Dissecting the Higgs Discovery: The Anatomy of a 21st Century Scientific Achievement

Transcription

1 Dissecting the Higgs Discovery: The Anatomy of a 21st Century Scientific Achievement Lauren Tompkins Arthur H. Compton Lectures October 19th, 2013 Lecture 7 Digesting the Data: Triggering and Data Processing

2 Schedule of Lectures [10/5] Welcome to the Theater: Introduction to the Standard Model and Higgs Boson [10/12] Accelerators: Creating particles out of (very) thin air [10/19] Seeing the Higgs with light [10/26] Guest Lecture: Martin Bauer On Theory [11/2] Seeing the Higgs with heavy particles [11/9] Adding particles with a little help from Einstein [11/16] Digesting the Data: Triggering, Data Processing [11/23] Finding the Needle in the Haystack: Data Analysis and Statistics [11/30] No Lecture for Thanksgiving [12/7] No Lecture for Physics with a Bang [12/14] What's next for the LHC? 2

3 Outline Brief Review of last week Deciding what data to keep Making sense of the data The GRID 3

4 Last week on Level 4

5 Last week Special relativity states that the laws of physics are the same in all reference frames on Level 4

6 Last week Special relativity states that the laws of physics are the same in all reference frames Observers in different reference frames measure different Energy & Momentum but always the same invariant mass on Level 4

7 Last week Special relativity states that the laws of physics are the same in all reference frames Observers in different reference frames measure different Energy & Momentum but always the same invariant mass on Level Quarks and gluons form jets in the detectors 4

8 Jet Events 5

9 Outline Brief Review of last week Deciding what data to keep Making sense of the data The GRID 6

10 Data Deluge 7

11 Data Deluge 40 million times per second! 7

12 Data Deluge 8

13 Data Deluge Each event is ~ 1.25 MB 1MB ~ 500 page book Human genome = 800MB 8

14 Data Deluge Each event is ~ 1.25 MB 1MB ~ 500 page book Human genome = 800MB 40 million events per second = 50 TB/second 5x library of congress s printed collection! $2,500 of 2TB disks! 8

15 Data Deluge Each event is ~ 1.25 MB 1MB ~ 500 page book Human genome = 800MB 40 million events per second = 50 TB/second 5x library of congress s printed collection! $2,500 of 2TB disks! WAY TOO MUCH! 8

16 Most events look like this (minus the muons) 9

17 Discerning Decisions Need to reduce the data to a manageable rate Luckily interesting physics happens rarely Higgs is produced ~ 1 out of every billion events Solution: Triggering Throw out % of the events but make sure we keep the Higgses! may-2009/gallery-sergio-cittolin 10

18 Multistep Approach 11

19 Step 1: Quick & Dirty 12

20 Step 2: Selective Sight 13

21 Step 3: The (almost) full picture 14

22 The Numbers First stage: Reduces rate from 40MHz to 100kHz All but 0.25% Second stage: Another factor of 25 Last stage: Another factor of 8 Output: 500Hz or 625MB/s 54 TB/day! 15

23 The Hardware 16

24 Now what? The 54TB/day of saved data gets reconstructed Computer algorithms find physics objects. E.g., Associate calorimeter clusters to tracks to find electrons Match trajectories in the muon system with those in the inner tracking detectors Calculate the momentum balance in an event 17

25 Complexity Millions of lines of code Hundreds of developers (including me!) Up to 30 million pieces of data to be looked at per event! 18

26 Where and How? Where is all this data stored?: the World Wide LHC Computing Grid How is it all processed?: the World Wide LHC Computing Grid 19

27 The GRID 20

28 ATLAS Snapshot 21

29 Yearly Consumption 22

30 Perspective 23

31 Improving Triggering 24

32 Fast Tracker 25

33 Many Working Parts 26

34 UChicago s Contribution 27