october 1999the first events from belle first events from belle hep seminar brookhaven national lab...

October 1999 The First Events from BELLE

First Events from BELLE

HEP Seminar

Brookhaven National Lab

Daniel Marlow Princeton University

October 21, 1999


Physics MotivationDirect CP violation is perhaps the simplest case. Consider the CP mirror processes:

))(

))(

fBfB

fBfBACP

fBfB and

The CP asymmetry is defined as

The decay amplitudes are

and SWSW iiff

iiff eeAAeeAA

Note that the weak phase changes sign.


Direct CP Violation

Note that

Yielding

22

ffff AA

221121

SWSW iiii

f eeAeeAA

221121

SWSW iiii

f eeAeeAA

We need some sort of interference, two amplitudes, for example

)cos( 2 21

2

2

2

1 SWf AAAA

)cos( 2 21

2

2

2

1 SWf AAAA


Direct CP ViolationDespite its conceptual and experimental simplicity, there are two problems with direct CP violation:

•Cases where there are two comparable amplitudes that are large are (probably) rare.

•The strong phases are poorly understood, making it difficult to extract the weak (KM) phases that are of greatest interest.

This leads one in the direction of asymmetric B factories aimed at the study of indirect CP violation.


Indirect CP Violation

022

02

(0 sincos)( BeiBetB mimtmtimi

In this approach we provide the interference using state mixing, i.e.,

00BB


Indirect CP ViolationThus for a decay where is a CP eigenstate, we have two “indistinguishable” decay paths

fB 0

f0B0B f

Working through the algebra, yields a time-dependent CP asymmetry )(2sin)sin(2

)()(

)()()(

00

00

DMf

CP

tm

fBfB

fBfBtA

M DWhere and are the weak phases for the mixing and decay diagrams, respectively and

1

f

f ffCP


The Kobayashi-Maskawa Mixing Scheme

Where the second matrix is the Wolfenstein parameterization.

0* tbubtsustdud VVVVVV

Quark mixing is described via

The “d b” unitarity relation yields 3* AVV ubtd

1)1(

21

)(21

23

22

32

AiA

A

iA

VVV

VVV

VVV

M

tbtstd

cbcscd

ubusud


CP Phases in the Gold-Plated Mode

0DSKJB /0

)arg( tdM V

Decay

Mixing

The KM phase comes from the mixing.


The Unitarity Triangle

3A

Vtd

,

0,1

3A

Vub

3A

Vcb

1

2

3

The gold-plated mode determines the angle which is also called .

1


Existing Constraints

Existing measurements

of mixing and

limit the

allowed region in the

plane.

00BB

ubV

,


The Measurement

0B

0B

tag

CP

z

0DNeed to:

•Measure momenta

•ID leptons & K’s

•Measure vertices

e e

0K

/J


The Measurement

The time-dependent asymmetry appears mainly as a mean shift in the distribution between events tagged

as decays and

events tagged as

decays.

z

0B0B


The KEK-B Asymmetric Collider

KEK-B is similar to PEP-II in many ways, although there is a (potentially) important difference in the way in which the beams are brought into collision.

ee

ee


Beam Crossing Schemes

By colliding the beams at an angle, the KEK-B design achieves a simplified interaction region.

Moreover, every RF bucket (2 ns spacing) can be filled toachieve maximum luminosity. However, this approach risks destabilizing couplings between transverse and longitudinal modes of the machines.

A crab-crossing cavity is under development in case this proves to be a problem.


Linac Parameters

HER e- LER e+Parameter Design Achieved Design Achieved

Beam Energy 8 GeV 8.5 GeV 3.5 GeV 4.0 GeV

Charge/bunch 1.2 nC 1.2 nC .64 nC .60 nC

Transmission 100% 80-100% 100% 70%

Rep. Rate 50 Hz 50 Hz 50 Hz 50 Hz

Emittance <0.1 um .06 um <.25 um .4 um


IP @ / yx

HER e- LER e+

Parameter Design Achieved Design Achieved

Beam Current 1100 mA 514 mA 2600 mA 532 mA

Single BunchCurrent .22 mA 4 mA .52 mA 2.3 mA

Number ofBunches

5000 800 5000 1024

33/1 cm 100/1.1 cm 33/1 cm 100/1 cm

InjectionEfficiency

100% 80% 100% 80%

Ring Parameters


Luminosity

The luminosity is a factor of ~30 below design, but steady progress was made before the summer shutdown.


The BELLE Collaboration

About 10 Countries, 50 Institutes, & 200 People


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!!!!!

• June 1999 About 1200 hadron events obtained before vacuum pipe mishap.

• July 1999 More data (30K events) and lots learned.


June 1, 1999: Our First Hadronic Event


More Fun: SVD Included


First J/Candidate

• J/ee

– M(ee) = 3.1 GeV


SVD Performance


SVD Performance

e

e

Bhabha miss distance


SVD Performance


SVD Tomography

X-Z distribution of primary vertices for all triggers, including beam gas.

The IP, the beam crossing angle, and various flanges etc in the IR are clearly evident.


CDC Performance


CDC Performance (Cosmic Rays)


Particle ID (dE/dx, ToF, & Aerogel)


Particle ID (dE/dx, ToF, & Aerogel)

0DD K


CsI EM Calorimeter Performance

MeV 50E

tionReconstruc 0

tionReconstruc


More CsI


Electron ID


Muon ID


0LK Detection

LKP

missP

hi

iS PPP,

4miss

First ~1000 hadronic events.


Physics from the First Runs: Energy Scan


Lepton-pair Spectrum


A “Typical” Dimuon event

• J/

– M() = 3.1 GeV

–both muons tracks clearly evident in magnet return yoke

This event is consistent with

although there were no hits in the RPCs

LKJB /


candidate KJB /


Charm Mass Plots KD0

KD

4SOn

4S Off


Charmed Baryon

pKc


Unstable Particles


Unstable Particles

Impossible without PID


D Lifetimes

selection 0D

Decay-time distribution.

(PDG)

ps )004.415.0( c.f.

ps )05.38.0(

0

0

D

D


D Lifetimes

(PDG)

ps )015.057.1( c.f.

ps )2.0.1(

D

D


Truth in Advertising

• CDC backgrounds higher than expected– Wire currents somewhat high

– Crosstalk raises effective occupancy

– Problem under study, one option is to reduce Q/T converter ramp-down time

– Cause appears to be reflected synchrotron radiation.

– Early indications are that steps taken to mitigate this problem during the recent shutdown have been effective . . . Confirmation needed.


. . . Truth in Advertising

• SVD inner layer destroyed by synchrotron radiation. – 20 um gold added to inside of beampipe

– new SVD installed during shutdown

– SVD #3 and #4 in the works!

– Once again, early indications are that the steps taken to mitigate the problem have been effective.


Conclusions & Outlook

• The KEK-B accelerator is working with luminosity of before shutdown.

• The entire Belle detector, including the DAQ and offline reconstruction software, is working.

• We face daunting challenges in terms of increasing the luminosity while keeping the backgrounds under control.

• If steady rate of improvement continues, we should be competitive.

• The months ahead will be interesting!

-1-232 scm 103

october 1999the first events from belle first events from belle hep seminar brookhaven national lab...

Documents

belle cp phases

belle direct cp violation

belle indirect cp violation

cp eigenstate

study of indirect cp

belle linac parameters

time dependent cp asymmetry

cp mirror processes