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**Searches for Beyond the Standard Model Physics at the LHC**

Andy Parker Cavendish Lab

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**The Cambridge SUSY Working Group**

Formed in 1998 with Bryan and Ben Allanach: ideal combination of youth and experience! Theorists and experimentalists work together with weekly discussions and joint papers.

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Bryan has been mainstay of group: many analyses have relied on Herwig, suitably modified, on new processes being simulated, or on understanding of QCD. A great success: still going after 12 years, 58 papers on website posted by group members Many students and post-docs who worked in the group have gone on to successful careers Will pick a few themes from this work.

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**Some big themes Measuring SUSY Finding extra dimensions**

Things may not be as they seem…

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Measuring SUSY In 2000: many models, studies showing that particular model could be seen with particular cuts. Measuring sparticle masses in non-universal string inspired models at the LHC. JHEP 0009:004,2000 (Allanach, Lester, Webber, MAP) String models from BA, event generation BRW, reconstruction CL/MAP, analysis by all. 155 citations (not even in BRW top ten!)

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**Killer plasma ready to devour the Earth! **

Daily Telegraph website Sep 2001 SUSY points under study assumed universal scalar and fermion masses and couplings These were not compatible with weakly coupled string theory scenarios: generate charge/colour breaking minima (CCB) or infinitely negative potentials (UFB). -> construct an “optimised” non-universal string model without CCB and UFB problems. Dr Benjamin Allanach, a research associate at Cern, the European particle laboratory, said that a chance fluctuation of the "vacuum universe" would disintegrate all atoms. He said: "The universe is perched on a terrible precipice. It could catastrophically tunnel to a new state, disintegrating every atom.” And if that does not wipe out all known life anywhere in the universe, Dr Allanach said so-called killer strangelets could "eat up the Earth from the inside out".

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**Can one distinguish this from the most similar mSUGRA model (S5)?**

Herwig adapted to study observables: models show different slepton rates Use kinematic constraints from long decay chains

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**Kinematic edges then simulated and likely errors determined.**

Use MT2 to deal with neutralino emission Same analysis for both models

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**Particle masses extracted successfully, and models distinguished from each other.**

First steps towards model independent analysis of SUSY signals

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**10 years on… and a few papers later…**

Measuring supersymmetric particle masses at the LHC in scenarios with baryon-number R-parity violating couplings
B.C.Allanach, A.J.Barr, L.Drage, C.G.Lester, D.Morgan, M.A.Parker, P.Richardson, B.R.Webber
JHEP 0103:048,2001 Extracting the flavor structure of a baryon number R-parity violating coupling at the LHC
B.C. Allanach, A.J. Barr, M.A. Parker, P. Richardson, B.R. Webber
JHEP 0109:021,2001 Detecting exotic heavy leptons at the Large Hadron Collider
B.C. Allanach, C.M. Harris, M.A. Parker, P. Richardson, B.R. Webber
JHEP 0108:051,2001 and a few papers later…

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**…Mass determination in sequential particle decay chains**

B.R. Webber JHEP 09 (2009) 124 Abstract: A simple method is proposed for determining the masses of new particles in collider events containing a pair of decay chains (not necessarily identical) of the form Z → Y + 1, Y → X + 2, X → N + 3, where 1,2 and 3 are visible but N is not. Initial study of a possible supersymmetric case suggests that the method can determine the four unknown masses in effectively identical chains with good accuracy from samples of a few tens of events.

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**Make use of correlated masses in two decay chains in same event.**

Do not require chains to be identical. Applicable to SUSY or other long chain processes

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**3 constraints x 2 chains + 2 missing pT constraints = 8 constraints total**

Elegant matrix solution which generates c2-like variable to identify most likely mass assignments Likely to be as influential as the 2000 paper.

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Extra Dimensions ADD model with LED produces mono-jet signature with missing energy: not very appealing experimentally But RSS/UED models give more interesting phenomenology -> SUSY working group became active in this area

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Charybdis Charybdis: A black hole event generator
C.M. Harris, P. Richardson, B.R. Webber
JHEP 0308:033,2003 Charybis2: James A. Frost, Jonathan R. Gaunt, Marco O.P. Sampaio, Marc Casals, Sam R. Dolan, M. Andrew Parker, Bryan R. Webber, arXiv: v1 A full event generator for black hole events, including Hawking radiation with correct grey-body factors, spin down, and treatment of hadronization and final decay of remnant.

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Into the black hole… Searching for narrow graviton resonances with the ATLAS detector at the Large Hadron Collider.
B.C. Allanach, K. Odagiri, M.A. Parker, B.R. Webber
JHEP 0009:019,2000 Exploring small extra dimensions at the Large Hadron Collider
B.C. Allanach, K. Odagiri, M.J. Palmer, M.A. Parker, A. Sabetfakhri, B.R. Webber
JHEP 0212:039,2002. Exploring Higher Dimensional Black Holes at the Large Hadron Collider
C. M. Harris, M. J. Palmer, M. A. Parker, P. Richardson, A. Sabetfakhri, B. R. Webber
JHEP 0505 (2005) 053

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**Black Hole production cross-section**

Classical approximation to cross-section Controversial…see review by Gingrich hep-ph/ Very large rates for n=2-6 See hep-ph/ Almost independent of n

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Black Hole Decay Decay occurs by Hawking radiation, modified by “grey body” factors Hawking Temperature TH Black Hole radius rh Use observed final state energy spectrum to measure TH and hence n? But we have no model of decay near Planck mass

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Modelling BH events Modelling performed using Charybdis, TrueNoir or CatFish BH loses hair, spins down, then decays - only decay phase is modelled in C1, spin also in C2. Theory doesn’t cover phase when MBH~MPl and final state decay is forced to 2 or 4 bodies.

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BH remnant decay n=2 n=4 2 body 4 body Look at photon energy as example of primary emission - spectrum strongly dependent on assumption on remnant decay.

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BH shape parameters Black hole generators gives spherical events, very different from high mass QCD and tt events - but beware of modelling systematics CMS Not true if BH is hairy, or spinning, or if remnant decay has dynamics “The thermal nature of Hawking radiation requires the distribution of BH final state particles to be spherical”

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**BH Temperature variation**

Effect of varying temperature as BH decays. True n= Fit TH against Black Hole mass: fixed T n=1.7± varying T = 3.8 ± 1.0 Cannot measure T with sufficient accuracy - about 10 GeV. Also black hole is boosted by each decay, changing successive energy distributions

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**Black Hole Searches Can measure characteristic T at average mass**

-> combine this with cross section data to extract n. Assume 20% error on s

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**Doomsday! Big Bang machine could destroy the planet**

– telegraph.co.uk 2008 Who you gonna call? BRW reviews LSAG report for CERN SPC – planet is safe!

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**The snark was a boojum, you see***

How can we tell SUSY from ED models, or any other scenario involving a spectrum of TeV-scale new particles? Masses and charges are not enough: need spin as well. * In the midst of the word he was trying to say In the midst of his laughter and glee He had softly and suddenly vanished away For the Snark was a Boojum, you see. Lewis Carroll, The Hunting of the Snark, 1874

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**ATLAS status report LHCC today**

SUSY search 2j+Etmiss: almost into signal region q* search already beyond Tevatron Set limit at m(q*) > 1.26 TeV

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Distinguishing Spins in Supersymmetric and Universal Extra Dimension Models at the Large Hadron Collider
Jennifer M. Smillie, Bryan R. Webber
JHEP 0510 (2005) 069 Distinguishing Spins in Decay Chains at the Large Hadron Collider
Christiana Athanasiou, Christopher G. Lester, Jennifer M. Smillie, Bryan R. Webber
JHEP 08 (2006) 055

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Spin-doctoring SUSY predicts TeV-scale partners to SM particles, with same gauge couplings, differing in spin by ½ unit UED predicts TeV-scale partners to SM particles, with same gauge couplings, with the same spin. BRW: “the number of unknowns and arbitrary assumptions in each case is so great that the exclusion of either class of model in favour of the other would only be truly convincing if their spin structures could be distinguished.”

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Barr: spin correlations produced in pp collisions – more squarks than antisquarks (Phys Lett B , 2004) Method extended to UED

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**Some discrimination possible if SUSY spectrum is**

hierarchical as expected

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**Standing on the shoulders of Giants**

"Bernard of Chartres used to say that we are like dwarfs on the shoulders of giants, so that we can see more than they, and things at a greater distance, not by virtue of any sharpness of sight on our part, or any physical distinction, but because we are carried high and raised up by their giant size.” The Metalogicon of John Salisbury 1159

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