Transcript Document

Recent results from KLOE
Cesare Bini
Universita’ “La Sapienza” and INFN Roma
1.
2.
3.
4.
5.
6.
The KLOE physics program
The KLOE detector
Status of the experiment
Results on neutral kaon decays
Results on f radiative decays
Conclusions and perspectives
1. The KLOE physics program.
e+e  f
W = mf = 1019.4 MeV
Decay channels
 K+K = 49.2%
 K0K0 = 33.8%
 p+pp0 = 15.5%
 hg
= 1.3%
 p0g
= ~10-3
 h’g
= ~10-4
 ppg
= ~10-4
 hp0g = ~10-4
 h e+e = ~10-4
 p0e+e = ~10-5
sf~3 mb
Charged Kaon decays + CP/CPT tests
Neutral Kaon decays + CP/CPT tests ( e’ / e )
3 pion decay  rp (r shape parameters)
Radiative decays: pseudoscalar: h physics
“
“  pseudoscalar mixing angle
scalar  f0
“  a0
Conversion decays: transition form factor Ffh
“
“
Ffp
e+e  p+pg Initial state radiation  s(e+e  p+p) 2mp < W < mf
e+e  f around f peak (energy scan)  f resonance parameters
2. The KLOE detector: Drift chamber:
Drift chamber
Calorimeter (Pb-scint.fib.)
Magnetic field = 0.56 T
Large volume d=4m l=3.3m
He – Isob 90-10 gas mixt.
Momentum resolution
dp/p < 0.4%
Calorimeter:
Energy resolution:
s/E = 5.4% / (E(GeV))
Time resolution
st = 55 ps / (E(GeV))40 ps (cal.)120 ps (coll.time)
3. Status of the experiment
Data taken from april 1999 to
december 2001~ at f peak
+ 1 energy scan
Analysis status:
2000 data
~completed
(25 pb-1  7.5 x 107 f)
2001 data
in progress
(190 pb-1  5.7 x 108 f)
Present day performance:
peak
L(cm2 s1)
5·1031
day L dt (pb1)
3
average
3.5·1031
1.8
All results are still preliminary
4.Results on Neutral Kaon decays
Example of f  KSKL
Neutral kaons produced in a
pure quantum JPC = 1 state:





1
K 0  p  K 0  p   K 0  p  K 0  p 
2
N
 K S  p  K L  p   K L  p  K S  p  

2
i 

pK = 110 MeV lS = 6 mm lL = 3.5 m
Tagging:
pure KS and KL beams
 analysis of kaon decays
 double ratio  ( e’ / e )
Interferometry studies
p0 p0
p +p 
KS tagging by identification of KL interacting
in the EmC (“KL crash”) [ ~50% of KL ]
Selection cuts:
 Eclus > 200 MeV
 |cos(qclus)| < 0.7
b* distribution of “KL crash”
 0.1950  b*  0.2475
(b* = KL velocity in the f rest frame)
Example of f  KSKL  p+p “crash”
Position of the KL  KS momentum
Tagging efficiency etag~ 30%
KLOE has now about 6 107 tagged KS.
All channels are accessible.
Results from 2000 data (5.4 106 tagged KS) on:
(1)
R=G(KS  p+p- ) / G(KS  p0p0 )
(2)
BR(KS  p e n )
(1) R=G(KS  p+p- ) / G(KS  p0p0 )
Motivations:
 First part of double ratio
 Extractions of Isospin Amplitudes and Phases A0 A2 and d0-d2  consistent treatment
of soft g in KS  p+p- (g) (PDG data contain ambiguities)
[Cirigliano, Donoghue, Golowich 2000]
Selection procedure:
1. KS tagging
2. KS  p+p-(g) two tracks from I.P + acceptance cuts: fully inclusive measurement
(Eg* up to Eg*max=170 MeV) eppg (Eg*) from MC  folded to theoretical g spectrum
 correction
D = (-3.4 ± 0.1) x 10-3
3.KS  p0p0
neutral prompt cluster
(Eg>20 MeV and (T-R/c) < 5st )
at least 3 neutral prompt clusters
(p0 e+e-g included)
Result:
Nev (KS  p+p- ) = 1.098 x 106
Nev (KS  p0p0 ) = 0.788 x 106
R = 2.239 ± 0.003stat ± 0.015syst
 stat. uncertainty at 0.14% level
 contributions to “systematics”:
tagging eff. Ratio
0.55%
photon counting
0.20%
tracking
0.26%
Trigger
0.23%
-------------------------------------Total syst. uncertainty 0.68%
PDG 2001 average is
2.197 ± 0.026
( without clear indication of Eg*cut )
With 2001 data (180 pb-1) improvement on:
 absolute scale  tagg.eff. Bias
 statistics of control sub-samples
 Eg* spectrum
(2) BR(KS  p e n )
Motivation:
ToF selection illustrated for MC:
1. KS  p+ p MC events
 If (CPT ok) .AND. (DS=DQ at work):
G(KS  p e n ) = G(KL  p e n )
BR(KS  p e n ) = BR(KL  p e n ) x (GL/GS)
= ( 6.704 ± 0.071 ) x 10-4
(using all PDG information).
Only one measurement (CMD-2 1999):
= ( 7.2 ± 1.4 ) x 10-4
Selection procedure
 Vertex with two tracks from I.P.
 kinematics (against huge p+p “background”)
 time of flight ( electron vs pion)
 final signal variable = Emiss-|pmiss|
BR evaluation:
 normalization to KS  p+ p (s(BR)~0.5%)
 both charge states are considered
(well separated  charge asymmetry)
2. KS  p e n MC events
Result:
 Nev(KS  p e n = 627 ± 30
[after the fit, residual background subtraction is included]
BR(KS  p e n ) = (6.79 ± 0.33stat ± 0.16syst) x 10-4
BR(KS  p e n )
 stat. uncertainty at 4.7% level
 contributions to systematics:
tag eff, ratio
0.6%
tracking + vertex
2.0%
time of flight
0.8%
trigger + t0
0.9%
----------------------------------Total systematics
2.4%
5.Results on f radiative decays
1. f  Pseudoscalar + g
 hg
 p0g
 h’g
According to quark model:
 assuming: no other content (e.g. gluonic))  assuming: no OZI-rule violations
p0 = (uu-dd)/2
h = cosaP (uu+dd)/2 + sinaPss
h’ = -sinaP (uu+dd)/2 + cosaPss
 assuming: f = ss state (aV=0)
g(f  h’g) = FscosaVcosaP – FqsinaVsinaP
g(f  hg) = FscosaVsinaP + FqsinaVcosaP
( aV aP = mixing angles in the flavour base)
( Fs Fq = form factors)
G(f  h’g)
R=
G(f  h g)
Kh’
= cotg2aP (
)3
Kh
Decay chain used: (same topology 2T + 3 photons / final states different kinematics)
(a) f  hg  p+pp0g  p+p 3g
(b) f  h’g  h p+pg  p+p 3g
Selection:
 2t (ET1+ET2<430 MeV) + 3g: kin. fit (no mass constraint)
 only (a) and (b) (negligible bkg.) BUT [N(b) ~ N(a) / 100]
Results:
N(a) = 50210  220
N(b) = 125  13stat +bck
Invariant mass spectrum
of h’g
BR(f  h’g)
R=
BR(f  hg)
= (5.0  0.5stat  0.3syst) x 10-3
 aP = ( 40.8  1.7)o [ qP = (-13.9  1.7)o ]
aP = ( 39.3  1.0)o
J/y decays and others
[Feldmann Kroll 2002]
BR(f  h’g ) = (6.5  0.6stat  0.4syst) x 10-5
2. f  Scalar (0++ quantum numbers) + g [f0(980) I=0, a0(980) I=1]
 p0p0g
(f0g sg, f0 , s  pp)  5g final state
 p+pg
(
“
)
 2t + 1g final state: huge background from:
ISR (radiative return)
FSR + interference (signal “hidden”)
 hp0g
a0g
a0
 hp)
[ h  gg ]
 5g final state
(40%)
[ h  p0p0p0 ]  9g final state
(32%)
[ h  p+pp0 ]  2t + 5g final state (23%)
Motivations:
f0, a0, not easily interpreted as qq states; other interpretations suggested:
 qqqq states (lower mass) [Jaffe 1977];
 KK molecule (m(f0,a0)~2m(K)) [Weinstein, Isgur 1990];
 f0(980) , a0(980) and s  lowest mass scalar qq nonet [Tornqvist 1999]
f  f0g , a0g  sensitive to f0,a0 nature [Achasov, Ivanchenko 1989]:
phenomenological framework (kaon loop model)  coupling constants
radiative g
f
g(fKK)
from G(fK+K-)
g(f0KK) g(a0KK)
f0, a0 model
g(f0pp) g(a0hp)
M(p0p0) M(hp) spectra
f0,a0
Kaon loop
final state
f  p0p0g
Main background sources (5g final states):
e+e  wp0 w  p0g
f  hp0g h  gg
Other background sources (not 5g final states):
f  hg h  gg 3g or h  p0p0p0 7g
Selection procedure:
 5 prompt g Eg > 7 MeV
 kinematic fit (without mass const.)
Result:
Nev = 2438  61
 BR(f  p0p0g )=(1.09  0.03stat  0.05syst)x10-4
CMD-2 (0.92 0.08 0.06)x10-4
SND
(1.14 0.10 0.12)x10-4
Fit to the Mp0p0 spectrum (kaon loop):
contributions from
f  f0g
f  sg
+ “strong” negative interference
negligible contribution
f  r0p0 p0p0g
Fit results:
M(f0) = 973  1 MeV
g2(f0KK)/4p = 2.79  0.12 GeV2
g(f0pp) /g(f0KK) = 0.50  0.01
g(fsg) = 0.060  0.008
BR(f  f0g  p0p0g ) = (1.49  0.07)x10-4
f  hp0g
Measured in 2 final states:
(Sample 1) h  gg
(5g)
 p0p0g is the main background
 5g selection (see p0p0g) + kinem. fit
(Sample 2) h  p+pp0
(2t + 5g)
 Negligible bckg with the same topology:
e+e  wp0 w  p+pp0
2t + 4g
f  KSKL (KL prompt decay) 2t + 4/6g
 2t + 5g selection + kinem.fit
Results:
(Sample1) Nev = 916 Nbck = 309  20
 BR(f  hp0g) = (8.5  0.5stat  0.6syst)x10-5
(Sample2) Nev = 197 Nbck = 4  4
 BR(f  hp0g) = (8.0  0.6stat  0.5syst)x10-5
CMD-2 (9.0 2.4 1.0) x 10-5
SND
(8.8 1.4 0.9) x 10-5
Combined fit to the Mhp0 spectra:
dominated by f  a0g
negligible
f  r0p0 hp0g
Fit results:
M(a0) = 984.8 MeV (PDG)
g2(a0KK)/4p = 0.40  0.04 GeV2
g(a0hp) /g(a0KK) = 1.35  0.09
BR(f  a0g  hp0g) = (7.4  0.7)x10-5
Interpretation of KLOE results on scalars (within the context of kaon-loop framework):
(preliminary)
parameter
g2(f0KK)/4p
(GeV2)
g(f0pp) /g(f0KK)
g2(a0KK)/4p
KLOE result
4q model
qq(1) model
2.79  0.12
“super-allowed”
“OZI-allowed”
0.50  0.01
(GeV2)
g(a0hp) /g(a0KK)
0.40  0.04
1.35  0.09
0.3-0.5
qq(2) model
“OZI-forbidden”
0.5
2
“super-allowed” “OZI-forbidden” “OZI-forbidden”
0.91
 4q doesn’t describe a0 parameters;
 4q compatible with f0 parameters;
1.53
f0 = ss
a0 = (uu-dd)/2
1.53
f0 = (uu+dd)/  2
a0 = (uu-dd)/  2
 f0/a0 ratio sensitive to isospin mixing [Close Kirke 2001]:
BR(f  f0g )
BR(f  a0g)
= 6.0  0.6 ;
g2(f0KK)
= 6.9  1.0
g2(a0KK)
if Ff0(R) = Fa0(R)  qS= (47  2)o [no isospin mixing  qS = 45o]
6. Conclusions and perspectives
 DAFNE performance has improved considerably
during the first two years of KLOE data taking
 KLOE detector well performing and under control
 From 2000 data (25 pb-1) results on:
KS decays
f radiative decays
improve previous “PDG” knowledge
 Analysis of 2001 data (190 pb-1) in progress. Expected new results will be:
rare KS decays [p+pg ,  gg , limits on  3p]
KL decays
[gg ,
 p0p0 ….]
K decays
h decays (6 x106 h produced) [chiral perturbation theory checks]
hadronic cross-section s(e+e  p+p) 2mp < W < mf
 Data taking 2002 starting now  500 pb-1 realistic by end of the year
Detector calibrated on-line
(run by run ~ ½ hour):
- Drift Chamber s-t relations
“ momentum scale
(MK)
- Calorimeter energy scale (e+e- gg)
“
time scale + offset “
- s and pf evaluated (Bhabha KS, KL)
  Start reconstruction and
event classification (~ 1 hour delay)
Efficiencies are evaluated and monitored
using data control samples:
 photon detection efficiency
~ 99% on most of the energy range
+ decrease below 100 MeV
 tracking efficiency
~ 97.5% + decrease at small pT and q
 trigger efficiency
in case of KSKL configuration
if KS triggers  measure KL
trigger efficiency
if KL triggers  measure KS
trigger efficiency
Decay chain used: (same topology 2T + 3 photons / final states different kinematics)
(a) f  hg  p+pp0g  p+p 3g
(b) f  h’g  h p+pg  p+p 3g
 (a) vs. (b)
[N(b) ~ N(a) / 100]
Photon energy spectra
from MC  cut on Eg
(E1, E2 two largest energy
photons)
[MeV]
Selection:
 2 tracks (ET1+ET2<430 MeV) + 3 photons: kin. fit (no mass constraint)
 only (a) and (b) selected
(negligible bkg.)
MC
MC
g spectrum (MeV) for hg
E1 vs E2 (after kin. fit)
g spectrum (MeV) for h’g
E1 vs. E2 for MC h’g
[MeV]
Results on data (17 pb-1)
N(a) = 50210  220
N(b) = 125  13stat +bck
Data
Invariant mass spectrum
of h’g is ok.
E1 vs E2 (after kin. fit)
e(hg)
N(h’g)
R=
x
[MeV]
BR(h  p+pp0) BR(p0  gg)
x
= (5.3  0.5stat  0.4syst) x 10-3
N(hg) e(h’g) BR(h’  p+ph) BR(h  gg)
 aP = (40.0  1.6)o [ qP = (-14.7  1.6)o in the octet-singlet base]
( aP = (39.3  1.0)o world average
[Feldmann Kroll 2002])
BR(f  h’g ) = (6.8  0.6stat  0.5syst) x 10-5
(improve respect to previous measurements)
5.Results on f radiative decays
Mesons below 1 GeV accessible:
f is ~ ss state  G(fMg) probe quark s content of meson M
1.
f  Pseudoscalar + g
 hg
 p0g
 h’g
g
According to quark model:
 assuming: no other content (e.g. gluonic))
p0 = (uu-dd)/2
h = cosaP (uu+dd)/2 + sinaPss
h’ = -sinaP (uu+dd)/2 + cosaPss
f
Meson coupling
to final state
Meson
final
state
Kaon loop
K+KMeson coupling
to KK loop: probe
of s content
 assuming: no OZI-rule violations
g(f  hg) = FscosaVsinaP + FqsinaVcosaP
g(f  h’g) = FscosaVcosaP – FqsinaVsinaP
G(f  h’g)
Kh’
( aV aP = mixing angles in the flavour base)
( Fs Fq = form factors)
R=
= cotg2aP (
)3
G(f  h g)
Kh
 assuming: f = ss state (a =0)
V
(1) R=G(KS  p+p- ) / G(KS  p0p0 )
Motivations:
 First part of double ratio
 Extractions of Isospin Amplitudes and
Phases A0 A2 and d0-d2  consistent
treatment of soft g in KS  p+p- (g)
(PDG data contain ambiguities)
[Cirigliano, Donoghue, Golowich 2000]
Selection procedure:
1. KS tagging
2. KS  p+p-(g)
two tracks from I.P + acceptance cuts.
fully inclusive measurement
(Eg* up to Eg*max=170 MeV)
3.KS  p0p0
neutral prompt cluster
(Eg>20 MeV and (T-R/c) < 5st )
at least 3 neutral prompt clusters
(p0 e+e-g included)
Soft photon emission:
eppg (Eg*) not uniform  correction
Theoretical g spectrum folded with
experimental efficiency
 D = (-3.4 ± 0.1) x 10-3
2. f  Scalar (0++ quantum numbers) + g
 p0p0g
(f0g sg, f0 , s  pp)  5g final state
 p+pg
(
“
)
[f0 I=0, a0 I=1, s I=0]
 2t + 1g final state: huge background from:
ISR (radiative return)
FSR + interference (signal “hidden”)
 hp0g
a0g
a0
 hp)
[ h  gg ]
 5g final state
(40%)
[ h  p0p0p0 ]  9g final state
(32%)
[ h  p+pp0 ]  2t + 5g final state (23%)
Motivations:
f0, a0, not easily accomodated in a qq nonet;
 qqqq states (lower mass) [Jaffe 1977];
 KK molecule (m(f0,a0)~2m(K))
[Weinstein, Isgur 1990];
f  f0g , a0g  sensitive to f0,a0 nature
[Achasov, Ivanchenko 1989]:
g
f
Kaon loop
f0,a0
Final
state