1 / 14

Measurement of cross section   K + K –

Measurement of cross section   K + K –. M. Martemianov Last results of  (  K + K – ) Method of cross section measurement Selection criteria Radiative correction for cross section Results. 2nd KLOE Physics Workshop, Otranto, 10-12 June 2002.   K + K – cross section.

tavita
Télécharger la présentation

Measurement of cross section   K + K –

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Measurement of cross section   K+ K– • M. Martemianov • Last results of  (  K+ K–) • Method of cross section measurement • Selection criteria • Radiative correction for cross section • Results 2nd KLOE Physics Workshop, Otranto, 10-12 June 2002

  2.   K+ K– cross section Cross section : • trig - trigger efficiency • rec - reconstruction efficiency • geom - geometrical acceptance • L - luminosity rad - radiation coefficient, where '(S) / (S) - measured / real cross section

  3. CMD-2 / SND results World data (obtained in VEPP-2M collider / Novosibirsk) 1995 CMD -2:  = 2001  65  82 nb Total L  300 nb-1 Peak value : 2317 nb New results will come soon 2001 SND :  = 1968  20  140 nb Total L  4400 nb-1 CMD-2 SND

  4. Method for   K+ K– cross section • Method to calculate cross section used on K0 • Two types events are used : • NKK (and) - two of charged kaons has K0 decay and NKK (and) = 2geom (and) trig  2recBR(K0 )2NKK • NKK (OR) - one of charged kaons has K0 decay and N(or)NKK (OR)= 2NKKrec  trig BR(K0 ) [geom (or) (1–BR(K0 ))+geom (and)(1-rec)BR(K0 )] NKK (and) K+ K +  NKK (or) K+ +

  5. Charged kaon selection 1. Kaon tag Rxy(PCA) < 10 cm |Z| < 20 cm 70 MeV/c < P < 130 MeV/c 2. Secondary vertex tag Number of tracks at vertex : 2 Same charge 40 cm < Rxy < 150 cm 180 MeV/c < P (CM of kaon) < 270 MeV/c |pK - psecondary | > 120 MeV/c | pK - psecondary | < 320 MeV/c MC Data P, MeV/c Momenta distribution in the rest frame of charged kaon

  6. K 0 - selection / I • Charged kaon selection • Momenta in the rest frame of kaon and pion hypothesis of secondary particles (P) | P - 205 MeV/c | < 6 MeV/c • E > 25 MeV • E 1+ E 2 > 100 MeV • t1 = t  1 - R1(cl - vertex)/c • t2 = t  2 - R2(cl - vertex)/c • |t1 - t2 | < 3 ns MC Data MeV 0 - mass distribution Meff (MC) = 134.45 MeV Meff (Data) = 133.04

  7. K 0 - selection / II MC Data MC Data E, MeV P, MeV/c Total enegry E+ E0 Missing momenta : PK - P0 - P

  8. Angle distribution / I • In Tag selected events background is below few % level. • The K geometrical acceptance seems well reproduced by MC. • Coefficient is extracted from MC data directly for cross section measurement MC Data K Angle distribution for charged kaons

  9. Angle distribution / II K2 K1 (K1 + K2)/2 NKK / R - function of acceptance (?)

  10. Geometrical acceptance tot 1 tag 2 tag Acceptance Acceptance geom(and) • The number of kaon events NKKis a function of geometrical acceptances and NKK (and) , NKK (or) only • Sample of 50000 events, where no K - decays Acceptance geom(or) Acceptance vs min. number of hits / track R = 0.975

  11. Radiative corrections / I Radiative correction for  - meson peak  e+ K+ (1020) K e • Corrections known with accuracy 0.5 % • Radiative corrections for charged kaons is negligible MeV - peak calculated by BW formula (red) and BW + rad. corrections (blue)

  12. Radiative corrections / II 1+rad 1+rad MeV MeV Radiation coefficient at peak vs beam energy spread Radiation coefficient vs beam energy at beam energy spread 300 keV at peak 1+rad  70.9 %

  13.   K+ K– cross section Results of   K+ K– Integrated luminosity : Lum = 6.331 pb-1 Nkk(or) = 44838 events Nkk(and) = 5065 events Background less than 1 % for double tag and few for single tagged Krad = 1/(1+ rad )  1.4 Nkk = 10117434 events Method takes us :  (  K+ K–) = NKK  Krad /Lum 1598 nb 1.4  2200 nb  (  K+ K–) = NKK/(Lum BR(K0))  3200 nb

  14. Conclusion • Preliminary estimation of (  K+ K–) was performed at the peak of  - meson resonance at high statistics • Obtained result is close to world data • Method of calculation don’t depend from trigger and reconstruction efficiencies • Background to be evaluated • Next step: investigation of  - meson launch resonance shape

More Related