The Aʹ′ Experiment (APEX) - Jefferson Lab

27 Pages·2013·6.57 MB·English

The Aʹ′ Experiment (APEX)
Searching for New Gauge Bosons in the Aʹ
Experiment at Jefferson Laboratory
Natalia Toro (Perimeter Institute)
for the APEX Collaboration
S. Abrahamyan, Z. Ahmed, K. Allada, D. Anez, T. Averett, A. Barbieri, K. Bartlett, J.
Beacham, J. Bono, J.R. Boyce, P. Brindza, A. Camsonne, K. Cranmer, M.M. Dalton,
C.W. de Jager, J. Donaghy, R. Essig (co-spokesperson), C. Field, E. Folts, A.
Gasparian, N. Goeckner-Wald, J. Gomez, M. Graham, J.O. Hansen, D.W.
Higinbotham, T. Holmstrom, J. Huang, S. Iqbal, J. Jaros, E. Jensen, A. Kelleher, M.
Khandaker, J.J. LeRose, R. Lindgren, N. Liyanage, E. Long, J. Mammei, P.
Markowitz, T. Maruyama, V. Maxwell, S. Mayilyan, J. McDonald, R. Michaels, K.
Moffeit, V. Nelyubin, A. Odian, M. Oriunno, R. Partridge, M. Paolone, E. Piasetzky,
I. Pomerantz, Y. Qiang, S. Riordan, Y. Roblin, B. Sawatzky, P. Schuster (co-
spokesperson), J. Segal, L. Selvy, A. Shahinyan, R. Subedi, V. Sulkosky, S.
Stepanyan, N. Toro (co-spokesperson), D. Walz, B. Wojtsekhowski (co-
spokesperson), J. Zhang and The Hall A Collaboration
1
Outline
In brief: APEX is a spectrometer-based search, at JLab Hall A,
for 50-500 MeV hidden-sector photons decaying promptly to e+e–.
0.001 0.01 0.1 1
-4 -4
10 10
1) The APEX experiment:
a
-5 m,5s -5
10 10
general setup and rationale VEPP3
KLOE
a few important details a favored
m,±2 s
-6 -6
10 10
BaBar
JHEP 1102:009,2011, arxiv:1001.2557
E774 APEX MAMI
a Test Runs
e
2) Test run (July 2010) -7 -7
10 10
a ê APEX
DarkLight
HPS
results
ê
'
a -8 -8
PRL 107:191804,2011, arxiv:1108.2750 10 10
E141
3) Full APEX
-9 Orsay HPS -9
10 10
extended target
SciFi optics calibration for
-10 -10
10 10
better mass resolution
U70
new septum
-11 -11
10 10
0.001 0.01 0.1 1
m GeV
A'
2
H L
APEX Concept and Dark Photon Production
m 3/2
l
A
(narrow) �
� E
� ⇥
e
� A m
A
�
� E
+
l
Energy = E m 1/2
A
(wide)
� E
E ≃E -m
� ⇥
Aʹ′ beam Aʹ′
e
� E ≃m
e- Aʹ′
.
Electron, P = E0/2
e
� Septum HRS−left
A
�
e +
� e
Beam
Nucleus W target
HRS−right
Positron, P = E0/2
3
.
The High Resolution Spectrometers
Lead Glass
S2m
Calorimeter
S0

VDC
Gas Cherenkov
Range Acceptance Resolution
0.3<p<4.0 GeV/c -4.5%<Δp/p<4.5% δp/p ≤ 2 10-4
12.5º<θ <150º 6msr δφ=0.5 mrad (H)
0
δθ=1 mrad (V)
(4.5 msr at θ =5º with septum)
0 4
Aʹ′ Production and Background Kinematics (m ≪E )
Aʹ′ beam
A′ Production QED Backgrounds
γ*
e
�
A
�
e +
� e
Nucleus
dσ~α2/m3 dm
σ ~ αʹ′/m2 = ε2α/m2
(rates before angular cuts)
Distinctive kinematics
35
-6
A' a' a=3 10
30 Aʹ products carry (almost)
25 full beam energy!
s
20 ê
s H ê L
t 3 Symmetric energy, angles in two
v QED Background 10
15
E
arms optimize A′ acceptance
10
5
E+ ≈ E– ≈E /2
ê
beam
0
0.0 0.2 0.4 0.6 0.8 1.0
also suppresses e– singles &
E +E E
+ - beam other pair backgrounds
After rejecting accidental e–π+ (demonstrated in test run), event rate
5
dominated by HQED Lbê ackgrounds above
APEX test run
•
Test run performed in Hall A, July 2010
Many thanks to JLab & Hall A staff for tremendous support!
•
Verified all key aspects of apparatus performance
–
VDC tracking performance at 4–6 MHz singles rates
–
Gas Cerenkov detector in coincidence trigger to reject π+’s
–
spectrometer optics & mass resolution
–
measurement of physics backgrounds
•
Resonance search on 700K good trident events
100 200 300 400 500
1100--44
Data
9000 QED
80800000 (no efficiency
V 7000 correction)
e
M
60600000
5 1100--55
.
0 5000
BaBar
/

s (cid:95)
nt40400000 /
e ' KLOE
v (cid:95)
E 3000 MAMI
a
(cid:43)
20200000 Accidental
1100--66
1000
APEX
00
130070 180 190 200 210 220 230 240 250 Test
l 200
a 200
u
d 0100
i 0
s
e -100
R -200-200 1100--77
-300 100.10 22000.200 300.30 44000.400 500.50
181800 191900 202000 212100 222200 232300 242400 252500
6
[ ]
m MeV
e+e- mass [MeV]
A'
Full APEX run plan and sensitivity
100 200 300 400 500
100 200 300 400 500
-4 Sensitivity of Proposed Run Plan
11110000---444
0.1 0.3 0.5
1 Month Beam Time
1110110000-----55555 10-5
– 6 days at 1,2,3 GeV
BaBar
L BaBar
y(cid:95)
(cid:95)
t/
i''/(cid:95) KKLLOOEE – 12 days at 4.5 GeV)
v(cid:95) MAMI
MAMI
i a
t a(cid:43)
i (cid:43)
ns 1110110000-----66666 10-6 >100x test-run statistics
e APEX
APEX
s
s TTeesstt
2
H
B
a 1110110000-----77777 100.10 22000.200 D300.30 44000.400 500.50 10-7
100.10 22000.200 300.30 44000.400 500.50
ê
a' C A m [[MeV]]
m MeV
A'
A'
-8 -8
10 10
0.1 0.3 0.5
+ -
e e A' Mass GeV
Approved by JLab PAC 37 with recommendation to run as soon
as possible
H L H L
Explores parameter space with unparalleled efficiency
(particularly above ~300 MeV)
7
APEX in Context
A1 Experiment
Mainz MAMI/A1 experiment
– superficially similar
(spectrometer e+e– coincidence)
– similar test-run sensitivity
but...
-4
10
Achim Denig Dark Photon Search @ MAMI
PRL
 106
 251802
(g-2)
– hitting detector rate limits µ
1303.2540
at least 6mo run needed to 10-5 KLOE
match APEX below 200 MeV 2er ε (g-2)e vs. α |(g-2)µ|< 2σ MAMI
et
m
a 10-6
r
a
P APEX
g
– Search above ~200 MeV also n
xi
Mi
E774
hitting beam current and
-7
10
This work:
radiation limits
E141 MAMI 2012
MESA, 10°
MESA, 20°
-8
10
10 100
Bottom line: m [MeV]
γ’
Figure 12. Compilation of existing exclusion limits and our predictions: For a better visualization we restrict ourselves to the
APEX has unique advantage redgionucurerent lytacocess iblhe atifixged-tharge-t erxpaerimtenets. Ocnlyaexisptingalimbits ais lpuiblitshyed in Raefsn. [16d, 21, 36, 37, 39, 40] are
shown, represented by the shaded regions. We do not show the predictions for other experiments [25, 28–30] in this figure
which are scheduled to probe the same region of parameter space. The limits of MAMI and APEX are those as given in their
septum magnet (small angle ⇒publicati onhs [2i6,g27].hTheeprredi ctisoniofgthisnworak folr t heaexccluscionelimipt extpeactednforctheeMA)MI 2012 experiment discussed
in section IIIB is depicted by the dashed curves. The prediction for MESA obtained in section IV is indic8ated by the dotted
(dashed-dotted) curve for the setups with a central scattering angle of 10◦ (20◦).
signal cross section given in Ref. [21].
For comparison we show in Fig. 10 the acceptance integrated cross section depending on me+e− for a proton target
with a beam energy of E =80MeV. In the left panel the same curves as in Fig. 9 are plotted. In the right panel of
0
Fig. 10 it is demonstrated, that the VCS contributioncorresponding with the Feynman diagramsin Fig. 2 aresmaller
by more than 6 orders of magnitude in the chosen kinematic setting, and can thus be neglected. As indicated by the
shape of the curves for ∆σSL+TL and ∆σTL in Figs. 9 and 10, the ratio of these two quantities is equal and thus
γ∗,D+X γ∗,D
the kind of target does not affect the exclusion limit concerning the QED background.
Fig. 11 shows the calculated ratio ∆σ /∆σTL which reaches a value around 8 10 for the proposed settings. The
γ γ −
expected exclusion limit on ε2 as obtained from Eq. (14), to the invariant mass spectra of Fig. 9, is presented on
Fig. 12, where a mass resolution of 0.125MeV was assumed. The dotted (dashed-dotted) curve on Fig. 12 represents
the settings with central angle of 10◦ (20◦). At very low masses below 10MeV Eq. (14) does not serve as a good
approximation for the exclusion limit anymore, since Eq. (19) of Ref. [21] overestimates the γ" signal cross section by
up to 50%.
A compilation of the existing exclusion limits is presented in Fig. 12, which shows the region 5MeV mγ#
≤ ≤
600MeV and 10−8 ε2 10−4 accessible at fixed-target experiments. Furthermore, existing limits as published in
≤ ≤
Refs. [16, 21, 36, 37, 39, 40] are also shown, and are represented by the shaded regions. Let us mention that other
planned experiments [25, 28–30] arescheduled to probe the same regionof parameter space. The limits of MAMI and
APEX are those as given in their publications [26, 27]. Our prediction for the exclusion limit expected in the MAMI
2012 experiment discussed in section IIIB is depicted by the dashed curves. The prediction for MESA obtained in
sectionIVisindicatedbythedotted(dashed-dotted)curvesforthesetupswithacentralscatteringangleof10◦ (20◦).
Our calculation shows, that the 2012 experiment is well suited to exclude a large region of the parameter space and
14
APEX in Context
A1 Experiment
Mainz MAMI/A1 experiment
– superficially similar
(spectrometer e+e– coincidence)
– similar test-run sensitivity
0.01 0.1
but...
-4 -4
10 10
-4
10
Achim Denig Dark Photon Search @ MAMI
PRL
 106
 251802
(g-2)
– hitting detector rate limits µ
1303.2540
-5 -5
10 10
at least 6mo run needed to 10-5 KLOE
match APEX below 200 MeaV102-meter ε6 (g-2)e vs. α |(g-2)µ|< 2σ MAMI 10-6
a 10-6 ê
' ar
a P APEX
g
– Search above ~200 MeV also n
xi
Mi
E774
-7 -7
hitting beam current and 10 10
10-7 APEX
full
This work:
radiation limits
E141 MAMI 2012
MESA, 10°
-8 MESA, 20° -8
10 10
-8
10
10 100
0.01 0.1
Bottom line: m [MeV]
γ’
m GeV
Figure 12. Compilation of existing exclusion limits and oAur'predictions: For a better visualization we restrict ourselves to the
APEX has unique advantage redgionucurerent lytacocess iblhe atifixged-tharge-t erxpaerimtenets. Ocnlyaexisptingalimbits ais lpuiblitshyed in Raefsn. [16d, 21, 36, 37, 39, 40] are
shown, represented by the shaded regions. We do not show the predictions for other experiments [25, 28–30] in this figure
which are scheduled to probe the same region of parameter space. The limits of MAMI and APEX are those as given in their
septum magnet (small angle ⇒publicati onhs [2i6,g27].hTheeprredi ctisoniofgthisnworak folr t heaexccluscionelimipt extpeactednforctheeMA)MI 2012 experiment discussed
in section IIIB is depicted by the dashed curves. The prediction for MESA obtained in section IV is indic8ated by the dotted
(dashed-dotted) curve for the setups with a central scattering angle of 10◦ (20◦).
H L
signal cross section given in Ref. [21].
For comparison we show in Fig. 10 the acceptance integrated cross section depending on me+e− for a proton target
with a beam energy of E =80MeV. In the left panel the same curves as in Fig. 9 are plotted. In the right panel of
0
Fig. 10 it is demonstrated, that the VCS contributioncorresponding with the Feynman diagramsin Fig. 2 aresmaller
by more than 6 orders of magnitude in the chosen kinematic setting, and can thus be neglected. As indicated by the
shape of the curves for ∆σSL+TL and ∆σTL in Figs. 9 and 10, the ratio of these two quantities is equal and thus
γ∗,D+X γ∗,D
the kind of target does not affect the exclusion limit concerning the QED background.
Fig. 11 shows the calculated ratio ∆σ /∆σTL which reaches a value around 8 10 for the proposed settings. The
γ γ −
expected exclusion limit on ε2 as obtained from Eq. (14), to the invariant mass spectra of Fig. 9, is presented on
Fig. 12, where a mass resolution of 0.125MeV was assumed. The dotted (dashed-dotted) curve on Fig. 12 represents
the settings with central angle of 10◦ (20◦). At very low masses below 10MeV Eq. (14) does not serve as a good
approximation for the exclusion limit anymore, since Eq. (19) of Ref. [21] overestimates the γ" signal cross section by
up to 50%.
A compilation of the existing exclusion limits is presented in Fig. 12, which shows the region 5MeV mγ#
≤ ≤
600MeV and 10−8 ε2 10−4 accessible at fixed-target experiments. Furthermore, existing limits as published in
≤ ≤
Refs. [16, 21, 36, 37, 39, 40] are also shown, and are represented by the shaded regions. Let us mention that other
planned experiments [25, 28–30] arescheduled to probe the same regionof parameter space. The limits of MAMI and
APEX are those as given in their publications [26, 27]. Our prediction for the exclusion limit expected in the MAMI
2012 experiment discussed in section IIIB is depicted by the dashed curves. The prediction for MESA obtained in
sectionIVisindicatedbythedotted(dashed-dotted)curvesforthesetupswithacentralscatteringangleof10◦ (20◦).
Our calculation shows, that the 2012 experiment is well suited to exclude a large region of the parameter space and
14
APEX vs. Mainz
Detector, beam, and radiation limitations ⇒ Mainz
probably can only access high-coupling & low-mass
portion of APEX sensitivity (without major upgrades)
Dashed green is updated sensitivity estimate for ~14
total beam-days (9 settings)
[1303.2540
 Beranek,
 Merkel,
 Vanderhaeghen]

0.01 0.1
-4 -4
– no publishable result 10 10
-4
10
1303.2540
(g-2)
µ
expected from 2012 run
-5 -5
10 10
10-5 KLOE
– present dark-force plans a 102-meter ε6 (g-2)e vs. α |(g-2)µ|< 2σ MAMI 10-6
a 10-6 ê
focus on lower Aʹ′ mass, a' Par APEX
g
n
xi
Mi
including MESA E774
-7 -7
10 10
10-7 APEX
full
This work:
E141 MAMI 2012
MESA, 10°
-8 MESA, 20° -8
10 10
-8
10
10 100
0.01 0.1
m [MeV]
γ’
m GeV 9
Figure 12. Compilation of existing exclusion limits and oAur'predictions: For a better visualization we restrict ourselves to the
region currently accessible at fixed-target experiments. Only existing limits as published in Refs. [16, 21, 36, 37, 39, 40] are
shown, represented by the shaded regions. We do not show the predictions for other experiments [25, 28–30] in this figure
which are scheduled to probe the same region of parameter space. The limits of MAMI and APEX are those as given in their
publications [26, 27]. The prediction of this work for the exclusion limit expected for the MAMI 2012 experiment discussed
in section IIIB is depicted by the dashed curves. The prediction for MESA obtained in section IV is indicated by the dotted
(dashed-dotted) curve for the setups with a central scattering angle of 10◦ (20◦).
H L
signal cross section given in Ref. [21].
For comparison we show in Fig. 10 the acceptance integrated cross section depending on me+e− for a proton target
with a beam energy of E =80MeV. In the left panel the same curves as in Fig. 9 are plotted. In the right panel of
0
Fig. 10 it is demonstrated, that the VCS contributioncorresponding with the Feynman diagramsin Fig. 2 aresmaller
by more than 6 orders of magnitude in the chosen kinematic setting, and can thus be neglected. As indicated by the
shape of the curves for ∆σSL+TL and ∆σTL in Figs. 9 and 10, the ratio of these two quantities is equal and thus
γ∗,D+X γ∗,D
the kind of target does not affect the exclusion limit concerning the QED background.
Fig. 11 shows the calculated ratio ∆σ /∆σTL which reaches a value around 8 10 for the proposed settings. The
γ γ −
expected exclusion limit on ε2 as obtained from Eq. (14), to the invariant mass spectra of Fig. 9, is presented on
Fig. 12, where a mass resolution of 0.125MeV was assumed. The dotted (dashed-dotted) curve on Fig. 12 represents
the settings with central angle of 10◦ (20◦). At very low masses below 10MeV Eq. (14) does not serve as a good
approximation for the exclusion limit anymore, since Eq. (19) of Ref. [21] overestimates the γ" signal cross section by
up to 50%.
A compilation of the existing exclusion limits is presented in Fig. 12, which shows the region 5MeV mγ#
≤ ≤
600MeV and 10−8 ε2 10−4 accessible at fixed-target experiments. Furthermore, existing limits as published in
≤ ≤
Refs. [16, 21, 36, 37, 39, 40] are also shown, and are represented by the shaded regions. Let us mention that other
planned experiments [25, 28–30] arescheduled to probe the same regionof parameter space. The limits of MAMI and
APEX are those as given in their publications [26, 27]. Our prediction for the exclusion limit expected in the MAMI
2012 experiment discussed in section IIIB is depicted by the dashed curves. The prediction for MESA obtained in
sectionIVisindicatedbythedotted(dashed-dotted)curvesforthesetupswithacentralscatteringangleof10◦ (20◦).
Our calculation shows, that the 2012 experiment is well suited to exclude a large region of the parameter space and
14