(*:15528

crystal. OCR Output

the interaction of high energy y with the strong macroscopic field of a

measurement of the mass spectrum of the (e+ e-) or (yy) pairs produced inexperimental and theoretical puzzle around the Darmstadton, oy a preciseouasi-atoms coulomoian strong field. we propose to solve thestates of the "Darmstadton" (around L8 MeV) produced in heavy

There are now several indications in favour of the existence of several

ADSLFQ

contectman, spokesman.**

Udine.

lstituto di Fisica Generale, l.N.F.N.· Dip. Gi Fisica Sperimentale, ‘Ulstituto di fisica ,2)5)

Ferrero, F2. Garfagnini, l>.Gianotti, L. Santi(Torino)2) ml ) 2)G. Bolognal). MP. Bussa2), G. Bonazzolaw, 5. Costaw, A. Fe»liciello?>

Kirsch. I.P.N. (Lyon). Chevallier. B. Farizon-Mazuy, MJ. Gaillard, R Genre, B. llle, R

**

D. Sillou", ri. Gpighel. L.A.P.P. (Annecy)G. Bassompierre, J. Dufournaudm. Gouanere, L. ilassonnet, JP. Peigneux,

Annecy (LAPD), Lyon UPN), Torino (iFG, lFS. li~lFN) Collaboration

inteiractii o im y ~ clryst ll.til ritii it olton hunting in the

C§QN¢-SRS c${:00000542

iecernoer. With @38{/ONE lllllllllllllllllllllllllllllllllM j

{DSC 885com uBnARms, cENevA

. . C,

[new li . OCR Outputflgl: Atgmic processes occuring in the quasi—atom strong

-2 t[10 'sec]-x ’/-3Q -\Q —\ O +\ •\O +3OW +®

induced positron:

spontaneous

<Z=Zl +22; i/oz)(fig.l>,"‘· `=~—"¤•

field of the ouasi-atom

·-··»··¢G·»·l creation in the strongNo

6-•l•¤rr¤¤s emission and pair•L0 radiation, positron

Drocesses such as.s. ° `

well as associatedT@~nig ;°':fZ;:;— T- _7’in this interaction as_1_ ‘*°S0quasi-molecule produced

100 the structure of the

were designed to studycollide with heavy atoms,

500 oarrler (6MeV/nucleomZ _184 “ '

near from the CoulombXH

~·~·¤·¤· 53 §;5i§$£L§?€5E“$§§‘F2The experiments at

L).:§

measure precwsely me mass of sucn a partwcle

FNUHWOBF Of GVGIWIS UWBD HW DEFHWSISOI EXDEFWWGDIS, HW WTNCTW W9 WIN

we 0r000se here an expemment. wmcn snould aff0r<:1 a mucn larger

OITUCUYI IO BCCOUIWI TOI" Dy EVN QKOFTNC DFOC€SS[9·m}OH UWB OUWQF N300. [H6 CHEFBCKGNSUCS OT UWB D3f`!WWS{3GI GTTGCK SEQTTNS VQFV

r?><D€f`1mE?¤K8} 3f`QUm€¤[SPXISK IO OQDV UWB QXISKQHCQ Of SUCH 3 OBFKICNE,i8}O@FI1C\€··~BFOUDG LB MEV OI`} ODE MDG. DOUW UWQOFQUCBI 800H567}SDECKFUVTTL i *25} THESE SEFUCKLIFES COUEG INJICQKG ENG DFGSQDCQ OT 3 NSWNQVQ ODSQVVQG SKFUCLUFQS ID U18 Sm1[K€G DOS1U`O¤ 300 I0 UWB (9*,9% €¤€Fqy

From @83, several exwerxmenns nerrmrmec an me L¤.54&A ww Darmszam

fig.3; e*. e -. coincidence spectrum ['· 2]

E,. + E,- [keV],.Hn c'(ke OCR Output400 $00 gag 20% aga9001O$;) 1100 1200

%"‘i"1·M1

{I | "%”·1.

·~+··· _ , I _ = HJ! I itil!B- Q ZU

, . .._ _ _ JIM'? 1!1”:I. il|·T10

0 12

c ll

"/10

l8

ia)l 1 F4 201 1 1 1 1 ~¤A~ -—¤22

1 ` ' apos 6 #

rig. 2;sing1e e* spectrum observed at Darmstadtm]

E3 (Lab) [keV]0 100 200 300 400 500 600

g_¤;..&

0.2

'__--•·•·•*•·- -~% 0.4

Lu- 0.5

S 0.0

%¤ 1.0

1.2}- z0•< 9,, < 35•

(5.6 • 5.9) MeV/u U * U1.1

i1'10€D€fiG2l1`iI ’3><D€i”ii'T1Qf`1I$.

<fig.2), ine existence of wnicn nas now been confirmed by two otner

QOSIKFOU ‘5[>€C‘C\”U|'T1 BOOVG E1 weii UTWGGFSKOOG OUTUD of HWGUCBG oositrons

THQ SUFDFISG Caml? 1"FOFT1 [UG ODSEFVBKIOD of 3 F13f`1"OW DGBK 10 {DG GITNKKSG

TTBGG .5

=50prad. wide angular distribution. OCR OutputTOpm. in amorphous Ge and 7COpm. when created around the <l lO> axis in crystal assuming a es

The mean free path of an object having an inelastic cross section of 150 Barns would beobservgg in emulsion experiments. This fact if confirmed would not clarify the situation.Notes:*Others results [ l 4,1 5] exist which claim that such particles have already been

from an amorphous target**

between the crystal rows ( =2 Al and should emerge much more easily thanln an aligned crystal this particle will see a rather wide "free space"

experiments.

interaction with matterpreventing its observation in beam dumplmlobjects produced in the strong field, which have a high cross-section ofThe answer to these ouestions could be that these particles consist in new

Zl—Such particles were not observed in beam dump experiments [8]

which one photon is exchanged is disputable.processes which favour multiphoton exchange, and Bhabba scattering inoy a factor lo. On the other hand, this comparison between strong field

r 9,.6,- = F but for a oranching ratio of .5, this limit on t would be divided

(F < l.9 lO `J ey. t z 55 lu ‘ ' J s.> corresponds to the hypothesis

e— channel, l` total width). The most recent value

which fixed a limit on the ratio l‘·‘€+€- / 1‘ (Pye- partial width of the e+2)-Such particles are not seen in Bhabba scattering experiments [*3]

DECK emission and for the constancy of the e’ e` energies. with respect to

complicated. in particular, it seems difficult to account for the back to

rorocessesl’·‘O]. even if the structure of the ouasi—atom could be quite?1i—lt seems now impossible to explain such a structure by atomic

Thus, The present. situation with the observed structure in Darmstadt is;

experimentsl *2}*‘5>·Several lines at 255, 557 and 596 l<eV have been observed by different

time t~ l O`2O si.¢ii·l_lfetime tsucn as ll}-:**1 > ltl ` ‘ O much greater than the CO|llSlOTi

5i-General agreement with the one particle decay simulations

il-lndependance Ol the e+ energy on Z.

·Emission Ol e` and e‘ iorreiated in enerdy and annie

inaracteristics of inese results are

of the emission ot e' n correlation with the ei <‘flq,3l The

nese observations have been completed bv the i;;·oservaticn

oaoe ¤

where KL and l< are the transverse and total energies of the incident OCR Output

kzl/2k = Ve, + Ve- + (m+ple+ l/2pe, + (m+pLc- )/2pe2222plane;

in the crystal, we may write the equivalent equation in the transverse

created e+ and e-. The SPC corresponds to the case where it/9,, + Ve- i> 2m.

where T€,_ Te-, Ve, V9- are the kinetic energy and potential of the

hv = Te, + Te- + Ve, + V€-+2mphotons transfers its energy hv to the system:exchange of many photons. (el l in Darmstadt). One of these virtualhgln these diagrams, the interaction in the strong field proceeds through THQ

fig 4. induced pair creation in strong field.

XtalZl+Z2

it t`3 S`

Zi

hvhv

The (IPC) is illustrated in figure 4;

with respect to Z (eZ 2Oll *8].the Dirac sea and which should display an energy dependance of the linescreation (SPC) which occurs when the the deeper atomic level dives into

process which has not been observed in Darmstadt, is the spontaneous

keV for 1/to z2. i O‘¢’ s.) may induce the creation of a pair UPC). An othercollision. This variation of the field, equivalent to a photon (with hto¤3OO

due to the variation of the strong field ( Z > l73 in practice i during thees seen in figure i, the processes occuring in Darmstadt[‘7·‘8·‘9] ar

fig.5 Meaning of X in pair production in strong fieldOCR Output

Fo= 0 . . . I.33 l0 V/A (critical field)2 5 M r

1eFc)

AE AI 2 =$ = }l = m < h I Y JE

eFc

AE=Fed=>d= .[I1...=> At=.m.

i<·»=2p:.->nE=2‘i[p2+m2 —2p=m/y

y= E0/2m *P¤ l/y== d/cAt

(Xtal field)

Y l< Z I *I*¤1/y I d

x=yF/FO where v= EO/2m and FO = m2c3/(eh)is defined py:

production is tne strong field parameter X. For an incident y of energy Eq` Xtne crystal case, tne essential parameter wnicn descripes tne pair

in Darmstadt, tne parameter Zo fixes the intensity of the potential. ln

onoton in tne case or oeriect aiionment. i< E =·..>. we can ooserye only SPC

oaoe o

me Betne—Heitieri2il. OCR Outputexcitation· Pair production in crystal at CERN normalised to[‘8]fig. 6 e+ production in Darmstadt normalised to the nuclear

lPC=5. l0'°/ ylPC=2.lO‘°/collision U—U (b<2O fm.)

zu : 92 _ Z2mclnzm ni-iomu ENERGY icavi

120 1LO 160 180 200 ° 5° '°° "·°

I I i i i i i

Ni Pd Sm T0 eu u Cm` " " "£2`E;ww“”°'°”°"°'"°°'

.. .. - .. - - .........ll c$*3 ¢ `“Sm

i5l.Sm *£i/at _;

ut _ T g, ap¤rc¤.lU. .A.) r /unnthld

;'» ; g ‘

,@A ? @33 on 5

o 5.2MeVIu ¢ BH L ' um. \ Q, ‘¤ S.9MeVlu 5% ll gis ° gg

gl. s =¢.s•:i0°E7

U+Z2

process is due to the interaction in the strong field.

one can estimate l see 3.4) the expected rate at CERN, in case where this

From this picture, and from the rate of e* in Darmstadt lines @-3%),crystal and the rate of induced positron production creation in Darmstadt.

which represents the pair creation rate measured at CERNpy yon a GeIZ']Darmstadt with Zozzl and at CERN with I ill is illustrated in fig. 6

The similarity between the two cases (production in strong field in

place in a time At such as AME sh.

energy acquired by the pair in the field. This compensation should tal<edefault of energy AE due to this creation should he compensated by the

created by an incident y in the strong crystal transversal field F, theThe interpretatmn of this parameter is illustrated in fig. 5; a pair is

oroouctton of a mass as tf=2EOh/m¥cJ= ZOO A <¤ 1 OO atoms) in our case.

20]rnacroscoptc strong Helo tn wmcn the formation lengtn $for tnem a constant Hem, tnis ts practtcaily tne case inthe case ofthe crystal

Stmcxly speaxwnq, cms parameter cnaraczerxzes the ¤a1r procuctmn rate

OBGQ 1

calculated from the data obtained in NA33 [2‘] OCR Outputthese pairs will generate a broad mass spectrum which has beendue to the multiple scattering, and to the presence of the strong field,crystal assisted pair creation (fig. 8). when created inside the crystal,t.e+ e-> pairs originating either from the Darmstadton decay or from theThe incldent y interact in the crystal Xtal. The outgoing particles are

converted e- onto the tagging calorimeter TCA.

The duasl achromatic system consisting in B2 and L] directs theThe experimental setup is shown in fig. 7;

3,3).-Experimental set

The expected y rate under these conditions is 2. to 5. IOJ y / burst.

with a small calorimeter.

and a decentered duadripole will allow the measurement of the e- energy.ouasi achromatic system consisting of a conventional bending magnet

Lead Glass calorimeter.

range l0O to i60 GeV by measuring the e- energy with the help of a SF8

¤O,l L ,30 converter we will thus obtain a KBQQEG y beam in the energyThis e- beam will be used to produce a y tagged beam by conversion in a

3,2)·Ta<1qed y beam.

intensity ¤ 0.5 to l. lOJ e-/burst.

¤ 180 Gev e- beam, with ap/p ¤O.5% cb ¤ 6/8 mm., dg = 50 urad.

beam conditions similar to these OY MA33/NA42 experiments:

To produce this particle in the strong field of the crystal, we need

3. 1 )—incident DCQHI

step, we will focuse on the (e+ e—l decay channel in yproduction.

y or e- with crystal in tts possible decay modes <e+ e-) or (yy l. In a firstwe propose to search for the Darmstadton in the interaction of high energy

§_)—ExperimentaI setupi

lnucn nioner rate

small otemoer of events tssome l00th per vveel<> AK CERN we expect a

and small angular acceptance} are verv difficult and thus can afford only;

Darmstadt lverv thin targets =¤lO° A ot snort lifetime

he evperlmentai ·TCV'lGlElOW5 tor the observation ot tnis parttcie in

ilade 8

produced inside the crystal. OCR Outputover background ratio by a factor f=l0 to 400 by rejecting the pairscrystal will act as a solid state detector which could improve the signalMoreover, we intend to use (if possible) an active target in which thewe already have 3 high quality Ge crystal (thicknesses; 70, i85, 400 tt).

3.4)<Thu;itst

distributions and intensity.

The beam control stations (BC) perform the measurements of the beam

and above all to align the crystal.from the bremsstrahlung of either the e- or e+ in the crystal strong field*The Pl-lCA calorimeter is used to detect eventually the radiation of ayThis energy will also be measured inthe calorimeters e-CA and e+CA.

pair with a pmax/pmm ratio ¤ G

(MWPC) 200><200 mms will perform the measurement of the energy of the

*The B4 dispersion magnet and a multi—wire proportionnal chambertarget and the ustrip detector.reduce the effect of the earth magnetic field in the ~80m. between theA pmetal and iron Armco shielding will strongly (by a factor =200)

be measured before any magnetic deflection by a microstrip detector.

*The very small angle of the produced e+ e- pair (some l0th of urad.) will

b)production and decay of a particle outside the crystal.fig.8 alpair creation in crystal (origin of the background).

30

ul l

a) 1AF"; 1 i broad mass spectrum

strong F. effects

Mult. scatt.

give a narrow peal< in the mass spectrum

nn the contrary, a long lived Darmstadton will decay outsioe me target ang

OCR OutputOEGE M)

resoitsml <riq.oi. OCR Outputassisted pair creation which has been calculated from our previousAs said before, the expected spectrum will include a background due to the

distances.

performed directly by interposing materials after the target at different

lifetime and of its cross section of interaction in matter should be

After observation of this mass, a more precise measurement of its

allow us to detect the production of such a particle.ln the first case, only a very good performance of the active target couldparticle decaying before the last detector.particles after the target will allow us to count the number of long livedin the second case, the use of the magnet B3 to sweep away all charged

will be unable to perform a precise measurent of the mass. Nevertheless.

too far from it to allow a precise mass reconstruction. in both cases, we

Outside these limits in 1, the particle will decay either in the target or

expected mass resolution is AM/M = 3% at 2 MeV.

2 ]?such as l00 pm. < vcr < l0m.(0.5 l0"> 1 >0.5 IO`s). Themeasurement of the mass inthe range l.2 < r1 < l7. Nev, for a lifetime 1

The above setup will allow to perform for the first time a direct

4)-Perfo;

system will be; pmax/pmm_ ¤ 9.independantly by SF6 lead glass calorimeters.The acceptance of the

200><2OO mmé wire chambers or a scintillation HOGOSCODG andThe e+ and e—_energies will be measured by a dispersion magnet and a

a distance of »·¤8O m.

measured by a 20x2O mme Ei microstrips detector with a step of E-O ttm at

conoitions, the angie of the pair is emm ¤ 20 to 30 grad. it will be

decay into a0 = e+ e- , at an energy EEO ~ l 30 s 3=3 Gel/. in these

The process under SKUGY is the formation OT a mass ag ij¤2l*lev.i ano its

page

detector. There are some indications for the existence of another line OCR Output

peeing the interposition of a y converter in front of the microstripsthe experimental setup, the main one necessary for processes (2) and (4)The processes (2) to (4) can be studied without any signicative change in

e- Xtal => a0 e- Xtal a0 = yy (4)

e- Xtal = a0 e- Xtal a0 => e+ e- (3)

y Xtal :> a0 Xtal a0 =>yy (2)

3 others processes are of interest namely;

y xtal :aO XK3} aO:»e+ e- (l)The above set-up is fitted to the study of the process;

5)-P.oss

Darmstadt. The active target will improve the sensitivity by a factor JiThis sensitivity should be compared to the 3% branching ratio measured ina 7 days run amount to s=2.l0‘signal we need 800 particles so that the sensitivity of the experiment infrom which 24000 inthe mass region L8 Mev z 50 keV. To obtain a 5othick Ge crystal. in 7 days we would obtain 4 i0° background eventsmeasured in Darmstadt we would observe 85 pairs/burst in a i85p.m.Assuming for the Darmstadton a production rate identical to the one

multiple scattering for a 7 days run.f ig. 9 Background from crystal assisted pair production

rn (MeV)

{ 2 T, 6 e 10 12 TL

20000NON ACTIVE CRYSTAL

toooo

x 10000000

ACTIVE CRYSTAL lf=iO0)

CBGB if

this time OCR Output

first results ODI2ll'l€G, and on the experimental and theoretical situation at

in l<99O we reduire 2 to 3 weeks of beam time depending on the

i.vl'lOl€ aboaratus

To oeriorm this experiment, we need a l week test run in l989, to test the

lll the existence oi new particlescould give an answer to the Question wether {EBSQ lines have their origin

experimental limitations in Darmstadt, we think that this experiment

e+e-it The presence of these lines is how well ESEBDIISUBG. Due to the

observations lll e+, in e+e—l and 396 kev i2 observations in e+ and 3 in

oiiferent setups; at 255 keV (4 observations in e+l, at 337 kev <l3

Three bositrons lines have been observed in Darmstadt with three

6)-Conclusions

the photon splitting in strong field.corresponding SQIUD would allow to measure also a very exciting process

arouno l hlevt W|WlCY’l would decay accoroino to orocess @[22} The

fade

Fielo. p. 289 and 367 (1985) Springer-verlag, Berlin. OCR Output[19)Greiner W., Muller B., Rafelski J. Ouantum Electrodynamics of Strong

Sci. 1986. 36:605-48.

[18]l<ienle, P. Positrons from Heavy lOl) Collisions. Ann. Rev. Nucl. Part.2,3 183 (1978).Emission in Pb-Pb and Pb-U Collisions. Physics Letters vol. 788, Number

[I7lRe1nharo J., Oberacker B., Muller B., Greiner W., ano Soff G. Positron

(1987)D. 191.

Extenoeo Particle as a Source of e+ e- Coincioence.G.S.1. Annual Report[l6]5cnramm S., Muller B., Reinharot J., Graf S., Greiner W. Decay of anBosons in Nuclear Emulsions. Phys. Rev. Lett. 61 (1988) 1274[15loe Boer F.W.N., van Dantzig R. Possible Observation of Lignt NeutralHigh-Energy Collisions. Phys. Rev. Lett. 61 (1988) 1271[14lEl-Naoi 1"l., Baoawy O.E. Proouction of a New Light Neutral Boson inBhabba Scattering in tne Nev Range. Nucl. Phys. A478 (1988) 297c.{l3]l<ien1e P Electron-positron Pair Creation in Heavy—lon Collisions andCollisions. Z. Phys. A 328 ( 1987) 129.[I2]l<oen1g W et al. Positron Lines from Subcritical Heavy 1on—atomCollision systems. Preprint GSI-84-43.[1 1]Bokemeyer H. Positron Spectroscopy of Supercritical Heavy lon

(1988).

at Mel! Energies in the Framework of OED. Ann. of Phys. 185, 284-300[10]Grabiak M., Muller B., Greiner W Exclusion of Ouas1—Bouncls e+e- States[9]Reinnarot J., Muller B. and Greiner W. Phys. Rev. C3 (1986) 194.oe Moriono. Les Arcs, Savoie, France, 8- 1 5 March 1987.{8]Davier,1*1. Axion: a Review. Rapporteur talk given at the >(>(ll RencontresParticle Decay 7 Physics of Strong Fielos. iriaratea ( 1986)[7lReinharot J., Muller B., Greiner W Are the G.S.l. Events causeo byComments Nucl. part. phys. vol l7 n94 21 1-213 (1987).[6]Chooos A. Narrow e+ e— DGBKS in Heavy—lons Collisions; Fact and Fancy.(1987)

[5]Pecce1 R.D., Sola J., Wetterich C. A New Phase of OED 7 DESY 87-168Heavy—1on Collisions.Phys. Rev. Lett. 55 ( 1 985) 461[4]Balantekin A. B. On the Possibility oi New Particle Proouction inemitted in Heavy-ion collisions. G.S.l. Annual Report 1987 p. 175[3]Blank et al. Angular Correlation Stuoy of the Electron—Positron PairsCollisions. Nucl. Phys A488 ( 1988) 683c—688c[2]Beoermann E. et al. irionoenergetic (e+ e-) Pairs from Heavy-ionsfrom Suberneavy Collision Systems

[1]Cowan TE., Greenberg J. S. Narrow Correlateo Pos1tron—Electron QQBKS

page 14

5.9-1*1eV/Nucleoh 0+Th Co111s1ohs. Phys. Rey. Lett. 59(1987> 1 185. OCR Output[22]Dahzmahh 1<. on 211. 1809 Corremeo E<1ual—Ehergy Photohs from

58 (19871 1196.

ahcmeht oh a Germamum Crystal m Ahghmeht Cohomohs. phys. Rey Lett[21]Be11<a<:em A en a1. 51.uoy of s+ e- 1>21r1jr@·a1;1oh oy 20-150 Gov DhonohsDhys. 0so. 30 (19871 197Rao1at1oh of ro1at1y1st1c Dart1c1ss 1h amorphous aho crystallme Meo1a.5ov[2OlA1<h1eser A1 sho Shulga NF. 1hf1oe-hoe orMo1L1o1e Scattermg oh the

oaoe 15