k charged wg activity report (part i)
DESCRIPTION
Next talk. This talk. K charged WG activity report (part I). P.Branchini, E. De Lucia, P. De Simone, E.Gorini, M.Martemianov, L.Passalacqua, M.Primavera, B.Sciascia, A.Ventura, R.Versaci, V.Patera. K mn : first absolute BR evaluation K pp 0 decay: selection efficiency study - PowerPoint PPT PresentationTRANSCRIPT
KGM 14/11/03 V.Patera
K charged WG activity report (part I)
K : first absolute BR evaluation
K0 decay: selection efficiency study
Ratio k/K0: analisys refinement
Kl4, Ke3 ; analysis on going
K decay vertex eff. under way
Background on K tag: first look
K tracking efficiency measurement
DE/DX : test of new hardware setup
P.Branchini, E. De Lucia, P. De Simone, E.Gorini, M.Martemianov, L.Passalacqua, M.Primavera, B.Sciascia, A.Ventura, R.Versaci, V.Patera
Next talk
This talk
KGM 14/11/03 V.Patera
dE/dx upgrade
• The ADC system has been completely revised and upgraded
• ADC integration time stretched from 1.8 to 3.1 s to collect most of the released charged in the cell
• Unefficiency in collecting charge released at short distance from the wire fixed
• Data with cosmic and magnetic field finally collected last week (!!)
• Analisys in progress: preliminary results on efficiency and resolution
KGM 14/11/03 V.Patera
dE/dx : ADC signal
RED = 2.2 s (short)BLUE = 3.1 s (long)BLACK = 1.8 s (old)
(adc count/cm)
(adc count/cm)
New dE/dx distribution from cosmic taken with two different ADC gate value (2.2 and 3.1 s) compared with 2002 cosmic data (1.8 s)
KGM 14/11/03 V.Patera
dE/dx : efficiency
The longer gate improved the ADC sampling efficiency by more then 30%
coscos
NA
DC
/Nhi
t
NOW
OLD
KGM 14/11/03 V.Patera
dE/dx : average energy loss
NEW OLD
The comparison between old 2002 cosmic and the newly collected cosmic shows a substantial agreement of the B.B. energy loss
KGM 14/11/03 V.Patera
dE/dx : resolution
The resolution with respect the number of samples in the truncated mean is improved by 30% @ 10 samples and by 25% @ 20 samples ( Nsampletrmean = 0.82 NsampleADC). At Nsample >20 the resolutionis almost flatten noise ?
OLDNOW
Prototype resolution
Nsampletrmean Nsampletrmean
Res
olut
ion
KGM 14/11/03 V.Patera
dE/dx : noise?
To test the noise hypothesys we use the pedestal runs. We sum the charge
over a road trough 58 planes that fakes a track. The RMS of this sum is
compared to the incoherent sum of the i for each ADC of the road. We find a
very little difference….
This amount of noise cannot be responsible for the resolution behaviour.(Maybe the noise analysis should not be done on ped runs ??)
KGM 14/11/03 V.Patera
dE/dx upgrade summary
The efficiency loss of the ADC sample has been fixed The resolution with respect to the T.M. sample is now
better by 30 % for track with 20-30 hits For track with a given hit number the gain is twofold: more
ADC samples and better resolution with respect of the T.M. sampling
Yet the prototype resolution has not been achieved There is a flat behaviour in the resolution at high sample
value The analysis is in progress
KGM 14/11/03 V.Patera
K tracking efficiency & geometrical acceptance : K(pK,K)
We use the tag in the handle emisphere to have in the signal
emisphere a “pure” beam of K+(K-)
The signal is flagged as Kaon with standard cut on momentum and
IP distance
Background to the signal is mainly due to early 3 body decay of the
K, where a low momentum doughter mimic a K coming from the IP
We use the minimum distance between the candidate K track and
the extrapolated K track from the handle as check parameter
The shape of the r distribution for background is taken from MC
“ “ for signal is taken from MC and
from double tagged event
KGM 14/11/03 V.Patera
K(pK,K) signal vs background
K definition cuts :1) q opposite to the “handle”2) 70 < PK < 130 MeV3) Rpca < 10 cm4) -20 < zpca < 20 cm
Once found a “candidate” K we compute the distance of closest approch between the first hit of its track and the track extrapolated from the handle:
Handle: K+ track with
tagged decay
K- extrapolated
K- candidate
We monitor the background contamination of the signal looking at the tracks minimum distance r computed at the point of closest aproach.
KGM 14/11/03 V.Patera
K track eff. = fit to r
r (cm)
BLUE K from MCRED K from 2 tagGREEN bck from MC
The fit to the r distribution between the candidate track and the extrapolated track is made using MC or 2 tag shape for the signal and MC for the background shape
K- extrapolated
K- with tag decay
K+ with tag decay
Signal shape from DATA:
KGM 14/11/03 V.Patera
K shape uncertainties
The r distribution in the K region is slightly overestimated by the fit with K shape from MC and underestimated by the fit with the K shape from 2 tag. The differences between the 2 fits gives the sistematic on the K shape
Fit – signal : MC shape
Fit – signal : 2tag shape
r (cm)
r (cm)r (cm)
signal
KGM 14/11/03 V.Patera
K- versus time and shape
systematic
We check the stability of K versus time. The 2001-2002 data were divided in chunk of 6 pb-1 each. The two different results account for the 2 different shape choice for the K contribution.
K-
IntLum/6 (pb-1)
2001
2002
Handle : K+
Signal : K-
BLUE = MC shapeRED = 2Tag shape
Systematic due to the shape uncertainty 2x10-3
KGM 14/11/03 V.Patera
K-
IntLum/5 (pb-1)
K sistematic : tag bias
Systematic on the K tracking eff. can also be due to what happen in the opposite emisphere. Thus we measured the tracking efficiency with respect to the kind of tagged decay of the other K ( the “handle”)
BLUE: K0
RED : KBLACK: all tag
The maximum bias found on K was between opposite tag : (7.5 ± 2.0) x 10-4
KGM 14/11/03 V.Patera
K+ with respect K and pK
K-
bin
Pbin
We divide the K in 6 bin in the range 30< K <90 and the K momentum in 6 bin in the range 70< pK<130 (Mev/c)
bin = 10 degPbin = 10 MeV/c
Nev
ents
bin
Pbin
pK 100 MeV/c 900
KGM 14/11/03 V.Patera
K: average 2001-2002 values
We show the value of the for both charge, relative to the full 2001 2002 data set, based on the dst production version 16 and 15, with the corresponding evaluated systematic errors
2001-2002 K(%) stat(%) shape (%) tag (%)
K+ 41.84 0.04 0.15 0.18
K- 40.77 0.04 0.15 0.17
MC : K+ = 46.98 % truth = 46.97 % MC : K
+ = 46.27 % truth = 46.27 %
Still missing a quantitative evaluation of the Tag background… seems to be negligible even at few per mill level, but we are working on it.
KGM 14/11/03 V.Patera
K+ vs K
- The nuclear interactions of K- in the beam pipe and in the DC wall reduce K
- in comparison to K
+ by more than 1 %
IntLum/6pb-1
K
BLUE = K+
RED = K-
IntLum/6pb-1
K
K
The K integrated over and pK is (10.4 ± 4) x10-3
KGM 14/11/03 V.Patera
K- nuclear interactions from K (??)
PnuclK C1 + C2/sin
1
22
1
If we assume that K is totally due to K- nuclear interactions, then it should contain a costant term due to BP, plus a bigger term proportional to 1/sin due to DC wall (and BP)
Work in progress…it is just a first look
K
cos
KGM 14/11/03 V.Patera
K summary
The K tracking efficiency times the geometrical acceptance K has been measured using the tag
tecnique at fraction of % level
The K has been measured independently for positive
and negative K
The sistematics due to the uncertainty on shape of the signal and due to tag bias have been evaluated
The K has been measured versus the time in step of
6pb-1
A memo is in preparation
KGM 14/11/03 V.Patera
First look at tag background evaluation
The use of the K+(K-) tag decay ( K and K0) allow us to select a pure K-(K+) beam. Eventual pollution of the tag reflects in a systematic underestimation of the absolute BR measured on the other emisphere. We made a first attempt to estimated this background using a sample of 4 pb-1 of 2002 data
We assumed that the background fraction in the events with one tag decay is small. There is no background in the events where both K+ and K- undergo a tag decay (double tagged events) We compare the single and double tag kinematic distribution: the differences can be due to the background ( and , to some extent, to slightly different acceptance ) The statistical power of this analysis is limited by the rate of double tagged decay in K+K- events ( 10% of the total in the stream)
KGM 14/11/03 V.Patera
Tag bck: Kinematic variables
The control variables was chosen both in the lab and in the center of mass
frame:
1. Momentum of the K charged secondary in the K frame2. Angle between the K flight path and the charged secondary in the K
frame3. Angle between the charge secondary and the K in the lab4. Number of clusters associated at the K decay product ( ≤1 for K and
≤3 for K0)5. Energy of the cluster associated to the charged secondary6. Time of flight of the charged secondary
Only the shape can be compared due to the different yelds of single and double tag events
KGM 14/11/03 V.Patera
Charged secondary momentum in K frame
Red = difference of the 2 histoBlue = statistic uncertainty
Normalized comparison between single and double tag events
Linearscale
Logscale
Mev/cMev/c
Mev/c
KGM 14/11/03 V.Patera
Cos() between K and secondary in K frame
Red = difference of the 2 histoBlue = statistic uncertainty
Linearscale
Logscale
KGM 14/11/03 V.Patera
Cos() between K and secondary in lab frame
Linearscale
Logscale
KGM 14/11/03 V.Patera
Number of secondary cluster associated
Ncluster ≤1 for K
Ncluster ≤3 for K0
Red = difference of the 2 histoBlue = statistic uncertainty
Linearscale
Logscale
KGM 14/11/03 V.Patera
Energy of the cluster associated to the charged secondary
Linearscale
Logscale
MeV MeV
MeV
KGM 14/11/03 V.Patera
Time of flight of the charged secondary
Linearscale
Logscale
ns
ns ns
KGM 14/11/03 V.Patera
What about dE/dx ?
dE/dx is a very powerful PID for K± but:
1) Was not available in 2001 data2) Due to low efficiency of ADC sampling in 2002 the DE/dx
measurement select the K with 900
KTruncated mean (count/cm)
KaonsNon Kaons
K with dE/dxK with nodE/dx
KGM 14/11/03 V.Patera
Background statistic estimator
To build a conservative background estimator I have to measure the deviation from statistic fluctuation of the difference of the two sets of histos. We define:
n) = abs [ his2tag(n) – his1tag(n) ]
For each bin I consider the quantity (n) = n) - (n) . This variable gives
the deviation of (n) from the statistical fluctuation and is > 0 if the bin is bigger then statistica fluctuation and < 0 is underfluctuate. The sum over all the bins of (n) is a upperlimit to the background.
n)2 = ( his1(n))2 + (his2(n))2
For bin n
KGM 14/11/03 V.Patera
First results on 3 pb-1 of 2002
Variable ii ii ii
Pseccm 0.0219 0.0160 0.0059
coscm 0.0258 0.0301 -0.0043
coslab 0.0249 0.0298 -0.0050
Ncluass 0.0070 0.0038 0.0032
Eass 0.0318 0.0745 -0.0427
Tofass 0.0285 0.0491 -0.0205
Positive Tag
KGM 14/11/03 V.Patera
First results on 3 pb-1 of 2002
Variable ii ii ii
Pseccm 0.0303 0.0161 0.0142
coscm 0.0280 0.0303 -0.0024
coslab 0.0267 0.0300 -0.0032
Ncluass 0.0085 0.0038 0.0047
Eass 0.0331 0.0715 -0.0384
Tofass 0.0304 0.0386 -0.0083
Negative Tag
KGM 14/11/03 V.Patera
Backgroung on negative tag?
The difference between the 1 tag and the 2 tag distribution settles on the signal region.. True background ???
Conclusion:
There is no evidence for a clear background contamination in the single tag events, at least at % level
We are working out a robust statistic estimator for the background level (or limit)
Work in progress..