# Presentation: 381404

## CP Violation in the B Meson System: The Belle Measurement of sin21

*Eric Prebys, Princeton University*
- for the
**BELLE Collaboration**

- Fermilab

- April 26, 2001

## The BELLE Collaboration

- 300 people from 49 Institutions in 11 Countries:
- Australia, China, India, Korea, Japan, Philippines, Poland, Russia, Taiwan, Ukraine,  and USA

- Fermilab

- April 26, 2001

## Parity Violation

- The “parity” operation transforms the universe into its mirror image (*goes from right-handed to left-handed*).
- Maxwell’s equations are totally parity invariant.
- BUT, in the 50’s huge parity violation was observed in weak decays...

-  decay of polarized **Co:**

- electron preferentially emitted opposite spin direction

- Fermilab

- April 26, 2001

## CP (almost) Conservation

- It was found that by applying the **C**[harge Conjugation]  operation to all particles, the overall symmetry seemed to be restored (neutrinos are left-handed, anti-neutrinos are right-handed).
- This symmetry fit nicely into the current algebras, and later the gauge theories being used to describe weak interactions.
- Unfortunately, it wasn’t *quite* exact...

- Fermilab

- April 26, 2001

## CP Violation

- In 1964, Fitch, Cronin, *etal*, showed that physics is not *quite* invariant under the CP operation, essentially by proving that neutral kaons formed mass eigenstates

- where

- This generated great interest (not to mention a Nobel Prize), and has been studied in great detail ever since, but to date has only been conclusively observed in the kaon system.

- Fermilab

- April 26, 2001

## Weak Interactions in the Standard Model

- In the Standard Model, the fundamental particles are leptons and quarks

- In this model, weak interactions are analogous to QED.

- OR

- quarks combine as
- to form hadrons

- leptons exist
- independently

- Fermilab

- April 26, 2001

## Quark Mixing

- In the Standard Model, leptons can only transition *within* a generation (NOTE: probably not true!)

- Although the rate is *suppressed*, quarks can transition *between* generations.

- Fermilab

- April 26, 2001

## The CKM Matrix

- The weak quark eigenstates are related to the strong (or mass) eigenstates through a unitary transformation.

- Cabibbo-Kobayashi-Maskawa (CKM) Matrix

- The only straightforward way to *accommodate** *CP violation in the SM is by means of an irreducible phase in this matrix (requires at least three generations, led to prediction of *t* and *b* quarks)

- Fermilab

- April 26, 2001

## Wolfenstein Parameterization 

- The CKM matrix is an SU(3) transformation, which has four free parameters.  Because of the scale of the elements, this is often represented with the “Wolfenstein Parameterization”

- CP Violating phase

- First two generations *almost* unitary.

- Fermilab

- April 26, 2001

## “The” Unitarity Triangle

- Unitarity imposes several constraints on the matrix, but one...

- Results in a triangle in the complex plane with sides of similar length                , which appears the most interesting for study

- Fermilab

- April 26, 2001

## The Plane

- Remembering the Wolfenstein Parameterization

- we can divide through by the magnitude of the base....

- CP violation is generally discussed in terms of this plane

- Fermilab

- April 26, 2001

##  Direct CP Violation

- CP Violation is manifests itself as a difference between the physics of matter and anti-matter

*Direct* CP Violation is the observation of a difference between two such decay rates; however, the amplitude for one process can in general be written

- Weak phase changes sign

- Strong phase does not

- Since the observed rate is only proportional to the _amplitude_, a difference would only be observed if there were an *interference* between two diagrams with different weak *and* strong phase*.*

*** *Rare and hard to interpret

- Fermilab

- April 26, 2001

## Indirect CP Violation

- Consider the case of B-mixing

- Mixing phase

- Fermilab

- April 26, 2001

## Indirect CP Violation (cont’d)

- If both                  can decay to the same *CP eigenstate** f,* there will be an *interference*

- And the time-dependent decay probability will be

- Decay phase

- CP state of* f*

- Mixing phase

- Difference between B mass eigenstates

- Fermilab

- April 26, 2001

## The Basic Idea

- We can create          pairs at the           resonance.
- Even though both *B’*s are mixing, if we tag the decay of one of them, the other must be the CP conjugate *at that time**.* We therefore measure the time dependent decay of one B relative to the time that the first one was tagged (EPR “paradox”).
- PROBLEM:  At the          resonance, B’s only go about 30 m in the center of mass, making it difficult to measure time-dependent mixing.

- Fermilab

- April 26, 2001

## The Clever Trick

- If the collider is *asymmetric*, then the entire system is Lorentz boosted.
- In the Belle Experiment, 8 GeV e-’s are collided with 3.5 GeV e+’s  so

- 

- So now the time measurement becomes a *z* position measurement.

- Fermilab

- April 26, 2001

## “Gold-Plated” Decay

- Total state CP

- Fermilab

- April 26, 2001

## Predicted Signature

*t* = Time of tagged decays

- Fermilab

- April 26, 2001

## “Tin-Plated” Decay

- Complicated by “penguin pollution”, but still promising

- Fermilab

- April 26, 2001

## Make LOTS of       pairs at the (4S) resonance in an asymmetric collider.
Detect the decay of one B to a CP eigenstate.
Tag the flavor of the other B.
Reconstruct the position of the two vertices.
Measure the z separation between them and calculate proper time separation as
Fit to the functional form

Write papers.

- Detect the decay of one *B* to a CP eigenstate.
- Tag the flavor of the other *B.*
- Reconstruct the position of the two vertices.
- Measure the *z* separation between them and calculate proper time separation as
- Fit to the functional form
- Write papers.

- Review - What B-Factories Do...

- Fermilab

- April 26, 2001

## Motivations for Accelerator Parameters

- Must be asymmetric to take advantage of Lorentz boost.
- The decays of interest all have branching ratios on the order of 10-5 or lower.
- Need lots and lots of data!
- Physics projections assume 100 fb-1 = 1yr @ 1034 cm-2s-1
- Would have been pointless if less than 1033 cm-2s-1

- Fermilab

- April 26, 2001

## The KEKB Accelerator

- Asymmetric Rings
- 8.0GeV(HER)
- 3.5GeV(LER)
- Ecm=10.58GeV= M((4S))
- Target Luminosity: 1034s-1cm-2
- Circumference: 3016m
- Crossing angle: 11mr
- RF Buckets: 5120
-  2ns crossing time

- Fermilab

- April 26, 2001

## Motivation for Detector Parameters

- Vertex Measurement
- Need to measure decay vertices to <100m to get proper time distribution.
- Tracking...
- Would like p/p.5% to help distinguish B decays from BK  and BKK decays.
- Provide dE/dx for particle ID.
- EM calorimetry
- Detect ’s from slow, asymmetric ’s   need efficiency down to 20 MeV.
- Hadronic Calorimetry
- Tag muons.
- Tag direction of KL’s from decay BKL .
- Particle ID
- Tag strangeness to distinguish B decays from Bbar decays (low p).
- Tag ’s to distinguish B decays from BK  and BKK decays (high p).

*Rely on mature, robust technologies whenever possible!!!*

- Fermilab

- April 26, 2001

## The Detector

- Fermilab

- April 26, 2001

## All Finished!!

- Fermilab

- April 26, 2001

## June 1, 1999: Our First Hadronic Event!!

- Fermilab

- April 26, 2001

## Best Beam Parameters

- (17)

- (2600)

- (1100)

- (4600)

- (18)

- (.24)

- (.56)

- (0.6)

- (8)

- (140)

- (140)

- (1.4)

- (1.4)

- (1)

- (1)

- (.05/.05)

- (.05/.05)

- () = design

- Fermilab

- April 26, 2001

## A (not a-)Typical Day

**   ****STOP Run**** +HV Down **** +Fill HER**** +Fill LER**** +HV Up**** +START Run**
** ****= 8 Minutes!**

- Fermilab

- April 26, 2001

## Luminosity

- Daily integrated luminosity

- Total integrated luminosity

- Total for first CP Results (Osaka):

- Total for *these* Results:

- Our Records:
- Instantaneous:
- Per (0-24h) day:
- Per (24 hr) day:
- Per week:
- To date:

- (on peak)

- Note: integrated numbers are accumulated!

- World Records!!

- Fermilab

- April 26, 2001

## The Pieces of the Analysis

- Event reconstruction and selection
- Flavor Tagging
- Vertex reconstruction
- CP fitting

- Fermilab

- April 26, 2001

## J/ and KS Reconstruction

- J/ and KS Reconstruction

- Mev
- Require mass
-  within 4of PDG

- Fermilab

- April 26, 2001

## BKS Reconstruction

*B****K**S** *Reconstruction

- In the CM, both *energy* and *momentum* of a real B0 are constrained.
- Use “Beam-constrained Mass”:

- Signal

*123 Events*
*3.7 Background*

- Fermilab

- April 26, 2001

## All Fully Reconstructed Modes (i.e. all but L)

| Mode | Events | Background |
| --- | --- | --- |
| BS | 123.0 | 3.7 |
| All Others | 71.0 | 7.3 |
| Total | 194.0 | 10.0 |

- Fermilab

- April 26, 2001

## BKL Reconstruction

- Measure direction (only) of *K**L** *in lab frame
- Scale momentum so that M(*K**L**+***)=M(*B**0*)
- Transform to CM frame and look at *p(B**0**)*.

- KLM Cluster

*J/**** *daughter particles

*K**L*

- Fermilab

- April 26, 2001

## BKL Signal

*0<p**B*****<2 *GeV/c

- Biases spectrum!

*131 Events*
*54 Background*

- Fermilab

- April 26, 2001

## Complete Charmonium Sample

**Total **                                                   325               65

- Fermilab

- April 26, 2001

## Flavor Tagging           

- X

- Fermilab

- April 26, 2001

## Flavor Tagging (Slow Pion)

- Very *slow* pion

- Fermilab

- April 26, 2001

## Comparison Between MC and Data

- +   Data
- --- MC

- Events

- Diluted B-Mixing

- Fermilab

- April 26, 2001

## Tagging Efficiency

- Tagging efficiency = 99.4% (vs. 99.3% in MC)
- Effective efficiency eff = (1-2w)2  = **27.0%** (vs. 27.4% in MC)

- Experimentally determined w values in each *r* region

- Fermilab

- April 26, 2001

## Vertex Reconstruction

- Common requirements in vertexing
- # of associated SVD hits > 2 for each track
- IP constraint in vertex reconstruction
*CP* side vertex reconstruction
- Event is rejected if reduced 2 > 100.
- Tag side vertex reconstruction
- Track parameters measured from *CP* vertex must satisfy:
- |*z*|<1.8mm, |*z*|<500m, |*r*|<500m
- Iteration until reduced 2 < 20 while discarding worst track.
- |*z**CP* - *z*tag|<2mm (****10***B*)

- Overall efficiency = ~87%.    In total 282 events for the CP fit.

- Fermilab

- April 26, 2001

## CP Fit (Probability Density Function)

*f**BG* = background fraction.  Determined from a 2D fit of *E* vs *M.*
*R(**** t) = *resolution function.  Determined from *D*****’s* and MC.
*PDF**BG**(**** t) = *probability density function of background. Determined from  sideband (210 events).

- Fermilab

- April 26, 2001

## Resolution Function

- Fit with a double-Gaussian...

- Fermilab

- April 26, 2001

## Test of Vertexing – B Lifetime

- pdg2000

- [ps]

**Lifetime (ps)**

**Mode**

- Combined

- Fermilab

- April 26, 2001

## The Combined Fit (All Charmonium States)

- Fermilab

- April 26, 2001

## Individual Subsamples 

**Fit  ****(stat. err.)**

**Mode**

- CP = -1

- CP = +1

- Non-CP

- All CP

- Fermilab

- April 26, 2001

## Consistency Check

- Plot asymmetry in individual time bins...

- ACP

- Fix at PDG value

- Our fit

- Fermilab

- April 26, 2001

## Sources of Systematic Error

- Bottom Line

- Published in **Phys.Rev.Lett. 86, 2509 (2001)**

- Fermilab

- April 26, 2001

## “Measurement of B0d - B0d-bar Mixing Rate from the Time Evolution of Dilepton Events at Upsilon(4S)” PRL 86,3228
"Observation of Cabibbo suppressed B -> D(*)K- decays at Belle" (submitted to PRL )
"A Measurement of the Branching Fraction for the Inclusive B->Xs gamma Decays with Belle“ (submitted to PLB)
"Measurement of Inclusive Production of Neutral Pions from Upsilon(4S) Decays” (submitted to PRL)

- "Observation of Cabibbo suppressed B -> D(*)K- decays at Belle" (*submitted to PRL*** )**
- "A Measurement of the Branching Fraction for the Inclusive B->Xs gamma Decays with Belle“ (*submitted to PLB)*
- "Measurement of Inclusive Production of Neutral Pions from Upsilon(4S) Decays” (*submitted to PRL)*

- Other Recent Publications

- + Several More in the Pipeline!!

- Fermilab

- April 26, 2001

## Belle is working very well!!
Our current value of sin2based on 10.5 fb-1 of data is

This is consistent with the BaBar value of 

and with other previous results (CDF, LEP)

The probability of observing this value if CP is conserved is 4.9%
The next few years should be very exciting!

- Our current value of *sin2*******based on 10.5 fb-1 of data is
- This is consistent with the BaBar value of
- and with other previous results (CDF, LEP)
- The probability of observing this value if CP is conserved is 4.9%
- The next few years should be very exciting!

- Summary and Outlook

- Fermilab

- April 26, 2001

## Key Belle Milestones

- Early 1990’s: Japanese groups begin working.
- January 1994: Collaboration forms.
- April 1995: TDR Submitted.
-     ...lots of work by lots of people in lots of places...
- Dec 18, 1998: Belle detector completed (including SVD)
- Jan 26, 1999: First cosmic ray with full detector.
- May 1, 1999: Belle rolled into place.
- June 1, 1999: First hadronic event!!!!!
- November 9, 1999: Integrated luminosity exceeds 100 pb-1
- February 29, 2000: Integrated luminosity exceeds 1 fb-1
- July 28, 2000: First CP results presented at Osaka (used 6.2 fb-1)

- Fermilab

- April 26, 2001

## What about 3?

- Corresponding decay would be Bs KS,, but...
- Require move to (5s) resonance (messier)
- Time dependent Bs mixing not possible.
-  Have to find another way.

- Fermilab

- April 26, 2001

## Are Two B-Factories Too Many?

- These are not discovery machines!
- Any interesting physics would manifest itself as small deviations from SM predictions.
- People would be very skeptical about such claims without independent confirmation.
- Therefore, the answer is NO (two is not *one* too many, anyway).

- Fermilab

- April 26, 2001

## Differences Between PEP-II (BaBar) and KEKB (Belle)

- PEP-II has complex IR optics to force beams to collide head-on.	Pros: 	Interaction of head-on beams well understood.	Cons: 	Complicates IR design.		More synchrotron radiation.		Can’t populate every RF bucket.
-  In KEK-B, the beams cross at ±11 mr.	Pros: 	Simple IR design.		Can populate every RF bucket.		Lower (but not zero!!!) synchrotron radiation.	Cons: 	Crossing can potentially couple longitudinal 		and transverse instabilities.

*At present, both designs seem to be working.*

- Fermilab

- April 26, 2001

## Differences (cont’d)

- Readout:
-  BaBar uses an SLD-inspired system, based on a continuous digitization. The entire detector is pipelined into a software-based trigger.	Pros: 	Extremely versatile trigger.		Less worry about hardware-based trigger systematics.		Can go to very high luminosities.		Cons: 	Required development of lots of custom hardware.
-  Belle’s readout is based on converting signals to time-pulses. The trigger is an “old-fashioned” hardware-based level one. Events satisfying level one are read out after a 2 μs latency.	Pros: 	Simple.		Readout relies largely on “off-the-shelf” electronics.	Cons: 	Potential for hardware-based trigger systematics.		Possible problems with high luminosity.

- Fermilab

- April 26, 2001

## Particle ID needs

- Fermilab

- April 26, 2001

## Nuts and Bolts: Readout

- Philosophy: Signal  Time Pulse  TDC (LeCroy 1877)  Generic DAQ

- Binary Data

- Pulse Train Encoding (Hit  Edge)

- 

- Analog Signal

- Variable *Length *Pulse

- 

- Fermilab

- April 26, 2001

## DAQ Overview

- Fermilab

- April 26, 2001

## Nuts and Bolts: Analysis Framework 

- Belle AnalysiS Framework (Pronounced “BASF”):
- Developed entirely with freeware (GNU, Cernlib, CLHEP, etc)
- Script Driven
- Based on individual data generation/processing modules (C++ classes), with common members (hist_def, begin_run, event, etc).
- All data (raw, intermediate, physics, constants) arranged in named banks based on the PANTHER bank system and stored in files.
- Individual banks or groups of banks can be read or written to files at any point in data processing.
- Constants stored in database based on Postgresql.
- Multiprocessing supported for read/write file access and histogram/ntuple generation.

- Fermilab

- April 26, 2001

## Example BASF full MC Job

- path add_module main qq98 gsim acc_mc path add_module main calcdc calsvd reccdc recsvd trasan trak path add_module main AnadEdx ext rectof rececl_cf path add_module rececl_match rececl_gamma path add_module main rececl_pi0 rec_acc mu2 klid path add_module v0finder rec2mdst evtcls sakurapath add_module main kid_mc_mon AnadEdx_mc_mon tof_mc_monpath add_module main table_list
- nprocess set 5
- module put_parameter qq98 USER_TABLE\b02psikl.dec
- histogram define signal_tag.hbk
- initialize
- table savebr belle_begin_runtable save belle_eventtable save mdst_alltable save evtcls_alltable save gsim_randtable save hepevt_all
- output open signal.evt
- generate_event 10000
- terminate

- Specify Processing Modules

- Number of Processors

- Pass Parameters to Modules

- Specify Tables to Save

- Histogram File

- Output File

- Go!

- Fermilab

- April 26, 2001

## Example BASF Analysis Job

- path add_module main user_ana histogram define user.hbk
- initialize
- process_event signal.evt
- terminate

- Will look for user_ana.so

- Could be real data or MC

- Fermilab

- April 26, 2001

## Example User Analysis (user_ana.cc)

- // Charged tracksMdst_charged_Manager &ChgMgr = Mdst_charged_Manager::get_manager();
- for(vector<Mdst_charged>::iterator it = ChgMgr.begin();          it != ChgMgr.end() ; it++) {
-     // Form a 4-vector for this particle    Vector3 p_i(it->px(),it->py(),it->pz());    Vector4 p4_i(p_i,sqrt(p_i.mag2()+EMass2));
-     // Now loop over the second particle    for(vector<Mdst_charged>::iterator jt = it+1;	jt != ChgMgr.end() ; jt++) {
-       // Require opposite charges      if((jt->charge())==(it->charge())) continue;         // If we're here, we have two tracks of opposite charge.         // Calculate the pair mass         Vector3 p_j(jt->px(),jt->py(),jt->pz());         Vector4 p4_j(p_j,sqrt(p_j.mag2()+EMass2));         Vector4 p4 = p4_i+p4_j;
-          float pairMass = p4.mag();  // Calculate the pair mass
-     }}

- Access charged track PANTHER bank

- Loop over list of individual objects (tracks)

- Manipulate using standard tools

- Fermilab

- April 26, 2001

## Event by Event Tagging Quality

- If we tag events wrongly, we’ll measure CP violation as

- So the measurement is *diluted* by a factor

- Ideally, we can determine this on an event by event basis to be used in the CP fit
- Example, for high*-p* lepton

- p*

- right

- wrong

- Fermilab

- April 26, 2001

## Multi-dimensional Flavor Tagging

- Fermilab

- April 26, 2001