Precision Electroweak Measurements with the LBNF Near Detector

Transcription

1 Precision Electroweak Measurements with the LBNF Near Detector R. Petti University of South Carolina, USA CETUP Near Detector Physics Workshop Deadwood, SD, USA, July 10-21, 2014

2 MOTIVATIONS A new measurement of sin 2 θ W at LBNF would have a major physics interest if it can achieve a precision comparable to the Collider measurements: Different scale of momentum transfer with respect to LEP/SLD (off Z 0 pole) = Experimental test of the running of sin 2 θ W Direct measurement of neutrino couplings to Z 0 = Only other measurement LEP Γ νν Independent check of the anomalous value of sin 2 θ W reported by NuTeV by measuring NC and CC rates for BOTH ν and ν A precisions measurement of sin 2 θ W requires many ancillary measurements of (anti)neutrino fluxes, cross-sections, structure functions etc., which will be crucial to reduce systematic uncertainties on the Long-baseline oscillation analysis as well. = Complementarity of precision ND measurements and oscillation analysis in the FD Potential advantages of the LBNF ND measurement: high intensity beam (larger statistics) and high resolution detector (smaller systematics) Potential disadvantages of the LBNF ND measurement: low energy spectrum (reduced rate of DIS, lower Q 2 ) and large beam contaminations (larger beam systematics)

3 MEASUREMENT OF sin 2 θ W FROM ν-n DIS Most precise value of sin 2 θ W from NuTeV by comparing the NC and CC rates for both neutrinos and antineutrinos with PASCHOS-WOLFENSTEIN relation: ν ν ν ν Z 0 0 Z R def σν NC σ ν NC σ ν CC σ ν CC = ρ ( 1 2 sin2 θ W ) R = q q q q ν µ ν µ+ W+ W large cancellation of systematics = use dedicated ν AND ν beams ν(ν) in ν( ν) mode ( ) q q q q Rely upon a simple detector, a massive (690 t) calorimeter, and CC identification provided by the presence of a long track (µ), not absorbed by the passive material (Fe) = only calorimetric energy available for the hadronic system.

4 The final analysis from NuTeV achieved a total precision of 0.7% on sin 2 θ W and reported a discrepancy of about 3σ with respect to SM predictions: R ν = σν NC ; σcc ν RExp ν RPred ν = ± R ν = σ ν NC ; CC R ν Exp RPred barν = ± = A discrepancy of 3σ with respect to SM in the NEUTRINO data Measurements of sin 2 θ W without ν( ν) interactions consistent with SM predictions: Atomic Parity Violation (APV) at low Q; Parity Violating Moller electron scattering (SLAC E158); Electroweak fits at Z 0 pole (LEP/SLD); Hadron collider measurements at Z 0 pole (Tevatron, CMS).

5 2 Default Antineutrino Mode Event Rates at 670m THE LBNF sin 2 θ W MEASUREMENT WITH ν-n DIS Figure 2 compares the NuMI-based antineutrino mode fluxes at 670m to those in neutrino mode. The ν µ flux in antineutrino mode is similar to the ν µ flux in neutrino mode. As can be seen, there is a sizable contamination of neutrinos in the antineutrino beam, hence both contributions are listed The in measurement the corresponding of sinevent 2 θ W rate based table upon (Table DIS 2). events After cross practically section uses weighting, only the beam high isenergy almost tail a 50/50 of the mixspectrum. of neutrinos and antineutrinos: ν µ (ν µ ) interactions comprise 57% (43%) of the total antineutrino mode muon-flavor event rate. The contributions for all neutrino flavors efault Neutrino Mode Event Rates at 459m are Due listed to in thetable LARGE 4 for νthecontamination 1.04km flux - the in numbers the ν beam are very mode similar in LBNF at 670m. not possible to use the anti-neutrino beam for the sin 2 θ W analysis. HiResMν: Costs and Detector Design umed neutrino mode flux at 459m is shown in Figure 2. Table 2 lists the relative conns to the total expected Comparing events. Tables 13 and gives the 2, the resultant total event ν µ + yields ν µ rate forinindividual antineutrino mode is estimated to be types. Note that about Compensate the total 66% ν of µ CCthe event total absence rate ν µ rate (fluxin of times neutrino ν data crossmode, with section) dedicated so the 459m overall is ancillary about event yields ν measurements are somewhat smaller to of 2.5 larger than in antineutrino prior estimates running. that were calculated at 670m [1]. constrain systematic uncertainties (dominant over statistics). R. Petti University of South Carolina LBNE Near Detector Workshop Columbia SC, December 12, 2009 : Predicted ν µ (solid) Figureand 2: ν Comparison µ (dashed) fluxes of in predicted neutrino neutrino mode at theand LBNE antineutrino near detectormode fluxes at the LBNE near

6 Value of sin 2 θ W extracted from a simultaneous FIT TO BOTH R ν AND CC differential cross-section. The CC sample constraints theoretical uncertainties:! exp 3\\EGE3OGE3[ #$# ## /6 ## 7R ## /6R & '!""#" K2 96 Z K]"K^ 2!"# $ $! GFI[[ [3GHEIO"SIK3JEON () [EO" 2 ( $ $% The analysis is simply an event classification between NC AND CC, which is achieved by two independent steps: muon identification and kinematics = main efforts devoted to reduction of systematics uncertainties.

7 Reconstruction of kinematics HiResMν: HiResMν: A High P µ T Resolution θ ν Costs and Detector φ µh Design Near Detector for the LBNE ν P m T P µ m φ h R. Petti University University of South of South Carolina, Carolina USA Pt-Vector Measurement P T y θ µ h x P h Out of plane LBNE Collaboration meeting LBNE Deadwood Near SD, Detector October Workshop 5, 2009 Columbia SC, December 12, 2009 The reconstruction of the detailed event kinematics from individual tracks Figure 5: Diagram illustrating various kinematic measureables in the proposed detector. and neutral clusters is a powerful tool to identify topologies z 5.1 The Traditional Neutrino Physics South Carolina Group The proposed experiment will measure the relative abundance, the energy spectrum, and the detailed topologies for ν µ /ν µ /ν e /ν e induced interactions including the momentum vectors of

8 LBNF ND spectrometer with ρ 0.1g/cm 3 : Precise measurement of p and E of final state particles (charged and γ s); Reconstruction of the full event kinematics. = Resolution allows reduction of systematics CC events with the muon not identified in the Muon System (mainly at large y Bj ) have a second chance to be tagged as CC kinematically. Kinematic identification of NC interactions with a likelihood function (ε 70% in NOMAD) % unidentified (6% of NC events) Efficient kinematic tagging of ν e CC events reduces systemstics due to ν e beam contamination = Same analysis as in NOMAD ln λ NC

9 HADRONIC ENERGY CUT Low energy spectrum implies large fraction of non-scaling interactions & small Q 2 = Impossible to model with the required accuracy Use hadronic energy cut (E H ) to harden the Q 2 distribution and suppress the non-scaling component: Cut higher than 4 GeV (used by CHARM experiment) to reach the region of constant sin 2 θ W ; Select the highest E H cut compatible with minimal required NC statistics for δr ν /R ν < 0.1%. E H > 5 GeV E H > 7 GeV CC events NC events δr ν /R ν (%) = Define 2 cuts E H > 5 GeV and E H > 7 GeV to check systematics. With a dedicated run with a Medium (High) Energy beam tuning expect 3( 9) more events with the same E H cuts = ME (HE) run will also provide complementary measurements of oscillations.

10 NC/CC 0.6 No radiative corrections Eh > 4 GeV HiResMν: Costs and Detector Design NOMAD R. Petti University of South Carolina First measurement of NC/CC as a function of hadronic energy LBNE Near Detector Workshop Columbia SC, December 12, Ehad (GeV)

11 ANTINEUTRINO CONTAMINATION In ν mode the ν CC DIS (W >2) contamination is about 10% of the main ν CC DIS = Systematic uncertainty on subtraction of ν NC from R ν ; Can reduce systematic uncertainty by a factor of about 4 by adding the ν CC to the denominator of the R ν ratio as well (R ν =0.31, R ν =0.39): σν+ ν R ν+ ν NC = σcc ν+ ν Need to know the ν/ν flux ratio to about 1% precision in order to make negligible the systematic uncertainty on the ν subtraction: Low ν 0 method to extract φ ν (E) and φ ν (E); Use ratio of coherent π /π + can achieve precision < 0.7% on the ν/ν flux ratio Expect 100k coherent π and 1M coherent π + in ν mode run. = Same requirement as for long-baseline oscillation analysis

12 CHARM PRODUCTION IN ν-n CC Dominant systematic uncertainty on sin 2 θ W from ν-n DIS. WiththeLBNFLEν spectrum charm from 1.7% to 5% of CC depending on E H cut. Current knowledge mainly from charm dimuon production: Recent NOMAD measurement of charm dimuon production [NPB 876 (2013) ]; NuTeV/CCFR measurement of charm dimuon production; Direct charm detection in emulsion experiments: E531 and CHORUS. = Uncertainty on charm cross-section < 5% Existing knowledge of charm cross-section results in δr ν /R ν from 0.14% to 0.23% in LBNF ND, depending upon the E H cut = Sufficient for a competitive measurement of sin 2 θ W in LBNF Substantial reduction of uncertainties with dedicated in-situ measurements exploiting the 350k inclusive ν CC charm events expected in LBNF ND: Measurement of exclusive charmed particles: D +,D s, Λ c etc. and charm production fractions; Measurement of BOTH µµ and µe charm dileptons in the low density ND;

13 ADIRECTPROBEOFSTRANGESEA!! " W + W +!! Charm dimuon production in ν( ν) DIS d 2 σ µµ dxdydz = d2 σ c dxdy D c(z)b µ ; z = P L(h c ) PL max s or d c s or d B µ = h f h Br(h µ + X); h = D 0,D +,D + s, Λ + c nucleon Hadronic shower D c (z) average fragmentation function Charm production in ν and ν DIS provides a clean and direct access to s(x) and s(x) [ F 2,c (x, Q) =2ξ V cs 2 s(ξ,µ) + V cd 2 u(ξ,µ)+d(ξ,µ) 2 ξ = x ( 1+m 2 c/q 2),µ= Q 2 + m 2 c where simple LO approximations are given for illustration purpose { ν : s/(dv + d s ) c 50% ν : s/ d s c 90% ]

14 FCAL DCH μ+ MCH μ + Overall statistics collected: ν µ CC interactions on Fe (FCAL) and ν µ CC interactions on C (DCH)

15 CHARM DIMUON PRODUCTION FROM NOMAD / cc!! "10 NOMAD CHORUS CCFR E53A+E53B Model NOMAD fit / cc!! 2 " NOMAD Model NOMAD fit E (GeV) x Bj Measure RATIO of cross-sections to reduce systematics: R µµ σ µµc /σ cc N µµc /N cc (x); x = E ν,x Bj, ŝ Require leading µ and Q 2 1 GeV 2 σµµc φ dx dy de ν = (5.15 ± 0.05 ± 0.07) 10 3 ν µ CC Total systematic uncertainty (17 different sources) 2% Agreement with model calculation based upon global fits with NuTeV+CCFR only

16 Exp. Publ. Stat. (N µµ ) E ν (GeV) Charm dimuons in νn CDHS (20) CHARM II (24) NuTeV (157.8) CCFR (150) CHORUS (27) NOMAD (27) Charm dimuons in νn CDHS CHARM II NuTeV CCFR CHORUS κ AKP09 MSTW06 CTEQ Q 2 (GeV 2 ) The new NOMAD measurement has the largest sample of ν-induced charm dimuons and the lowest energy threshold [NOMAD Coll. NPB 876 (2013) ] QCD fit to NOMAD σ µµ /σ CC data at NLO (partial NNLO) allows reduction of s(x) uncertainty by a factor 2 w.r.t. NuTeV+CCFR fits, down to 3%: κ s (Q 2 =20GeV 2 ) 1 0 x [s(x,q 2 )+ s(x,q 2 )]dx 1 0 x [ū(x,q 2 )+ d(x,q 2 )]dx =0.591 ± 0.019

17 Δs (%) μ=3 GeV, n f =3 NuTeV/CCFR (s+s - )/2/d µ 2 =1.9 GeV 2, n f =3 ATLAS ABM12 NuTeV/CCFR + NOMAD + CHORUS CMS NuTeV/CCFR + NOMAD + CHORUS -0.2 CHORUS + CMS + ATLAS x x Global PDF fit including DIS, Drell-Yan and charm (anti)neutrino data from NuTeV/CCFR, NOMAD, CHORUS, E531 (S. Alekhin, J. Blumlein, L. Caminada, K. Lipka, K. Lohwasser, S. Moch, R.P., R. Placakyte, [hep-ph]) Improved determination of the MS running mass: m c (m c )=1.222 ± Comparison with CMS and ATLAS W + c data and consistency checks = No evidence of s(x) enhancement reported by ATLAS collaboration = Small tension between dimuon (anti)neutrino data and other data

18 HIGH TWIST CONTRIBUTIONS ν 5/18H l 2 H H 3 ν x No evidence for sizeable twist-6 terms from global fit to e, µ DIS and DY data (upper limit 0.02 well below twist-4) HT similar in F T and F 2 indicate HT contributions to F L very small HT on F 2 and F T from CHORUS ν( ν) cross-section data consistent with charged leptons after charge rescaling. Simultaneous extraction of HT in xf 3 from neutrino data S. Alekhin, S. Kulagin and R.P., arxiv: [hep-ph], arxiv: [hep-ph]

19 LONGITUDINAL STRUCTURE FUNCTION F L Axial Current is only Partially Conserved (PCAC) and dominates F L at low Q 2 : A = f π m 2 πϕ = F L = f 2 πσ π π The finite PCAC contribution to F L strongly affects the asymptotic behaviour of R = σ L /σ T for Q 2 0: F T Q 2 R=F L /F T νc νfe νpb ν(p+n)/2 x = M PCAC = 0.8 GeV F L f 2 πσ π π > 0 so that R is divergent for vanishing Q 2 = Substantial difference with respect to charged lepton scattering e/µ(p+n)/2 CCFR (Fe) CHORUS (Pb) SLAC (p,d) 1 10 Q 2 [ GeV 2 ] S. Kulagin and R.P., PRD 76 (2007)

20 ANCILLARY MEASUREMENTS Charm dilepton production in µµ channel; Charm dilepton production in µe channel; Exclusive charmed particle production: D +,D s, Λ c, etc.; Charm production fractions f h ; Measurement of neutrino differential cross-section d 2 σ ν /dxdq 2 = Systematic uncertainties for long-baseline oscillation analysis Measurement of anti-neutrino differential cross-section d 2 σ ν /dxdq 2 = Systematic uncertainties for long-baseline oscillation analysis Determination of xf 3 =(xf ν 3 + xf ν 3 )/2 structure function (valence q distribution); Determination of ratio of longitudinal to transverse structure functions R L = F L /F T ; Determination of High Twist contributions to F 2,F T,xF 3 ; Determination of F νn 2 = F νp 2 and F νn 2 = F νp 2 from isospin relations on H target. Study of fragmentation and µ decays of hadrons inside the hadronic system = Background for long-baseline disappearance analysis Measurement of NC/CC ratio as a function of hadronic energy E H = NC background for long-baseline analysis = Ratio NC/CC signal in searches for sterile neutrinos

21 MEASUREMENT OF sin 2 θ W FROM ν-e ELASTIC Pure leptonic process well known in the Standard Model: σ(ν l e ν l e)= G2 µ m ee ν 2π σ( ν l e ν l e)= G2 µ m ee ν 2π [ 1 4sin 2 θ W sin4 θ W ] [ sin2 θ W sin4 θ W ] Cross-sections σ/e cm 2 /GeV = About 6,000 times smaller than inclusive CC ν-n e ν Z 0 ν Elastic scattering off electron e Weak mixing angle can be extracted from the RATIO : R νe def σ( ν e ) σ(ν e ) Cancellation of systematics from reconstruction and event selection; Subtraction of backgrounds from NC single π 0, γ and CC Quasi-elastic interactions; Need to know integrated ν/ν flux ratio to better than 1%. = Same requirement as for ν-n DIS and long-baseline oscillation analysis

22 THE CHARM-II MEASUREMENT Massive calorimeter (692 tons) collected overall 10 8 neutrino interactions Background subtraction from fit to Eθ 2 distribution, extrapolated to Eθ 2 0: Single NC π 0 production; ν e n e (p) with undetected final proton. = Extrapolation affected by systematics = Solution: measure backgrounds Achieved a precision of 3.6% on sin 2 θ W : 2677 ± 82 ν 2752 ± 88 ν sin 2 θ W = ± ±

23 ue vs E calc Events w/ E e (1 cos e ) < GeV Events THE 100 LBNF MEASUREMENT (GeV) 350 True E e Calculated using reco. CC 2 10 NC HiResMν: Background MC Costs and Detector Design (Rad) 120 Signal efficiency 70% with benign background from ν e QE and NC π 0, γ 100 θ! e e Calculated using true 160 Main kinematic cut on E e (1 cos θ ν+e e ν +e ) < GeV to reject CC and NC backgrounds ν+e ν+e 200 MC In-situ measurement of bkgnd from wrong sign analysis (e + )withe + /e separation With default 1.2 MW beam and 5y ν +5y ν run select 5,500 (3,100) ν( ν) events = Measurement of sin 2 θ W to 1% precision, limited by statistics = Same process used to measure absolute flux 1(see talk by X. Tian) THE 20 LBNF MEASUREMENT R. Petti E University 16 of 18South 20Carolina e (1-cosθ e ) (GeV) (GeV) E ν Main kinematic cut on E e (1 cos θ e ) < GeV to reject CC and NC backgrounds = Exploit the excellent angular resolution of LBNF ND Signal efficiency 70% with benign background from ν e QE and NC π 0, γ In-situ measurement of bkgnd from wrong sign analysis (e + )withe + /e separation With default 1.2 MW beam LBNE and Near 5y ν Detector +5y ν Workshop run select 5,500 (3,100) ν( ν) events = Measurement of sincolumbia 2 θ W to SC, 1% December precision, 12, limited 2009 by statistics = Same process used to measure absolute flux (see talk by X. Tian) Events = Exploit the excellent angular resolution of LBNF ND CC NC Background E e (1-cosθ e ) (GeV) Xinchun Tian et al. (, Columbia) NDWG@ / un Tian et al. (, Columbia) NDWG@ / 15 NC elastic e -2 Roberto Petti

24 IMPROVING THE SENSITIVITY FROM ν-e Since the measurement of sin 2 θ W from ν-e elastic scattering is limited by statistics need to increase the target mass and/or the exposure Adding a LAr TPC ( 100t) in front of LBNF ND could provide the required statistics to achieve a competitive measurement of sin 2 θ W from ν-e NC elastic scattering Ideally, the optimal analysis uses a combination of TWO DETECTORS : Low-density ND provides precise measurement of backgrounds and an overall calibration for LAr; LAr ND provides the actual statistics for sin 2 θ W and a good electron identification. Overall with a LAr mass of 100 tons expect 110,000 (62,000) ν( ν) events = Potential to measure sin 2 θ W at the level of 0.3%, comparable to DIS channel Expect (anti)neutrino events within a 10 µs spill in a 100 ton LAr detector, without considering the interactions in the material/cavern surrounding the detector = Challenging for a LAr TPC characterized by drift time of the order of ms

25 RELEVANCE OF THE LBNF sin 2 θ W MEASUREMENT Default 1.2 MW beam with 5y ν (5y ν) datatakingissufficient to achieve competitive electroweak measurements with LBNF ND: The measurement of sin 2 θ W with ν-n DIS can reach a precision 0.35% The measurement of sin 2 θ W with ν-e elastic scattering can reach a precision 1% HiResMν: Costs and Detector Design Additional channels can provide further constraints and checks: νp νp elastic scattering via the NC/CC ratio (νp νp)/(νn µ p) Coherent ρ 0 production via the NC/CC ratio ρ 0 /ρ + = Combined electroweak analysis of several independent channels like LEP R. Petti University of South Carolina ν-e elastic LBNE ν-n DIS LBNE Near Detector Workshop Columbia SC, December 12, 2009 E=120 GeV, FV 5 tons, 1.2 MW 5y+5y

26 SUMMARY Compelling case for new electroweak measurements exploiting the potential of the (anti)neutrino probe to precisions comparable to Collider measurements = The unprecedented statistics and resolution of the LBNF ND can overcome the limitations of past (anti)neutrino measurements With the default 1.2 MW beam and a 5y ν data taking the LBNF ND can measure sin 2 θ W with a precision of about 0.35% exploiting different independent physics processes covering a wide range in momentum transfer Q Possible to further increase the precision on sin 2 θ W with only a 1y ν run in the HE tuning (and/or with a beam upgrade to 2.3 MW) = Interesting also to study ν τ appearance or non-standard oscillations/interactions; Precision electroweak measurements imply a comprehensive program of ancillary measurements in the LBNF ND characterized by a deep synergy and complementarity with the long-baseline oscillation analyses

27 Backup slides

28 Table 7.2: Comparison of uncertainties on the R measurement between NuTeV and LBNE with a 5 t fiducial mass after an exposure of POT (5 year) with the CDR reference 120-GeV beam. The corresponding relative uncertainties on sin 2 W must be multiplied by a factor of 1.4, giving for LBNE a projected overall precision of 0.35%. Source of uncertainty R /R Comments NuTeV LBNE Data statistics Monte Carlo statistics Total Statistics HiResMν: Costs and Detector Design e, e flux ( 1.7%) e /e + identification Energy measurement Shower length model n.a. Counter efficiency, noise n.a. Interaction vertex n.a. µ flux n.a Large contamination Kinematic selection n.a Kinematic identification of NC R. Petti Experimental systematics d,sæc, s-sea University of South Carolina Based on existing knowledge Charm sea n.a. r = / n.a. Radiative corrections Non-isoscalar target N.A. Higher twists Lower Q 2 values R L (F 2,F T, xf 3 ) Lower Q 2 values Nuclear correction LBNE Near Detector Workshop Model systematics Columbia SC, December 12, 2009 Total The Long-Baseline Neutrino Experiment