Transcript Neutrino-Nucleon sin2theta_W

PHYS 5326 – Lecture #7
Monday, Feb. 10, 2003
Dr. Jae Yu
1. Improvements in Sin2qW
2. Interpretation of Sin2qW results
3. The link to Higgs
No class this Wednesday  Will make up on Fridays.
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
1
How is sin2qW measured?
( 3)
coupling  I weak
( 3)
coupling  I weak
 QEM sin 2 qW
• Cross section ratios between NC and CC proportional to sin2qW
• Llewellyn Smith Formula:
 ( )
R

σNC( )
σCC( )
Monday, Feb. 10, 2003
 ( )


σ
1
5
 ρ 2   sin2 θ W  sin4 θ W  1  CC( )
2
9
σ CC


PHYS 5326, Spring 2003
Jae Yu
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



Experimental Variable
Define an Experimental Length variable
Distinguishes CC from NC experimentally in statistical manner
Compare experimentally measured ratio
R Exp
Monday, Feb. 10, 2003
NNC Candidates
NShor t
L  L Cut



NLong
L  L Cut
NCC Candidates
to theoretical prediction of R
PHYS 5326, Spring 2003
Jae Yu
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Past Experimental Results
Shell
sin2θ On
W
 MW
M2W
 1  2  0.2277  0.0036
MZ
OnShell
 80.14  0.19GeV/c 2
The yellow band represents a correlated uncertainty!!
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
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2
sin qW
Theoretical Uncertainty
• Significant correlated error from CC production of charm quark (mc)
modeled by slow rescaling mechanism
• Suggestion by Paschos-Wolfenstein by separating  and` beams:

R 
σNC  σNC
σCC  σCC


1
 R R
2
 ρ   sin θ W  
1 r
2

2
Reduce charm CC production error by subtracting sea quark contributions
Only valence u, d, and s contributes while sea quark contributions cancel out
Massive quark production through Cabbio suppressed dv quarks only
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
5
Improving Experimental Uncertainties
• Electron neutrinos, e, in the beam fakes NC events from CC
interactions
– If the production cross section is well known, the effect will be
smaller but since majority come from neutral K (KL) whose x-sec is
known only to 20%, this is a source of large experimental
uncertainty
• Need to come up with a beamline that separates neutrinos from
anti-neutrinos
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
6
Event Contamination and Backgrounds
•SHORT m CC’s (20% , 10% `)
m exit and rangeout
•SHORT e CC’s (5%)
eNeX
•Cosmic Rays (0.9%)
•LONG m NC’s (0.7%)
hadron shower
punch-through effects
•Hard m Brem(0.2%)
Deep m events
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
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Other Detector Effects
Sources of experimental uncertainties kept small, through modeling using  and TB data
Size(dsin2qW)
Effect
Tools
Zvert
0.001/inch
m+m- events
Xvert & Yvert
0.001
MC
Counter Noise
0.00035
TB m’s
Counter Efficiency
0.0002
 events
Counter active area
0.0025/inch
 CC, TB
Hadron shower length
0.0015/cntr
TB p’s and k’s
Energy scale
0.001/1%
TB
Muon Energy Deposit
0.004
 CC
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
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•
•
Measurements of e Flux
 
K   p 0e  
e )
Use well known processes (Ke3:
Shower Shape Analysis can provide direct measurement e events,
though less precise
Nmeas /NMC
1.05  0.03  e 
 
Weighted average
used for e
dRexp~0.0005
1.01  0.04  e
 e from very short events (E>180 GeV)
• Precise measurement of e flux in the tail region of flux  ~35% more
`e in ` than predicted
• Had to require (Ehad<180 GeV)
due to ADC saturation
Results in sin2qw shifts by +0.002
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
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MC to Relate Rexp to R and sin2qW
• Parton Distribution Model
– Correct for details of PDF model  Used CCFR data for PDF
– Model cross over from short m CC events
•
Neutrino Fluxes
 m,e,`m,`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
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
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sin2qW Fit to Rexp and R`exp
Thanks to the separate beam  Measure R’s separately
exp
exp
Use MC to simultaneously fit R and R to sin2qW and mc, and sin2qW and r
•
•
R ( ) 
•
•
σNC( )
σCC( )
 ( )  


σ
1
5
 ρ 2   sin2 θ W  sin4 θ W  1  CC( )  
2
9
σ CC  


R Sensitive to sin2qW while R` isn’t, so R is used to extract sin2qW and R` to
control systematics
Single parameter fit, using SM values for EW parameters (r0=1)
sin2 θ W  0.2277  0.0013 (stat)  0.0009 (syst)
m c  1.32  0.09 (stat)  0.06 (syst) w/ m
2
c
 1.38  0.14 GeV/c as input
•Two parameter fit for sin2qW and r0 yields
sin2 θ W  0.2265  0.0031
ρ 0  0.9983  0.040
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
Syst. Error dominated
since we cannot take
advantage of sea
quark cancellation
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NuTeV sin2qW Uncertainties
Dominant
uncertainty
d sin2qW
Source of Uncertainty
Statistical
0.00135
e flux
0.00039
Event Length
0.00046
Energy Measurements
0.00018
Total Experimental Systematics
0.00063
CC Charm production, sea quarks
0.00047
Higher Twist
0.00014
Non-isoscalar target
0.00005
 /
0.00022
RadiativeCorrection
0.00011
RL
0.00032
Total Physics Model Systmatics
0.00064
Total Systematic Uncertainty
0.00162
DMW (GeV/c2)
Monday, Feb. 10, 2003
1-Loop Electroweak Radiative
Corrections based on Bardin,
Dokuchaeva JINR-E2-86-2 60 (1986)
2 (On  shell)
W
δsin θ
 M 2t  175GeV 2 

 0.00022  
2

 50GeV 

 MH 
 0.00032  ln

150GeV


0.08
PHYS 5326, Spring 2003
Jae Yu
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NuTeV vs CCFR Uncertainty Comparisons
}Beamline worked!
}Technique worked!
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
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Homework Assignments
• Process the transferred TMB data files and
convert them into TMBtree for root analysis
– You can work together on this one
– One person can produce TMBtree for all
– Due next Monday, Feb. 17
• Produce an electron ET spectrum of the highest
ET electrons in your samples
– Due next Wednesday, Feb. 19
Monday, Feb. 10, 2003
PHYS 5326, Spring 2003
Jae Yu
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