lhcb masterclasslhcb-public.web.cern.ch/.../lhcbmasterclasswrapup.pdf · piano string 4⋅10–3 s...

LHCb MasterclassGood Times

Jonas Rademacker Good Times LHCb Masterclass 2013

Time scales

2

1 102010–20 10–10 1010seconds


Time scales

2

1 1020

D0

Average lifetime of a D0 meson

4⋅10–13s

10–20 10–10 1010seconds


Time scales

2

1 1020

birth of the universe 4⋅1017s ago

D0


4⋅10–13s

10–20 10–10 1010seconds


Time scales

2

1 1020


typical life-span of a person 2.4⋅109s

D0


4⋅10–13s

10–20 10–10 1010seconds


Time scales

2

1 1020



Heart beatsonce every 1s

D0


4⋅10–13s

10–20 10–10 1010seconds


Time scales

2

1 1020




extinction of dinosaurs

2⋅1015 s ago

D0


4⋅10–13s

10–20 10–10 1010seconds


Time scales

2

1 1020





2⋅1015 s ago

D0


4⋅10–13s

10–20 10–10

First homo sapiens

6⋅1012 s ago

1010seconds


Time scales

2

1 1020





2⋅1015 s ago

This talk: ca 103 sD0


4⋅10–13s

10–20 10–10

First homo sapiens

6⋅1012 s ago

1010seconds


Time scales

2

1 1020





2⋅1015 s ago

This talk: ca 103 s

T=1/f of a piano string

4⋅10–3 s

D0


4⋅10–13s

10–20 10–10

First homo sapiens

6⋅1012 s ago

1010seconds


Time scales

2

1 1020





2⋅1015 s ago

This talk: ca 103 s


4⋅10–3 s

T=1/f of an atomic clock

10–10 s

D0


4⋅10–13s

10–20 10–10

First homo sapiens

6⋅1012 s ago

1010seconds


Time scales

2

1 1020





2⋅1015 s ago

This talk: ca 103 s


4⋅10–3 s


10–10 s

D0


4⋅10–13s

Average lifetime of a Higgs

boson 1.6⋅10–22s

10–20 10–10

First homo sapiens

6⋅1012 s ago

1010seconds


Time scales

3


D0


4⋅10–13s

You measured an incredibly short amount of time!


Time scales

3


D0


4⋅10–13s


≈Heart beats

once every 1s

First homo sapiens

6⋅1012 s ago


Time scales

3


D0


4⋅10–13s


≈Heart beats

once every 1s

First homo sapiens

6⋅1012 s ago

≈extinction of dinosaurs

2⋅1015 s ago

This talk: ca 103 s


Time scales

3


D0


4⋅10–13s


≈Heart beats

once every 1s

First homo sapiens

6⋅1012 s ago

≈extinction of dinosaurs

2⋅1015 s ago

This talk: ca 103 s

2h≈birth of the universe

4⋅1017s ago


How did you do it?

4


How did you do it?• Trick: very high speeds! D mesons travel nearly at the

speed of light at LHCb. Typically v ≈ 0.99919 × c

4




• v × 0.41 ps = 0.12 mm

4




• v × 0.41 ps = 0.12 mm

• However, they really fly typically ~3 mm, much further.

4




• v × 0.41 ps = 0.12 mm


• This is because of time dilation (Special Relativity). Fast D0 mesons live longer. A lifetime at rest of 0.41 ps means a lifetime inside our experiment of ca 10ps

4




• v × 0.41 ps = 0.12 mm


• This is because of time dilation (Special Relativity). Fast D0 mesons live longer. A lifetime at rest of 0.41 ps means a lifetime inside our experiment of ca 10ps

• So with incredibly high speeds, we win twice: The D0 travels further in any given time, plus it lives longer -> measurable distances (several mm).

4


What you found• It’s tricky. There is background, and there are D

mesons that don’t come from the primary vertex

5

primary vertex

D0

K

πa few mm




5

primary vertex

D0

K

πa few mm

B

primary vertex

D0

K

πa few mm




5

primary vertex

D0

K

πa few mm

a few

mor

e mm

B

primary vertex

D0

K

πa few mm




5

primary vertex

D0

K

πa few mm

a few

mor

e mm

B

primary vertex

D0

K

πa few mm

IP


What you found

6


Decay time distribution

7

You found an exponential decay time distribution.

log-scale linear scale


Decay time distribution

7

You found an exponential decay time distribution.

log-scale linear scale

Is this really expected?


Same distribution for humans

8

!!!!!0!

!!!500!

!1,000!

!1,500!

!2,000!

!2,500!

!3,000!

!3,500!

!4,000!

!4,500!

!5,000!

!!0! !20! !40! !60! !80! 100! 120!

(death probability vs age for female New Zealanders)


!!!!!0!

!1,000!

!2,000!

!3,000!

!4,000!

!5,000!

!6,000!

!!0! !10! !20! !30! !40! !50! !60! !70! !80! !90! 100!

Decay/death probability

9

particlespeople


0.00000#

0.05000#

0.10000#

0.15000#

0.20000#

0.25000#

0.30000#

0.35000#

0.40000#

##0# #20# #40# #60# #80# 100# 120#

Probability to die/decay next year

10

particlespeople

Particles can decay, but they don’t age.

The shape of the decay time

distribution is a direct consequence

of that.

probability that, given person/particle survived until year x, she/it will die/decay within the following year.


Summary• You measured an incredibly short

amount of time!

• You did so exploiting enormous speeds, and special relativity.

• ... and one of the most sophisticated machines in the world.

• You found an exponential decay rate -> particles don’t age.

• The exact value of your fit result is an important parameter in particle physics.

11


D0


4⋅10–13s

≈Heart beats

once every 1s

First homo sapiens

6⋅1012 s ago

!!!!!0!

!1,000!

!2,000!

!3,000!

!4,000!

!5,000!

!6,000!

!!0! !10! !20! !30! !40! !50! !60! !70! !80! !90! 100!


Backup

12


• Higgs: 1.56e-22

• D0: 4.1e-13

• Middle C: 261.63 Hz -> 3.8e-3

• second: 1e0

• minute: 6.0e1

• hour: 3.6e3

• day: 8.6e4

• year: 3.2e7

• human lifetime: 2.4e9

• Fall of Rome 4.7e10 (ca 1,500 years ago)

• end of last ice age 3.2e11 (10,000 years ago)

• Last neanderthal: 9.5e11 (30,000years ago)

• first homo sapiens 6.3e12 (200,000 years ago)

• end of dinosaurs: 2.1e15 (66 M years ago)

• The alpes: 1.0e16

• planet earth: 1.4e17

• universe: 4.3e17 (13.77 billion years)

• 2 hours/age of univers = tauDo/1 second.

13


Probability to die/decay next year

14

!0.00!

10.00!

20.00!

30.00!

40.00!

50.00!

60.00!

70.00!

80.00!

90.00!

!!0! !20! !40! !60! !80! 100! 120!

particlespeople

Particles can decay, but they don’t age.

The shape of the decay time

distribution is a direct consequence

of that.


Time scales

15

1 10201010



Last Neanderthalca1012 s ago



2⋅1015 s ago

This talk: ca 103s


4⋅10–3 s


10–10 s

D0


4⋅10–13s

Average lifetime of a Higgs

boson 1.6⋅10–22s

10–20 10–10

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