Search for L epton F lavor V iolation in the m + N -> t + N conversion (preliminary)

1. Search for Lepton Flavor Violation in the m + N -> t + N conversion (preliminary) S.N. Gninenko INR, Moscow SPSC meeting, Villars, September 22-28, 2004

2. Outline • Introduction • m+N->t+N conversion • Choice of signature • Experimental setup • Signal/Background simulations • Results • Summary

3. Introduction • SuperK'98 result: nu and/or ntare not massless, nu-ntmixing is large. First observation of the LFV process with neutral leptons. SM has no LFV: New physics. • Suggests LFV for associated m, t –leptons • LFV involving charged leptons has never been observed. In many models LVF is natural - SUSY - Left-Right Symmetric Model - Top seesaw, - Extra dimensions - Higgs mediated LFV • In some models LFV processes for tau are enhanced over muon processes

4. Experimental Limits on LFV Future Plans Focus on m-e sector: BNL:m -+Al->e-+Al < 10-16 PSI: m -->e-+g < 10-14 J- Parc : m -->e- < 10-18 For m-t sector limits are quite modest

5. Why m + N -> t + N ? e ~105 MeV • What is the m+A->e+A conversion? stop capture m target matom g.s. conversion • The similar experiment to search for t+A->m+A would be very interesting, but too short t-lifetime (< 0.3 ps) makes it unrealistic. • Inverse process m+ N->t+N is possible for muon energy Em > ~3 GeV at p or n. • Is it interesting? Gninenko at el.(2002), Sher & Turan. (2004) • More theoretical attention is required compare to m+A->e+A

6. Phenomenology Limits on L Black et al. m t S PS V A q’ q 1/L2(m G t) (qa G qb) • t-> c : week limit onLfor (mt)(u c) • enhances motivation to search for m-t conversion • emphasizes need to test LFV in both rare t decays and in m-t conversion at high energies Note: L~Br(t->. . .)-1/4

7. Cross section for DIS m + N -> t + N • cross section is model dependent • S cross section is ~ 1fb at ~100 GeV • V cross section is suppressed by the limit on L, s~1/L4 • primary muon energy should be more than ~20 GeV L=2.6 TeV Scalar L=12 TeV Vector

8. Rate estimate for m + N -> t + N t N m->t = Nm s L r N ABr(t->..) e m • muon energyEm=100 GeV • cross section s ~ 1 fb • muon integral flux Nm=10 15 • target length L = 100 cm • target density r ~10 g/cm3, e.g. PWO crystals • branching ratio Br(t->..) ~ 17 % • t->m n n 17% • t->en n 17% • t->p n 11% • efficiency e~100 % Target For (m t)(q q), q=u,d N m->t = 120 events For (m t)(u c) N m ->t could be much higher

9. m + N -> t + N: Choice of the Signature • DIS:m + N -> t +X (e, g, m, h, ..) • for any t decay mode, the • m photoproduction is the main • source of background, • s(m-t)/sm(g) < 10-10 • complicated final state and analysis • many possibilities for background • quasi-elastic (QE) m + N ->t + N’, and/or coherent m + A-> t + A (?) • two-body reaction, • low momentum transfer • smaller cross sections • enhancement for coherentm-t ? • monoenergetic t • small energy of N’ or N* , < ~ 1 GeV • So fart->m n n, p n • Signature: • single m, p • large missing E • missing Pt • small ETARGET

10. Comment on background Large missing energy is one of the keys, good hermiticity is important m m <50 GeV 100 GeV If detector is hermetic- leakages are mostly due to X neutrino decays: X -> n + Ln (associated lepton, LF conservation !). If neutrino energy is ~a few 10s GeV, small E L from X -> n + Ln is very unlikely. High suppression of photoproduction. Week m->n reactions are another source of background, s(m->t)/s(m->n) ~10-4- 10-2 L X N n >50 GeV of missing E

11. Experimental Setup • high rate capability: simple design • active target with low energy threshold • hermetic (good ~4p coverage) detector • electromagnetic & hadronic calorimeter energy resolution, granularity • high in/out going muon momentum resolution • particles ID • Signature: • single m, p • large missing E • missing Pt • small ETARGET • no EHCAL ECAL target m/p m HCAL Hermiticity might confront m/p precision measurements

12. Simulations Analogy with n-induced reactions used in simulations, e.g. : Nomad configuration/software (WA-96, Search for nm->nt) • nt + n -> t+ p m + n -> t+ n • nt + p -> t+ n m + p -> t+ p • nCC mCC • . . . . . .

13. QE: m+ N->t+N signal simulation m n n • monochromatic t • ~60%m below 50 GeV • ECAL energy <1 GeV • Pt < 1.5 GeV/c

14. Background sources for QE (m->t) + t->m n n The goal is to search for a few, at most ~100 m-t induced events among ~1012 m interactions. Background sources have to be explored down to 10-12 m n n final state • Beam related: - low energy tail E < 50 GeV - p /K decays in flight: fp x PDec x Pm(E<E cut) x PECAL • K decays are more dangerous • DIS like QEL • m+N->m’+ neutrals + leakage • m+N->m’+ X->L+ n +…… • mCC:m+N->n+X->m+ … • QE or Coherent trilepton productionm+A->m+n+n+A • Coherent p production m+A->n+p+A m+n • Single charm production: m+d,s->n+c -> s+m+n (beam sign is important !) • . . . .

15. m+ N >n+X (mCC) sample m+... 104 simulated events at 100 GeV 1 event found

16. Coherent m+A->n+p+A m+n • Additional suppression due to p decay in flight • ~50%m < 10 GeV • ECAL < 1 GeV • Pt < 1.5 GeV/c

17. Coherent trilepton production m+A->n+m+n+A CHARM II ’91: s~0.03 fb at <E>~24 GeV

18. Summary of background for the QE reaction : m+ N->t + N->m n n + N

19. People/Institutes involved Experimental groups • LAPP, Annecy • INR, Moscow • IHEP, Protvino • ETH, Zurich (help/experience with simulations, A.Rubbia’s group) Theoretical groups • College William and Merry, Williamsburg • INR, Moscow Also, • Osaka Univ. , S. Kanemura et al., talk at Tau’04, 16 Sept. 2004. • JINR, Dubna, S. Kovalenko • H. Kosmas’s group (Ioannina and Tuebingen) , coherent m-t cross section

20. Summary • search for LFV in muon to tau conversion would be interesting and challenging • further work is required to study • muon beam : energy, intensity, purity, … • target: composition, mass, … • detector: rate capability, precision, ... • production mechanism and cross sections • best experimental signature • signal/background: MC simulations, tools, … and demonstrate feasibility of the experiment