News from the LHC Experiments. David Milstead

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1 News from the LHC Experiments David Milstead

2 Outline Standard Model LHC and the Experiments pp Heavy ions Outlook

3 A brief history of collider physics Energy 50 years of colliders with steadily increasing energy Discoveries come with increasing energy Energy sets the distance scale for which interactions are studied λ=h/p LHC now occupies the high energy frontier. λ

4 What we know: Standard Model SM: The known and expected subatomic particles Gauge theory of three forces: em, weak (electroweak) and strong. 1/coupling Electromagnetic Standard Model Weak Strong Still to be discovered Log(Momentum transfer, Q(GeV) )

5 Energy scales of interest Electroweak 100 GeV -~TeV Higgs mass Mass generation Dark matter (WIMP) LHC Grand unified scale Postulated grand unified theories inc em, weak, strong Planck scale GR collides with quantum physics. Gravity becomes important. 1/coupling Standard Model Electromagnetic Weak Strong Energy scale (log(gev))

6 Large Hadron Collider 27km ring at CERN, Geneva Protons accelerated to 3.5 TeV 7 TeV c.m energy collisions ns bc, cm -2 s -1 To be upgraded to 25ns, 14 TeV, cm -2 s -1 2 large general purpose experiments: ATLAS and CMS 2 large experiments with some general capability but more specific program: Alice (heavy ions) and LHCB (Bphysics) + 2 small experiments

7 ATLAS Detector Multipurpose detector with inner tracking, calorimetry and muon detection Collaboration consists of several thousand physicists and engineers

8 Luminosity what we have and what we need Cross section LHC running extremely well. So far accumulated ~1fb-1 at 7 TeV c.m. Expect ~ 100 fb-1 per year at 14 TeV over coming years. Large lumi required for detailed study of high mass/energy processes

9 Publication output of ATLAS Data analysis Representative of the LHC multipurpose experiments Does not include papers on detector operation, preliminary results etc.

10 Tests of the SM SM is a predictive theory Important for early data to measure well understood processes and check for discrepancies: new physics, new detector Strong electromagnetic and weak forces

11 Testing the SM strong force Measuring and testing the strong sector of the SM up to ~TeV scale

12 Cross sections for SM processes compared with theory

13 Higgs Within SM the Higgs mechanism accounts for the masses of the fundamental particle Prediction of a Higgs scalar boson with mass ~ GeV Precision electroweak fits and previous searches tightly bound possible Higgs mass Not much room left..

14 Higgs hunting Many different possible decay channels. Large analysis effort required to cover all bases.

15 How close are we to discovery or rejection? First sets of LHC limits produced. Techniques established. Aim for more concrete conclusions for data taken during 2012.

16 Assessing the Standard Model and looking beyond Criteria Rating Predictivity and testability Collider measurements electron anomalous dipole moment g-2/2 = x 10^-12 (exp) g-2/2 = x 10^-12 (th) Completeness X no quantum theory of gravity? unifies weak and em forces, what about the strong force? Compactness --Dark matter? Based on 19 free parameters not bad for describing EM,weak and strong forces below ~ 1TeV. FK

17 Dark matter 23% of universe's energy budget. Astrophysical observations - galaxy cluster rotations - velocity dispersion of galaxies - gravitational lensing - structure formation Cold Dark Matter (non-relativistic) Weakly interacting massive particle (WIMP) Most models of WIMPs with masses from 10 GeV -> ~10 TeV

18 Hierarchy problem why is gravity so weak? 19 Gravity can't be ignored for energy scales > Planck scale Λ pl 10 GeV Renormalisation: particle mass calculations contains contributions from decoupled regions: SM ( energy scales < Λ ) and "new physics" region (energy scales > Λ pl m = SM + new physics theory at high momenta= δ m + m( Λ ) physical Fermion, eg electron m δ m m( Λ ) e e pl pl pl ) Higgs m 100 GeV = Ο(10 ) Ο(10 ) H Extraordinary fine tuning required!!

19 Supersymmetry Every Standard Model has a supersymmetry partner (~TeV mass) Symmetry between bosons and fermion Symmetry is broken otherwise SM and SUSY particles (sparticles) would have the same mass. 19 FK7003

20 Why look for SUSY? Many reasons for looking for SUSY, amongs them... (1) It predicts a dark matter candidate: i.e. a WIMP with mass TeV. ɶ χ 0 Neutralino: a mixed state of SUSY partners of the Higgs, Z and (2) Unification of the couplings is more exact if SUSY sparticles exist. γ. 1/coupling Electromagnetic Standard Model 1/coupling Standard Model+SUSY Electromagnetic Weak Weak Strong Strong Log(Momentum transfer, Q(GeV) ) Log(Momentum transfer, Q(GeV) ) (3) Introduces cancellations which suppress fine tuning/hierarchy problem. 20 FK7003

21 SUSY searches (1) Look for events in which two neutralinos escape undetected and leave missing transverse momentum. So far no SUSY for masses up to ~ GeV (model-dependent)

22 SUSY searches (2) Look for events in which the lightest SUSY particles are electrically charged. Model dependent limits on masses up to ~600 GeV.

23 Extra spatial dimensions Original ideas on extra dimensions from T. Kaluza and O. Klein (1921). Several different models incorporating extra dimensions on the market today. Large Extra Dimensions. Hierarchy problem gravity is weak since it propagates in extra dimensions (bulk) and we see a diluted form of it in our 3+1 dimension world (brane). 1 Gravitational potential V ( r) (15.08) where r < R n+ 1 r n = number of extra dimensions. R = distance scale for interactions at which the effects of extra dimensions are observed. n 2 R < 1 mm (15.09) In general, many extra dimensions theories often predict "new" heavy particles with masses TeV and provide dark matter candidates. Predictions of micro black holes 23 FK7003

24 Micro Black Holes at the LHC In general, when two particles pass each other with enough energy, a micro black hole can be formed. With some extra dimensions theories gravity becomes stronger, micro black holes can be created. "Normal" black hole: size km, mass m, temperature 0.01K, τ sun 18 "Micro" blackhole: size 10 m, mass 1 TeV, τ temperature 10 K, s (evaporate through Hawking radition.) 24 FK7003

25 Looking for mini-black holes No discrepancy with SM seen

26 The Heavy Ion Program of the LHC Several heavy ion (pb-pb) runs since 2010 Centre-of-mass energy per particle pair of max 2.76 TeV Complementary to pp program. Paradigm shift work leads the theory.

27 Centrality Study particle and jet production for peripheral and central collisions.

28 Jet Quenching at the LHC Heavy ion collisions quark, gluon plasma (QGP). QGP deconfined state of quarks and gluons. QCD multiple interactions of quarks/gluons as they propagate through the dense matter.

29 Jet quenching with increasing centrality ATLAS ATLAS Pb+Pb, %, Peripheral ATLAS ATLAS Pb+Pb, 0-10%, central

30 Precision measurements of charged particle multiplicity

31 Summary The LHC has opened up a new energy regime The physics program has barely started pp experimental program Test the SM at multi-tev scales Chasing down the Higgs Searches for a range of blue sky and topical exotica. Heavy ion program Studying the strong force in an extreme environment High impact work.

How To Teach Physics At The Lhc

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