# Presentation: 255788

## Elastic scattering of 

- Elastic scattering of
- electron -neutrinos and
- measurement of the
- weak mixing angle at a reactor

-  Motivation and physics

-  Standard model coupling constants

-  Backgrounds

-  DIS and the NuTeV anomaly

-    See Janet’s talk
-   Tuesday!

- A new initiative at
- Krasnoyarsk.

## The neutrino has mass. This implies the existence of right-handed neutrinos. 

- Direct measurements of g and g**’** should provide good sensitivity
- to a possible departure from the conventional Standard Model.
- The neutrino is the particle that has a new property, so it seems
- a good idea to search in neutrino interactions.

- Hep-ph/0412099; R.N. Mohapatra *et al*.

- where the coupling constant associated with the SU(2)*L* and U(1)
- are g and g’ respectively. It is evident that *R* only interacts via U(1)
- gauge boson and *L* interacts via both U(1) and SU(2)*L* gauge bosons.

- The SM Lagrangian is:

## Atomic Parity Violation measurements test the photon’s role in weak interactions.

**hep-ph/0407251**

- Moller scattering is done with e + e reactions.
- www.slac.stanford.edu/exp/E158

- Measured above the Z
- mass; the ratio of the
- Z and W mass normalize
- the weak scale.

- Measured with neutrinos;
- That may be a source
- of corrections in the SM.

**It may be the case that,**
**except for neutrino DIS,**
**the measurements agree **
**with the SM. **
**interactions.**

- tanW= g/g’

- Marciano and Rosner;
- PRL Vol 65 No. 24, 2963; Dec 10, 1990

## From the Qweak proposal: the anticipated error in

- measurement of the weak charge of
- parity violating e-p scattering at JLAB.

- Reactor experiment

## How do we measure deviations from the SM?  

- Conventionally this is broken into two parts. eviations caused by vacuum polarization; generally parameterized by the S, T, and U
- variables. These are called the oblique corrections. Additional
- corrections caused by physics BSM and require further corrections -
- and e.We’ll make use of these later in the talk.

- hep-ph/0403306 Loinaz, *et al.*
- hep-ph/9603391;J.L. Hewett, *et al.*

- 1. The electroweak gauge group is the standard SU(2)L × U(1)Y . The only
- electroweak gauge bosons are the photon, the W±, and the Z.
- 2. The couplings of new physics to light fermions are highly suppressed so that
- ‘direct’ corrections from new physics can be neglected (with the possible
- exception of processes involving the b quark). Only oblique corrections need
- to be considered.
- 3. The new physics scale is large compared to the W and Z masses.

- We might expect that l might be caused by the existence of the
- right-handed neutrino and could be directly related to the NuTeV result.

## NuTeV measured gV in Deep Inelastic  scattering on nuclei.  

*R**** *manifestly insensitive to sea quarks
- Charm and strange sea error negligible
- Charm production small since enters from *d**V** *quarks only, which is Cabbibo suppressed and at high-x
*But R*** requires separate and beams so needed to develop a high-intensity separated beam     NuTeV SSQT (Sign-selected Quad Train)

- To minimize systematic effects, the Paschos – Wolfenstein Relation was used: Cross-section differences remove sea quark contributions, and reduce uncertainties from charm production and the sea.

## NuTeV Experimental Setup

**The Quad Triplet Neutrino beam was an important innovation that made this measurement possible.**
**Beam is almost pure ******** or************ in ******** mode 3******************** in ******** mode 4**************
**Beam only has ********electron neutrinos**
******  ****Important background for isolating true NC event**

- Dipoles make sign selection - Set  type - Remove e from Klong

**690 ton ********target****Steel-Scint-Chambers**

**Solid Steel Magnet ****Drift Chamber Spectrometer**

## Agrees with other

- DIS  measurements,
- but with much smaller
- errors...

- SM=0.2227

- The number of light neutrino families is determined by comparing the Z width, as measured in the Breit-Wigner line-shape with the visible lepton and quark-decay channels. The difference determines the number of light neutrino species to be:
- Nν = 2.985 ± 0.008.
- 2  < 3

## Perhaps the explanation for the NuTeV effect may lie in the application of new results to the data. 

**Changes in quark distributions sets **
**	****	****Cross-section models:  **
**	****Leading Order (LO) vs Next to Leading Order (NLO)**
**2.****	****Changes in standard model radiative-corrections**
**     ****Perhaps the explanation involves small effects due to physics**
**	****we are already familiar with such as QCD** **:**
**       ****1. Is there a Strange vs anti-strange quark asymmetry?**
**       ****2. Are there Shadowing and other nuclear effects involved?**
**       ****3. Are there small violations of “isospin” symmetry caused by **
**	****	****	****EM effects in final state interactions?**

## Or perhaps the explanation lies in BSM Physics: 

**In a better understanding of neutrino properties  (g g****’****)**
**The existence of couplings to new particles (SUSY)**
**Mixing and oscillation Effects (PNMS matrix)**
**New Z****’**** or lepto-quark exchanges**
**New particle loop corrections in neutrino interactions (seesaw and heavy neutrinos)**

-  The deviations from the SM in neutrino DIS, and the Z decay to neutrino pairs, begs the question:
- 	Can we exploit these effects to gain further insight into the nature of 		BSM physics?
-  These measurements directly involve neutrinos in a way that is manifestly dependant on the coupling constants g and g’, and may thereby be giving us a hint of the dynamics of what is unknown in EW interactions.
-  Wouldn’t it be interesting to search for similar effects in other systems? We propose taking a look at:
- at the Braidwood reactor near Joliet Illinois.

- Let’s look at Braidwood,
- then get back to NuTeV and
- compare results.

## More and better measurements are needed!! Elastic scattering in a reactor generated neutrino beam may provide another opportunity.

- 	T = electron recoil KE
- = neutrino magnetic moment, generally assumed small.
- tag recoil events with 3 < T < 5 MeV
- use                                 to normalize
- U/Th contamination
- calibrate the energy scale
- test of NuTeV measurement !

- The differential cross-section:

-      gA= -1⁄2
-      gV= 1⁄2+2sin2W
-      tanW= g/g’

- Conrad, Link, and Shaevitz, hep-ex/0403048

## The Braidwood Design:

**The Braidwood Design:**
**	****2 reactors @ 3.6 GW**
**	****224 m from reactors to near detectors**
**	****~1000 to 2000m to far detectors**
**	****900 live-days of running**
**	****detectors are in two 600****’**** deep shafts**

**Use the near detector**

**The elastic scattering experiment is a rate-limited measurement, so you need to be as close as possible to the reactor while maximizing overburden.**

##  450 mwe shielding 

-  450 mwe shielding
-  Shaft ~200 m from Reactor
-   20-30 m at Krasnoyarsk
-  2 Detectors, 7 m radius

- To measure coupling constants at a reactor
- use the antineutrino-electron **elastic scattering **(ES)

*g**V* = 1⁄2 + 2** sin****2**** ********W**

*g**A* = 1⁄2

- T = electron KE energy
- E = neutrino energy
- m= mass of electron
- This assumes =0

- Mineral Oil

## Remove the reactor flux uncertainty by normalizing to 

- 	inverse beta decay (IBD)

- This cross section is known to 0.2%
- because of recent precision measurements of the neutron lifetime.
- T*his reduces the flux error from 2%  *
*   **...  A crucial improvement over past experiments!*

-  Why can this experiment do better than past reactor-based WMA measurements?

##   Use the window from 3-5 MeV to reduce backgrounds

-   Use the window from 3-5 MeV to reduce backgrounds

- Contamination:
- 	Basically only the Th chain
- Spallation
- 	Reduce by going deep,
- 	by trigger/analysis methods
- Reduce error by using far detectors
- to get accurate measurement

*This window is substantially*
*higher than that needed by*
*magnetic moment experiments*

-  Why can this experiment escape the problems faced by neutrino
- 	magnetic moment measurements?

## Contamination:   208Tl

**Contamination:  **** 208****Tl**

- In pure scintillator, the required
- contamination rate is already
- demonstrated (Kamland, Borexino-
- CTF)

- What about the Gd doping?

- Looks like we can achieve
- 10-12 g/g of Th in Gd,
- which is then diluted to 0.1%
- in scintillator oil

## The decay modes of   208Tl. The “event type” number designates the

- The decay modes of   **208**Tl. The “event type” number designates the
- Type of decay as noted in the Table.

- Each event type contains a 2.6 MeV  and a 1.0 to 1.8 MeV 
- These EM interactions in the scintillator leave an identifiable signature.

## From a Monte Carlo study

- it appears that the events
- form patterns, with
- some of the energetic
- gammas  migrating as far
- as the detector wall.
- The events evolve in
- time, so that the timing
- information provides a way
- to cut on the data and
- exclude this background
- with minimal loss of signal

- Event display of 5 MeV **208**Tl type 1 decays.

## A comparison of the log likelihood of the reconstructed timing 

- A comparison of the log likelihood of the reconstructed timing
- distribution for 500 ES (black) and Tl type 1 (red) events.
- The proposed cut is at logl=20(line). Top: PPO. Bottom: Butyl PBD.

## Backgrounds generated as spallation products of muon interactions:

-  Most spallation-produced isotopes have accompanying 's that can be observed. (CTF) Reduces the spallation backgrounds by 55%.
-  Many have accompanying neutrons that are detected.
-  The remainder are cut by a muon-hadron veto,
- 	which cuts out a window following a high energy shower.

- Spallation products that contain
- two alpha particles:

## End point below 8.72 MeV
Is identification possible through cascade :
8He -> 8Li -> 8Be

- End point below 8.72 MeV
- Is identification possible through cascade :
- 8He -> 8Li -> 8Be

- Decay of 8He

- T. Björnstad *et al*. Nucl.Phys. A366 (1981)461

## dN/N=1.3%      d(sin2 W)=±0.0019

- The goal to shoot for:
- 	dN/N	= 1.3%....... Looks like we can do that
- 		= 1.0%.......	May be attainable
- 		= 0.7%...... 	Hard!

- Compare to NuTeV: 0.0016

## Sensitivity to S and T

- Unusual in strong
- S-dependence

**(1.3%)**

**(0.7%)**

- _Rosner_, hep-ph/0404264

- Fit which does not include NuTeV
- and uses a light Higgs...

- indicates
- Higgs
- dependence

## Include NuTeV in the fit (expressed as gL and gR)

- Include NuTeV in the fit (expressed as gL and gR)

- 1.3%

- 0.7%

- Solution without
- NuTeV
- is about here.
- Downward shift
- is consistent
- with a _heavy_ Higgs

- _Loinaz,_ *et al*,
- hep-ph/0403306

## Sensitivity to 

- A better fit is obtained if neutrinos are allowed to have non-oblique corrections (adjusted by ~0.3%). Idea has now been expanded to consider flavor dependence, with fits to world's data on lepton couplings...

-  The NuTeV result provides 	information on .

-   Reactor experiments provide information on e, although there is slight sensitivity that comes through GF and muon  decay.

- 1.3%

- PRELIMINARY

- _Loinaz,_ *et al*,  hep-ph/0403306

## Summary:

- The discovery of neutrino mass, and neutrino right-handedness
- May be an indication of departrure from Standard Model physics.
- Elastic scattering should provide a additional source of information
- regarding the Standard Model coupling constants.
- Two initiatives are being studied: at Braidwood and more
- recently at Krasnoyarsk.
- The proposals are in the formative state, so please give us your input.

- See also...

- http://braidwood.uchicago.edu/
- http://faculty.washington.edu/josephf/beyond_theta13.html

- Thanks!