Coherent-Rho 0 Production in Neutrino Neutral-Current Interactions - PowerPoint PPT Presentation

Coherent-Rho 0 Production in Neutrino Neutral-Current Interactions ν µ A ֌ ν µ ρ 0 A Chris Kullenberg Sanjib R. Mishra July 7, 2015 Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 1 / 52

ν µ A ֌ µ ρ A Neutrino-Induced Coherent Rho Production: µ ( l ′ ) ν µ ( l ) ∗ Structure of Weak-Current and its W + Hadronic-Content: u ¯ ρ + d Piketty-Stodolsky Model ⇒ CVC Vector meson Dominance (VMD) P A ( p ′ ) A ( p ) d 3 σ � ν µ A → µ − ρ + A � � 2 = G 2 f 2 � � d σ T ( ρ + A → ρ + A ) � | q | Q F ρ (1 + ǫ R ) Q 2 + m 2 dQ 2 d ν dt 4 π 2 1 − ǫ E 2 dt ν ρ where G F is the weak coupling constant, Q 2 = − q 2 = − ( k − k ′ ) 2 , ν = E ν − E µ , the 4 E ν E µ − Q 2 4 E ν E µ + Q 2 +2 ν 2 , and R = d σ L / dt polarization parameter ǫ = d σ T / dt with σ L and σ T as the longitudinal and transverse ρ -nucleus cross-sections. f ρ is the coupling constant of the ρ meson to the W boson. Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 2 / 52

Coherent- ρ 0 -vs- Coherent- ρ + : ∗ Coherent ρ ± observed by E546, E632, SKAT, and BEBC Precision of ± 25–30% ∗ Measurement of Coherent- ρ 0 has never been reported. Inclusive- ρ 0 has been measured: the most precise measurement is by NOMAD ( Nucl. Phys. B601 , 3[2001] ) ∗ Simple relation between Coherent ρ 0 & Coherent ρ ± ֌ d 3 σ ( ν µ A → ν µ ρ 0 A ) d 3 σ ( ν µ A → µ − ρ + A ) � � = 1 � 2 1 − 2 sin 2 θ W � dQ 2 d ν dt dQ 2 d ν dt 2 ⇒ σ ( Coherent- ρ 0 ) ∼ = 0.15 × σ ( Coherent- ρ + ) Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 3 / 52

Conditions for Coherent Events: ∗ Wavelength of exchange particle compatible with entire nucleus (diffractive, low Q 2 ) ∗ Nucleus recoils as a whole ∗ Nucleus remains in ground state ∗ No transfer of quantum numbers ∗ Generally very forward mesons Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 4 / 52

The NOMAD Detector ∗ High resolution tracking ∗ Fine-grained calorimeter ∗ Unambiguous charge separation Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 5 / 52

Signal ∗ π − π + with little else ( ππ ) vector ( P , θ ) consistent with Coherent- ρ 0 such that ζ ππ = E V 0 ∗ (1 − cos θ V 0 ) ≤ Cut (0.075) Background [1] NC-induced (NC-DIS) background ⇒ 2-Track (+,-) [2] CC-induced (CC-DIS) background ⇒ 2-Track (+,-) where ”-” is a µ − w/o µ ID SPACER ⇒ K 0 s from outside-interactions [3] Outside-Background (OBG) Control Sample: CC Data Simulator Correction ∗ ν µ -CC events where the µ − identified and then ’removed’; the remaining hadronic (+,-) tracks subjected to the analysis. Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 6 / 52

What we are looking for: π − π + Coherent- ρ 0 Candidate Event P π + =3.1; P π − =2.3 (GeV) M ππ = 0.74 GeV ζ ππ = 0.008 Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 7 / 52

E ππ Number of Events ⇒ E ππ ≥ 2 GeV 0.05 NC-DIS 0.04 0.03 ✟ ✙ ✟ CC-DIS 0.02 Coh ρ 0 0.01 0 0 2 4 6 8 10 12 14 16 18 20 E ππ (GeV) (200MeV) Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 8 / 52

φ ππ Number of Events 0.12 CC-DIS 0.1 20 0 ≤ φ ππ ≤ 160 0 ⇒ ⇐ 0.08 0.06 NC-DIS Coh ρ 0 0.04 0.02 0 0 20 40 60 80 100 120 140 160 180 Φ π +- (Deg) Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 9 / 52

Analysis of Coherent ρ 0 : Kinematic Shape Comparison Number of Events Number of Events ζ ππ M ππ 0.14 0.3 Coh ρ 0 OBG K 0 s 0.12 0.25 ✻ 0.1 0.2 0 . 075 ✛ ✲ ∼ 85% of ρ 0 0.08 0.15 0.06 0.1 0.04 NC-DIS 0.05 ✁ 0.02 ☛ ✁ ✟ CC-DIS ✟ ✟ ✙ ✟ 0 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 M ππ (GeV/c 2 ) 30MeV ζ ππ 0.6 ≤ M ππ ≤ 1.0 ζππ ( ) Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 10 / 52

Coherent- ρ 0 Analysis: ∗ 2-Track ( π + π − ) Events in Fiducial Volume w/o µ -ID passing kinematic preselection cuts ∗ Calibrate OBG ⇒ 2-Track events with vertex outside ⇒ Normalize it to the K 0 peak ∗ Calibrate the shape of NC-DIS The most important variable is the shape of ζ ππ ⇒ Use CC-DS (3-&-4 Track events w. µ ); ⇒ The π + π − subjected to the standard selection ⇒ Obtain a MC(NC-DIS) Re-Weight based on Data/MC [ P π ± , P t π ± , M ππ , ζ ππ ] ∗ Normalize NCDIS (shapes reweighted using Data-Simulator) ⇒ Use φ ππ distribution with ζ ππ > 0 . 075 ∗ Result ⇒ Plot M ππ ; impose 0 . 6 ≤ M ππ ≤ 1 . 0 GeV ⇒ Using ζ ππ , fit for Coh ρ using ≤ 0 . 1 region ⇒ Check CC-DIS normalization ⇒ Systematic error analysis Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 11 / 52

Shape of NC-DIS used in Coherent ρ 0 Analysis: CC Data-Simulator E ππ 1400 1200 ∗ ν µ -CC with µ − π + π − 1000 Weighted MC Un-weighted MC ∗ DIS weight based upon: 800 [ P π ± , P t π ± , M ππ , ζ ππ ] ⇒ 600 400 200 0 0 2 4 6 8 10 12 14 16 18 20 E ππ E ππ E ππ Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 12 / 52

M ππ 1400 1200 Weighted MC 1000 Un-weighted MC 800 600 400 200 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 M ππ M ππ M ππ Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 13 / 52

ζ ππ 0 . 6 ≤ M ππ ≤ 1 . 0 2250 1000 2000 1750 800 Weighted MC Un-weighted MC Signal ⇒ 1500 600 1250 1000 400 750 500 200 250 0 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 ζ ππ ζ ππ ζ ππ ζ ππ (0.6 ≤ M ππ ≤ 1.0) ζ ππ (0.6 ≤ M ππ ≤ 1.0) ζ ππ (0.6 ≤ M ππ ≤ 1.0) Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 14 / 52

Preselection NC-DIS ( ∼ x4 Data) 0.44M ֌ CC-DIS ( ∼ x4 Data) 1.44M ֌ Coh π + 10k ֌ Coh ρ 0 1,000 ֌ ∗ Fiducial Cut, Muon-Veto, 2-Tracks Sample #-Events NC-DIS ( ∼ x4) 18 , 400 CC-DIS ( ∼ x4) 4 , 600 Data 39 , 500 Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 15 / 52

Selection ∗ ’Other’ includes QE, Res, Coh π + , Coh π 0 ∗ Vetos: DC-Veto/tube, Upstream-hanger, V 0 -from-vertex Coh ρ 0 ∗ Selection NC-DIS ∗ CC-DIS ∗ OBG Other Total Data Veto/UpHanger 10 , 262 2 , 498 1 , 520 526 395 15 , 202 15 , 850 Photon Veto 6 , 846 1 , 506 359 260 368 9 , 339 9 , 490 20 0 ≤ φ ππ ≤ 160 0 5 , 321 870 255 104 305 6 , 854 6 , 852 Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 16 / 52

Normalization of NC Background Number of Events χ 2 500 1 . 043 ± 0 . 023 400 300 NCDIS-Norm 200 ∗ Coh ρ 0 MC 100 ∗ NC-MC Bkg(DS-Wt) ∗ CC-MC Bkg ∗ OBG-K 0 s Bkg 0 0 20 40 60 80 100 120 140 160 180 Φ π +- (Deg) ζππ> 0.075 Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 17 / 52

0 . 6 ≤ M ππ ≤ 1 . 0 Number of Events 700 Number of Events 300 ∗ Coh ρ 0 MC (669 ± 116 evts) CC-Data 1000 ∗ NC-MC Bkg(DS-Weighted) ∗ CC-MC Bkg 600 ∗ OBG-K 0 s Bkg 250 800 Coh ρ 0 500 ✟ ✟ ✙ 600 200 χ 2 400 400 150 0 . 669 ± 0 . 116 200 300 (17 . 3%) ✄ ✗ 0 100 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 ζ ππ (0.6 ≤ M ππ ≤ 1.0) ζ ππ (0.6 ≤ M ππ ≤ 1.0) ζ ππ (0.6 ≤ M ππ ≤ 1.0) ✄ Normalization (Coh ρ 0 ) 200 NC-MC CC-MC ✁ Total BKG 50 ✁ ☛ 100 ✁ ☛ ✁ OBG-K 0 ✟ ✙ ✟ 0 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 ζ ππ ζ ππ 0.6 ≤ M ππ ≤ 1.0 Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 18 / 52

Coherent Region: ζ ≤ 0 . 075 non-Coherent Region: ζ > 0 . 075 Number of Events Number of Events 250 ∗ Coh ρ 0 MC 180 ∗ NC-MC Bkg(DS-Weighted) ∗ CC-MC Bkg 160 ∗ OBG-K 0 s Bkg 200 140 120 150 100 80 100 60 40 50 20 0 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 M ππ (GeV/c 2 ) ζππ≤ 0.075 M ππ (GeV/c 2 ) ζππ> 0.075 Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 19 / 52

Systematic Error ⇒ ∗ Data-Simulator: (Shape of ζ in NC-DIS) Using only ζ -Wt (which does not describe the ππ system in CC-data well) ⇒ ± 0 . 072 ( 10 . 8 %) ================================ ∗ NC-DIS: Using ± 2 . 3% variation (constrained by φ ππ in the background region) ⇒ ± 0 . 048 ( 7 . 17 %) ∗ CC-DIS: ⇒ ± 0 . 015 ( 2 . 24 %) Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 20 / 52

Systematic Error ⇒ ∗ OBG ( K 0 ): With 833 data events used to simulate the OBG, a 3 . 5% variation in its normalization had a negligible effect on the Coh ρ 0 normalization. ⇒ ± 0 . 000 ( 0 . 0 %) ∗ Total Systematic Error: ⇒ ± 0 . 088 ( 13 . 2 %) ∗ Total Error: ⇒ 0 . 669 ± 0 . 116 ± 0 . 088 ( ± 21 . 8 %) Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 21 / 52

ν µ A ֌ ν µ ρ 0 A Conclusion ⇒ ∗ We have conducted a measurement of Coherent- ρ 0 production. A clear signal of Coherent- ρ 0 is observed. ∗ The analysis is data-driven; the backgrounds are constrained using control samples. ∗ We observe: 669 ± 116 ( Stat . ) ± 88 ( Syst . ) fully corrected Coherent- ρ 0 events. ∗ The rate with respect to -CC events ( 1 . 44 ∗ 10 6 ) is: ( 4 . 65 ± 1 . 01 ) ∗ 10 − 4 Coh ρ 0 Production Kullenberg, Mishra July 7, 2015 22 / 52