Cosmic Ray Physics with the MINOS Detectors. Jeff de Jong Oxford Particle Seminar Feb 24, 2009

Transcription

1 Cosmic Ray Physics with the MINOS Detectors Jeff de Jong Oxford Particle Seminar Feb 24, 2009

2 A Quick ShoutOut This is a brief summary of alot of work from different people within the MINOS collaboration : Eric,Alec,Brian,Stu,Maury,Giles...(to name but a few) My contribution was completed while at the Illinois Institute of Technology in Chicago Illinois 2

3 Seminar Outline The MINOS detectors. Cosmic Rays & muon production Physics Measurements I.Atmospheric muon charge ratio II.Seasonal variations III.Moon & Sun Shadow > Composition? Summary 3

4 The Near Detector Detector Dimensions : 3.8mx4.8mx15m Detector Mass 0.98 kton Location: Fermilab iron/scintillator tracking calorimeter magnetized 1 steel planes <B>~1.3T Scintillating strips 1.0cm x 4.1 cm (Orthogonal Planes) GPS time stamping to synchronize FD to ND OverBurden Cosmic Muon Rate Minimum Energy Average Muon Energy 225 mwe(95m) 30 Hz ~55 GeV 100 GeV The MINOS detectors were optimized for horizontal neutrino induced muons. Since the planes are oriented vertically, this limits zenith angular acceptance of cosmic muons. 4

5 The Far Detector Detector Dimensions : 8mx8mx30m Detector Mass 5.4 kton Location: Soudan, MN ~ 735 km from Fermilab OverBurden Cosmic Muon Rate Minimum Energy Average Muon Energy ~2100mwe(0.72km) 0.5 Hz ~ 730 GeV ~ TeV range Two identical detectors and two depths, we can probe the same physics process at two different energy scales!! 5

6 Cosmic Ray (Muons) In a nut shell : Earths B Field/IMF to observe the muons underground and from these measurements infer cosmic ray and shower composition Satellite experiments What do we expect? decay to µ's Primaries are mostly protons, so there will be an excess of π+ and K+ (over π,k ) R=N / N Balloon experiments Tend to get more + from Ks than s, therefore the more decayed Kaons in the shower (energy dependent) the higher the charge ratio. 5=5 Muon Rate increases with Temperature as more mesons decay over interact! Muons tend to point in the direction of the primary, and the (different) primaries bend (differently) in the various magnetic fields. Surface Detectors Underground Detectors Note: s are produced in conjunction with s so these measurements should help at ν fluxes, as well as shower modelling. (image borrowed from JLAB) 6

7 Let's get to the Physics 7

8 Atmospheric Muon Charge Ratio A little back story : In 2001 R=1.268 ± p(gev)] ~ Flat to 300 GeV!! (Hebbeker & Timmermans) MINOS Far detector publishes R=1.374±0.004 stat syst A large difference a TeV measurement 8

9 Atmospheric Muon Charge Ratio A little back story : In 2001 R= p(gev)] ~ Flat to 300 GeV!! (Hebbeker & Timmermans) MINOS Far detector publishes R=1.374±0.004 stat syst A large difference a TeV scale measurement Is this a true physical Effect? Is the offset a systematic error? 9

10 Atmospheric Muon Charge Ratio A little back story : In 2001 R= p(gev)] ~ Flat to 300 GeV!! (Hebbeker & Timmermans) MINOS Far detector publishes R=1.374±0.004 stat syst A large difference a TeV scale measurement Is this a true physical Effect? Is the offset a systematic error? (New) Minos Near Detector Result R=1.2703± stat. ± syst. Doesn't appear to be a systematic since the ND result is consistent with previous GeV scale measurements? We made a simple toy model. 10

11 Interpretation of the Charge Ratio Increase The differential muon spectrum (Gaisser's formula) dn de 0.14 E 2.7 = 2 cm sr GeV E cos Z GeV 1.1 E cos Z ~ contribution from Kaons 850 GeV ~ contribution from s If we define f and fk to be the fraction of /K that decay with a detected + then πk model R= N N f 1 = 1.1 E cos Z GeV 1 f 1.1 E cos Z 115GeV f K 1.1 E cos Z 850 GeV f K E cos Z 850 GeV Energy (E,0) always appears in conjunction with cos( Z) Assumes f,f are independent of energy. Does not account for solely energy dependent effects. Best Fit f =0.5488±0.0016, f K =0.7021±

12 Seasonal Variation of the Muon Flux density( ) is proportional to 1/Temperature(T) Fraction of ( /K) that decay (to ) vs interact f i = 1 1 DECAY / INTERACT = 1 1 c E i LIFE / i mi Note the similarity with Gaissers's differential muon spectrum. Problem: the observed muons come from different regions of the atmosphere! Find an Effective Temperature N Stratosphere Temperature T eff = n=0 x n T X n W n W nk N n=0 X n W n W nk weighting weighting How does muon rate change? Troposphere R Ground Level R = T T T 12

13 Seasonal Variation Results Far Detector Near Detector Preliminary Compilation of All T =0.881±0.010 stat ±0.015 syst Seasonal Results Large Fraction of mesons are interacting expect T~1 Large Fraction of mesons already decaying, expect T~0 lim X df i dt = fi T Can also observe sudden stratospheric warmings! 13

14 Sun And Moon Shadow Both the sun and the moon have angular diameters on the order of ½. At any given time we know very accurately where the moon and the sun are. Generally use deficit in muon flux(from the moon or sun direction) to determine Pointing Accuracy of your detector. Both near and far detectors have a pointing resolution of ~ 0.6, optimized using a multi muon sample set. Use the moon(sun) earth distance as a spectrometer positively charged protons will get bent west by ~1.6 /Ep[TeV] (between the earth and moon) There will be a deficit of muons then at 1.6 /Ep [TeV] east if the moon position. Location of other deficits base on charge and mass of other primaries (ie He,CNO,pbar) E (FarDet)~10 TeV, ~ TeV at the Near primary 4 years of data at the far detector(seen here) 14

15 Far Detector 1D Results A 1 Dimensional shadow can be fit to the expression N = 1 R 2 m 2 e average muon flux angular radius of moon Resolution term(from multimuon study) a) detector resolution b) geomagnetic effects c)multiple column scattering sun shadow moon shadow 3x10 5 chance probability this is flat =0.41± x10 4 chance probability this is flat =0.41±

16 Far Detector 2D Results Do a likelihood fit to nbin obs x, y, I =2 i=1 [ N i N i N i ln where: Th obs back N Th =N I s x, y i i Flat background Define the quantity: N Th i ] shadowing strength = x, y, 0 x, y, I s =23.5, 5 moon obs Ni =17.5, 4.3 sun 16

17 Summary Slide Increase in charge ratio at the Far detector is consistent with an increase probability that the muons come from Kaons. Seasonal Variation results are also consistent with expectations linked to detector depth and the assumed K content. Shadows of both the moon and sun can be observed in 1 and 2 dimensions, but deflection is too small for composition measurement. Near Detector should give a better handle due to lower cosmic ray primary energy. 17