Measurement of the neutrino velocity with the MINOS detectors and NuMI neutrino beam

1. Magali Besnier Measurement of the neutrino velocity with the MINOS detectors and NuMI neutrino beam hep-ex – 0706.0437v3 GdR Saclay – 11/04/08

2. Previous measurements Theory : if Mn < 3 eV/c² *  |v-c| / c < 10-9for a 10 GeV n *best limit on neutrino mass (cosmological measurement, 2005) But : some theories allow|v-c| / c ~ 10-4 Previous terrestrial measurement with Fermilab neutrino beam :  comparison between detection of µ and nµ emitted in the same time (p+/K+ decays) 1) First direct n velocity measurement (1976) : |βn-βμ|< 4×10-4(99% confidence level), with |1-βμ|<10-5 En: 30 - 200 GeV. D ~500m Phys. Rev. Lett. 36, 837 - 840 (1976) 2) Second measurement (1979) : |βn (n)-βμ|=|βn (n)-1|<4×10-5(95% confidence level) Phys. Rev. Lett. 43, 1361 - 1364 (1979)

3. MINOS detectors @Fermilab MINOS measurements of neutrino velocity Difference with previous measurements : Absolute transit time measurement of an ensemble of neutrinos by comparing arrival times between ND and FD CCevents @ND <En>=3 GeV (LE) D=732 km ND FD

4. Event selection ( ) • ND selections for nmCC-like events: • | Tarrival-Texpected | < 7µs • At least 1 “good ” reconstructed track select nm or nmevents • Track-Vertex inside the fiducial volume Remove cosmic background • Evreco <30 GeV(Evreco =Eµ + Phad ) • Cut on a likelihood-based variable (PID) to separate NC and CC events ( ) • FD selections : • | Tarrival-Texpected | < 50µs • 1 “good” track reconstructed with direction within 53° of that of the beam • Track-Vertex inside the fiducial volume • Neutrino-induced rock muons(track entering from the front face of the detector with direction within 26°) and shower events inside detector volume (mostly NC) also accepted 473 induced events, with 258 nmCC-events 1.6 106 events

5. Timing measurement FD d= (t2- t1) – t ? Deviation from the expected TOF t (massless neutrino) : NO ! The neutrino beam pulse is not instantaneous … but 9.7 µs long ! Identical GPS receiver underground connected to surface with optical fibers MI ND t0 tND tFD time t1=tND - t0 - dND t2=tFD - t0 - dFD t0 : time of proton extraction magnet signal tND and tFD : time of the earliest scintillator hit dND anddFD : known timing delays (readout time, electronic latency, GPS antenna fiber delays) Uncertainty : D(|dND – dFD|) = 64 ns @ 68% CL, mostly due to GPS optical fibers Uncorrelated jitter of the GPS clocks  s(tND - tFD)=150 ns.

6. Timing measurement FD P25(t2-t) P26(t2-t) time of FD events relative to prediction after fitting the TOF d s(tND - tFD)=150 ns d= -126 ± 32(stat.) ± 64(sys.) ns @68% C.L. Expected PDF @ FD : P2n(t2)=1/(2ps) exp (- (t2-t’)/(2s²)) P1n(t’) dt’ ( Remember : D(|dND – dFD|) = 64 ns ) NuMI beam pulse is 9.7 µs long with 5 or 6 batches ND P15(t1) P16(t1) n profile interactions measured @ND PDF P1n(t1) measured @ ND Deviation d from the expected time t2-t maximisation of L=ln(P2(t2i -t-d))

7. Relativistic mass measurement t Tmn(En)= ( 1-mnc²/En) mn=14+42-98(stat.+syst.) MeV/c² @99%C.L. With d=-99 140 (stat) ns mn=17+33-56(stat.+syst.) MeV/c² @99%C.L. With d=-46 ns Log-likelihood function : Eireco < 10 GeV mn: free parameter Eireco: reconstructed energy R(Eiv , Eireco) : detector response parametrised through MC Eiv : fitted true energy constrained by R and Eireco. d : free parameter constrained by earlier systematic measurement by a gaussian with sd=64ns. Mn=50MeV/c² Mn=17Mev/c² Time of flight of a relativistic n with a mass mn

8. Velocity measurement Remember : d= -126 ± 32(stat.) ± 64(sys.) ns @68% C.L. |v-c|/c=|-d/(t+d)|=5.1 ±2.9 (stat.+syst.)10-5 @68%C.L. For n between 1-30 GeV Consistent with the speed of light at less than 1.8s. Most sensitive test of neutrino velocity : Arrival time comparison of photons and neutrinos from SN1987a : |v-c|/c< 2 10-9 ,but only for En~10 MeV L.Stodolsky,Phys. Lett. B201, 353 (1988) Neutrino velocity could be strong function of En. MINOS is the only one measurement constraining vn in the 1-30 GeV range. But no improvements wrt previous terrestrial measurements.

9. Future measurements OPERA is a long baseline neutrino experiment at Gran Sasso laboratories, receiving a nm beam (<En>=17 GeV) from CERN, 730 km away.  It will be able to provide another measurement of vn in the 1-30 GeV range • Possible improvements : • Actual OPERA GPS system is equivalent to the one of MINOS. • New timing system based on GPS/atomic clock will be installed in the next months both at CERN and LNGS, 10-100 times more precise. • Combination withother neutrino experiments at LNGS will improve statistics. Talk from D. Autiero will give more informations on this subject in following GdR meetings

11. OPERA neutrino velocity measurement Long base=730 km T= L/c = 2.4 msec L and T from GPS expected as the best T < 10 nsec L < 5 cm ( ? ) Then | -1|~  ~ 4*10-6 Remember : FNAL(1976-77) -> 10-4 CNGS – time of proton bunches OPERA – time of  event using RPCs Expected OPERA accuracy Worse case : GPS > p bunch interspace ( 5ns now) T ~ p batch length/12N (now 2 batchs with 10.5 s length) At present t ~ 10 s/ 121000 ~ 100ns   ~ 4*10-5 Is it possible to have 20 p batchs with 1 s length ? Better case : GPS < p bunch interspace ( 25ns as for LHC) T ~ GPS ~ 10 ns  ~ 4*10-6