1. Recent results from KLOE Cesare Bini Universita’ “La Sapienza” and INFN Roma 1.The KLOE physics program 2.The KLOE detector 3.Status of the experiment 4.Results on neutral kaon decays 5.Results on  radiative decays 6.Conclusions and perspectives

2. 1. The KLOE physics program. e + e   W = m  = 1019.4 MeV    b Decay channels  K + K  = 49.2% Charged Kaon decays + CP/CPT tests  K 0 K 0 = 33.8% Neutral Kaon decays + CP/CPT tests (  ’ /  )        = 15.5% 3 pion decay   (  shape parameters)   = 1.3% Radiative decays: pseudoscalar:  physics     = ~10 -3 “   ’  = ~10 -4 “  pseudoscalar mixing angle   = ~10 -4 scalar  f0     = ~10 -4 “  a0  e + e  = ~10 -4 Conversion decays: transition form factor F     e + e  = ~10 -5 “ “ F  e + e        Initial state radiation   (e + e       ) 2m  < W < m   e + e   around  peak (energy scan)   resonance parameters

3. 2. The KLOE detector : Drift chamber Calorimeter (Pb-scint.fib.) Magnetic field = 0.56 T Drift chamber: Large volume d=4m l=3.3m He – Isob 90-10 gas mixt. Momentum resolution  p/p < 0.4% Calorimeter: Energy resolution:  /E = 5.4% /  (E(GeV)) Time resolution  t = 55 ps /  (E(GeV))  40 ps (cal.)  120 ps (coll.time)

4. Present day performance: peak average L(cm  2 s  1 ) 5·10 31 3.5·10 31  day L dt (pb  1 ) 3 1.8 3. Status of the experiment Data taken from april 1999 to december 2001~ at  peak + 1 energy scan Analysis status: 2000 data ~completed (25 pb -1  7.5 x 10 7  ) 2001 data in progress (190 pb -1  5.7 x 10 8  ) All results are still preliminary

5. 4.Results on Neutral Kaon decays Neutral kaons produced in a pure quantum J PC = 1  state: p K = 110 MeV S = 6 mm L = 3.5 m  Tagging: pure K S and K L beams  analysis of kaon decays  double ratio  (  ’ /  )  Interferometry studies Example of   K S K L        

6. K S tagging by identification of K L interacting in the EmC (“K L crash”) [ ~50% of K L ]  Selection cuts:  E clus > 200 MeV  |cos(  clus )| < 0.7  0.1950     0.2475 (   = K L velocity in the  rest frame)  Position of the K L  K S momentum Tagging efficiency  tag ~ 30% K S tagging by identification of K L interacting in the EmC (“K L crash”) [ ~50% of K L ]  Selection cuts:  E clus > 200 MeV  |cos(  clus )| < 0.7  0.1950     0.2475 (   = K L velocity in the  rest frame)  Position of the K L  K S momentum Tagging efficiency  tag ~ 30%  * distribution of “K L crash” Example of   K S K L      “crash” KLOE has now about 6 10 7 tagged K S. All channels are accessible. Results from 2000 data (5.4 10 6 tagged K S ) on: (1) R=  (K S   +  - ) /  (K S   0  0 ) (2) BR(K S    e  )

7. (1)R=  (K S   +  - ) /  (K S   0  0 ) Motivations:  First part of double ratio  Extractions of Isospin Amplitudes and Phases A 0 A 2 and  0 -  2  consistent treatment of soft  in K S   +  - (  ) (PDG data contain ambiguities) [Cirigliano, Donoghue, Golowich 2000] Selection procedure: 1. K S tagging 2. K S   +  - (  ) two tracks from I.P + acceptance cuts: fully inclusive measurement (E   up to E   max =170 MeV)   (E  *) from MC  folded to theoretical  spectrum  correction  = (-3.4 ± 0.1) x 10 -3 3.K S   0  0 neutral prompt cluster (E  >20 MeV and (T-R/c) < 5  t ) at least 3 neutral prompt clusters (  0  e + e -  included)

8. Result: N ev (K S   +  - ) = 1.098 x 10 6 N ev (K S   0  0 ) = 0.788 x 10 6 R = 2.239 ± 0.003 stat ± 0.015 syst  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 E   cut ) With 2001 data (180 pb-1) improvement on:  absolute scale  tagg.eff. Bias  statistics of control sub-samples  E   spectrum

9. (2) BR(K S    e  ) Motivation:  If (CPT ok).AND. (  S=  Q at work):  (K S    e  ) =  (K L    e  ) BR(K S    e  ) = BR(K L    e  ) x (  L /  S )  = ( 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     “background”)   time of flight ( electron vs pion)   final signal variable = E miss -|p miss |  BR evaluation:   normalization to K S   +   (  (BR)~0.5%)   both charge states are considered  (well separated  charge asymmetry) ToF selection illustrated for MC: 1. K S   +   MC events 2. K S    e  MC events

10. Result:  N ev (K S    e   = 627 ± 30 [after the fit, residual background subtraction is included] BR(K S    e  ) = (6.79 ± 0.33 stat ± 0.16 syst ) x 10 -4  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% BR(K S    e  )

11. 5.Results on  radiative decays   Pseudoscalar +          ’  According to quark model:  assuming: no other content (e.g. gluonic))  0 = (uu-dd)/  2  = cos  P (uu+dd)/  2 + sin  P ss  ’ = -sin  P (uu+dd)/  2 + cos  P ss  assuming:  = ss state (  V =0)  assuming: no OZI-rule violations g(    ’  ) = F s cos  V cos  P – F q sin  V sin  P g(    ) = F s cos  V sin  P + F q sin  V cos  P (  V  P = mixing angles in the flavour base) ( F s F q = form factors)  (    ’  ) K  ’ R = = cotg 2  P ( ) 3  (     ) K 

12. Decay chain used: (same topology 2T + 3 photons / final states different kinematics)  (a)                   (b)    ’               Selection:  2t (E T1 +E T2 <430 MeV) + 3  : 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  13 stat +bck Invariant mass spectrum of  ’  BR(    ’  ) R = = (5.0  0.5 stat  0.3 syst ) x 10 -3 BR(    )   P = ( 40.8  1.7) o [  P = (-13.9  1.7) o ]  P = ( 39.3  1.0) o J/  decays and others [Feldmann Kroll 2002]  BR(    ’  ) = (6.5  0.6 stat  0.4 syst ) x 10 -5

13.     Scalar (0 ++ quantum numbers) +  [f 0 (980) I=0, a 0 (980) I=1]        (f 0  , f 0,    )  5  final state        (  “ )  2t + 1  final state: huge background from: ISR (radiative return) FSR + interference (signal “hidden”)      a 0  a 0   ) [    ]    5  final state (40%) [          ]    9  final state (32%) [         ]  2t + 5  final state (23%) Motivations: f 0, a 0, not easily interpreted as qq states; other interpretations suggested:  qqqq states (lower mass) [Jaffe 1977];  KK molecule (m(f 0,a 0 )~2m(K)) [Weinstein, Isgur 1990];  f 0 (980), a 0 (980) and   lowest mass scalar qq nonet [Tornqvist 1999]   f 0 , a 0   sensitive to f 0,a 0 nature [Achasov, Ivanchenko 1989]: phenomenological framework (kaon loop model)  coupling constants g(  KK) from  (   K + K - ) g(f 0 KK) g(a 0 KK) f 0, a 0 model g(f 0  ) g(a 0  ) M(     ) M(  ) spectra f0,a0f0,a0 Kaon loop final state  radiative 

14.        Main background sources (5  final states): e + e    0              Other background sources (not 5  final states):       or          Selection procedure:  5 prompt  E  > 7 MeV  kinematic fit (without mass const.) Result: N ev = 2438  61  BR(        )=(1.09  0.03 stat  0.05 syst )x10 -4 CMD-2 (0.92  0.08  0.06)x10 -4 SND (1.14  0.10  0.12)x10 -4 Fit to the M     spectrum (kaon loop): contributions from   f 0     + “strong” negative interference negligible contribution              Fit results: M(f 0 ) = 973  1 MeV g 2 (f 0 KK)/4  = 2.79  0.12 GeV 2 g(f 0  ) /g(f 0 KK) = 0.50  0.01 g(  ) = 0.060  0.008 BR(   f 0        ) = (1.49  0.07)x10 -4

15.      Measured in 2 final states: (Sample 1)    (5  )       is the main background  5  selection (see      ) + kinem. fit (Sample 2)         (2t + 5  )  Negligible bckg with the same topology: e + e    0         2t + 4      K S K L (K L prompt decay) 2t + 4/6   2t + 5  selection + kinem.fit Results: (Sample1) N ev = 916 N bck = 309  20  BR(      ) = (8.5  0.5 stat  0.6 syst )x10 -5 (Sample2) N ev = 197 N bck = 4  4  BR(      ) = (8.0  0.6 stat  0.5 syst )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 M   spectra: dominated by   a 0  negligible            Fit results: M(a 0 ) = 984.8 MeV (PDG) g 2 (a 0 KK)/4  = 0.40  0.04 GeV 2 g(a 0  ) /g(a 0 KK) = 1.35  0.09  BR(   a 0      ) = (7.4  0.7)x10 -5

16. Interpretation of KLOE results on scalars (within the context of kaon-loop framework): (preliminary) parameter KLOE result 4q model qq(1) model qq(2) model g 2 (f 0 KK)/4  (GeV 2 )  2.79  0.12 “super-allowed” “OZI-allowed” “OZI-forbidden” g(f 0  ) /g(f 0 KK) 0.50  0.01 0.3-0.5 0.5 2 g 2 (a 0 KK)/4  (GeV 2 )  0.40  0.04 “super-allowed” “OZI-forbidden” “OZI-forbidden” g(a 0  ) /g(a 0 KK) 1.35  0.09 0.91 1.53 1.53  4q doesn’t describe a 0 parameters;  4q compatible with f 0 parameters;  f 0 /a 0 ratio sensitive to isospin mixing [Close Kirke 2001] : BR(   f 0  ) g 2 (f 0 KK) = 6.0  0.6 ; = 6.9  1.0 BR(   a 0  ) g 2 (a 0 KK) if F f0 (R) = F a0 (R)   S = (47  2) o [no isospin mixing   S = 45 o ] f 0 = ss f 0 = (uu+dd)/  2 a 0 = (uu-dd)/  2 a 0 = (uu-dd)/  2

17. 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: K S decays  radiative decays improve previous “PDG” knowledge  Analysis of 2001 data (190 pb -1 ) in progress. Expected new results will be: rare K S decays [      ,  , limits on  3  ] K L decays [  ,      ….] K  decays  decays (6 x10 6  produced) [chiral perturbation theory checks] hadronic cross-section  (e + e       ) 2m  < W < m   Data taking 2002 starting now  500 pb -1 realistic by end of the year

18. Detector calibrated on-line (run by run ~ ½ hour): - Drift Chamber s-t relations “ momentum scale (M K ) - Calorimeter energy scale (e + e -   ) “ time scale + offset “ -  s and p  evaluated (Bhabha K S, K L )   Start reconstruction and event classification (~ 1 hour delay)

19. 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 p T and   trigger efficiency in case of K S K L configuration if K S triggers  measure K L trigger efficiency if K L triggers  measure K S trigger efficiency

20. Decay chain used: (same topology 2T + 3 photons / final states different kinematics)  (a)                   (b)    ’              MC Selection:  2 tracks (E T1 +E T2 <430 MeV) + 3 photons: kin. fit (no mass constraint)  only (a) and (b) selected (negligible bkg.) [MeV] MC E 1 vs E 2 (after kin. fit) [MeV]  (a) vs. (b) [N(b) ~ N(a) / 100] Photon energy spectra from MC  cut on E  (E 1, E 2 two largest energy photons)  spectrum (MeV) for   spectrum (MeV) for  ’  E1 vs. E2 for MC  ’ 

21. Data E 1 vs E 2 (after kin. fit) [MeV] Results on data (17 pb -1 ) N(a) = 50210  220 N(b) = 125  13 stat +bck Invariant mass spectrum of  ’  is ok. N(  ’  )  (  ) BR(         ) BR(      ) R = x x = (5.3  0.5 stat  0.4 syst ) x 10 -3 N(  )  (  ’  ) BR(  ’       ) BR(    )   P = (40.0  1.6) o [  P = (-14.7  1.6) o in the octet-singlet base] (  P = (39.3  1.0) o world average [Feldmann Kroll 2002])  BR(    ’  ) = (6.8  0.6 stat  0.5 syst ) x 10 -5 (improve respect to previous measurements)

22. 5.Results on  radiative decays   Pseudoscalar +          ’  Mesons below 1 GeV accessible:  is ~ ss state   (   M  ) probe quark s content of meson M Meson final state Kaon loop K + K -   Meson coupling to KK loop: probe of s content Meson coupling to final state According to quark model:  assuming: no other content (e.g. gluonic))  0 = (uu-dd)/  2  = cos  P (uu+dd)/  2 + sin  P ss  ’ = -sin  P (uu+dd)/  2 + cos  P ss  assuming: no OZI-rule violations g(    ) = F s cos  V sin  P + F q sin  V cos  P g(    ’  ) = F s cos  V cos  P – F q sin  V sin  P (  V  P = mixing angles in the flavour base) ( F s F q = form factors)  assuming: f = ss state (  V =0)  (    ’  ) K  ’ R = = cotg 2  P ( ) 3  (     ) K 

23. (1)R=  (K S   +  - ) /  (K S   0  0 ) Motivations:  First part of double ratio  Extractions of Isospin Amplitudes and Phases A 0 A 2 and  0 -  2  consistent treatment of soft  in K S   +  - (  ) (PDG data contain ambiguities) [Cirigliano, Donoghue, Golowich 2000] Selection procedure: 1. K S tagging 2. K S   +  - (  ) two tracks from I.P + acceptance cuts. fully inclusive measurement (E   up to E   max =170 MeV) 3.K S   0  0 neutral prompt cluster (E  >20 MeV and (T-R/c) < 5  t ) at least 3 neutral prompt clusters (  0  e + e -  included) Soft photon emission:   (E  *) not uniform  correction Theoretical  spectrum folded with experimental efficiency   = (-3.4 ± 0.1) x 10 -3

24.     Scalar (0 ++ quantum numbers) +  [f 0 I=0, a 0 I=1,  I=0]        (f 0  , f 0,    )  5  final state        (  “ )  2t + 1  final state: huge background from: ISR (radiative return) FSR + interference (signal “hidden”)      a 0  a 0   ) [    ]    5  final state (40%) [          ]    9  final state (32%) [         ]  2t + 5  final state (23%) Motivations: f 0, a 0, not easily accomodated in a qq nonet;  qqqq states (lower mass) [Jaffe 1977];  KK molecule (m(f 0,a 0 )~2m(K)) [Weinstein, Isgur 1990];   f 0 , a 0   sensitive to f 0,a 0 nature [Achasov, Ivanchenko 1989]: f 0,a 0  Kaon loop Final state 