# Presentation: 025261

## Past, Present and the Future of Precision sin2W Measurements

**Jae Yu (for NuTeV Collaboration)**
- University of Texas at Arlington
- NuFact’03, June 9, 2003
- Columbia University, New York

- Introduction
- Past measurements
- Current Improvement
- Measurement at a Neutrino Factory
- Conclusions

## NuTeV Collaboration

- T. Adams4, **A. Alton****4**, **S. Avvakumov****7**, L.de Babaro5, P. de Babaro7, R.H. Bernstein3, A. Bodek7, T. Bolton4, S. Boyd8, J. Brau6, D. Buchholz5, H. Budd7, L. Bugel3, J. Conrad2, R.B. Drucker6, **B.T.Fleming****3**, **J.A.Formaggio****2**, R. Frey6, **J. Goldman****4**, **M. Goncharov****4**, D.A. Harris3, R.A. Johnson1, **J.H.Kim****2**, S.Kutsoliotas9, M.J. Lamm3, W. Marsh3,  **D. Mason****6**, J. McDornald8, K.S.McFarland7, **C. McNulty****2**, **Voica Radescu****8**, W.K. Sakumoto7, H. Schellman5, M.H. Shaevitz2, P. Spentzouris3, E.G.Stern2, **M. Vakili****1**, **A. Vaitaitis****2**, **U.K. Yang****7**, J. Yu3*, **G.P. Zeller****2**, and E.D. Zimmerman2#

- University of Cincinnati, Cincinnati, OH45221, USA
- Columbia University, New York, NY 10027
- Fermi National Accelerator Laboratory, Batavia, IL 60510
- Kansas State University, Manhattan, KS 66506
- Northwestern University, Evanston, IL 60208
- University of Oregon, Eugene, OR 97403
- University of Rochester, Rochester, NY 14627
- University of Pittsburgh, Pittsburgh, PA  15260
- Bucknell University, Lewisburg, PA 17837
- *: Current affiliation at the University of Texas at Arlington
- #: Current affiliation at the University of Colorado, Boulder

- June 9, 2003

## sin2W and -N scattering

- In the electroweak sector of the Standard Model, it is not known *a priori* what the mixture of electrically neutral electomagnetic and weak mediator is This fractional mixture is given by the mixing angle
- Within the on-shell renormalization scheme, sin2W is:
- Provides independent measurement of MW & information to pin down MHiggs
- Comparable size of uncertainty to direct measurements
- Measures light quark couplings  Sensitive to other types (anomalous) of couplings
- In other words, sensitive to physics beyond SM  New vector bosons, compositeness,-oscillations, etc

- June 9, 2003

## How did we measure?

- Cross section ratios between NC and CC proportional to sin2W
- Llewellyn Smith Formula:

- Some corrections are needed to extract sin2W  from measured ratios (radiative corrections, heavy quark effects, isovector target  corrections, HT, RL)

- June 9, 2003

## Previous Experiment

- Very small cross section  Heavy neutrino target
- e are the killers (CC events look the same as NC events)

- Conventional neutrino beam from /k decays
- Focus all signs of /k for neutrinos and antineutrinos
- Both  ,  in the beam (NC events are mixed)

- June 9, 2003

## How Do We Separate Events?

- June 9, 2003

## Event Length

- Define an Experimental Length variable
- Distinguishes CC from NC experimentally in statistical manner

- Compare experimentally measured ratio
-  to theoretical prediction of R

- June 9, 2003

## Past Experimental Results

- Significant correlated error from CC production of charm quark (mc) modeled by slow rescaling, in addition to e error

- June 9, 2003

## The NuTeV Experiment

**The NuTeV Experiment**

- Suggestion by Paschos-Wolfenstein by separating andbeams:
- Reduce charm CC production error by subtracting sea quark contributions
- Only valence u, d, and s contribute while sea quark contributions cancel out
- Massive quark production through Cabbio suppressed dv quarks only
- Smarter beamline
- Separate  and beam
- Removes all neutral secondaries to eliminate e content

- June 9, 2003

## Events and EHad After Event Selection

- Events passing cuts: 1.62M 350k (<E>~100GeV)

- June 9, 2003

## NuTeV Event Length Distributions

- Energy Dependent Length cut implemented to improve statistics and reduce systematic uncertainties.

- Good Data-MC
- agreement in
- the cut region

- June 9, 2003

## Event Contamination and Backgrounds

**Event Contamination and Backgrounds**

**SHORT ****************CC’s (20% ********10%********)**
-  exit and rangeout
**SHORT ********e**** CC’s (5%)**
** **eNeX
**Cosmic Rays (0.9%)**

**LONG** **************NC’s (0.7%)**
- hadron shower
- punch-through effects

**Hard** ******Brem(0.2%)**
- Deep events

- June 9, 2003

## Sources of experimental uncertainties kept small, through modeling using  and TB data 

**Other Systematic Effects**

| Effect | Size(sin2W) | Tools |
| --- | --- | --- |
| Zvert | 0.001/inch | +- events |
| Xvert & Yvert | 0.001 | MC |
| Counter Noise | 0.00035 | TB ’s |
| Counter Efficiency | 0.0002 |  events |
| Counter active area | 0.0025/inch |  CC, TB |
| Hadron shower length | 0.0015/cntr | TB ’s and k’s |
| Energy scale | 0.001/1% | TB |
| Muon Energy Deposit | 0.004 |  CC |

- June 9, 2003

## MC to Relate Rexp to Rand sin2W

**MC to Relate R********exp**** to R********and sin****2********W**

- Parton Distribution Model (<Q2> ~ 25 GeV2 for , 16 GeV2 for )
- Correct for details of PDF model  Used CCFR data for PDF
- Model cross over from short  CC events
- Neutrino Fluxes
- ,e,,e in the two running modes
- e CC events always look short
- Shower length modeling
- Correct for short events that look long
- Detector response vs energy, position, and time
- Continuous testbeam running minimizes systematics

- June 9, 2003

## sin2W Fit to Rexp and Rexp

- Thanks to the separate beam  Measure R’s separately
- Use MC to simultaneously fit           and           to sin2W and mc, and  sin2W and 
- R Sensitive to sin2W while R isn’t, so Ris used to extract sin2W and R to control systematics
- Single parameter fit, using SM values for EW parameters (=1)

- Two parameter fit for sin2W and yields

- Syst. Error dominated since we cannot take advantage of sea quark cancellation

- June 9, 2003

## NuTeV sin2W Uncertainties

- 1-Loop Electroweak Radiative Corrections based on Bardin, Dokuchaeva **JINR-E2-86-2 60 (1986****)**

- 0.00005

- Non-isoscalar target

- 0.00014

- Higher Twist

**0.08**

******M****W**** (GeV/c****2****)**

**0.00162**

**Total Uncertainty**

**0.00064**

**Total Physics Model Systmatics**

- 0.00011

- RadiativeCorrection

- 0.00022

- 0.00032

- RL

- 0.00047

- CC Charm production, sea quarks

**0.00063**

**Total Experimental Systematics**

- 0.00027 (23)

- Length (Other effects)

- 0.00030

- Event Vertex

- 0.00039

- e flux

**0.00135**

**Statistical **

******sin****2********W**

**Source of Uncertainty**

- Dominant uncertainty

- June 9, 2003

## Past vs Present Uncertainty Comparisons

- June 9, 2003

## The Present (NuTeV) sin2W

**Confidence level in upper M****higgs ****limit weakens slightly.**

**The Present (NuTeV) sin****2********W**

**Comparable precision but value smaller than other measurements **

- June 9, 2003

## Performed the fit to quark couplings (and gL and gR)
For isoscalar target, the N couplings are

From two parameter fit to          and 

- Performed the fit to quark couplings (and gL and gR)
- For isoscalar target, the N couplings are
- From two parameter fit to          and

**Model Independent Analysis**

-  (SM: 0.3042 -2.6deviation)

-  (SM: 0.0301  Agreement)

- Difficult to explain the disagreement with SM by:
- Parton Distribution Function or LO vs NLO or Electroweak Radiative Correction: large MHiggs

- June 9, 2003

## R- technique is sensitive to q vsq differences and NLO effect
Difference in valence quark and anti-quark momentum fraction 
Isospin symmetry assumption might not be entirely correct
Expect violation about 1%  NuTeV reduces this effect by using the ratio of  and cross sections  Reducing dependence by a factor of 3
s vss quark asymmetry
s ands needs to be the same but the momentum could differ if +30% asymmetry
NuTeV LO di- measurement shows s=s -s ~-0.0027 
NuTeV NLO analysis show no-asymmetry (D. Mason, et al., ICHEP02 proceedings)
NLO and PDF effects
PDF, mc, Higher Twist effect, etc, are small changes
Heavy vs light target PDF effect (Kovalenko et al., hep-ph/0207158)
Using PDF from light target on Iron target could make up the difference  NuTeV result uses PDF extracted from CCFR (the same target)

- Difference in valence quark and anti-quark momentum fraction
- Isospin symmetry assumption might not be entirely correct
- Expect violation about 1%  NuTeV reduces this effect by using the ratio of  and cross sections  Reducing dependence by a factor of 3
- s vss quark asymmetry
- s ands needs to be the same but the momentum could differ if +30% asymmetry
- NuTeV LO di- measurement shows s=s -s ~-0.0027
- NuTeV NLO analysis show no-asymmetry (D. Mason, et al., ICHEP02 proceedings)
- NLO and PDF effects
- PDF, mc, Higher Twist effect, etc, are small changes
- Heavy vs light target PDF effect (Kovalenko et al., hep-ph/0207158)
- Using PDF from light target on Iron target could make up the difference  NuTeV result uses PDF extracted from CCFR (the same target)

**What is the discrepancy due to (Old Physics)?**

- June 9, 2003

## Heavy non-SM vector boson exchange: Z’, LQ, etc
LL coupling enhanced than LR needed for NuTeV
Propagator and coupling corrections
Small compared to the effect
MSSM : Loop corrections wrong sign and small for the effect
Gauge boson interactions
Allow generic couplings  Extra Z’ bosons???
LEP and SLAC results says < 10-3
Many other attempts in progress but so far nothing seems to explain the NuTeV results 
Lepto-quarks
Contact interactions with LL coupling (NuTeV wants mZ’~1.2TeV, CDF/D0: mZ’>700GeV)
Almost sequential Z’ with opposite coupling to 

- LL coupling enhanced than LR needed for NuTeV
- Propagator and coupling corrections
- Small compared to the effect
- MSSM : Loop corrections wrong sign and small for the effect
- Gauge boson interactions
- Allow generic couplings  Extra Z’ bosons???
- LEP and SLAC results says < 10-3
- Many other attempts in progress but so far nothing seems to explain the NuTeV results
- Lepto-quarks
- Contact interactions with LL coupling (NuTeV wants mZ’~1.2TeV, CDF/D0: mZ’>700GeV)
- Almost sequential Z’ with opposite coupling to 

**What other explanations (New Physics)?**

- Langacker *et al*, Rev. Mod. Phys. **64** 87; Cho *et al.*, Nucl. Phys. **B531**, 65; Zppenfeld and Cheung, hep-ph/9810277; Davidson et al., hep-ph/0112302

- June 9, 2003

## To address concerns within the community
Don’t expect to see large effects
LO x-sec model describe CC x-sec data well
Gambino, et al., (hep-ph/0112302) shown little NLO PDF effect to R-
 level shifts to R- small (Davidson, hep-ph/0112302 & Kulagin, hep-ph/0301045)
To calculate O(s) pQCD corrections to the differential X-sec for  DIS
NuTeV (Zeller & McFarland) is collaborating with Theorists
FNAL Theory group: K. Ellis, B. Dobrescu, W. Gigele
DESY: Seven-Olaf Moch
others
Approach based on Altarellu, Ellis & Martinelli, NP B143, 521 (1978)
X-sec’s written in terms of xF1, F2, xF3
pQCD corrections affect 2xF1-F2=FL & xF3-F2
FL effect taken into account via RL
Need s correction of xF3-F2, because s2 is small (Zijlstra, PLB297, 377, 1992)
 Calculations and Implementation of the correction in progress

- Don’t expect to see large effects
- LO x-sec model describe CC x-sec data well
- Gambino, et al., (hep-ph/0112302) shown little NLO PDF effect to R-
-  level shifts to R- small (Davidson, hep-ph/0112302 & Kulagin, hep-ph/0301045)
- To calculate O(s) pQCD corrections to the differential X-sec for  DIS
- NuTeV (Zeller & McFarland) is collaborating with Theorists
- FNAL Theory group: K. Ellis, B. Dobrescu, W. Gigele
- DESY: Seven-Olaf Moch
- others
- Approach based on Altarellu, Ellis & Martinelli, NP B143, 521 (1978)
- X-sec’s written in terms of xF1, F2, xF3
- pQCD corrections affect 2xF1-F2=FL & xF3-F2
- FL effect taken into account via RL
- Need s correction of xF3-F2, because s2 is small (Zijlstra, PLB297, 377, 1992)
-  Calculations and Implementation of the correction in progress

**NLO Upgrade of sin****2********W ****Analysis**

- June 9, 2003

## Neutrinos come from  decays
Good understanding of the beam content and flux
Better collimated than conventional beam
Large neutrino flux (105~106 higher than the current)
But...
Always two neutrinos simultaneously in the given beam ( e+ or e)
Traditional heavy target detector will not work
Will screw up NC counting due to e CC events
Need light target detectors  Can afford to do this
Might need new techniques for NC to CC ratio
Can’t distinguish e vs  induced NC events  

- Good understanding of the beam content and flux
- Better collimated than conventional beam
- Large neutrino flux (105~106 higher than the current)
**But...**
- Always two neutrinos simultaneously in the given beam ( e+ or e)
- Traditional heavy target detector will not work
- Will screw up NC counting due to e CC events
- Need light target detectors  Can afford to do this
- Might need new techniques for NC to CC ratio
- Can’t distinguish e vs  induced NC events

**sin****2********W ****Measurement at a NuFact**

- June 9, 2003

## A Light Target sin2W Detector at a NuFact

- A Light Target sin2W Detector at a NuFact

- e and  from muon decays are in the beam at all times
- Must use light target (D2) detectors

- June 9, 2003

## Expectation at a NuFact

- Using a 1m thick D2 target, one can obtain about 20M  CC events per yearWith the help of good p-id, the stat doubles  Length related uncertainties become irrelevant

- June 9, 2003

## Experimental Issues 
Must be able to reverse beam polarity and measure current well
Detector must be light weight
Must be able to distinguish primary e, and  
Need to control overall p-ID efficiency to be better than 10-3
High electron detection efficiency
Good EM and Hadronic shower ID
Good charged particle momentum measurement
Good vertex measurement w/ triggering capability at the target
Theoretical Issues
Better measured charm CC x-sec
Need to understand radiative correction better
Better understanding of higher twist effects

- Must be able to reverse beam polarity and measure current well
- Detector must be light weight
- Must be able to distinguish primary e, and  
- Need to control overall p-ID efficiency to be better than 10-3
- High electron detection efficiency
- Good EM and Hadronic shower ID
- Good charged particle momentum measurement
- Good vertex measurement w/ triggering capability at the target
**Theoretical Issues**
- Better measured charm CC x-sec
- Need to understand radiative correction better
- Better understanding of higher twist effects

**Experimental and Theoretical Issues**

- June 9, 2003

## Conclusions

- NuTeV has improved sin2W
- NuTeV result deviates from SM prediction by about +3(PRL 88, 091802, 2002)
- Interpretations of this result implicates lower left-hand coupling (-2.6but good agreement in right-hand coupling with SM
- NuTeV discrepancy has generated a lot of interest in the community
- Still could be a large statistical fluctuation (5 has happened before)
- No single one can explain the discrepancy
- NuTeV working on NLO analysis of sin2W
- A Neutrino factory can provide a dramatic improvement in sin2W
- Large neutrino flux (both e and )
- Significant improvement in uncertainties (MW<25MeV)
- Light target detector with p-id would be necessary
- Theoretical improvement will help further improving the measurement

- June 9, 2003