1. Evidence for a Near-Threshold Structure in the J/ from B+J/K+ Decay at CDF
Jane Nachtman
University of Iowa
(for CDF Collaboration)
Rencontres de Moriond QCD
March 2009

2. A Little Background
In recent years, several interesting particles have been discovered
Y(3940)
M≈3940 ± 11 MeV
 ≈ 92 ± 24 MeV
X(3872)J/+-
M=3871.8±0.7±0.4 MeV
< % CL
Y(4260)
M=4259  8 MeV  = 88  23 MeV
Unusual decays of these mesons lead to speculation of exotic mesons (hybrids, four-quark states

3. Next place to look: J/ channel through B decays?
Hints of exotic mesons  look for “relatives”
J/ channel (threshold at GeV, VV, C=+) is accessible to:
hybrid: 0-+, 1-+ , 2-+ expected nearby Y(4260) (1--, m=4.26 GeV)
multi-quark states: X(3872)J/+// etc, Y(3940)J/+ (threshold)
glueball and other possibilities
Normal charmonium with mass above GeV has tiny BF to this channel
Experimentally easy to search through clean BJ/K channel.
vacuum polarization
gluon coupling

4. Why search at CDF? B hadrons boosted at Tevatron
CDF II
B hadrons copiously produced at Tevatron
B hadrons boosted at Tevatron
smooth acceptance for potential structures
CDF has excellent mass/vertex resolution and hadron particle id (PID)

5. CDF detector Muon ID Track momentum PID from dE/dx Kaon ID
Muon: muon ID
ToF: kaon PID from TOF
COT: track momentum
kaon PID from dEdx
Silicon: track momentum
vertex position
Track momentum vertex position

6. With excellent Tevatron performance, we certainly can expect more!!!
To tape
2.7 fb-1
Used for this result
With excellent Tevatron performance, we certainly can expect more!!!

7. Search for structure in J/ mass spectrum inside B+ mass window
Analysis strategy
Reconstruct B+ as:
B+ J/ +
J/ +-
+-
Search for structure in J/ mass spectrum inside B+ mass window + - + -
J/  B+
Lxy
primary
vertex
secondary
Search?
Vertex separation
Particle Identification
(Kaon LLR)
Reconstruct control channels : ~3 000 BsJ/, ~ B+J/K+ before Lxy and kaon LLR cuts

8. Reconstructed B+J/K+
Before Lxy>500 um, kaon LLR>0.2
7510
( in 3 B+ window ~80%pure
After Lxy>500 um, kaon LLR>0.2
~20% signal eff.
x20K bkg reduction
Check inside B+ mass window for  with relaxed K+K- mass window, B+ sideband subtraction
A P-wave relativistic BW only good fit to data
2 probability 28%, no f0K+K- or K+K- phase space components
We conclude that the signals in the B+ peak are pure B+J/K+

9. Investigate J/ mass spectrum in MC
MC simulated in phase space  smooth Dalitz plot, no structure in mass
M=m(+-K+K-)-m(+-)
Check for reflections –found (Bs(2S), (2S)J/ +-) B+J/K+ due to kaon mis-identification
Bs contamination at M>1.56 GeV,
cut it off for simplification

10. Search for structures in J/ mass--Data
An enhancement at threshold is observed
M=m(+-K+K-)-m(+-)
We model the Signal (S) and Background (B) as: S: S-wave relativistic Breit-Wigner B: Three-body decay Phase Space
The fit returns: Yield =14 m =  2.9 (stat) MeV/c2
Width = (stat) MeV sqrt(-2log(Lmax/L0 ))=5.3
Significance: it would be 5.3 if there were a priori predictions for mass and width BUT there were NOT!

11. Significance study
We determine significance from simulation (Toy MC):
--Using Three-body decay Phase Space only to generate the m spectrum
--Find the most significant fluctuation in the Toy events for each trial anywhere in m between 1.02 and 1.56 GeV, and with a width between 1.7 MeV (resolution) and 120 MeV (10 times of the observed width)
--count the number of times that a fluctuation with -2log(Lmax/L0 ) greater or equal to the value in the data and calculate a p-value
Significance:
the p-value obtained from simulation is 9.3X10-6, corresponding to 4.3
drops from 5.3 to 4.3 (absence of a priori predictions for mass and width)
3.8 using Phase Space and flat background for non-B background for cross-check

12. Results Yield =145 m = 1046.3 2.9 (stat) 1.2 (syst) MeV/c2
See Kai Yi’s Wine and Cheese talk Tuesday at Fermilab (available on streaming video)
Including systematics:
Yield =145
m =  2.9 (stat) 1.2 (syst) MeV/c2
Mass =  2.9 (stat) 1.2 (syst) MeV/c (adding J/ mass)
Width = (stat)  3.7(syst) MeV
Significance: 4.3
after taking absence of prediction of mass and width into account.
tentatively name it Y(4140)
Width indicates a strong decay

13. Backup slides

14. The current status The current status through B J/ K :
CLEO, PRL 84,1393
J/ and ee, 10 B+ and B0
BaBar 2003, PRL 91,
23 B+
13 B0
J/ and ee
statistically limited, no structures reported

15. dE/dx parameterized using D*+(-)→D0π+(-) sample
CDF hadron PID
1.5σ
dE/dx parameterized using D*+(-)→D0π+(-) sample
dE/dx efficiency ~100%
dEdx residual
CDF Time-of-flight: Tevatron store /23/2001
Excellent resolution
TOF acceptance+efficiency ~60%
Make use both dEdx and ToF for hadron PID
Summarizing dEdx and ToF into a log-likelihood ratio

16. CDF Di-muon trigger
Scale to ~2.7 fb-1, ~20M J/ with silicon hits

17. The challenge
Start with typical requirements for B hadron at CDF:
--p(2) for B+ vertex fit>1%
--pT(track)>0.4 GeV,
-- >=4 r- silicon hits
--pT(B+)>4 GeV
--mass window:
J/ (50 MeV) and  ( 7 MeV)
constrain +- to J/ PDG mass value
NOT applied yet: Lxy and kaon PID
B+ mass
Typical hadron collider environment, help from Lxy and kaon PID?

18. The answer to challenge—Lxy and kaon PID
After Lxy>500 um, kaon LLR>0.2
7510
Justification on S/sqrt(S+B) of B+J/K+ Signal
Justified cuts:
Lxy>500 m, kaon LLR>0.2
The largest B+J/K+ to date:
75 (CDF)
BaBar 2003, PRL 91,
23 B+
13 B0
J/ and ee
define 3 as B+ signal region
(17.7 MeV obtained from MC)
Purity ~80% in the defined region

19. What is it? Y(4140) Well above open charm pair threshold
Expect tiny BF to J/
Does not fit into charmonium
Close J/ threshold like Y(3940)
What is it?
from Estia Eichten

20. Backup 2 Not close from the PDF comparison although they both have C=+
X(4160)D*D*