Search for Invisible Decay of Y(1S) Osamu Tajima (KEK) for Belle Collaboration Oct. 17, QWG 2007 (DESY)

“Dark Matter” is 1/4 of universe B-factory may have strong sensitivity !? Main issue of B-factory is study for anti-matter which is 0% in the universe !! 0% antimatter

Status of Dark Matter Search LEP c c N’ 90% CL upper limits (Excluded region) N Energy deposition ? LHC Direct measurements have no sensitivity for ~GeV mass region LHC will reach ~TeV mass region Who will search ~GeV mass region ?

Status of Dark Matter Search (cont.) LEP Invisible width of Z Limit for coupling with Z single photon counting (e+e-  g invisible) Limit for coupling with e+e- Limit for coupling with qq ? Not covered well, Can be applied LEP limit in simple MSSM However … We can construct qq favored model as we like PRD 72, 103508 (2005), B.McElrath, “Invisible quarkonium decays as a sensitive probe of dark matter” hep-ph/0510147 “Probing MeV Dark Matter at Low-Energy e+e- Colliders” hep-ph/0509024 “Light neutralino dark matter in the next-to-minimal” hep-ph/0601090 “Dark matter pair-production in bs transitions” Charge of the Experiment : test all possibilities We are very lucky if we find DM with Dark Horses e+ e- Z DM LEP e+ e- g DM M _ q DM M _ _

Br( Y(1S)cc ) ~ 6x10-3 (mc<4.73GeV/c2 ~ mb) How many events ? Relic density is denoted as follows W : relic density h : Hubble constant v : 1/20 ~ 1/25 0.1 pb ・ c Wh2 @ <s(ccSM) v > Wh2 = 0.113  WMAP c q _ c q _ s(ccSM) ~ 18 pb see PDG s(SMcc) @ s(ccSM), G(U(1S)cc) = fU2MUs(bbcc) Br( Y(1S)cc ) ~ 6x10-3 (mc<4.73GeV/c2 ~ mb) Assuming Time reversal … PRD 72, 103508 (2005) , B.McElrath, “Invisible quarkonium decays as a sensitive probe of dark matter” Past Best limit < 23x10-3 (90% CL) by ARGUS (1986)

How do we search such a “invisible” decay ?

KEKB accelerator & Belle detector The world highest luminosity collider, KEKB, can provide ~1 million U per day Belle Multi purpose detector, Belle, catch the invisible decay signals KEKB Linac

What is the most efficient way ? p+ Usual operation on this resonance p- Y(3S) Y* Y(1S) Y(3S) runs : 2.9 fb-1 (Feb, 2006 : 4days) Invisible No Signal

Reconstruction of “Invisible” No direct detection of Y(1S) decay, Detectable information momentum of p+, p- energy of initial state (EY(3S)) Missing particle is resonance  recoil mass peak p+ p- Y(3S) Y* Y(1S) Y(3S) runs : 2.9 fb-1 (Feb, 2006 : 4days) Invisible

Reconstruction of “Invisible” Demonstration with Y(1S)  m+m- decay p+ 4902 events p- Y* Y(3S) Y(1S) m+ Y(3S) runs : 2.9 fb-1 (Feb, 2006 : 4days) U(1S)m+m- m-

Trigger logic is important To improve the detection efficiency Trigger logic is important For trigger issue, we need two charged tracks Reach to outer most layer of CDC (pt ~250 MeV/c) Reach to middle layer of CDC (pt ~120 MeV/c) “Opening angle cut” is necessary to distinguish tracks p+ p- x y

Special Trigger for Y(3S)p+p-Y(1S)invisible Control sample U(3S)  p+p-U(1S) U(1S)  m+m- data MC Too low efficiency with usual condition (>135o) Higher efficiency with looser condition Special trigger condition was implemented 　　 (~850 Hz, twice rate as usual) Single track trigger was implemented, too with 1/500 pre-scale rate (pt>250 MeV/c) 2-track trigger & 1-track trigger 1-track trigger for efficiency monitoring ?

Special Trigger for Y(3S)p+p-Y(1S)invisible Control sample U(3S)  p+p-U(1S) U(1S)  m+m- data MC Too low efficiency with usual condition (>135o) Higher efficiency with looser condition Special trigger condition was implemented 　　 (~850 Hz, twice as usual condition) Single track trigger was implemented, too with 1/500 pre-scale rate (pt>250 MeV/c) 2-track trigger & 1-track trigger 1-track trigger for efficiency monitoring Trigger eff. = 89.8% qrf > 30o ptfull > 0.30 GeV/c ptshort > 0.17 GeV/c other cuts (following slides) 244 events predicted Br(Y(1S)invisible)=6x10-3

What is background source ?

Y(3S)p+p-Y(1S)invisible Background Two-photon 2 prong pp, ee, mm … pt is balanced Boosted (q distribution) p+p-p0 ... p0 veto, g energy cut U(1S) S/N: 1/301/8 recoil mass of p+p- signal BG

Y(3S)p+p-Y(1S)invisible Background Two-photon BG recoil mass of p+p- Y(1S) m+m-, e+e- … (outside of acceptance) p m 244 events predicted Br(Y(1S)invisible)=6x10-3

Results

Results Br(Y(1S)invisible) < 2.5x10-3 (90%C.L.) Nsignal = 38 ± 39  0 consistent Br(Y(1S)invisible) < 2.5x10-3 (90%C.L.) data Fit BG Prediction Br(Y(1S)invisble)=0.6%

Originally, it was introduced to explain Solar neutrino anomaly Another Impact Originally, it was introduced to explain Solar neutrino anomaly

Another DM Search : B  h  χχ Dark Matter Dark Matter Dark Matter Dark Matter Belle 535M BBbar, to appear in PRL

Summary Invisible decay of Y may indicate the existence of light dark matter (mass < mb) Direct search experiments have no sensitivity Max. prediction : Br( Y(1S)invisible ) ~ 6x10-3 We took 2.9fb-1 data on Y(3S) with special trigger  Search for invisible decay of Y(1S) No indication whereas we reach the prediction Br( Y(1S)invisible ) < 2.5x10-3 (90%CL) Phys. Rev. Lett. 98, 132001 (2007)

Prospects

Prospects e- e+ 90 %C.L Super-forward m-detector and Super-forward cal. Can reach 2x10-4 ~500 fb-1 SM : Y(1S)nnbar

Recent results from others Submitted to PRD(RC) with one month decay Belle still has the best limit UL 3.9x10-3 (90%CL)  2.5x10-3 (Belle) Based on 1.2 fb-1 on Y(2S) resonance Y(2S)  p+p-Y(1S)invisible with pre-scaled trigger 1/20

Other light Dark Matter physics by B-factory

FWD/BWD muon detectors U(1S)m+m- : ~1/50 of now +/-5o +/-5o We can cover < +/-1.5o region in principle Because we have 100m straight section in tunnel Belle >99 % of acceptance is covered for muon

~99 % of acceptance is covered for e+e- EFC Pb shield  active detector !?

Other Impacts (2) our results gives lower limit for describes U our results gives lower limit for gravitino mass m3/2 > 1.5x10-7 eV previous limit: m3/2 > 0.3x10-7 eV

eff. = 9.2% (reconstruction) x 89.8%(trigger) = 8.2%