Near Detector Working Group for ISS Neutrino Factory Scoping Study Meeting 24 January 2006 Paul Soler University of Glasgow/RAL

2 Neutrino Factory Scoping Study Meeting KEK, January, 2006 Contents 1.Near Detector Aims 2.Organisation 3.Flux measurement and control 4.Muon polarization 5.Cross-sections 6.Charm production 7.Possible technologies

3 Neutrino Factory Scoping Study Meeting KEK, January, Near detector aims o Control of the systematics for the long baseline oscillation measurement –Flux measurement and control –Neutrino beam angle and divergence –Beam energy and spread –Control of muon polarization o Near detector neutrino physics: –Neutrino cross-section measurements (DIS, QES, RES scattering) –Determination of charm production spectra for background studies at far detector –Parton Distribution Functions (polarized and unpolarized?) –Other physics: sin 2  W -  sin 2  W ~  S from xF 3 -  S ~0.003 D 0 / D 0 bar mixing  polarization ….

4 Neutrino Factory Scoping Study Meeting KEK, January, Organisation o What has been done so far? –Set up webpage: –I have contacted an ad hoc group of people from different communities: theoreticians interested in near detector physics (eg. PDFs …), experimentalists working on near detectors at neutrino experiments, … –List can be found on webpage: not exhaustive, so please contact me if you would like to be included. –Not much else! o What (I think) needs to be done? –Set-up a generic simulation of a near detector –Define a series of potential detector geometries to run on near detector –Carry out physics studies needed for the ISS report: 1.Study flux normalisation through: 2.Use quasi-elastic and elastic interactions to determine neutrino spectrum 3.Reconstruct muon polarization from spectrum 4.Sensitivity for cross-section measurements: low energy? 5.Determination of charm: remember this is main background for golden channel! 6.….suggestions ….

5 Neutrino Factory Scoping Study Meeting KEK, January, Flux normalisation o Neutrino beams from decay of muons: Spectra at Production (e.g. 50 GeV) Number CC interactions Polarisation dependence P  =+1: gone! Need to measure polarization!!

6 Neutrino Factory Scoping Study Meeting KEK, January, Flux normalisation (cont.) o Rates: — E  = 50 GeV — L = 100 m, d = 30 m — Muon decays per year: — Divergence = 0.1 m  /E  — Radius R=50 cm 100 m Yearly event rates High granularity in inner region that subtends to far detector. E.g. at 25 GeV, number neutrino interactions per year is: 20 x 10 6 per 100 g/cm 2. With 50 kg  10 9 interactions/yr

7 Neutrino Factory Scoping Study Meeting KEK, January, Flux normalisation (cont.) o Neutrino flux normalisation by measuring: o Signal: low angle forward going muon with no recoil o Calculable with high precision in SM o Same type of detector needed for elastic scattering on electrons: E.g. CHARM II obtained value of sin 2  W from this

8 Neutrino Factory Scoping Study Meeting KEK, January, Muon polarization o Fit neutrino spectrum for polarization: Compare fitted polarization to measured one from polarimeter:

9 Neutrino Factory Scoping Study Meeting KEK, January, Cross sections o Measurement of cross sections in DIS, QE and RES.  Coherent  o Different nuclear targets: H 2, D 2 o Nuclear effects, nuclear shadowing, reinteractions o With modest size targets can obtain very large statistics o What is lowest energy we can achieve? E.g. with LAr can go down to ~MeV

10 Neutrino Factory Scoping Study Meeting KEK, January, Charm Production o Remember that main background to golden channel is production of charm:  Q t = P  sin 2  cut eliminates backg at not detected NC CC Hadron decay o Can use near detector to measure Pt and Qt distribution of charm, if we can reconstruct explicitly: o With silicon detector can reconstruct more than 10 6 charm states per year Cervera et al.

11 Neutrino Factory Scoping Study Meeting KEK, January, Charm (cont.) o NOMAD-STAR silicon detector was able to reconstruct 45 charm events in NOMAD. o Measured charm rate:  Fully active silicon target (ie. 52 kg with 18 layers of Si 500  m thick, 50 x 50 cm 2 =4.5 m 2 ) for full charm event reconstruction. o Optimal design: fully pixelated detector (e.g. Monolithic Active Pixels MAPS)

12 Neutrino Factory Scoping Study Meeting KEK, January, Possible technologies o Apart from silicon, there are other possibilities: o Liquid argon TPC in a magnetic field would be able to perform as a near detector as well. Can it withstand the rate? o Scintillating fibre tracker o Scintillator (like Minerva) o Standard gas TPC (like T2K near detector) o …. o Need to develop proper simulation to compare options. 2.5 GeV e, 1.5T