1 SELECTED SPECTROSCOPY RESULTS FROM THE BABAR EXPERIMENT Veronique Ziegler J-Lab Theory Seminar, March 7, 2012
2 OUTLINE I. The BaBar Experiment II. Selected Baryon Spectroscopy Results III. Selected Meson Spectroscopy Results IV. Summary
THE PEP-II STORAGE RINGS AT SLAC 3 Bunches are accelerated in the SLAC Linear Accelerator and injected into the storage rings in order to collide at the BaBar detector
(1.5 T) 6580 3.1 GeV DCH 9.03 GeV [Y(4S)] 8.65 GeV [Y(3S)] 8.10 GeV [Y(2S)] DIRC Charged tracks momentum de/dx for PID Charged particle ID by means of velocity measurement Angles and positions of charged tracks just outside the beam pipe 4
BaBar integrated luminosity since startup 5
Largest U(nS) Data Sets 6 Samples (1S) (2S) (3S) (4S) (5S) BaBar 14 fb -1 30 fb -1 433 fb -1 3.2 fb -1 (scan) Belle 6 fb -1 24 fb -1 3 fb -1 711 fb -1 121 fb -1 Interesting new results s
7 BaBar as a Charm Baryon Factory Excellent resolution > 450 M U(4S) BB events (s = 1.05 nb) Present data sample contains: > 1600 M e e- qq events (s = 3.39 nb) > 610 M e e - cc events (s = 1.30 nb) High statistics charm baryon production Provides access to rare decay modes & High precision studies of charm baryon properties...
8 Charm Baryon Spectroscopy Observation of new decay modes First observation of charm baryon to charm meson decay Evidence for new states
Charm Baryon to Charm Meson Decay Observation of two states decaying to D 0 p previously observed L c (2880) (in L c p p - ) [Q ~ 317 MeV/c 2 ] BaBar measurements from D 0 p [Q ~ 79 MeV/c 2 much greater precision]: M = 2881.9±0.1(stat)±0.5(syst) MeV/c 2 G = 5.8±1.5(stat)±1.1(syst) MeV new state: M = 2939.8±1.3(stat)±1.0(syst) MeV/c 2 G = 17.5±5.2(stat)±5.9(syst) MeV First observation of a charm baryon decaying to a charm meson No evidence in D p of doubly charged partners Signals correspond to observation of excited L c states, not S c states [First measurement] 287 fb -1 L c u d c 9 D 0 mass sidebands wrong-sign D 0 p cands.
X 0, c u,d sc The Search for charm Cascades Decaying to L c K - (K S ) p (-) and L c K - (K S ) p - p Final States 10 Confirmation of the existence of the X c (2980), X c (3077) and X c (3077) 0 Evidence for the X c (3055) and X c (3123) natural widths consistent with strongly decaying states Excited Cascade charm baryons X c (*) observed to decay to G.S. X c by pion or photon emission X c u s c g u s c X c X (2980 c ) s c u s u u c d d u - K L c p The X c (2980),0 and X c (3077),0 seen in decays in which the s and c quark are in separate hadrons implications for the internal quark interactions inside these states predicted excited charm baryons with J P =1/2 ±, 3/2 ± J P =5/2 radial excitations
Results on excited charm Cascades decaying to L c K p L c K - p Results L c p M(L c K - p ) (GeV/c 2 ) Fit to two-dimensional invariant mass distribution M(L c K - p ) versus M(L c p ) incorporate intermediate resonances S c (2520) and S c (2455) in the fit show the M(L c K - p ) distribution for M(L c p ) ranges w/in 3-s of the S c (2455) and 2-s of the S c (2520) 11
Results on excited charm Cascades decaying to L c K p Very close to threshold very important to take account of phase space L c K - p Results L c p 12 Similar results for M(L c K S p ) versus M(L c p ) although more statistically limited No evidence for structure in (L c K S p p ) nor (L c K - p p ) No evidence for X cc seen by SELEX in L c K - p (p )
* W c c s s The Search for the W c * ( J P =3/2 ) All L=0 singly-charm baryons discovered, J P =3/2 W c* (css) state missing Splitting M(W c* )-M(W c ) predictions range from ~70-100 MeV/c 2 Search for W c * in e e - W c * X processes 13
Observation of * 0 W c W c g Splitting M(W c* )-M(W 0 ) 70. 810. (stat) 11. (syst) consistent with pqcd predictions M(W c* )=2768.3±3.0 MeV/c 2 c MeV/c 2 Ratio of the inclusive production cross sections - * * s ( e e Wc X, xp ( Wc 0.5) ) R - 0 0 s ( e e W X, x ( W 0.5) ) 14 101. 0. 23(stat) 0.11(syst) c p c
Charm Baryon Spectroscopy Insight into Light Baryon Spectroscopy Study of Cascade baryons 15
Relevance of Cascades to Baryon Spectroscopy Quark content ( u or d, s, s ) QCD calculations easier to handle Developments in fast algorithms raised expectations from Lattice QCD Narrow widths reduces potential overlap with neighboring states G(N) G(X) X(1530) Predictions of mass, width, spin/parity rely on model-based calculations Experimental validations are essential Very little known about X states which might populate the [70, 1 - ] 1 and [56, 2 ] 2 of SU(6) X O(3) Properties of X(1690) are crucial: first excited state not used as input in predictions 16 16
Cascade Physics from Charm Baryon Decay 17
18 Helicity Formalism Examine implications of W - spin hypotheses for angular distribution of L from W - decay 2 *, 2,,0), ( 2 1 2 1 f f i i f i f i i f i A D A I J J [density matrix element for W - spin projection i = density matrix element for charm baryon parent ] Spin measurement of W - from X c 0 W - K, W - L K - decays 18
The X(1530) 0 From L c X - p K Decay 19
Reconstructed L c X - p K, X - L p - Events p K L 0 p - p - p PID Information Proton Kaon p, p - de/dx & Cherenkov info (DIRC) 3-σ mass cut on intermediate states interm d. states mass-constrained [L, X - ] ct = 7.9 cm p* > 2.0 GeV/c [reduces background]. x L c ct = 60 μm X - ct = 4.9 cm m(x - p ) L c mass-signal region m(x - p ) L c mass-sideband region.. m(x - p ) (L c ) mass-sideband-subtracted L L > 2.0 mm r X > 1.5 mm [outgoing]. Uncorrected N ~13800 events HWHM ~ 6 MeV/c 2 L c X - p K Data ~230 fb -1 (L c )Mass-sideband-subtracted X(1530) 0 X - p 20 20 PDG mass
Resonant Structures in the L c X - p K Signal Region Only obvious structure: X (1530) 0 X - p Rectangular Dalitz plot L c signal region Note: m 2 (X - K ) depends linearly on cos X 21
Using Legendre Polynomial Moments to Obtain X(1530) Spin Information L c signal region uncorrected X(1530) unweighted 0 efficiency-corrected unweighted m(x - p) distribution in data Efficiency-corrected P 4 Moment Dist. w j = (7/ 2) P 4 (cos) from L c signal region Spin 5/2 Test P L moments (L 6) give no signal 22 Efficiency-corrected P 2 Moment Dist. w j = 10 P 2 (cos) wfrom j = 10 L c Psignal 2 (cos) region Spin 3/2 Test spin 3/2 clearly established spin 5/2 ruled out Schlein et al. showed J P =3/2 or J P =5/2 -, and claimed J>3/2 not required. [Phys.Rev.Lett.11, 167 (1963), Phys.Rev.142,883 (1966)] Spin-parity 3/2 is favored by the data [PDG (2006)] Present analysis by establishing J=3/2 also establishes positive parity by implication [i.e. P-wave resonance] Other interesting aspects of Dalitz plot not as simple as it first appears!
23 The X(1690) 0 From L c L K 0 K Decay
Reconstructed L c L K S K Events 24 π - π π - p Data ~200 fb -1 N ~2900 events HWHM ~ (3.1 ± 0.5) MeV/c 2 K 0 s ct = 2.7 cm Λ 0 ct = 7.9 cm x Λ c ct = 60 μm K Selection Criteria: PID Information Proton Kaon p, p - de/dx & Likelihood Cherenkov Selectors info (DIRC) 3-σ mass cut on intermediate states interm d. states mass-constrained [L, K S ] p*(l c ) > 1.5 GeV/c (reduces background) L L, L Ks > 2.0, 1.0 mm [sign outgoing].
The X(1690) 0 from L c (L K S ) K Decay 25 m(l K S ) L c mass-signal region m(l K S ) L c mass-sideband region.. m(l K S ) (L c ) mass-sideband-subtracted (L c )Mass-sideband-subtracted N ~2900 events HWHM ~ (3.1 ± 0.5) MeV/c 2 X(1690) 0 L K S L c Low-mass sideband limit Note skewing
Using Legendre Polynomial Moments to Obtain X(1690) Spin Information efficiency-corrected, background-subtracted unweighted m(l K S ) distribution in data X(1690) 0 w j = (7/ 2) P 4 (cos) from L c signal region Spin 5/2 Test Efficiency-corrected P 4 Moment Dist. w j = 10 P 2 (cos) from L c signal region Spin 3/2 Test Efficiency-corrected P 2 Moment Dist. efficiency-corrected, bckgr.-subtracted dist. in data for 1.665<m(L K S )<1.705 GeV/c 2 26 however cos L clearly not flat as expected for J = 1/2 WHY?
Dalitz plot for L c L K S K Accumulation of events in K S K near threshold evidence of a 0 (980) 27 cos L a 0 (980) m 1682.9 0.9( stat) 0.8( syst) 2.0 G 9.3-1.7 ( stat) 0.4( syst) MeV J 1/2 favored MeV/c Background-subtracted, efficiency-corrected data Integrated signal function smeared by mass resolution [Histogram] Signal function with no resolution smearing A(a 0 (980) 2 contribution A(X(1690) 2 contribution Interference term contribution For J(X[1690]) = 1/2 2 X(1690) 0 m(l K S ) (GeV/c 2 )
Evidence for the X(1690) in L c X - p K Efficiency-corrected P 1 (cos) moment X(1690) seen in inclusive environment in hyperon beam expt. M.I. Adamovich et al. Eur.Phys.J. C5, 621 (1998) S-P interference -- dip at 1690 MeV/c 28 Im A X(1530) 0 X(1690) 0 Speculation: Dip (~1680 MeV/c 2 ) may be due to resonant X(1690) 0 S-wave Coherent superposition of resonant S-wave non-resonant S-wave i.e. slowly-varying amplitude Re A & phase negative parity for X(1690) Implications for Lattice calculations and models of level structure of X excited states
29 Remarks Lots of progress in charm baryon spectroscopy Insight into charm baryon production Measurements of charm baryon spin from exclusive B decay processes Insight into light quark spectroscopy from hyperon resonances produced in charm baryon decay L (2940 c ) L (2880 c ) L (2625 c ) L (2393 c ) L c S c (2800) S c (2520) X c (3123) X c (3077) X c (3055) X c (2980) X c (2815) X c (2790) X c (2645) Xc X c * W c 0 W c
Possible Similar X Studies in 30 Photoproduction o Exclusive t-channel (i.e. meson exchange) Processes Production of two-body systems with a X e.g. g p. K (X - K ) K (X 0 K 0 ) K 0 (X 0 K ) would enable the study of high mass L* and S* states decaying via these gp K X X X - K X modes.
Possible Similar X Studies in Photoproduction (ctd.) Production of three-body systems with a X, or a X* system with two-body decay: with a forward K 0 : S*, L* 31 e.g. g p. K 0 (X - p ) K, K 0 (X 0 p 0 ) K, K 0 (X 0 K 0 ) p States analyzed K 0 (L K 0 ) K - can observe in a totally different context in L c decay gp K 0 X X X - p K with a forward K : m(l c ) e.g. g p. K (X - p ) K 0, K (X - p 0 ) K K (X 0 p - ) K, K (X 0 p 0 ) K 0 K (L K - ) K Interesting four-body possibilities when add pion e.g. g p. K (L K - p ) K, accessible at BaBar via X c0 LK - p, complicated Dalitz plot 31
32 Quarkonium Spectroscopy Insight into Bottomonium Spectroscopy Searches for missing states
Radiative bottomonium transitions from U(3S) events using g e e - conversions 33 SVT (5 layers) SVT supports Phy.Rev. D 84, 072002(2011) Drift Chamber inner wall (Be) Reconstructed Vertices Support tube (carbon fiber) Energy in C.M. frame Significantly improves energy resolution [see later] Precise BF Measurements Efficiency ~(0.1 1)%
Inclusive photon energy regions for U(3S) events 34 ( i) E g 2 mi - m 2m i 2 f [207,243] MeV Resolution dominated Small Doppler broadening b0 ( 2P) g U(2S) bj
Inclusive photon energy regions for U(3S) events 35 ( i) E g 2 mi - m 2m i 2 f [430,484] MeV ( i) E g 2 mi - m 2m i 2 f [391,442] MeV from U(3S) to U(1S)
Inclusive photon energy regions for U(3S) events Search for the Bottomonium Ground State h b (1S) 36 ( i) E g 2 mi - m 2m i 2 f [743,777] MeV U(3S) g h b (1S) photons from calorimeter With converted photons h b significance < 3s
The BaBar Observation of the h b 37 bj Peak Yield : 821841 ± 2223 g ISR Y(1S) Yield : 25153 (fixed) h b Yield : 19152 ± 2010 R(ISR/ bj ) ~ 1/33 R(h b / bj ) ~ 1/43 19152 ± 2010 events All backgrounds subtracted Non-peaking Background subtracted fixed g ISR h b
Comparison of E g Spectra for U(3S) and U(2S) Events 38 U(3S) U(2S) Results from Y(2S) and Y(3S) analyses are consistent!
Summary of Results 39 BF measurements: B((3S) gh b (1S)) = (5.1 ± 0.7) 10-4 B((2S) gh b (1S)) = (3.9 ± 1.5) 10-4 Compatible with predictions S. Godfrey, J.L. Rosner PRD 64 074011 (2001) Combined values of mass and HF splitting: m hb (1S) = 9390.9 ± 2.8 MeV/c 2 (G hb (1S) 10 MeV) (m (1S) m hb (1S)) = 69.3 ± 2.8 MeV/c 2 Unquenched lattice QCD calculations (~50-60 MeV/c 2 ) agree better than NRQCD predictions (~40 MeV/c 2 ) Tension with Belle measurement in (5S) pp h b (1P) gh b (1S)) : (m (1S) m hb (1S)) = 59.3 ± 1.9 2.4-1.4 MeV/c 2 arxiv:1110.3934v1
Searches for the h b (1P) State of Bottomonium at BaBar 40 Essential to measure the hyperfine mass splitting for P-wave states to understand the spin dependence of qq potentials for heavy quarks. Hyperfine splitting between h b (1P) mass & spin-weighted center of gravity of the bj (1P) states (9899.87±0.27 MeV/c 2 ) expected to be ~0 [confirmed for h c ]. Hyperfine mass splitting larger than 1 MeV/c 2 might be indicative of a vector component in the confinement potential. BaBar searched for the h b (1P) meson in the transitions: U(3S)p p - h b (1P) U(3S)p 0 h b (1P) (requiring a photon consistent with subsequent h b gh b (1S) decay)
Expected Mass of the h b (1P) State Hyperfine splitting for L=1 states M [c.o.g.(1 3 P J )] M(1 1 P 1 ) 41 M HF ( nl) 1 M (1 P ) ~ 1 3 M ( n LJ ) J 1) M J / (2 ) ~ 0 J J 3 3 3 ( M (1 P ) 3M (1 P ) 5M (1 P ))/ 9 0 (2J 1) 1 - M ( n L 1 J L 2 = 9899.87 ± 0.27 MeV/c 2 bj (1P) U(3S) h b (1P) m Search for a peak in invariant mass of system recoiling against p p - or p 0 * * 2 * 2 recoil( X ) ( EU( 3S ) - EX ) - ( px ) h b (1S)
Search for the h b (1P) in the decay U(3S)p p - h b Phys.Rev. D 84, 011104(R) background-subtracted result: 42 h b? h b signal region U( 3S) p p - U(2S) U ( 3S) X U( 2S) p p - U(1S ) 0 K S - p p - b 1.2( 2P) p p b 1. 2(1P ) No h b observation: -1106 ± 2432(stat.) signal events (mass fixed at 9.9 GeV/c 2 ) BF(U(3S)p p - h b )<1.0x10-4 (@90% C.L.) --suppressed by a factor >3 compared to p 0 mode First separate observation of b1,2 (2P)p p - b1,2 (1P) transitions and BF measurements: BF( b1 (2P)p p - b1,2 (1P)) = (9.2±0.6±0.9) 10-3 BF( b2 (2P)p p - b1,2 (1P)) = (4.9±0.4±0.6) 10-3 see later
Evidence for the h b (1P) in the decay U(3S) p o h b Phys.Rev. D84, 091101(2011) background-subtracted result: h b signal region 43 uncertainty from background fit 2 fit of m recoil (p o ) distribution: h b (1P) signal: Double Crystal Ball function Background: 5 th order polynomial Parameters determined with h b signal region excluded (i.e. blind analysis strategy) 10814± 2813 signal events M(h b ) = 9902±4 ±2 MeV/c 2 (C.G.=9899.87±0.27 MeV/c 2 ) Stat. Signif. = 3.8s ( 2 ); including systematic errors = 3.3s B(U(3S)p 0 h b (1P) = (4.1±1.1±0.9)10-4 < 6.110-4 (@ 90% CL) Existence subsequently confirmed by Belle in Υ(5S) p p - h b (1P) (arxiv:1103.3419 (*) ) with combinatorial bkg. 2X BaBar U(3S) search also observe h b (2P) ( (*) La Thuille 2011)
Confirmation of the existence of the h b (1P) by Belle in e e - p p - transitions at the U(5S) 44 Observation of the h b (1P) and h b (2P) states background subtracted results arxiv:1103.3419 Measured h b (1,2P) mass values consistent with predictions Observed h b production rate enhancement may be indicative of exotic process violating HQ spin-flip suppression Consistent with BaBar measmt. Resonant structures in h b (1P, 2P) p seen in (5S) h b (1P, 2P) p p - events (also in (5S) (ns) p p - ) charged exotic candidates Z b1, Z b2
2011 Picture of the Bottomonium Spectrum 45 U( 6S) U( 5S)? U(11020) U(10860) U( 4S) bb states below Y(3S) not yet discovered: 2 S-wave (h b (2S,3S)), 3 D-wave & possibly 4 F-wave. Recently discovered states including the h b (1P) and h b (2P) states BB threshold? h b ( 3S ) U( 3S) hadrons g h b ( 2P ) b 0( 2P ) ( 2 ) ( 2 P ) b 2 b1 P (nl) where n is the principal quantum number and L indicates the bb angular momentum in spectroscopic notation (L=S, P, D, ) J P C? h b ( 2S ) h b ( 1S ) S-wave U( 2S) hadrons U( 1S ) g g h b ( 1P ) b 0( 1P ) P-wave b1( 1P ) b 2( 1P ) - - - - 0 1 1 0 1 [Orbital Ang. Momentum between quarks] 2
47 Quarkonium Spectroscopy Insight into Charmonium Spectroscopy Evidence for unconventional states
Charmonium Spectrum (year 2000) 47 (E835 experiment - year 2000) in the same year -B factories started to take data Charmonium properties were well understood up to y(3770) (i.e. about the DD threshold) with some missing pieces (like the h c (2S)) No new cc states were discovered between 1980 and 2002 cc states above open charm threshold are expected to have significant width values and to decay mainly to open charm Channels Contributions of B factories to charmonium spectroscopy
Charmonium Spectrum (year 2012) 48 In a few years the situation changed rapidly There were discoveries of new charmonium states like the h c (1P), h c (2S) and c2 (2P) And several new charmonium-like states Eur. Phys. J. C71, 1534 (2011)
Charmonium production mechanisms B cc K(*) decay at the B-factories Initial state radiation 49 J PC = 1 - - States of any Quantum Number can be formed Two-photon collision Double charmonium production C=, J P = 0 ±, 2 ±, Recoil against J/y C =
50 Some Unconventional States B cc K(*) decay X(3872) Narrow state above DD threshold First Observed by Belle in J/y p p Confirmed by BaBar, CDF, D0, LHCb Measured width much smaller than that expected for a conventional charmonium state Seen in J/y g, y(2s) g decay C= Angular analyses inconclusive: J P =1, OR 2 -
Some Unconventional States 51 B cc K(*) decay B 0 b d c c s u u d y (2S) K - p X(3872) Y(3940) Z(4430) - Z 1 (4050) - Z 2 (4250) - Y(4140) A state Z - y p - would have hidden charm & charge candidate for ccud tetraquark
Some Unconventional States 52 B cc K(*) decay X(3872) Y(3940) Z(4430) - Z 1 (4050) - Z 2 (4250) - Y(4140) Initial state radiation J PC = 1 - - Y(4260) Y(4008) Y(4350) Y(4660) Two-photon collision C=, J P = 0 ±, 2 ±, Z(3930) (?= c2 (2P)) Y(3915) Double charmonium production Recoil against J/y C = X(3940)
Topics not covered today 53
Current Status 54 charmonium bottomonium open BB threshold open DD threshold All states below open flavor threshold well understood & conform to quark model qq interpretation Little exploration of the region above Region above open cc flavor more U(4S) Recent Belle evidence for Z b complicated states (structures in U(nS)p and h b (1P,2P)p from U(5S)) No analogues to the X,Y states found yet Much higher statistics needed: Spin-parity information from charmonium decays to exclusive final states Information in the bottomonium sector in the region above the U(4S)