U

Physics Letters B720(2013) 111–115 arXiv:1404.7772, Submitted to PLB Preliminary

Preliminary

KLOE Detector – Drift Chamber

Drift Chamber

σp/p= 0.4% (for 90^◦tracks) σxy∼150µm,σz ∼2 mm Excellent momentum resolution

Full stereo geometry, 4m diameter, 52140 wires,90% Helium, 10% iC4H10

KLOE Detector – Electromagnetic Calorimeter

Electromagnetic Calorimeter σE/E= 5.7%/p

E(GeV) σt= 54 ps /p

E(GeV) 100 ps Excellent timing resolution

Pb / scintillating fibers (4880 PMTs) Endcap – Barrel – Modules

The search for U in φ → ηU , U → e

e

with

η → π

π

π

or η → π

π

π

Phys. Lett. B720(2013) 111–115

Di-electron mass spectrum

• Peak search inM_ee distribution of irreducible φ→ηe⁺e⁻ background

• η→π⁰π⁰π⁰

∼31,000 events

∼3% background

• η→π⁺π⁻π⁰

∼13,000 events

∼2% background

φ→ηe⁺e⁻→π⁺π⁻π⁰e⁺e⁻

φ→ηe⁺e⁻→π⁰π⁰π⁰e⁺e⁻ e⁺

e⁻

φ U

e⁻

e⁺

η

Published limit on

using φ → ηU , U → e

e

with

η → π

π

π

or η → π

π

π

Phys. Lett. B720(2013) 111–115

Compared with limits at time of publication

MAMI/A1PRL106(2011)

APEXPRL107(2011)

KLOEPLB720(2013)

Gray band could explain gµ−2 anomaly

µ⁻

µ⁺ U

The search for U in e

e

→ Uγ , U → µ

µ

e⁻ γ

e⁺

γ

µ⁺ µ⁻

γ U Small angle selection

θγ<15^◦, θγ>165^◦

→high statistics ISR 2 oppositely charged tracks

µ µ

Significant suppression of φ→π⁺π⁻π⁰ background Good pion / muon separation

The search for U in e

e

→ Uγ , U → µ

µ

e⁻ γ

e⁺

γ

µ⁺ µ⁻

γ U Peak search in

di-muon mass spectrum

²=^α_α⁰ = ^N_ε^CLS

eff

1 H·I·L

NCL_s = number of U boson signal events excluded at 90% C.L.

εeff∼1–10 %

Systematic uncert.: 1.4–1.8 %

H= _σ(e^dσ_+e^µµγ−→µ^/dM+µ^µµ−,M)

I =R

σU dMU L=R

L= 239.3 pb⁻¹

Submitted limit on

using e

e

→ Uγ , U → µ

µ

Compared with limits at time of submission to PLB

KLOEPLB720(2013)

APEXPRL107(2011)

WASAPLB726(2013)

HADESPLB731(2014)

A1arXiv:1404.5502 (April 2014)

KLOEarXiv:1404.7772 (April 2014)

The search for U in e

e

→ Uγ , U → e

e

e⁻ γ

e⁺

γ

e⁺ e⁻

γ U Large angle selection

50^◦< θγ<130^◦ 2 oppositely charged tracks

e e

High statistics radiative Bhabha events in KLOE data

∼per mil level background contamination, or better

The search for U in e

e

→ Uγ , U → e

e

e⁻ γ

e⁺

γ

e⁺ e⁻

γ U

2) (GeV/c (ee) Minv

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 )2Events / (0.5 MeV/c

0 1000 2000 3000 4000 5000 6000 7000

Measurement Simulation

Di-electron mass spectrum Large angle selection Approaches e⁺e⁻ threshold

²=^α_α⁰ = ^N_ε^CLS

eff

1 H·I·L

NCL_s = number of U boson signal events excluded at 90% C.L.

εeff∼1.5–2.5 %

Systematic uncert.<2 %

H= _σ(e^dσ_+e^eeγ−→e^/dM+e^−ee,M)

I =R

σU dMU L=R

L= 1.54 fb⁻¹

Preliminary limit on

using e

e

→ Uγ , U → e

e

Compared with current limits

KLOE

APEXPRL107(2011)

WASAPLB726(2013)

HADESPLB731(2014)

A1arXiv:1404.5502 (April 2014)

KLOEsubmitted April 2014

BaBararXiv:1406.2980 (Jun 2014)

KLOEPreliminary

New Preliminary KLOE results for ICHEP 2014

The search for U in

e

e

→ Uh

, U → µ

µ

, h

invisible

Two different scenarios:

mh⁰ >2mU

with decays: h⁰→UU→4`,π+ 2`,π m_h⁰ <m_U

whereh⁰ is “invisible”

e⁺

e⁻ U

h⁰

µ⁺ µ⁻

Assuming∼10⁻³ α_D=α_EM

m_U= 100 MeV

⇒τh⁰>5 µs⇒βγcτ >100 m⇒

h⁰ invisible at KLOE up to∼10⁻²–10⁻¹ depending onmh⁰

The search for U in

e

e

→ Uh

, U → µ

µ

, h

invisible

Results from onφ-peak data sample from KLOE (1.65 fb⁻¹)

Binning such that 90–95% of signal would be in one bin Sliding 5×5 bin matrix (excluding the central bin) used to determine

background MC scale factors

α_D²= ^N_ε^90%

eff

1 L·σ(αD²=1)

σhU∝ ¹_s ¹ 1−^m_s^2U

2

Preliminary limits from

e

e

→ Uh

, U → µ

µ

, h

invisible

Combined results from on- and off-peak KLOE data.

Limit onαDײ vsmU at 90% CL translates to a limit on

²of 10⁻⁶to a few 10⁻⁸(ifαD=αEM)

Limit onαDײ vsmh⁰ at 90% CL

Conclusions

KLOE has performed four searches in the Dark Sector

• φ→ηU , U→e⁺e⁻

• e⁺e⁻→Uγ, U→µ⁺µ⁻

• e⁺e⁻→Uγ, U→e⁺e⁻

• e⁺e⁻→Uh⁰ , U→µ⁺µ⁻ , h⁰ invisible

• KLOE has placed limits on²in the mass range 2<m_U<980 MeV.

• KLOE has placed limits onαDײin the range 2mµ<mU<1000 MeV

Physics Letters B720(2013) 111–115 arXiv:1404.7772, Submitted to PLB Preliminary

Preliminary