physics of the large hadron collider - durham...

Physics of the

Large Hadron Collider

Chris Quigg

Fermilab

mailto:[email protected]

Why Hadron Colliders?

Discovery machines

W±, Z 0, t, H , . . .

Precision instruments

MW , mt , Bs oscillation frequency, . . .

Large energy reach · High event rate

Chris Quigg (FNAL) LHC Physics . . . Invisibles · 10–15.7.2013 1 / 54

Why Hadron Colliders?

Explore a rich diversity of elementary processesat the highest accessible energies:

(qi , qi , g , . . .)⊗ (qi , qi , g , . . .)

Example: quark-quark collisions at√s = 1 TeV

If 3 quarks share half the proton’s momentum (〈x〉 = 16),

require pp collisions at√s = 6 TeV

; Fixed-target machine with beam momentump ≈ 2× 104 TeV = 2× 1016 eV (cf. cosmic rays).


Cosmic-ray Spectrum

[eV]E

1310 1410 1510 1610 1710 1810 1910 2010

]-1

sr

-1 s

-2 m

1.6

[G

eVF

(E)

2.6

E

1

10

210

310

410

Grigorov

JACEE

MGU

Tien-Shan

Tibet07

Akeno

CASA-MIA

HEGRAFly’s Eye

Kascade

Kascade Grande 2011

AGASA

HiRes 1

HiRes 2Telescope Array 2011

Auger 2011

Knee

Ankle

dI

dE(2× 1016 eV) = (3 - 5)× 10−16 m−2 s−1 sr−1 eV−1


http://pdg.lbl.gov/2012/reviews/rpp2012-rev-cosmic-rays.pdf

http://www-ik.fzk.de/publication/JournalArticles/JASR-2013-KASCADE-Grande_Mario.pdf



How to achieve?

Fixed-target, p ≈ 2× 104 TeVRing radius is

r =10

3·( p

1 TeV

)/( B

1 tesla

)km.

Conventional copper magnets (B = 2 teslas) ;

r ≈ 13 × 105 km.

≈ 112 size of Moon’s orbit

10-tesla field reduces the accelerator to mere Earth size(R⊕ = 6.4× 103 km).


Fermi’s Dream Machine (1954)

5000-TeV protons to reach√s ≈ 3 TeV

2-tesla magnets at radius 8000 km

Projected operation 1994, cost $170 billion(inflation assumptions not preserved)


Key Advances in Accelerator Technology

Alternating-gradient (“strong”) focusing, invented byChristofilos, Courant, Livingston, and Snyder.

Before and After . . .

Synchrotron Beam Tube Magnet Size

Bevatron (6.2 GeV) 1 ft× 4 ft 912

ft× 2012

ft

FNAL Main Ring (400 GeV) ∼ 2 in× 4 in 14 in× 25 in

LHC (→ 7 TeV) 56 mm (SC)

The idea of colliding beams.

Superconducting accelerator magnets based on“type-II” superconductors, including NbTi and Nb3Sn.Chris Quigg (FNAL) LHC Physics . . . Invisibles · 10–15.7.2013 6 / 54

Key Advances . . .

Active optics to achieve real-time corrections of theorbits makes possible reliable, highly tunedaccelerators using small-aperture magnets. Also“cooling,” or phase-space compaction of storedantiprotons.

The evolution of vacuum technology. Beams storedfor approximately 20 hours travel ∼ 2× 1010 km,about 150 times the Earth–Sun distance, withoutencountering a stray air molecule.

The development of large-scale cryogenic technology,to maintain many km of magnets at a few kelvins.


Hadron Colliders through the Ages

CERN Intersecting Storage Rings: pp collider at√s → 63 GeV. Two rings of conventional magnets.

SppS Collider at CERN: pp collisions at√s = 630(→ 900) GeV in conventional-magnet SPS.

Fermilab Tevatron Collider: pp collisions at√s ≈ 2 TeV with 4-T SC magnets in a 2π-km tunnel.

Brookhaven Relativistic Heavy-Ion Collider: 3.45-Tdipoles in 3.8-km tunnel. Polarized pp,

√s → 0.5 TeV

Large Hadron Collider at CERN: 14-TeV pp collider inthe 27-km LEP tunnel, using 9-T magnets at 1.8 K.

High-energy collider parameters, 2012 Review of Particle Properties §28


http://pdg.lbl.gov/2012/reviews/rpp2012-rev-hep-collider-params.pdf#page=4

Large Hadron Collider at CERN

LHCb

ATLASALICE

CMS


http://lpc.web.cern.ch/lpc/

√s = 8 TeV Interaction Rates

extracted and applied as a function of the T2 track multi-plicity and affects only the 1h category. The systematicuncertainty is estimated to be 0.45% which correspondsto the maximal variation of the background that gives acompatible fraction of 1h events (trigger and pileup cor-rected) in the two samples.

Trigger efficiency: This correction is estimated from thezero-bias triggered events. It is extracted and applied as afunction of the T2 track multiplicity, being significantfor events with only one track and rapidly decreasing tozero for five or more tracks. The systematic uncertainty isevaluated comparing the trigger performances with andwithout the requirement of having a track pointing to thevertex and comparing the overall rate correction in the twosamples.

Pileup: This correction factor is determined from thezero-bias triggered events: the probability to have a bunchcrossing with tracks in T2 is 0.05–0.06 from which theprobability of having n 2 inelastic collisions with tracksin T2 in the same bunch crossing is derived. The systematicuncertainty is assessed from the variation, within the samedata set, of the probability to have a bunch crossing withtracks in T2 and from the uncertainty due to the T2 eventreconstruction efficiency.

Reconstruction efficiency: This correction is estimatedusing Monte Carlo generators (PYTHIA8 [13], QGSJET-II-03 [14]) tuned with data to reproduce the measuredfraction of 1h events which is equal to 0:216 0:007.The systematic uncertainty is assumed to be half of thecorrection: as it mainly depends on the fraction of eventswith only neutral particles in T2, it accounts for variationsbetween the different Monte Carlo generators.

T1 only: This correction takes into account the amountof events with no final state particles in T2 but one ormore tracks in T1. The uncertainty is the precision withwhich this correction can be calculated from the zero-biassample plus the uncertainty of the T1 reconstructionefficiency.

Internal gap covering T2: This correction takes intoaccount the events which could have a rapidity gap fullycovering the T2 range and no tracks in T1. It is estimatedfrom data, measuring the probability of having a gap in T1

and transferring it to the T2 region. The uncertainty takesinto account the different conditions (average chargedmultiplicity, pT threshold, gap size, and surroundingmaterial) between the two detectors.Central diffraction: This correction takes into account

events with all final state particles outside the T1 and T2pseudorapidity acceptance and it is determined from simu-lations based on the PHOJET and MBR event generators[15,16]. Since the cross section is unknown and the uncer-tainties are large, no correction is applied to the inelasticrate but an upper limit of 0.25 mb is taken as an additionalsource of systematic uncertainty.Low mass diffraction: The T2 acceptance edge at jj ¼

6:5 corresponds approximately to diffractive masses of3.6 GeV (at 50% efficiency). The contribution of eventswith all final state particles at jj> 6:5 is estimated withQGSJET-II-03 after tuning the Monte Carlo prediction with

TABLE IV. Summary of the measured cross sections with detailed uncertainty composition.The uncertainty follows from the COMPETE preferred-model extrapolation error of0:007. The right-most column gives the full systematic uncertainty, combined in quadratureand considering the correlations between the contributions.

Systematic uncertainty

Quantity Value el. t-dep el. norm inel ) full

tot (mb) 101.7 1:8 1:4 1:9 0:2 ) 2:9inel (mb) 74.7 1:2 0:6 0:9 0:1 ) 1:7el (mb) 27.1 0:5 0:7 1:0 0:1 ) 1:4el=inel (%) 36.2 0:2 0:7 0:9 ) 1:1el=tot (%) 26.6 0:1 0:4 0:5 ) 0:6

FIG. 1 (color). Compilation [8,20–24] of the total (tot), in-elastic (inel) and elastic (el) cross-section measurements: theTOTEM measurements described in this Letter are highlighted.The continuous black lines (lower for pp, upper for pp) repre-sent the best fits of the total cross-section data by the COMPETEcollaboration [19]. The dashed line results from a fit of theelastic scattering data. The dash-dotted lines refer to the inelasticcross section and are obtained as the difference between thecontinuous and dashed fits.

PRL 111, 012001 (2013) P HY S I CA L R EV I EW LE T T E R Sweek ending5 JULY 2013

012001-4

σtot (101.7± 2.9) mb

σinel (74.7± 1.7) mb

σel (27.1± 1.4) mb


http://prl.aps.org/abstract/PRL/v111/i1/e012001

Collider Cross Sections

0.1 1 1010

-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

108

109

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

108

109

σσσσZZ

σσσσWW

σσσσWH

σσσσVBF

MH=125 GeV

WJS2012

σσσσjet

(ET

jet > 100 GeV)

σσσσjet

(ET

jet > √√√√s/20)

σσσσggH

LHCTevatron

eve

nts

/ s

ec f

or L

= 1

03

3 c

m-2s

-1

σσσσb

σσσσtot

proton - (anti)proton cross sections

σσσσW

σσσσZ

σσσσt

σ

σ

σ

σ

(( ((nb

)) ))

√√√√s (TeV)


http://www.hep.phy.cam.ac.uk/~wjs/plots/plots.html

Standard-model Cross Sections

W Z WW Wt

[pb]

tota

lσ

1

10

210

310

410

510

-120 fb

-113 fb

-15.8 fb

-15.8 fb

-14.6 fb

-12.1 fb-14.6 fb

-14.6 fb

-11.0 fb

-11.0 fb

-135 pb

-135 pb

tt t WZ ZZ

= 7 TeVsLHC pp

Theory

)-1Data (L = 0.035 - 4.6 fb

= 8 TeVsLHC pp

Theory

)-1Data (L = 5.8 - 20 fb

ATLAS PreliminaryATLAS PreliminaryATLAS Preliminary

σtot ≈ 1011 pb


https://twiki.cern.ch/twiki/pub/AtlasPublic/CombinedSummaryPlots/SM_SummaryPlotMoriondEWK2013.pdf

Luminosity

Number N of events of interest

N = σ

∫dt L(t)

L(t): instantaneous luminosity [in cm−2 s−1]

Bunches of n1 and n2 particles collide head-on atfrequency f :

L(t) = fn1n2

4πσxσy

σx,y: Gaussian rms ⊥ beam sizes

Edwards & Syphers, 2012 Review of Particle Physics, §27LHC lumi calculator Zimmerman, “LHC: The Machine,” SSI 2012


http://pdg.lbl.gov/2012/reviews/rpp2012-rev-accel-phys-colliders.pdf

http://lpc.web.cern.ch/lpc/lumi.html

http://www-conf.slac.stanford.edu/ssi/2012/Presentations/Zimmermann.pdf

Exercise 1

(a) Estimate the integrated luminosity required to make aconvincing observation of each of the standard-model finalstates shown in the ATLAS plot above . Take into accountthe gauge-boson branching fractions given in the 2012Review of Particle Physics.

(b) Taking a nominal year of operation as 107 s, translateyour results into the required average luminosity.


http://pdg.lbl.gov/2012/tables/rpp2012-sum-gauge-higgs-bosons.pdf

LHC Luminosity, 2012

Lpeak ≈ 7.7× 1033 cm−2 s−1 ATLAS & CMS


http://lpc.web.cern.ch/lpc/lumiplots.htm

Collider kinematics

Because of its properties under Lorentz boosts, rapidity,

y ≡ 12 ln

∣∣∣∣E + pzE − pz

∣∣∣∣,is a highly convenient longitudinal variable for anindividual particle or a jet. Pseudorapidity,

η ≡ − ln tan(θ?/2),

is a close approximation to y in the setting of colliderdetectors, and can be measured, even when the mass ofthe outgoing object is unknown.


Exercise 2(a) Expand the definition

y ≡ 12 ln

∣∣∣∣E + pzE − pz

∣∣∣∣of rapidity for an object with mass m, under theassumption that p m, to show that as m/p → 0,

y → η ≡ − ln tan(θ?/2).

cf. 2012 Review of Particle Physics §43.5.2

(b) For pion production, compute the maximum c.m.rapidity at

√s = (8, 14) TeV and deduce the angular

coverage required to observe the full range.Chris Quigg (FNAL) LHC Physics . . . Invisibles · 10–15.7.2013 17 / 54

http://pdg.lbl.gov/2012/reviews/rpp2012-rev-kinematics.pdf#page=8

Charged-particle density, η ≈ 0

Eur. Phys. J. C (2010) 68: 345–354 353

there is a large spread of values between different models:PHOJET is the lowest and PYTHIA tune Perugia-0 the high-est.

Fig. 2 Charged-particle pseudorapidity density in the central pseudo-rapidity region |η| < 0.5 for inelastic and non-single-diffractive colli-sions [4, 16–25], and in |η| < 1 for inelastic collisions with at leastone charged particle in that region (INEL > 0|η|<1), as a function ofthe centre-of-mass energy. The lines indicate the fit using a power-lawdependence on energy. Note that data points at the same energy havebeen slightly shifted horizontally for visibility

6 Conclusion

We have presented measurements of the pseudorapidity den-sity and multiplicity distributions of primary charged par-ticles produced in proton–proton collisions at the LHC, ata centre-of-mass energy

√s = 7 TeV. The measured value

of the pseudorapidity density at this energy is significantlyhigher than that obtained from current models, except forPYTHIA tune ATLAS-CSC. The increase of the pseudora-pidity density with increasing centre-of-mass energies is sig-nificantly higher than that obtained with any of the modelsand tunes used in this study.

The shape of our measured multiplicity distribution is notreproduced by any of the event generators considered. Thediscrepancy does not appear to be concentrated in a singleregion of the distribution, and varies with the model.

Acknowledgements The ALICE collaboration would like to thankall its engineers and technicians for their invaluable contributions to theconstruction of the experiment and the CERN accelerator teams for theoutstanding performance of the LHC complex.

The ALICE collaboration acknowledges the following fundingagencies for their support in building and running the ALICE detec-tor:

– Calouste Gulbenkian Foundation from Lisbon and Swiss FondsKidagan, Armenia;

– Conselho Nacional de Desenvolvimento Científico e Tecnológico(CNPq), Financiadora de Estudos e Projetos (FINEP), Fundação deAmparo à Pesquisa do Estado de São Paulo (FAPESP);

Fig. 3 Measured multiplicity distributions in |η| < 1 for the INEL >

0|η|<1 event class. The error bars for data points represent statisticaluncertainties, the shaded areas represent systematic uncertainties. Left:The data at the three energies are shown with the NBD fits (lines).Note that for the 2.36 and 7 TeV data the distributions have beenscaled for clarity by the factors indicated. Right: The data at 7 TeV

are compared to models: PHOJET (solid line), PYTHIA tunes D6T(dashed line), ATLAS-CSC (dotted line) and Perugia-0 (dash-dottedline). In the lower part, the ratios between the measured values andmodel calculations are shown with the same convention. The shadedarea represents the combined statistical and systematic uncertainties


http://link.springer.com/content/pdf/10.1140%2Fepjc%2Fs10052-010-1350-2.pdf

Charged-particle multiplicity, |η| < 1

Eur. Phys. J. C (2010) 68: 345–354 353

there is a large spread of values between different models:PHOJET is the lowest and PYTHIA tune Perugia-0 the high-est.

Fig. 2 Charged-particle pseudorapidity density in the central pseudo-rapidity region |η| < 0.5 for inelastic and non-single-diffractive colli-sions [4, 16–25], and in |η| < 1 for inelastic collisions with at leastone charged particle in that region (INEL > 0|η|<1), as a function ofthe centre-of-mass energy. The lines indicate the fit using a power-lawdependence on energy. Note that data points at the same energy havebeen slightly shifted horizontally for visibility

6 Conclusion

We have presented measurements of the pseudorapidity den-sity and multiplicity distributions of primary charged par-ticles produced in proton–proton collisions at the LHC, ata centre-of-mass energy

√s = 7 TeV. The measured value

of the pseudorapidity density at this energy is significantlyhigher than that obtained from current models, except forPYTHIA tune ATLAS-CSC. The increase of the pseudora-pidity density with increasing centre-of-mass energies is sig-nificantly higher than that obtained with any of the modelsand tunes used in this study.

The shape of our measured multiplicity distribution is notreproduced by any of the event generators considered. Thediscrepancy does not appear to be concentrated in a singleregion of the distribution, and varies with the model.

Acknowledgements The ALICE collaboration would like to thankall its engineers and technicians for their invaluable contributions to theconstruction of the experiment and the CERN accelerator teams for theoutstanding performance of the LHC complex.

The ALICE collaboration acknowledges the following fundingagencies for their support in building and running the ALICE detec-tor:

– Calouste Gulbenkian Foundation from Lisbon and Swiss FondsKidagan, Armenia;

– Conselho Nacional de Desenvolvimento Científico e Tecnológico(CNPq), Financiadora de Estudos e Projetos (FINEP), Fundação deAmparo à Pesquisa do Estado de São Paulo (FAPESP);

Fig. 3 Measured multiplicity distributions in |η| < 1 for the INEL >

0|η|<1 event class. The error bars for data points represent statisticaluncertainties, the shaded areas represent systematic uncertainties. Left:The data at the three energies are shown with the NBD fits (lines).Note that for the 2.36 and 7 TeV data the distributions have beenscaled for clarity by the factors indicated. Right: The data at 7 TeV

are compared to models: PHOJET (solid line), PYTHIA tunes D6T(dashed line), ATLAS-CSC (dotted line) and Perugia-0 (dash-dottedline). In the lower part, the ratios between the measured values andmodel calculations are shown with the same convention. The shadedarea represents the combined statistical and systematic uncertainties


http://link.springer.com/content/pdf/10.1140%2Fepjc%2Fs10052-010-1350-2.pdf

Charged-particle spectrament follows this trend. The choice of the jj interval caninfluence the average pT value by a few percent.For jj< 0:5, the average charged multiplicity density

is dNch=d ¼ 5:78 0:01ðstatÞ 0:23ðsystÞ for NSDevents. The

ffiffiffis

pdependence of the measured dNch=

dj0 is shown in Fig. 5, which includes data from

various other experiments. The dNch=d results reportedhere show a rather steep increase between 0.9 and 7 TeV,which is measured to be ½66:1 1:0ðstatÞ 4:2ðsystÞ%.Using a somewhat different event selection, the ALICECollaboration has found a similar increase of ½57:60:4ðstatÞþ3:6

1:8ðsystÞ% [5]. The measured charged-particle

multiplicity is accurate enough to distinguish amongmost sets of event-generator tuning parameter values andvarious models. The measured value at 7 TeV significantlyexceeds the prediction of 4.57 from PHOJET [9,10], and thepredictions of 3.99, 4.18, and 4.34 from the DW [17],PROQ20 [18], and Perugia0 [19] tuning parameter values

of PYTHIA, respectively, while it is closer to the predictionof 5.48 from the PYTHIA parameter set from Ref. [8] and tothe recent model predictions of 5.58 and 5.78 fromRefs. [20,21]. The measured excess of the number ofcharged hadrons with respect to the event generators isindependent of and concentrated in the pT < 1 GeV=c

η-2 0 2

η/d

chdN

0

2

4

6

CMS NSD

ALICE NSD

UA5 NSD

0.9 TeV

2.36 TeV

7 TeV

CMS

FIG. 3. Distributions of dNch=d, averaged over the threemeasurement methods and compared with data from UA5 [23](p p, with statistical errors only) and ALICE [24] (with system-atic uncertainties). The shaded band shows systematic uncer-tainties of the CMS data. The CMS and UA5 data are averagedover negative and positive values of .

[GeV]s10 210 310 410

[GeV

/c]

⟩Tp⟨

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

ISR inel.

UA1 NSD

E735 NSD

CDF NSD

CMS NSD

s 2 + 0.00143 lns0.413 - 0.0171 ln

CMS

FIG. 4. Average pT of charged hadrons as a function of thecenter-of-mass energy. The CMS measurements are for jj<2:4. Also shown are measurements from the ISR [25] (pp), E735[26] (p p), and CDF [27] (p p) for jj< 0:5, and from UA1 [16](p p) for jj< 2:5. The solid line is a fit of the functional formhpTi ¼ 0:413 0:0171 lnsþ 0:001 43ln2s to the data. The errorbars on the CMS data include the systematic uncertainties.

[GeV]s10 210 310 410

0≈η η/d

chdN

0

1

2

3

4

5

6

7 UA1 NSD

STAR NSD

UA5 NSD

CDF NSD

ALICE NSD

CMS NSD

NAL B.C. inel.

ISR inel.

UA5 inel.

PHOBOS inel.

ALICE inel.

s 2 + 0.0267 lns2.716 - 0.307 ln

s 2 + 0.0155 lns1.54 - 0.096 ln

CMS

FIG. 5. Average value of dNch=d in the central region as afunction of center-of-mass energy in pp and p p collisions. Alsoshown are NSD and inelastic measurements from the NALBubble Chamber [28] (p p), ISR [29] (pp), UA1 [16] (p p),UA5 [23] (p p), CDF [30] (p p), STAR [31] (pp), PHOBOS [32](pp), and ALICE [24] (pp). The curves are second-order poly-nomial fits for the inelastic (solid) and NSD event selections(dashed). The error bars include systematic uncertainties, whenavailable. Data points at 0.9 and 2.36 TeV are slightly displacedhorizontally for visibility.

PRL 105, 022002 (2010) P HY S I CA L R EV I EW LE T T E R Sweek ending9 JULY 2010

022002-4


http://prl.aps.org/abstract/PRL/v105/i2/e022002

PileupTypical LHC operation: 1.5× 1011 protons / bunch

bunch separation 50 ns

; multiple interactions / crossing

Mean Number of Interactions per Crossing0 5 10 15 20 25 30 35 40 45 50

/0.1

]-1

Rec

orde

d Lu

min

osity

[pb

0

20

40

60

80

100

120

140 =8 TeVsOnline 2012, ATLAS -1Ldt=20.8 fb0> = 20.7µ<


https://twiki.cern.ch/twiki/bin/view/AtlasPublic/LuminosityPublicResults#Data_Taking_Efficiency_and_Pileu

Pileup: Z → µ+µ− in 25 interactions in ATLAS


https://twiki.cern.ch/twiki/bin/view/AtlasPublic/EventDisplayStandAlone#2012_Z_mu_mu_event_with_high_pil

Pileup: 78 interactions in CMS


http://cms.web.cern.ch/news/reconstructing-multitude-particle-tracks-within-cms

Exercise 3

Consider the reaction p±p → jet1 + jet2 + anything atc.m. energy

√s. Denote the rapidity of the dijet system

as yboost ≡ 12(y1 + y2) and the individual jet rapidity in the

dijet rest frame as y ∗ ≡ 12(y1 − y2).

(a) Neglecting the invariant masses of the individual jetswith respect to p⊥, show that the invariant mass of thedijet system, and thus of the colliding partons, is√s = 2p⊥ cosh y ∗.

(b) Deduce the momentum fractions carried by the twocolliding partons. Show that xa,b =

√τe±yboost, where

τ ≡ s/s.


ATLAS


http://iopscience.iop.org/1748-0221/3/08/S08003

http://atlas.ch

CMS (Compact Muon Solenoid)

SUPERCONDUCTING SOLENOIDNiobium titanium coil carrying ~18,000A

PRESHOWERSilicon strips ~16m! ~137,000 channels

SILICON T!CKERSPixel (100x150 μm) ~16m! ~66M channelsMicrostrips (80x180 μm) ~200m! ~9.6M channels

MUON CHAMBERSBarrel: 250 Dri" Tube, 480 Resistive Plate ChambersEndcaps: 468 Cathode Strip, 432 Resistive Plate Chambers

FORWARD CALORIMETERSteel + Quartz #bres ~2,000 Channels

STEEL RETURN YOKE12,500 tonnes

HADRON CALORIMETER (HCAL)Brass + Plastic scintillator ~7,000 channels

CRYSTAL ELECTROMAGNETICCALORIMETER (ECAL)~76,000 scintillating PbWO! crystals

Total weightOverall diameterOverall lengthMagnetic "eld

: 14,000 tonnes: 15.0 m: 28.7 m: 3.8 T

CMS DETECTOR


http://iopscience.iop.org/1748-0221/3/08/S08004/

http://cms.web.cern.ch

LHCb

14 AAAS, 2011 First physics from the LHC Monica Pepe Altarelli Studying beauty at LHCb

pp collision Point

Vertex Locator

VELO

Tracking System

Muon System RICH Detectors

Calorimeters

• ~ 1 cm

• B

Movable device

35 mm from beam out of physics /

7 mm from beam in physics

LHCb



http://lhcb-public.web.cern.ch

ALICE



http://aliceinfo.cern.ch

ALICE (Pb–Pb event)


http://aliceinfo.cern.ch

Computing Cross Sections: factorization

i √s

a b

j_

σ

ˆ

dσ

dy1dy2dp⊥=∑i j

2πp⊥(1 + δij)s

[f(a)i (xa, s)f

(b)j (xb, s)σij(s, t, u) + (i ↔ j)

]. . . + fragmentation (partons → particles)


What Is a Proton?

(For hard scattering) a broad-band, unselected beam ofquarks, antiquarks, gluons, & perhaps other constituents,characterized by parton densities

f(a)i (xa,Q

2),

. . . number density of species i with momentum fractionxa of hadron a seen by probe with resolving power Q2.

Q2 evolution given by QCD perturbation theory

f(a)i (xa,Q

20): nonperturbative


Asymptotic Freedom1

αs(Q)=

1

αs(µ)+

(33− 2nf)

6πln

(Q

µ

)

100 101 102 103

Q [GeV]

2

3

4

5

6

7

8

9

10

11

121/α s

Group: 1Group: 2Group: 16Group: 5Group: 6Group: 7Group: 8Group: 9Group: 10Group: 11Group: 12Group: 13Group: 14Group: 29


QCD Tests: e+e− → hadrons

10-1

1

10

10 2

10 3

1 10 102

R

ω

ρ

φ

ρ

J/ψ ψ (2S)Υ

Z

√s [GeV]


QCD Tests: Quark Confinement

-4

-3

-2

-1

0

1

2

3

0.5 1 1.5 2 2.5 3

[V(r)

-V(r 0

)] r 0

r/r0

β = 6.0β = 6.2β = 6.4Cornell Potential

0


Deeply Inelastic Scattering ; f(a)i (xa,Q

20 )

107

106

105

104

103

102

10

1

10–1

10–2

10–3

Q2 (GeV2)

σ r (x

,Q2 )

NC

102 103 104 10510

x=6.18•10–5

x=9.5•10–5

x=2•10–4

x=3.2•10–4

x=5•10–4

x=8•10–4

x=1.3•10–3

x=2•10–3

x=3.2•10–3

x=5•10–3

x=8•10–3

x=1.3•10–2

x=0.015 (x40)

x=0.045 (x12)

x=0.08 (x6)

x=0.125 (x3.5)

x=0.175 (x2)

x=0.225 (x1.5)

x=0.275 (x1.2)

x=0.35

x=0.45

x=0.55

x=0.65

x=0.75

NuTeVCCFR 97CDHSWNuTeV fit

x=2•10–2

x=3.2•10–2

x=5•10–2

x=8•10–2

x=0.13x=0.18

x=0.25

x=0.4

x=0.65

10

1

0.1

xF3(x

,Q2 )

Q2 (GeV2)100101


Parton Distribution Functions fi(x ,Q2)

x-410 -310 -210 -110 1

)2xf

(x,Q

0

0.2

0.4

0.6

0.8

1

1.2

g/10

d

d

u

uss,

cc,

2 = 10 GeV2Q

x-410 -310 -210 -110 1

)2xf

(x,Q

0

0.2

0.4

0.6

0.8

1

1.2

x-410 -310 -210 -110 1

)2xf

(x,Q

0

0.2

0.4

0.6

0.8

1

1.2

g/10

d

d

u

u

ss,

cc,

bb,

2 GeV4 = 102Q

x-410 -310 -210 -110 1

)2xf

(x,Q

0

0.2

0.4

0.6

0.8

1

1.2

MSTW 2008 NLO PDFs (68% C.L.)


http://mstwpdf.hepforge.org

Example reaction: quark–quark scattering

μ ig_2

– λaαβ γμ

β

α

a

σ(ud → ud) =4πα2

s

9s2· s

2 + u2

t2

; dσ/dΩ∗ ∝ 1/ sin4(θ∗/2)


Exercise 4

(a) Express the ud → ud cross section in terms of c.m.angular variables, and verify that the angular distributionis reminiscent of that for Rutherford scattering.

(b) In the search for new interactions, the angulardistribution for quark-quark scattering, inferred from dijetproduction in p±p collisions, is a sensitive diagnostic.Show that when re-expressed in terms of the variableχ = (1 + cos θ∗)/(1− cos θ∗), the angular distribution forud scattering is dσ/dχ ∝ constant.


Compositeness search in CMS (|yboost| < 1.11)

JHEP05(2012)055

dijetχ

2 4 6 8 10 12 14 16

dije

tχ

/ddi

jet

σ d

dije

tσ

1/

0.1

0.2

0.3

0.4

0.5

0.6

0.7

> 3.0 TeVjjM (+0.5)

< 3.0 TeVjjM2.4 < (+0.4)

< 2.4 TeVjjM1.9 < (+0.3)

< 1.9 TeVjjM1.5 < (+0.25)

< 1.5 TeVjjM1.2 < (+0.2)

< 1.2 TeVjjM1.0 < (+0.15)

< 1.0 TeVjjM0.8 < (+0.1)

< 0.8 TeVjjM0.6 < (+0.05)

< 0.6 TeVjjM0.4 <

CMS = 7 TeVs

-1L = 2.2 fb

DataQCD prediction

= 7 TeV (NLO)+LL/RRΛ

Figure 1. Normalized dijet angular distributions for |yboost| < 1.11 in several Mjj ranges. For

clarity, the distributions are shifted vertically by the additive amounts shown in parentheses in

the figure. The vertical error bars represent the statistical and systematic uncertainties added in

quadrature. The horizontal bars correspond to the χdijet bin width. The results are compared with

the predictions of NLO QCD with CTEQ6.6 PDF (shaded band) and with predictions for QCD+CI

from [12] at the CI scale Λ+LL/RR = 7 TeV (dashed histogram). Non-perturbative corrections due

to hadronization and multiple parton interactions are applied to the predictions. The shaded band

indicates the total uncertainty on the NLO QCD predictions due to µr and µf scale variations,

PDFs, as well as the uncertainties from the non-perturbative corrections, which have all been

added in quadrature.

certainties are represented by nuisance parameters which affect the χdijet distribution. The

nuisance parameters are varied within their Gaussian uncertainties when generating the

distributions of q. The QCD+CI model is considered to be excluded at the 95% confidence

– 7 –

χdijet = e |y1−y2|


http://link.springer.com/article/10.1007/JHEP05%282012%29055

Parton Luminosity

Hard scattering: σ ∝ 1/s; Resonance: σ ∝ τ ; form

τ

s

dLdτ≡ τ/s

1 + δij

∫ 1

τ

dx

x[f

(a)i (x)f

(b)j (τ/x) + f

(a)j (x)f

(b)i (τ/x)]

[dimensions σ] measures parton ij luminosity (τ = s/s)

σ(s) =∑i j

∫ 1

τ0

dτ

τ· τs

dLij

dτ· [sσij(s)]

Dmensionless factor [· · · ] ≈ determined by couplings.Logarithmic integral typically gives a factor of order unity.

My luminosity page Stirling luminosities


http://lutece.fnal.gov/PartonLum11/

http://www.hep.phy.cam.ac.uk/~wjs/plots/plots.html

Parton Luminosity: gg

10-2 10-1 100 10110-610-510-410-310-210-1100101102103104105106

Parto

n Lu

min

osity

[nb]

0.9 TeV2 TeV4 TeV6 TeV7 TeV

10 TeV14 TeV

8 TeV

CTEQ6L1: gg

[TeV]


http://arxiv.org/abs/1101.3201

Parton Luminosity: ud

10-2 10-1 100 10110-610-510-410-310-210-1100101102103104105106

Parto

n Lu

min

osity

[nb]

0.9 TeV2 TeV

4 TeV6 TeV7 TeV

10 TeV14 TeV

Tevatron

8 TeV

[TeV]

CTEQ6L1: ud—



Parton Luminosity (light quarks)

10-2 10-1 100 10110-610-510-410-310-210-1100101102103104105106

Parto

n Lu

min

osity

[nb]

0.9 TeV2 TeV4 TeV6 TeV7 TeV8 TeV10 TeV14 TeV

CTEQ6L1: qq

[TeV]



Parton Luminosity: gq

10-2 10-1 100 10110-610-510-410-310-210-1100101102103104105106

Parto

n Lu

min

osity

[nb]

0.9 TeV2 TeV4 TeV6 TeV7 TeV8 TeV10 TeV14 TeV

CTEQ6L1: gq

[TeV]



Luminosity Ratios: gg

10-2 10-1 100 10110-3

10-2

10-1

100R

atio

to 1

4 Te

V

R.9R2R4R6R7

R10R8

CTEQ6L1: gg

[TeV]



Luminosity Ratios: ud

10-2 10-1 100 10110-3

10-2

10-1

100R

atio

to 1

4 Te

V

R0.9R2RTevR4R6R7

R10R8

CTEQ6L1: ud—

[TeV]



Luminosity Ratios (light quarks)

10-2 10-1 100 10110-3

10-2

10-1

100R

atio

to 1

4 Te

V

R0.9R2R4R6R7

R10R8

CTEQ6L1: qq

[TeV]



Luminosity Ratios: gq

10-2 10-1 100 10110-3

10-2

10-1

100R

atio

to 1

4 Te

V

R0.9R2R4R6R7R8R10

CTEQ6L1: gq

[TeV]



Luminosity Contours: gg

2 103 4 5 6 7 8[TeV]

0.1

1

10

0.20.30.40.5

2345

[TeV

] 0.1 pb1 pb10 pb100 pb1 nb10 nb

CTEQ6L1: gg

14



Luminosity Contours: ud

2 103 4 5 6 7 8[TeV]

0.1

1

10

0.20.30.40.5

2345

[TeV

] 0.1 pb1 pb10 pb100 pb1 nb10 nb

CTEQ6L1: ud—

14



Luminosity Contours (light quarks)

2 103 4 5 6 7 8[TeV]

0.1

1

10

0.20.30.40.5

2345

[TeV

]

0.1 pb1 pb10 pb100 pb1 nb10 nb

CTEQ6L1: qq

14



Luminosity Contours: gq

2 103 4 5 6 7 80.1

1

10

0.20.30.40.5

2345

0.1 pb1 pb10 pb100 pb1 nb10 nb

CTEQ6L1: gq

[TeV]14

[TeV

]



Venerable OverviewSupercollider physics

E. Eichten

Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Illinois 60510

I. Hinchliffe

Lawrence Berkeley Laboratory, Berkeley, California 94720

K. Lane

The Ohio State University, Columbus, Ohio 43210

C. Quigg

Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Illinois 60510

Eichten et al. summarize the motivation for exploring the 1-TeV (= tol2 eV) energy scale in elementary particle interactions and explore the capabilities of proton-(anti)proton colliders with beam energies between 1 and 50 TeV. The authors calculate the production rates and characteristics for a number of conventional processes, and discuss their intrinsic physics interest as well as their role as backgrounds to more exotic phenomena. The authors review the theoretical motivation and expected signatures for several new phenomena which may occur on the 1-TeV scale. Their results provide·a reference'point for the choice of machine parameters and for experiment design.

CONTENTS 1. Gaugino pair production 668

I. Introduction A. Where we stand B. The importance of the 1-TeV scale c. The purpose and goals of this paper

II. Preliminaries A. Parton model ideas B. Q2-dependent parton distributions c. Parton-parton luminosities

III. Physics of Hadronic Jets A: Generalities B. Two-jet final states c. Multijet phenomena D. Summary

IV. Electroweak Phenomena A. Dilepton production B. Intermediate boson production c. Pair production of gauge bosons

1. Production of w+ w- pairs 2. Production of w±zo pairs 3. Production of Z 0Z 0 pairs 4. w±r production 5. Z 0y production

D. Production of Higgs bosons E. Associated production of Higgs bqsons and gauge

bosons F. Summary

v. Minimal ExtenSions of the Standard Model A. Pair production of heavy quarks B. Pair production of heavy leptons c. New electroweak gauge bosons D. Summary

VI. Technicolor A. Motivation B. The minimal technicolor model c. The Farhi-Susskind model D. Single production of technipions E. Pair production of technipions F. Summary

VII. Supersymmetry A. Superpartner spectrum and elementary cross

sections

Reviews of Modern Physics. Vol. 56, No.4, October 1984

579 580 581 582 583 583 585 592 596 596 598 607 617 617 618 621 624 625 628 630 631 632 633

640 642 642 643 645 648 650 650 650 652 655 660 662 665 666

667

2. Associated production of squarks and gauginos 669 3. Squark pair production 670

B. Production and detection of strongly interacting superpartners 672

C. Production and detection of color singlet super-partners 676

D. Summary 683 VIII. Composite Quarks and Leptons 684

A. ~aD.ifestations of compositeness 685 B. Signals for compositeness in high-p1 jet production 687 C. Signals for composite quarks and leptons in lepton-

pair production 690 D. Summary 695

IX. Summary and Conclusions 696 Acknowledgments 698 Appendix. Parametrization& of the Parton Distribuiions 698 References 703

I. INTRODUCTION

The physics of elementary particles has undergone a remarkable development during the past decade. A host of new experimental results made accessible by a new generation of particle accelerators and the accompanying ra-. pid convergence of theoretical ideas have brought to the subject a new coherence. Our current outlook has been shaped by the identification of quarks and leptons as fundamental constituents of matter and by the gauge theory synthesis of the fundamental interactions. 1 These developments represent an important simplification of

1For expositions of the current paradigm, see the textbooks by Okun (1981), Perkins (1982), Aitchison and Hey (1982), Leader and Predazzi (1982), Quigg (1983), and Halzen and Martin (1984) and the summer school proceedings edited by Gaillard and Stora (1983).

Copyright @ 1984 The American Physical Society 579


http://rmp.aps.org/abstract/RMP/v56/i4/p579_1

Anticipating the LHC . . .

ANRV391-NS59-21 ARI 17 September 2009 18:15

Unanswered Questions in theElectroweak TheoryChris QuiggTheoretical Physics Department, Fermi National Accelerator Laboratory, Batavia, Illinois 60510

Institut fur Theoretische Teilchenphysik, Universitat Karlsruhe, D-76128 Karlsruhe, Germany

Theory Group, Physics Department, CERN, CH-1211 Geneva 23, Switzerland

Annu. Rev. Nucl. Part. Sci. 2009. 59:505–55

First published online as a Review in Advance onJuly 14, 2009

The Annual Review of Nuclear and Particle Scienceis online at nucl.annualreviews.org

This article’s doi:10.1146/annurev.nucl.010909.083126

Copyright c© 2009 by Annual Reviews.All rights reserved

0163-8998/09/1123-0505$20.00

Key Words

electroweak symmetry breaking, Higgs boson, 1-TeV scale, Large HadronCollider (LHC), hierarchy problem, extensions to the Standard Model

AbstractThis article is devoted to the status of the electroweak theory on the eveof experimentation at CERN’s Large Hadron Collider (LHC). A compactsummary of the logic and structure of the electroweak theory precedes an ex-amination of what experimental tests have established so far. The outstandingunconfirmed prediction is the existence of the Higgs boson, a weakly inter-acting spin-zero agent of electroweak symmetry breaking and the giver ofmass to the weak gauge bosons, the quarks, and the leptons. General argu-ments imply that the Higgs boson or other new physics is required on the1-TeV energy scale.

Even if a “standard” Higgs boson is found, new physics will be implicatedby many questions about the physical world that the Standard Model cannotanswer. Some puzzles and possible resolutions are recalled. The LHC movesexperiments squarely into the 1-TeV scale, where answers to important out-standing questions will be found.

505

Ann

u. R

ev. N

ucl.

Part

. Sci

. 200

9.59

:505

-555

. Dow

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from

arj

ourn

als.

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129

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n 10

/29/

09. F

or p

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nly.


http://arjournals.annualreviews.org/eprint/ddwfJ7EGrVG2qcPwVysY/pdfplus/10.1146/annurev.nucl.010909.083126

physics of the large hadron collider - durham...

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