experimentswith internal t mainz energy-recovering...
TRANSCRIPT
EXPERIMENTS WITH INTERNAL TARGETS AT THE
MAINZ ENERGY-RECOVERING SUPERCONDUCTING ACCELERATOR
Harald MerkelJohannes Gutenberg-Universitat Mainz
International Workshop on (e,e′p) ProcessesBled (Slowenia), July 4th, 2017
The MESA Accelerator
MAGIX
High resolution magnetic spectrometersInternal targets: Gas Jet Target or Polarized Target
Physics program
Electric and Magnetic Radius of the ProtonAstropyhsical S-FactorSearch for exotic particlesFew body physics
Summary
Harald Merkel, Bled 2017 2/33
Energy Recovery Linac - Idea
Radio Frequency
RF-Cavity
Recirculation: l = n · λ
Injection External Beam
Wave length λ
Recirculating Linear Accelerator→ increase beam energy
Harald Merkel, Bled 2017 2/33
Energy Recovery Linac - Idea
Radio Frequency
RF-Cavity
Recirculation: l = n · λ
Last Recirculation: l = (m + 1/2) · λ
Target
Injection Beam Dump
Wave length λ
Recirculating Linear Accelerator→ increase beam energy
Last return path: l = (m+ 12)λ→ Phase shift
Energy feed back to cavities→ increase beam current
Harald Merkel, Bled 2017 3/33
MAMI - Floorplan
Using Halls of former A4 Experiment
Extension with new Hall
MAMI stays in operation!
Harald Merkel, Bled 2017 4/33
MESA - Mainz Energy Recovery Superconducing Acclerator
Super-conducting, recirculating LINAC
Energy of up to 155 MeV
Operation for external targets, 1 mA, polarized beam
Operation in Energy Recovery Mode
Energy of up to 105 MeVHigh beam current (up to 10 mA)Large fraction of the beam can be used for an Internal Target
...funded, under construction!
Harald Merkel, Bled 2017 5/33
Magix - Design Considerations
Using the full power of the MESA beam quality
Beam intensity
⇒ High count rate capability (MHz)
Nuclear Physics: Separate energy levels at 100 MeV at 100keV distance
⇒ momentum resolution δpp < 10−4
Precision measurement of electron scattering cross sectionsproportional to Mott cross section
dσ
dΩ≈ 1
Q4 ≈1
sin4θ/2
⇒ angular resolution δθ < 0.05
Low energetic particles (e, p, below π threshold)
Negligible energy loss in window-less gas targetVacuum until first detector layerExcellent position detection in first layer, modest angular detection later
⇒ Focussing spectrometers
Harald Merkel, Bled 2017 6/33
Magix - Optics
0 500 1000 1500 2000 2500
z [mm] scale 1:180
x [
mm
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0
500
1000
1500
2000
2500
0
0.175
0.35
0.525
0.7B [T]
-60
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-10 0
10
20
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40
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60
0 5
00
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y [mm]
pa
th le
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ff c
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ea
m [
mm
]
Vertical: Point-to-Point
⇒ Momentum Resolution
Horizontal: Parallel-to-Point
⇒ Angular Resolution
Harald Merkel, Bled 2017 7/33
Magix
Harald Merkel, Bled 2017 8/33
Magix - Possible Targets
Simple “Tube”-Target
Polarized Gas
Beam
Target cell
Polarized Hydrogen target
Flow is limited by polarizator (Laser driven/Atomic beam)
Luminosities of up to L = 2×1031 s−1cm−2
Polarization |~Pe| ≈ 80%
Established technique, e.g. BLAST, OLYMPUS, ...
Harald Merkel, Bled 2017 9/33
Supersonic Jet Target
Hypersonic gas jet by Laval nozzle
Cool down to Cluster mode
Gas jet caught by vacuum system
Expensive part: Pumping system 1 mbar at target→ 10−11 mbar at RF-Cavity
Beam quality allows for narrow flow delimiters
Luminosities of up to L = 1036 s−1cm−2 at 10 mA
Harald Merkel, Bled 2017 10/33
Supersonic Jet Target
Stabilized Temperature Tnozzle
Gas flow: 40 l/min
Density > 1019 Particles/cm2
First cluster jet seen!
S. Grieser, A. Khoukaz, ... (U Munster)
Harald Merkel, Bled 2017 11/33
Physics Program at Magix
Physics Program to employ the strenghtes of MESA and Magix
High beam intensity⇔ low target density
Excellent beam quality⇒ Precision physics
High degree of beam/target polarization
Tuneable to very low energies
Selected Examples:
Electric and Magnetic Radius of the Proton
Astrophysical S-Factors
Search for exotic particles:
Search for Dark PhotonsInvisible Decay of Dark PhotonsDark matter beam
Tests of ab-initio Calculations in Few-Body Physics
Harald Merkel, Bled 2017 11/33
Proton Form Factor
Harald Merkel, Bled 2017 12/33
Form Factor of the Nucleon
Elastic Cross Section (Rosenbluth-Formula):
dσ
dΩe=
(dσ
dΩe
)Mott
1(1+ τ)
[G2
E(Q2)+
τ
εG2
M(Q2)]
with τ = Q2
4m2p
ε =(1+2(1+ τ) tan2 θe
2
)−1
Structure of the Nucleon:
GE(Q2): Electric Form Factor → related to charge distributionGM(Q2): Magnetic Form Factor → related to distribution of magnetic moments
Normalization: GpE(Q
2 = 0) = 1 GnE(Q
2 = 0) = 0
GpM(Q
2 = 0) = 2.79 GnM(Q
2 = 0) = −1.91
Proton Charge/Magnetic Radius:
r2E = −6
ddQ2 GE(Q2)
∣∣∣∣Q2=0
r2M = − 6
µp
ddQ2 GM(Q2)
∣∣∣∣Q2=0
Harald Merkel, Bled 2017 13/33
Radius of the Proton
> 5σ Discrepancy between atomic physics and electron scattering
Situation still unclear
Serious problem far beyond nuclear physics: e.g. Rydberg Constant
Triggered extensive experimental program in atomic and nuclear physics
Harald Merkel, Bled 2017 14/33
Radius of the Proton
Experiment: Elastic scattering — Rosenbluth-Separation
Example kinematics:
Q2 = 0.0001 GeV2
E0 = 38.0 MeVE ′ = 37.9 MeVθ′ = 15
L = 1036 1s cm2
⇒ Count Rate N = 300 MHz/msr
“infinite” count rate
Very clean experiment
No target walls
Four-Momentum-Transfer 0.00001 GeV2 < Q2 < 0.03 GeV2
⇒ Classical determination of electric Radius
Harald Merkel, Bled 2017 15/33
Magnetic Radius of the Proton
Magnetic Radius from limit Q2→ 0
Suppressed by τ = Q2
4m2p
in cross section
dσ
dΩe=
(dσ
dΩe
)Mott
1ε(1+ τ)
[ε G2
E(Q2)+ τ G2
M(Q2)]
Beam-Recoil polarization is limited by proton recoil momentum |~pp|> 300 MeVc
Beam-Target polarization:
A(θ∗,φ∗) = AI sinθ∗ cosφ
∗+AS cosθ∗
AI = −2√
τ(1+ τ) tanθ
2GE GM
G2E +
(τ+2τ(1+ τ) tan2 θ
2
)G2
M
AS = −2 τ
√1+ τ+(1+ τ)2 tan2 θ
2tan
θ
2G2
M
G2E +
(τ+2τ(1+ τ) tan2 θ
2
)G2
M
φ∗ = 0θ∗ = 0, π
2
⇒ A⊥ =
Al
As∼ GE
GM
Harald Merkel, Bled 2017 16/33
Magnetic Radius of the Proton - Asymmtry
]2/c2 [GeV2Photon Virtuality q
0.03 0.025 0.02 0.015 0.01 0.005
[
%]
Asym
metr
y A
70
60
50
40
30
20
10
0
Asymmetry (Calc) o
= 42.0e
θSetting o
= 61.8e
θSetting o
= 79.3e
θSetting o
= 96.9e
θSetting o
= 116.2e
θSetting o
= 141.8e
θSetting
= 100 MeV0
Beam Energy E
= 80%beam
Beam polarization P
= 75%T
Target polarization P
Time per setting t = 10d
2cm1 s31
10×Luminosity L= 2
(Conservative) assumptions for target ≈ Blast target
Statistical error only (systematic error should be small!)
Harald Merkel, Bled 2017 17/33
Magnetic Radius of the Proton - Errors
— Belushkin (Disp. Analysis 2007)MESA projected errorJones (JLab 2000)Gayou (JLab 2001)Dietrich (MAMI 2001)Pospischil (MAMI 2001)Punjabi (JLab 2005)Jones (JLab 2006)MacLachlan (JLab 2006)Crawford (Bates 2007)Zhan (JLab 2011)
– Bernauer (MAMI 2010)
Q2 / (GeV2/c2)
µpG
p E/G
p M
1010.10.01
1.1
1
0.9
0.8
0.7
0.6
Maybe a little bit optimistic...
Harald Merkel, Bled 2017 17/33
Astrophysical S-Factors
Harald Merkel, Bled 2017 18/33
Nuclear Astrophysics α(12C,16 O)γ
Cross sections of stellar burning
Crucial for Nucleo-Synthesis
Supernova Explosions
Abundance of elements
Temperature of the sun⇒ Gamow Window
← He-Burning σ≈ 10−17 barn
Gamow Window
0+
0
0+
6049
3−
6129
2+
6917
1−
7116
2−
8871
12C+α
7162
16O
Harald Merkel, Bled 2017 19/33
Astrophysical S-Factor for α(12C,16 O)γ
S-Factor: divide out “trivial” cross section σ(E) = 1E e−2π
z1 z2 α
v ·S(E)
Very low count rates
Reduce backgrund⇒ best results from underground labors, e.g. LUNA at Gran Sasso
Still large errors
Extrapolation to Gamow-Window
Harald Merkel, Bled 2017 20/33
Astrophysical S-Factor for α(12C,16 O)γ
α
EE'
γ*
Silicon Strip Detector
O16 C
12
Spectrometer
Time reversal (enhancement by factor 10 due to spin weight):
γ+16 O→12 C+α
Covering the Threshold: Electroproduction in limit Q2→ 0
e+16 O→ e′+12 C+α ⇔ γ∗+16 O→12 C+α
Electron has large momentum, but virtual photon energy goes to zero!
High resolution for e-detection⇒ high resolution of γ detection
Detection of slow recoil α⇒ gas target, recoil detector ⇒ e+α coincidence
Harald Merkel, Bled 2017 20/33
Search for Exotic Particles
Harald Merkel, Bled 2017 21/33
Search for exotic particles: Motivation
Overwhelming evidence for Physics beyond the Standard Model
One of the most pressing Problems: Dark Matter, Dark Energy
Particle Physicists approach:
New unkown particlesResidual interaction with SM very likely (produced in the same Big Bang)...... but very weak
Direct search
Expensive experiments: XENON, CRESST, ...Very senistiveNo Signal yet
If particles, is there a whole Dark Sector of particles?
⇒ look e.g. for gauge bosons of dark sector
Harald Merkel, Bled 2017 22/33
Search for exotic particles: Dark Photons
How to model new physics:
Postulate new symmetry group
Symmetry Breaking to restore Standard Model at low energies
Consequences:
Extra U(1) gauge bosons ubiquitous in well motivated extensions
large gauge symmetries must be broken
U(1)s are the lowest-rank local symmetries
U(1) gauge bosons may be hidden (no interaction with SM)
Example: U(1) gauge factors in string compactifications:
E8×E8→ E6×E8→ SU(3)c×SU(2)L×U(1)Y︸ ︷︷ ︸standard model
×U(1)hidden
from breaking of second E8
No reason for U (1) boson to be heavy! ⇒ Dark Photon
Harald Merkel, Bled 2017 23/33
Search for exotic particles: Dark Photons
γ'
Z
e− e−
Z Z
e− e−
Z
(a) (b) γ'
Dark photon: Force carrier of the Dark Sector
Radiative production
e+Z → e+Z + γ′
→ e++ e− (detected in Magix)
] 2 [GeV/c'γm-210 -110
ε
-410
-310
-210
e(g-2)
KLOE 2013
KL
OE
201
4
WASA
HADESPHENIX
σ 2±µ(g-2)
favored
E774
E141
AP
EX
A1NA48/2
B A B AR2009
B A B AR2014
BESIII
MESA
Harald Merkel, Bled 2017 24/33
Dark Photons at MESA: Invisible Decay
0o
90o
180o
270o
360o
10−2
10−1
1
10
102
103
104
105
106
107
108
dσ
/dE
’dΩ
’dΩ
γ [nb/G
eV
sr2
]
θγγ
Bethe−Heitler Cross Section
γ’−Produktion mγ’=50 MeV
e+ p → e′+ p+ γ′
→ χ+ χ
γ ′ detection via missing mass m2γ ′ = (e+ p− e′− p′)2
No restriction by decay
Background: virtual Compton scattering: e+ p→ e′+ p+ γ + radiative tail
Recoil angular resolution needed→ Silicon strip detectors
Harald Merkel, Bled 2017 25/33
Beam-Dump Experiments: Motivation
1 10 100 1000 10410!5010!4910!4810!4710!4610!4510!4410!4310!4210!4110!4010!39
10!1410!1310!1210!1110!1010!910!810!710!610!510!410!3
WIMP Mass !GeV"c2#
WIMP!nucleoncrosssection!cm2 #
WIMP!nucleoncrosssection!pb#
7BeNeutrinos
NEUTRINO C OHER ENT SCATTERING
NEUTRINO COHERENT SCATTERING(Green&ovals)&Asymmetric&DM&&(Violet&oval)&Magne7c&DM&(Blue&oval)&Extra&dimensions&&(Red&circle)&SUSY&MSSM&&&&&&MSSM:&Pure&Higgsino&&&&&&&MSSM:&A&funnel&&&&&&MSSM:&BinoEstop&coannihila7on&&&&&&MSSM:&BinoEsquark&coannihila7on&&
8BNeutrinos
Atmospheric and DSNB Neutrinos
CDMS II Ge (2009)
Xenon100 (2012)
CRESST
CoGeNT(2012)
CDMS Si(2013)
EDELWEISS (2011)
DAMA SIMPLE (2012)
ZEPLIN-III (2012)COUPP (2012)
SuperCDMS Soudan Low ThresholdSuperCDMS Soudan CDMS-lite
XENON 10 S2 (2013)CDMS-II Ge Low Threshold (2011)
SuperCDMS Soudan
Xenon1T
LZ
LUX
DarkSide G2
DarkSide 50
DEAP3600
PICO250-CF3I
PICO250-C3F8
SNOLAB
SuperCDMS
Direct detection experiments:
No clear signal yet
Limit of sensitivity (solar ν background) will be reached soon
Lower masses (i.e. low recoil energy) not accessible
P. Cushman, et al., arXiv:1310.8327
Harald Merkel, Bled 2017 26/33
Beam-Dump Experiments: Idea2
Beam
e
Dump
10 m 10 mDirt
Detector
1 m
1 m
1 m
OptionalShieldingDetector
FIG. 1: Schematic experimental setup. A high-intensitymulti-GeV electron beam impinging on a beam dump pro-duces a secondary beam of dark sector states. In the basicsetup, a small detector is placed downstream so that muonsand energetic neutrons are entirely ranged out. In the con-crete example we consider, a scintillator detector is used tostudy quasi-elastic -nucleon scattering at momentum trans-fers > 140 MeV, well above radiological backgrounds, slowneutrons, and noise. To improve sensitivity, additional shield-ing or vetoes can be used to actively reduce cosmogenic andother environmental backgrounds.
.
A0a)
Z
e
e
p, n
b)
A0
Z
FIG. 2: a) pair production in electron-nucleus collisionsvia the Cabibbo-Parisi radiative process (with A0 on- or o↵-shell) and b) scattering o↵ a detector nucleus and liberatinga constituent nucleon. For the momentum transfers of inter-est, the incoming resolves the nuclear substructure, so thetypical reaction is quasi-elastic and nucleons will be ejected.
Production in beam dump, e.g. via pair production (actually: we don’t care...)2
MeV GeV dark matter are those whose interactionswith ordinary matter are mediated by new GeV-scale“dark” force carriers (for example, a gauge boson thatkinetically mixes with the photon). Such models readilyaccount for the stability of dark matter and its observedrelic density, are compatible with observations, and haveimportant implications beyond the dark matter itself. Inthese scenarios, high energy accelerator probes of sub-GeV dark matter are as ine↵ective as direct detectionsearches, because the missing energy in dark matter pairproduction is peaked well below the Z ! backgroundand is invisible over QCD backgrounds[? ? ].
Instead, the tightest constraints on light dark matterarise from B-factory searches in (partly) invisible decaymodes [? ], rare kaon decays [? ], precision (g 2) mea-surements of the electron and muon [? ], neutrino ex-periments [? ], supernova cooling, and high-backgroundanalyses of electron recoils in direct detection [? ]. Theseconstraints and those from future B-factories and neu-trino experiments leave a broad and well-motivated classof sub-GeV dark matter models largely unexplored. Forexample, with a dark matter mass > 70 MeV, existingneutrino factories and optimisitic projections for futureBelle II sensitivity leave a swath of parameter space rel-evant for reconciling the (g 2)µ anomaly wide open(see Figure 3). More broadly, the interaction strengthbest motivated in the context of models with kineticallymixed force carriers (mixing 105 . . 103) lies justbeyond current sensitivity across a wide range of darkmatter and force carrier masses in the MeVGeV range.These considerations, along with the goal of greatly ex-tending sensitivity to any components of MeVGeV darkmatter beyond direct detection constraints motivates amuch more aggressive program of searches in the comingdecade.
The experimental setup we consider can dramaticallyextend sensitivity to long-lived weakly coupled states (seeFig. 3), including GeV-scale dark matter, any componentof dark matter below a few GeV, and milli-charged parti-cles. This includes a swath of light force carrier parame-ters motivated by the (g2)µ anomaly, extending beyondthe reach of proposed neutrino-factory searches and BelleII projections (see Figure 3). The setup requires a small1 m3-scale detector volume tens of meters downstreamof the beam dump for a high-intensity multi-GeV elec-tron beam (for example, behind the Je↵erson Lab Hall Aor C dumps or a linear collider beam dump), and couldrun parasitically at existing facilities. All of the above-mentioned light particles (referred to hereafter as “”)can be pair-produced radiatively in electron-nucleus col-lisions in the dump (see Fig. 2a). A fraction of theserelativistic particles then scatter o↵ nucleons, nuclei, orelectrons in the detector volume (see Fig. 2b).
Within a year, Je↵erson Laboratory’s CEBAF (JLab)[53] will produce 100µA beams at 12 GeV. Even a simplemeter-scale instrument capable of detecting quasi-elasticnucleon scattering, but without cosmic background re-jection, positioned roughly 20 meters downstream of the
A0a)
Z
e
e
p, n
b)
A0
Z
FIG. 2: a) pair production in electron-nucleus collisionsvia the Cabibbo-Parisi radiative process (with A0 on- or o↵-shell) and b) scattering o↵ a detector nucleus and liberatinga constituent nucleon. For the momentum transfers of inter-est, the incoming resolves the nuclear substructure, so thetypical reaction is quasi-elastic and nucleons will be ejected.
Hall A dump has interesting physics sensitivity (upper,dotted red curves in Fig. 3). Dramatic further gainscan be obtained by shielding from or vetoing cosmogenicneutrons (lower two red curves), or more simply by us-ing a pulsed beam. The lower red curve corresponds to40-event sensitivity per 1022 electrons on target, whichmay be realistically achievable in under a beam-year atJLab. The middle and upper red curves correspondto background-systematics-limited configurations, with1000 and 2 · 104 signal-event sensitivity, respectively, per1022 electrons on target. Though not considered in de-tail in this paper, detectors sensitive to -electron elas-tic scattering, coherent -nuclear scattering, and pionproduction in inelastic -nucleon scattering could haveadditional sensitivity. With a pulsed beam, comparableparameter space could be equally well probed with 1 to3 orders of magnitude less intensity. A high-intensitypulsed beam such as the proposed ILC beam could reacheven greater sensitivity (orange curve). The parameterspaces of these plots are explained in the forthcomingsubsection.
The beam dump approach outlined here is quite com-plementary to B-factory + invisible searches [50], withbetter sensitivity in the MeVGeV range and less sen-sitivity for 1 10 GeV (see also [54]). Compared tosimilar search strategies using proton beam dumps, thesetup we consider has several virtues. Most significantly,beam-related neutrino backgrounds, which are the lim-iting factor for proton beam setups, are negligible forelectron beams. MeV-to-GeV are also produced withvery forward-peaked kinematics (enhanced at high beamenergy), permitting large angular acceptance even for asmall detector. Furthermore, the expected cosmogenic
We now have a “Dark Matter Beam”!
Dark Matter particles have enough recoil energy!
Detection with simple detector, e.g. scintillator cube
... or with sophisticated DM Detector ...
Harald Merkel, Bled 2017 27/33
New Hall
Dedicated new hall for experiment
Space for high resolution experiment
Additional space for beam dump experiment: 1 mA beam on target for 50%/a
Harald Merkel, Bled 2017 28/33
FLUKA Simulation
Neutrons can be shielded
Below pion threshold: negligible ν background
Clean conditions, detailed layout of hall needed for further design
Harald Merkel, Bled 2017 29/33
Magix Sensitivity
Reasonable sensitivity for low mass region
Multidimensional plot: Assumptions for dark photon mass, mχ
Calculations: G. Krnjaic, Perimeter Institute
Harald Merkel, Bled 2017 30/33
Tests of ab-initio Calulations in Few-Body Physics
Ab initio calculations e.g. with Effective Field Theory
Consistent chiral expansion of elementary NN-interaction
Consistent expansion of Few-Body-Systems
Very promising, but...
⇒ Talk by Jacek
Harald Merkel, Bled 2017 30/33
Waiting for the Accelerator...
Harald Merkel, Bled 2017 31/33
Initial State Radiaion
Final State Interaction contains known form factor (elastic Li ne)
Initial State Interaction: Cross section changes linear with form factor
Disentangle via comparison Simulation↔ Data
Harald Merkel, Bled 2017 32/33
First Results
102
103
104
105
106
107
Cou
nts
/(0.
1m
C·5
MeV
)
-3%
-2%
-1%
0%
1%
2%
3%
100 150 200 250 300 350 400 450 500
Dat
a/Sim
ula
tion
−1
Electron energy E ′ [MeV]
SimulationData at 495MeVData at 330MeVData at 195MeV
H(e, e′)nπ+ andH(e, e′)pπ0 ContributionsBackground
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Systematic uncertainty
Radiative corrections of O(α2)necessary
Better than 1% achievable
First measurement of GEp(Q
2)in range0.001GeV2 < Q2 < 0.004GeV2
Systematic errors:
Target wallsBackscattering on target framePion productionBackscattering entrance flangeRadiative corrections
⇒ Cluster Jet Target
M. Mihovilovic, A. B. Weber, et al., PLB 771 (2017) 194–198
Harald Merkel, Bled 2017 33/33
Summary
MESA:
High beam current in Energy Recovery mode
Excellent beam quality
MAGIX:
High Resolution Spectrometers
High density or high polarization internal target
Multi-purpose setup for precision physics
Physics Program
Precision form factors: Magnetic Radius of the Proton
Nuclear Astrophysics: S-Factor measurements
Few-Body physics
Search for exotic particles
Contributions from other groups are very welcome!