beam purity for light dark matter search in beam dump … · 2016. 5. 18. · beam dump experiments...

Review ArticleBeam Purity for Light Dark Matter Search inBeam Dump Experiments

D Banerjee P Crivelli and A Rubbia

Institute for Particle Physics ETH Zurich 8093 Zurich Switzerland

Correspondence should be addressed to P Crivelli paolocrivellicernch

Received 23 March 2015 Accepted 16 June 2015

Academic Editor Torsten Asselmeyer-Maluga

Copyright copy 2015 D Banerjee et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited Thepublication of this article was funded by SCOAP3

This paper reviews the search for light dark matter in beam dump experiments with a special emphasis on the necessity of beampurity for precise background rejection at the sensitivities aimed at these experiments As a case study we cite the P348 experimentwhich has test beam time in Fall 2015 at the SPS H4 beam line at CERN and aims to search for the 1198801015840(1) gauge boson 1198601015840 whichas per one model of dark matter mediates a weak interaction between ordinary matter and dark matter via mixing of these ldquodarkphotonsrdquo with ordinary photon The experiment aims to probe the still unexplored area of mixing strength 10

minus5le 120598 le 10

minus3 andmasses 119872

1198601015840 le 100MeV by using 10ndash300GeV electron beam from the CERN SPS This paper presents the simulation results for

rejection of background due to beam impurity by tracking the incoming particles with Micromegas detectors at a level lt10minus10

1 Introduction

The existence of dark matter has been postulated primarilybecause of the observation that the motion of galaxies withina cluster suggests they are bound by a total gravitationalforce due to about 5ndash10 times as much matter as can beaccounted for from luminous matter in the said galaxies It ispossible to measure the rate of rotation of the stars about thegalactic centre The resultant ldquorotation curverdquo related to thedistribution of matter in the galaxy suggests the outer starsseem to rotate too fast for the amount of observable matter inthe galaxy These results can be explained assuming there isa ldquodark matter halordquo surrounding every galaxy which unlikenormalmatter does not interact via the electromagnetic forcemaking it extremely hard to detect Further observations andtheories supporting the existence of dark matter are reviewedin [1ndash3] Various experiments are underway which aim tosearch for dark matter in the GeV-TeV mass range the so-called WIMPs (most popular candidate for dark matter)but these experiments are essentially blind to the search forlight dark matter in the MeV-GeV range Models of darkmatter in our specified mass range (MeV-GeV) can accountfor its observed abundance through either thermal freeze-out or nonthermal mechanisms [4ndash8] Among the better

motivated models of MeV-GeV dark matter are those whoseinteractionswith ordinarymatter aremediated by new ldquodarkrdquoforce carriers namely a1198801015840(1) gauge boson1198601015840 (dark photon)that kinetically mixes with ordinary photon as in [9 10]

119871 int = minus12120598119865120583]1198601015840120583]

(1)

where 119865120583] 1198601015840120583] are the ordinary and dark photon fields

respectively and parameter 120598 is their mixing strength Ina class of models 1198601015840 may have a mass 119872

1198601015840 le 100MeV

and 120574 minus 1198601015840 mixing strength as large as 120598 sim 10minus5ndash10minus3

which is in the experimentally accessible and theoreticallyinteresting region [11 12] Dark matter in this mass rangecan be probed in beam dump experiments or through rareparticle decay for example if the 1198601015840 mass is below the massof 1205870 it can be searched for in the decay of 1205870

rarr 1205741198601015840 and

the subsequent decay of 1198601015840 to 119890+119890minus pairs [13ndash16] Recently

stringent constraints on the mixing parameter 120598 in the sub-GeVmass range have been derived from a search of this decaymode with existing data of neutrino experiments [17 18] andfrom SN1987A cooling [19] This makes further searches fordark mediators interesting

Hindawi Publishing CorporationAdvances in High Energy PhysicsVolume 2015 Article ID 105730 6 pageshttpdxdoiorg1011552015105730

brought to you by COREView metadata citation and similar papers at coreacuk

provided by Open Access Repository

2 Advances in High Energy Physics

2 Principle of Detection

The experimental principle of these searches includes havinga detector downstream of a high energy electron beam todetect these ldquodarkrdquo force carriers from their SM decay prod-ucts quasi-elastic nucleon scattering or detecting missingenergy downstream of the beam from their invisible decayproducts In this paper we will focus mainly on the invisibledecay channel A high-intensity high energy electron beamimpinges on a beam dump target producing dark sector stateswhich are detected downstream with various detectors andvetoes

The visible decay channel that is 1198601015840 rarr 119890+119890minus can be

searched for in a ldquolight-shining-through-a-wall-experimentrdquowherein 119860

1015840 does not interact with any component of thedetector geometry but 119890+119890minus are tracked by trackers placeddownstream which does not appear to originate from anyprimary particle like a light shining through a wall Theinvisible decay channel can be searched for by detectingmissing energy downstream Such an approach has beentaken in the P348 experiment due in CERNwith a beam timein Fall 2015 at the SPS H4 beam line

For the invisible decay channel when1198601015840rsquos produced decayinto dark matter particle pairs the decay products do notinteract with any detector thereafter Thus the total of theincoming beam energy will not be accounted for in thetotal deposited energy downstream of the target For suchsignatures it is very important to ensure there is no leakageof energy to minimise the possibility of false signal and alsothe incoming energy should be well known to accuratelycalculate the percent of missing energy These searches arelimited mainly due to leakage of energy beam impurity(contamination from hadrons) with the hadrons decaying toneutrinos and a lepton before the detector with the neutrinocarrying most of the energy undetected and due to a broadenergy spectrum of the primary beam For the first twocases it is important to ensure complete hermeticity of thedetector to minimise leakage and proper primary particleidentification to reject hadrons Since these experimentsrequire sensitive searches it is absolutely crucial to estimatethe energy of the incoming particles to accurately rejectbackground from possible low energy tail of the primarybeam mimicking a positive signal As a case study we willpresent the P348 experiment which aims to use Micromegasdetectors to accurately track these incoming particles in amagnetic field to estimate their energy

3 P348 Experiment

TheP348 experiment aims to search for the dark force carriersmentioned above and probe the still unexplored area ofmixing strength 10minus5 le 120598 le 10minus3 and masses 119872

1198601015840 le

100MeV using the 10ndash300GeV electron beam present at theCERN SPS 1198601015840rsquos with such parameters are short-lived anddecay with a lifetime lt10minus10 s into their SM 119890

+119890minus pairs or

dark particles Figure 1 shows the exclusion plots expectedfrom the 1198601015840 rarr 119894119899V119894119904119894119887119897119890 channel search and also the alreadyexisting constraints obtained from previous experimentsThe light blue and blue area show the expected 90 CL

10minus2

10minus3

10minus4

10minus5

Mix

ing120576

1 10 102 103 104

MA998400 (MeV)

Figure 1 Exclusion region in (1198721198601015840 120598) plane for invisibly decaying

1198601015840 into a pair of light darkmatter particles120594120594 provided119872

1198601015840 gt 2119898

120594

exclusion areas corresponding respectively to 109 and 1012accumulated electrons at 100GeV for the background-freecase Other existing constraints mostly adapted from [20]are also shown The constraint from the BaBar monophotonsearch is given as the light grey shaded region Furtherlimits are shown from the anomalous magnetic moment ofthe electron ((119892 minus 2)

119890) and DarkLight the rare kaon decay

119870+

rarr 120587+1198601015840 (E787) and LSD experiments The LSND area

is determined assuming 1198601015840minus 120594 coupling 120572

119863= 01 and that

120594 cannot decay to other light dark sector states which do notinteract with 119860

1015840rsquos [21] The red shaded region is preferred inorder to explain the discrepancy between the measured andthe predicted value of the anomalous magnetic moment ofthe muon

31 Experimental Setup for P348 The P348 experiment hasthe same basic experimental setup for both 119860

1015840rarr 119890+119890minus and

1198601015840

rarr 119894119899V119894119904119894119887119897119890 searches as shown in Figure 2 [22] withECAL1 and ECAL2 for detecting electromagnetic showers adecay volume (DV) for the decay of 1198601015840 tracking detectorsDHRMM1 and DHRMM2 for tracking the 119890+119890minus tracks anda HCAL mainly for the invisible decay channel and vetoesThe setup before the ECAL1 is to tag the incoming electronsas is explained later

4 The Invisible Decay Channel

The rate of events of 1198601015840 production and its subsequent decayto dark particles in the previouslymentioned parameter spaceis at le10minus10 with respect to the ordinary photon productionrate In order to be able to reach such statistics and observea successful 119860

1015840 event the P348 experiment aims to use

Advances in High Energy Physics 3

eminus 12

0GeV

S1S2

SMM1

SMM2

SMM3

Magnet

Magnet

SMM4

ECAL1

S3

Veto1

Decay v

olumeeminus

DHRMM1DHRMM2

ECAL2

Veto2

HCAL

A998400

e+

Figure 2 Experimental setup for the P348 experiment

the CERN SPS H4 119890minus beam at an energy sim100GeV and a

maximal beam intensity of sim105 119890minus for one typical SPS spillcycle of 148 s including 48 s spill duration and maximumfour cycles per minute The beam impurity from othercharged particles in the beam is below 10minus2 and the size ofthe beam at ECAL1 is of the order of a few cm2 To estimatethe exact beam energy spectrum and its low energy tail a fullbeam line simulation is required at a high level of precisionhowever the fraction of electrons with energy 119864 lt 119864th where119864th = 10GeV is expected to be lt10minus6 The origin of thelow energy tail is mainly due to the interactions of the beamwith passivematerials such as entrance windows of the beamlines and residual gas and also due to the in-flight decayof pions and muons in the beam line The incoming high

energy electron beam impinges on the ECAL1 and interactswith the material 1198601015840rsquos are produced through mixing withbremsstrahlung photons from the electrons scattering off thenuclei in ECAL1 A fraction (119891) (10) of the beam energy1198641 = 1198911198640 = 10GeV where 1198640 is the beam energy = 100GeVis deposited in the ECAL1 while the remaining 90GeV iscarried by the 119860

1015840 It goes undetected through the first vetointo the decay volume (DV) where it decays into dark matterparticles The decay products go undetected through S1 S2veto1 ECAL2 veto2 and the HCAL So there is a missingsim90GeV energy signal for this channel in the downstreampart of ECAL1 Instead if a low energy electron sim10GeVimpinges on the ECAL1 and deposits all its energy there nosignal thereafter in the detectors downstream will mimic our


asymp100120583mHV2

Readoutstrips

HV1

eminus

3m

m

Drift cathode

Amplification cathode

Figure 3 Schematic of the principle of operation of a Micromegasdetector showing an incoming charged particle ionising the gas andleaving a signal on the readout strips

event signature and give false signal It is therefore crucial tobe completely certain of the energy of the incoming particleto eliminate the background at the level required

We propose to use a scheme to tag the incoming electronbeam by tracking them in a magnetic field using 119883-119884Micromegas detectors

5 Micromegas Detector for Low EnergyBackground Rejection

The detector is a two-stage parallel plate avalanche gas-chamber with Ar-isobutane mixture (95-5) groundedcopper readout strips and nickel electroformed micromeshfor the drift and amplification cathodes The drift cathodeis maintained at 3mm from the amplification cathode witha drift voltage of 1 kVcm and the amplification cathode ismaintained at 128120583m from the readout strips as shown inFigure 3with an amplification voltage of 40 kVcmA chargedparticle entering the detector ionises the gas and producessecondary electrons which drift towards the amplificationmesh under the applied 119864-field The secondary electronson reaching the amplification mesh produce avalanche likesecondary ionisation due to the high amplification field Theresultant signal thus induced is a sum of the electron and ionsignalTheP348 experiment aims to use the119883-119884Micromegasdesign with 250 120583m strip pitch The designs of the detectorwith the corresponding strip widths are shown in Figure 4The detectors for this experiment will be equipped with aresistive layer as shown to limit the sparks due to the highbeam rate The material budget of the detector is minimisedusing a ldquohoney combrdquo structure for the PCB which includestwo 100 120583m FR4 PCBs with supporting pillars between themin the active area and 3mm FR4 PCB outside the active areaThis has been designed and produced in the Micromegasworkshop of Rui de Oliveira at CERN

In order to track the incoming particle the detectors willbe placed in the yoke of a magnet already present in theH4 beam area with a field strength of 15 T for a yoke of17 cm over a distance of 2m As shown in Figure 2 there aretwo scintillators (S1 and S2) placed before the Micromegas

250150120583mx and resistive layer

y 25080120583m

Mesh

x-strips

Resistive strips

y-stripsPCB

Figure 4 119883-119884 Micromegas detectors showing the dimensions ofthe strips and the resistive layer The resistive layer helps to limitthe spark at high rate The 119883-119884 module helps to determine thehit position of the incoming particle and track it precisely in themagnetic field

modules (SMM1 SMM2 and SMM3) and the magnet whichwill be used to monitor the beam and as a trigger forthe Micromegas modules Between each Micromegas in themagnet area will be a vacuum tube to reduce secondaryinteraction of the primary beam with air The beam willgo through the scintillators and enter the magnet where itwill be tracked by the three Micromegas modules The threeMicromegas modules will be placed about 1m apart in the2m magnet The ECAL1 will be placed 15m (vacuum tubein between) from SMM3 To get the hit point of the primarybeam on the ECAL1 with good spatial resolution a fourthMicromegas module (SMM4) will be placed right before theECAL1 followed by another scintillator (S3) for good timeresolution of the beam entering the ECAL1 The ECAL1 withSMM4 and S3 will be placed offset by 12 cm in the directionof the deflection to account for the deflection of the electronin the magnetic field

Simulations have been carried out with Geant4 to esti-mate the level of background rejection with this setupThe momentum reconstruction is limited mainly due tothe interactions of the primary beam with the material ofthe detector The simulations included Mylar windows asthe in- and output flanges to the vacuum tubes in eachdetector module The beam divergence 120590 sim 50 120583rad andbeam diameter 120590 sim 07 cm (values obtained from IliasEfthymiopoulos of CERN SPS) were also taken into accountDue to the limitation of the magnet yoke diameter thedimension of the Micromegas modules that can be placedin the magnet is = 8 cm times 8 cm Because of the size of themodules the detector efficiency the beam diameter anddivergence simulations show 95 efficiency for tracking 106events with 10GeV and 30GeV primaries were simulated andthemomentumof the trackwhen there is an electron enteringthe ECAL1 was reconstructed Due to the offset of the ECALnone of the 10 GeV primaries hit the ECAL 15m away even ata level of 10minus7

Figure 5 shows the spectrum of momentum recon-structed for 30GeV primary electrons As seen from the plotout of the 106 simulated events sim01 had an actual hit inECAL1withmajority of the primary being deflected away dueto the magnetic field Of the events when there is some hitin ECAL1 there is no reconstructed momentum gt50GeV tomimic a false signalThe tail of lower reconstructedmomentais due to the loss of energy of the primary electrons due tointeraction in the detector materials The reconstruction was


Energy (GeV)0 10 20 30 40 50

Entr

ies

1

10

EntriesmomCal

951Mean 2981RMS 07224

102

Reconstructed momentum for 30GeV electron tail when ECAL hit

Figure 5 Reconstructed momentum of 30GeV primaries fromGeant4 simulation when there is an actual hit in ECAL1

PrimenergyEntriesMeanRMS

9485322

118

9481

Cou

nts

Energy (Gev)

107

106

105

104

103

102

0 20 40 60 80 100 120 140

Figure 6 Spectrum of energy of 120GeV primary beam afterinteraction with the detector materials before the ECAL1 Theinefficiency in the beam with 119864 lt 50GeV is sim07

also checked for higher statistics sim107 simulated events andit was noticed that due to the interaction of the primarieswith the detector materials and the hit points being givenby the secondary tracks instead of the primary there were 7events with reconstructed momenta gt50GeV for the 30GeVprimaries Thus the background can efficiently be rejected bytracking at the level of 10minus6 for the 30GeV primaries

As seen from Figure 6 the spectrum of the energydeposited in ECAL1 by 120GeV primary electrons has along low energy tail which results in an inefficiency of theexperiment and is also a source of background wherein thehigh energy primary after losing most of its energy hitsthe ECAL1 as a low energy primary or in case the highenergy primary after interacting with the trackers completelymissed the ECAL1 and its low energy secondaries hit theECAL1 (as shown in Figure 7) It is thus important to makesure that these primaries do not add to any false signalprobability when they reach the ECAL1 The inefficiency dueto these interactions is sim07 An analysis was done to checkat what level this low energy background can be rejectedwith tracking and the level at which such backgrounds canbe effectively suppressed is lt10minus10 This beam spectrometer

ECAL1

Low-E secondaries

SMM1

SMM2

SMM3

eminus

Figure 7 Track showing primary high energy missing the ECAL1and the low energy secondaries hitting the ECAL1 which canbe rejected from the hit point on SMM4 before the ECAL1 andthe trajectory of the primary track in the first three Micromegasmodules

system using the Micromegas modules in a magnet thuseffectively suppresses the low energy background at the levelrequired andmeets the necessity for beampurity as explainedpreviously for detectingmissing energy in these experiments

6 Conclusion

Thus we present the importance of beam purity in thesearches of dark force mediators by their invisible decaychannel with the P348 experiment as a case studyWe presenta scheme and preliminary simulation results to use 119883-119884Micromegas detectors as a mass spectrometer to tag theincoming beam in amagnetic field as will be done in the P348experiment at CERN The experiment has test beam time inFall 2015 wherein the scheme for tracking can be tested andthe simulation results can be verified experimentally as well

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] D N Spergel and P J Steinhardt ldquoObservational evidence forself-interacting cold dark matterrdquo Physical Review Letters vol84 no 17 pp 3760ndash3763 2000

[2] G Bertone D Hooper and J Silk ldquoParticle dark matterevidence candidates and constraintsrdquo Physics Reports vol 405no 5-6 pp 279ndash390 2005

[3] L Bergstrom ldquoNon-baryonic dark matter observational evi-dence and detection methodsrdquo Reports on Progress in Physicsvol 63 no 5 pp 793ndash841 2000

[4] D B Kaplan ldquoSingle explanation for both baryon and darkmatter densitiesrdquo Physical Review Letters vol 68 no 6 pp 741ndash743 1992

[5] M Pospelov and A Ritz ldquoAstrophysical signatures of secludeddark matterrdquo Physics Letters B vol 671 no 3 pp 391ndash397 2009

[6] J L Feng ldquoNon-WIMP candidatesrdquo in Particle DarkMatter Observations Models and Searches G Bertone


Ed chapter 10 pp 190ndash204 Cambridge University Press 2010httpwwwcambridgeorgchacademicsubjectsphysicscos-mology-relativity-and-gravitationparticle-dark-matter-obser-vations-models-and-searchesformat=HB

[7] A Katz and R Sundrum ldquoBreaking the dark forcerdquo Journal ofHigh Energy Physics vol 2009 no 6 article 003 2009

[8] S Pirandola A Serafini and S Lloyd ldquoCorrelation matrices oftwo-mode bosonic systemsrdquo Physical Review A vol 79 ArticleID 052327 2009

[9] L B Okun ldquoLimits of electrodynamics paraphotonsrdquo ZhurnalEksperimentalnoi i Teoreticheskoi Fiziki vol 83 pp 892ndash8981982

[10] L B Okun ldquoLimits of electrodynamics paraphotonsrdquo SovietPhysicsmdashJETP vol 56 p 502 1982

[11] J Jaeckel and A Ringwald ldquoThe low-energy frontier of particlephysicsrdquo Annual Review of Nuclear and Particle Science vol 60no 1 pp 405ndash437 2010

[12] J L Hewett HWeerts R Brock et al ldquoFundamental physics atthe intensity frontierrdquo httparxivorgabs12052671

[13] F Archilli D Babusci D Badoni et al ldquoSearch for a vectorgauge boson in120601mesondecayswith theKLOEdetectorrdquoPhysicsLetters B vol 706 no 4-5 pp 251ndash255 2012

[14] B Aubert Y Karyotakis J P Lees et al ldquoSearch for dimuondecays of a light scalar boson in radiative transitionsΥ rarr 120574A0rdquoPhysical Review Letters vol 103 no 8 Article ID 081803 7pages 2009

[15] S N Gninenko ldquoConstraints on dark photons from 1205870 decaysrdquo

Physical ReviewD vol 87 no 3 Article ID035030 4 pages 2013[16] G Agakishiev A Balanda D Belver et al ldquoSearching a dark

photon with HADESrdquo Physics Letters B vol 731 pp 265ndash2712014

[17] S N Gninenko and N V Krasnikov ldquoOn search for a newlight gauge boson from 120587

0(120578) rarr 120574 + 119883 decays in neutrino

experimentsrdquo Physics Letters B vol 427 no 3-4 pp 307ndash3131998

[18] J Altegoer P Astier D Autiero et al ldquoSearch for a new gaugeboson in1205870 decaysrdquoPhysics Letters B vol 428 pp 197ndash205 1998

[19] J B Dent F Ferrer and L M Krauss ldquoConstraints onlight hidden sector gauge bosons from supernova coolingrdquohttparxivorgabs12012683

[20] R Essig J Mardon and T Volansky ldquoDirect detection of sub-GeV dark matterrdquo Physical Review D vol 85 Article ID 0760072012

[21] P deNiverville M Pospelov and A Ritz ldquoObserving a lightdark matter beam with neutrino experimentsrdquo Physical ReviewD vol 84 no 7 Article ID 075020 2011

[22] S N Gninenko ldquoSearch for MeV dark photons in a light-shining-through-walls experiment at CERNrdquo Physical ReviewD vol 89 no 7 Article ID 075008 10 pages 2014

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


FluidsJournal of

Atomic and Molecular Physics

Journal of



Advances in Condensed Matter Physics

OpticsInternational Journal of



AstronomyAdvances in

International Journal of


Superconductivity


Statistical MechanicsInternational Journal of


GravityJournal of


AstrophysicsJournal of


Physics Research International


Solid State PhysicsJournal of

Computational Methods in Physics

Journal of



Soft MatterJournal of

Hindawi Publishing Corporationhttpwwwhindawicom

AerodynamicsJournal of

Volume 2014


PhotonicsJournal of


Journal of

Biophysics


ThermodynamicsJournal of


2 Principle of Detection

The experimental principle of these searches includes havinga detector downstream of a high energy electron beam todetect these ldquodarkrdquo force carriers from their SM decay prod-ucts quasi-elastic nucleon scattering or detecting missingenergy downstream of the beam from their invisible decayproducts In this paper we will focus mainly on the invisibledecay channel A high-intensity high energy electron beamimpinges on a beam dump target producing dark sector stateswhich are detected downstream with various detectors andvetoes

The visible decay channel that is 1198601015840 rarr 119890+119890minus can be

searched for in a ldquolight-shining-through-a-wall-experimentrdquowherein 119860

1015840 does not interact with any component of thedetector geometry but 119890+119890minus are tracked by trackers placeddownstream which does not appear to originate from anyprimary particle like a light shining through a wall Theinvisible decay channel can be searched for by detectingmissing energy downstream Such an approach has beentaken in the P348 experiment due in CERNwith a beam timein Fall 2015 at the SPS H4 beam line

For the invisible decay channel when1198601015840rsquos produced decayinto dark matter particle pairs the decay products do notinteract with any detector thereafter Thus the total of theincoming beam energy will not be accounted for in thetotal deposited energy downstream of the target For suchsignatures it is very important to ensure there is no leakageof energy to minimise the possibility of false signal and alsothe incoming energy should be well known to accuratelycalculate the percent of missing energy These searches arelimited mainly due to leakage of energy beam impurity(contamination from hadrons) with the hadrons decaying toneutrinos and a lepton before the detector with the neutrinocarrying most of the energy undetected and due to a broadenergy spectrum of the primary beam For the first twocases it is important to ensure complete hermeticity of thedetector to minimise leakage and proper primary particleidentification to reject hadrons Since these experimentsrequire sensitive searches it is absolutely crucial to estimatethe energy of the incoming particles to accurately rejectbackground from possible low energy tail of the primarybeam mimicking a positive signal As a case study we willpresent the P348 experiment which aims to use Micromegasdetectors to accurately track these incoming particles in amagnetic field to estimate their energy

3 P348 Experiment

TheP348 experiment aims to search for the dark force carriersmentioned above and probe the still unexplored area ofmixing strength 10minus5 le 120598 le 10minus3 and masses 119872

1198601015840 le

100MeV using the 10ndash300GeV electron beam present at theCERN SPS 1198601015840rsquos with such parameters are short-lived anddecay with a lifetime lt10minus10 s into their SM 119890

+119890minus pairs or

dark particles Figure 1 shows the exclusion plots expectedfrom the 1198601015840 rarr 119894119899V119894119904119894119887119897119890 channel search and also the alreadyexisting constraints obtained from previous experimentsThe light blue and blue area show the expected 90 CL

10minus2

10minus3

10minus4

10minus5

Mix

ing120576

1 10 102 103 104

MA998400 (MeV)

Figure 1 Exclusion region in (1198721198601015840 120598) plane for invisibly decaying

1198601015840 into a pair of light darkmatter particles120594120594 provided119872

1198601015840 gt 2119898

120594

exclusion areas corresponding respectively to 109 and 1012accumulated electrons at 100GeV for the background-freecase Other existing constraints mostly adapted from [20]are also shown The constraint from the BaBar monophotonsearch is given as the light grey shaded region Furtherlimits are shown from the anomalous magnetic moment ofthe electron ((119892 minus 2)

119890) and DarkLight the rare kaon decay

119870+

rarr 120587+1198601015840 (E787) and LSD experiments The LSND area

is determined assuming 1198601015840minus 120594 coupling 120572

119863= 01 and that

120594 cannot decay to other light dark sector states which do notinteract with 119860

1015840rsquos [21] The red shaded region is preferred inorder to explain the discrepancy between the measured andthe predicted value of the anomalous magnetic moment ofthe muon

31 Experimental Setup for P348 The P348 experiment hasthe same basic experimental setup for both 119860

1015840rarr 119890+119890minus and

1198601015840

rarr 119894119899V119894119904119894119887119897119890 searches as shown in Figure 2 [22] withECAL1 and ECAL2 for detecting electromagnetic showers adecay volume (DV) for the decay of 1198601015840 tracking detectorsDHRMM1 and DHRMM2 for tracking the 119890+119890minus tracks anda HCAL mainly for the invisible decay channel and vetoesThe setup before the ECAL1 is to tag the incoming electronsas is explained later

4 The Invisible Decay Channel

The rate of events of 1198601015840 production and its subsequent decayto dark particles in the previouslymentioned parameter spaceis at le10minus10 with respect to the ordinary photon productionrate In order to be able to reach such statistics and observea successful 119860

1015840 event the P348 experiment aims to use


eminus 12

0GeV

S1S2

SMM1

SMM2

SMM3

Magnet

Magnet

SMM4

ECAL1

S3

Veto1

Decay v

olumeeminus

DHRMM1DHRMM2

ECAL2

Veto2

HCAL

A998400

e+







asymp100120583mHV2

Readoutstrips

HV1

eminus

3m

m

Drift cathode









y 25080120583m

Mesh

x-strips

Resistive strips

y-stripsPCB






Energy (GeV)0 10 20 30 40 50

Entr

ies

1

10

EntriesmomCal

951Mean 2981RMS 07224

102




9485322

118

9481

Cou

nts

Energy (Gev)

107

106

105

104

103

102

0 20 40 60 80 100 120 140




ECAL1

Low-E secondaries

SMM1

SMM2

SMM3

eminus



6 Conclusion




References

































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




eminus 12

0GeV

S1S2

SMM1

SMM2

SMM3

Magnet

Magnet

SMM4

ECAL1

S3

Veto1

Decay v

olumeeminus

DHRMM1DHRMM2

ECAL2

Veto2

HCAL

A998400

e+







asymp100120583mHV2

Readoutstrips

HV1

eminus

3m

m

Drift cathode









y 25080120583m

Mesh

x-strips

Resistive strips

y-stripsPCB






Energy (GeV)0 10 20 30 40 50

Entr

ies

1

10

EntriesmomCal

951Mean 2981RMS 07224

102




9485322

118

9481

Cou

nts

Energy (Gev)

107

106

105

104

103

102

0 20 40 60 80 100 120 140




ECAL1

Low-E secondaries

SMM1

SMM2

SMM3

eminus



6 Conclusion




References

































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




asymp100120583mHV2

Readoutstrips

HV1

eminus

3m

m

Drift cathode









y 25080120583m

Mesh

x-strips

Resistive strips

y-stripsPCB






Energy (GeV)0 10 20 30 40 50

Entr

ies

1

10

EntriesmomCal

951Mean 2981RMS 07224

102




9485322

118

9481

Cou

nts

Energy (Gev)

107

106

105

104

103

102

0 20 40 60 80 100 120 140




ECAL1

Low-E secondaries

SMM1

SMM2

SMM3

eminus



6 Conclusion




References

































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Energy (GeV)0 10 20 30 40 50

Entr

ies

1

10

EntriesmomCal

951Mean 2981RMS 07224

102




9485322

118

9481

Cou

nts

Energy (Gev)

107

106

105

104

103

102

0 20 40 60 80 100 120 140




ECAL1

Low-E secondaries

SMM1

SMM2

SMM3

eminus



6 Conclusion




References

































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





























FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



beam purity for light dark matter search in beam dump … · 2016. 5. 18. · beam dump experiments...

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