Transcript University of Virginia Chad J Materniak for the HyperCP Collaboration SESAPS 2006

University of Virginia
Search for CP Violation in Hyperon Decays
with the HyperCP Spectrometer at Fermilab
Chad J Materniak
for the HyperCP Collaboration
SESAPS 2006
9 November 2006
Chad J Materniak
1
HyperCP (FNAL E871)
Collaboration
Chan, Y.C. Chen, C. Ho, P.K. Teng
Academia Sinica Taiwan
W.S. Choong, Y. Fu, G. Gidal, P. Gu, T. Jones, K.B. Luk, B. Turko, P. Zyla
University of California at Berkeley and Lawrence Berkley National Laboratory
C. James, J. Volk
Fermilab
R. Burnstein, A. Chakravorty, D. Kaplan, L. Lederman, W. Luebke, D. Rajaram,
H. Rubin, N. Solomey, Y. Torun, C. White, S. White
Illinois Institute of Technology
N. Leros, J.P. Perround
Universite de Lausanne
R.H. Gustafson, M. Longo, F. Lopez, H.K. Park
University of Michigan
C.M. Jenkins, K. Clark
University of South Alabama
C. Dukes, C. Durandet, T. Holmstrom, M. Huang, L.C. Lu, K. Nelson
University of Virginia
9 November 2006
Chad J Materniak
2
Motivation for CP Violation Studies
• Mystery: Why didn’t all the matter and antimatter annihilate leaving
nothing but an empty universe? What caused the asymmetry?
• Sakharov’s ingredients: Proposed in 1967
1) Baryon number violation - a way to get rid of matter (or antimatter)
without annihilation.
2) Violation of both C and CP - allow for different
particle/antiparticle decay rates.
3) Departure from thermal equilibrium when antimatter was turning
into matter.
• CP violation has been observed in the K and B systems.
• However, the observed CP violation is insufficient to explain the
asymmetry!
Studies of CP violation may help us understand the matterantimatter asymmetry and may lead to new physics
9 November 2006
Chad J Materniak
3
Why Search for CP Violation in
Hyperon Decays?
•
Hyperons are sensitive to sources
of CP violation that kaons are not.
–
•
•
•
Possible CP violation in hyperons
is not constrained by kaon sector
measurements of ’/
Calculation of constraints on A
from ’/ measurements for
various SUSY models.
Many scenarios for new physics
allow for large CP asymmetries in
Hyperons.
SM prediction for CP asymmetries
are small so any signal strongly
suggests new physics.
Hyperons are experimentally
accessible.
–
–
No new accelerators needed
Experimental apparatus is modest
in scope and cost.
9 November 2006
Chad J Materniak
He et al., PRD 61 (2000) 071701(R)
4
Parity Violation in Hyperon Decays
•
•
•
•
Decay modes are two-body
non-leptonic.
Daughter particle decay
distributions are anisotropic
 parity violating.
The slope of the daughter
baryon cos distribution is
given by PPP.
Magnitudes of parity
violation, i.e the  parameters,
are generally large.
slope   P PP

Anisotropic proton decay
distribution:
dN
d cos
dN
N
 0 (1   P cos )
d cos 2



E.g.   p
-1
9 November 2006
0
1
Chad
J Materniak
5
Parity Violation in Hyperon Decays
•
•
•
•
Decay modes are two-body
non-leptonic.
Daughter particle decay
distributions are anisotropic
 parity violating.
The slope of the daughter
baryon cos distribution is
given by PPP.
Magnitudes of parity
violation, i.e the  parameters,
are generally large.
slope   P PP
dN
d cos


-1
9 November 2006
0
1
Chad J Materniak
6

CP Violation in Hyperon Decays

E.g.   p
The daughter baryon preferentially decays in the direction of the parent
particles polarization.

If CP is conserved:
    
dN( p)

d cos
dN( p)

d cos
9 November 2006
Np
(1   P cos )
2
Np
(1  P cos
  )
2
  p 
slope    P
dN
d cos
 p 
slope   P
dN
d cos


-1
Chad J Materniak
0 
1
-1
0
1
7
Producing ’s with Known
Polarization
We produce ’s of known polarization through unpolarized  decays.
Targeting at zero degrees insures that our produces ’s are unpolarized.
   
   
If the  is produced unpolarized, then the  is found in a helicity state.

P   pˆ 
dN( p) N p

(1   cos )
d cos
2

If CP is good, then
9 November 2006
    

P    pˆ 
dN( p) N p

(1    cos  )
d cos 
2
If CP is conserved, the slopes of
the proton and antiproton cos
distributions are equal!
Chad J Materniak
8
Producing ’s with Known
Polarization
We produce ’s of known polarization through unpolarized  decays.
Targeting at zero degrees insures that our produces ’s are unpolarized.
   
   
If the  is produced unpolarized, then the  is found in a helicity state.

     p  
slope    P

dN
d cos
-1
If CP is good, then
9 November 2006
dN
d cos



     p  
slope   P
0

1
    
-1
0
1
If CP is conserved, the slopes of
the proton and antiproton cos
distributions are equal!
Chad J Materniak
9
CP Violating Asymmetry: A
From the cos distributions we seek to extract the asymmetry
parameter A.


    
A 
 A  A
     
The slope is measured in the  rest
frame where the orientation of the
polar axis is defined by the 
momentum in the  rest frame.
where,
  
A    




A      


    



  0.458 PDG Ave.
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HyperCP Spectrometer at Fermilab
•
•
•
Spectrometer sat in Fermilab’s
meson line.
Data taking runs completed in
1997 & 1999.
Spectrometer specifications:
–
–
–
–
–
Tevatron
Main Ring
800 GeV incident proton
beam
167 GeV secondary beam
High rate DAQ (100k evts/s)
High rate, narrow pitch wire
chambers for tracking
Two hodoscopes and hadron
calorimeter at rear for
triggering
Designed to minimize
bias when switching
from - to + modes.
9 November 2006
Chad J Materniak
11
HyperCP Spectrometer at Fermilab
•
•
•
Spectrometer sat in Fermilab’s
meson line.
Data taking runs completed in
1997 & 1999.
Spectrometer specifications:
–
–
–
–
–
800 GeV incident proton
beam
167 GeV secondary beam
High rate DAQ (100k evts/s)
High rate, narrow pitch wire
chambers for tracking
Two hodoscopes and hadron
calorimeter at rear for
triggering
Designed to minimize
bias when switching
from - to + modes.
9 November 2006
A look up the Meson Line
Chad J Materniak
12
HyperCP Spectrometer at Fermilab
•
•
•
Spectrometer sat in Fermilab’s
meson line.
Data taking runs completed in
1997 & 1999.
Spectrometer specifications:
–
–
–
–
–
800 GeV incident proton
beam
167 GeV secondary beam
High rate DAQ (100k evts/s)
High rate, narrow pitch wire
chambers for tracking
Two hodoscopes and hadron
calorimeter at rear for
triggering
Designed to minimize
bias when switching
from - to + modes.
9 November 2006
Chad J Materniak
13
Accounting for -,+ Acceptance
Differences
•
Differences in production
mechanisms for the - and +
lead to spectrometer
acceptance differences.
Fix: Weight - and +
momentum distributions and
force them to be identical.
•
–
–
–
Weight the ’s momentum
dependent parameters at exit
of the collimating magnet.
106 total bins.
Perform measurement of cos
distribution.
This method equalizes
acceptance between - and +
events
9 November 2006
-
+
p
-
data
+ data
Chad J Materniak
p
Pass 1
Bin data
in 106 bins
Pass 1
Bin data
in 106 bins
calculate -weights and
fill histograms
calculate +
weights and
fill histograms
14
Accounting for -,+ Acceptance
Differences
Differences in production
mechanisms for the - and +
lead to spectrometer
acceptance differences.
Fix: Weight - and +
momentum distributions and
force them to be identical.
•
–
–
–
Weight the ’s momentum
dependent parameters at exit
of the collimating magnet.
106 total bins.
Perform measurement of cos
distribution.
-: red
AU
+: blue
GeV
unweighted
Ratio
•
weighted
This method equalizes
acceptance between - and +
events
9 November 2006
Chad J Materniak
GeV
15
Accounting for -,+ Acceptance
Differences
Differences in production
mechanisms for the - and +
lead to spectrometer
acceptance differences.
Fix: Weight - and +
momentum distributions and
force them to be identical.
•
–
–
–
Weight the ’s momentum
dependent parameters at exit
of the collimating magnet.
106 total bins.
Perform measurement of cos
distribution.
-: red
AU
+: blue
GeV
unweighted
Ratio
•
weighted
This method equalizes
acceptance between - and +
events
9 November 2006
Chad J Materniak
GeV
16
Extracting the CP Asymmetry from
Data
• The cos ratios for the
proton and antiproton
are:
dN( p) N p

(1   cos )
d cos
2
dN( p) N p

(1    cos
)
d cos
2
     p  
slope    P
dN
d cos
     p  
slope   P
dN
d cos


-1
0 
1
-1
0
1

• We fit the ratios to:

R(cos , ) 
N p (1    cos )
N p 1 (     )cos 
Ratio
        
• Then we extract the
asymmetry.



A 

      2 
9 November 2006
good CP
dN
d cos


Chad J Materniak
-1
0
1
17
Extracting the CP Asymmetry from
Data
• The cos ratios for the
proton and antiproton
are:
dN( p) N p

(1   cos )
d cos
2
dN( p) N p

(1    cos
)
d cos
2
     p  
slope    P
dN
d cos
     p  
slope   P
dN
d cos


-1
0 
1
-1
0
1

• We fit the ratios to:

R(cos , ) 
N p (1    cos )
N p 1 (     )cos 
Ratio
        
• Then we extract the
asymmetry.



A 

      2 
CP
dN
d cos


-1
0
1
No MC necessary to extract result!
9 November 2006
Chad J Materniak
18
Published Result
•
•
•

Approximately 10% of data broken
into 18 analysis subsets and
analyzed.
 extracted for each data subset and
A calculated from:


A 

      2 
The weighted average from the 18
measurements is (BKG subtracted):
A  [0.0  5.1(stat)  4.4(syst)] 104
(*)

Proton/antiproton cos ratio before
() and after (∆) weighting.
(*) PRL
9 November 2006
Chad J Materniak
31 Dec. 2004
19
Published Result
•
•
•

Approximately 10% of data broken
into 18 analysis subsets and
analyzed.
 extracted for each data subset and
A calculated from:


A 

      2 
The weighted average from the 18
measurements is (BKG subtracted):
A  [0.0  5.1(stat)  4.4(syst)] 104
(*)
20X better

(*) PRL
9 November 2006
Chad J Materniak
31 Dec. 2004
20
Published Result
•
•
•

Approximately 10% of data broken
into 18 analysis subsets and
analyzed.
 extracted for each data subset and
A calculated from:


A 

      2 
The weighted average from the 18
measurements is (BKG subtracted):
A  [0.0  5.1(stat)  4.4(syst)] 104
(*)

•
•
9 November 2006
MC only used to validate the
analysis technique.
Most systematic uncertainties can
be reduced with the analysis of the
full data set.
Chad J Materniak
21
Expanding the Analysis to the Full
Data Set
•
•
Approx 1 billion  decays separated
into 10 analysis sets using the entire
1999 HyperCP data sample.
10 billion MC events generated at
Fermilab in order to verify the
analysis technique.
Expect sensitivity better than
A = 2 10-4..
Detailed systematic error studies
underway.
MC Data: 0.5B events
2/ndf =19.7/18
C = 1.000
Ratio (Negative/Positive)
•
input = 0.0 10-4
fit = 1.7 10-4
Proton/antiproton cos ratio before
() and after (∆) weighting.
9 November 2006
Chad J Materniak
22
Expanding the Analysis to the Full
Data Set
•
•
Approx 1 billion  decays separated
into 10 analysis sets using the entire
1999 HyperCP data sample.
10 billion MC events generated at
Fermilab in order to verify the
analysis technique.
Expect sensitivity better than
A = 2 10-4..
Detailed systematic error studies
underway.
Real Data: >100M events
Ratio (Negative/Positive)
•
Proton/antiproton cos ratio before
() and after (∆) weighting.
9 November 2006
Chad J Materniak
23
Expanding the Analysis to the Full
Data Set
•
•
•
Approx 1 billion  decays separated
into 10 analysis sets using the entire
1999 HyperCP data sample.
10 billion MC events generated at
Fermilab in order to verify the
analysis technique.
Expect sensitivity better than
A = 2 10-4..
Detailed systematic error studies
underway.
Future CP
Sensitivity
9 November 2006
Chad J Materniak
24
Expanding the Analysis to the Full
Data Set
•
•
•
Approx 1 billion  decays separated
into 10 analysis sets using the entire
1999 HyperCP data sample.
10 billion MC events generated at
Fermilab in order to verify the
analysis technique.
Expect sensitivity better than
A = 2 10-4..
Detailed systematic error studies
underway.
Results already constrain
upper SUSY limits.
9 November 2006
Chad J Materniak
25
Conclusions and Outlook
• Using the largest sample of hyperon decays ever amassed by an
experiment, the HyperCP collaboration is making a precision search for
CP violation from exotic sources.
• Measurements are complementary to those carried out in the K and B
sectors.
• Thus far we have found no evidence of CP violation in ± and 
decays
– A= [0.0 ± 5.1(stat) ± 4.2(syst)] 10-4
• Analysis of the entire 1999 data sample is underway.
–
–
–
–
MC running on Fermilab Grid
Weighting technique working
Systematic studies in progress
Shortly we will push our uncertainty to our statistical limit and reach an
uncertainty A~ 2 10-4.
9 November 2006
Chad J Materniak
26
Backup Slides
9 November 2006
Chad J Materniak
27
HyperCP Experimental Goals
•
•
•
Primary goal:
–
Search for CP violation in ±±p decays.
Secondary goals:
1)
Search for CP violation in   K.
2)
Lepton number violation in -  p--.
3)
Flavor changing neutral currents in hyperon and charged kaon
decays:
+  p+-, K  +-.
4)
S > 1 decays: -  p--, -  5)
Search for + pentaquark.
Measurement of hyperon production and decay parameters:
1)
 and  polarization.
2)  decay parameter in - decays   strong phase shift.
3)
 decay parameter in   K.
4)
Hyperon production cross sections.
9 November 2006
Chad J Materniak
28
Phenomenology of CP Violation in
Hyperon Decays
•
•
CP violation is manifestly direct with S = 1.
Three ingredients are necessary to get a non zero asymmetry:
1)
At least two channels in the final state: S- and P-wave amplitudes.
2)
The CP violating weak phases must be different for the two channels
3)
There must be unequal final state strong phase shifts.
A  (     ) /(     )   tan( P   S )sin(P  S )
A  (     ) /(     )   tan( P  S )sin(P  S )
strong phases
•
weak phases
Asymmetry greatly reduced by strong phase shifts.
•
Strong phases shift measured by HyperCP!
9 November 2006
Chad J Materniak
29
Comparison of A, A with ’/
/
A, A
•
•
•
Thought to be due to Penguin diagram in
Standard Model
Expressed through a different CP-violating
phase in S- and P-wave amplitudes
Probes parity-violating and parityconserving amplitudes
•
Thought to be due to Penguin diagram in
Standard Model
•
Expressed through a different CP-violating
phase in I=0 and I=2 amplitudes
Probes parity-violating amplitudes
•
“Our results suggest that this measurement is complementary to the
measurement of /, in that it probes potential sources of CP violation at a
level that has not been probed by the kaon experiments.”
9 November 2006
He and Valencia, PRD 52 (1995), 5257.
Chad J Materniak
30
Expanding the Analysis to the Full
Data Set
•
•
•
•
Approx 1 billion  decays separated
into 10 analysis sets using the entire
1999 HyperCP data sample.
10 billion MC events generated at
Fermilab in order to verify the
analysis technique.
Large systematic uncertainties in
the previous measurement
revisited.
Expect sensitivity better than
A = 2 10-4..
9 November 2006
Weighted vs. unweighted ratios
AU
Ratio
AU
Chad J Materniak
Ratio
31
Expanding the Analysis to the Full
Data Set
•
•
Weighted vs. unweighted ratios
AU
Ratio
•
Approx 1 billion  decays separated
into 10 analysis sets using the entire
1999 HyperCP data sample.
10 billion MC events generated at
Fermilab in order to verify the
analysis technique.
Large systematic uncertainties in
the previous measurement
revisited.
Expect sensitivity better than
A = 2 10-4..
AU
Ratio
•
Ratio
AU
9 November 2006
Chad J Materniak
32
HyperCP Publications
• Observation of Parity Violation in the -K- Decay.
Phys. Lett. B 617, 11 (2005)
• Search for the Lepton-Number-Violating Decay -p--.
Phys. Rev. Lett. 94, 181801 (2005)
• HyperCP: A high-rate spectrometer for the study of charged hyperon
and kaon decays.
Nucl. Instrum. Methods A 541, 516 (2005)
• Search for S=2 Nonleptonic Hyperon Decays.
Phys Rev. Lett. 94, 101804 (2005)
• Measurement of the  Asymmetry Parameter for the -K- Decay.
Phys. Rev. D 71, 051102(R) (2005)
• Evidence for the Decay +p+-.
Phys. Rev. Lett. 93, 262001 (2005)
• Search for CP Violation in Charged- and  Hyperon Decays.
Phys. Rev. Lett. 93, 262001 (2005)
9 November 2006
Chad J Materniak
33
HyperCP Publications II
• High Statistics Search for the + Pentaquark State.
Phys. Rev. D 70, 111101(R) (2004)
• New Measurement of -- Decay Parameters.
Phys. Rev. Lett. 93, 011802 (2004)
• Tripling the Data Set for the HyperCP Experiment.
IEEE Trans. Nucl. Sci. 49:568-576, 2002
• Observation of the Decay K-- +- and Measurements of the
Branching Ratios for K±± +.
Phys. Rev. Lett. 88, 111801 (2002)
• Upgraded DAQ System for the HyperCP Experiment.
Nucl. Intrum. Methods A 474, 67 (2001)
• A High-Throughput Data Acquisition System for the HyperCP
Experiment.
Nucl. Instrum. Methods A 455, 424 (2000)
9 November 2006
Chad J Materniak
34