rare decays program @kloe
DESCRIPTION
Rare decays program @KLOE. LNF, INFN May 26 th -27 th 2005. Matteo Martini INFN Laboratori Nazionali di Frascati On behalf of the KLOE Collaboration. DA F NE: the Frascati f - factory. e + e - collider @ s = M f = 1019.4 MeV 2 interaction regions (KLOE – DEAR/FINUDA) - PowerPoint PPT PresentationTRANSCRIPT
Rare decays program @KLOERare decays program @KLOE
Matteo Martini
INFN Laboratori Nazionali di Frascati On behalf of the KLOE Collaboration
LNF, INFNLNF, INFNMay 26May 26thth-27-27thth 2005 2005
DANE: the Frascati - factory
ee collider @ s = M= 1019.4 MeV 2 interaction regions (KLOE –
DEAR/FINUDA)
Separate e, e rings to minimize beam-beam interactions
Crossing angle: 12.5 mrad ( px12.5
MeV )
M. Martini, K rare decaysM. Martini, K rare decays 1
KLOE: data taking
2001: 176 pb1
550×106 decays
2002: 296 pb1
920×106 decays
First published results
2000: 25 pb1
80×106 decays
Days of running
Inte
grat
ed lu
min
osit
y (p
b1 )
2002
2001
2000
Analysis
in progress
New KLOE running in progress:• Lpeak= 1.4 × 1032 cm-2s-1
• 2004: integrated Lum.: 700 pb-1
Goal: collect 2 fb-1 by Dec. 2005
M. Martini, K rare decaysM. Martini, K rare decays 2
The KLOE detector
Superconducting coil (B = 0.52 T)
Drift chamber Gas mixture: 90% He + 10% C4H10
4 m 3.75 m, CF frame 12582 stereo–stereo sense wires almost squared cells
Al-Be beam pipe (spherical, 10 cm , 0.5 mm thick) Instrumented permanent magnet quadrupoles (32 PMT’s)
Electromagnetic calorimeter lead/scintillating fibers (1 mm ), 15 X0
4880 PMT’s 98% solid angle coverage
p/p0.4 % (tracks with > 45°)
xhit150 m (xy), 2 mm (z)
xvertex ~1 mm
(M) ~1 MeV
E/E5.7% /E(GeV)t 54 ps /E(GeV) 50 psvtx() ~ 2 cm ( from KL )
3M. Martini, K rare decaysM. Martini, K rare decays
Kaon production and properties
S = 6 mm: KS decays near IP
L = 3.4 m: Appreciable acceptance
for KL (~0.5L)
NSL ~106 /pb-1 ; p* = 110 MeV/c
1,p , p , p ,p
2L S L Si K K K K
Tagging: observation of KS,L (K+,-) signals presence of KL,S (K-,+)
precise measurement of absolute BR’s and interference measurement of KS KL system
KSKL (KK) produced in pure JPC = 1 state:
KS (K KL (K
The meson decays at rest providing monochromatic and pure kaon beams
Contamination ~10-10
= 0.9 m: 60% acceptance for
kaon tracking
N ~ 1.5106 /pb-1 ; p* = 127 MeV/c
4M. Martini, K rare decaysM. Martini, K rare decays
Tagging of KS and KL “beams”
KL tagged by KS vertex at IPEfficiency ~ 70% KL angular resolution: ~ 1°KL momentum resolution: ~ 1 MeV
KKSS
KKLL 2 2
KS tagged by KL interaction in EmCEfficiency ~ 30% KS angular resolution: ~ 1° (0.3 in )
KS momentum resolution: ~ 1 MeV
KKLL “crash”“crash”= 0.22 (TOF)= 0.22 (TOF)
KKSS ee
4 x105 tags/pb-1 3x105 tags/pb-1
5M. Martini, K rare decaysM. Martini, K rare decays
Rare Kaon physics at KLOE
6
KS 30
- final results - prospects @2 fb-1
KS
- status of the analysis - prospects @2 fb-1
KS
- preliminary study
Outlook:
M. Martini, K rare decaysM. Martini, K rare decays
hep-ex/0505012 submitted to PLB
analysis inprogress
Paving theroad
Observation of KS 30 signals CP violation in mixing and/or in decay:
Uncertainty on KS 30 amplitude limits precision of CPT test from unitarity (Bell-Steinberger):
CPLEAR ’99 : Im = (2.4 5.0) x 10-5 30 uncert. dominates
after NA48 meas. : Im = (-0.2 2.0) x 10-5 error now dominated by
CPTCP
*1 tan SW S Lf
mei i A K f A K f
SM prediction: S000
= L000|+000|2, giving: BR(KS 30) = 1.9 x 109
Best limit from direct search SND ’99 : BR(KS 30) < 1.4 x 105
Interference meas. NA48 ’05: BR(KS 30) < 7.4 x 107
M. Martini, K rare decaysM. Martini, K rare decays 7
Search for KS 000
-- KS30 (MC)-- MC BKG DATA
A kinematic fit is applied on the Ks side requiring the conservation of 4-momentum (NDOF=11). 2
FIT
Search for KS 000
Preselected signal sample (KLCRASH and 6 photons): 39538 events
Normalization Sample (KLCRASH and 4 photons): 23.5x106 events
DATA=450pb-1 (2001+2002); MC =0.9fb-1 (all available statistics)
2FIT/NDF < 3 is not enough
(2/3 of bkg rejected)!Other discriminating variable have to be used:
(2, 3M. Martini, K rare decaysM. Martini, K rare decays 8
Search for KS 000 Rejection of bkg:
KS + 2 accidental/split ’s
Define signal box in (2, 3 plane:
3 pairing of 6 clusters with best 0 mass estimates 2 best pairing of 4’s out of 6: 0 masses, E(KS), P(KS), c.m. angle between 0’s
DataMC KS 30
In the (2 , 3) plane we define a signal and five control boxes. The agreement between DATA and MC, after each analysis step, is better than 10% in each region.
Signal generated with BR=10-5 (SND)
M. Martini, K rare decaysM. Martini, K rare decays 9
Search for KS 000
DataMC KS 30
Signal generated with BR=10-5 (SND)
Other analysis cuts:
-Track veto to reject events with tracks coming from IP
- Final cut on residual KS energy: E(KS)-EM. Martini, K rare decaysM. Martini, K rare decays 10
Nsel(data) = 2 events selected as signal, with efficiency = 24.5%
Nsel(bkg) = 3.130.82stat0.37sys bkg events expected from MC
Which translates into a limit on |000| @90% c.l.:
Measuring 3=24.5% from MC generated signal and normalizing signal counts to KS 00 in the same data set we obtain @90% c.l.:
Can state: N3<.45@9%CL
Search for KS 000
3
0 0 73
2
2
3 2 1.2 10S S
N
BR K BR KN
0 0
000 0 0
3 30.018
3 3
S SL
SL L
A K BR K
A K BR K
NA 48
KLOE
M. Martini, K rare decaysM. Martini, K rare decays 11
Search for KS 000
M. Martini, K rare decaysM. Martini, K rare decays 12
• Increased statistics: x 6.5 improvement– Luminosity x 5
– Add tagging by KL vertex in DC x 1.3
• Increased background rejection– Largest bkg source after all cuts is the splitting of e.m. clusters
• Merging procedure removes bkg but leaves signal untouched
• Candidates in data go from 2 to 0, in MC from 3.13 to 2
– Optimization of kinematic fit in progress
– Overall better reduction of the known background expected
If we will be able to suppress the background to a ~negligible levelUL will improve by 6.5 x 1.5 ~ 10
Search for KS +-0
Present status for the BR(KS):
• Decay amplitude is composed of CPC (3x10-7) and CPV (1.2x10-9) parts
• Direct measurement of the BR is possible using the entire KLOE data set.
• Measurement can be used to verify PT predictions. These predictions are poorly tested.
Currently, we have performed the search using a sample of 740 pb-1 of data:
- 373 pb-1 from 2001-2002 data taking
- 367 pb-1 from 2004 data taking
Assuming BR(KS) = 3 x 10-7 230 signal events produced
M. Martini, K rare decaysM. Martini, K rare decays 13
Search for KS +-0
Selection: KL-crash tag with 2 low momentum tracks from IP
Preselection algorithm:
- Require vertex at origin with zero net charge
- Require 2 prompt neutral clusters
- Each pair of clusters is a 0 candidate. For each:
- close 3-body kinematics using m(0), m(KS)- set t0 using pair of clusters- use p(KS) and p() to search KL-crash cluster in 20° cone
- choose 0 pair that best agrees with reconstructed KL momentum
-
KL
M. Martini, K rare decaysM. Martini, K rare decays 14
Search for KS +-0
Application of kinematic fit to reject bkg. Using 2 < 30 (NDOF = 8):
- Cut efficiency = 48.5% - 98.8% of bkg rejected - MC(SIG) = 3.3% 3.9 events expected
2 after preselection for MC signal and
background
MC gives 93 bkg events after kinematic fit
K+
+
The ’ bkg are due to charged kaon
events
M. Martini, K rare decaysM. Martini, K rare decays 15
Search for KS +-0
We studied more in detail the various background classes and developed a set of cuts to reduce them:
K± events
K± has monochromatic ± momentum at 206 MeV; cut on p*
Dalitz
dedicated MC production of Dalitz events; require TCA cuts for significant reduction of this background
After these cuts we still have 3 ’ bkg events
’
dedicated MC production of K± (Ke3 + K3 + ’), K all Cut on the energy of prompt clusters not associated to any tracks or to 0 (Efree)
±
M. Martini, K rare decaysM. Martini, K rare decays 16
Search for KS +-0
Compare DATA and MC:
DATA
Standard BackgroundMC
25130 eventsin the data with no cuts applied
M. Martini, K rare decaysM. Martini, K rare decays 17
TOF p
EFREE
Search for KS +-0
At the end of analysis signal efficiency 1.5%
Preliminary results with 740 pb-1:
- candidates: 6 events - background: ~ 3.5 events - observed events consistent with expectation within the statistical error (100%) - evaluation of systematic error in progress
Scaling the values of signal and background to 2 fb-1 we expect:
- 16 events, of which 9 background- 60% statistical accuracy on BR(KS)
M. Martini, K rare decaysM. Martini, K rare decays 18
BR differs from CHPT O(p4) by 30%,useful to fix one O(p6) counterterm
Projections based on– 150 pb-1 of 2001 background MC– 10K events of signal MC
With 2 + 0.5 fb-1 we expect– 500x106 KS events tagged by
Klcrash
– N(KS, tagged) = 500x106 x 2.8x10-6 = 1400 events
– acceptance 0.4
– Nsig = 560 events
2 fb-1: with good background rejection ~ 4% statistical error
M. Martini, K rare decaysM. Martini, K rare decays 19
Paving the road for KS
• Strategy of analysis
– No recover splitting and
large angular acceptance
– Kinematic fit to exploit two body kinematics
• Distribution of kinematic variables after fit
• Background separation
looks promising
bkg signal
A.U
.
A.U
.
bkg signal
MC distributions, no data yetN. of events in A.U.
After fit
Reco
ns.
M. Martini, K rare decaysM. Martini, K rare decays
Paving the road for KS
20
Conclusion
21M. Martini, K rare decaysM. Martini, K rare decays
A direct search for KS30 decay has been performed using the whole statistics collected at KLOE during 2001- 2002 data taking.
We set an upper limit on the branching ratio at:
BR(KS30) < 1.2x10-7 @ 90% C.L.
We have started the direct search of the KS+-0.
For the moment we have analyzed only 740 pb-1 of data. Now we are analyzing the other 300 pb-1 already on disk. The prospects at 2 fb-1 is promising.A statistical accuracy of 60% can be reached.
We are paving the road to study KS.
With 2 fb-1 we can reach a statistical error of 4% and contributeto test the PT prediction for the branching ratio.
BackupBackup
Adding in quadrature all the sources of systematic error, we obtain:
2001 91.8 0.2 0.3 %SEL stat sys
Using these results and the efficiency on trigger and cosmic veto, we can calculate the number of events of the normalization sample:
0 62 37.8 0.2 10L SN K crash and K
This value enters directly in the upper limit calculation.
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
The 22 is built selecting 4 out of 6 clusters
which satisfies better the kinematics of KS 20
The parameters used are:
mass distribution
opening angle between pions in KS C.M. frame
4-momentum conservation
The calibration is done using KS20 sample (see
next slide)
The 23 is based only on the 3 “best
reconstructed” pion masses
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
DATA MC
DATA MC
M
EE
M
In the construction of 2 we use a different sigma
for each sample. DATA and MC
(OLDMC, NEWMC) (2001 ,2002 ).
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
To better calibrate data and MC, we have also questioned how well the MC reproduces the amount of double shower fragments and double accidental clusters. To understand and calibrate this we have divided the MC KL-crash events into 2 further classes:
2A: events of Ks20 in overlap with 2 accidental (~ 60% )
2S: events of Ks20 with 2 splitted clusters or 1 accidental + 1 splitted cluster (~ 35%)
To do this, we perform a 3 components fit (2S, 2A and fake events)
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
23
22
23
23 2
3
22
22
22
DATA 2 S
2 A Fake
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
Summing up 2001-2002 for each MC, we can compare DATA with the two different MC productions.
DATA data MC MC
282 17 280 17,6
5037 71 4761 59,3
452 21 424 27,1
10132 101 9993 145,6
326 18 379 13,9
22309 149 22728 269,6
DATA data MC MC
282 17 283 18,9
5037 71 4870 61,5
452 21 413 26,9
10132 101 9962 146,9
326 18 381 14,2
22309 149 22636 266,8
NEW OLD
A reasonable data-MC comparison is found for both samples at the beginning of the analysis.
SboxCSbox
UPCup
Down
CDown
M. Martini, K rare decaysM. Martini, K rare decays
BackSearch for KS 000
DATA-- MC ALL
22>40
22<14
4<22<40
ALL
23 2
3
23
23
We apply a track veto to reject events with tracks coming from IP.
We reject events with:
PCA < 4 cm|ZPCA| < 10 cm
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
DATA-- MC ALL
TRK veto+
E/E
23 2
3
23
23
22 down
22 up2
2central
ALL
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
DATA-- MC ALL 2
2 down
22 up2
2central
ALL
23 2
3
23
23
END OFANA
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
DATA data MC MC EV TOT tot
2 1 3,125 0,8 17 4
520 23 446,5 10,1 2402 49
0 0 0 0,0 0 0
4 2 3,2 0,8 17 4
3 2 2,45 0,8 11 3
326 18 388,5 9,6 1961 44
Comparison between DATA and MC after the optimization procedure.
Sbox
CSbox
UP
Cup
Down
CDown
Nobs = 2 Bexp = 3.13 ± 0.82
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
Adding in quadrature all the contribution found, we obtain:
Source Bexp/Bexp
MC calibration 1.6 %
Fakes definition 1.8 %
Track veto 4.8 %
Energy resolution 6.6 %
Energy scale 6.7 %
2FIT 5.0 %
TOTAL 11.5 %
Bexp = 3.13 ± 0.82stat ± 0.37sys
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
For each sample we generate 3 poissonian centered around N2S, N2A and Nfake. Weighting eachdistribution for the proper calibration factor, obtained with the 2D-fit, we sum them up to build our PDFfor the background. The obtained PDF is reasonably similar to a Gaussian with average 3.15 and with equivalent to the ext. stat.
Folding the previous PDF with a Gaussian distribution centered around 0 and with a width equivalent to the whole systematic uncertainty we obtain the PDF for bkg that we use on the upper limit calculation.
The RMS include statistic and systematic uncertainty.
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS 000
THE UNIFIED APPROACH: when exp is greater than Nobs, the classical method does not provide a perfect coverage. In this condition is better to use Feldman-Cousin-Neyman method based on likelihood ratio.
Classical Neyman
N3 = 2.42 N3 = 3.45
Bexp = 3.13 ± 0.82stat± 0.37sys
We observe Nobs = 2 candidates on data and we estimate:
With this counting we obtain the following UL @ 90% C.L.:
In our case, the exp. background is greater than Nobs.
M. Martini, K rare decaysM. Martini, K rare decays
BackSearch for KS 000
Search for KS +-0
Current values for the BR
Decay amplitude is composed of CPC (3x10-7) and CPV (1.2x10-9)
Selection requiring KL-crash, 2 tracks from IP (zero net charge), 2 prompt neutral clusters
• Data 740 pb-1 (2001+2002+ some 2004 runs)• Assuming BR=3x10-7 230 signal events produced• Major bkg: charged kaons, dalitz, ’• bkg reduced using: TCA , Tcut, P*• Use kinematic fit to select events kinematically closed (2 cut)• veto events with additional neutral prompt clusters below acceptance.
The set of cuts designed grants SIG 1.38% with very high background rejection
We expect to measure this BR integrating the whole collected data so far.M. Martini, K rare decaysM. Martini, K rare decays
Search for KS +-0
M. Martini, K rare decaysM. Martini, K rare decays
Back
Search for KS +-0
M. Martini, K rare decaysM. Martini, K rare decays
Back
Search for KS +-0
M. Martini, K rare decaysM. Martini, K rare decays
Back
Search for KS +-0
M. Martini, K rare decaysM. Martini, K rare decays
Back
Search for KS +-0
Summary of signal efficiency:
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS +-0
Because of Data/MC discrepancies, especially in TOF, we want to obtain Nbkg from sidebands in data after cuts on TOF and p*.
Assuming no correlation beween 2 and EFree,
Study systematics by inverting cuts, varying acceptances
A/B=C/D
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS +-0
M. Martini, K rare decaysM. Martini, K rare decays
Search for KS +-0
M. Martini, K rare decaysM. Martini, K rare decays
ConclusionWith the data collected during 2001-2002 data taking, KLOE has:
- determined the best upper limit on KS30
- measured the main KL BR’s with 0.5% accuracy- measured in two independent ways the KL lifetime with 0.5 % accuracy Important contribution to the measurement of Vus
Next in line:
- Direct search for BR(KS)- Final result on KSe BR- Analysis of KL semileptonic form factor slopes
KLOE expects to collect 2 fb-1 by the end of 2005:thus allowing to improve the search for rare KS decays and KSKL interference studies.
M. Martini, K rare decaysM. Martini, K rare decays