Upload
lucretia-armando
View
32
Download
0
Embed Size (px)
DESCRIPTION
The η - mass measurement with the Crystal Ball at MAMI. A. Nikolaev for the Crystal Ball @ MAMI and A2 Collaborations Helmholtz Institut f ür Strahlen - und Kernphysik, University Bonn. The h mass measurement at MAMI. The h production threshold measurement from γ p → p η . - PowerPoint PPT Presentation
Citation preview
LOGO
The η-mass measurement with the Crystal Ball at MAMI
The η-mass measurement with the Crystal Ball at MAMI
A. Nikolaev for the Crystal Ball @ MAMI and A2 CollaborationsHelmholtz Institut für Strahlen- und Kernphysik, University Bonn
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 2
The mass measurement at MAMI
The production threshold measurement from γp→pη. The mass of is calculated from relation:
where mp is the proton mass, Ethr – production threshold.
22 2
c
Emmmm
thr
ppp
Recently published measurements:
A. Duane et al.: Phys. Rev. Lett. 32 (1972) π -p → n neutrals
F. Plouin et al.: Phys. Lett. B276 (1992) dp → 3 He ηB. Krusche et al.: Z. Phys. A351 (1995) γp → pη
A. Lai et al.: Phys. Lett. B533 (2002) η → 3π 0
M. Abdel-Bary et al.: Phys. Lett. B 619 (2005) dp → 3 He ΧE. Ambrosino et al.: Acta Phys. Slov. 56 (2006) φ → γη
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 3
Crystal Ball/TAPS detector
Crystal Ball detector: 672 NaI crystals
measures Eγ and Өγ
TAPS 510BaF2 detectors
Particleidentificationdetector
Crystal Ball672 NaI detectors
Particle identification detector: 24 plastic bars of size 30 cm x 2 cm 0.2 cm marks charged particles
Forward wall detector TAPS: 510 BaF2 single plastic detectors with
individual vetos
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 4
The tagging facility
The energy E of the photon is determined (tagged) by:
Incoming MAMI electron beam energy E0 is known with an accuracy of = 68 keV.
Scattered electron energy Ee- is known with an accuracy of e = 78 keV.
eEEE 0
222
0
eEEE
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 5
Tagger microscope detector
An array of 96 plastic scintillator fibres (3 mm x 2 mm).
Each single fibre overlaps by 1/3 with its neighbor. The overlap region defines microscope detector channel
μch (191 channels in total). The energy resolution is 0.3 MeV per
microscope channel μch. Tagger microscope is positioned to
cover electron energies 153 to 209 MeV. At a beam energy of 883 MeV this corresponds to tagged photons between 674 MeV and 730 MeV (η threshold ~707 MeV).
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 6
Tagger microscope energy calibration
Direct calibration: Direct position measurement of the MAMI electron beam for the
energies Ee- = 180.1 MeV, 195.2 MeV and 210.2 MeV using the same
dipole magnetic field as in the experiment (Bcal = Bexp = 1.049 T).
Scan beam through microscope varying the dipole field: Increase tagger dipole magnetic field Bcal in small steps.
Measure new electron beam position supposing equivalent electron beam energy for a given field setting Bcal :
cal
exp
e B
BEE 0
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 7
Tagger microscope energy calibration
# Date Beam energy, MeV Dipole field, Tesla
1 12.12.2003 180.12 ± 0.16 1.01-1.072 20.01.2004 180.10 ± 0.16 0.89-1.083 21.01.2004 210.18 ± 0.16 1.05-1.214 23.01.2004 180.21 ± 0.16 0.90-1.215 27.05.2004 195.24 ± 0.16 0.98-1.216 07.12.2004 185.90 ± 0.16 0.92-1.23
Blue arrows show direct position measurements of the electron beam of energies 180.1, 195.2 and 210.2 MeV.
180.1 MeV1.049 T
210.2 MeV1.055 T
195.2 MeV1.049 T
Expected η threshold
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 8
Total energy measurement uncertainty
Standard deviation of data points from fit:
was calculated for
each scan individually:
N
ie iEbaich
N 1
2]}[{][2
1
Average uncertainty: = 0.27 ch = 78 keV (electron energy Ee-).
Add electron beam energy E0 determination uncertainty of MAMI 68 keV ()
# Date N data points ch1 12.12.03 18 0.3032 20.01.04 26 0.2113 21.01.04 33 0.2014 23.01.04 11 0.3985 27.05.04 32 0.1906 07.12.04 19 0.224
(threshold) = 103 keV(m) = 65 keV
:222
0
eEEE
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 9
The mass beamtimes
7.12.2004-13.12.2004 11.01.2005-20.01.2005Tagger dipole field 1.0494 Tesla 1.0490 TeslaMAMI beam current 35 nA 12 nAHours 57 h 114 hN of →2 decays ~725 000 ~638 000N of →3 ° decays ~218 000 ~198 000MAMI beam energy 4 measurements with mean: 3 measurements with mean:
883.19 ± 0.16 MeV 883.24 ± 0.16 MeV
Two beamtimes for the mass measurement:
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 10
Identification of meson
mesons are identified via their uncharged decay modes.
Events with 2 photons and 6 photons (with or without proton) are investigated.
Photons are identified with Crystal Ball/TAPS detector.
Particle identification detector serves as a veto for charged particles in CB.
TAPS crystals have individual veto detectors for marking charged particles.
→2γ and →3π0 decays are analyzed independently.
)%29.051.32(3
)%26.043.39(20
Particleidentificationdetector (PID) Crystal Ball
672 NaI crystals
TAPS 510 BaF2 crystals with individual vetos
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 11
Identification of photons and protons
Crystal Ball Uncharged particles = photons.
Charged particles: ΔE(PID) vs. ECB:
cut the proton.
TAPS forward wall Vetos: charged particles. Pulse shape analysis: cluster energy
deposition in short Eshort vs. in long
Elong integration interval.
Time of flight:
ETAPS cl. vs. ( tTAPS cl. – tCB photons ).
protons
protons, neutrons
protonsphotons
photons
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 12
CB time walk correction
Investigate γp→pπ0 with γγp final state. For each of 672 NaI crystals:
ECB hit vs. ( tCB photons – tPID proton ) fit the peaks with t(E) function.
7-13 Dec 2004 #4924-5088: faulty crystals #: 168, 183, 194, 205, 221, 352.
11-20 Jan 2005 #5200-5452: faulty crystals #: 41, 168, 205.
MicroscopeFWHM = 1.7 nsSigma = 0.7 ns
LadderFWHM = 2.3 nsSigma = 1.0 ns
33.02
1)(E
ppEt
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 13
Invariant mass distributions
2 (with or without proton) final state invariant mass distribution.
30 (6with or without proton) final state invariant mass distribution.
Cut on invariant mass distribution. Time coincidence peak between
tagger microscope and detector: cut the coincident events.
Cut on lost proton missing mass.
Mean = 568 MeVSigma = 20 MeV
Mean = 138 MeVSigma = 8 MeV
Mean = 558 MeVSigma = 16 MeV
FWHM = 1.7 nsSigma = 0.7 ns
η
π0
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 14
Tagger dipole field / Jan 2005
NMR = 1.049057±0.000535 T (± 0.01 MeV in Ee). Very good!
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 15
Tagger dipole field / Dec 2004
NMR = 1.049527±0.015 T (± 2.78 MeV in Ee).
Need to refine data with faulty NMR!
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 16
Microscope channel efficiency
Investigate γp→pπ0 with 2 photons and 1 proton final state using tagger.
Prompt - random time windows. In microscope region (tagger
channels 55-85) “pion yield” looks constant.
Investigate the same with microscope.
Microscope channels have different efficiencies!
Use “pion yield” distribution as microscope channels efficiency to correct the η yield!
Microscope region
pion
yie
ld in
mic
rosc
ope
p
ion
yiel
d in
tagg
er
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 17
Eta yield for reaction γp→pη (η→2γ)
Fit range: 0-75 μch
Without acceptance correction!
Fit function: f(x)=a0+a1 x+a2 x2+a3 x3
η→2γ
Eγ
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 18
Eta yield for reaction γp→pη (η→3π0)
Without acceptance correction!
Fit function: f(x)=a0+a1 x+a2 x2+a3 x3
η→3π0
Fit range: 0-75 μch
Eγ
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 19
Very preliminary
Result dependence on fit rangeη→2γ η→3π0
1. η→2γ: mη=547.683 ± 0.013fit MeV
2. η→3π0: mη=547.743 ± 0.013fit MeV
Fit range: 0 to 75 μch10 to 75 μch20 to 75 μch30 to 75 μch40 to 75 μch50 to 75 μch60 to 75 μch70 to 75 μch
Fit range: 0 to 75 μch10 to 75 μch20 to 75 μch30 to 75 μch40 to 75 μch50 to 75 μch60 to 75 μch70 to 75 μch
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 20
Conclusions
New threshold data on γp→pη. The η identified by η→ γγ and η→3π0.
Energy calibration for Ee- (tagger microscope) done.
Energy calibration E0 (Mainz Microtron) final checks for
systematical error underway.
22 2
c
Emmmm
thr
ppp
eEEE 0
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 21
MAMI energy determination uncertainty
B = 1.3260 T ± 0.13 mTΔE = ~7.81 ± 0.02 MeVD73 = 3768.45 ± 0.4 mm
RTM 3
D73
turn 73 Cavity 2
turn 90 Cavity 1
ΔE
E73 = 751.649 ± 0.107 MeVExtrapolate to end energy:Eout = 883.X ± 0.16 MeV (FWHM)
σEout = 68 keV
2
DBceE
Eout = Ein + z·ΔE, z = 90 Ein = 180 MeV
Dipole 1 Dipole 2
where e is electron charge, B is dipole magnetic field, D - electron track diameter.
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 22
Proton missing mass distributions p→p
p→p (→2)
p→p (→2)
p→p (→3)
p→p (→3)
Microscope Microscope
Main tagger Main tagger
Missing mass / MeV Missing mass / MeV
Missing mass / MeV Missing mass / MeV
hits
hits
hits
hits
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 23
Photon beam position Jan 2005
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 24
The mass beamtimes
7.12.2004-13.12.2004 11.01.2005-20.01.2005Tagger channels 1 to 80 1 to 284Microscope channels 1 to 191 1 to 191Radiator Diamond DiamondCollimator 3 mm 4 mmTagger dipole field 1.049 Tesla 1.049 TeslaMAMI beam current 35 nA 12 nAHours 57 h 114 hN of →2 decays ~725 000 ~638 000N of →3 ° decays ~218 000 ~198 000MAMI beam energy 4 measurements with mean: 3 measurements with mean:
883.19 ± 0.16 MeV 883.24 ± 0.16 MeV
Two beamtimes for the mass measurement:
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 25
MAMI energy measurements
7.12.2004-13.12.2004 11.01.2005-20.01.2005Date Beam energy Date Beam energy7.12.2004 883.17 MeV8.12.2004 883.20 MeV 10.01.2005 883.23 MeV10.12.2004 883.22 MeV 11.01.2005 883.26 MeV13.12.2004 883.16 MeV 13.01.2005 883.24 MeV
Mean 883.19 ± 0.16 MeV Mean 883.24 ± 0.16 MeV
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 26
Result dependence on fit rangeη→2γ η→3π0
1. η→2γ: σ = 0.023 MeV (in mη)
2. η→3π0: σ = 0.025 MeV (in mη)
Function fits the points very good!
0.1
MeV
Fit range: 0 to 75 μch10 to 75 μch20 to 75 μch30 to 75 μch40 to 75 μch50 to 75 μch60 to 75 μch70 to 75 μch
Fit range: 0 to 76 μch10 to 76 μch20 to 76 μch30 to 76 μch40 to 76 μch50 to 76 μch60 to 76 μch70 to 76 μch
A.Nikolaev, Bonn CB Meeting, Basel 10/5/06 27
Result dependence on fit rangeη→2γ η→3π0
1. η→2γ: σ = 0.023 MeV (in mη)
2. η→3π0: σ = 0.100 MeV (in mη)
Function fits the points good!0.1
MeV
Fit range: 0 to 75 μch10 to 75 μch20 to 75 μch30 to 75 μch40 to 75 μch50 to 75 μch60 to 75 μch70 to 75 μch
Fit range: 0 to 75 μch10 to 75 μch20 to 75 μch30 to 75 μch40 to 75 μch50 to 75 μch60 to 75 μch70 to 75 μch