(2S) cross section and search for narrow resonances below the Upsilon mesons at CDF
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Transcript of (2S) cross section and search for narrow resonances below the Upsilon mesons at CDF
(2S) cross section and search for narrow resonances
below the Upsilon mesons at CDF
Alberto Annovi - INFN Frascati
for the CDF collaboration
International Workshop on Heavy Quarkonia 2008
Nara Women's University2-5 December 2008
Dec 4th, 2008 Alberto Annovi 2
The CDF detector @ Fermilab
Silicon Microstrip Tracker
Drift Chamber
Central Muon ||<0.6
Solenoid
Muon Extension ||<1.1
Calorimetersystem
Tevatronp pbar @ 1.96 TeV
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(2S) cross section
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Why (2S) cross section?
Charmonium production as test of QCD models
NRQCD can account for J/ and (2S) cross-section
NRQCD *not* able to describe polarization
(2S) is clean: small feed-down from higher charmonium states
Extend differential xsec up to 30 GeV
Phys. Rev. Lett. 99, 132001 (2007)
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Measurement principle
Select a clean di-muon sample Unbinned fit to separate
signal from backgrond prompt (2S) from long lived ones fit in pT bins
Calculate acceptance, efficiency and luminosity
Get differential cross-section:
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Data selection
1.1 fb-1 from low-pT dimuon trigger Trigger selection
2 central muons pT > 1.5 GeVOff-line selection
2 central muons pT > 2 GeV 3 r- silicon (SVX II) hits / muon tracks, muons and vertex quality cuts
Analysis kinematical limits 2 GeV < pT((2S)) < 30 GeV | y((2S)) | < 0.6
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Fitting the data Unbinned maximum likelihood fit variables
reconstructed mass reconstructed ct
Signal likelihood mass: Gaussian + crystal ball function ct (prompt): double Gaussian ct (long lived): exponential conv. Gaussian
Background likelihood mass: 1st order polynomial ct : combination of prompt, long lived symmetric and
long lived asymmetric
ct Lxy
pT /meffective ct:only ’ is
reconstructed
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Fit projections
5.5 < pT < 6.0 GeV
5236 (2S)signal events
4213 prompt1023 long liv.signal events
CDF preliminary 1.1fb-1 CDF preliminary 1.1fb-1
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Acceptance and efficiency
Geometric acceptance from CDF simulation (2S) generated uniform in , pT and y (2S) decayed with EVTGEN
different polarization are generated
Trigger efficiency measured on data Offline reconstruction efficiency
measured on data in combination with MC Nominal luminosity 1.1fb-1
effective luminosity is 0.95fb-1
due to trigger dynamic prescale @ high luminosity
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Polarization Acceptance depends upon polarization
Acceptance and its systematics are determined assuming: prompt : = 0.01 ± 0.13
A=2% @ pT=3 GeV A=20% @ pT=23 GeV
from B decays eff = 0.35 ± 0.25 ± 0.03 A=1.5% @ pT=3 GeV A=19% @ pT=23 GeV
Inclusive measurement uses weighted average acceptance
dN
dcos1 cos2
Phys. Rev. Lett. 99, 132001 (2007)
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Systematics uncertanities
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Differential cross-section
CDF preliminary 1.1fb-1
pp (2S)X Br (2S) 3.28 0.06(stat.) 0.31(syst.)nb
2 < pT((2S)) > 30 GeV | y((2S)) | < 0.6
Inclusive total cross-section:
pp (2S)X Br (2S) 2.62 0.05(stat.) 0.25(syst.)nb
Prompt component tot. xsec:
preliminary
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Comparison with Run I
Run II (1.96TeV) pointscentered on bin <pT>.
Run I (1.8TeV) points areon bin centers.
B decay points scaleddown by 0.1
CDF preliminary 1.1fb-1
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Ratio of cross-sections
PRD to be submitted soon
Ratio of (2S) to J/ Ratio of ratio
CDF preliminary 1.1fb-1 CDF preliminary 1.1fb-1
http://www-cdf.fnal.gov/physics/new/bottom/071018.blessed-psi2S-xsec/
prompt
longlived
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Comparisons with NNLO*
Theory curve courtesy of P. Artoisenet et al., according to Phys.Rev.Lett.101:152001,2008. [arXiv:0806.3282]see also proceedings for HP2008 submitted to EPJC
Yield better described at low-pT.High-pT data (>17 GeV) from this measurement not compatible with theory.
Theory progress here is welcome!
NNLO* CSM
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search for narrow resonances below the Upsilon mesons
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Why looking for light dimuon resonances?
Low mass sbottom not completely excluded D.G. Aschman et al., Phys.Rev.Lett.39:124 (1977) A. M. Boyarski et al., Phys. Rev. Lett. 34, 762 (1975) CLEO, Phys. Rev. D 63, 051101 (2001) DELPHI, Phys. Lett. B 444, 491 (1998)
Some models include low mass sbottom M. Carena et al., Phys.Rev.Lett.86:4463 (2001) E. L. Berger et al., Phys.Rev.Lett.86:4231 (2001)
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Dimuon spectrum in Run I data
G. Apollinari et al.using CDF Run I data
Phys.Rev.D72:092003,2005
3.5 excess
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Analysis method
Search for prompt dimuon pairs look for resonances (epsilon) with detector resolution
Report results as *BR relative to Y(1S) Leptonic width of hypotetical sbottomonium
Assumptions for *BR relative to Y(1S) Assume to be unpolarized Assume pT
to scale with mass w.r.t. (1S) i.e. <pT
>/ <pTY(1S)> = mEpsi/ mY(1S)
Assume to be prompt Not produced inside a jet, i.e. isolated
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Data sample
630pb-1 from dimuon trigger June 2006 - January 2007
Trigger selection 1st central muon pT > 3 GeV, || < 0.6
2nd muon pT > 2 GeV, || < 1.1
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Data selection
First reconstruct all dimuon candidates passing trigger confirmation
Data contains a large contamination of dimuons from bbbar and ccbar
Require isolation < 4 GeV for both muons Isolation is sum of all tracks pT in a cone around each muon
Promptness cuts on 3D vertex Vertex probability > 0.001 Lxy/xy < 3 (Lxy w.r.t primary vertex)
Isolationtracks
pT<4GeV
2 2 r 0.4
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Dimuon mass spectrum
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Upsi region fit
Fit withBkg: 5th degree polynomialSig: Double Gaussians
Fit results52780 ± 350 Y(1S) eventsbkg of 13976 events
9.3 < M < 9.55 GeVMY(1S) 9459 ± 1 MeVM 52 ± 1 MeV
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Resonance search
2/NDF 66/55Probability 0.14
Background only: 5th degree
polynomial fit
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Resonance search
Add a Gaussian to the fit We fit in the region 6 to 9.1
GeV
perform 108 fits in steps of 25MeV starting at 6.3 GeV
Peak width is fixed to expectations from simulation:
40 to 48 MeV
Probe Gaussian in blue
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Upper limits
90% Bayesian limits assuming prior probability flat above zero acceptance correction is
Arel=65.5% of Y(1S) at 6.3 GeV Arel=97.4% of Y(1S) at 9.0 GeV
N
bayes
NY (1S )
Arel
Where N is number of reconstructed events
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Upper limits
90% CL
Red is expected limit. Blue is observed limit.
Systematic is 6% relative acceptance due to Y polarization resonance line shape modeling
The excess in PRD72:092003,2005was (36±9)*10-3
at 7.2 GeV
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Upper limits
90% CL 90% CL
Sbottomoniumleptonic width
http://www-cdf.fnal.gov/physics/new/bottom/080703.blessed-Dimuon_resonance/
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Conclusions
(2S) cross section in Run II provides data up to 30 GeV for the first time adds input for quarkonia production understanding
Search for narrow resonances below the Upsilon mesons no evidence for new signals --> set limits almost exclude light sbottomonium (6.3 < m < 9 GeV)
not fully excluded within (not shown) theoretical uncertainties
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BACKUP
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Comparison with Run I
Run II (1.96TeV) pointsscaled to 1.8 GeV (-14%)centered on bin <pT>.
Run I (1.8TeV) points areon bin centers.
NRQCD uses a fit to Run I data described inE. Braaten et. Al., hep-ph/0008091Phys.Rev.D63:094006,2001
CDF preliminary 1.1fb-1