P.Pakhlov ITEP, Moscow (for Belle collaboration) e+e- collision from to Novosibirsk, BINP, 2006
Novosibirsk’06, P.Pakhlov Theory introduction Last 30 years NRQCD serves to calculate charmonium production: factorization perturbative (cc production) and non-perturbative (cc hadronization into charmonium) = n (cc) O n cc = n (cc) O n cc Color Singlet Model (ignore (cc) 8 ) was ok before Tevatron ’ surplus problem appears (1994) Color Octet Model was believed can solve the Tevatron problem Purely phenomenologic approach: free parameters -- O n cc , to tune to the data If tune parameters to the observed p ( (2S)) spectra, still have problem to predict polarization
Novosibirsk’06, P.Pakhlov Charmonium production in e + e - Big surprise # CLEO: e + e - J/ X exists! 15.2 4.6 J/ events above kinematical limit for B-decays (p>2.0 GeV/c) in (4S) data (e + e - J/ X )~2 pb Was not predicted by theory, but first observed experimentally L ~1fb -1
Novosibirsk’06, P.Pakhlov Theory: production in e + e - Color-Singlet e + e - J/ cc was estimated to be very small by Kiselev et al. (1994) ~0.05 pb should be unobservable even at high luminosity B-factories Color-octet e + e - (cc) 8 g J/ g (with O n cc fixed to Tevatron and others data) should not be large as well (but can be significant around the end-point of J/ momentum) Braaten-Chen (1996) Color-Singlet e + e - J/ gg is the best candidate! Predicted CS ~1-2 pb Cho- Leibovich (1996)
Novosibirsk’06, P.Pakhlov Belle’s first result Idea is to study the recoil mass against reconstructed J/ using two body kinematics (with a known initial energy) M recoil = (E cms - E J/ ) 2 - P J/ 2 ) M recoil = (E cms - E J/ ) 2 - P J/ 2 ) 2002, Belle found large cross-sections for: e + e - J/ c e + e - J/ c0 e + e - J/ c ‘ L ~45fb -1
Novosibirsk’06, P.Pakhlov Belle’s first result Not the whole story! In addition, also observed associated production e + e - J/ D (*+) X e + e - J/ D 0 X Immediately demonstrates large e + e - J/ cc unlike theory prediction Based on LUND cc D *+ /D 0 fragmentation rates calculated: (e + e - → J/ cc)/ (e + e - → J/ X) =0.59 0.14 0.12
Novosibirsk’06, P.Pakhlov Using more data Belle 2004: Full analysis of double charmonium production Reconstructed charmonium: J/ (2S) Recoil charmonium: All known charmonium states below DD threshold L ~155fb -1
Novosibirsk’06, P.Pakhlov Cross-sections Interesting: Orbital excitations are not suppressed! Only S,P states are seen recoiling to V charmonium! cccc J/ c0 c1 + c2 c (2S) (2S) J/ (2S) 25.6 2.8 4.6 3.9 <9.1< 1.7 3.8 3.1 <5.3< 1.7 4.6 3.9 <9.1<16.9 Born cross-sections: * BR (recoil charmonium >2charged) Reconstructed R e c o i l
Novosibirsk’06, P.Pakhlov Can theory adopt this result The first NRQCD estimates: R= J/ c / ~ s 2 (m c v/E beam ) 6 (e + e - →J/ c )=2.3 1.1 fb ~10 times lower! (e + e - →J/ c )=2.3 1.1 fb ~10 times lower! matrix elements are fixed from annihilation constants using J/ → e + e -, c Bodwin-Braaten-Lee 2003; confirmed by Liu- He-Chao, Brodsky-Ji-Lee Bodwin-Braaten-Lee 2003; confirmed by Liu- He-Chao, Brodsky-Ji-Lee Double photon annihilation also can not resolve the disagreement: experimentally e + e - → J/ J/ is not seen; theoretically (after correcting mistake) e + e - → → J/ cc is small.
Novosibirsk’06, P.Pakhlov BaBar’s confirmation 2005, BaBar also see double charmonium events e + e - J/ c e + e - J/ c0 e + e - J/ c ‘
Novosibirsk’06, P.Pakhlov New ideas We need to solve an order of magnitude disagreement Kaydalov NRQCD is wrong! Use instead Redge trajectories approach – tune free parameters from D meson production get reasonable agreement for e + e - → J/ cc ( ~1 pb) and predict ~10% of J/ cc are double charmonium (M cc <2M D ) Bondar Chernyak Try to save NRQCD! Light cone expansion formalizm. Use wider wave functions. Manage to “predict” (e + e - J/ c )~30 fb Braguta Likhoded Luchinsky Similar approach to BC applied for all final states: reasonable agreement All approaches are phenomenological. Need to predict something that can be checked.
Novosibirsk’06, P.Pakhlov Angular analysis Fit M recoil (J/ ) in bins of J/ production and helicity angles Correct on efficiency Fit with ~(1+ cos 2 ) production and helicity angles separately simulteneously: prod = hel prod hel prod = hel L min NRQCDglueball c c0 c ’
Novosibirsk’06, P.Pakhlov Angular analysis Measure: L=1 for J/ c and J/ c ‘ as expected L=0 is measured for J/ c0 ; NRQCD expects L=0,2 with similar fractions ( c0 is a P-wave) Can be used to check BC & BLL models. We pay their attention to this measurement
Novosibirsk’06, P.Pakhlov New state Add more data and extend searching region above DD threshold Add more data and extend searching region above DD threshold New peak at M~3.9 GeV, Temporary called X(3940) New peak at M~3.9 GeV, Temporary called X(3940) Two peaks are not excluded, but the second is not significant with the present statistics Two peaks are not excluded, but the second is not significant with the present statistics Significance 5.0 Significance 5.0 =39 26 MeV (< 90%C.L.) =39 26 MeV (< 90%C.L.) L ~450fb -1
Novosibirsk’06, P.Pakhlov X(3940) decays Expect X DD or DD * Expect X DD or DD * Try to find these decays: Try to find these decays: Reconstruct J/ & two D’s – no chance Reconstruct J/ & two D’s – no chance J/ & one D & see the unreconstructed D in M recoil (D J/ ) -- challenging J/ & one D & see the unreconstructed D in M recoil (D J/ ) -- challenging D and D * are well separated ~2.5 Clearly seen in the data
Novosibirsk’06, P.Pakhlov X(3940) DD (*) X (3940) DD * : X (3940) DD * : Clear peak Clear peak N=24.5 6.9 (5.0 ) N=24.5 6.9 (5.0 ) =15.1 10.1 MeV =15.1 10.1 MeV M=3.943 GeV M=3.943 GeV B (X(3940) DD * )=( ±22)% X(3940) DD: no signal X(3940) DD: no signal N = < 8.1 N = < 8.1 B (X(3940) 90 C.L.
Novosibirsk’06, P.Pakhlov Summary Double charmonium production is interesting and still not completely understood phenomena Belle luminosity & theory’s wisdom grow! Hope to have more interesting results soon.