Th MTV Exprimnt: from T Violation To Lorntz Violation 1, H. Baba 2, J.A. Bhr 3, F. Goto 4, S. Inaba 1, H. Kawamura 5, M. Kitaguchi 4, C.D.P Lvy 3, H. Masuda 1, Y. Nakaya 1, K. Ninomiya 1, J. Onishi 1, R. Opnshaw 3, S. Ozaki 1, M. Parson 3, Y. Sakamoto 1, H. Shimizu 4, Y. Shimizu 1, S. Tanaka 1, Y. Tanaka 1, R. Tanuma 1, Y. Totsuka 1, E. Watanab 1, M. Yokohashi 4 1 Dpartmnt of Physics, Rikkyo Univrsity, Tokyo 171-851, Japan 2 Nishina Cntr, RIKEN, Saitama 351-198, Japan 3 TRIUMF, Vancouvr, BC V6T 2A3, Canada 4 Dpartmnt of Physics, Nagoya Univrsity, Nagoya 464-814, Japan 5 Frontir Rsarch Institut for Intrdisciplinary Scincs, and Cyclotron and Radioisotop Cntr, Tohoku Univrsity, Sndai, Miyagi 98-8578, Japan Th MTV Mott Polarimtry for T-Violation) xprimnt is running at TRIUMF-ISAC Isotop Sparator and ACclrator), sarching for a larg T violation in polarizd 8 Li β dcay via masurmnts of th tripl vctor corrlation, R, in th β dcay rat function. Th lft/right backward scattring asymmtry of Mott scattring from a thin mtal foil is masurd using an lctron tracking dtctor including a cylindrical drift chambr CDC). To achiv 1-ppm prcision in th Mott scattring asymmtry, w prformd multipl studis on th xpctd systmatic ffcts. Th sourcs of th systmatics hav bn idntifid and calibration systms hav bn dvlopd to valuat th fak ffcts. Th first physics data was collctd in 216 and significantly improvd on th rsult of our prvious masurmnt, which achivd 1-ppm prcision in 21 using th first gnration dtctor planr drift chambr) at TRIUMF. Th data masurmnt status, togthr with th rsults of th systmatics studis, is dscribd hr. In addition to th T violation, w ar prparing to tst th Lorntz invarianc in th wak sctor via our Mott analyzr systm. Unxplord Lorntz violating corrlations can b tstd using th MTV xprimntal stup. Th tsting principl and prparation status ar also dscribd hr. PoSINPC216)185 Th 26th Intrnational Nuclar Physics Confrnc 11-16 Sptmbr, 216 Adlaid, Australia Spakr. c Copyright ownd by th authors) undr th trms of th Crativ Commons Attribution-NonCommrcial-NoDrivativs 4. Intrnational Licns CC BY-NC-ND 4.). http://pos.sissa.it/
1. Introduction It has bn ovr a half cntury sinc th formalism of β dcay was stablishd. Howvr, thr ar still unmasurd corrlation cofficints [1, 2]. Of thm, th two most intrsting corrlations ar th D and R corrlations, which violat tim rvrsal symmtry [3, 4]. Th β dcay rat function xprssd with all th possibl corrlations rlatd to th lctron spin can b xprssd as ω 1 + b m + p A < J > ) + Gσ E + σ E J [ N < J > + Q p J E + m < J > J ) p + R < J > p ]. 1.1) E J E Whn th lctron s longitudinal polarization is not masurd, on can ignor th rlatd trms such that ω 1 + b m + A p < J > + Nσ < J > [ < J > + Rσ p ]. 1.2) E E J J J E By dfining th lctron s vlocity vctor as β = p /E, and th nuclar polarization vctor as P < J > /J, th rat function bcoms ω 1 + Aβ P + Nσ P + Rσ [P β ]. 1.3) Hr, th Firtz intrfrnc trm b is tratd as ngligibly small. Th thr corrlations in Eq. 1.3), A, N, and R, ar masurd in our prsnt study. In an xprimnt that is snsitiv to th lctron s transvrs polarization, th masuring snsitivity is th analyzing powr S. In ral xprimnts using th Mott scattring as th transvrs polarimtr, two additional paramtrs, ε th dtction fficincy) and S th analyzing powr of th Mott scattring), nd to b includd for th counting rat function n such that n ε 1 + Aβ P + NSσ P + RSσ [P β. 1.4) Th A corrlation is masurd as a wll-known parity violating β anisotropy, which nds to b masurd to dtrmin th nuclar polarization P. Thn, th lftward and rightward Mott scattring asymmtry will giv th cofficints N and R. PoSINPC216)185 2. Th MTV xprimnt Th MTV xprimnt will masur th N and R corrlations with th aim of dtcting nonzro valus for th first tim in a nuclar systm [5, 6]. With this as motivation, w invstigat polarizd 8 Li β dcay, which is a pur Gamow-Tllr transition. It is prdictd that N FSI = γ m E A 2.1) R FSI = αzm p A. 2.2) Ths ar calld final stat intractions FSIs). Indd, R FSI lads to a T violating obsrvabl. Howvr, it dos not violat tim rvrsal symmtry. Our primary goal is to rach sufficint snsitivity to dtct nonzro N FSI and R FSI. Prcision masurmnts of N can prob th ral part of th 1
xpctd nw tnsor intraction in wak dcay. In addition, larg R byond th standard R FSI will indicat th xistnc of an imaginary part of th nw tnsor intraction [7]. W aim to masur N and R at th sam tim. In this way, w can cancl th ambiguity in S by combining thir rsults. With this as motivation, w startd th MTV xprimnt at TRIUMF-ISAC [8] using a highly polarizd 8 Li bam. Th polarizd 8 Li bam is producd via th collinar lasr optical pumping tchniqu. Th 8 Li bam, at approximatly 3 kv, is stoppd at our bam stoppr foil aluminum 1 µm). Thn, th dcayd lctron xits th vacuum chambr, which is surroundd by a cylindrical Mott analyzr [9]. bam dirction) Z Analyzr Foil CDC Y bam spin + ψ θ V-Track Lftward β Rightward Figur 1: Coordinats of th MTV Mott analyzr using th CDC. Th Mott scattring angl θ is dfind as th scattring angl of th V-track. Th lctron s azimuthal mission angl β is dfind as th angl from th bam spin dirction in th spin + configuration [1]. If th bam spin polarization is not dirctd toward th X-axis, th rotation angl around th Y-axis is dfind as α. Th dirction toward th Z-axis th bam dirction) corrsponds to α = +π/2. As shown in Figur 1, th spin-polarizd 8 Li bam is stoppd at th bam stoppr placd in th cntr of th cylindrical stup. Part of th mittd lctrons is backwardly scattrd from th cylindrical analyzr foil. Th scattring tracks, calld V-tracks, ar dtctd using th cylindrical drift chambr CDC). Th lctron s mitting angl β and th Mott scattring angl ψ ar rcordd vnt-by-vnt. Hr, ψ > ψ < ) is dfind as rightward lftward) Mott scattring. In addition, α is th rotation angl of th nuclar polarization around th Y-axis from th X-axis. Th dfinition of th sign of α is shown in Figur 1. In idal cass of nuclar spin, + ) corrsponds to α = α = π). α X PoSINPC216)185 3. R and N corrlations Each vnt is rcordd with its β and ψ angls. From this information, a counting numbr N ± ψ,β) is obtaind for th bam spin ± cass. Using Eq. 1.4), th xpctd count rat is N + ψ,β) E accptanc ε 1 + Aβ P + NSσ P + RSσ [P β dωde. 3.1) 2
In our cas, th accptanc covrs th ± z rgion along th axis dirction of th cylindrical dtctor and small β. By calculating ths gomtrical corrction factors, Eq. 3.1) can b r-writtn as N + ψ,β) ε 1 + A f A β P + N f N Sσ P + R f R Sσ [P β, 3.2) using th man fficincy ε, th accptanc corrction factors f A, f N, and f R, and th man β = β / β < β >. For ach cas of bam spin ± and lftward rightward) Mott scattring ψ < ψ > ), N + ψ <,β) εψ,β) 1 + A f A β P + N f N Sσ P + R f R Sσ [P β N + ψ >,β) εψ,β) 1 + A f A β P N f N Sσ P R f R Sσ [P β [P β N ψ <,β) εψ,β) N ψ >,β) εψ,β) Thn, th convntional doubl ratio can b dfind as 1 A f A β P N f N Sσ P R f R Sσ 1 A f A β P + N f N Sσ P + R f R Sσ Dψ,β) N+ ψ <,β) N ψ >,β) N + ψ >,β) N ψ <,β) 1 + A fa β P cos α cos β + N SP sin α + R f R S β P cos α sin β ) = 1 + A fa β P cos α cos β N SP sin α R f R S β P cos α sin β ) 1 A fa β P cos α cos β + N SP sin α + R f R S β P cos α sin β ) 1 A fa β P cos α cos β N SP sin α R f R S β P cos α sin β ) 1 + Â cos β + ˆN + ˆR sin β ) 1 Â cos β + 1 + Â cos β ˆN ˆR sin β ) ˆN + ˆR sin β ) 1 Â cos β ˆN ˆR sin β ) = 1 + 4 ˆN + ˆR sin β) 1 Â cos β) 2 ˆN, ˆR << 1) [P β. 3.3) = 1 + 4 ˆN + ˆR sin β). Â << 1) 3.4) PoSINPC216)185 From Eq. 3.4), it is clar that dviation from D = 1 implis a non-zro ˆN as a constant componnt and ˆR as a sin-curv componnt as a function of β. Usually, asymmtry is usd instad of D such that D 1 A sym ψ,β) ˆN + ˆR sin β. 3.5) D + 1 Th xpctd signal is shown in Figur 2. 4. Systmatic Effcts on R Th fficincy inhomognity can b cancld in th doubl ratio analysis via bam spin flipping. In our prvious studis, w rcognizd two major systmatic ffcts that cannot b cancld using this bam spin flipping tchniqu. Th sourc of ths systmatics is th parity violating A corrlation. Th parity violating β anisotropy flips with th bam spin flipping. As of 215, w had found two typs of systmatics. 3
Asym ) = L-R)/L+R) β R-corrlation π 2π N-corrlation β =, if α = β azimuthal angl) azimuthal angl) Typ 1. A sym > at β = π/2 Typ 2. A sym < at β = π/2 Figur 2: Expctd signal of N and R on a A sym vrsus β plot. Thir proprtis ar shown in our prvious rport [1]. In 216, w prformd an intnsiv study of this systmatic ffct by studying: [A] th sourc position dpndnc, [B] th bam polarization dpndnc, [C] th coincidnc window dpndnc, and [D] th bam intnsity dpndnc. In Figur 3, typical valus of A sym ar plottd as a function of β. W intgratd Nψ,β) ovr ψ in our prsnt analysis. Thrfor, th ffctiv analyzing powr S nds to b stimatd undr th ψ intgration. Th rgion around β π/2 is mpty bcaus w rmovd th analyzr foil in this rgion to stimat th foil ON/OFF ffcts, such as th signal to nois ratio. Th vnts obsrvd in th foil OFF configuration ar not thought to originat from Mott scattring on th analyzr foil. Thrfor, such vnts rduc th analyzing powr. W stimat th ffctiv analyzing powr S by including th accptanc corrction and this nois contribution ffct. Th Typ-I systmatic shows a clar dpndnc on th width of th coincidnc window. This strongly suggsts that this ffct rsults from an accidntal coincidnc. If a coupl of straight tracks from two diffrnt β dcay vnts is rcognizd as a V-Track, such an ffct must incras as a function of th coincidnc window width. Bcaus th accidntal hit rat is incrasd with th radiation intnsity, this ffct is synchronizd with th parity violating β anisotropy. Th sin β) shap obsrvd in Figur 3 is undrstood as bing this ffct. It is also confirmd that this ffct incrass with th bam intnsity, which is consistnt with our intrprtation. To study this Typ-I ffct without using a ral spin polarizd bam, w dvlopd a linar robot calibration systm to simulat parity violating β anisotropy. In this cas, th dtctor stup constantly changs th location, oscillating in th ± X dirction. Th Typ-I ffct was confirmd for th robot calibration systm and for th polarizd bam tst in 216. As for th Typ-2 ffct, a sourc intnsity dpndnc was not clarly obsrvd. Th coincidnc window dpndnc cannot asily b stimatd indpndntly from th Typ-I ffct. Rcntly, w concludd that this Typ-2 ffct has nithr a coincidnc window dpndnc nor a sourc intnsity dpndnc. Our prvious intrprtation of this ffct was th gain rduction of th PoSINPC216)185 4
Asym coincidnc window = 2 ns.1.5.5.1 Asym Asym 2 4 6 β [rad] coincidnc window = 3 ns.1.5.5.1 2 4 6 β [rad] coincidnc window = 1 ns.1.5.5.1 2 4 6 β [rad] PoSINPC216)185 Figur 3: Typical plot of A sym vrsus β for th coincidnc windows top) 2 ns, middl) 3 ns, and bottom) 1 ns. dtctor [1], which should, howvr, show a bam intnsity dpndnc. Currntly, w bliv that this is simply a gomtrical ffct du to changing th scattring angl. Th changing of th scattring angl lads to a chang in th scattring cross sction; thrfor, this ffct should not show a bam intnsity dpndnc. In a ral xprimnt, th Typ-2 ffct dos not xist, unlss w artificially chang th dtctor position synchronizd with th bam spin flipping. Th robot calibration systm was blivd to b ffctiv in stimating all th parity violation rlatd systmatics. Howvr, w must conclud that this assumption was not corrct. Th robot systm causs an additional Typ-2 ffct, which dos not xist in th ral masurmnt. Thrfor, w built a diffrnt systmatics valuation systm for 5
th Typ-1 ffct. Th accidntal hit ffct for th spin ± can b tratd as εψ,β) εψ,β)1 + δ ± β)), by adding th contribution of th fficincy from th accidntal hits. This additional trm δ ± cannot b cancld by th convntional doubl ratio tchniqu bcaus δ ± is not constant ovr spin flipping. Instad, w masur A asym as a function of th coincidnc window width and th bam intnsity. A typical rsult is shown in Figur 4. This figur shows a clar scaling to ths two factors, which is consistnt with th intrprtation of accidntal coincidnc. Asym.4.3.2.1.1 6 1 2 4 6 8 1 12 14 16 coincidnc window * intnsity [a.u.] Figur 4: Typical plot of th sin-curv amplitud of A sym β) vrsus th coincidnc window intnsity. 5. Masurmnt of N At our original xprimntal stup, α =. th contribution from th N corrlation is zro. To produc α, w installd a nw rotational tabl systm to rotat th dtctor stup. Th configuration with α producs a bam longitudinal polarization P L = P Z = P sin α and a transvrs polarization P T = P X = P cos α. Th chang in α is obsrvd as a chang in th offst componnt of A asym β) apart from th sin componnt. Th stup is shown in Figur 5. Th systmatic ffcts originat from th parity violation. Thrfor, thr is no such ffct on th constant componnt. Th contribution from th R and N contributions is obtaind at th sam tim by th A sym β) fitting with th sam ordr of statistical prcision. Th N corrlation is usful to chck th calculation of th ffctiv analyzing powr S, which is common with th R masurmnt. In addition, th masurmnt of th N corrlation itslf can tst th xistnc of a ral part of th unknown tnsor intraction. PoSINPC216)185 6. Lorntz Violation and Solar Nutrinos Apart from th physics of th R or N corrlations in convntional β dcay formalism [1], th MTV xprimnt can prob othr physics that rquir tim-varying proprtis of th wak intraction. For xampl, it has bn pointd out that th MTV is snsitiv to unmasurd corrlations in 6
α > α = bam dirction α < Figur 5: Nw rotational tabl systm to produc nonzro α for th N corrlation masurmnt. th χ µν framwork, which is proposd as a st of Lorntz violating cofficints [11]: ω 1 2 3 χ r + 2 3 χl r + χ i l )β l 1 3 [1 χ r )β P + χl i P l + χ lk βp l k + χ l i β P)l ]. 6.1) Th nw cofficints, χ s, ar th proposd nw Lorntz violating cofficints. Th last trm can b tstd as a sidrian variation of β P). In our cas, th lctron s mission dirction β about P should b masurd as a tim squnc. W can also masur th liftim diffrnc of 8 Li btwn th spin + and cass as a tim squnc. This is similar to th work at KVI [12]. Th MTV xprimnt is snsitiv to th trm χ l i Pl. If day variation in th liftim asymmtry ovr th spin ± PoSINPC216)185 A τ = τ+ τ τ + + τ 6.2) is obsrvd, it mans that thr is a spcial dirction χ i l in th wak intraction. It may b possibl to tst not only th Lorntz violation but also Solar nutrino-rlatd phnomna [13] using this masurmnt. Evn though it is not includd in 6.1), it is also possibl to xamin th variation of σ, which rquirs our Mott analyzr. In addition, to prform long-trm calibration masurmnts using an unpolarizd sourc, th trm 2 3 χl r + χ i l)β l can b tstd. 7. Exprimntal Status In 216, w prformd th first physics production run using th currnt CDC stup. Th obsrvd accidntal ffct was confirmd as consistnt with th Typ-1 ffct, which is wll undrstood and controlld. Th xpctd statistical and systmatic prcision was approximatly 7
A asym 1-ppm ovr th two days of data production. Th physics intrprtation of R and N in th 216 datast will b publishd soon. Data production is also schduld in and aftr 217, whn w will rach a prcision of A asym 1-ppm. In th 216 datast, w prformd a masurmnt of th liftim asymmtry A τ as th daily sidral) variation with a prcision of 1-ppm. Othr Lorntz violation obsrvabls ar also rcordd. Th analysis rsults will b rportd soon. Rfrncs [1] J. D. Jackson, S. B. Triman, and H. W. Wyld, Jr., Phys. Rv 1957) 517; Nucl. Phys. 4 1957) 26. [2] N. Svrijns, M. Bck, and O. Naviliat-Cuncic, Rv. Mod. Phys. 78, 26) 991. [3] J. Sromicki t al., Phys. Rv. Ltt. 82 1999) 57. [4] R. Hubr t al., Phys. Rv. Ltt. 9 23) 2231. [5] t al., EPJ Wb of Conf. 66 214) 517. [6] t al., Hyprfin Intract. 225, 214) 193-196. [7] N. Yamanaka t al., J. High Enrgy Phys. 214, 12 214) 1-54. [8] C.D.P. Lvy, t al.. Nucl. Instrum. Mth. B24, 23) 689-693. [9] S. Tanaka t al., Nucl. Instrum. Mth. A752 214) 47-53. [1] t al., Hyprfin Intract 216) 237:12. [11] J.P. Noordmans, H.W. Wilschut, and R.G.E. Timmrmans, Phys. Rv. C 87, 5552 213). [12] S. E. Mullr t al., Phys. Rv. D 88, 7191 213). [13] P.A. Sturrock, E. Fischbach, J.D. Scargl, Solar Physics, 291, 216) 3467. PoSINPC216)185 8