Biagio Di Micco  mass measurement Systematics on   mass measurement Biagio Di Micco

 mass measurement What we bless... The results actually presented at conferences have been blessed more than one year ago; Until now we preferred to not give further preliminary result to give directly the final result; In this way, large part of the work on systematic could not be shown until now. We are blessing all this work and we can discuss if give another preliminary result; Main part of these plots come from KLOE Memo n. 333

Biagio Di Micco  mass measurement Motivation M  = ( ± ± 0.032) MeV/c 2 Reaction used: p + d → 3 He +  High discrepancy with NA48! Using   3   from     p →  n : M  = ( ± ± ) MeV/c 2 [ A, Lai et al., Phys. Lett. B 533 (2002) 196] The most precise measurements differ by 8s GEM is in good agreement with old measurements GEM result:

Biagio Di Micco  mass measurement Method and selection. f  hg (h  gg) f  p 0 g (p 0  gg) A kinemati fit is performed imposing energy-momentum conservation and time of flight of photons the energy momentum conservation imposes 4 constraints the energies of the three photons are over constrained and determined by the angles through the kinematic fit. h mass p 0 mass |t – r/c | < min(5  t,2ns) 50  <   < 130  the kinematic fit is performed on all combination and that with the smallest c 2 is retained. Selection c 2 < 35 At least 3 photons with the requirements: 3g final state

Biagio Di Micco  mass measurement 5 Measurement method constraints equation ● energy-momentum conservation ● t-r/c of clusters ● cluster position x,y,z ● cluster energies ● cluster times from e + e -  e + e ev./run  = 3 MeV/c 2  = 39 MeV/c 2 before kin. fit after kin. fit the kinematic fit squeeze the distribution because of the very good angular resolution.  = 3 MeV/c 2 ●  s ● momentum ● vertex position measured quantities

Biagio Di Micco  mass measurement Dalitz plot The photons are ordered according their energies p0p0  2 < 35 DATA Accepted region E 1 < E 2 < E 3  cut h p 0 cut signal region

Biagio Di Micco  mass measurement DATA MC Fit of the gg invariant mass double gaussian for  0 single gaussian for  Fit to the invariant mass distribution

Biagio Di Micco  mass measurement Cuts Dalitz plot cut c 2 photon angle dependence azimuthal and polar angle; vertex position vertex position determination; DC – EMC global misalignment calorimeter energy response energy scale knowledge deviation from linearity fit distortion sqrt(s) systematic checks

Biagio Di Micco  mass measurement Dalitz cut systematic The cut on the Dalitz produces a small distortion on the invariant mass distribution that shifts the measured mass. The distortion is null in the limit of infinite resolution and can be easily corrected using MC.  The effect is evaluated using a toy MC that just generate  decays with a gaussian mass spectrum with  (DATA)

Biagio Di Micco  mass measurement Dalitz cut correction - slope 13 keV residual systematic corrected Toy MC Dalitz m MeV DATA 200 keV variation

Biagio Di Micco  mass measurement Dalitz cut correction - constant 11 keV systematic rms of the points without correction. mhmh MeV

Biagio Di Micco  mass measurement p 0 case M p MeV Slope cut Constant cut

Biagio Di Micco  mass measurement c 2 cut

Biagio Di Micco  mass measurement Angular dependence The 3 photons are boosted back in the  rest frame. The normal to the plane of the 3 photons is evaluated. vertical line   photon plane 15 keV rms normal 10 keV rms

Biagio Di Micco  mass measurement A sample of      has been used to determine shifts in the vertex position and displacement between DC and EMC. ++   The p + p - vertex is compared with that coming form e + e -  e + e -. The tracks are extrapolated from the vertex to the calorimeter, and compared with the cluster position. ++ Minimum approach point Vertex position and DC-EMC alignment

Biagio Di Micco  mass measurement Mis-determination of the I.P x   x eeee y   y eeee z   z eeee We keep the vertex from the tracking algorithm and compare it with the ee values event by event 2 normal dist. 1 normal distr. 2 normal dist.

Biagio Di Micco  mass measurement The standard deviation respect to the zero value is taken as systematic displacement as a function of run n.

Biagio Di Micco  mass measurement 2002 EMC-DC displacement ++  x y z

Biagio Di Micco  mass measurement Global systematic Uncertainty on the mass values (fractional error)

Biagio Di Micco  mass measurement Energy response linearity deviation are 2% at most. Applying these correction we find: energy scale  m/m = 8  (4 keV) lin. dev.  m/m = 7  (4 keV) E clu = 0.994xE true – 0.2 MeV The same ppg sample can be used to check the energy response of the calorimeter, comparing the g energy evaluated from the pp tracks with the cluster energy. Different approach using f  p + p - p 0 (p 0  gg) The same result in the overlapping region (different g energy allowed by the kinematics)

Biagio Di Micco  mass measurement Global check of the method M fit = M input + (41 ± 3) keV/c 2    n.d.f  50pb -1 for each point linearity is perfect. A correction for the constant term is needed. To check possible distortions due to the algorithm itself. m  fit MeV

Biagio Di Micco  mass measurement Correction source The correction comes from a distortion of the energy distribution respect to the true value DUMMY (smearing of the true MC informations) GEANFI (Efit – Etrue)/s -(Efit-Etrue)/s This asymmetry is able to produce 30 keV correction on the mass out from the blessing

Biagio Di Micco  mass measurement GEANFI DUMMY SMEARING t=(Efit – Etrue)/s This effect produce a correction of -52 keV, to be conservative we assume 26 keV error for the moment. out from the blessing

Biagio Di Micco  mass measurement We can compute Smearing according the previous distribution. Dm h  30 keV

Biagio Di Micco  mass measurement Unluckily the residuals are not sensitive to these distortions. DATA MC-DUMMY GEANFI x y z E t out from the blessing

Biagio Di Micco  mass measurement Systematic summary p fit dist.

Biagio Di Micco  mass measurement Fit quality (data sample divided in 8 periods) hp0p0

Biagio Di Micco  mass measurement Fit results

Biagio Di Micco  mass measurement sqrt(s) correction The mass shows an high sensitivity to the sqrt(s) value.  m   m  ×  m   m  × 10 -3

Biagio Di Micco  mass measurement sqrt(s) determination The absolute scale of the  s is obtained fitting the cross section e + e -  K s K L (f line shape). The fit takes into account the ISR effect and the phase space factor of the KK couple. m f (CMD-2) = ± ± MeV The ratio m f (CMD-2)/m f (KLOE) is used to set the absolute  s scale.

Biagio Di Micco  mass measurement sqrt(s) not affected estimate: D PDG = 1s

Biagio Di Micco  mass measurement p 0 gg 2005 m(h  p 0 gg) Br(    stat  syst    Using the Br evaluated on 2002 data. ½ 2005 statistics 600 pb -1 MC shape from rad04 bkg  1s signal 434 pb -1

33 Results and systematics Systematic due to the vertex position determination have been also evaluated, the sqrt(s) is calibrated by fitting the  line shape. M(  0 ) = (  6 stat  30 syst ) keV M(  0 ) PDG = (  0.6 ) keV  NA48 compatibility: 0.24   Independent measurement with the        decay mode in progrees: m       MeV/c   very preliminary fully in agreement with the  channel  M(  ) = (  5 stat  69 syst ) keV KLOE PRELIMINARY m(f) = ± ± CMD-2 Phys. Lett. B578, 285 the energy calibration has been determined using      and e + e -  events, the calorimeter calibration is know at better than 2%  m/m = 11  (6 keV) on the  mass. radiative return and threshold effects included in the fit

Results and systematics Systematic due to the vertex position determination have been also evaluated, the sqrt(s) is calibrated by fitting the  line shape. M(  0 ) = (  6 stat  30 syst ) keV M(  0 ) PDG = (  0.6 ) keV  Systematics dominated by √s knowledge  NA48 compatibility: 0.24   Cross check with  →       decay mode: m       MeV/c  M(  ) = (  5 stat  69 syst ) keV KLOE PRELIMINARY m(f) = ± ± CMD-2 Phys. Lett. B578, 285