Post on 13-Jan-2016
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Experiment NA48/2Experiment NA48/2
A Precision Measurement of Charged Kaon Decay Parameters (CERN/SPSC 2000-003)
Status Report (SPSC-2003-033)
CERN, Chicago, Dubna, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Torino, Vienna
Cambridge, Edinburgh, Siegen
Collaboration:
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NA48 Collaboration (Pisa, September, 2003)
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Report content
• Goals• New beam line• Set-Up upgrade• Beam detector KABES• Trigger• Data taking in 2003• Asymmetry express analysis:
- observable definition- major systematics estimation
• Ke4 & Rare decay examples• Semileptonics• Conclusions & beam request
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Direct CP violation
in K± ± + -, K± ± 0 0
(Ag ) 10 – 4 (limited by statistics)
GoalsGoals
g + - g -
Ag = ———— g+ + g -
Requirements to experiment:
• high statistics (> 2109 decays)• stability in time• set –up symmetry
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Ke4 to measure - scattering length ( ) < 1102
required statistics > 106 (430k )
Rare decays to test PT & search for ACP
K , K 0 DE K
e+ e, K + , Ke2
K l l+l
K 0 , K 0 l+l, … etc.
Semileptonic decay Br’s: Ke3, K
3
to improve precision of |Vus|
& check CKM unitarity
Goals Goals (continuation)00a
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Simultaneous K+ and K- beam line(schematic vertical section)
not to scale
axes are steered to coincide within 1 mm
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-=4.0, mm +=4.1,mm
0
<x->=1.230.01, mm <x+> = -0.08 0.01, mm
K-
K- K+
Beam spots on the DCH1
-50 0 +50x, mm
+50
y,mm
-50 0 +50x, mm
-50
achromat: K+ Down (HD)
K+
K+ K+K-
-50 0 +50x, mm
-50 0 +50x, mm
achromat: K+ Up (HU)
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New K12 beam line built for NA48/2
first achromat
second achromat
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Set-up Upgrade
• Beam detector KABES (TPC micromegas) 3 double stations + read-out: put in operation
• DCH3: fully instrumented
• DCH1- 4 read-out electronics: re-mapped to be Right –Left (Saleve – Jura) symmetric
• L2 trigger: new processors & interface to neutral part
• Decay vacuum tank: extended (+24 m)magnetic field remeasured
• Beam profile monitor: new pixel detector
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Upgraded NA48 Set-Up (schematic top view)
not to scale
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KABES-1/2
entrance window
K+
time resolution67 ps
K-
time resolution63 ps
T/2 ns, Station2 – Station3
Beam rate ~20 MHz
P0/P(K) - P0/P(S)
Momentum
resolution 1.1%
P(S) , GeV/c
50 60 70
P
(K),
GeV
/c
-0.2 0 +0.2
5
0 60 7
0
Beam rate ~20 MHz
K+, K-
X,Y space resolution~100 m
-10 0 10T/2 ns, Station2 – Station3
moved out by ~20 cm
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Three stage logic for (satisfies Ke4):
• pre-trigger: 2 tracks in Hod & no surrounding anti
• L2 processor (mass-box) 2 vertices (~ 94%)
or 1 vertex (~ 98%)
or “fake track” (excluding ±0 mode) (~99.5%)
• L3 software flags (to simplify splits)
Trigger logic
Logic for K± ± 0 0: • pre-trigger: clusters in LKr Cal (Nx > 2 or Ny > 2) • L2 “fake track”• L3 flags
+ various triggers for: rare decays, semileptonics, efficiency study, random events, ...
K
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Stability of trigger efficiencies
day-sample u
1% level
trigger inefficiency trigger inefficiency
0 0
for K+ + + - ( ) & K- - - + ( )
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• MNP33 current alternation each day (BU / BD )
• swapping of achromat magnetic fields (HU / HD)
during each MD on Wednesday
(due to long tuning procedure)
• data taking cycle two weeks - a supersample
Running conditions
to compensate variation in time of beam and set-up:
more frequent alternation desirable
(even on the expense of statistics)
as learned from 2003:
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Beam availability & supersamples
SS-1August 6- 20
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Statistics for asymmetry
Statistics of supersamples in raw K± ± + -
without acceptance cuts (not to scale to the Proposal)
HD BU
HD BD
HU BU
HU BD
154 166 38 358 150 58 76 284
127 162 50 339 130 142 60 332
1 2 3 total
total 561 528 224 1313
~ 450 mln K± ± + - events of SS-1 reprocessed for the express analysis
in 106
~ 50 millionsof K± ± 0 0
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Reconstructed K± ± + -
PK, GeV/c40 50 60 70 80
K-
0
PGeV/c
K+
0
M(3)+ GeV/c2
K+ K-
M(3)- GeV/c2
~120 mln~220 mln
SS-1: 1 - 12 day-samples
1 - 6 samples
1 - 3 - HD
4 - 6 - HU
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Dalitz for accepted
u = (2MK/m2)(MK/3 - E*)
M(u,v)2 1 + gu + hu2 + kv2
v = (2MK/m2)E*2
Square of matrix element
u
vrun 15323
K
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N+(u) a+(u) (1 + g+u)
N- (u) a- (u) (1 + g-u) Ag = —————
if a+(u) = a-(u) - acceptance cancel
R(u) = N+(u) / N- (u) ~ 1 + gu
g = (g+- g-) 2gAg
R(0) = 1 - normalizationg – 0.2
- 1.170 < u < 1.267
Definitions for asymmetry
u = (2MK/m2)(MK/3 - ) u = (m22 -M2
K/3) / m2 - 1
g+ - g-
g+ + g-
slope
K
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u- spectra & their Ratios
N+(u) N- (u)
R(u) (not normalized)
statistics of SS-1 (each plot - one momentum bin)
beam pipe cut
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Observable: AS & AJ - slopes of R(u)
BU N+(u)
if aS(u) & aJ(u) are stable in time
t ~ 1 day
AS = AJ g
A = 0.5 (AS + AJ) g
if Ra(u) = aS(u)/aJ(u) is stable in time
BU N-(u)
BD N+(u)
BD N-(u)
aS(u)
-acceptanceaS(u)
AS
aJ(u)
aJ(u)
AJ
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BU N+(u)
BU N-(u)
BD N+(u)
BD N-(u)
Systematic checks
A+
t = 1 day
A-
AU
AD
Ra(u) = aS(u)/aJ(u): Sa - slope AU g + Sa; AD g - Sa
if Sa is stable in time
A+ + Sa; A- - Sa; (A+ + A-)/2 0
-Sa +Sa
+Sa
-Sa
(AU + AD)/2 g
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Selection criteria
• radial cuts around the beam centres (in DCH1,4)
to symmetrize acceptances
• day-by-day definition of the beam COG’s in each momentum bin
to reduce acceptance variations in time
Conservative cuts:
R(DCH1) > 11.5 cm
R(DCH4) > 13.5 cm
leave 60% of raw statistics( beam stability dependent )
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Spectrometer alignment
MK – MPDG, KeV/c2
~ 35 KeV/c2
~4 m / dayx DCH4
day-sample
BUK+ & BDK- (to Jura)
BDK+ & BUK- (to Saleve)
surprising effect
time variation term was compensated
(after fine tuning of B)
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Acceptance cancellation check
< A± > = (A+ + A-)/2 = (1.2 2.3)10-4
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Beam geometry effects
A± for different achromat polarities
HD HU
> 0
< 0
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Time stability of acceptancesin momentum bins
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A stability with momentum
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Time stability of acceptances
HD HD HUHU
different achromats different achromats
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Time stability of A
HD HU
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Systematics summary• Major systematics related to
- acceptance asymmetry- time variation effects
are under control
• Other possible systematics:
- residual (+ Earth) magnetic fields
- trigger efficiencies
- DCH’s efficiencies
- accidentals
- …..
are found to be less significant
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First look on K± + - e±
15807 events in SS-1 BR = (3.87 ± 0.20)10-5
(PDG: (4.08 ± 0.09)10-5)
7105 expected K± + - e±
in 2003
Background
~1% of Ke4
from K± +- ±
~1% of Ke4
from K± ± 0D
M(3) GeV/c2
PK, GeV/c
K mass
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Rare decayRare decay K K e+ e-
0.40 0.44 0.48 0.52 0.56 0.60
500
400
300
200
100
0
1400 events in 1 month of data taking ~ 3500 events expected in 2003 run
Me + e -GeV/c2
Even
ts /
2
MeV
/c2
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Semileptonics study
In addition, all major modes:• leptonic & semi..
Ke2, K
e3, K2, K
3
• hadronic K2, K
3
are accumulated with min. bias trigger
strong constraint for Br’s0
(missing mass)2, (GeV/c2)2
0
70 example of K eselected from ~1700 burts
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Conclusion
• NA48/2 experiment has been prepared:beam line, detector and trigger
are put in operation & tuned• the major systematics are under control
& do not exceed statistical precision• to reach the proposal goals
quoted statistics are neededcan profit from more
Beam Request for 2004
• as much proton time as possible
(400 GeV protons ~1·1012 ppp on T10)• as few beam interruptions as necessary