BNL - 67466CAP-284-Muon-OOC

MUON STORAGE RINGS - NEUTRINO FACTORIES

Zohreh ParsaBrookhaven National Laboratory

Physics DepartmentUpton, New York

February 2000

Submlcted to Proceedings ~f the Workshop on the “Next Generation I?ucleon Decay and

Neutrino Detector (NNN99)”, SUNY, Stony Brook, NY, Sept. 23-25, 1999, AIP Press.

Muon Storage Rings=Neutrinc) Factories*

Z. Parsa

Brookhaven National Laboratory,Physics Department 51OA

Upton, New York 11973-5000, USA

E-mail: parsa(ii)bnl.~ov

February 2000

* Supported by U.S. Department of Energy Under Contract No. DE-AC02-98CH 10886.*Invited Paper; Submitted for Proceedings of the Workshop on the” Next generation Nucleon

decay and Neutrino detector (NNN99)”, SUNK, Stony Brook, September23-25, 1999, AIP-Press.

r t

Muon Storage Rings - Neutrino FactoriesZ. IRtrsa”

Bmokhaven National Laboratory, Physics Depaflment 510A, Upton, NY 11973-5W?0E-mail: parsa@bnl.gov

Abstract. The concept of a muon storage ring based Neutrino Sourre (Neutrino Factory) has sparked considerable

interest in the High Energy Physics Icommunity. Besides providing a first phase of a muon collider facility, it would

generate more intense and well collimated neutrino beams than currently available. The BNL-AGS or some other proton

driver would provide an intense proton beam that hits a target produces pions that decay into muons. The muons must be

cooled, accelerated and injected into :~storage ring with a ‘long straight section where they decay. The decays occurring

in the straight sections of the ring would generate neutrinct beams that could be directed to detectors located thousands

of kilometers away, allowing studies of neutrino oscillations with precision not currently accessible. For example, with

the neutrino sotuce at BNL, detectors at Soudan, Mimesota (1715 km), and Gran Sasso, Italy (6527 km) become very

interesting possibilities. The feasibilityy of constructing and operating such a muon-storage-ring based Neutrino-Factory,

including geotechnical questions mla[ed to building non-planar storage rings (e.g. at 8° angle for BNL-Soudan, and 310

angle for BNL-Gran Sasso) along with the design of the muon capture, cooling, acceleration, and storage ring for such

a facility is being explored by our growing Neutrino Factory and Muon Collider Collaboration @FMCC). We present

overview of Neutrino Factory concept based on a muon storage ring, its components, physics opportunities, Possible

upgrade to a full muon collider, latest simulations of front-end and a new bowtie - muon storage ring design.

INTRODUCTION

Although many of the recen~ exciting results in neu-trino physics have been obtained by non-accelerator ex-periments, the neutrino mass and mixing parameters ap-pear to require a new generation of accelerator based ex-periments. For this, an intense source of well-collimatedneutrinos is needed.

Excitement is high in the accelerator physics com-munity because atrnospheric-neutrino results suggest thatthe long-baseline accelerator experiments such as MI-NOS [3], K2K [2], and NGS [4] should also find neu-trino oscillations. Further, the LSND experiment thatwas conducted at a short-baseline accelerator facility,can be confirmed by future accelerator cxperimenta suchas MiniBooNE [5], ORLanD [6], and lCERN P311 [7].Moreover, physics associated with some interpretationsof the solar-neutrino deficit may be accessible to studiesin accelerator-based experiments, if neutrino-beam fluxescan be improved by 1-2 orders of magnitude.

To obtain a factor of 100 improvement in neutrino flux,the best prospeet appears to be neutrino-beams derivedfrom a muon-storage-ring, rather than from direct pion

* Su~ed by US Department of Energy contract DE-AC02-98CHI0886

decays. However, such an approach requires considerabledevelopment before it can be realized in the laboratory.The idea of muon storage rings has been discussed sinceat least 1960 [8]. However, storage rings with enough cir-culating muons to provide higher intensit y neutrinos thanfrom conventional horn beams have only been consideredmore recently, in the context of muon collider technology[9].

The neutrino fluxes from the proposed muon-basedbeams would be higher than ever previously achievedwith a much better-understood flavor composition. Inaddition, since the neutrino beams from these sourceswould be secondary beams from high energy muon de-cays, they would be extremel y well collimated. Distancesbetween production and detection COUIQtherefore spanthe globe. Using the precisely known flavor compositionof the beam, one could envision an extensive program tomeasure the neutrino oscillation mixing matrix, includingpossible CP violating effects.

A schematic concept of a Neutrino Factory Facilitybased on a muon storage ring, its components and physicsopportunities are briefly discussed in section 2. A possi-ble upgrade to a full muon collider is discussed in see-tion 3. The examples described are based on some ofthe scenarios being expIored by our Neutrino Factory andMuon Collider Collaboration (NFMCC),[ 10].

NEUTRINO FACTORY

A neutrino factory based on a muon storage ring is achallenging extension of present accelerator technology.Conventionally, neutrino beams employ a proton beam ona target to generate pions, which are focused and allowedto decay into neutrinos and muons [3]. The muons arestopped in the shielding, while the muon-neutrinos are di-rected toward the detector. In a neutrino factory, pions aremade the same way and allowed to decay, but it is the de.cay muons that are captured and used. The initial neutri-nos from pion decay are discard@ or used in a parasiticlow-energy neutrino experiment. But the muons are ac-celerated and allowed to decay in a storage ring with longstraight sections. It is the neutrinos from the decayingmuons (both muon-neutrinos and anti-electron-neutrinos)that are directed to a detector.

Components

In a Neutrino Factory, a proton driver of moderate en-ergy (< 50 GeV) and high average power,(e.g., 1-4 MW,similar to that required for a muon collider, but with aless stringent requirements on the charge per bunch andpower is needed. This is followed by a target and a pion-muons capture system. A longitudinal phase rotation isperformed to reduce the muon energy spread at the ex-pense of spreading it out over a longer time interval. Thephase rotation system may be designed to correlate themuon polarization with time, allowing control of the rela-tive intensity of muon and anti-electron neutrinos. Somecooling may be neede4 to reduce phase space, about afactor of 50 in six dimensions. This is much smaller thanthe factor of 106 needed for a muon collider. Productionis followed by fast muon acceleration to 50 GeV (for ex-ample), in a system of linac and two recirculating linearaccelerators (RLA’s), which may be identical to that fora tirst stage of muon collider such as a Higgs Factory. Amuon-storage ring with long straight sections could pointto one or more distant neutrino detectors for oscillationstudies, and to one or more near detectors for high inten-sity scattering studies.

Figure 1 illustrates components of a Neutrino Factorybased on a racetrack - shaped muon storage lattice [10].Alternately a planar bowtie - shaped ring can be designedand oriented to send neutrino beams to any two detectorsites. Since,there is no net bending, the polarization maybe preserved. (A disadvantage of the Bowtie - shaped ringis that it may need extra bending. Since there is geom-etry constrains on the ratio of short to long straight sec-tions, the ring circumference may increase.) With the ringin a tilted plane, both long straight sections would pointdown into the earth, such that neutrinos can be directed

(-iU-- “0’0”‘“”r

b.) TargetPhase Rotate #1Mini Cooling

L“riftPhase Rotate #2cooling

Linac

Recim Linac #1

Recirc. Linac #2

Storage R@

(: 50 m rf)(: 3 m H,)

(: 150 m)

(: 10 n, rf)(: 100 n,)

(2 GeV)

(2.8 Gev)

(?3.50 Gev)

(50 GeV, = 1 km cirr. )

Neutrino Beam

FIGURE 1. Overview of a NeuEino Factory Concept, with aRacetrack Muon - Storage Ring

Protonbesm on mercury nucleus and ta!gel in solenoid (S0=20 Tj

Tw4 LT4 cm, RT=O.75 cm w75 mw MA RS12@S) 0S122,9S0.5

~04 ;.- ) :. . ..—~~c1

//:

~ 0.3-------------------------------------------------------..7/ .........J....... ...........g ,/v

3

/

L

:0.2 -- ~-.,...- ~~

~J

-------. . .A:f,.. .....m ..------- ~*z / ......-~ 0.1 . . . . _. ... ..... ............. . ............... . . . .

.,s

0.0 —,o 5 10 15 m 25 30

Protonkinstk energy (OeV)

FIGURE 2. The number of pions produced per proton incidenton a mercury target vs. proton energy. The yield at the target isshown by the circles, and the yield 3 m downstream of the targetin a solenoid capture system is shown by the triangles.

into two very distant detectors. Triangular-shaped storagerings also have this advantage. In the following sections,a description of the targets, a simulation of target throughcooling-charnel and a new example of a bowetie-shapedmuon storage lattice will be discussed.

Driver

The number of pions per proton produced with an op-timized system varies linearly with the proton energy, asshown in Fig. 2. Thus, the number of pions, and thenumber of muons into which they decay, is essentiallyproportional to the proton beam power. The total six-

I 1 I Ie a & e

. (d

FIGURE 3. A Schematic of Targetry, Pion Capture, and begin-..:-,. ,.KDL--- D-+.+: --nu,,~ “, . ,,*3C K“LUU”,,.

dimensional ernittance of the produced muons dependson, e.g., the pion bunch length, and thus on the rms pro-ton bunch length 6P if that length is longer than the char-J–––-actenstic decay process length c ‘c”W’y:

(1)

where TXis the pion lifetime and yn~ is the pion energy.The pion yield peaks at En % 300 MeT~ with @~Y = 1nsec. if the proton energy is low, this may imply a largetune shift

AV ccnP C nPK—

~ Q %zLaverw YP(B)~t Etmmverse(2)

in the proton ring before extraction, where C is the cir-cumference of the proton driver, {B) is ihe average “bena-ing field and ~wsve~e is the transverse ernittance of the—--.-—_ n- -l ____>–—–—>-—.-. c-.. –..-pululm. L IK WJLJVLS uqxsnucnuy mvurs a higiier prO-

ton energy. The total six-dimensional emittance of the-.,.,-6..-L..L..:,..... ,6...--..A” ,.1--- . . +L,. _... -L.,.- -cp UUULAAI pulm uGpclIua almu uu ulc u ulllucl ui p ucuu

------

bunches employed to fill the storage ring. This favorsn “m.llc. “...Ha.a. -f 1,,.,. - . . . ...+-” r.....,. ha. :.. ●I-.,. AA... -..a .lLLcultil 111.ULIW1 (J1 Lalgb p ULV1l Uullb Llca Ill L.LIG Lu 1 VG1,

and thus a larger tune shift. Table 1 :presents possiblefiomtiafm-. fnw R.-+-- AA., --- .-.* RM3 .-,.. ,4 12NTA T l%. +,,.ywculm..tia. LU. y.utuuullveln a. -Ilk allu A ..-. l,,L Lal -

get requirements are very similar to those for the muoncnllibr avm=nt the inctnntmt-m,. ah-k hentimm i. .nrna–-“u.-”., “-””p. UIv -1. -.-.-” s.. ..1”., - .WLWUIS ,. .v,,,w–

what less because protons are distributed in a larger numb-er of bl~~~he~. LVLhesche~.e nrt=cenf d here it ic a c-3’=-“---- — ..-. “, . . .“ -“

surned that the liquid mercury jet solution is used. Thecanture WIennid is !ike!v tn he the M_rn_eas clL?wriheLIin. ..=.-.- --- , .- -- —-------—the muon collider status report [9]. Figure 3, shows thepion production targe~ solenoidal capture, decay channeland beginning of phase rotation. At the end of this firstphase rotation stage, the bunch length increases by abouta factor of 6 and the energy spread decreases by the sameamount. Whether this first stage of phase rotation can beeliminated is being investigated.

FLf Cawas Phase Rotatbn

Irll”+:

HI rll— -——

LJu mlnkoonng

o 55 110 165 220 275 330 385 440 465 Odo

z (m)

FIGURE 4. Schematics of the Muon Source from Target toLinac.

T-.. –_. n--l:.. – C-–-4 –-.lurget - uwung Decwm

in this section a new integrated design for the NeutrinoFactory front-end subsystem is described. Other designs-.-J . . ...–.–..–mu sunurduuns are being expiored by WMCC. ‘m the

latest muon cooling simulation all the available subsys-..— .-1-.. 1-.:---- .-. -L -- d- .--—-. —,-— -—2 J–LCIU MLllU1aUU1lS SUU1l dS UK (d2gC\ ~lU1l Ud~LL3K iUIU L31S-

-- —L ___

cay, phase rotation, matching, bunching and cooling were:..to-..,..a,r .,.”-.6--- :.. . ..-L. - ..,-. , +3.-+ +3.,-.“---- -mA:,.l,.-LLub.~L aLGU LUgGUIG1 Ml 3UL,LL a way ulaL ulc rxullc pa ubmim

generated at the target travels all the way to the end of thee-limm ohommal Tm th; . evo__lta r 1<1 1K fl.a\I -.-+,..-.“wllnl~ -..-=. -.. AL’ .,Il. “A(.u,,y’ti ~ , 4,, , “ U- , y.”.”,,.

hits a carbon target generates pions which then decay torn.l~~n~oFig~. A 12ioc 5 _ Go< 1 ‘1 ~~yw.et;vslv chnw,, ..a”. - - -e”. -“* y-.. ,-.J, “..”..

schematics of Target to Linac Muon channel. (RF cavitiesa_r~ l~se~ f~~ t_h~ i Sf nhme. r~t~~~~ ~~~ ~~~. ~V&gL~OQ ~.~n.~~r.-—-.

for the second phase rotation). In addition the longitudi-nal arnd transverse nhase rlistrihutinn nlnts ~~ z=Q (t~r-~.. —-- —-- —--—----- =--_,

get), z=370m (just before bunching), z=388m (just afterbunching), and z=605m (after cooling) are shown. Parti-cle composition in the target-to-linac charnel is shown inFig. 14, and in table 2. The muon emittance variation inthe target-to-linac channel is shown in Fig. 15.

Cooling and Acceleration

The challenges of further acceleration and storage of+2.- -.. -.. Lam- ..,:11 L... . .. L. A-.-Grill.. .-....:,-... :4? . ..- -- A....,.LUG lllUUL1 UGCU1l w lU w auumkallu ally Caalcl u w G lGUUL,G

the transverse phase area of the beam by an additionalf..tn. -f 1n ‘6%;. m.., “n+ & .,.r.,wnml; .h,.w’r :“ . .&.,Tl,a.- .“. “, . “. . ,LL. ,’ua, ,.”. m atib”u.y,..,,tiu ,,, a .ll,~,b

step of ionization cooling, but involves alternating ioniza-tinmrnnlinm ~nrl A .r-oslarafiam 011 in . rnommotio -hommal. . . . . -“”-.. s . . . . . . ..--”. ”.-..”.., -. U. u ...u~.,”..v V.,(ALU.”..

The acceleration from w 100 MeV to e.g., N 50 GeV isbest ~~~~rn-nli ch~d in r~&~l~i&n@ I in arc w~~h SIJpCOH-~— ----- ~ ------

ducting rf cavities, after which muons are injected intoa rn_UOnStOrage n~ng. ~.e deStie fQr rn_UltiPl~dirmtedneutrino beams with very small angular divergence mayrequire a more novel design for the storage ring, with aplane that is far from horizontal. The R&D needs for amuon collider are very similar, but with additional chal-lenges in cooling and storage ring design. At least four

Thble 1. Example of parameters for various Proton driver sce-nariosat 13NLand FNAL.

A) Thelongitudinaldktributionatz. Om

BNL1 BNLz FNAL1 FNAL2

Energ,y [GeV] 24 24 16 16

Power [MW] 1 4 1 4

Rep. Rate [Hz] 2.5 5 15 15

p’sltill 10’4 21014 2.51013 10’4Bunches 6 6 4 4

Circumference[m] 807 807 474 474Bunchspacing[m] I35 135 “ 118 118 “

at (nsec] 1 1 1 1

Pz.nma”= 0.878E+M G*prowl. = 0.0?9 &v- = 0.252 mmllz = 0.187E+01 -R nom!.En~,s nutid at

O.OW 8,90B 16.KI~ GNM “I*I. Ihc ,DmkC” = 1.00t-mm. . +.0,1 mt.rd = moo “sPz_”A =&mllE+OO GWIC

M .mlde Ykl*wp.r **.16.mo

r I

I /7

M! add, c.trcm et m“0.36113

●W*

LI

{

O.mli+oo

,[-1

FIGURE 5. Longitudimd Phase distributions at z=O (target).The scatter plot shows the distribution in f\[GeV/c] vs t[ns],and the graphs above and to the left show the projection on totime and PZ axis.

orders of magnitude more cooling (including continualexchange between transverse and longitudinal emittance)are required for a muon collider than a neutrino factory.Also, a different ring is needed to maxi rnize collider lu-minosity than simply to hold the muons while they decay.

Figure 16 shows a schematic of Ionization Coolingconcept. Ionization cooling that has been proposed in-volves passing the beam through an absorber in whichthe muons lose transverse- and longitudinal-momentumby ionization loss (dEjdx). The longitudinal momentumis then restored by coherent re-acceleration, leaving a netloss of transverse momentum (transverse cooling). Theprocess is repeated many times to achieve a large coolingfactor. The beam energy spread can also be reduced using

3,0

B) The horlmntal distributionat z. OmAu *CIC —rz . 0.00mm. = #.033 rM

n- = 0.301 GeVlc

emm . m163E+oo In* “m.

W. = D.02T m

pyrms = 0221 G,vltemlty = 0.146EMB In-Fl“-,

m

AllD9UCICliwkoatd PIWIC0,14E*KI

A:111 -10.0 Xp34 Inn

All ptdcle scam PM InR-X Ra-10 ‘=. :y

,. ‘

-+ d:*.:...-’F)q13wq F?.wcvlq

,. ..r.< “;.,. /.- .1 .

-30 -3.00.002 !?4!=uOmE m.mo -10.0 Ww 160

FIGURE 6. HorizontalPhasedistributionsat z=O(target).Thescatterplot showsthe distributionin PX[GeVic]vs x[m]andthegraphsaboveand to the left showtie projectionon to x and P,axis.

ionization cooling by introducing a transverse variation inthe absorber density or thickness (e.g. a wedge) at a loca-tion where there is dispersion (the transverse position isenergy dependent). Theoretical studies have shown that,assuming realistic parameters for the cooling hardware,ionization cooling can be expected to reduce the phase-space volume occupied by the initial muon beam by afactor of Id – ld. Ionization cooling is a new techniquethat has not yet been demonstrated. Special hardwareneeds to be developed to perform transverse and longi-tudinal cooling. It is recognized that understanding thefeasibility of constructing an ionization cooling channelthat can cool the initial muon beams by factors of 1~ –106 is on the critical path to the overall feasibility of the

4

‘lkble2. Partice composition at various locations from Target to Linac, (with 16 GeV proton).

location Z[m] e+/p+ p+/p+ R+lp+- klp+ p+ total/p+

Just after target o 0.000 0.000 1.000 0.000 0.000 1.000

Just before minicooling 62 0.009 0.407 0.057 0.000 0.000 0.472

Just after minicooling 80 0.003 0.334 0.031 O.CM)O O.000 0.367

Just before bunching 370 0.039 0.265 0.001 0.000 0.000 0.305

Just after bunching 388 o.tX)O 0.222 0.001 0.000 0.000 0.224After coolimz 605 0.000 0.101 0.000 0.000 0.000 0.101

.

c) The Vwrica! (!isLrihLt!innd z = nm.

~1 ‘“’’’”’(--nI Unks.o.,,,E+lnrn+t Mm. j JI.1

F, = 0.027 mc,= 0.220 GWk

mnity - 0.146E+w -R mu,mI,

‘-{ (Z\

L

plot shows the distribution in P,[GeV/c] vs y[m] and the graphs.–above and to the left show the pmjecti[

II)Thelomgltudhaldistdbutionat z. 37om*“ SWIM,,

z = O.om mR_m,,”=~.20=+M G,VICpm, = tolm GCvmm. = 16.37S m,* .s lmtm MTt..m,EH#C, ,,Ikd ,,

M1O@ 0.200 0,310 GW.* MM the .**. = 0.26t.”,” = 1413.037 n,t_lWl = 1417.021 n,R_ml =O.1O5E+O8Cd//C

s.36E-I z

N81P

m.LlOE.m

non to y and FIVaxis.

~,,”, ti*erJmo”

imr- W 150.6

‘3”~ ““Em--J ‘k’<

Pm.vict -_:4-.’...’....’“[’”m 1 -““ &*vw,+ ~J ““ lw,, J

tl..l 150.0

FIGURE 8. Longitudinal Phase distributions, same as Fig. 5but for z= 370 m @st before bunching).

I) The horkcmtal dlstibulion at z. 370 mMm Mtic, b“ Hmlzml.I MIIC,= ,j,.@orJm #,52E*Mm. = 0.021.-, = K023 GcVIC.Ink = O.loma m.Flmm

yrms = 0.020 m H-, = 0.023 G,VI%WINY = 9.17X41 rn+l Mm.

‘-l /‘1

11/;1

W=wd

4.1

--4< -—,

. ... . ..,:...>....,‘-%::-”., ..

,... ~....“-.+:.

..:.‘i~m”“..

4:. -

“’:~$m”e....Lo Xlcml 40.s

371~-111217 O u,w4,,w.*01 Dh.,c,m A:cAL.1+:-..o L.O-O . . 12; ,, L hm.*. .U w.- ,. . ,”,-”,,-, , ,,aoe U,. u,””uu, u., .aJ,,v - , ,5. “ “u,

for z= 370 m (just before bunching).

3 The lon@ttiinal distributionat z = 3SS m‘‘ M“” .%WIC*

.= B.rnm I 030E12

R_mes”=9.201E+MGWcp.m. = mom(5Wmm.- 16.047.m,* , # ,, . . . . . -. .“.-. .. . ..- .- . 1Ener#es mati at

0.1m 0.200 0 no GM

.*.~tim=b,m = 0.21 I ~P*

I ! ~:.= ::,!=*=

,:mt = 106.135”,

*_& =0.197E*m Gwt

~ 0“’”’

-..1-./ D.w..h+-,-- .>

\ -’-”’7a.lol 1 10.100

o.m6 nl”lwevperO* O.aoo m--- I!&! 1s0

FIGURE 10.Longitudinal Phase distributions, same as Fig. 5,but for z= 388 m (just muterimnci3ingj.

K) The borixmt,ddisbibutionat z = 3S8m

K:ri

M) Tbe borigyd dkibutign al z = 605m—.. —... . .Mum SWistics

R“K

1

Muon Fx t%dle

~ ‘“’,). .’,(

*

,+ +’.+,,,:$ Jx.

,, t. . . .,. ,.

#A. r,.,‘. ~. ,,. ,:. ,,~.,

2 -“1..,549 m PROFILE 0.000 -,” Lo XICh!l 10.0

FIGURE 13.Horizontal Phase distributions, same as Fig. 6, butfor z= 605 m (after cooling).FIGURE 11.Horizontal Phase distributions, same as Fig. 6, but

for z= 388 m (just after bunching).

a&wlJile Cumml per pm.”

L)Tbe longitudinal distribution at z .605 m Partiie Cornposkiin VarMcm

in the Target40-Linac Chatmel

06

051(

muons

plms

elecbwa04

~---- Idd:i ; :“---,

03 i:1 \

ml “w SUusdc,z= O.omm

P2.11w*=0.249EWEQeV/cpmnls= U29 acvzm = 0.184.emik =K53E-D1 M-R“m

l’%%’”:-”Amps/p.* *IR M. .attwc=0.00

t.mc.” = +s05 “

t.rd = 0.900 In

R-ret =0.CME+OO“ml.

1.00E+IX

U325o 10I 200 SW 400 500 500

Z (M]

FIGURE 14.Particle Composition from Target to Linae.

Muon Emittance Variation

in theTarget+o-Linac Channel

‘ln I..-.----...-–---__]5.- 0.1 5.0

FIGURE 12.Longitudinal Phase distributions, same as Fig. 5,

0.040~

I II

‘1 -— .. ._.. .. .. .-,, -_.d,,/ ,

but for z= 605 m (after cooling).

muon collider concept. In Fig. 17, a schematic of theernittance exchange is shown.

Muon Storage Ring

A muon collider requires as its starting point, a veryintense beam of muons with a small momentum spread.Such beams would be accelerated to collider energiesand be used to search for new short distance high energy

0.0000 100 200 300 400 500 600

Z(M)

FIGURE 15.Muon emittance variation in Target to Linac thannel.

*

Bowtie - quarter ring

200 I I I

[ II I16

FIGURE 16.Schematic of Ionization Cooling concept (Ioniza-tion takes away momentum, and the RF acceleration puts mo-mentum back along the z-axis, resulting in a Transverse Cool-ing).

u

FIGURE 17.Schematic of the emittance exchange concept.

phenomena. A neutrino factory based on a muon stor-age ring is a natural path to muon collider tecbnolog y,since both facilities share essentially the same subcom-ponents prior to the storage ring. In previous sections wediscussed some advantages and disadvantages of variousshaped muon storage rings. Fig. 1 illustrated a racetrack- shaped configuration, with two long straight sections.

In this section a bowtie-shaped ring with a bypass isdiscussed. The planar ring can be designed and orientedto send neutrino beams to any two detector directions andwith bypass(es) that could be added, to send beams to ad-ditional detector sites. In the bowtie-shaped lattice design[16], the lattice has two long-straight sections, two short-straight sections and two arcs. The description shown inFigs. 18-21 follows one quarter of the ring, starting at thecenter of the short straight section on thleleft side of thefigure, and ends at the crossing point at the center of thebowtie. Tab1e3gives the parameters of the bowtie shapedring. [Note, parameter optirnizaton and additional lattice

\iv ‘“.,, ,,, .,,.,,, ,.

$,, ,., ,,,., ,>, ”&do 30 w w ,20 ,50 ,40 Z,D 2,0 270

path length (m)

FIGURE 18.OneQuarter of Bowtie MuonStorage Ring.

BOWTIE RING ARC

p(m)

0

poth I.ngth (m)

FIGURE 19.Bowtie-shaped Arc Lattice Functions.

designs and simulations are being explored by NFMCC].The short straight sections may be used for injection, andfor RF. Half of the short straight section consists of two14m arc cells without dipoles, and can be configured toprovide (20m) free space for injection.

Each arc contains eight FODO cells, two withoutdipoles. There are 60 deg cell phase advances, and thedipole-free cells act as dispersion suppressors. llvelve5m long dipoles each bend the beam by 10 deg, so the archas 120 deg of bending. This amount of bending causesthe long beam-lines to intersect at 60 deg (a typical an-gle, whose exact value depends on the selection of ringand detector sites). The long dispersion-free straight sec-tion provides a muon beam such that the decaying muonsgenerate low divergence neutrinos. Two different config-urations are shown in Fig. 20 and Fig. 21. In one, the longstraight section has quadruples in the center (around thecrossing point) making two beam waists, each with 50m

, I

lhble 3. Lattice Parameters for a Bowtie- Shaped Muon Storage Ring.

Energy

Circumference

Lshortstraightsection.s

Lofiongstraig~sections

Dipole field

@dientMm~m

Dipole length

Arc cell length

Cell phase advance

Ring tunes

Betaf unctionMu~a:

Arc

Long straight sections

Ring

Dispersion:

Maximum

Minimum

Momentum compaction

Chromaticity:

Horizontal

Vertical

50 GeV

l150m

20 m

200 m

5.82 T

3ClT/m

5 m

14m

60 deg

9.85,9.23

28 m

100 m

151 m

6 m

-6 m

0025

12.5

11.5

500

p(m)

o

I

r ,,,.!/

‘\. ,,/”,/

‘\.,

“=.---’’”/,, ,

. :,,,

o m & ,0 ,20 750 ,8, ,;, MC 27.

path length (m]

FIGURE 21. Lattice functions for Bowtie-shaped - Long

Straight Section AlternativeConfiguration.

BYPASS

Beam crossing angle 60 deg

SOwtie - Mt ring

xx ,6

p(-) q(~)

0 –, 60 , m ZOO m. .00 300

path length [m)

FIGURE 20. Lattice Functions for Bowtie+haped Half Ring.

beta function values. In the other configuration, a 200-meter magnet-free beam-line is provid.~ with a beamwaist at the center with 100 m beta values.

A racetrack muon storage - ring can be configured todeliver one neutrino beam to an arbitrary detector site.Bowtie - shaped, triangle shaped rings can be configuredto deliver neutrino beams to two arbitrarily selected de-tector sites. This can be done by appropriate choice of, 1)the ring plane, 2) the orientation of the ring in that plane

FIGURE 22. Lattice functions for Bowtie-shaped Ring withBypass. The arrow illustrates direction of a neuh-ino beam to

additional detector site(s) via the Bypass.

and 3) the angle at the crossing point between the twolong straight sections. By inclusion of bypasses, addi-tional detector sites may be accessible from a single muonstorage-ring source.

A bypass would lie in a plane that includes the origi-nal long straight section (but differs from that of the ring),and begin and end on one of the long straight sections. Itsmagnets would be powered when one desires to send themuons along the deformed bypass path rather than alongthe normal straight path. In such a bypass, dipoles wouldproduce a roughly triangular path in the bypass plane, oneof whose sides would point to the desired detector. Thetwo necessary degrees of freedom are provided by the an-gle between the bypass and ring planes and by the mag-nitude of the deflection given by the bypass dipoles. To

suppress the dispersion pairs of dipoles should be placed180 deg ap@ in FODO cells.

A Schematic of Neutrino Factory concept with abowtie-shaped muon storage ring is illustrated in Fig. 23.The geometry of the storage ring depends on locationsof the ring and detector . Table 5 shows direct distances

# 1

Table4.Thenumbers of surviving muons after various stagesin the accelerator complex.

beam-forming straight section [17]. The rates are listedfor oscillations:

P driver energy I 24[GcV] 16 [GeV]

Factor J1/~1 lllp

Pions Aftec Match* 0.615 0.44

1st Phase Rotation 0.45 o.~, .2

2nd Phase Rotation 0.7 0.21 .14

RF Capture 0.7 0.15 .1

cooling 0.9 0.1:3 .09

Acceleration 0.7 0.092 .061

np/(np EP) [GeV–l] .0038 .0038

* (< 1 GeV, forward)

from rings at BNL or FNAL to Gran Sasso, Soudan andSLAC.

Physics Potentials - EvenlLRates

A neutrino factory has a strong independent physicscase. It would be easier to build, less expensive than a fullmuon collider, and could demonstrate most of the compo-nents of a collider. For the example of Neutrino FactoryFacility based on a muon storage ring (Fig. 1), the numberof surviving muons, per incident proton, at various stagesof the accelerator complex are surnrmuized in Table 4,[10].

The number of neutrino interactions per unit mass of adetector at distance L from a muon storage ring operatingat energy EMscales as

N,venu cc NPE; L-2. (3)

Table 4 illustrates the muon survival efficiencies, for theexample of a proton source with 1.5 MW power, in oneyear (107 s) of operation, there would be about 4 x 1020muons per year decaying in the storage ring. Assumingthe fraction of the ring pointing to a given detector to beabout 0.25 (as in example of a bowtie-shaped muon stor-age) then the number of decays pointing to the given de-tector will be approximately 1020. It may be noted thatthe number of events with the 1.5 MW neutrino factory,in a detector at the same 730 km, is approximately 100times that in the proposed CERN - Gran Sasso experi-ment (NGS [4]), and about 40 times the maximum eventrate that MINOS [3] can expect. Upgrading the protondriver to 4 MW, the factors become about 300 and 100for Gran Sasso and Soudan, respectively.

Table 5 gives charged current neutrinc~interaction rates(per kiloton-year) as a function of baseline length L for anE~ = 50 GeV muon storage ring in which there are 1 x1020unpolarized muon decays per year within a neutrino

1) v= + vP: fQfi2= 3.5 x 10-3 eV21c4&sin220 = 0.1,

2) v= ~ vP: Am2= 1 x 10-4 eV2/c4 & sin22(l = 1,

3) v, --) vx: Am2= 3.5 x 10-3 eV21c4& sin220 = 0.1,

4) VP~v,: Am2= 3.5 x 10-3 eV21c4& sin22tl = 1,

The rates for the unoscillated neutrino interactions, thecorresponding statistical significance of the disappear-ance signal (numbers in parenthesis), and the rates forthe antineutrino interactions, are also included in Table 5

Neutrino Oscillation

With only two massive neutrinos, with mass differenceAm2 = m; – mf, mass eigenstates VI and V2with mixingangle (J,the flavor eigenstates become:

The probability that a neutrino of flavor v. and energyE appears as flWOr Vb after traversing distance L in vac-uum is

P(V. + Vb) = sin (2 1.2’7~2[ev2]= )E[GeV] ‘in2 26”(5)

Since the atmospheric neutrino data involves GeVmuon neutrinos with distance scales of the Earth’s diame-ter, this suggests Am*of order 10–3 (eV)2 for sin22(3% 1.The solar neutrino data involves MeV electron neutrinosand distance scales of the radius of the Earth’s orbig sug-gesting Am2 of order 10-10 (eV)2 with sin226 x 1 forvacuum oscillations [18]. The LSND result involves 30-MeV muon antineutrino and a distance scale of 30 m,suggesting Am2of order 1 (eV)2; large mixing angles areexcluded by reactor data [19], thus, sin22f3 can only beof order 10–2 in this case. Obviously, four different mas-sive neutrinos are required to accommodate all three re-sults, given their disparate scales of Am2. The StandardModel presently includes only three neutrinos with stan-dard electrowealzcouplings and m, < mz/2, so a “sterile”neutrino is required if all the data are correct [20]. Evendiscarding the LSND result, three massive neutrinos arerequired with a corresponding 3 x 3 mixing matrix, e.g.

()[v, c’,~c~j ,12.13 ,lFis v,

VP = ‘S12C23“12s13s23r’* c12c23- s12s13s23c’s)( )

c,js~ .2W $1293 -.12,13.23./5 -,12%? -,12s1 Fn.’s V3C13C23

(6)

* 1

PM.<. r(,ldl![rI \I, I

.4? 111r

drift 160 mph:tw r,btlli ‘n ?4, 2

,rcL, r. Ulu[[lr I.ma’

2 x (;L’\,

]rt.lr. uI:lRIr [Lmw

$ $(1 I ;Li

prIIl, III drlbcr

wg c{

mini-cooling

3.5 m Hydrogen

cooling 80 m

11[1,1.: l.rev

\lol. i&!c Ilrlg

‘, — $(1 ( ,,,,, WI] ,,, L, KL,,,, !L’, C,] L,,

~-.7. ______/____:’=_=z’””-” -,----”--~neuirino beam neutrino beam

FIGURE 23. Neutrino Factory Concepts,with a Bowtie-ShapedMuonStorageLattice.

a ~N.s rn.a~& D 11 where c, o n cmf), ~. err. .. In the three,_ .,, ------ ., ---- _, A,- .-. .,— . .. .. ——. .

massive neutrino mode~ the neutrino oscillation proba-hib~~~ of int~.re~tdepends on six measurable parameters:----------– —.—--- = ____________

three mixing angles (t312,813, 823); a phase 6 related toCP vin!aticm as indicated in eq. [6); and two differencesof the squares of the neutrino masses (Am~2and Am~3forinstance). The interpretation of the solar and atmosphericneutrino data in terms of the t.hree-neutrino oscillation hy-pothesis suggests lAm~2I << @n% 1.with hn~z and Am~3being responsible for the transitic% and/’oroscillations ofthe solar and atmospheric neutrinos, res!)eetively.

The description of the atmospheric neutrino data re-quires A@3 N (2 – 6) x 10-3 eV2 and large mixing an-gle 823: Sin22023 x (0.9 – 1.0). For lh~zl < lAm~31and with A@g in the above range, the non-observationof oscillations of the reactor electron antineutrinos inthe CHOOZ experiment [22] implies a limit on the an-gle 013: sin2&s <0.11. Given these constraints, thetransitions/oscillations of the solar neutrinos in the tbree-neutrino mixing scheme under discussion depend largelyon the remaining two parameters: Am~2and Sti220 12.

Further, the presence of matter may modify the os-cillations of electron neutrinos because of their charged-current interaction (MSW effect [23]). hI particular, theoscillations can be resonantI y enhanced by the matter ef-fects even when the oscillation probabilities are small invacuum. This leads to additional interpretations of thesolar neutrino data in which Am~2can be of order 10–5(eV)2 [24]. In effect at the present time , there are fourviable interpretations of the sohw neutrino data:

~) V~~~~~l ficci I i at inn (V()) Qrd Iltinll w~(h @2 N““”. -.... -.. \ . -/ “v. -... -..

(0.5 -5.0) x 10-10 eV2 and sin22(3iz = (0.7 - 1.0),

2) Low MSW solution corresponding to Am~2% (0.5 –2.0) x 10-7 eV2 and sin22Ellz x (09 – 1.0),

3) Small mixing angle [SMA) MSW solution with&n~2 % (4.0 – 9.0) x 10–6 eV2 and sin226112w(0.001 –0.01),

4) Large mixing angle (LMA) MSW solution, @2 x(0.2- 2.0) x 10-4 eVz and sin’llz % (0.65 -0.96).

\xT:.1-r- ... :-. -—---- d---- -c .L- .- 1-- --. .4-- . . ..w 1111lulu Irlux p Gliluuus U1 LUG sulill llGUU lllU Uala, ai-ld

the two interpretations of the LSND data as either right or....-.. - +1.,..-..- . +,-.+.1 -C ..:”r. * .,. a.. AAz.o #,-.. a “-1 . . . . ..”..-.”.W lU1l& UIG1 G CU G a WI(4Z1 U1 G1/jll L &G1lLU LUD LUl UA~lCLllCLLW.1.

of the data. The experimental challenge is to reduce these+- . .:--la o,.a...=n . . ..i+,.-.&a .,..,, -*O -mo.,,.am.=mt.LU c1 BH1~lk Dtit,Lltti lU, CU,U L“ ,.-ti CL--- UW ‘,.WOW “,,,”,1s0

of the parameters of that scenario.m,l’- .X,:th●ha .n,o; lohla .a”n.nxrncmtnl Im, b+,=lirlo. 9.1 ,, U., w AU, u,” u, CL,,CI”,W WAp,, ,,’.”.’-, ~L.1-.,llu”. ..”

to the parameters of neutrino masses and rnixings, one,.o_ hn-i- +n-10” fn. mn..a ~vt.an.i.rta .+-AL=. rmmr=]., withecu, ww~lll .“ p,-,. ,“. ..’”, ” “n.”,’-. . w .7.!------ lLC.U.”. J, . . . . .

neutrino beams derived from the decay of muons in a stor-. . . A“- Rmth J,– ~q~ ~+ e~m ha ctnrwl in the rino hilt-~w 1111~. -vu. p . . . ““ ..-. — . . . ---- . . ..~. ----

only one sign would be used at a time. For example if p–-VPctnred their rbrav-. . . . ..- . . ..- .----J

u– + e–vPTe, (7)

leads to beams with nearly equal numbers of VAand V.

with spectra that are well known.At the detectors, the neutrino and the antineutrino may

or may not have changed their flavor, leadlng to the ap-pearance of a different flavor or the disappearance of theinitial flavor, respectively. When detected by a charged-current interaction, there are 6 classes of signatures in athree-neutrino model: 1) VP+ v,+ e- (appearance); 2)VP+ VP+ p- (disappearance); 3) VP+ VT+ ~ (ap-pearance); 4) V, + V. + e’ (disappearance); 5) V, +Vu-+ p+ (appearance); 6) V, + V7+ ~+ (appearance).

For operation with positive muons, a similar list ofprocesses may be written. The 5th process where a muon

9’. t

Table 5. Neutrino Interaction Rates at a Neutrincj Factory.

Source at

Detector at

L (km)

LCase Mode

P+ v~ -+Vp

Ve +Ve

. Vp -+ VP.-

L.

2) p+ v~-+Vpv~ +Vc

v +V

L

3) //+ Ve +v~

Vc -+Ve

vp+vp -

L.

4) p- Vp-+ ?llq

Vp -+Vp

Vc -+Ve

BNL BNL BNL

G. Sasso SLAC Soudan

6528 413’? 1712

90 16C1 190

1400 3600 16000

(2.40) (2.7u) (1.56)

890 2200 9300

5X I0-* 0.86 1.5

1500 3800 16(KK)

890 2200 9400

31 60 70

1400 3700 1.6x Id

(2.4cr) (2.7c~) (1 .50)

890 2200 9400

450 570 650

760 3100 1.7X104

(350) (23@ (120)

770 1900 8100

of different sign from the parent muon appears, has a veryunique possibilities at a neutrino factory based on muonstorage rings. Since they are the only sources of intensehigh energy electron (anti)neutrino beams. The ~ appear-ance (cases 3 and 6) are practical ordy for neutrino beamswith 10’s of GeV energy.

It is anticipated that by the time a muon storage ringwould be built the two angles ((123and Et12),and the mag-nitudes of two mass squared differences I(M3 and Am~2)would be known, from the solar and atmospheric neu-trino measurements (which would have been verified bylong baseline and reactor experiments), for example, MI-

NOS and KarnLAN1l. The remaining pieces of the puz-zle would be 613, the CP-violating phase 6 and the signsof the Arr$ Moreover, the indicated long-baseline ex-periments will not be sensitive to the lmatter effects inneutrino oscillations because the distances between thesources and detectors are not sufficiently large. Verifyingthe existence of matter effects in neutrino oscillations byobserving directly the modification of the neutrino oscil-lation probabilities by these effects, would also be funda-mental and interesting.

The third mixing angle (313can be measured in severalchamnels at a neutrino factory [25]. The detector mustbe far to avoid background but not too far (< 1000 km)so that the effects of Am~2remain negligible and thus 6can formally be set to zero. Fig. 24 shows the achievablesensitivity to the yet-unknown value of [II3.

Fig. 24 illustrates sensitivity reach in the

FNAL FNAL FNAL

G. Sasso SLAC Soudan

7332 2899 732

63 180 200

1100 8000 1.2 XI05(1.90) (2.OcJ) (0.60)700 4800 7.0 x 104

3 x 10-5 1.3 1.61200 8200 1.2X105700 4800 7.0 x 104

20 67 731100 8000 1.2X105

(1.9cJ) (2.06) (0.60)700 4800 7.0 x 104

410 620 680

490 8000 I.4X 105

(400) (160) (4.60)

6(K) 4100 6.1 X 104

1~:

E

..,,,,.,,, .,,,,,,,, ,,.,,..,, .,.7N,

a

10

-310

-410

F. ....I . . . . . ..1. . . . . ...1 . . . ...1. J10-5 10-4 10-3 10-2 10-’

Sin’ IJ,,

FIGW 24. Sensitivity reach in the (sin* 6+3, h~~) pl~e.

(sin*(313,An#3) plane for a 10 kton detector and aneutrino beam from 2 x 1020decays of 20 GeV muonsin a storage ring at distance 732 km. The appearanceprocess V, + Vfl+ p+, shown by the lines on the left, hasmuch greater sensitivity than the disappearance processVP+ Vp + p–, shown by the lines on the right. Theinterior of the box is the approximate region allowed bySuper-Kamiokande data [25].

* 1

CP V?olation

The three-neutrino scenario [26] can lead to CP viola-tion in for example

P(V. +’ V/J – P(ve + Vp)Acp = (8)

~(ve ~ Vp) + P(V. ‘> Vp) ‘

or time-reversal violation

AT = P(ve +’ Vp) – P(vp + v,)

P(ve + VP)+ P(VM .+- “(9)

The asymmetry (8) can be measured using wrong-signmuons and the two charges of the muon beam. However,the genuine CP violating contribution to (8) due to a non-vanishing phase 6 competes with terms related to mat-ter effects, i.e., to the different rates of evolution for veand Vebetween source and detector. The relative strengthof the matter-induced asymmetry increases quadraticallywith distance, and dilutes the signal of CP violation in afar detector.

If the solution to solar neuhino problem involves, largemixing angles and matter enhancement (LMA MSW,sin22012 % sin22t)23 w 1), then there i:sa possibility ofmeasuring the CP violating asymmetry (8), with expres-

provided the detector is located sufficiently far and highstatistics (> 1021muons per year) are available. For allthe other solar neutrino solutions Acp is extremely small,being suppressed by a factor of either sin22612 or Am~2.Figure 25 Show the CP violating asymmetry (8) dividedby statistical uncertainties vs. distance L for a 10 kton de-tector in a beam from 2 x l@l muon decays. A largeangle MSW scenario is supposed, with &n~2 = 10–4eV2, ~3 = 2.8 x 10-3 eV2, 612 = 22.5°, 013 = 13°,en = 45°, and 6 = –90° (corresponding to large CP vi-olation). The dashed curves ignore matter effects, whilethe solid curves include them; the matter effects domi-nate the asymmetry for distances beyond 1000 km. Thelower (upper) curves are for EP = 20 (50) GeV, from [hep-ph/9909254].

The asymmetry (9) is not sensitive to matter effects,but relies on distinguishing the process Vg+ v, + e-from V. + V. + e+. In the detector, it will be very dif-ficult to distinguish electrons from positrons but the rela-tive VPand V=fluxes can be varied by varying the polar-ization of the muons in the storage ring 127].

If future experiments confirm the interpretation of theLSND data that there exist more than three light neutri-nos, then use of the neutrino factory flaver-rich beamswould be even more crucial, because the parameter spacefor CP/T violating effects would be considerably enlarged

17.5

15

12.5

10

7.5

5

2.5

00 2000 4000 boo13 soOO

L (km)

FIGURE 25. CP violationsignal over statistical uncertaintiesversus distance.

and could be explored in experiments with such beams[28].

Precision Physics

Muon storage ring based neutrino beams would bringabout new neutrino oscillation measurements, and a newera for high-precision neutrino scattering experiments[29]. For example, with a detector located 30 m from a150 m straight section of a 50-GeT( l@l -@yr muon stor-age ring, the event rate is 40 million events per kilogramper year over a 10 cm radius. Oscillation-related mea-surements may be interpreted precision measurements ofthe total neutrino and antineutrino cross sections, as wellas of the beam divergence. As precision probes of nuclearand nucleon structure, the neutrinos may be used to pro-vide additional information to that obtained with chargedlepton beams, in related studies. It is known that, neutrinoscattering allows a clean separation of the valence and seaquark distributions, and use of a polarized target permitscharacterization of the spin dependence of these distribu-tions. Thus, near detectors are the natural successor tonucleon structure measurements presently underway atHERA, HERMES, Jefferson Lab, RHIC and elsewhere.For example, scattering of the four neutrino types VP,VP,v,, and V, off electrons could lead to measurements of theWeinberg angle ten times better than known at present.

Note tha~ a high-flux multi-GeV neutrino beam is acharm factory, in which a Vp beam leads to c quarks

.

that are tagged by a final-state p- (vPd + I.-c), whileVP beam leads only to tagged E quarks. For example,for the above described beam parameters, there wouldbe 107 leptonic tagged charm decays in only 40 kg-years(not kton-years!), permitting measurements of VCdto frac-tion of a percent, and perhaps even direct observation of

Do – d mixing.

MUON COLLIDER

A muon collider with center of mass energy less thanabout 10 TeV can be circular and rellative to NLC (aNext Linear Collider) of the same energy, it could be farsmaller in size. For the same luminosity a muon collidercan tolerate a f~ larger spot size than an electron lin-ear collider since the muons make about 1000 crossings.Since there is little bearnstrahlung, very small energyspread is easily obtainable. Fig. 26 shows a schematicof a muon collider components [9]. A high intensity pro-ton source is bunch compressed and focused on a heavymetal target. The pions generated are captured by a highfield solenoid and transferred to a solermidal decay chan-nel within a low frequency linac. The linac reduces, byphase rotation the momentum spread of the pions and ofthe muons into which they decay.

Subsequently, the muons are cooled by a sequence ofionization cooling stages. Each stage consists of energyloss, acceleration, and emittance exchange by energy ab-sorbing wedges in the presence of dispersion. Once theyare cooled the muons must be rapidly accelerated to avoiddecay losses. This can be done in recirculating accelera-tors (as at CEBAF) or in fast pulsed synchrotrons. Muoncollisions occur in a separate high field collider storagering with a single very low beta insertion.

It is expected that the first stage, prclton driver wouldbe 16 to 30 GeV, but would be much faster pulsed, keep-ing the number of protons per pulse the same or smallerthan the AGS, which is about 6 x 1013lprotons per pulseand with some upgrade to about 1014protons per pulse.

Roughly one expect to get 1 muordproton on targetwhich would give luminosity between 1034to l@5 the en-visioned muon collider. Although the accelerating com-ponent is large, the other components can fit within it andthe whole machine is compact enough to fit on existingBrookhaven or Ferrnilab sites.

For more information on the Muon Collider and pa-rameters under study, see e.g. [9],[30] - [36]. Ta-ble 6 shows the parameters of potential muon collidersat 100 GeV, 500 GeV and 4 TeV center of mass energy.The 100 GeV collider would be ideal for the study of thelowest mass Higgs. The 4 TeV collider should be in the

I&&-1

BzEl

—

IFIGURE 26. Schematic of a Muon Collider.

/-\ /~

[1-.----

‘m& \ ,.””~.:,? ;::)TCV P P

f\

o

\/ ,’

*_-”/ SSC 40 Te;\

/ (2 TeV) \

f\

LHC 14 TeV p–pI (1.5 TeV)

\

/\

I\I

I NIX .5–1 TeV e–eI

\\ - Higgs p’p O 1 T.V ‘\

\Q /.b’p- 04 I,?v /1

\\

\ 0j W+W” 3TW ,~’ “-,

\ /,/ ~m \

‘. .

1 km------ - ‘,/

3“_~_=~::-- P,peatron 100 T.V

(5 TeV)

FIGURE 27. Comparison of relative sizes of Muon Collider,Large Hadron Collider (LHC), and Next Linear Collider (NLC),relative to the BNL and FNAL sites.

..

lkble 6. Parametem of p+p– collider Rings.

Energy (C. M.) TeV 4 0.5

Beam Energy TeV 2 0.25

Beam y 19,000 2,400

Rep. rate Hz 15 2!.5

p Energy GeV 30 :~4

PJutdse I 1014 I 1014

0.1

0.05473

15

16

5x 10’3

@bunch 2x 10’2 4 x 10’* 4x 10’*

Bunches/sign 2 1 1

Beam Power MW 0.7

I E,vn mtn-rnrad I ;: l!)O1 :9:1Bending Field T 9 9

I Circumference km I 8 I 1.3 I 0.3 I

Ave.ring fieldB T 5 ] 3.5 J

I Effectiveturns I 9: 18001450i

D*mm 3 I 8 I 9

1P beam size pm 2.8 1!7 187

Chromaticity 2ooo4m 40-80

flm km I 200400 I 10-20 I 1.5 I

Lurnin. cm–2s-’ 1035 1(P3 ] 2X103’

energy range of most of the heavy Higgs in the minimalSUSY model (if that is the correct theory).

Although muon colliders remain a promising com-plement, to e+e– and hadron collider>, much work isstill neede~ including demonstration of p production andcooling, detector, and radiation.

DISCUSSION

The muon collider concept promises to extend the highenergy frontier to an unprecedented domain, with centerof mass energies of 3 TeV or beyond as its goal. Consid-erable effort has already gone into the conceptual designof muon colliders, but much R&D remains to be carriedout. Of particular importance are production targetry andcooling tests. The Muon Collider Collaboration repre-sents a dedicated effort to address those issues and pavethe way for a future muon accelerator cclmplex.

A full high energy muon collider may take consider-able time to realize. However, intermediate steps in its di-rection are possible and could help facilitate the process.Employing an intense muon source to carry out forefrontlow energy research, such as the search for muon - num-ber non - conservation, represents one interesting possi-bility. For example, the MECO proposal at BNL aims for

2 x 10-17 sensitivity in their search for coherent muon -electron conversion in the field of a nucleus. To reachthat goal requires the production, capture and stopping ofmuon at an unprecedented 1011~. If successful, suchan effort would significant y advance the state of muontechnology.

More ambitious ideas for utilizing high intensity muonsources are also being explored. Building a muon storagering for the purpose of providing intense high energy neu-trirto beams is particularly exciting. Such neutrino facto-ries could have their own world class research program,with neutrino oscillation studies as the primary focus. In-deed, if very high intensities, N 1021 ~, are attainedand nature has been kind in her neutrino mass and mixingparameters, one could envision a complete exploration ofthe 3 x 3 neutrino mixing matrix and even the detectionof CP violation in the oscillation phenomena.

If a neutxino factory is successfully accomplished, itwould provide a major advancement. Its ambitious goalswould test essentially all aspects of the muon colliderconcep~ muon production, collection, cooling and accel-eration. Furthermore, if properly coordinated, the neu-trino factory complex might be suitably expanded into theFirst Muon Collider, perhaps a Higgs factory with centerof mass energy N 100 GeV.

High intensity muon experiments, neutrino factories,and other intermediate steps toward the muon collider areextremely important. They will greatly expand our abili-ties and build confidence in the credibility of high energymuon colliders. Progress may be slower than many wouldprefer, but remember, Rome was not built in a day.

ACKNOWLEDGMENTS

The author appreciates NNN99’s organizers interestand invitation to write this paper. Special thanks toDr. Diwan for extending the time, and to Dr. Paige forassisting with the latex problems; that made the comple-tion of this report possible. This document was assem-bled largely from NFMCC existing sources, which havebeen cited among the references. Thanks to those indi-viduals who contributed graphics, information, and assis-tance.

REFERENCES

1. fie Neutrino Factory and Muon Collider Collaboration(NFMCC) home page: http://www.cap.bnl.gov/mumu/

2, http://neutrino.kek.jp/- melissaK2K/K2K2 ./htmthttp://www.awa.tohoku.ac.jp/html/KamLAND/

3. See, for example, sec. 3.4 of the MINOS Technical Design Re-port, http://www.hep.anl.gov/NDIUHypertext/minos_tdr.htenl

.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

91e..

-1?,2A

23.

24.

25.

http:/lwww.tern.chlNGS/ngs99.pdf

R- u:-:u-r.m .-.:. +. h-. JJ.. ... ....--.. ti -- I.- I .-... m,.,. xm, UC ,.U,,,DW,. L p,”,cw. ,.,,p.,, w w w.,,=””, ,,”. LalLL.~”v, LIuu L.b

l%e Oak Ridge Large v Detector http://www.orau. org/orland/

Search for VP+ v. Oscillationsat CERN PS,http://chorusOl .cern.ch/- pzucchel/loi/

A.C. Melissinos unpublished note (1960).

C.M. Ankenbrandt et o1., Status of muon coUider research anddevelopment and future plans, Phys. Rev. ST Aced. Beams 2,081001 (1999), and refrences therein.

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