PPC - Chasing a Dream at the LHC(Lecture 02)

PHYS 823

1

SummaryPPC1) Why? … Dark Matter and SUSY2) Where? … LHC & CMS Detector3) How? … SUSY Searches

PrologueIt has been 13.8 B years, sincethe LHC machine was set up. Themachine finally started providingproton-proton collisions at acenter-of-mass energy of 7 TeVon March 30, 2010 and becamethe energy frontier machine tolead discoveries of new particles.The Standard Model (SM) iscurrently well tested up to ~100GeV, but is expected to breakdown in the TeV domain where newphysics should occur. This isprecisely the domain that we willstudy at the LHC.

PPC CubePPPC Cub

22

� SLAC: Stanford Linear Accelerator Center, in California, discovered thecharm quark (also discovered at Brookhaven) and tau lepton; ran anaccelerator producing huge numbers of B mesons.

� Fermilab: Fermi National Laboratory Accelerator, in Illinois, where thebottom and top quarks and the tau neutrino were discovered.

� CERN: European Laboratory for Particle Physics, crossing the Swiss-French border, where the W and Z particles were discovered.

� BNL: Brookhaven National Lab, in New York, simultaneously with SLACdiscovered the charm quark.

� CESR: Cornell Electron-Positron Storage Ring, in New York. CESRperformed detailed studies of the bottom quark.

� DESY: Deutsches Elektronen-Synchrotron, in Germany; gluons werediscovered here.

� KEK: High Energy Accelerator Research Organization, in Japan, is nowrunning an accelerator producing huge numbers of B mesons.

� IHEP: Institute for High-Energy Physics, in the People's Republic ofChina, performs detailed studies of the tau lepton and charm quark

The World's Major Accelerators

33

Livingstone Curve

44

B-factory

Z-factory

Center-of-mass energies of beam

W/Z

top I

Hadron (p,p)colliders

Ce

nte

r-o

f-m

ass

en

erg

y o

f e

lem

en

tary

co

mp

on

en

ts (q

ua

rks,

ele

ctr

on

s) in

Ge

V

Year to start running

Lepton (e+e-)colliders

History

ccharmtau

5 6

Inside CERN

09.07.28

09.07.29

09.10.22

09.10.23

11.04.14

77

Big Bang, Back to the Future

88

13.8 Billion Years Ago

99 Hadron Collisions at the Tevatron and the LHC

1976 …

110

Upsilon (bb) �� �+��

Aspen, 2001

1977 …

11

ZZ in 1987W in 1982

1980’sUA2UA1

12

CERN Courier (July/August 2009)

1983 … Discovery of W’s1984 … Nobel prize to Carlo Rubbia and Simon van der Meer

1983

13

1985~1995

114

1983

WWhen I had a problem and couldn’tsleep:

“Kamon-kun, the safety is the number onepriority since you are at a foreign country.”

15

1985

Pencil and ruler?

16

Tim Berners-Lee““We learned Englishfrom WWW.”

World Wide Web (WWW)

1989

Twenty-two years ago an event at CERNchanged the world forever. Tim Berners-Leehanded a document to his supervisor MikeSendall entitled “Information Management : aProposal”. “Vague, but exciting” is how Mikedescribed it, and he approved it to go forward.The following year, the World Wide Web wasborn.

17

1991

OOn Analysis of Top Quark:

“Kamon-kun, it doesn’t make sense toignore jets in hadron collider experiments.

18

1994

““Individual, chasing the nature’s truth;;Big science, providing the answer.”

19

1995443 candidates

from 3.4x1012 collisionsDiscovery of Top in 1995

20

3 Years Ago

221

22009.11.23: First 900-GeV pp Collisions

2 Years Ago2009.11.20: International Video Conference

4 pm CERN

10 am Maryland

9 am FNAL

11 pm Daegu

22

Then, Cube with Real Collision

DDark Matter

Feynman Diagram

pp Collision at CMS

LHC

23

Sunghyun Chang

Youngdo Oh & Adil Khan

1 Year Ago

224

7:467:467:15 7:50

9:11 10:08

12:4612:33 12:48

12:58

10:13

March 30, 2010

225

Time What is happening==== ===================================================================13:00 7 TeV Collisons at CMS (6 am in Texas)12:56 Collapsing the separation bumps12:36 E = 3.5 TeV -- Flat Top

(B1 ~ 1.8E10; B2 ~ 1.8E10) 12:29 E = 3 TeV11:52 Ramping11:46 Prepare for ramp: Fill #1005 (B1 ~ 2E10; B2 ~ 1.9E10) 11:37 Inject both beams ... 2 bunches/beam11:13 Injection beam probe11:13 Global beam permit for B1 and B2 -- green11:11 E = 450 GeV11:02 Preparing for injection10:40 Beam expected in 30 min10:19 Beam expected in one hour9:25 Preparing to ramp down9:22 E = 3.5 TeV8:53 Beams dumped8:50 Lost Beam2 @ 1386 GeV8:36 Ramp starts up to 3.5 TeV (E = 1 TeV at 8:46)8:27 Preparing the ramp: Fill #1004 (B1 = 1.9E10; B2 = 1.8E10)8:16 Injecting with colliding bunch pattern; correcting chromaticity,

tune and orbit: E = 450 GeV8:04 Injection probe beam7:58 Prepare for injection6:53 No beam until 8:15 am GVA (1:15 am in Texas)

226

2010 …

2.5x1012 Collisions227

2011 …

350x1012 Collisions228

2012 …

700x1012 Collisions229

Luminosity

221

4��NN

fL �sizebeamis

beameachinparticles#arefrequencycollisionis

21

�

NNf

,

� The beam area is products of accelerator properties and of beamproperties

30

Higher Luminosity� TTo reach higher luminosity…

� More beam � Higher collision frequency (more bunches)� Smaller beam� All can be hard to achieve due to instabilities that may

develop

� WWant high luminosity to study rare processes� Luminosity Cross Section = Event Rate� e.g., 1 1033 cm-2 s- 1 1 pb = 3.6 events/hr

� Fast detector signals & Fast trigger decision

31

Dream, but, not SF

Texas-style hunting

32

SUSY is :a) Supersymmetrized Standard Model

(“DDemocratic” solution betweenFermions and Bosons);

b) An elegant solution to solve theproblem associated with the Higgsmass;

Supersymmetry (SUSY)

+

Unification!

c) Beautifully connecting the Standard Modelwith an ultimate unification of thefundamental interactions;

d) Cosmologically consistent with a DarkMatter candidate – stable neutralino.

01�~

Neutral

Lightest

SUSY

Particle type33

nf = 6 (quark flavors); nc = 3 (colors)

e.g., QCD

IIntroduction toHigh Energy Physics

by D. H. Perkins

�s

Q2 (GeV2)

)/log()2(1112)( 22

2

�

�Qnn

Qflavorcolor

s ��

The Nobel Prize in Physics 2004

Running Couplings

34

I think so.Unification – Attractive?

We can construct a SUSYmodel with a stableneutralino to have the grandunification of the forces.

SM SM+SUSY

35

SUSY

Cosmological Connection: ���� � DM

SUSY

CDM = Neutralino ( )01�~

Ast

roph

ysic

s

SUSY is an interesting classof models to provide a weaklyinteracting massive neutralparticle (M ~ 100 GeV).

SM

��� � 23%

Neutral-ino s-leption s-quark

36

“Number” density (nn) ��

Cross section (��)

SUSY Masses (at the LHC)masses)(SUSY2

01

D�h~�

]Mpcskm100[ 11 �� � /Hh

� �3 22eqnnHn

dtdn

� ��� v�

22

����

�

�

����

�

�

�

����

�

�

����

�

�

�ann� + …. + ….

Co-annihilation (CA) Process (Griest, Seckel ’91)

37

~0.0000001 seconds

Now

CMB

annihilation

combination

LHC

http://www.damtp.cam.ac.uk/user/gr/public/bb_history.html

Probing Early Universe

Probing 10-7 sec. after Big Bang

38

SUSY is :a) Supersymmetrized Standard Model

(“DDemocratic” solution betweenFermions and Bosons);

b) An elegant solution to solve theproblem associated with the Higgsmass �� around 1 TeV;

Minimal Scenario

+

Unification!

c) Beautifully connecting the Standard Modelwith an ultimate unification of thefundamental interactions � around 1 TeV;

d) Cosmologically consistent with a DarkMatter candidate – stable neutralino �around 1 TeV.

39

Minimal Supersymmetric Standard Model(MSSM) – more than 100 parameters

Impossible to have more than 100measurements at the LHC

It looks like you have 5 conditions for 100unknowns. How can we solve 100 unknowns?

MSSM

MManyparameters

40

Elegant(?) SUSY World

441

MSSM – more than 100 parameters

Impossible to have more than 100measurements at the LHC

����� consider a way to test a minimalscenario, first. Then, expand to non-minimal scenarios.

Minimal scenario = mSUGRA (two Higgsdoublets and Universality)

SUSY Philosophy

MManyparameters

Fewparameters

)tan(masses)(SUSY 01/202

01

A,,m,mh~ ��

DD ��

442

Probe Metric at the LHC

Minimal SUGRA

Non-Universal SUGRA

)tan( 1/2 002

~ ,,,01

Ammh �� D�

),tan( 1/2 ��� 002

~ ,,,01

Ammh D�

Future Collider

E

LHC

Tevatron

Precision

We test “mSUGRA” cases first,followed by a “non-universal SUGRA”case.

43

Excess in Inclusive ETmiss + Jets

Even

ts/1

0 G

eV

TH��

Even

ts/1

00

VeVG

e�

Even

��

An Excess – Not Good Enough

44

Data

How Many Giraffes?

445One snap-shot is not good enough!

Shot #1

Always Statistical Significance

446

Shot #2 Shot #3 Shot #4

SUSY Mass Techniques

FFewassumptions

Manyassumptions

Christopher Lester et al., ICHEP2010, arXiv:1004.2732 � MMissing momentum� MMeff, Razor, HT

� sshatmin� MMTGEN

� MMT2 / MCT

� MMT2 (with “kinks”)� MMT2 / MCT ( parallel /

perp )� MMT2 / MCT ( “sub-

system” )� ““Polynomial”

constraints� MMulti-event

polynomial constraints

� WWhole dataset variables

� MMax Likelihood / Matrix Element

Teruki Kamon 47Cosmological Connection

m1/2 = Common gaugino mass at MGUTm0 = Common scalar mass at MGUTA0 = Trilinear couping at MGUT

sign(��)= sign of � in � HuHd

<Hd>

<Hu>�

2 Higgs Doubles + Supersymmetrized Standard Model + Universality

>>> +

Minimal Supergravity (mSUGRA)

(We choose � > 0 and A0 = 0 for simplicity.)

tan� = <Hu>/<Hd> at MZ

+

(spin ½)

(spin 0)

Teruki Kamon 48Cosmological Connection

“Universality” allowsus to simplify theSUSY world in a 2Dplane (m0 – m1/2).

1) MHiggs > 114 GeV2) Mchargino > 104 GeV3) 2.2x10��4 <Br(b�s �) <4.5x10�4

4) (g�2)� : 3 � deviation from SM5) 12101060 2

01

.h. ~ ���

?

In the SUSY World

Higgs Slepton Gluino &Squark

n Gnn GSGNeutralino

& Chargino

Teruki Kamon 49Cosmological Connection

Allowed Region

CCDM allowed region?

Magnetic Moment of Muon

Higgs Mass (Mh)

Branching Ratio b� s�

Excl

ude

d

Mas

s of

Squ

arks

an

d Sl

epto

ns

Mass of Gauginosm1/2

m0

Teruki Kamon 50Cosmological Connection

Cosmologically Allowed Region

CDM allowed region

Magnetic Moment of Muon

Higgs Mass (Mh)

Branching Ratio b� s�

Excl

ude

d

Mas

s of

Squ

arks

an

d Sl

epto

ns

Mass of Gauginosm1/2

m0

01�~

1�~

What are the signals from the narrow co-annihilation corridor?

Co-annihilation (CA) Process (Griest, Seckel ’91)

Teruki Kamon 51Cosmological Connection

Excluded by1) Rare B decay b�� s�2) No CDM candidate3) Muon magnetic moment

abc

CDMS II

Rouzbeh Allahverdi, Bhaskar Dutta, Yudi SantosoarXiv:0912.4329

Cosmologically Consistent Signals

552

Stau - neutralino co-annihilation scenario (e.g., Arnowitt, Dutta, Gurrola, Kamon, Krislock, Toback, PRL100 (2008) 231802)

M�Small

Tevatron

01��� ~~ �� �

LHC

��� h

��� A

53

LHC at CERN

27 km ring

54

The LHC at CERN (known as European Organization for Nuclear Research in Geneva, Switzerland) provides the proton-proton (pp) collisions. The smashing power is 3.5 times larger than that of the Tevatron at Fermilab (Batavia, IL, USA).

The LHC is :� Accelerator to provide 7-TeV proton beams from a H

bottle;� Big (27 km circumference);� Cool (1.9K using 60 tons of

Liquid Helium);� Hot (synchrotron radiation,

in media);� Enormous and very

sophisticated magnetic system;� Powerful (14 TeV(*) collisions,

Total magnetic energy storedis that of Aerobus A380 flyingat 700 km/h).

Large Hadron Collider (LHC)

55

14 TeV Proton-Proton Collisions

Proton Collisions 1 billion (109) Hz

Bunch Crossing 40 million (106) Hz

7.5 m (25 ns)

One “discovery” event in 10,000,000,000,000

14,000 x mass of proton (14 TeV) = Collision EnergyProtons fly at 99.999999% of speed of light

2808 = Bunches/Beam100 billion (1011) = Protons/Bunch

Parton Collisions

New Particles 1 Hz to 10 micro (10-5) Hz(Higgs, SUSY, ....)

Discovery Path at the LHC

Cosm

olo

gica

lly

Con

sist

ent

Sig

nals

10 trillion collisions 56

The CMS (21 m x 15 m x 15 m, 12,500 tonnes) is one of two super-fast & super-sensitive detectors,consisting of 15 heavy elements, collecting debris from the collision and converting a visualimage for us. “Particle” Telescope at CERN vs. Hubble Space Telescope in outer space

Compact Muon Solenoid

As of Aug 22

57

Compact? No! Huge DetectorBut, smaller than ATLAS

558

EExxaammppllee:: SSUUSSYYg~g~ , q~g~ , or q~q~ production will be dominant, followed

by their decays (e.g., 02��~qq~� ). �� JJeettss

R parity conservation � Stable lightest supersymmetric particle (LSP)

� If LSP is the lightest neutralino ( 01��~ ),

it will escape the detector �� MMEETT (( TE�� )) 0

1~�� = Cold Dark Matter candidate �� CCoossmmoollooggyy

� Thus, the evidence of SUSY-like new physics will appearin the Jets+MET final states.

CCoossmmoollooggyy !!! LLHHCC= [Exciting Motivation]!![Right Place&Timing]

Missing ET(& Jets) at the LHC

MET - inferring new physics (e.g., Dark Matter)59

""

"

eb

b ��

eb

b"

"

�slash

��0��p

ecteddetecteddetppppp ����������#��

""

Hint for DM: Missing ET

slashpExperimentally, we measure a momentum imbalance intransverse plane and call it “missing transverse energy”( or ).TE�miss

TE

60

� All physics objects (jets, leptons, HT, MHT etc) are reconstructed with the PF algorithm.

� Basic idea:� Reconstruct and identify all different types of particles� Apply corresponding calibrations� The list of “particles” is given to the jet clustering and missing ET

(MET) reconstruction algorithm

Particle Flow (PF) Algorithm

61

CCharged hadrons~65% of jet energy

Use the high resolution tracker~1% at 100 GeV

62

PPhotons~25% of jet energy

Use high resolution / good granularity ECALGranularity: 0.02 (�$%�&)Energy resolution: ~2%/'E

63

NNeutral hadrons~10% of jet energy

Use HCALGranularity: 0.1 (�$%�&)Energy resolution: ~100%/'E

64

JJet:Charged hadron (solid)Photon (dashed line)Neutral hadron (dotted line)

Particles clustered in jets

65

� PPF algorithm improves the performance of jet and missing ETreconstruction significantly.

Calorimeter jet

PF jet

Jet energyresponse

Calorimeter jet

PF jet

PF Jet and MET Performance

Jet energyresolution

66

http://cdsweb.cern.ch/record/1343076/files/SUS-10-005-pas.pdf

2.5x1012 pp Collisions

667

�“All hadronic inclusive” analysis with key variables:� HHT = scalar sum of Jet pT (selecting large s-hat production)� MHT = negative vector sum of Jet pT

�Baseline Event selection: � HHT Trigger� 3 jet with pT > 50 GeV & |�| < 2.5 (central production)

� Veto events with isolated electrons & muons (suppress EWK background)

� �((MHT, Jet1,2,3) > (0.5, 0.5, 0.3) (reduce QCD background)� HT > 300 GeV & MHT > 150 GeV � baseline selection

�Final Event Selection: � High HT (HT > 500 GeV): High eff. for signals with long cascade

decay chains� High MHT (MHT > 250 GeV): High background rejection

Analysis Strategy

68

Baseline selectionw/o MHT cut

Baseline selection

HHT > 300 GeV & MHT > 150 GeV An out-of-box comparison of Data vs MC for HT and MHT

Baseline Selection

High HTHigh MHT

>150 GeV

>300 GeVMajor BGs:� Invisible Z(�"") +

Jets .. Irreduciblebackground

� Top / W + Jets� QCD Jets

Data-driven BGEstimate

0,0,10tan,250,60]1[

0

2/10

)����

��

GeV GeV LM

Amm

69

� MMHT = 693 GeV & HT = 1132 GeV

� Meff = MHT + HT = 1.83 TeV

� No b-tagged jet & No isolated lepton

� Incompatible with W or top mass

� Invisible Z???

For Future Excitement

HT

MHT

00,10tan

25060]1[

0

2/1

0

)�

���

�

�

GeV

GeV LM

Amm

70

No excess of observed events over expected StandardModel prediction. �� … Setting limits.

ResultsHT > 300 GeV

& MHT > 150 GeVHT > 500 GeV MHT > 250 GeV

71

� Gluino masses up to ~700 GeV are excluded. Less sensitive to tan��*(see Next page)� Sensitivity greater than ATLAS at high m0. High HT search region was effective.� Sensitivity lower than ATLAS at high m1/2. Need to look at 2 jet events

(currently only �3 jets)

Within the mSUGRA/cMSSM

10tan ��

� 44 parameters and a sign: m0, m1/2, tan�, A0, sign(�)– mm0: common mass for “spin 0” particles at the GUT scale

– mm1/2: common mass for “spin 1/2” particles at the GUT scale

10tan ��

72

� Less sensitive to tan��

SUSY Large tan� Case

50tan ��10tan ��

Low tan� vs. High tan�

73

CHALLENGE: All hadronicinclusive search iscomplete at the samepace as other searches.

ROBUST data-driventechniques for all SUSYsearches in 36 pb-1 in2010

GOOD agreement withthe SM predictions

HOT: ~1 fb-1/month. Bigexcitement in 2011 &2012

74

From 2010 to 2011

• Cross-section limits 0.5 – 30 pb,excluding m(gluino) < 700 GeV inthe mSUGRA/cMSSM plane.

0,0,10tan,250,60]1[

0

2/10

)����

��

GeV GeV LM

Amm

Personal Remarks

Discovery with 3rd generation particles

775

My Daughter’s View

I need �1, �2, …

Uh…Oh!The hosts are in …

76

CSI: Supersymmetry

at the LHCCollider Scene Investigation

Summary

LHC – keep going!777

TriggerTThe detector generates unmanageably large amounts of raw data,about 25 megabytes per event (raw; zero suppression reduces this to1.6 MB) times 40 million beam crossings per second (or 40 MHz) in thecenter of the detector, for a total of 1 petabyte/second of raw data. Thetrigger system uses simple information to identify, in real time, the mostinteresting events to retain for detailed analysis.

There are two primary trigger levels, the first based in electronics onthe detector and the other running on a large computer cluster nearthe detector.

After the first-level trigger, about 100,000 events per second have beenselected. After the 2nd-level trigger, a few hundred events remain to bestored for further analysis. This amount of data will require over100 megabytes of disk space per second — at least a petabyte eachyear.

78

Simplest ConceptMeasurement of Muon Lifetime

TDC

start

stopdelay

��

�ee"�"

S1

S2

S3

79

QuestionsTThe muon flux (Hz) is of order of a few Hz.

If the flux were 40 MHz (1 muon per 25 ns), what should we do?Fast response detectorFast data readout systemFast data storage system

But you can store the data at 300 Hz, what should we do?Fast response detectorFast data readout systemFast event-rate reduction system (“trigger”)Fast data storage system

Now you have to handle more than 50M channels, what should we do?Fast response detectorFast&parallel readout with zero suppression and powerful processing systemFast&massive parallel event-rate reduction system (“trigger”)Fast&huge data storage system

80

Beam Crossings: LEP, TeV, LHC

� LHC has ~3600 bunches� And same length as LEP (27 km)� Distance between bunches: 27km/3600 = 7.5m� Distance between bunches in time: 7.5m/c = 25ns

81

LHC Physics & Event Rates�At design L = 1034 cm-2s-1

� 23 pp events/25 ns X-ing�~ 1 GHz input rate�“Good” events contain

~ 20 background events� 1 kHz W events� 10 Hz top events� < 104 detectable Higgs

decays/year�Can store ~300 Hz events�Select in stages

� Level-1 Triggers� 1 GHz to 100 kHz

� High Level Triggers (HLTs)� 100 kHz to 300 Hz

882

Collisions (pp) at LHC

Event size: ~1 MByteProcessing Power: ~X TFlop

All charged tracks with pT> 2 GeV

Reconstructed tracks with pT > 25 GeV

Operating conditions:one “good” event (e.g., H��4 muons )

+ ~20 minimum bias events)Event rate

83

PProcessing LHC Data

884

LHC Trigger & DAQ Challenges

116 Million channels3 Gigacell buffers

40 MHzCOLLISION RATE

100 - 50 kHz1 MB EVENT DATA 200 GB buffers 1 Terabit/s

READOUT50,000 data

channels

~400 Readout memories

500 Gigabit/s

5 Tera IPS

~ 400 CPU farms

Gigabit/sSERVICE LAN

Petabyte ARCHIVE

Energy Tracks

300 HzFILTERED

EVENT

EVENT BUILDER.A large switching network (400 + 400 ports)with total throughput ~400 Gbit/s forms theinterconnection between the sources (deepbuffers) and the destinations (buffers beforefarm CPUs).

EVENT FILTER.A set of high performance commercialprocessors organized into many farmsconvenient for on-line and off-lineapplications.

LEVEL-1TRIGGER

Computing Services

Charge Time Pattern

SWITCH NETWORK

DETECTOR CHANNELS

Challenges:

1 GHz of Input Interactions

Beam-crossing eevery 25 ns with ~23 interactions pproduces over 1 MB of data

Archival Storage at about 300 Hz of 1 MB events

85

CChallenges: Pile--uup

886

Challenges: Time of Flightc = 30 cm/ns ����������d = 7.5 m

87

TTrigger Timing & Control

� Single High-Power� Laser per zone

� Reliability, transmitter upgrades

� Passive optical coupler fanout

� 1310 nm Operation� Negligible chromatic

dispersion� InGaAs photodiodes

� Radiation resistance, low bias

� S� L

� 1

� I

Optical System:

888

RRecap: Simplest ConceptMeasurement of Muon Lifetime

TDC

start

stopdelay

��

�ee"�"

S1

S2

S3

Timing Control, here!

89 990