Some thoughts on neutrino beams for. neutrino cross-section measurements. A. Bueno, S. Navas, A. Rubbia. (ETH Zürich)

Transcription

1 Some thoughts on neutrino beams for neutrino cross-section measurements A. Bueno, S. Navas, A. Rubbia (ETH Zürich) The First International Workshop on Neutrino-Nucleus Interactions in the Few GeV Region December 13-16, 2001, KEK, Tsukuba, Japan

2 The low energy region Many channels have to be studied... Charge Current (CC) interactions ( n N Æ l X ): Quasi-elastic ( n N Æ l N ) dominant atmospheric reaction Resonant ( n N Æ l N* ) and Single/Multi pion production ( n N Æ l N p ) Deep inelastic ( n q Æ l q or n q Æ n q ) multi-pion production via fragmentation Neutral Current (NC) interactions ( n N Æ n N ) specially important are the n N Æ n N p 0 events Elastic (electron) scattering ( n e - Æ n e - ) Coherent production n N Æ n N π The physics is complex the neutrino flux beam should be «simple»!!

3 Region of interest E (GeV) Cha 0.2 QE 0.4 DIS 0.6 CC µ /E NUX /E for muon neutrinos (isoscalar) 1.2 Ciampolino, Phys.Lett. B84, 281 (1979) CCFR, Zeit.Phys. 26, 1 (1984) Baltay, Phys.Rev.Lett. 44, 916 (1980) Colley, DPhPE (1979) Eichten, Phys.Lett. B46, 274 (1973) Baranov, Phys.Lett. B81, 255 (1979) Morfin, Phys.Lett. B104, 235 (1981) Anikeev, HEP (1995) Allasia Baker, Phys.Rev. D25, 617 (1982) Barish, Phys.Rev. D16, 3103 (1977) Barish, Phys.Rev. D19, 2521 (1979) Belikov, ZP A-Atom.Nucl. 320, 625 (1985) Vovenko, Sov.J. Nuc.Phys. 30, 527 (1979) Kitagaki, Phys.Rev. D28, 436 (1983) Comparison of s/e n for QE and total processes between data and NUX The region of interest is certainly between 100 MeV and 10 GeV!

4 Unfolding cross-sections Number of events Detector systematics Clean event reconstruction and classification s = N / e - N observed background f Neutrino flux!

5 Shopping list Goals Measure cross-section from kinematical threshold, through quasi-elastic dominated region, study single-pion production, study opening of multi-pions final states ª0.1 < E n < ª3 GeV Study neutrino and antineutrino cross-sections Measure both n e and n m? Study nuclear effects (i.e. compile various targets in same beam) Experimental aspects: Different types of target (nuclear effects) Capability to measure exclusive final states (low density, high granularity) Capability to measure inclusive final states (high density) Beam aspects Statistics k Sufficient flux also at the lowest energies (cross-section decreases and meson decay kinematics less focalized at lower energy) Systematics k In the range of 1%, 10% or 20%?

6 Neutrino beam candidates Traditional «pion» beams K2K FNAL Booster NUMI-LE, ME, HE JHF Storage ring beams (e.g. antiproton accumulators) FNAL Debuncher CERN AD Neutrino factories

7 Traditional beams FNAL Booster NUMI LE NUMI ME NUMI HE Peak E n ª1 GeV 3.5 GeV 7.5 GeV 13 GeV n m CC rate per ton/year anti-n m CC rate per ton/year n e CC rate per ton/year Anti-n e CC rate per ton/year Flux uncertainty % % % % From S. Geer s page:

8 FNAL Booster Running in 2002 FNAL Booster Peak E n ª1 GeV n m CC rate per ton/year anti-n m CC rate per ton/year n e CC rate per ton/year Anti-n e CC rate per ton/year Flux uncertainty %

9 FNAL (NuMI) beam characteristics (low energy configuration): M.I.: 120 GeV/c Proton. 4*10 13 PoT/spill - 1spill / pulse - pulse=1.87 s RUN time: 1 year = 3 * 10 7 s * live time (%) See talk of F. Cavanna fi Systematics dominated Systematic error in the range E n <1.5 GeV? Region of interest: 0.1<E n <2 GeV

10 KEK beam characteristics: PS: 13 GeV/c Proton. 5.5*10 12 PoT/spill - 1 spill (1.1ms) /pulse - pulse = 2.2 s RUN time: 6 months/year = 1.5 * 10 7 s See talk of F. Cavanna fi Systematics dominated OFF-AXIS

11 E (GeV) E n A. Guglielmi 10 4 A tough job! 10 5 Black: nubeam500 + GEANT-FLUKA Dashed: nubeam500 + FLUKA standalone Red: new transport + FLUKA standalone Blue: +tuning of yields to SPY data µ /GeV n m flux at NOMAD 10 6 NOMAD beam MC prediction

12 Cross-sections at neutrino factories 1. Use a muon beam : ( m Æ n m n e e ) 2. known flux and no contamination M. Campanelli, S. Navas, A.Rubbia, hep-ph/ , May 2001 Presented at NUFACT 01, Tsukuba 3. Measurement of both, n m and n e cross sections (and both helicities!! ) The assumptions... a. low energy beam E m ~ 2 GeV Measure s n /E b. low intensity beam m / year c. short baseline experiment 20 meters d. detector mass 100 tons below E m ~ 2 GeV with 100 MeV bins in energy and 6% minimum statistical error

13 The «modest» machine The machine could deliver very low intensities compared to neutrino factories (~ 5 orders of magnitude less) This could fit to staging scenario of the neutrino factory m storage (10 16 m/year) Example : CERN complex 1. The PS as a proton booster 2. The SPL tunnel to focalize and accelerate m s cooling + acceleration p target 3. A m storage ring (E m ~ 2 GeV) (after discussions with H. Haseroth) Protons ( ~10 19 p/year) Scenario within the CERN complex

14 and the detector We assume, for definiteness, the following configuration: Accelerator straight section 30 m 10 m BASELINE E m = 2 GeV n m n e 100 ton detector m 1m radius Total number of events _ ne n m Charge-current (Total) useful m/year Quasi-elastic (QE)

15 n energy 1E+15 µ - events: E µ = 2 GeV, Dist = 10 m, (1m,100Ton) detector, Spread = 30 m, Arclen = 0 m, RingPart =1 m e Energy (GeV) µ Energy (GeV) # Events / 100 MeV QE 50 Mean RMS ALLCHAN # Events / 100 MeV QE _ n QE e n m QE 200 Mean RMS ALLCHAN Events / 0.1 GeV e Energy (GeV) µ Energy (GeV) # Events / 100 MeV MeV bins! 100 n cc CC e Mean RMS ALLCHAN # Events / 100 MeV n cc CC m _ 450 Mean RMS ALLCHAN µ - beam useful m - decays, E m = 2 GeV, 100 Tons detector, 1m radius, 10 m baseline, 30 m straight section

16 1E+15 µ - events: E µ = 2 GeV, Dist = 10 m, (1m,100Ton) detector, Spread = 30 m, Arclen = 0 m, RingPart =1 m n energy e Energy (GeV) µ Energy (GeV) Relative Error (%) 10 2 QE _ n QE e Relative Error (%) n QE QE m 10 2 Relative error (%) e Energy (GeV) µ Energy (GeV) % % 6% Relative Error (%) 10 2 _ n CC cc e Relative Error (%) CC n cc m MeV energy bins useful m - decays, E m = 2 GeV, 100 Tons detector, 1m radius, 10 m baseline, 30 m straight section µ - beam

17 / E Tons detector, 1m radius, 10 m baseline, 30 m straight section n m s cc / E useful m - decays, n m s QE / E Em = 2 GeV, n m s RES / E E+15 µ - events: E µ = 2 GeV, Dist = 10 m, (1m,100Ton) detector Spread = 30 m, Arclen = 0 m, RingPart =1 m E (GeV)

18 Antiprotons Accumulators P-pbar physics is based on technique of beam cooling, which allows to accumulate pbar in sufficient number within a phasespace of an accelerator. Design of pbar sources has led to extensive studies of production and capture of pbar in storage rings, in order to optimize the accumulation rate Optimum choice of target, incident proton beam parameters, focusing optics to provide largest possible particle density inside transverse and longitudinal admittance of storage ring Two machines: CERN AC & AA, PS proton energy=26gev, p=3.57 GeV/c, admittance 200p mm.mrad in both planes, Dp/p=±3%, circumference = 182m, four straight sections, longest account for 14% of total FNAL AD, p=8.9 GeV/c, admittance 25p mm.mrad in both planes, Dp/p=±2%, circumference = 500m, triangular, longest straight section account for 13% of total

19 A parasitic run During their normal operation, the ring accumulates negative particles, including p, K, µ and e s. To a large extent, the optimization for the pbar s is also an optimum focalization for other negative particles like pions! The muons are produced in the decays of p and K s. These decays can occur anywhere, that is, within the focusing system, the transfer lines between the target region and the storage ring, or within the storage ring itself. Only a small fraction of the muons has a sufficiently small transverse emittance and a momentum within the required bite of the ring to stay captured as well. A parasitic run is fully justified!! W. Lee et al., FNAL PROPOSAL P-860, December 1992 «A Search for nu oscillations using the FNAL Debuncher»

20 What do we expect? For simplicity we consider only particles stored into the ring. The lifetime of pions is sich that they will decay within a few revolutions. The few captured muons that remain trapped into the ring will subsenquently decay. p -,K - Æ m - n m m - Æ e - n n e m Short burst Long burst A. Bross et al., FNAL-PUB-92/357, December 1992 «Measurement of the Circulating Muon Flux in the FNAL Debuncher Ring» This has been measured! Ï Ô m Ì ÓÔ m - / p = 10. ± 02. = ± ( ) / pot

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22 . CERN AD: proton beam Focusing devices Z dist PS Target pion decay tunnel AD muon storage ring DETECTOR neutrino beam p m = 3.57 GeV/c( 3%), CC (total) QE DIS Anti-n m n m Anti-n e Estimated event rate for pots in a 0.1 kton detector 10m downstream of a CERN AD straight section

23 Focusing horn shape optimized for AD acceptance CERN AD optimization study: Full MC simulation FLUKA on Be target, 70cm long, 2cm radius 200pmm.mrad admittance Consistent with measurement at FNAL ª N pots ª N pots (0.02) (0.03) (0.04 ) N m = N pots Yp Aoptics ep Æ m

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25 E n (GeV) n e _ n µ n m prompt # neutrinos / 200 MeV delayed _ n m n µ µ - 5 e - m - Æ e - e _ n µ m n e π - 5 µ - n µ p - Æ m - n m _ Expected number of neutrinos reaching the detector (5X10 19 protons) CERN AD : Normalized to protons on target

26 CERN AD : Normalized to protons _ n m n m 200 MeV energy bins _ Very strong energy-angle correlation n e fi Lowest energies (unfortunately) are cut out

27 Statistics ª 6% protons Statistics ª 10% E n (GeV) E n (GeV) s n / E n n m n e s n / E n 0.5 n cross section spectrum n e CERN AD : 200 MeV energy bins cross section spectrum

28 The prompt neutrinos are much more than the delayed ones, and all at lower energy! Statistics ª 20% s n / E n 0.4 CERN AD : n m n cross section spectrum 200 MeV energy bins Statistics ª 3% protons E n (GeV)

29 FNAL PROPOSAL P-860, December 1992 Estimated event rate for 4 years running in a 0.1 kton detector 15m downstream of a FNAL-Debuncher straight section S. Geer, FNAL-FN-706, June 2001.

30 S. Geer, FNAL-FN-706, June years running in a 0.1 kton detector 15m downstream 200 MeV energy bins 20% 10%

31 Systematics Storage ring of pions or muons provide the cleanest way to measure neutrino cross-sections In particular, muons are the cleanest since they can be better monitored (long lifetime) Muon polarization k Not dominant Bending arcs of storage ring Negligible Statistics ª 5-10% for ª10 15 muons Systematics ª 1% (Could aim at ª10 16 muons)

32 Effect of muon polarization fi Not dominant! S. Geer, FNAL-FN-706, June % 2%

33 Conclusion Traditional «pion» beams are the most realistic choice for performing neutrino cross-section measurements Already existing Event rates are generally very high But systematics dominated! Low energy neutrino factories will provide the «cleanest» environment to measure cross-sections Equal amount of neutrinos and antineutrinos Flux systematics small, certainly at the level of few % s But is it (financially) realistic? Antiproton accumulators are certainly an interesting compromise. They already exist A parasitic run is possible Pion and muon decays offer interesting features