1. Study of Forbush decreases with a WC detector Luis Villaseñor in collaboration with Angelica Bahena UMSNH Symposium CINVESTAV-UNAM In memoriam Augusto Garcia ICN, December 1,2009

2. Cosmic rays (1912) Forbush effect (1937)

3. Can we see the Forbush effect with a single WCD? Auger (muons)~ 4% (ICRC 2009) McMurdo (neutrons)~ 15%

4. Detectors  Volume 1m height by 1.15m diameter.  We use a tyvek bag  PMT: EMI 8 in to get  Difuse reflection Two water tanks

5. Detectors Tipical muon Amplitude ~150 mV ~200 MeV Our threshold 22 mV ~0.15 VEM

6. Stopping muon at 0.1 VEM Decay electron at 0.17 VEM = 41 MeV Crossing muon at 1 VEM Alarcón M. et al., NIM A 420 [1-2], 39-47 (1999). Auger, NIM 2006 Water Cerenkov Detector

7. Water Cerenkov Detector

8. H.Salazar and L. Villasenor, NIM 2005 Water Cerenkov Detector

9. Electronics We started with two setups CAMAC Discriminator Amplificator Scalers GPIB LabView

10. Electronics GPS Custom-made ADC Pressure and temperature sensors FPGA + VHDL Serial port, Linux tools

11. Electronics One reason Why We prefered Our custom FPGA-based Electronics Baseline Changed Rate did not Change Because our Thresholds Are anchored To the baseline Inside the FPGA Besides Programming FPGAs is fun!

12. Raw Data

14. Data analysis: Anticorrelation Between R and P Data from October, 2009

15. Data analysis: Anticorrelation Between R and P Data from November, 2009

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17. Data Analysis

18. Corrected Data

19. Comparison with neutron detector data

20. Conlusions Stable operation of WCD FPGA-based electronics performs well Good anti-correlation of rate with atmospheric pressure at the 0.5% level Our periodic variations <~1% Sensitive to variations > 2% We will take data during the upcoming period of solar activity T he answer to our initial question: Yes, provided the sun cooperates