Accelerator based searches for a Dark Force Mediator · James Beacham (NYU) Dark Forces Workshop -- Frascati, Italy -- 16 October 2012 APEX Center for Cosmology and Particle Physics

B. Wojtsekhowski seminar at LNF, Frascati, Italy, Sept. 26/2013

Bogdan Wojtsekhowski, Jefferson Lab

Accelerator based searches for a Dark Force Mediator

1

•  Motivation ��

•  Existing searches

•  Experiments under preparation, APEX

•  Plan for the positron storage ring

•  Specialized e+e- collider for low s


Where is new physics

2

In the middle of the 18th century:


Where is new physics

3


SM tests, constraints on new physics (per PDG)

4


SM tests, constraints on new physics (per PDG)

5

from STORY05, Y. Semertzidis


The motivation is the nature of dark matter

6

1985ApJ...295..422C

Dark Matter: In 1933 by F. Zwicky. This plot from D. Clemens, 1985


The motivation is the nature of dark matter

7


The DAMA/LIBRA experiment

Bernabei et al. 250 kg radiopure NaI(Tl) the Gran Sasso

NIM A592:297-315,2008

8



DAMA collab., arXiv:1308.5109

9

Energy (keV)

S m (c

pd/k

g/ke

V)

-0.05

-0.025

0

0.025

0.05

0 2 4 6 8 10 12 14 16 18 20

2-5 keV

Time (day)

Res

idua

ls (c

pd/k

g/ke

V) DAMA/LIBRA 250 kg (1.04 ton yr)



Recoil detection experiment indicates a massive particle.

Where is a mediator of DF?

10

2-5 keV

Time (day)

Res

idua

ls (c

pd/k

g/ke

V) DAMA/LIBRA 250 kg (1.04 ton yr)


How to search for new physics

11

W±, Z

Standard Modelquarks, leptons

γg

Hidden Sectordark matter?

A� (massive)X

A�γ

The photon and Aʹ can mix !

mixing induces coupling between ordinary matter and hidden sector matter

�

HoldomGalison, Manohar


How to search for new physics

12

X A��

γ

Generated by heavy particles X interacting with andγ A�

X A�γ

� could even be O(1) (theoretically)

∆L =�

2FY,µνF �

µν “Kinetic Mixing”

our photon “heavy photon”

= mixing strength�


(“dark photon”)

small coupling

• Large interest in Aʹ search

• Number of considerations

naturally give Aʹ mass ~ 1 - 100s MeV

DM annihilation

Motivation for light dark photon

13


Positron/electron Antiproton/proton DM annihilation

(“dark photon”)

small coupling

• Large interest in Aʹ search

• Number of considerations

naturally give Aʹ mass ~ 1 - 100s MeV

Motivation for light dark photon

14

B. Wojtsekhowski seminar at LNF, Frascati, Italy, Sept. 26/2013 15

Recent summary of the searches

S. Andreas, C. Niebuhr, A. Ringwald, arXiv:1209.6083

E774

E141Orsay

KEK

E137

Ν-Cal I

CHARMNOMAD& PS191

aΜaeK�ΜΝΓ�KLOE

APEX A1

SM PM

e�e��ΓΜ�Μ�

10�2 10�1 1 10 102

10�7

10�6

10�5

10�4

10�3

10�2

10�1

mΓ' �GeV�

Χε

= g e

A’/g

em

g-2 of muon and electron

Missing particle in e+e- to ..

Decay to SM (e+/e-) - Beam Dump Mass reconstruction




E774

E141Orsay

KEK

E137

Ν-Cal I

CHARMNOMAD& PS191


APEX A1

SM PM


10�2 10�1 1 10 102

10�7

10�6

10�5

10�4

10�3

10�2

10�1

mΓ' �GeV�

Χε

= g e

A’/g

em


Missing particle in e+e- to γA’




E774

E141

Orsay

KEKE137

10�2 10�1

10�7

10�6

10�5

10�4

10�3

10�2

mΓ' �GeV�

Χ


E774

E141Orsay

KEK

E137

Ν-Cal I

CHARMNOMAD& PS191


APEX A1

SM PM


10�2 10�1 1 10 102

10�7

10�6

10�5

10�4

10�3

10�2

10�1

mΓ' �GeV�

Χε

= g e

A’/g

em

ε

Lsh Ldec

target

shield

detector

Ltot

E0

e!! "

E!"

e!

e+

No mass reconstruction

Decay inside dump

Statistics limitation




E774

E141Orsay

KEK

E137

Ν-Cal I

CHARMNOMAD& PS191


APEX A1

SM PM


10�2 10�1 1 10 102

10�7

10�6

10�5

10�4

10�3

10�2

10�1

mΓ' �GeV�

Χε

= g e

A’/g

em


Missing particle in e+e- to ..



Experiments under preparation

slide from R.Essig lecture at PATRAS2012

Detect both e+ and e-: mass reconstruction


Searches for a gauge boson A’ at JLab

Jefferson Lab site!

C!

A!

B!

D!

FEL!

J.R. Boyce. DARK2012, INFN, Frascati, Italy. 16-19 Oct. 2012. Slide 27 !

20



James Beacham (NYU) Dark Forces Workshop -- Frascati, Italy -- 16 October 2012

APEX Center for Cosmology and Particle Physics

10

Experimental signature

Direct production at JLab‣ Produce low mass hidden gauge bosons with weak coupling to SM via high energy

electron beam incident on fixed high-Z (Ta) target‣ decays to pair with opening angle ~mA�/Ebe+e−A�

e+

e!

e!

Z

A"

!

Θ0 ≈ 5◦

Dipole septum magnets allow for detection of produced at

small anglese+e−

APEX

21



APEX

James Beacham (NYU) Dark Forces Workshop -- Frascati, Italy -- 16 October 2012

APEX Center for Cosmology and Particle Physics

20

Final invariant mass spectrum QED radiative trident / Bethe-Heitler events‣ Bump hunt for small, narrow resonance

Bump hunt / resonance search

)2 (MeV/ce+e-m180 190 200 210 220 230 240 250

Even

ts /

( 0.0

5 )

0

200

400

600

800

1000

APEX Test Run Data, ~770K evtsAPEX Test Run Data, ~770K evts

Rescaled Mass0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Even

ts /

( 0.0

0166

389

)

0

100

200

300

400

500

600

700

800

900

=224.525, edm=0.000204, CQ=3A'

TestRunData_6_30_10_27, Wind 30, Cheb O(7), m =224.525, edm=0.000204, CQ=3A'

TestRunData_6_30_10_27, Wind 30, Cheb O(7), m

Window size = 30.5 MeV7th order polynomial fit

P (me+e− | mA� , σ, S, B, ai) =S · N(me+e− | mA� , σ) + B · Polynomial(me+e− , ai)

S + B

λ(S) =L(S, ˆB, ˆai)L(S, B, ai)

Probability model and profile

likelihood ratioTest mass:m = 224.525 MeV

209.525 MeV 240.025 MeV

Test run mass resolution: ~ 0.85 - 1.11 MeVσ

A�

(0.0

5)

APEX Test Run Data: Example Window

224.5 MeV

240.0 MeV 209.5 MeV

22


Searches for a gauge boson A’

the g-2= ae, aµ,

VEPP-3, and a portion of DarkLight

are sensitive

to “invisible” A’ decay modes

23


Ways to search for a new particle

  Search for a bump in the mass spectra

  As it was done - Vector Mesons, Z, H

  Required beam: energy, intensity, duty factor��

  How small is the e+e- decay branching fraction?

24

e+e− ↔ γ∗ and e+e− ↔ A�


Options for an e+e- experiment at low s

A “very” low energy, s1/2 ~ 30-100 MeV

a)  15 MeV x 15 MeV e+e- collider =>

b) Sliding beams of e+e- (500 MeV x 500 MeV at 25o)=> Project needs a specialized accelerator with two rings

c)  Current approach is a positron beam + atomic electrons

25

L ∼ 1024


Where to find a positron beam?   A beam of 25 nA 400 MeV was produced at Saclay in 1980s

  Beam of 1 µA was used for SLC (120 Hz)

  SLAC positron damping ring up to 1.2 GeV, 200 mA

  DORIS

  DAΦNE

  VEPP-3 energy of 0.5-2 GeV, 50 mA

26


Where to find a positron beam?   A beam of 25 nA 400 MeV was produced at Saclay in 1980s

  Beam of 1 µA was used for SLC (120 Hz)

  SLAC positron damping ring up to 1.2 GeV, 200 mA

  DORIS

  DAΦNE

  VEPP-3 energy of 0.5-2 GeV, 50 mA

27


Concept of an experiment with a positron beam

28

electron

positronphoton

U boson

!"cm

electron

positronphoton

!"cm

photon

a)

b)

[MeV] !E0 50 100 150 200 250 300 350 400 450 500

]-1

s•pe

r 5 M

eV [

pho

tons

R

ate

210

310

410

o=60

CM !"

o=120

CM !"

Kinematics


Concept of an experiment with a positron beam

29

500 MeV beam

Proposal of an experiment at VEPP-3: BW, Nikolenko, Rachek, arXiv:1207.5089

DETECTORREGION 2

DETECTORREGION 1

T

W1

W2

RF Cavity

Q1 Lens Q2 LensS

extu

pole

Target

6 m0 4 m2 m 8 m


Experimental layout

30

Le+e− ∼ 1032

2.6!" =

o

!"4.5=

o

o

Pu

mp

2,3

Sex

tup

ole

Val

ve

Pum

p 4

Pu

mp

1

Val

ve

Photon Detector

Q3Q2

D3

D2

Q1

D1

Sandwich

Co

ld H

ead

Pump 5

217 cm

10.7o

Storage Cell


Basic QED: e+e- → γ γ (mono-energetic) Search for : e+e- → γ U (peak below main)

Basic QED: e+Z → γ (smooth brems.)

The photo-production processes

•  Detect γ at fixed angle with the beam:

reconstruct the mass •  Variation with the angle: control systematic

•  Target Z Hydrogen vs. 12C

31

[MeV]!E50 60 70 80 90100 200 300 400

[de

g]!

"

1

2

3

4

5

6

7

8

1

10

210

310

410

510

gamma background

[MeV]!E50 60 70 80 90100 200 300 400

[de

g]!

"

1

2

3

4

5

6

7

8

=15 MeVA'

A' for M! #

--+e+e

! ! #--+e

+e

! H + e#+H+e

! H + e#+H+e


Positron beam on internal Hydrogen target

32

Anti-coincidence with the positron counters

reduce QED background

e+E = 450 MeV

e+ = 1.5oe+E = 100 MeV

e+ = 4.5o

e+ = 1.5o

e+ = 4.5oSandwich #1

Sandwich #2

vacuum chamber

400

70

Physics background is the bremsstrahlung radiation

[MeV]Threshold energy 0 50 100 150 200 250

]-1

s•[ p

hoto

ns

Rat

e

410

510

610

710 total

o- 4.5o = 1.5! "

-1s-2 cm32= 500 MeV L = 10+e EBremsstrahlung Rate -1s-2 cm32= 500 MeV L = 10+e EBremsstrahlung Rate


Kinematical correlation

33

[deg] LAB!"

1 1.5 2 2.5 3 3.5 4 4.5 5

[M

eV]

LAB

!E

0

50

100

150

200

250

300

350

400

450

500

=10 MeV U

M

=15 MeV U

M

=20 MeV UM

!!

LAB!E

σ = πr2e

γ+· (ln 2γ+ − 1)

NUγ = 2α�

α· Nγγ

The U/A’ mass resolution ~ 3%


Positron beam on internal Hydrogen target

34

[MeV]!E60 70 80 100 200 300 400 500

Rat

e p

er 5

MeV

, [H

z]

-310

-210

-110

1

10

210

310

410

510

[MeV]!E60 70 80 100 200 300 400 500

Rat

e p

er 5

MeV

, [H

z]

-310

-210

-110

1

10

210

310

410

510 + X! " + H +e o-0.8o = 0.4!#

o-2.0o = 1.6!#o-3.2o = 2.8!#o-4.4o = 4.0!#o-6.4o = 6.0!#

Projected event rate

A bump is e+e-2γ

[MeV]!E60 70 80 100 200 300 400 500

Rat

e p

er 5

MeV

, [H

z]

-310

-210

-110

1

10

210

310

410

510

[MeV]!E60 70 80 100 200 300 400 500

Rat

e p

er 5

MeV

, [H

z]

-310

-210

-110

1

10

210

310

410

510 + X! " + H --e o-0.8o = 0.4!#

o-2.0o = 1.6!#o-3.2o = 2.8!#o-4.4o = 4.0!#o-6.4o = 6.0!#

Projected for an electron beam for systematic check


Photon detector

35

Potential source of crystals:


VEPP-3 operation during ��Two-Photon Exchange experiment

36

01:00 02:00 03:00 04:00 05:00 06:00 07:00

Lif

eti

me, s

210

310

410

510

electrons positrons lifetime

VEPP-3: experiment E = 1600 MeV November 22, 7:00

I = 35.6 mA LT = 1039 s

Cu

rren

t, m

A

0

10

20

30

40

50


Projected sensitivity in the parameter space

37

-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

!'/!

-1010

-910

-810

-710

-610

-510

-410

Projected sensitivity for the VEPP-3 measurement at Lep =1032 cm-2/s (aver. current of 25 mA) in the six-month run


Projected sensitivity in the parameter space

38

Projected sensitivity for VEPP-3 (at 500 MeV) measurement at Lep =1032 cm-2/s (aver. current of 25 mA) in the six-month run

- - - with 5 GeV beam

These searches are sensitive to “invisible”

-210 -110 1

-1010

-910

-810

-710

-610

-510

-410

BaBarKLOE

ea

DarkLight

VEPP3

A' is 'welcome'a

A' is excludeda

(GeV)Um-210 -110 1

'/

-1010

-910

-810

-710

-610

-510

-410

ae DarkLight ( to “invisible”)

Y. Kahn, J. Thaler, arXiv:1209.0777


Options for an e+e- experiment at low s

A “very” low energy, s1/2 ~ 30-100 MeV

a)  15 MeV x 15 MeV e+e- collider =>

b) Sliding beams of e+e- (500 MeV x 500 MeV at 25o)=> Project needs a specialized accelerator with two rings

c)  Current approach is a positron beam + atomic electrons

39

L ∼ 1024


A collider scheme for an e-e+ experiment at low s

40

s = (p+µ + p−µ )2

E+E−(1− cos θ+−)

L of 1033 at 1 GeV allows the L =1032 at s=100 MeV,

Angle is of 25 degrees between the beams will allow a U boson search with mass up to 100 MeV

L ∝ (1− cos θ+−) W.Pauli, 1933

Sliding beams


Summary

  Search for the A’/U boson in the photon recoil spectra is possible using a positron beam and internal hydrogen target in the 500 MeV storage ring.

  Available luminosity (~1032) allows a 10-100+�� improvement over the (g-2) limit in mass range 7-15 MeV. The range could be extended to 50 MeV with 5 GeV beam.

  A e+e- collider based on a sliding scheme could be a U boson factory for the low mass range.


Luminosity of the colliders

from W. Panovsky’s article in BEAM LINE

For Ecm=100 MeV L ∼ 1026 − 1029cm−2/s

Dashed line isL ∝ E2

cm


Luminosity using initial state radiation

∆L ∝ L × ∆ssmax

s ∼ 4E+ · (E− − Eγ)

when smax = 10 GeV and ∆s ∼ 100 MeV (APEX)∆L ∼ 10−4L


BABAR search using initial state radiation 2

Even

ts p

er 1

0 M

eV/c

5000

10000 (a)

0

J/(2S)

)2Candidate mass (GeV/c0 2 4 60

1000

2000

3000 (b)

J/

(2S)

PRL 107, 221803 (2011) Search for Hadronic

Decays of a Light Higgs Boson

in the Radiative Decay

Documents

Accelerator based searches for a Dark Force Mediator · James Beacham (NYU) Dark Forces Workshop -- Frascati, Italy -- 16 October 2012 APEX Center for Cosmology and Particle Physics