NKS2 Meeting with Bydzovsky NKS2 Experiment / Analysis Status 2007/11/08 K. Futatsukawa

Comparison -Spectrometer- NKS NKS2 This shows a comparison of the spectrometer between old NKS and new NKS2. The right-hand side is NKS, and the left-hand side is NKS2. We have improved NKS2 by the covering the forward region. Because, the NKS acceptance limits the data taking and comparison with theoretical calculation. . Improved by covering forward region

Comparison -Acceptance- NKS NKS2 0.90 GeV < Eγ < 0.95 GeV 0.90 GeV < Eγ < 0.95 GeV 0.5% 0.5% 1.05 GeV < Eγ < 1.10 GeV 1.05 GeV < Eγ < 1.10 GeV cosθlab cosθlab Here, I will show you a comparison of the acceptance between old and new spectrometer. Left-hand side corresponds to NKS and right-hand side is for NKS2. The detector acceptance is shown by black contour plots. The red contour is corresponding to the K0 cross-section of Kaon-MAID model. The difference of top and bottom is photon beam energy and upper figures are close to the threshold region. The maximum photon energy at the LNS is 1.1 GeV and its region is shown in the lower plots. The old spectrometer have less acceptance against the high energy photon region like this. On the other hand, NKS2 have better coverage as you can see. K0 momentum [GeV/c] K0 momentum [GeV/c] Black contour: Detector Acceptance Red contour: D2 target K0 production cross-section from Kaon-MAID model Monte Carlo simulation

NKS2 Experimental Condition Counter Commissioning Run 2006 6/05 – 6/16 9/25 – 10/03 Deuteron Target Run #photon trigger condition 11/02 – 11/13 2.4×1011 w EV 11/28 – 12/10 6.3×1011 w/o EV 2007 1/15 – 1/27 8.9×1011 w/o EV 6/11 – 7/01 12.7×1011 w/o EV Total 30.3×1011 This is the summary of NKS2 experiment. Four times of the deuterium target experiment was performed. The number of total gamma is 30.3 time 10 11.

Particle Identify (PID) An example from two tracks event Opening angle cut -0.9 < cosqOA < 0.8 is required to reduce e+e- p p+ charge*momentum [GeV/c] red line : p blue line : p p- This Figure is the particle identify. This direction is the beta inverse, and this direction is the particle momentum. Good enough. 1/b

Invariant Mass Spectrum p+p- Invariant Mass K0 pp- Invariant Mass L This is the invariant mass spectrum. The upper figure is pi plus and pi minus combination, the lower figure is pi minus proton conbination. We can see the k0 and lambda peaks.

K0 Momentum Dependence 0.9 < Eg < 1.0 [GeV] Yield Here, I will show the momentum dependence. In the left-hand side gamma energy is from 0.9 to 1.0 GeV, In the right-hand side from 1.0 and 1.1 GeV. If we select the red region, we can get the these distributions. If we chose the blue and green regions, thesis distributions are like these. We can assume the background is these distribution roughly. The momentum dependence after the subtraction of the background is like these. K0 momentum [GeV/c]

K0 Momentum Dependence 1.0% cosθlab 0.5% K0 momentum [GeV/c] Eg = 0.95 GeV Eg = 1.10 GeV 1.0% cosθlab 0.5% K0 momentum [GeV/c] Black contour : Detector Acceptance Red contour : D2 target K0 production cross-section from Kaon-MAID model 0.9 < Eg < 1.0 [GeV] 1.0 < Eg < 1.1 [GeV] In this slide, we will show the momentum dependence after the acceptance correction. These figures are the NKS2 acceptance. The both left and right figure is same. The cross axis is k0 momentum, and the vertical axis is cos theta in the laboratory frame. The red contour plot is k0 distribution from Kaon-MAID model. In the left figure gamma energy is 0.95 GeV, and right one is 1.10 GeV. If cos theta is from 0.9 to 1.0, the momentum dependence is like these red distributions. The left-hand figure is low gamma energy region, and the right-hand figure is high energy region in LNS-Tohoku. If we select that cos theta is from 0.8 to 1.0, we can get the green distribution. K0 momentum [GeV/c]

K0 Angular Distribution 0.9 < Eg < 1.0 [GeV] 1.0 < Eg < 1.1 [GeV] Yield I will show you that angular distribution. Like the momentum dependence, The left-hand side is low gamma energy region, and the right-hand side is high energy region. The upper figure is selected this red region including k0 mass spectrum. The background is estimated from side band. These distribution are blue and green line. The Lower figures is the spectrum after subtraction of the background. cosq

Finish Backup Presentation

K0 Angular Distribution Eg = 0.95 GeV Eg = 1.10 GeV 1.0% cosθlab 0.5% K0 momentum [GeV/c] Black contour : Detector Acceptance Red contour : D2 target K0 production cross-section from Kaon-MAID model 0.9 < Eg < 1.0 [GeV] 1.0 < Eg < 1.1 [GeV] cosqlab

Acceptance Monte Carlo Simulation : Geant4 1.0% 0.5% cosθlab cosθlab Eg = 0.95 GeV 1.0% 0.5% cosθlab Eg = 1.10 GeV cosθlab K0 momentum [GeV/c] Monte Carlo Simulation : Geant4 Generate K0 uniformly in Lab frame, 0 < momentum < 1.0 GeV/c, 0.5 < cosqK0,Lab < 1.0 Use the same analyzer for the experimental data. Analysis efficiencies are included. Double counted efficiencies are revised. K0 momentum [GeV/c] Black contour : Detector Acceptance Red contour : D2 target K0 production cross-section from Kaon-MAID model

Acceptance Projection X Projection Y 0.9 < cosqlab < 1.0 K0 momentum [GeV/c] cosqlab 0.8 < cosqlab < 1.0 K0 momentum [GeV/c]

Comparison –NKS Result- 0.9 < Eg < 1.0 [GeV] 0.9 < cosqlab <1.0 1.0 < Eg < 1.1 [GeV] 0.9 < cosqlab <1.0 This slide shows the result of our data and the theoretical calculations. PH1 and PH2 are calculated by the simple formula mentioned previous slide. SLA and PH1are adjusted by our data in the energy range of 0.9 to 1.0 GeV. PH2 gives inversed distribution to PH1 in the center of mass system. In both energy region, it is found that Kaon-MAID is large and the shape is far from the shape of data. Whereas, by adjusting the parameter, SLA can reproduce the spectrum shape, and PH1 also can. The difference between the shape of the momentum spectra is caused by the angular distribution in the center of mass system, like this. These shows the angular distributions in the center of mass system. If the angular distribution in the center of mass system has the enhancement among cos theta 0 to 1, the shape of momentum spectra becomes like Kaon-MAID or PH2. So, the result favors that the angular distribution in the center of mass frame is backward peak.