Study of charmonium charmonium Study of spectroscopy at BESIII - PowerPoint PPT Presentation

Study of charmonium charmonium Study of spectroscopy at BESIII spectroscopy at BESIII LiangLiang WANG WANG LiangLiang (For BESIII Collaboration) (For BESIII Collaboration) Institute of High Energy of Physics, Beijing, China of High Energy of Physics, Beijing, China Institute Hadron2011 München

Outline � BEPCII and BESIII � Observation of h c at BESIII � Precision measurement of the η c properties at BESIII � The first observation of the M1 transition ψ ’ � γη c (2S) � Summary 2

The Beijing Electron-Positron Collider II • Double ring • 11 mrad crossing angle • Beam energies 1.0-2.3 GeV • 93 bunches per beam • Design current 2 x 0.91 A • Design luminosity at 1.89 GeV:10 33 cm -2 s -1 3

4 The Beijing Spectrometer III (BESIII)

BESIII data samples Number of resonant Energy points luminosity events J/ ψ 65pb -1 226 million ψ ’ 150pb -1 106 million 45pb -1 3.65 GeV ψ (3770) 2900pb -1 Scan around ψ (3770) 76pb -1 (3.646~3.892 GeV) 4.01 GeV ( ψ (4040)) 470pb -1 5

6 c at BESIII at BESIII h c Observation of h Observation of

h c ( 1 P 1 ) in charmonium family � Spin singlet P wave (S=0, L=1) � Potential model if non-vanishing spin- spin interaction: Δ M hf (1P)=M(h c ) − 1/9(M( χ c0 )+3M( χ c1 )+5M( χ c2 )) ≠ 0 � E835 found evidence for h c in pp � h c � γη c � CLEO-c observed h c in ee � ψ ’ � π 0 h c , h c � γη c Δ M hf (1P)=0.08 ± 0.18 ± 0.12MeV/c 2 7

Observation of h c at BESIII (inclusive) BESIII Collaboration: PRL104, 132002, (2010) � Select inclusive π 0 ( ψ ’ � π 0 h c ) E1-tagged � Select E1-photon in h c � γη c (E1 tagged) or not (E1 untagged) � E1-tagged selection gives M(h c )=3525.40 ± 0.13 ± 0.18MeV ( Δ M hf (1P)=0.10 ± 0.13 ± 0.18MeV/c 2 ) Γ (h c )=0.73 ± 0.45 ± 0.28MeV E1-untagged (<1.44MeV at 90% CL) Br( ψ′ � π 0 h c ) × Br(h c � γη c )= (4.58 ± 0.40 ± 0.50) × 10 -4 � E1-untagged together with tagged selection gives the first measurement Br( ψ′ � π 0 h c ) =(8.4 ± 1.3 ± 1.0) × 10 -4 Br( h c � γ η c ) =(54.3 ± 6.7 ± 5.2)% 8

Measurements of the h c properties at BESIII (exclusive) π 0 Summed π 0 recoil mass � 16 decay modes are studied: recoil mass Summed ψ ’ � π 0 h c ,h c � γη c , η c � X i X i : ppbar, 4 π , 4K, 2 π 2K, ppbar ππ , 6 π , 2K4 π , KK π 0 , ppbar π 0 , KsK π , KsK3 π , ππη , KK η , 4 πη , 2 π2π 0 , 4 π2π 0 Simultaneous fit to π 0 recoiling mass Consistent with BESIII inclusive results PRL104,132002(2010) M(h c ) = 3525.31 ± 0.11 ± 0.15 MeV CLEOc exlusive results Γ (h c ) = 0.70 ± 0.28 ± 0.25 MeV M(h c )=3525.21 ± 0.27 ± 0.14 MeV/c 2 N = 832 ± 35 N = 136 ± 14 BESIII preliminary BESIII preliminary χ 2 /d.o.f. = 32/46 PRL101, 182003(2008) 9

η c lineshape from ψ′ � π 0 h c , h c � γη c Sum of 16 of Background η C decay modes subtracted The η C lineshape is not distorted in the h C →γη C Detail analysis of η c parameters is ongoing! Symmetric lineshape Asymmetric in γγ production lineshape in ψ decay 10

11 Precision measurement of the η c properties

Introduction � The lowest lying S-wave spin singlet charmonium η c was discovered in 1980 by MarkII. � Earlier experiments using J/ ψ radiative transition gives M( η c )~2978.0MeV/c 2 , Γ ( η c )~10MeV. � Recent studies using the two-photon processes gives M( η c )=2983.1 ± 1.0 MeV/c 2 , Γ ( η c )=31.3 ± 1.9 MeV. � The most recent study from CLEO-c pointed out the distortion of the η c line shape in ψ ’ decays. η c Measurement of the η � Measurement of the � properties at BESIII c properties at BESIII ψ ’ Data sample: 106M ψ -1 1 continuum data at 3.65 � Data sample: 106M � events, 45pb - ’ events, 45pb continuum data at 3.65 GeV GeV π , K π 0 ηπ + π − π , K π + π − π 0 KsK π − π , ηπ + π − , KsK3 , KsK3 π + K − π + π − π K − , K + K − � Decay modes X , K + + K 0 , 0 , � Decay modes X i : KsK , i : π + π − π + π − η � γγ , π 0 γγ 3( π + π � π + π , η � γγ , π � γγ − ), where − , Ks � 0 � ), where Ks 3( 12

Backgrounds for ψ ’ � γη c � γ X i � ψ ’ � π 0 X i With the optimized selection, the mass spectra for π 0 X i events are measured in data and scaled according to the full simulation to estimate the contribution in γη c candidates. � Non-resonant contribution ψ ’ � γ X i exact the same final states, can not be removed � Rare backgrounds Production rate or efficiency is very low, estimated based on the inclusive MC � Continuum events Estimated by using the 45pb −1 data taken at 3.65GeV 13

π + π − η 6π 14 Backgrounds for ψ ’ � γη c � γ X i (conti.) K + K − π 0 2K2 ππ 0 KsK3 π KsK π

Mass spectrum fitting � S : signal function (BW with mass width floated) � Non : non-resonant γ X i PDF (all assumed to 0 −+ ) � BKG : the sum of other backgrounds π 0 X i + other rare ψ ’ decays + continuum, fixed in the fitting � φ : interference phase between η c decay and non-resonant contribution Interference Fit results for individual modes: 15 Constant fitting gives χ 2 /ndf=5.142/5

The simultaneous fit The η c mass, width and interference phase φ are constrained to be the same K + K − π 0 π + π − η KsK π 6π KsK3 π 2K2 ππ 0 BESIII preliminary BESIII preliminary � mass = 2984.4 ± 0.5 stat MeV/c 2 � width = 30.5 ± 1.0 stat MeV � φ = 2.35 ± 0.05 stat rad 16 (the significance of the interference is 15 σ)

Comparison of BESIII preliminary results with other measurements PDG10 ave. : Earlier experiments using J/ ψ radiative transition BESIII preliminary BESIII preliminary BESIII preliminary BESIII preliminary 17

The first observation of the M1 18 transition ψ ’ � γη c (2S)

Introduction � First “observation” by Crystal Ball in 1982 (M=3.592, B=0.2%-1.3% from ψ ’ � γ X, never confirmed by other experiments.) � Published results about η c (2S) observation: Combined with the results based on two-photon processes from BaBar and Belle reported at ICHEP 2010, the world average Γ ( η c (2S))=12 ± 3 MeV � The M1 transition ψ ’ � γη c (2S) has not been observed. ( experimental challenge : search for real photons ~50MeV, ) � Better chance to observe η c (2S) in ψ ’ radiative transition with ~106M ψ ’ data at BESIII. � Decay mode studied: ψ ’ � γη c (2S) � γ KsK π (Κ + Κ − π 0 etc. in progress ) 19

Mass spectrum representation � The 4C kinematic fitting used to select the γ KsK π candidates ( χ 2 4C <50) � Still some KsK π BG events contribute the γ KsK π candidates with a fake photon. � The invariant mass from 4C-kinematic fits make the BG ψ ’ � KsK π contaminates the η c (2S) mass region (3.6~3.66GeV) . � The mass from 3C-kinematic fits (the measured energy of the photon is free) is little biased by the fake photon. � Difference small between 4C and 3C for signal events η c (2S) MC 4C Inc. MC 3C 3C 4C 20 So the 3C fit mass used to determine the yields and parameters

Mass fitting Γ ( η c (2S)) fixed to 12MeV (world average) � η c (2S) signal: Fixed to the linear M1 transition Extrapolation from σ(χ cJ ) � χ cJ : MC shape ⊗ a Gaussian � BG from π 0 KsK π : � BG from ψ ’ � KsK π ( γ FSR ) & continuum (KsK π(γ ISR)): Measurement + scaling with MC simulation With radiation Without radiation Novosibirsk function Ratio of the two is fixed in the final mass fitting 21

Mass fitting (conti.) χ 2 /ndf=0.9 BESIII preliminary BESIII preliminary � N( η c (2S)) = 50.6 ± 9.7 � Pure statistical significance more than 6 σ � Significance with systematic variations not less than 5 σ 22

Preliminary measurements from ψ ’ � γη c (2S) � γ KsK π � M( η c (2S))=3638.5 ± 2.3 stat ± 1.0 sys (MeV/c 2 ) � Br( ψ ’ � γη c (2S) � γ KsK π )=(2.98 ± 0.57 stat ± 0.48 sys ) × 10 -6 Br( η (2S) � KK π )=(1.9 ± 0.4 ± 1.1)% from BaBar BaBar Br( c (2S) � KK π )=(1.9 ± 0.4 ± 1.1)% from η c � Br( ψ ’ � γη c (2S))=(4.7 ± 0.9 stat ± 3.0 sys ) × 10 -4 CLEO- -c: <7.6 c: <7.6 × 10 − (PRD81,052002(2010)) CLEO × 10 4 (PRD81,052002(2010)) − 4 4 (PRL89,162002(2002)) Potential model: (0.1 − 6.2) × 10 − (PRL89,162002(2002)) Potential model: (0.1 − 6.2) × 10 − 4 23