MINOS

1. MINOS MINOS Cosmic Ray Physics: Atmospheric Meson Production Ratios Philip A. Schreiner Benedictine University, Lisle, IL USA For the MINOS Collaboration

2. MINOS The MINOS Collaboration • Three components: • Underground Near Detector • at Fermilab • Underground Far Detector • at Soudan, Minnesota • NuMI high-intensity neutrino beam 140 scientists 31 institutions Argonne • Athens • Benedictine • Brookhaven • Caltech • Cambridge • Campinas • Fermilab • Harvard • Holy Cross • IIT Indiana • Iowa State • Lebedev • Livermore Minnesota-Twin Cities • Minnesota-Duluth• Otterbein • Oxford Pittsburgh • Rutherford • Sao Paulo • South Carolina Stanford • Sussex • Texas A&M • Texas-Austin • Tufts • UCL Warsaw • William & Mary

3. The MINOS Underground Detectors Far Detector Near Detector Near and Far Detectors are functionally identical. Consist of 2.54 cm thick octagonal steel plates magnetized with a toroidal 1.2 T field interleaved with planes composed of 4.1 cm wide × 1 cm thick scintillator strips. Alternating U- and V-planes of scintillator are oriented at ±45◦ with respect to the vertical. The ND and FD contains 282/152 and 484/484 steel/scintillator planes. Near Far Detector Dimensions 3.8 x 4.8 x15 m 8 x 8 x 30 m Detector Mass 0.98 kTon 5.4 kTon Detector Depth ~ 100 m 730 m OverBurden 225 m.w.e. 2070 m.w.e Cosmic Muon Rate ~ 10 Hz ~ 0.5 Hz Location FNAL Soudan Mine, Minnesota

4. Cosmic Muon Physics Opportunities • Examine meson production in the atmosphere by primary cosmic rays • Determine the values of the meson production ratios in the • atmospheric showers that produce μ’s with E > 0.78 TeV at surface (Far Detector) • These ratios are somewhat energy dependent, but Feynman scaling • allows them to be approximated as energy independent p+/p-production ratio K+/K- production ratio K±/p± production ratio

5. MINOS Cosmic Muon papers 5

6. Muon Charge Ratio r± Modeling the Muon Intensity Start with a Gaisser’s popular parameterization of muon flux m from p m from K Θ = zenith angle at muon production point επand εK are “critical” energies for π and K decay η proportional to K/π production ratio (assumed E independent) Nμ = positive and negative muons from π and K decay

7. Surface Muon Charge Ratio r± fπ= fraction of pions that are positive, fK = fraction of kaons that are positive Scaling assumed so all meson production ratios are independent of energy. rπ = π+/π-  fπ/(1-fπ) a constant > 1 because more u quarks than d quarks in primaries rK = K+/K- fK/(1-fK) a constant > 1 because leading u or d quarks can give K+ but not K-

8. Equation for Surface Muon Charge Ratio r± • Energy dependence: appropriate variable is not E; instead it is Eμcosθ • What is the cause of the rise of μ+/μ- charge ratio with increasing Eμcosθ? • Rise not due to increase in kaon production • Rise due to increased relative contribution of μ’s from K± 8

9. Measuring the Muon charge Ratio: MINOS Cosmic Muons Triggers • The 2 MINOS underground magnetic calorimeters used • Triggered on atmospheric muons between Fermilab ν beam pulses • Near Detector: • Depth of 220 mwe. • Equal Forward and reverse magnetic field data runs • 716 x 106 triggers analyzed. • Far Detector: • Depth of 2070 mwe. • Equal Forward and reverse field data runs • 68 x 10 6 triggers analyzed

10. MINOS ND, FD charge ratio analysis • MINOS ND & FD analyzed using consistent event selections. • Very tight event selections to ensure correct charge ID. • Geometric mean of ratios used to remove biases due to geometric acceptance, alignment errors, selection cuts. • Requires nearly identical forward and reversed magnetic field live times. • Systematic error bars account for remaining charge randomization. • Simulations only used for guidance with systematic error bars. • Projection of underground value to surface does requires MC simulation.

11. Issues: r± affected by rock dE/dx Differences • Differences in catastrophic energy loss and brem/pairs (which involves μ scattering on nuclei.) • Differences in ionization (which involves μ scattering on e ) • μ+ lose slightly more energy than μ- • Comes from a small O(a) effect in ionization differences • The surface rμis higher than the underground rμby ~0.5% • Correction increases rμ so the true K+/K-is increased • Jackson 1998, Phys. Rev. D 017301

12. Surface Muon Charge Ratio vs. Eμcos(θ) ND is Preliminary PRL 2004

13. Charge Ratio Fits • ratio MINOS ND, FD MINOS, L3+C 2004 • rπ = π+/π- fπ/(1-fπ) 1.241±0.035 1.224±0.003 • rK = K+/K- fK/(1-fK) 2.26±0.29 2.28±0.06 • Notes on Error Bars from above fits: • Results are parameterizationdependent • All variables except Eμcos(θ) assumed energy independent • Muon charge ratio parameterization ignores charm • Using 2 functionally identical detectors, at 2 different mwe depths, • MINOS observes increase in the charge ratio at the deeper detector. • Eμcosθ is the correct variable to understand the energy dependency. • With a straightforward extension of Gaisser’s model, the charge ratio as a function of Eμcosθ • is well explained. • Rise consistent with an increase in fraction of observed μ’s from K decays in the air shower. • Not necessary to have K/π production ratio increase with Eμ

14. Measuring the forward K±/π± production ratio: Muon intensity dependency on atmospheric temperature/pressure • Temperature of upper atmosphere affects height of primary CR interaction. • This height is reflected in the μ intensity underground. • Method: study daily variations of underground μ intensity to obtain relationship • with atmosphere temp. • This relationship yields K/π ratio in the forward region for cosmic primary nucleons

15. Far Detector Daily Muon Intensity Variation for 5 years

16. Soudan Effective Temperature Variations Far Detector Daily Muon Intensity Variations for 5 years 16

17. Formalization for Intensity – Temperature Correlations

18. Teff obtained from temp measurements at 21 atmospheric levels, every 6 hours for 5 years in northern Minnesota • Points are interpolated to Soudan 1  1 grid (latitude & longitude) • Data and interpolation provided by Scott Osprey at European Center • For Medium-Range Weather Forecasts • Modeled temperature coefficient from π and K is Effective Atmosphere Temperature

19. Temperature-Intensity relationship

20. MINOS K±/π± Dependence upon αT Using Gaussian errors, a minimization to determine ratio 20

21. MINOS K/π Ratio atmospheric Measurementcompared to accelerator measurements

22. Summary: Fits to Meson production rates in atmosphere from primaries > 7 TeV/nucleon

23. Acknowledgements We express our gratitude to the many Fermilab groups who provided technical expertise and support in the design, construction, installation and operation of the experiment We thank the crew at the Soudan Underground Laboratory for keeping the Far Detector running amazingly well for many years We gratefully acknowledge financial support from DOE, STFC(UK), NSF and Minnesota DNR

24. Temperature coefficient comparisons(Zenith acceptances differ – so comparison is not precise)

25. Systematic errors on theoretical parameter inputs 25

26. αT measurement depends upon