MINOS Cosmic Ray Physics Atmospheric Meson Production Ratios

MINOS Cosmic Ray Physics: Atmospheric Meson Production Ratios Philip A. Schreiner Benedictine University, Lisle, IL USA For the MINOS Collaboration ISVHECRI 2010 1

MINOS The MINOS Collaboration 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 ISVHECRI 2010 Three components: Underground Near Detector at Fermilab Underground Far Detector at Soudan, Minnesota Nu. MI high-intensity neutrino beam 2

The MINOS Underground Detectors Far 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. Near Detector ISVHECRI 2010 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. Detector Dimensions Detector Mass Detector Depth Over. Burden Cosmic Muon Rate Location Near 3. 8 x 4. 8 x 15 m 0. 98 k. Ton ~ 100 m 225 m. w. e. ~ 10 Hz FNAL Far 8 x 30 m 5. 4 k. Ton 730 m 2070 m. w. e ~ 0. 5 Hz Soudan Mine, Minnesota

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 Te. V 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 ISVHECRI 2010 4

MINOS Cosmic Muon papers ISVHECRI 2010 5

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 επ and 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 ISVHECRI 2010 6

Surface Muon Charge Ratio r± fπ = fraction of pions that are positive, f. K = 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 r. K = K+/K- f. K/(1 -f. K) a constant > 1 because leading u or d quarks can give K+ but not KISVHECRI 2010 7

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 ? Ø Rise not due to increase in kaon production Ø Rise due to increased relative contribution of μ’s from K± ISVHECRI 2010 8

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: Ø Depth of 220 mwe. Ø Equal Forward and reverse magnetic field data runs Ø 716 x 106 triggers analyzed. Far Detector: Ø Depth of 2070 mwe. ØEqual Forward and reverse field data runs Ø 68 x 10 6 triggers analyzed ISVHECRI 2010 9

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. ISVHECRI 2010 10

Issues: r± affected by rock d. E/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 ) • Jackson 1998, Phys. Rev. D 017301 • • ISVHECRI 2010 μ+ lose slightly more energy than μComes from a small O(a) effect in ionization differences The surface rμ is higher than the underground rμ by ~0. 5% Correction increases rμ so the true K+/K- is increased 11

Surface Muon Charge Ratio vs. Eμcos(θ) ND is Preliminary PRL 2004 ISVHECRI 2010 12

Charge Ratio Fits ratio MINOS ND, FD MINOS, L 3+C 2004 • rπ = π+/π- fπ/(1 -fπ) 1. 241± 0. 035 1. 224± 0. 003 • r. K = K+/K- f. K/(1 -f. K) 2. 26± 0. 29 2. 28± 0. 06 Notes on Error Bars from above fits: • Results are parameterization dependent • 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 E μcosθ 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 13

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 ISVHECRI 2010 14

Far Detector Daily Muon Intensity Variation for 5 years ISVHECRI 2010 15

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

Formalization for Intensity – Temperature Correlations 17

Effective Atmosphere Temperature • 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 ISVHECRI 2010 18

Temperature-Intensity relationship ISVHECRI 2010 19

MINOS K±/π± Dependence upon αT Using Gaussian errors, a ISVHECRI 2010 minimization to determine ratio 20

MINOS K/π Ratio atmospheric Measurement compared to accelerator measurements ISVHECRI 2010 21

Summary: Fits to Meson production rates in atmosphere from primaries > 7 Te. V/nucleon ISVHECRI 2010 22

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 ISVHECRI 2010 23

Temperature coefficient comparisons (Zenith acceptances differ – so comparison is not precise) ISVHECRI 2010 24

Systematic errors on theoretical parameter inputs parameter Rock map uncertainty 10% 0. 013 Muon spectrum index 1. 7± 0. 1 0. 0031 Kaon critical energy 0. 851± 0. 014 Te. V 0. 0014 Pion critical energy 0. 114± 0. 003 Te. V 0. 0002 ISVHECRI 2010 25

αT measurement depends upon ISVHECRI 2010 26