1. The KLOE Drift Chamber Anna Ferrari - Universita’ di Roma Tre & INFN
on behalf of the KLOE Collaboration
8-th International Conference on Instrumentation for Colliding Beam Physics
Novosibirsk, 28th february-6th march 2002
Anna Ferrari

2. * KLOE at DAFNE Ldesign= 51032 cm-2 s-1 Design philosophy:
DEAR
KLOE at DAFNE
DAFNE is an electron-positron collider
at s = GeV (f – factory)
Design philosophy: *
Moderate Single
Bunch Luminosity
4·1030(VEPP-2M)
Large Number
of Bunches (120)
Ldesign= 51032 cm-2 s-1
sx sy sz
2mm 20 mm 3 cm
Bunch spacing : 2.7 ns
Bunch I.P.:
Beam-beam @ 5A/beam => 2 indep. rings
beam crossing angle: 25 mrad
Φ boost: px -13 MeV/c
Anna Ferrari

3. DAFNE performances In Y2001: L (cm-2 s-1) Lday (pb-1) ~ 1.5 ~ 3.0
global sum (pb-1)
daily integral (pb-1)
Luminosity/1030 (cm-2s-1)
July 2000
Fall 2000
April 2001
June 2001
415
865
1100
KLOE integrated luminosity
[pb-1]
Feb Apr Jun Aug Oct Dec
In Y2001:
Achieved higher single bunch luminosity,
close to 1 mb-1 s-1
Background more under control
More time dedicated to KLOE
~ 1.5
~ 3.0
Lday (pb-1)
~ 31031
~ 5.01031
L (cm-2 s-1)
Average
Peak
Anna Ferrari

4. KL decays: event topology
KL FV
30 < r < 150 cm
|z|<125cm
Decay channel
Momentum(MeV/c)
The distribution of charged KL vertices in the DC volume is isotropic
Physics
requirements:
large tracking volume
high and uniform reconstruction efficiency
transparency to reduce regeneration, multiple
scattering and conversion of low energy photons
(for kinematical rejection of Kl3 events)
good momentum 0.6 T +
Anna Ferrari

5. Construction solutions
I. Uniform cell structure on a large volume
4 m , 3.3 m length
12 inner layers:
2×2 cm2 cells
square cells, field:sense = 3:1
46 outer layers:
3×3 cm2 cells
12582 sense field guard wires
full stereo geometry:
Anna Ferrari

6. Construction solutions
II. Low mass
Field wires: Al(Ag), 80 μm 
Sense wires: W(Au), 25 μm 
Gas : 90% He - 10% iC4H10
X0 (wires + gas):  900 m
C-fiber composit 8 mm plate
Inner wall 0.7 μm C-fiber
Be-Al spherical beam pipe
Mechanical structure in carbon fiber: < 0.1 X0
Anna Ferrari

7. …a bit of history STRINGING OPERATION + HV & PRE INSTRUMENTATION
+ CLOSING  1 YEAR
ONLY 12 BROKEN WIRES !!!
THE KLOE DRIFT CHAMBER WAS MOVED INTO DAFNE HALL
IN APRIL 1999
 3 YEARS OF OPERATION TIME
NO BROKEN WIRES SINCE MAY 1999 !!!
Anna Ferrari

8. At each tracking step, energy loss and multiple scattering are estimated.
Dedicated algorithms are used to:
add hits missed by the PR
reject wrongly associated hits
identify kink
join split tracks
Tracking at KLOE
low momentum particles in a magnetic field B=0.6 T spiralizing tracks
full stereo geometry
charged vertices distribution in DCH volume
hits are grouped
into track candidates
for the two stereo views
and then merged together
in a 3Dim track candidate
1. pattern recognition
2. track fit
Parameters of the fitted helix
Measured times and s-t relations are used
3. vertex fit
Anna Ferrari

9. S-T Relations 232 s-t relations neededb s
Drift velocity is not saturated and depends on:
drift distance ( s )
cell shape ( b )
crossing angle ( )
gas conditions ( c(He), pressure,…)
Parametrization of s-t relations using:
6 reference cells ( b )
36 bins in crossing angle ( ) ns
3 × 3 cm2 cells
Constant
Different b cm ns
3 × 3 cm2 cells
Constant b
Different cm
232 s-t relations needed
Anna Ferrari

10. [ns] Drift distance [cm] 5th order Chebyshev polynomials
Linear and quadratic
Higher orders
Drift distance [cm]
5th order Chebyshev polynomials
Constant term
with:
and:
limit for the fit procedure
Anna Ferrari

11. STR Calibration cosmic data allow a complete cell coverage
in terms of and
to calculate the s-t coefficients,
an iterative procedure is used,
which minimizes the residuals:
New fit to s-t rel.
the iterations are stopped when
is at the level of 40 mm
Anna Ferrari

12. Reconstruction performances VS Calib. accuracy
Total reconstruction efficiencies
90.96
90.54
90.75
96.06
96.21
95.93
95.84
88.69
87.64
87.45
87.02
77.50
76.61
76.15
75.68
96.39
96.50
99.45
96.31
96.33
96.42
99.51
99.36
99.39
96.45
96.28
96.19
92.50
92.43
92.15
92.19
96.39
99.45
99.51
99.36
99.39
96.45
96.28
96.19
92.50
92.43
92.15
92.19
Vertex resolutions
400
470
500
550
1.3
1.35
1.45
1.6
Anna Ferrari

13. The spatial resolution
Resolution curve
The spatial resolution
well below 200 μm
in most of the impact parameter range
Fitted contributions to the resolution curve
Primary ionisation statistics:
σtot  150 μm
Longitudinal diffusion contribution:
Time measurement contribution:
Anna Ferrari

14. The online monitoring of s-t relations
2100 Hz
Data composition (y2000):
400 Hz Prescaled cosmics rays, Hz Unvetoed cosmics
900 Hz Mach.Bkg + Bhabha <20o
100 Hz Physics (f + Bhabha>20o)
Bha
Cluster reconstruction
Background filter
Event classification
Cosmic filter
Calibration Bhabhas
DC track/vertex recon.
Prescaled
cosmics
RAW
l3dcc ok
520Hz (~25% of raw)
50Hz
40Hz
KLKS K +K Rad rp m+m-
p+p-
Rate of level-3 filter: Hz
Anna Ferrari

15. Calibration vs ambient parameters
The changing of the
atmospheric pressure is the only ambient parameter
that influences the calibration.
100 μm
@ the cell border
Residuals(mm)
Impact parameter (cm)
Dp ~ 2% :
pressure at 1005 and 986 mbar
different colors mean different calibration
1 month
Anna Ferrari

16. Cell Efficiency Working point Using bhabha and cosmics
hardware eff. =
# Hits
# track crossing
# associated track-hits
software eff. =
Using bhabha and cosmics
cell
Working point (Y2000)
big cells
small cells
threshold 3 mV
Working point
Layer
Efficiency
All impact parameters
ε SW = 97 %
ε HW = 99 %
Anna Ferrari

17. Monitoring integrated charge and wire ageing
Charge integrated :
October 2000: Q  1  1030 cm-2 s-1
October 2001: Q  0.3 ~ 2 x 1031 cm-2 s-1
Wire ageing:
lab-tested: Q = mC/cm
simulating 1 design luminosity, no effect
literature: QMAX = mC/cm
Rate on inner layer
~ 15 KHz.
new working point in Y2000:
big cells
small cells
added 5 ‰ H2 0
… and a new working point
in Y2001:
small cells, layers 1- 4: V
Time distribution in the first layer (ns)
Single counting rate measured from the number of hit in a time window of 200 ns out
of the drift time signal region.
Anna Ferrari

18. The role of the drift chamber in the KLOE trigger system
The DC trigger is based on the information
of the multiplicity of hit wires
To take under control the electronic noise the
sum of signals is performed in several steps
As final step the signals are organized in 9 super-layer signals, each one representing the multiplicity in 4-6 contigous planes
Anna Ferrari

19. The momentum resolution
I. e+e- e+e-
sp (MeV/c)
sp/p < 0.3%
45°<<135°
Polar angle
II. f K +K-
After correcting for K  dE/dx:
mf= MeV
s = 1.2 MeV
Anna Ferrari

20. s vs. Run Number y f - x f +  60 μm  1 mm
Bhabha are used to measure and to monitor: s
1021
1020
1019
1018
1017
[MeV]
all the “jumps” are correlated
with machine energy changes
and f scan.
s vs. Run Number
Luminous region
finding the point of closest approach to the z axis
of the tracks,
and using f = azimuth angle of pT
D = distance from (0,0) x y D+ D-
f +
f -
positron
electron
(0,0)
p.c.a.
pT-
pT+
with few min of data L=1031 cm-2 s-1
(a) μ(x),μ(y) from D vs f fit
(b) L(x) from (D++D-)/2
(c) s from (D+-D-)/2
(d) μ(z),L(z) from Z
 60 μm
 1 mm
Anna Ferrari

21. KS  π+π- mpp = 497.7 MeV/c2 pc.o.m. = 110 MeV/c sm = 1 MeV/c2
sp = 1.8 MeV/c
497.8
497.6
497.4
497.2
497.0
[MeV]
Ks mass reconstruction is stable during the physics runs
m(Kspp) vs. Run Number
Anna Ferrari

22. Conclusions The KLOE drift chamber
About 3 years of running time show that:
the KLOE DC works efficiently and in stable way
all the calibrations of the detectors are fully reliable
the tracking performances are good, at the level of 1 ‰
in absolute momentum calibration
The KLOE drift chamber
completely fulfils design requirements
Anna Ferrari