1. Position of the target cell A strange peak in the distribution of e + e - vertices and thoughtless alignment of the target 22 Aug. 2007 H. Kanda

2. Circumstances Sep. 2006: Installation and alignment of the Liq. D 2 Target to the NKS2. Nov. 2006: The first exposure of the Liq. D2 target to the photon beam. Dec. 2006: The second beam time. Dec. 2006: A strange peak in the distribution of the vertex x-position was reported. The temperature sensor-C was suspected as the cause of the peak. Jan. 2007: A stay of the temp. sensor-C was still more bent and its z-position was lowered. Jan. 2007: The third beam time. Aug. 2007: No peak was found in the vertex distribution for the run1150 (Jan. 2007 beam time). Aug. 2007: Detailed size of the photon beam measured by the vertex distribution was reported (H: 3.64 mm, V: 1.67 mm (in Gaussian  )).

3. Peak in vertex distribution Vacuum cell region Opening angle cut -0.9 < cos   < 0.8 is required Decay vertex point [cm] number of counts This distribution is projected on beam axis direction Up: Vertex distribution from Kaneta’s presentation at HNP2007. Right: Magnified view of the peak. Be sure that it’s drawn in the log-scale. Down: Vertex distribution for run1150 from Tsukada’s report in the meeting on 15 Aug. 2007.

4. Bending of a stay of the temperature sensor-C reported by Kawasaki 1/ 11 Taito Kawasaki Replacing the temperature sensor C before after

5. Detailed value of the beam size Reported by Tsukada in the meeting last week. The profile of the photon beam measured by the vertex distribution was smaller than the known value of 5 mm in Gaussian . Run1150

6. Sensor position was really bad? Mmm, by seeing the first photograph shown by Kawasaki, the position of the sensor-C was not so close to the center of the photon beam. Moreover, the vertical size of the beam is much smaller than our old knowledge. If the sensor-C before bending overlaps with the photon beam, the shell of the new cell with smaller diameter might be hit by the beam. The beam profile was superposed to the photograph.

7. Target vertical position The vertical position of the target was fixed by Kanda on 25 Sep. 2006, using the designed value of the distance between the lower edge of the aluminum pipe of the cryostat and the center of the cell: 105 mm. The center of the cell is on the beam level in the room temperature. The lower edge of the aluminum pipe = The shoulder of the CFRP vessel. vertical distance from the beam level No care was paid to the thermal expansion of the objects inside the cryostat..!!

8. Design of the cryostat (in the room temperature) The cell in this drawing is shown as a simple rectangle. However its dimension is the same as the real cell.

9. Designs of the cell and the CFRP vessel (in the room temperature)

10. Thermal expansion of materials The coefficient of the thermal expansion (CTE) of usual metals in the room temperature is positive and typically 20 ppm per Kelvin. Decrease of the temperature by 300 K results 6000 ppm decrease of a length. A1.5m metal rod shrinks by 9 mm. The CTE is different with respect to the temperature. as shown in the right figure. Integration by temperature is needed for the estimation of the cumulative contraction of the material.

11. Contraction of the materials inside the cryostat Changed to copper linear temperature distribution was assumed

12. The beam and the cell Before bending Beam was hit on the sensor. Overlapping region was from 2 to 3 sigma of the beam profile. The material of the sensor can is copper and filled with epoxy resin. Its effect as the electromagnetic and hadronic target should be estimated. After bending Beam is not hit on the sensor. Anyway, thickness of the target is different from the nominal value. Estimation of the thickness and the effective luminosity is also needed.

13. Lakeshore Cernox sensor package Adapter material :Gold-plated cylindrical copper canister, BeO header, Stycast® epoxy Leads:Four 32 AWG × 15 cm (6 in) long (Rox™: Two 32 AWG × 15 cm [6 in] long) Lead material: Phosphor bronze insulated with polyimide (Rox™: copper insulated with Formvar® ) Mass:AA canister (empty): 0.091 g B Canister (empty): 0.080 g Once sensors are installed, total mass increases to 0.197 g to 0.416 g. Refer to individual sensor specifications. Limitation:The epoxy limits the upper useful temperature of this configuration to 400 K

14. Conclusion The vertical position of the target center is currently 8.3 mm higher than the beam level. We have to elevate the target by 8.3 mm. The new cell with smaller diameter can be safely used as the target. I’m very sorry for this carelessness.