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n Flux Measurements in the NuMI Beam

n Flux Measurements in the NuMI Beam. Sacha Kopp University of Texas at Austin on behalf of the MINERvA Collaboration. What are the challenges?. Experiments limited by statistics knowledge of flux f ( E n ). You Thought You Wanted… f n ( E n ). BUT.

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n Flux Measurements in the NuMI Beam

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  1. n Flux Measurements in the NuMI Beam Sacha Kopp University of Texas at Austin on behalf of the MINERvA Collaboration

  2. What are the challenges? • Experiments limited by • statistics • knowledge of flux f(En)

  3. You Thought You Wanted…fn(En) BUT What You Really Wanted…fn(xF,pT) LE BEAM pME BEAM pHE BEAM Pz (GeV/c) Pz (GeV/c) Pz (GeV/c)

  4. Why Do I say fn(xF,pT)?! • It is the dominant uncertainty in predicting the neutrino flux. • Calculating the fn(En) requires of • particle production off the target • ray tracing through beam optics • As demo, ab initio flux for NuMI compared to MINOS data. Flux error bars dominated by particle production off the target (calculated prior to tuning to nu data). “High” Energy Beam Setting “Medium” Energy Beam Setting “Low” Energy Beam Setting MINOS Data Calculated n flux

  5. Compare Hadron Production Models A perpexing situation for a poor experimentalist… Fluka2001 Fluka2005 MARS–v.14 MARS–v.15

  6. A Two-Part Proposal to Determine Beam Flux Hardware (extra targets) Dedicated Running For Special Configurations The “Two Buddha’s” Near Sensoji Temple, Asakusa, Tokyo

  7. Data Sets for Flux Determination • Special runs to constrain beam energy spectrum • Vary target position and horn current • 3-5 ton detector fiducial mass • Total ~ 1020 POT before and after “ME Config” for these studies

  8. Hardware Requirements (I) Drop-shaft from surface • Move horn 2 to ME setup • Extend the stripline • Switch to ME target • Fixed location upstream • Target doesn’t fit into horn • We want to delay the 2nd part power supply for horns target pile re-circulating air cooling system pre-target beamline target hall hot work cell Target

  9. Hardware Requirements (II) • After NOvA upgrades target motion will no longer be possible • Required special module -- requires lots of moving parts (deemed risky) • Module experiences too much thermal motion under high heat load. • The loss of this module removes ability to flexibly change En • MINERvA requests that Lab provides one of these + spare for our studies. • Could be useful to NOvA too! They need a spare (backup) target! Target/Baffle Carrier Allows for 2.5 m of target motion to vary the beam energy Baffle Target

  10. Hardware Requirements (III) • Target will be re-designed for for NOvA • Still 6.4mm wide, but not as tall • No longer fits inside horn for LE config • We therefore request • a fresh LE target to be used for our first set of test runs • a spare LE target to ensure success of test runs after ME switch (could be used as spare for NOvA, too).

  11. Past Techniques Used to Wrestle with Beam Flux Neutrino data Muon Monitors Hadron Production Experiments High School Sumo Championships Sumo Hall, Ryōgoku, Tokyo, 5 Aug. 2007

  12. FNAL NBB Fluxes came from these

  13. In situ Muon Monitor Flux • CERN PS • CERN WANF • IHEP • FNAL E616 • FNAL NuMI • Typical ~20%

  14. NuMI mMon Flux • Measurement of of hadron flux using mMon event rates (no error from n x-sec) • L. Loiacono, PhD thesis • 20% errors

  15. External Production Exp’t • Flux prediction based on HARP. • As a check: compare the HARP flux to QEL events. • Scale flux by 1.21! A. Aguilar et al., arXiv:0806.1449 MiniBooNE • What about K2K?! Never see their plot!

  16. … and yet … • reconciling the MiniBooNE event rate with HARP flux • Consistent within errors • Possible shift?

  17. In situ Flux Using Neutrinos P. Astier et al., Nucl. Instr. Meth. A 515 (2003) 800. NOMAD • Also see papers by • L. Ahrens et al, Phys. Rev. D 34, 75 - 84 (1986) • K. McFarland, et al., arXiv:hep-ex/9806013

  18. NuMI Flux Tuning • Fit all 7 beam runs. • Fit νμ and νμspectra • But uses inclusive events! Phys. Rev. D77, 072002 (2008). • To be replicated by MINERvA using QELs

  19. The Call of the Mermaid Does any one recall the fate of the person that answers the mermaid’s call? “I’ll just let [Harp/NA69/NA49/MIPP/SPY] solve my problems” -- Hans Christian Anderson

  20. Data Upon Which Models are Based NuMI LE Beam Atherton 400 GeV/c p-Be Barton 100 GeV/c p-C SPY 450 GeV/c p-Be pT (GeV/c) NuMI HE Beam p (GeV/c)

  21. Modern Data Sets are $%#&! Good! ds/dpT (mb/GeV/c) • Modern data sets better than original ‘beam surveys’ • single particle detection • particle ID • large acceptance • So can’t we just use this to map fn(xF,pT)?? eg: C. Alt et al, Eur.Phys.J.C49:897-917,2007 pT (GeV/c)

  22. No! (1) Thick Target Effects • Most ptcle production exp’ts on thin targets • Nu production target ~ 2lint • Reinteractions! • 20-30% effect MiniBooNE J-PARC CNGS NuMI figure courtesy Z. Pavlovic

  23. No! (2) In-beam variations • Temperature in NuMI target hall varies by 8°C as beam power cycles. • Causes change in horn current ~1 kA • Observe direct variation in beam flux (mMons) • Thermal variations in your beam MC? NuMI-only NuMI-Collider Combined mode figure courtesy L. Loiacono

  24. No! (3) Beam Degradations? Each data point is one month’s data • Started after installation of new target. • Have ruled out horns (swapped) • Have ruled out He leak in decay volume • Problem mitigated when swapped in new target Events / 1016POT / GeV figure courtesy M. Dorman Neutrino Energy (GeV)

  25. CNGS: Earth B Field?! Neutrino Focus p+ Anti-neutrino Focus p- They See shift of 6.4 cm (consistent with 0.3 Gauss) figure courtesy E. Geschwendtner

  26. A Cautionary Tale • CERN PS team did particle prod @ IHEP J.V. Allaby, et al., Phys. Lett. 29B 48 (1969) • In-situ flux using mMons suggested X2 off?! D. Bloess, et al, CERN-69-28 (1969), Nucl. Inst. Meth. 91 (1971) 605. • Particle production round two – ok to 15% J.V. Allaby, et al., CERN-70-12.

  27. MIPP Data Not Currently Competitive • MIPP uncertainties were bigger than the 5% uncertainty from the MINOS nu data fit (backgrounds, statistics, etc) • Must improve by factor 9 in statistics and extend (xF,pT) J. Paley, NuFact07

  28. Could MIPP Provide a Stronger Measurement? We would not accept a MIPP-like measurement alone. MIPP provides a MC input, not a measurement of the nu flux for the experiment! MIPP data feeds into our MC, just like the muon lifetime, K BR’s, etc. It provides no handles that our MC is right (real life variations and uncertainties). A cross section experiment like MINERvA must have in situ measurement Other experiments have all made statements like “Using HARP/MIPP/SHINE, we will measure sn to 5%.” These are strong promises! Past cross section experiments measured fluxes (NBB experiments like CCFR, CHARM/CDHS). Others are normalized to these. Biggest uncertainties in cross section measurements from WBB’s are always the flux. MIPP and E938 are complex experiments! Backgrounds to the desired particle species (eg K/pi) are substantial Kinematic coverage relevant for a neutrino beam has never been achieved. We demonstrated better coverage of (xF,pT) range in MINOS in situ data At the very least, we must pursue both in situ and external (MIPP-like) experiments!

  29. The Five Foundations of n Beams 5-story pagoda of Sensoji Temple, Asakusa, Tokyo

  30. Neutrino Beams 101 p + A→p+ + X • Feynman scaling in xF ~ pL/p0 • No scaling for • ‘Cocconi divergence’ • Tell me what p you want, I’ll tell you what angle to focus. p proton pT p0 pz q

  31. Neutrino Beams 102 q n p • ‘Cocconi divergence’ • Neutrino divergence • Reduce divergence ~3, flux goes up by ~ 25 We’ll be sensitive to “edges” where focusing fails. m L. Ahrens et al, Phys. Rev. D 34, 75 - 84 (1986)

  32. Neutrino Beams 103 Beam MC B i X B i i

  33. Neutrino Beams 104 Focusing peak • Focusing errors are fairly small. • Mostly pile up at edges of focusing system. figure courtesy Ž. Pavlović

  34. Neutrino Beams 105 “High” Energy target Horn 1 Horn 2 “Low” Energy proton target Horn 1 Horn 2 Pions with pT=300 MeV/cand p=5 GeV/c p=10 GeV/c p=20 GeV/c Vary n beam energy by sliding the target in/out of the 1st horn figure courtesy Ž. Pavlović

  35. Opportunity: Flexible Beam Energy M. Kostin et al, “Proposal for Continuously- Variable Neutrino Beam Energy,” Fermilab-TM-2353-AD (2002) figure courtesy Ž. Pavlović

  36. in situ Particle Production Off the Target Measurements using Flexible Beam Configurations Sensoji Temple, Asakusa, Tokyo

  37. NuMI Beam Configurations • Can vary • Horn current (pT kick supplied to p’s) • Target Position (xF of focused particles) • Plots show (xF ,pT) of p+ contributing to neutrino flux. • Similar plots exist for kaons • Acquired data from 8 beam configurations (here are shown 4) LE010/0kA LE010/185kA LE100/200kA LE250/200kA

  38. Parameterizing Hadron Production (I) • We tried to parameterize the Fluka’05 (xF, pT) distributions with an empirical formula. • In this fit, • A = A(xF) • B = B(xF) • C = C(xF) • This form is quite similar to BMPT (which has a D(pT)2 term – small??) • I cannot motivate the (pT)3/2 other than the fact that it fits the Fluka spectrum rather well. Fluka ‘05

  39. Parameterizing Hadron Production (II) • Both A(xF) and B(xF) fit reasonably well to following shape • All this says, of course, is that Fluka’05 is roughly consistent with BMPT • The values of the exponents are not in agreement with BMPT’s paper, but this is a thick target parameterization, and they quoted invariant cross section.

  40. Parameterizing Hadron Production (III) • Used empirical form similar to BMPT to parameterize Fluka2005: • Fit was to a MC of our thick-target yield estimated by Fluka2005. • Tune parameters of the fit to match ND data.

  41. ND Spectra After Reweighting (I)

  42. ND Spectra After Reweighting (II)

  43. ND Spectra After Reweighting (III)

  44. ND Spectra After Reweighting (IV)

  45. ND Spectra After Reweighting (V)

  46. ND Spectra After Reweighting (VI)

  47. ND Spectra After Reweighting (VII)

  48. ND Spectra After Reweighting (VIII)

  49. (xF,pT) weights • Result of the fit is set of weights in (xF,pT) plane that should be applied to p/K yields • Data prefers more low pT pi’s Region of LE beam focusing Region of insignificant focusing p+weights

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