Status of the LHC and

ATP common seminar 14 March 2012

Status of the LHC and

Anatomy of LHC events

Torbj¨ orn Sj¨ ostrand

What is happening at CERN/LHC in general?

How is Lund theory involved and affected?

A Brief LHC History

mid-70’ies: plans a new 27 km ring tunnel at CERN, with space for separate e^± and p beams

1979–1989–2000 design/construction and running of the LEP e^± machine, E_cm^max= 209 GeV limited by

synchrotron radiation

1984: first LHC physics workshop 1990: full-scale studies begin;

aim for start 1998

1995: LHC project approved 2000: civil engineering begins 1990–2008: drawn-out design &

construction process

LHC Tunnel View

2008: machine and detectors ready to go – commissioning

The “Incident”: 19 September 2008

one year of repair work, start out at 900 GeV in November 2009

First 7 TeV Collisions

 

 




2 Plenary ECFA, Frascati

The ATLAS Detector

25 m high, 45 m long, 7 000 tons, lots of electronics, . . .

Final 2011 Running Conditions

still 7 TeV CM energy 20 000 000 bunch crossings per second

∼ 10 pp collisions per crossing

∼ 400 saved per second

Cross Sections

master formulae hni = σR L dt L ≈ fn₁n₂/A σtot≈ 100 mb

= 10 fm² = 10⁻²⁹m² 2011: R L dt = 5 fb⁻¹

= 5 · 10⁴³ m⁻² so ntot= 5 · 10¹⁴ in each of ATLAS/CMS lower in ALICE/LHCb

σH(m=125 GeV)

σ_tot ≈ 10⁻¹⁰

Event Generator Reasons

An event generator is intended to simulate various event kinds as accurately as possible.

It uses random numbers to represent quantum mechanical choices.

It can be used to

predict event rates and topologies

⇒ estimate feasibility

simulate possible backgrounds

⇒ devise analysis strategies study detector requirements

⇒ optimize detector/trigger design study detector imperfections

⇒ evaluate acceptance corrections

// Pick pT2 (in overestimated z range) for fixed alpha_strong.

if (alphaSorder == 0) {

dip.pT2 = dip.pT2 * pow( rndmPtr->flat(), 1. / (alphaS2pi * emitCoefTot) );

// Ditto for first-order alpha_strong.

} else if (alphaSorder == 1) { dip.pT2 = Lambda2 * pow( dip.pT2 / Lambda2, pow( rndmPtr->flat(), b0 / emitCoefTot) );

// For second order reject by second term in alpha_strong expression.

} else {

do dip.pT2 = Lambda2 * pow( dip.pT2 / Lambda2, pow( rndmPtr->flat(), b0 / emitCoefTot) );

while (alphaS.alphaS2OrdCorr(dip.pT2) < rndmPtr->flat() && dip.pT2 > pT2min);

} wt = 0.;

// If crossed c or b thresholds: continue evolution from threshold.

if (nFlavour == 5 && dip.pT2 < m2b) { mustFindRange = true;

dip.pT2 = m2b;

} else if ( nFlavour == 4 && dip.pT2 < m2c) { mustFindRange = true;

dip.pT2 = m2c;

// Abort evolution if below cutoff scale, or below another branching.

} else {

if ( dip.pT2 < pT2endDip) { dip.pT2 = 0.; return; } // Pick kind of branching: X -> X g or g -> q qbar.

dip.flavour = 21;

dip.mFlavour = 0.;

if (colTypeAbs == 2 && emitCoefQqbar > rndmPtr->flat() * emitCoefTot) dip.flavour = 0;

// Pick z: either dz/(1-z) or flat dz.

if (dip.flavour == 21) {

dip.z = 1. - zMinAbs * pow( 1. / zMinAbs - 1., rndmPtr->flat() );

} else {

dip.z = zMinAbs + (1. - 2. * zMinAbs) * rndmPtr->flat();

}

// Do not accept branching if outside allowed z range.

double zMin = 0.5 - sqrtpos( 0.25 - dip.pT2 / dip.m2DipCorr );

if (zMin < SIMPLIFYROOT) zMin = dip.pT2 / dip.m2DipCorr;

dip.m2 = dip.m2Rad + dip.pT2 / (dip.z * (1. - dip.z));

if (dip.z > zMin && dip.z < 1. - zMin && dip.m2 * dip.m2Dip < dip.z * (1. - dip.z) * pow2(dip.m2Dip + dip.m2 - dip.m2Rec) ) { // Flavour choice for g -> q qbar.

if (dip.flavour == 0) {

dip.flavour = min(5, 1 + int(nGluonToQuark * rndmPtr->flat()));

dip.mFlavour = particleDataPtr->m0(dip.flavour);

slide 9/45

Event Generator Challenges

Structure of LHC events impossible to “solve”

from first principles;

e.g. QCD in perturbative and nonperturbative regimes.

(Perturbation theory helpful;

lattice QCD not much help.) Even if calculable somehow, need 1000-body expressions and phase space sampling.

Immense variability, with “typical events”

and “rare corners”.

Several competing mechanisms contribute.

Need to

• combine theory with models

• divide and conquer

Who was Pythia?

What is Pythia?

The Oracle of Delphi:

ca. 1000 B.C. — 390 A.D.

Generator development begun in Lund in 1978, for own physics studies. Increasingly tool for experimentalists, to “sell” our physics. Pythia (+Jetset) general-purpose “core”. Other special programs interfaced to Pythia. Most used generator at LEP and LHC. Lots of Lund people involved over the years.

Who was Pythia? What is Pythia?

The Oracle of Delphi:

ca. 1000 B.C. — 390 A.D.

Generator development begun in Lund in 1978, for own physics studies.

Increasingly tool for experimentalists, to “sell” our physics.

Pythia (+Jetset) general-purpose “core”.

Other special programs interfaced to Pythia.

Most used generator at LEP and LHC.

Lots of Lund people involved over the years.

The Main Physics Components (in Pythia)

Hides further layers of complexity, e.g. > 200 different ME’s,

> 400 different particles, > 6 000 different decay channels, . . .

Cylindrical Phase Space

Collision along z axis: wide variation of produced particles in p_z, but limited in p_x, p_y. Therefore often use

y = 1

2lnE + pz

E − pz

y ≈ η = 1

2ln|p| + p_z

|p| − p_z = − ln tan(θ/2) p⊥ =

q

p_x²+ p_y²

(η, ϕ, p⊥) standard coordinate choice:

Ed³σ

dp³ ≈ d³σ dη dϕ dp²_⊥

Total Inelastic Cross Section

Proton is getting bigger with energy: wavefunction tails find it easier to interact (multiparton interactions).

In line with expectations; if anything then below.

Diffractive Cross Section and Properties

If only one proton breaks up, then part of detector empty.

∆η = largest empty region counted from detector edge at η ≈ 5.

Expect dM_x²/M_x² ≈ d∆η.

Deviations from mass spectrum or hadronization modelling.

Using particles with p⊥> 0.2 GeV or p⊥ > 0.8 GeV:

Charged Rapidity Distribution

η

-4 -2 0 2 4

ρ

0 1 2 3 4 5 6 7

Pythia6 (default) Pythia6 (LHCb) Phojet Pythia8 (default)

=7 TeV s (a) LHCb

η

-4 -2 0 2 4

ρ

0 1 2 3 4 5 6 7

Pythia6 (Perugia0) Pythia6 (NOCR) No diffraction Pythia6 (Perugia0) Pythia6 (NOCR)

=7 TeV s (b) LHCb

Figure 4:The charged particle densities as a function of η (shown as points with statistical error bars) and comparisons with predictions of event generators, as indicated in the key. The shaded bands represent the total uncertainty. The events are selected by requiring at least one charged particle in the range 2.0 < η < 4.5. The data in both figures are identical with predictions from Pythia6, Phojet and Pythia 8 in (a) and predictions of the Pythia 6 Perugia tunes with and without diffraction in (b).

10

Dip around η = 0 artefact; absent if using y instead.

slide 16/45

Charged Rapidity Plateau

How does dn_ch/dη grow with energy? ∝ ln E or ∝ ln²E ? Provides information on several simultaneous subcollisions!

MPI = MultiParton Interactions.

Rapidity Plateau Correlations

Charged Multiplicity Distribution – 1

0 20 40 60 80 100 120 140 160 180n

nP

10-6

10-5

10-4

10-3

10-2

10-1

1 10 102

103 CMS Data

PYTHIA D6T PYTHIA 8 PHOJET 4)

7 TeV (x10

2) 2.36 TeV (x10

0.9 TeV (x1)

| < 2.4

|η > 0 pT

CMS NSD (a)

0 20 40 60 80 100n

nP

10-6

10-5

10-4

10-3

10-2

10-1

1 10 102

103 CMS Data

PYTHIA D6T PYTHIA 8 PHOJET 4)

7 TeV (x10

2) 2.36 TeV (x10

0.9 TeV (x1)

| < 2.4

|η > 0.5 GeV/c pT

CMS NSD (b)

We need to understand both average and spread.

“Ankle”: transition from one to ≥ 2 interactions?

High multiplicity tail driven by abundant MPI rate.

Broad spectrum of tunes even within given model.

Charged Multiplicity Distribution – 2

“Ankle” also present in ALICE and ATLAS data.

Benchmark comparisons ALICE/ATLAS/CMS generally successful.

Charged Transverse Momentum Distribution

hp_⊥i sensitive to colour correlations between MPIs!

Jet Transverse Momentum Distribution

(GeV) pT

20 30 100 200 1000

(pb/GeV) T/dydpσ2 d

10-1

10 103

105

107

109

1011

1024)

|y|<0.5 (×

×256)

|y|<1.0 ( 0.5≤

64)

×

|y|<1.5 (

≤ 1.0

×16)

|y|<2.0 ( 1.5≤

×4)

|y|<2.5 ( 2.0≤

×1)

|y|<3.0 ( 2.5≤

NLO pQCD+NP Exp. uncertainty

= 7 TeV

-1 s CMS preliminary, 60 nb

R=0.5 PF Anti-kT

(GeV) pT

20 30 100 200 1000

(pb/GeV) T/dydpσ2 d

10-1

10 103

105

107

109

1011

Dominated by QCD 2 → 2

qq⁰ → qq⁰ qq → q⁰q⁰ qq → gg qg → qg gg → gg gg → qq dσ dp_⊥² ∝ 1

p⁴_⊥

⊗ PDFs

Jet Fragmentation Profile

z ≈ p_⊥had

p_⊥jet ≈ Ehad

Ejet

r = q

(ηhad− η_jet)²+ (ϕhad− ϕ_jet)²

Number of Jets — QCD Events

W/Z Transverse Momentum

Here next-to-leading approaches do worse than leading ones!?

Number of Jets — W/Z Events

0-jet)≥(W + σ n-jets)≥(W + σ

10-3

10-2

10-1

data energy scale unfolding MadGraph Z2 MadGraph D6T Pythia Z2

CMS preliminary = 7 TeV s at 36 pb-1

eν W →

> 30 GeV

jet

ET

inclusive jet multiplicity, n (n-1)-jets)≥(W + σ n-jets)≥(W + σ 0

0.1 0.2

1 2 3 4

Pythia showers do much worse for W + multijets than for QCD multijets!

Need for matching to higher-order matrix elements (S. Prestel, L. L¨onnblad)

Tuning

RIVET: collection of experimental data, together with matching analysis routines.

Can be applied to generator events for comparison with data.

PROFESSOR: parameter tuning in multidimensional parameter space.

Generate large event samples at O(n²) random points in (reasonable) parameter space. Slow!

Analyze events and fill relevant histograms.

For each bin of each histogram parametrize

X_MC = A0+

n

X

i =1

B_ip_i

n

X

i =1

C_ip_i²+

n−1

X

i =1 n

X

j =i +1

D_ijp_ip_j

Do minimization of χ² to parametrized results. Fast!

MCPLOTS

Repository of comparisons between various tunes and data, mainly based on RIVET for data analysis,

see http://mcplots.cern.ch/.

Part of the LHC@home 2.0 platform for home computer participation.

η

-2 0 2

η/dch dNev1/N

2 3 4 5 6 7

8 ATLAS

Pythia 8 Pythia 8 (Tune 2C) Pythia 8 (Tune 2M) Pythia 8 (Tune 4C)

7000 GeV pp Minimum Bias

mcplots.cern.ch

Pythia 8.153 ATLAS_2010_S8918562

> 0.1 GeV/c) > 2, pT Distribution (Nch η Charged Particle

-2 0 2

0.5 1

1.5 Ratio to ATLAS

η

-2 0 2

η/dch dNev1/N

1 1.5 2 2.5 3 3.5

ATLAS Pythia 8 Pythia 8 (Tune 2C) Pythia 8 (Tune 2M) Pythia 8 (Tune 4C)

7000 GeV pp Minimum Bias

mcplots.cern.ch

Pythia 8.153 ATLAS_2010_S8918562

> 0.5 GeV/c) > 1, pT Distribution (Nch η Charged Particle

-2 0 2

0.5 1

1.5 Ratio to ATLAS

State of New Generators

New data leads to new tunes, even if progress is slow.

Also good way to find bugs and other problems.

State of new C++ generators early 2011:

ATLAS Pythia 8.145 Sherpa 1.2.3 Herwig++ 2.5.0

10⁻⁶ 10⁻⁵ 10⁻⁴ 10⁻³ 10⁻² 10⁻¹

Charged multiplicity,√s = 7000 GeV

1/NevdNev/dNch

20 40 60 80 100 120

0.6 0.8 1 1.2 1.4

N^ch

MC/data

ATLAS Pythia 8.145 Sherpa 1.2.3 Herwig++ 2.5.0

0.7 0.8 0.9 1.0 1.1 1.2 1.3

!p⊥" vs N^ch,√s= 7000 GeV

!p⊥"[GeV]

20 40 60 80 100 120

0.6 0.8 1 1.2 1.4

Nch

MC/data

A. Buckley et al., Phys. Rep. 504 (2011) 145 [arXiv:1101.2599[hep-ph]]

Cloud #1 : Bose-Einstein Effects

Cloud #2: Flavour Composition

Cloud #3: The Ridge

∆η -4 -2 0 2 4

∆φ 0 2 4

)φ∆,η∆

R( -2 -101

<3.0GeV/c 110, 1.0GeV/c<pT

(d) CMS N ≥

0 1 2 3

)φ∆R(

-1 0 1

<1.0GeV/c 0.1GeV/c<pT

N<35 _{CMS pp} PYTHIA8

0 1 2 3

)φ∆R(

-1 0 135 ≤ N<90

0 1 2 3

)φ∆R(

-1 0 1

N<110

≤ 90

φ

∆

0 1 2 3

)φ∆R(

-1 0 1

110

≥ N

0 1 2 3

-1 0 1

<2.0GeV/c 1.0GeV/c<pT

0 1 2 3

-1 0 1

0 1 2 3

-1 0 1

φ

∆

0 1 2 3

-1 0 1

0 1 2 3

-1 0 1

<3.0GeV/c 2.0GeV/c<pT

0 1 2 3

-1 0 1

0 1 2 3

-1 0 1

φ

∆

0 1 2 3

-1 0 1

0 1 2 3

-1 0 1

<4.0GeV/c 3.0GeV/c<pT

|<4.8 η

∆ 2.0<|

0 1 2 3

-1 0 1

0 1 2 3

-1 0 1

φ

∆

0 1 2 3

-1 0 1

Geometry of colliding protons (non-symmetric shapes)?

Collective phenomena?

Results Galore

# of papers 134 CMS 126 ATLAS

39 LHCb 28 ALICE + conference + “internal”

+ theses + . . .

27

Standard Model (including top) Concentrate on dibosons and new constraints on couplings

Typical Working groups: QCD, EW, B, quarkonia, top, Higgs, SUSY, Exotics, Heavy Ions

Higgs Results, December 2011

[GeV]

MH 110 115 120 125 130 135 140 145 150

Local P-Value

10-7 10-6 10-5 10-4 10-3 10-2 10-1 1

Observed Expected

m 2

m 3

m 4

m = 7 TeV 5

s

Ldt = 1.0-4.9 fb-1

0

ATLAS Preliminary 2011 Data

σSM

σ/ Best fit

-1 0 1 2 3 4 5

→ 4l

→ ZZ H

→ WW H

γ γ

→ H

τ τ

→ H

→ bb H

= 4.6-4.7 fb-1 Combined, Lint

= 7 TeV s CMS Preliminary, = 124 GeV/c2

mH σ

±1 Combined

σ

±1 Single channel

Higgs Results, March 2012

Combined exclusion limit

Zoom in:

Expected exclusion at 95% CL: 120-555 GeV

Observed exclusion at 95% CL: 110-117.5, 118.5-122.5, 129-539 GeV Observed exclusion at 99% CL: 130-486 GeV

Introduction / High-m_Hsearch: ��νν, ��jj, �νjj / Low-m_Hsearch: 4�, γγ• �ν�ν, bb, ττ / Combination /End? 21/24

Exclusion C.L.

•  !"#$%&$'())*+,)$"%-./012)3₄)02)56678+9+7:;)<$=)

•  >?/$@A$'()*+,)$"%-./012)3₄)02)56BC8+9DEE;)<$=) ))))))))))))))))))**,)$"%-./012)3₄)02)56B*9+B+;)<$=)

•  *+,)F--1G$')HF//)@F2I$()6678796BC8+)<$=)

•  >?/$@A$')-1G$@)-0H0&)J0IJ$@)&JF2)$"#$%&$')?$%F./$)1K)$"%$//)02)'F&F) F&)-1G)HF//)

O3P)'1%.H$2&)) 4R<96B9EES)

!"##$%&''$(&)*+$ ,-.$%&''$(+*/-)$

012$

Drifting terminology:

“SM Scalar Boson”

“Brout–Englert–Higgs Boson”

“BEH Boson”

“BEH Mechanism”

. . . but still “Higgs Boson” as well, and only gg → H, m_H

slide 35/45

Limits Galore – 1

Limits Galore – 2

!"##$#%"&'$()'*+

-.,- - -. -.^/

!"#$%&'"#()$*+,-./012"%3(456$*758*7

&&0 6

*'%123,&45'$06"35$7$89:$

ν0

&

6

*'%123,&45'$06"35$7$99:$

;4<'1 6 92&23$2%1'1$#%"&"3$7$

;4<'1 6

=>4?&62@#$7$

;4<'1 6 A>%41';$06"35#$7$;4<'1$3'#2@"@%':$^γ<'1

6 ,<'1$3'#2@"@%':$

γ

A>%41';$06"35#$7$_E^±±→µµCD-C$7$6µµ$B&45',#4?@C

$BFG$H32;I:$JKBL E

± L±

!"<23I$@'613I$BEKM!:$@2$N4>4@?C$7$/,&'H$O$<'1#

!"<23I$@'613I$BEKM!:$@2$N4>4@?C$7$/,&'H$O$<'1#

µ µ 6''P )'%Q@4,Q";32@#$7$;4&'H12@:$^9:N4##

1

$7$-,&'H$O$<'1#$O$

=.

$O$=. 1

→$1 R1Q$?'@I ) )

$S1S1$B/,&'H$MMC R→ R;

$?'@'3"142@$7$;

R1Q

$S0S0 R→ RT

$?'@'3"142@$7$%2&&I$N"##$4@$T R1Q

<<

ν µ

<<:

µ µ D-C$7$54@I$U"3#I$4@$

β M%"&"3$ET$H"43#$B

<<

ν D-C$7$54@I$U"3#I$4@$''<<:$' β

M%"&"3$ET$H"43#$B

µ 6):'P MM!$7$

µ µ 6''P MM!$7$ ^&&

6

$%2NV4@';:$

µ µ 00&&$%2@1"%1$4@1'3"%142@$7$'':$

;4<'1C 6 χB : 0000$%2@1"%1$4@1'3"%142@$7$ ⁹

Σ; DWC$7$&'H12@#$O$<'1#:$

<F )L$P

<

=FF$JL$B

%QI$H"31I

= DWC$7$MM$;4N62@:$

<F )L$P

<

=FF$JL$B

<'1#

= 9: Σ; DWC$7$N6&14<'1:$

<F )L$P

<

=FF$JL$B

1$O$X σ TJL$7$L4?Q,N"##$

χC B :

;4<'1: 6 T6"@16N$V&"%5$Q2&'$BTJLC$7$

:N4##

19 )$O

>

D,.I/.$7$

)# 00?YYP )

KM$Z41Q$ ^????

6

$D$.I-$7$[[$3'#2@"@%':$

\&

<

P

@ KM$Z41Q$

??

γ: 6γ

$%2NV4@';:$

µ µ :$'':$

γ γ

$D$.I-$7$

\&

<

P

@

KM$Z41Q$ ^9:N4##

1 γ$O$

γ ]AF$7$

E"3?'$AF$B=FFC$7$;4HQ212@

E"3?'$AF$B=FFC$7$N2@2<'1

TC νPN

$D$

κ0T T$N"##$B%26H&4@?$

!"#$%&'$

$()#**+$,-.&/01023.45 7*8#$9:6*

!

TC νPN 0T$D$

T$N"##$B%26H&4@?$κ

;##$%&'$

$()#**+$,-.&/01023.45 7*8#$9:6*

!

M%"&"3$3'#2@"@%'$N"##

*8;)$<&'$

$()#**+$,3.=0>?**#@8"A**5 7*8#$9:6*

!

=>4?&62@$N"##

A8A)$<&'$

$()#**+$,3.=0>?**#@8"A**5 7*8#$9:6*

!

0^$N"##

)8;;$<&'$

$()#**+$,3.=0>?**#@8"A**5 7*8#$9:6*

!

0^$N"##

)8B"$<&'$

$()#**+$,-.&/01023.45 7)8*$9:6*

!

$N"##

E

± L± A!C$%&'$

$()#**+$,DEFG6)#**6*)!5 7*8"$9:6*

!

B8C$_$`..$a'*C 6

$N"##$B/W.$_$

SA

*8AC#$<&'$

$()#*#+$,H<IHJ6DEFG6)#**6**C5 7AB$K:6*

!

C$D$-$)'*C BSA 6 8$N"##$B

!@#$%&'$

$()#*#+$,H<IHJ6DEFG6)#**6**C5 6*

7AB$K:

!

C$D$-..$a'*C π) B 6 )C$,$

ω )P ρ B 6

$N"##$B ω) )P ρ B!#$%&'$

$()#**+$,DEFG6)#**6*)C5 7*8*6*8)$9:6*

!

C$_$-R.$a'*C B=. 6 )$N"##$B B)#$%&'$

$()#**+$,3.=0>?**#;8B!)C5 7*8#$9:6*

!

$N"##

;R );#$%&'$

$()#*#+$,**#@8#A""5 7AB$K:6*

!

$N"##

TR )!#$%&'$

$()#*#+$,DEFG6)#**6#))5 7A!$K:6*

!

$?'@I$ET$N"##

/@;

B))$%&'$

$()#*#+$,3.=0>?**#B8BB@*5 7AC$K:6*

!

$?'@I$ET$N"##

-#1

""#$%&'$

$()#**+$,-.&/01023.45 6*

7*8#$9:

!

Sb$N"##

)8*C$<&'$

$()#**+$,3.=0>?**#@8*A*"5 7*8#$9:6*

!

[b$N"##

*8@A$<&'$

$()#**+$,3.=0>?**#@8*C@)5 7*8*6*8)$9:6*

!

$B%2@#136%14U'$4@1IC Λ

*#8)$<&'$

$()#**+$,-.&/01023.45 7*8*6*8)$9:6*

!

Λ

"8!$<&'$

$()#*#+$,3.=0>?**#A8A@"B$(L34&M032$/010N+5 7A"$K:6*

!

δDcC B$B

<

*8C$<&'$

$()#**+$,H<IHJ6DEFG6)#**6*B!5 7*8#$9:6*

!

δDcC B$B

<

*8)C$<&'$

$()#**+$,3.=0>?****8##@#5 6*

7*8A$9:

!

δDcC F$B

<

*8A!$<&'$

$()#*#+$,H<IHJ6DEFG6)#**6#"@5 7AC$K:6*

!

<B )8AC$<&'$

$()#*#+$,H<IHJ6DEFG6)#**6#!#5 7AA$K:6*

!

δDcC B$B

<

A8"!$<&'$

$()#*#+$,3.=0>?**#A8A@"B5 7A"$K:6*

!

YY$?&62@$N"##

@B#$%&'$

$()#**+$,H<IHJ6DEFG6)#**6*)A5 7*8#$9:6*

!

a3"U412@$N"##

C!C$%&'$

$()#**+$,H<IHJ6DEFG6)#**6*BB5 7*8#$9:6*

!

a3"U412@$N"##

*8;C$<&'$

$()#**+$,-.&/01023.4O$3.=0>?**#@8*C@)5 6*

7*8*6)8*$9:

!

92NH"%1I$#%"&'$-PK$BM\MdC

*8)A$<&'$

$()#**+$,3.=0>?****8B**"5 7*8*$9:6*

!

$BaKS$%61,2eeC

<C A8#$<&'$

$()#**+$,-.&/01023.45 7)8*$9:6*

!

δD/C B$B

<

A8)$<&'$

$()#**+$,H<IHJ6DEFG6)#**6#;"5 7*8#$9:6*

!

!*?D(3(7$?$E"58*(8F("#$(3G35?3H?$(%$7I?"7(?$345*)("8(6377(?565"7(7#8J*

^

$D$B.I.W$,$/I-C$eV,- +4"

∫ #$D$`$)'*

"#!"$

\3'&4N4@"3f H<IHJ$PQRN0SM$J&3.ST&MU$6$;CV$DI$IRW&.$I010NM$(JN3NXM?$Y&S8$)#**+

37

TH&%$3(

Rare Decays – Another Set of Limits

26

B _s,d !μμ

Sensitive to New Physics contributions: e.g.

can be enhanced in Susy models with high tan!

Helicity suppressed FCNC decay.

Small in Standard Model, but well predicted

B(B

_s

→ µ

⁺

µ

⁻

) = (3.2 ± 0.2) × 10

⁻⁹

B(B

d

→ µ

⁺

µ

⁻

) = (1.0 ± 0.1) × 10

⁻¹⁰

SM

Result on 400 pb

^-1

(2010 + early 2011) will be submitted to journal in next days

!!"#$"%$!! &'()*+,,-*.*/0*1,22345*.*(6*7894:,9 ;

!

_"

#$#!!%#&'("&')*+,'"##

-&&'(#.+/+*#'0*(1&2.1*+23

4+3#&('"'3)'#25#67#"+831.9 :/&.+)1*+23"#23#323;<3+,'("1.#

=+88"#/2>'.#?@&'#:

#A(2/#&(2B')*+23#*2#CDC#5E;C%##!F4!_"#"!!9#G##HI#J#CCK#0#CL;M

!"#$%&' CDC#5E^;C

2. Search for NP in B _s,d !µµ decays

B_(d,s)! µµ is the best way for LHCb to constrain the parameters of

the extended Higgs sector in MSSM, fully complementary to direct searches

Double suppressed decay: FCNC process and helicity suppressed.

!  very small in the Standard Model but very well predicted:

! Sensitive to NP contributions in the scalar/pseudo scalar sector:

Bs!"⁺"^-= (3.2±0.2)#10^-9 Bd!"⁺"^-= (1.0±0.1)#10^-10

Buras et al., arXiv:1007.5291 and references therein!

Main SM diagrams

~ |V

_ts

|

²

, C

_A

"!

#! $^%!

#! $

^%! MSSM, large tan! approximation

18

BR(B_s⁰ → µ⁺µ⁻) BR(B⁰ → µ⁺µ⁻) Standard Model (3.2 ± 0.2) · 10⁻⁹ (0.11 ± 0.01) · 10⁻⁹

CDF 10⁺⁸₋₆· 10⁻⁹ –

CDF 95% CL limit < 40 · 10⁻⁹ < 6.0 · 10⁻⁹

D0 95% CL limit < 51 · 10⁻⁹ –

CMS 95% CL limit < 7.7 · 10⁻⁹ < 1.8 · 10⁻⁹ LHCb 95% CL limit < 4.5 · 10⁻⁹ < 1.03 · 10⁻⁹ Only one example where BSM is being restricted from B physics.

slide 38/45

QCD and BSM Physics

QCD understanding crucial also for studies of “exotic” physics, since

incoming protons ⇒ production involves strong interactions production of new coloured states favourable

(squarks, Kaluza-Klein quarks/gluons, excited quarks, . . . ) Several different possibilities studied, e.g.

1 Gravitational scattering and black hole formation (G. Gustafson, L. L¨onnblad, M. Sj¨odahl)

2 Baryon number violation in SUSY decays (P. Skands, TS)

3 Hadronization and decay of long-lived SUSY particles (A. Kraan, TS)

4 Parton showers and hadronization in Hidden Valleys (L. Carloni, J. Rathsman, TS)

R-Hadrons

Long-lived coloured particle will hadronize, e.g. R⁻(˜g d u).

Particle can flip charge and baryon number by exhanging quarks with normal matter: R⁻(˜g d u) + p(uud ) → R⁺(˜g duu) + π⁻(d u).

Decays may or may not happen inside detector.

Pythia framework standard for LHC searches:

But, again, only limits.

Hidden Valleys: Motivation

Courtesy M. Strassler

Hidden Valleys: Setup

Hidden Valleys (secluded sectors) experimentally interesting if they can give observable consequences at the LHC:

coupling not-too-weakly to our sector, and containing not-too-heavy particles.

Here: no attempt to construct a specific model, but to set up a reasonably generic framework.

Either of twogauge groups,

1 Abelian U(1), unbroken or broken (massless or massive γv),

2 non-AbelianSU(N), unbroken (N²− 1 massless g_v’s), with matter q_v’s in fundamental representation.

Times three alternativeproduction mechanisms

1 massive Z⁰: qq → Z⁰→ q_vq_v,

2 kinetic mixing: qq → γ → γv → q_vq_v,

3 massive F_v charged under both SM and hidden group, so e.g. gg → F_vF_v. Subsequent decay F_v → fq_v.

Hidden Valleys: Showers

Interleaved showerin QCD, QED and HV sectors:

emissions arranged in one common sequence of decreasing emission p⊥ scales.

HV U(1): add qv → q_vγv and Fv → F_vγv.

HV SU(N): add q_v → q_vg_v, F_v → F_vg_v and g_v → g_vg_v.

Recoil effects in visible sector also of invisible emissions!

Hidden Valleys: Decays

Hidden Valley particles may remain invisible, or

Broken U(1): γv acquire mass, radiated γvs decay back, γv → γ → ff with BRs as photon (⇒ lepton pairs!) SU(N): hadronization in hidden sector,

with full string fragmentation setup, giving

• off-diagonal “mesons”, flavour-charged, stable & invisible

• diagonal “mesons”, can decay back q_vq_v → ff Even when tuned to same average activity, hope to separate

LHC Scheduled Future

2012 7 → 8 TeV, 5 → 15 fb⁻¹

2013–14 shutdown to improve safety system (+ retrain magnets);

slow restart likely

2015–17 run at 13–14 TeV, slowly increasing luminosity 2018 shutdown, preparing for upgrade

2019–21 continue to run at 14 TeV, collect 100 fb⁻¹/year 2022–23 shutdown, luminosity upgrade, slow restart 2024–30 high-luminosity run to collect 3000 fb⁻¹

Long-term future options:

(Re)install electron ring for ep/eA collisions.

New ∼ 20 T magnets to double the LHC energy.

∼ 3 TeV e⁺e⁻ linear collider.

Summary

After many delays/disappointments LHC is now doing well.

Flood of new results; impossible to keep track of all.

Signs of a 125 GeV Higgs, consistent with Standard Model.

No signs of physics Beyond the Standard Model.

Event generators continue to play a central role.

Qualitatively main features of data successfully predicted, in some cases over ten orders of magnitude.

Quantitatively many O(20%) discrepancies, and a few real bad ones.

Push towards higher precision: theory ↔ generators ↔ data.

Increasing luminosity smears many observables.

We live in interesting times!