14 sept 2004 d.dedovich tau041 measurement of tau hadronic branching ratios in delphi experiment at...
TRANSCRIPT
![Page 1: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/1.jpg)
14 Sept 2004
D.Dedovich Tau04 1
Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP
Dima Dedovich (Dubna)
DELPHI Collaboration
1. Final results on exclusive hadronic branchings (π/K blind) – submitted to E.Phys.J. C E.Phys.J. C
2.2. Preliminary results on inclusive single-prong Preliminary results on inclusive single-prong branching to charged kaonsbranching to charged kaons
![Page 2: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/2.jpg)
14 Sept 2004
D.Dedovich Tau04 2
The DELPHI detector
![Page 3: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/3.jpg)
14 Sept 2004
D.Dedovich Tau04 3
The first stage (common for both studies):the tau pair selection
• Almost full LEP-1 statistic was used (1992-1995)• Analysis was restricted to the barrel region• Standard LEP-1 tau selection based on kinematic criteria
was used: low multiplicity events with large missing energy
• Selection efficiency was about 52% (85% within acceptance) with background 1.5%
• In total, about 80,000 tau pairs were selected
![Page 4: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/4.jpg)
14 Sept 2004
D.Dedovich Tau04 4
Exclusive hadronic branchings Track counting
• “Track counting” – event classification into 1- , 3- , and 5-prong tau decays. Method was the same as in the published paper on topological branchings
• Charged pions from Ks decays were not counted due to requirement of Vertex Detector measurement on track
• The number of selected tau decay candidates was• 134421 for 1-prong• 23847 for 3-prong• 112 for 5-prong
![Page 5: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/5.jpg)
14 Sept 2004
D.Dedovich Tau04 5
Exclusive hadronic branchingscharged hadron selection
• 3- and 5- prong decays all are hadronic• For 1-prong the leptonic decays were rejected using:
dE/dx, EM calorimeter, Hadron calorimeter and muon chambers
Electron rejection
Muon rejection
DELPHI DELPHI
![Page 6: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/6.jpg)
14 Sept 2004
D.Dedovich Tau04 6
Exclusive hadronic branchings π0 counting
• 4 types of reconstructed π0 were accepted:– 2 separated photon showers– Photon shower and converted e+e- pair– Single energetic shower (overlapped photons)– Neutral shower + shower wrongly assigned to charged
track
• Neural networks was used to separate π0 and
single photons• Efficiency to reconstruct π0 was about 70% with
purity of about 90%
![Page 7: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/7.jpg)
14 Sept 2004
D.Dedovich Tau04 7
Exclusive hadronic branchings π0 invariant mass
![Page 8: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/8.jpg)
14 Sept 2004
D.Dedovich Tau04 8
Exclusive hadronic branchingsdecay mode identification
• 2 analyses were performed for 1- and 3-prong samples: one was based on sequential cuts and the other on neural network approach
• The final results were based on the NN ( trained on simulation) which provided better precision
• Only sequential cuts was used for 5-prong sample• The following semi-exclusive decay mode were
identified:– 1-prong: h±ν ; h± π0 ν ; h±2π0 ν ; h±≥3π0 ν – 3-prong: 3h ± ν ; 3h± π0 ν; 3h± ≥2π0 ν – 5-prong: 5h± ν ; 5h±≥1π0 ν
![Page 9: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/9.jpg)
14 Sept 2004
D.Dedovich Tau04 9
Exclusive hadronic branchingsinvariant masses of hadronic systems
![Page 10: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/10.jpg)
14 Sept 2004
D.Dedovich Tau04 10
Exclusive hadronic branchingsneural network outputs
e μ h
hπ0 h2π0 h3π0
3h 3hπ0 3h2π0
![Page 11: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/11.jpg)
14 Sept 2004
D.Dedovich Tau04 11
Exclusive hadronic branchingscalibration and systematic errors
• Careful checks of data/simulation agreement were performed using clean test samples selected from real data : ee→ee; ee→μμ ; ee→eeγ; ee→μμγ ; τ→hπ0ν
• When necessary, corrections were applied on simulation• Response of calorimeters, track momentum, dE/dx ,
secondary interactions, track and π0 reconstruction efficiency and muon chamber response were calibrated
• The uncertainties of these calibrations were the main source of systematic errors
![Page 12: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/12.jpg)
14 Sept 2004
D.Dedovich Tau04 12
Exclusive hadronic branchingsRESULTS
![Page 13: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/13.jpg)
14 Sept 2004
D.Dedovich Tau04 13
Inclusive branching to kaons
• DELPHI is the only LEP experiment capable to identify kaons using not only dE/dx but also with RICH detector
• So far only 1992 results on τ→K±Xν were published. • Current preliminary results cover full LEP-1 statistics
(1992-1995) and are supposed to replace the old results
• Only inclusive branching ratio is being presented
![Page 14: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/14.jpg)
14 Sept 2004
D.Dedovich Tau04 14
Inclusive branching to kaonshadronic sample selection
• To reduce systematic effects we actually measure the ratio Br(τ→K±Xν )/Br(τ→ π±Xν ). Many biases are canceled as kaons and pions are both hadrons
• As a first stage, a sample of 1-prong hadronic tau decays was selected using calorimeters and muon chambers.
• The efficiency of the hadronic selection was about 89%, the background was about 0.3% from non-tau events, and 3.7% from leptonic and multiprong tau decays
![Page 15: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/15.jpg)
14 Sept 2004
D.Dedovich Tau04 15
Inclusive branching to kaonsKaon identification
• At LEP1 kaons from tau decays are allowed to have momentum in the range 3.6-45 GeV/c
• Measurements of dE/dx in TPC provide π/K separation in
the full kinematic range at the level of 1.6-2.2 σ
• For momenta below 8.5 GeV/c kaons are also identified by VETO in DELPHI RICH detector
• For momenta between 8.5 and about 25 GeV/c identification is based on Cherenkov angle measurement in RICH (Ring measurements)
![Page 16: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/16.jpg)
14 Sept 2004
D.Dedovich Tau04 16
Inclusive branching to kaons Kaon identification
ππ
K
K
![Page 17: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/17.jpg)
14 Sept 2004
D.Dedovich Tau04 17
Inclusive branching to kaonsPull variables
The K identification was based on pull variables ΠH for hypothesis H=π/K/e/μ
For Cherenkov angle measurements a similar variables ΠRING was constructed
![Page 18: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/18.jpg)
14 Sept 2004
D.Dedovich Tau04 18
Inclusive branching to kaons dE/dx calibration
• dE/dx pull position and width were carefully calibrated as a function of particle velocity and direction using test sample of pions, muons and kaons selected from real data using RICH.
• Small discrepancy was found between pions and muons of same velocity. Therefore for final calibration clean pions sample was used.
• dE/dX of kaons and pions of same velocity was found in agreement, and the uncertainty of this comparison (2.4% of pull width) was assigned to systematic error
![Page 19: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/19.jpg)
14 Sept 2004
D.Dedovich Tau04 19
Inclusive branching to kaonsClean sample of pions (kaons suppressed by RICH)
![Page 20: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/20.jpg)
14 Sept 2004
D.Dedovich Tau04 20
Inclusive branching to kaonsKaon-enriched sample
dE/dx kaon pull
![Page 21: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/21.jpg)
14 Sept 2004
D.Dedovich Tau04 21
Inclusive branching to kaonsAll hadronic tau decay candidates
![Page 22: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/22.jpg)
14 Sept 2004
D.Dedovich Tau04 22
Inclusive branching to kaonsRing pull calibration
• Unlike the case of dE/dx, the ring pull has significant non-Gaussian tails. Therefore the following calibration procedure was adopted :
• Small corrections (few % of pull width) depending on velocity were applied to simulation to get agreement with the real data (clean pion samples selected using dE/dx)
• The pull distribution shapes obtained for simulation were used as probability density function in further fits
• The far parts of tails were combined into 2 single bins to avoid problems with shape description
![Page 23: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/23.jpg)
14 Sept 2004
D.Dedovich Tau04 23
Inclusive branching to kaonsClean sample of pions (kaons suppressed by dE/dx)
![Page 24: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/24.jpg)
14 Sept 2004
D.Dedovich Tau04 24
Inclusive branching to kaonsKaon-enriched sample
![Page 25: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/25.jpg)
14 Sept 2004
D.Dedovich Tau04 25
Inclusive branching to kaonsAll hadronic tau decay candidates
![Page 26: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/26.jpg)
14 Sept 2004
D.Dedovich Tau04 26
Inclusive branching to kaonsVETO identification
• The main source of systematic is the rate of false VETO identifications
• The data/simulation agreement was checked using clean samples of muons and pions
![Page 27: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/27.jpg)
14 Sept 2004
D.Dedovich Tau04 27
Inclusive branching to kaonsThe fit procedure
• The measured pulls were used to construct the probability W that the particle is a kaon: W=FK/(Fπ+FK)
• Here FK(ΠK) and Fπ(Ππ) are the probability density
functions for a given hypothesis • Gaussian PDF was used for dE/dx and the shapes
predicted by simulation in the case of RICH • Distribution of W in real data was fitted by a linear
combination of simulated pions and kaons• The results of dE/dX and RICH were fitted either
separately or combined into a single probability W
![Page 28: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/28.jpg)
14 Sept 2004
D.Dedovich Tau04 28
Inclusive branching to kaonsfit to dE/dx probability
![Page 29: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/29.jpg)
14 Sept 2004
D.Dedovich Tau04 29
Inclusive branching to kaonsfit to Ring probability
![Page 30: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/30.jpg)
14 Sept 2004
D.Dedovich Tau04 30
Inclusive branching to kaonscombined fit : Ring+dE/dx
![Page 31: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/31.jpg)
14 Sept 2004
D.Dedovich Tau04 31
Inclusive branching to kaonsSystematic errors
• The main source of systematic errors is the uncertainties in calibration of pull position and width. Even small bias results in large error in estimation of pion background
• However this error reduced dramatically if RICH and dE/dx are used in combination
• Therefore our results were obtained using combined measurement when possible (RICH was not always operational)
• Individual measurements were used for a cross-check
![Page 32: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/32.jpg)
14 Sept 2004
D.Dedovich Tau04 32
Inclusive branching to kaonsSystematic errors
The uncertainty of residual pion background (colored) Is strongly redused if pions were already suppresed
by another detector
![Page 33: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/33.jpg)
14 Sept 2004
D.Dedovich Tau04 33
Inclusive branching to kaonsSystematic errors in %
RING pull dE/dx pull VETO
Posi-tion
width Moment. depend.
Posi-tion
width Moment. depend.
K/π MIPagreem.
FalseID
dE/dx 3.3 5.3 2.0 2.4
Ring 4.6 3.1 4.2
veto 8.4
dE/dx+VETO 0.3 0.7 0.6 0.6 2.4
dE/dx+Ring 1.5 0.7 1.1 0.7 1.3 0.1 1.0
Other sources of systematic errors are MC statistics (1.2%) and tau decay branchings (1.9%)
![Page 34: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/34.jpg)
14 Sept 2004
D.Dedovich Tau04 34
Inclusive branching to kaonsThe results (in %)
χ2 = 3.26/3χ2 = 1.99/2
![Page 35: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/35.jpg)
14 Sept 2004
D.Dedovich Tau04 35
Inclusive branching to kaons Results of Individual measurements in %
Ring 1.745 ± 0.170 (0.126 stat 0.115 syst)
dE/dx 1.455 ± 0.131 (0.068 stat 0.105 syst)
VETO 1.685 ± 0.272 (0.231 stat 0.144 syst)
Total 1.579 ± 0.097
![Page 36: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/36.jpg)
14 Sept 2004
D.Dedovich Tau04 36
Inclusive branching to kaons Results of combined measurements in %
Ring+dE/dx 1.639 ± 0.112 (0.097 stat 0.054 syst)
VETO+dE/dx 1.594 ± 0.184 (0.172 stat 0.066 syst)
dE/dx only 1.346 ± 0.139 (0.082 stat 0.106 syst)
Ring only 1.871 ± 0.489 (0.462 stat 0.165 syst)
Total 1.545 ± 0.078
![Page 37: 14 Sept 2004 D.Dedovich Tau041 Measurement of Tau hadronic branching ratios in DELPHI experiment at LEP Dima Dedovich (Dubna) DELPHI Collaboration E.Phys.J](https://reader030.vdocuments.site/reader030/viewer/2022032723/56649cfb5503460f949cd071/html5/thumbnails/37.jpg)
14 Sept 2004
D.Dedovich Tau04 37
Summary
• We have measured tau semi-exclusive hadronic branching ratios. Some of them are at the level of world best.
• We also presented preliminary result for inclusive tau to kaons branching : 1.545±0.078%