Luminosity modeling update F Antoniou Y Papaphilippou BeamBeam

Luminosity modeling update F. Antoniou, Y. Papaphilippou Beam-Beam and luminosity studies meeting, 22/6/15

Luminosity model components • Beam current decay with time • Beam size (or emittance) evolution with time Fanouria Antoniou 2 13/4 /201 5

IBS Stable Beams IBS + unknown mechanism le b a St ms Bea IBS + SR + Burn-off + Other Current Loss mechanisms + Beam-beam + ? ? Ø All depending on the initial bunch parameters which have a big spread between the bunches Ø We need a model which takes the bunch-by-bunch variations into account! Fanouria Antoniou 3 Ramp Squeeze Flat Bottom Luminosity model components 13/4 /201 5

General Remarks on the IBS model •

Input parameters for the simulations • IBS simulations were done for a large range of input parameters: • Nb=1. 2 -2. 4 1011 ppb • εx 0=εy 0=1. 4 -2. 6 μm-rad • σl 0=0. 8 -1. 5 ns (4 sigma) • Need to find fit functions that are valid in the different regimes of the IBS effect

Constructing the IBS model •

IBS model at Flat Bottom •

IBS model at Flat Top @ 4 Te. V • Applying the function iteratively in small time-steps, the current (or any other parameter) variations during a fill can be taken into account

IBS model at Flat Top @ 6. 5 Te. V • To be finalized Applying the function iteratively in small time-steps, the current (or any other parameter) variations during a fill can be taken into account

IBS model for the Ramp • Ø To be finalized soon Ø The effect is small

Emittance slope at collisions • Based on the IBS model at Flat Bottom • εX 0=1. 5μm-rad • Nb=1. 6 1011 ppb • Emittance slope: • The ratio of the emittance at the end of Flat Bottom of the bunches that stayed at FB for 10 min to the ones stayed for 25 min • Bunch length slope: • The ratio of the BL values at injection

Observations from Run 1 data • Fills with WS data at Flat Bottom are chosen • Not always data for both beams and both plane • The convoluted emittance is used • The IBS model from injection to the beginning of collisions is applied • The expected conv. emittance of the selected 144 bunches (with WS data) at the beginning of collisions is calculated • Comparison with the measured one • The data from many Fills are put together

Data to model comparison • 28* Fills 2800 -2900, etc. • Only stable bunches are used • Linear dependence of the emittance ratio (or blow up factor) with the injected brightness

Data observations At low injected brightness At high injected brightness

Data to model comparison • The same exercise is repeated using the mean values for each Fill • The errorbars show the std from the mean for each Fill

Data to model comparison • Similar slope for both beams • Can we use a global fit?

Data observations at collisions

Run 2 data • All Run 2 Fills have been looked • Bunch length evolution decays faster than expected • Not clear yet why • To be looked if the bunch profile is Gaussian or not

Run 2 data • Bunch length evolution decays faster than expected • Not clear yet why • To be looked if the bunch profile is Gaussian or not

Run 2: Some of the Fills

Summary & Outlook • The IBS model for each part of the cycle is almost completed • Small pieces missing but almost finalized • Model parameterized with respect to vertical emittance is in progress • The tools are there to be checked and trained with the high energy data • Other emittance blow up components to be added • Noise + Beam-beam • The new data will “train” us • Impact to Luminosity studies are (almost) finalized • After having fully finalized the model it is straightforward • The last pieces of the model are needed coming very soon • Monte-Carlo code for IBS calculations: SIRE (Software for IBS and Radiation Effects) • Currently finalizing the setting up of the code and benchmarking with theories for LHC (S. Papadopoulou) • After that studies for non-Gaussian beam distributions

Thank you! Many thanks to Yannis for everything all these years! See you again in September