Some Concluding Remarks

IntroductionDark force experiments and related theory have come a long way since a similar workshop at SLAC 3 years ago.I hope the timescale for further progress is closer to 3 years than to Maxim’s 38. My goal is to lay out thoughts on future directions, in direct dark-force searchesThough this talk draws heavily on some aspects of the workshop, I won’t try to give a full summary talk.

In particular, though I learned a lot from talks on LHC data and dark matter, I can’t add anything by condensing further.

Outline

• Topic-specific summaries– Fixed-Target– Colliders & meson decays– Precision measurements & theory– Nuclear transitions

• Looking ahead– An inclusive message– Targeting (g-2)μ: why we aren’t done yet

I know least

about these!

!

Fixed Targets

• e– experiments have gone from glimmers in proponents’ eyes through test-runs & first physics results!

• Theory has advanced: from Weizsacker-Williams estimates to full LO and partial NLO calculations

• Along the way, improved understanding of constraints from past e– and p beam-dumps

• MiniBoone search for U-boson: I think this is first full p fixed-target proposal

Realizing e– Fixed-Target Experiments

Harald Merkel, Dark Forces at Accelerators 2012, Frascati

Extended mass range (data taking 2012, preliminary)

Extension to lower mass region

Several beam energy settings

Lower mass limit: minimum angle between spectrometers

Mix

ing P

ara

mete

r

!2

Dark Photon Mass m" ’ (MeV/c2)

10-7

10-6

10-5

10-4

0 50 100 150 200 250 300 350

(g-2)µ

(g-2)e

BaBar

A1-2011

e+e#$" µ

+µ

#

|(g-2)µ|< 2%

E774

KLOE

APEX

H. Merkel & J. BeachamPRL 106, 107; A1 to appear

Realizing e– Fixed-Target Experiments

Harald Merkel, Dark Forces at Accelerators 2012, Frascati

Extended mass range (data taking 2012, preliminary)

Extension to lower mass region

Several beam energy settings

Lower mass limit: minimum angle between spectrometers

Mix

ing P

ara

mete

r

!2

Dark Photon Mass m" ’ (MeV/c2)

10-7

10-6

10-5

10-4

0 50 100 150 200 250 300 350

(g-2)µ

(g-2)e

BaBar

A1-2011

e+e#$" µ

+µ

#

|(g-2)µ|< 2%

E774

KLOE

APEX

H. Merkel & J. BeachamPRL 106, 107; A1 to appear

Extrapolated Track Positions at Target Accurate to few mm

Fringe field corrects +/- displacement

Alignment will correct top/bottom displacement

HPS Test Run – J. Jaros

DarkLightJ. Boyce

Realizing e– Fixed-Target Experiments

Harald Merkel, Dark Forces at Accelerators 2012, Frascati

Extended mass range (data taking 2012, preliminary)

Extension to lower mass region

Several beam energy settings

Lower mass limit: minimum angle between spectrometers

Mix

ing P

ara

mete

r

!2

Dark Photon Mass m" ’ (MeV/c2)

10-7

10-6

10-5

10-4

0 50 100 150 200 250 300 350

(g-2)µ

(g-2)e

BaBar

A1-2011

e+e#$" µ

+µ

#

|(g-2)µ|< 2%

E774

KLOE

APEX

H. Merkel & J. BeachamPRL 106, 107; A1 to appear

Extrapolated Track Positions at Target Accurate to few mm

Fringe field corrects +/- displacement

Alignment will correct top/bottom displacement

HPS Test Run – J. Jaros

Harald Merkel, Dark Forces at Accelerators 2012, Frascati

Summary

Mix

ing

Pa

ram

ete

r

!

Dark Photon Mass m" ’ (MeV/c2)

10-7

10-6

10-5

10-4

10-3

10-2

10 100 1000

(g-2)µ(g-2)e vs. # BaBar

A1

e+e$%" µ

+µ

$

|(g-2)µ|< 2&

A1 w/o modifications

E137

E141

E774

MESA

'-CAL I

KLOEAPEX

Experimental Program:

Pair production on heavy target e > 4 ·10�4

Low energy – high currentmg 0 < 50MeV/c

2

Finite production vertex 10�6 < e < 10�4

Discrepancy on (g�2)µ

Region will be covered in the near future

A1+septum

Mainz prospects: MESA, A1+septum, collimator

DarkLightJ. Boyce

Realizing e– Fixed-Target Experiments

Harald Merkel, Dark Forces at Accelerators 2012, Frascati

Extended mass range (data taking 2012, preliminary)

Extension to lower mass region

Several beam energy settings

Lower mass limit: minimum angle between spectrometers

Mix

ing P

ara

mete

r

!2

Dark Photon Mass m" ’ (MeV/c2)

10-7

10-6

10-5

10-4

0 50 100 150 200 250 300 350

(g-2)µ

(g-2)e

BaBar

A1-2011

e+e#$" µ

+µ

#

|(g-2)µ|< 2%

E774

KLOE

APEX

H. Merkel & J. BeachamPRL 106, 107; A1 to appear

Extrapolated Track Positions at Target Accurate to few mm

Fringe field corrects +/- displacement

Alignment will correct top/bottom displacement

HPS Test Run – J. Jaros

Harald Merkel, Dark Forces at Accelerators 2012, Frascati

Summary

Mix

ing

Pa

ram

ete

r

!

Dark Photon Mass m" ’ (MeV/c2)

10-7

10-6

10-5

10-4

10-3

10-2

10 100 1000

(g-2)µ(g-2)e vs. # BaBar

A1

e+e$%" µ

+µ

$

|(g-2)µ|< 2&

A1 w/o modifications

E137

E141

E774

MESA

'-CAL I

KLOEAPEX

Experimental Program:

Pair production on heavy target e > 4 ·10�4

Low energy – high currentmg 0 < 50MeV/c

2

Finite production vertex 10�6 < e < 10�4

Discrepancy on (g�2)µ

Region will be covered in the near future

A1+septum

Mainz prospects: MESA, A1+septum, collimator

DarkLightJ. Boyce

-210 -110 1

-1010

-910

-810

-710

-610

-510

-410

BaBar

MAMIKLOE

ea

TestAPEX

Full

HPSE774

E141

E137

DarkLight

VEPP3

A' is 'welcome'µa

A' is excludedµa

(GeV)Um-210 -110 1

α'/α

-1010

-910

-810

-710

-610

-510

-410

JLab prospects:

Fixed-Target Theory UpdatesT. Beranek:

– double virtual Compton in proton targets– computational improvements– solid foundation for precision experiments– applications to many systems (e.g. K decay)

S. Andreas: improved beam-dump constraints

C. Wallace: E613 and light DM

New light-WIMP search at MiniBoone

Fix mχ, vary mVFix mV, vary mχ

(from M. Pospelov)

KLOE φ→ ηU (e+e–), e+e–→γU (μ+μ–)WASA@COSY π0→e+e–γ

sensitive to challenging <100 MeV massestogether probe much (all?) of remaining (g-2)μ-favored region for visible decays

+ many interpretable BaBar analyses

BES-III J/ψ→γA(μ+μ–), BaBar Y→γA(μμ,ττ)

BES-III η,η’→invisible

KLOE invisible hD+U(μ+μ–)Belle, BaBar visible hD+U→6leptons

low background ⇒ by loosening inv. mass cuts, can probably set strong limits on more general dark-sector cascades

Low-Energy Colliders & Meson Decays

I. Sarra; C. Gullstroem; E. Guido; F. Curciarello; J. Fu; I. Jaegle; A. Gaz; E. Graziani

Visible dark photon/U-boson

Visible light scalar

Invisible U-boson

Higgs’→Invisible U-boson

Nuclear Transitions

How robust? How consistent? New experimental tests forthcoming! –A. Krasznahorkay

[Quick estimate: decay to e+e– ⇒ stuck between improved (g-2)e bound and e– beam dumps]

FWN de Boer, et al

Precision Measurements & Theory

(g-2)μ G. Venanzoni

Parity Violation Tests of Kinetic and Mass Mixing –W. Marciano

Experimental PV prospects – F. Maas

– Different searches apply to different couplings (e.g. kinetic mixing vs. baryon # vs. e-τ …)

– Especially important distinction– visible– invisible (to DM)– cascade (e.g. multileptons)

Looking Forward

Decays to light DM

-210 -110 1

-1010

-910

-810

-710

-610

-510

-410

BaBar

MAMIKLOE

ea

TestAPEX

Full

HPSE774

E141

E137

DarkLight

VEPP3

A' is 'welcome'µa

A' is excludedµa

(GeV)Um-210 -110 1

α'/α

-1010

-910

-810

-710

-610

-510

-410

Visible (kinetic mixing)

very different experiments!

A lot left to do!

Parameter space too big for one plot!

Parameter space too big for one class of experiments!

Invisible: cf. Fayet; Battell, Pospelov, Ritz; C. Wallace’s talk

Cascade: BaBar 0908.2821 ...

A Worthy Goal

Decays to light DM

What does it take to probe this region?– for decays to DM

– inclusively?low m & low ε: inclusive recoil

(DarkLight? MESA?VEPP?)higher m & ε: e+e– decay

rate suppressed by ε2α/αD~equivalent to ε~10-4

not accessible with present proposals, but maybe possible

SummaryRapid progress in collider & fixed-target searches should continue to bring in exciting results!

Other frontiers – colliders, dark matter searches, Planck, precision measurements – will have important (complementary) interplay

Within direct searches for dark forces, three things to strive for:

– Complementary searches sensitive to different combinations of couplings

– Decays into dark matter or metastable states– Test the (g-2)-motivated parameter space inclusively

Thanks!